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The Dzyaloshinskii-Moriya antisymmetric exchange interaction (DMI) stabilises topological spin textures with promising future spintronics applications
the DMI can be categorized as four different types that favour different chiral textures
Unlike the other three extensively-investigated types
as the last type that favours in-plane chirality
Here we apply point-group-dependent DMI matrix analysis to show that out-of-plane DMI exists under reduced crystal symmetry
we show how Cs symmetry is realized in ultrathin magnets and observe the out-of-plane DMI stabilised in-plane chirality using spin-polarized electron microscopy
Our results show that extremely low out-of-plane DMI strengths at µeV/atom are sufficient to stabilise topological spin textures
We also demonstrate field-induced reversible control of the in-plane chirality and merons
Our findings open up untapped paths on topological magnetic textures and their potential applications
a Mathematical matrix and cartoon pattern representation of the DMI
with DMI vector configurations of all \({({{{{\rm{D}}}}}_{{mn}})}_{1\le m\le {{\mathrm{3,1}}}\le n\le 3}\) elements
b Major DMI types highlighted by various colourized DMI elements
The solid/striped areas represent the DMI vector with the same/different DMI strength
The area with the negative sign means that the sign of the DMI vector is opposite to the one with the same colour
c The DMI cartoon patterns corresponding to all non-centrosymmetric point groups (except C1) are shown
The definition of colours is the same as in panel b
due to the fact that the dipole energy also favours the in-plane magnetic configuration
The OOP-DMI is found to stabilise merons/bimerons
The reversible control of in-plane chirality and magnetic meron writing/deleting are demonstrated experimentally
Micromagnetic simulations reveal a similar role of the OOP-DMI on antiferromagnetic materials
For the Cs point group discussed in this paper
the \({{{{\rm{D}}}}}_{31}\) element appears when there is only one mirror plane \(\sigma\) along the \(y\)-direction
and \({{{{\rm{D}}}}}_{32}\) would appear with a mirror plane \(\sigma\) along the \(x\)-direction (see Methods)
d Compound SPLEEM image of 3 ML Co/ 3 ML Pd/ W(110)
e Pixel-by-pixel vector map of the black box in panel d
serving as direct evidence for the existence of OOP-DMI in the Co/Pd/W(110) system
a Top-view and side-view of the DMI vectors (orange arrows) at C3v interface
White and black balls correspond to the FM and heavy metal atoms
The blue triangle highlights the three-sites relevant to the adjacent DMI vector
The length of the DMI vector indicates the strength of DMI
b Micromagnetic simulation with C3v-type DMI and the histogram of angle χ
The colour wheel shows in-plane magnetization direction
and white/black indicates up/down magnetization direction
e Shifted atom and DMI configurations in the presence of compressive strain (panel c
highlighted in red) or tensile strain (panel e
The dashed circles outline the atom positions in panel a
f The micromagnetic simulation results of the strained system in panels c and e
The dashed black rectangle highlights the in-plane chiral structure
g Sketch of three OOP-DMI vector pairs under strain (marked by the blue arrows)
h Dependence of OOP-DMI vector changes (\(\Delta {D}_{{{{\rm{z}}}}1}\)
\(\Delta {D}_{{{{\rm{z}}}}3}\)) and effective OOP-DMI on strain calculated using the Fert-Levy model
the strength of the effective OOP-DMI could be estimated by considering all three factors
a–c Magnetic field dependent compound SPLEEM images of in-plane chiral Néel domain wall in the same locations on 3 ML Co/ 3 ML Au/ W(110)
d Evolution of the chirality as a function of magnetic field
e–g Magnetic field dependent compound SPLEEM images of a meron in the same locations on 3 ML Co/ 3 ML Au/ W(110)
h Evolution of the meron number as the function of a magnetic field
i Compound SPLEEM image of a meron bubble in 3 ML Co/3 ML Pd/ W(110)
The colour wheel shows in-plane magnetization
j Micromagnetic simulation of a meron bubble which is equivalent to a bimeron in the OOP-DMI system
and white/black indicates up/down magnetization
k Sketch of spin blocks similar to panel j
l Dependence of topological number Q on various combinations of the two merons’ core polarities
m Micromagnetic simulation of the in-plane chiral antiferromagnetic spin-spiral considering OOP-DMI
n Pixel-by-pixel vector map of the black box region in m
and S4 could be transformed into the C2 point group; C2v
C3h point groups could be converted to the Cs point group
where Mn3Sn contains out-of-plane \({{{{\bf{D}}}}}_{{ij}}\) that helps to stabilise non-collinear magnetic order; however
this case is distinguished from the in-plane ferromagnetic chirality reported here
we have observed the missing type of the DMI
the OOP-DMI that stabilises in-plane magnetic chirality in thin films
We revealed its Cs-symmetry-related physical origin through the combination of Fert-Levy model calculations
The required OOP-DMI for stabilising chirality can be a few orders of magnitude lower than the conventional interfacial DMI due to the different energy landscapes where both OOP-DMI and dipole energy favour planar magnetic configuration with DMI lifting the chiral degeneracy
We also demonstrate the reversible control of in-plane chirality and writing/deleting magnetic merons via a magnetic field
We expect such OOP-DMI to exist in many strained systems with (111) textures
and that it will play a similar role in antiferromagnetic systems
The experiments were performed on Elmitec SPLEEM III at the National Laboratory of Solid State Microstructures and the Department of Physics at Nanjing University
The W(110) substrate was cleaned by cycles of flashing to 1850 °C in 3.0 × 10−8 Torr oxygen until the surface was free of carbon
confirmed in the low-energy electron microscopy (LEEM) and low-energy electron diffraction (LEED)
an additional flashing at a higher temperature removes the surface oxygen
and Au layers were deposited by molecular beam epitaxy in the SPLEEM chamber under ultra-high vacuum
with a base pressure of \(\sim\) 4.0 × 10−11 Torr
The film thicknesses of the metal layers were detected via oscillations of the LEEM intensity
The spin-polarized source was obtained by photoemission from GaAs(001) activated by Cs and oxygen adsorption
The in-plane magnetic field applied to the sample surface is controlled by varying the distance between the sample and the objective lens with the field compensation coil turned off
atoms’ distance as \(a=0.25{{{\rm{nm}}}}\) and set the layer spacing as \(z=0.18{{{\rm{nm}}}}\)
The heavy metal atoms’ positions in another twinned C3v interface are:
We will discuss in the framework of micromagnetism (continuum model)
where an atom has only six nearest-neighbour atoms for cubic symmetry
The DMI energy density can then be written as
Utilizing the Liftshitz invariants \({{{{\mathcal{L}}}}}_{{ij}}^{(k)}={m}_{i}{\partial }_{k}{m}_{j}-{m}_{j}{\partial }_{k}{m}_{i}\)
Here, we discuss the reduction of the DMI matrix under the Cs point group as an example. For the axial tensor \(D\), \(D=\det \left(R\right){RD}{R}^{-1}\) is satisfied for all symmetry operations \(R\). We chose the symmetric operator element in the Cs point group to be the mirror operation along the y-z plane, which is the same situation as Fig. 3c, e
Substituting \(R\) into \(D=\det \left(R\right){RD}{R}^{-1}\) we find that \({D}_{11}={D}_{22}={D}_{23}={D}_{32}={D}_{33}=0\)
The DMI matrix in the Cs point group can be written as:
the OOP-DMI is oriented along the \(x\)-direction (direction along the strain)
which is consistent with the micromagnetic simulation results
The micromagnetic simulations were carried out based on a two-dimensional model35
where \({{{{\bf{S}}}}}_{i}\) and \({{{{\bf{S}}}}}_{j}\) are spin moments located on atomic sites \(i\) and \(j\) in a two-dimensional plane
\({{{{\bf{r}}}}}_{i}\) and \({{{{\bf{r}}}}}_{j}\) are the position vectors of the spin blocks in sites \(i\) and \(j\)
\({D}_{{{{\rm{dip}}}}}\) and \({K}_{{{{\rm{u}}}}}\) correspond to exchange interaction
dipole interaction and uniaxial anisotropy
each spin is surrounded by six neighbouring spins
The Hamiltonian of the OOP-DMI can be written as:
The data that support the findings of this study are available from the corresponding authors upon reasonable request
Real-space observation of helical spin order
Chiral magnetic order at surfaces driven by inversion asymmetry
Real-space observation of a two-dimensional skyrmion crystal
Spontaneous atomic-scale magnetic skyrmion lattice in two dimensions
Dynamics of Dzyaloshinskii domain walls in ultrathin magnetic films
Novel chiral magnetic domain wall structure in Fe/Ni/Cu(001) films
Magnetic skyrmions: advances in physics and potential applications
Skyrmion-based artificial synapses for neuromorphic computing
Topological properties and dynamics of magnetic skyrmions
Direct observation of the skyrmion Hall effect
Skyrmion Hall effect revealed by direct time-resolved X-ray microscopy
Direct Demonstration of Topological Stability of Magnetic Skyrmions via Topology Manipulation
Ultrasensitive Sub-monolayer Palladium Induced Chirality Switching and Topological Evolution of Skyrmions
Antiskyrmions stabilized at interfaces by anisotropic Dzyaloshinskii-Moriya interactions
Magnetic antiskyrmions above room temperature in tetragonal Heusler materials
Transformation between meron and skyrmion topological spin textures in a chiral magnet
Fractional antiferromagnetic skyrmion lattice induced by anisotropic couplings
Beyond skyrmions: Review and perspectives of alternative magnetic quasiparticles
A thermodynamic theory of “weak” ferromagnetism of antiferromagnetics
Anisotropic Superexchange Interaction and Weak Ferromagnetism
Dzyaloshinsky–Moriya interactions induced by symmetry breaking at a surface
Experimental observation of chiral magnetic bobbers in B20-type FeGe
Room-temperature antiskyrmions and sawtooth surface textures in a non-centrosymmetric magnet with S4 symmetry
Symmetry-breaking interlayer Dzyaloshinskii–Moriya interactions in synthetic antiferromagnets
Long-range chiral exchange interaction in synthetic antiferromagnets
Interlayer Dzyaloshinskii-Moriya Interactions
Role of Anisotropic Exchange Interactions in Determining the Properties of Spin-Glasses
Magnetic antiskyrmions in tetragonal Heusler materials with D2d structure
(Martin-Luther-Universität Halle-Wittenberg
Magnetic bimerons as skyrmion analogues in in-plane magnets
Imaging and tailoring the chirality of domain walls in magnetic films
Effects of Dzyaloshinskii–Moriya interaction on magnetic stripe domains
Measuring interfacial Dzyaloshinskii-Moriya interaction in ultrathin magnetic films
Emergence of skyrmions from rich parent phases in the molybdenum nitrides
Influence of the local atom configuration on a hexagonal skyrmion lattice
In-plane Néel wall chirality and orientation of interfacial Dzyaloshinskii-Moriya vector in magnetic films
Structural analysis of ultra-thin Pd films on W(110)
Manipulation of the Dzyaloshinskii–Moriya interaction in Co/Pt multilayers with strain
Large Dzyaloshinskii-Moriya interaction induced by chemisorbed oxygen on a ferromagnet surface
Asymmetric magnetic domain-wall motion by the Dzyaloshinskii-Moriya interaction
Antiferromagnetic half-skyrmions and bimerons at room temperature
First-principles calculations for Dzyaloshinskii–Moriya interaction
Phenomenology of chiral Dzyaloshinskii-Moriya interactions in strained materials
3D Interconnected Magnetic Nanowire Networks as Potential Integrated Multistate Memristors
Room-temperature spin–orbit torque in NiMnSb
Anatomy of Hidden Dzyaloshinskii-Moriya Interactions and Topological Spin Textures in Centrosymmetric Crystals
Triangular spin configuration and weak ferromagnetism of Mn3Sn and Mn3Ge
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This work has been supported by the National Key R&D Program of China (Grant No
2022YFA1403601) and the National Natural Science Foundation of China (Grants No
H.Y.K acknowledges support by the National Research Foundation of Korea (NRF) funded by the Korean Government (NRF-2021R1C1C2093113)
acknowledges support by the National Natural Science Foundation of China (Grant No
Department of Energy Early Career Research Program
11974079) and the Shanghai Municipal Science and Technology Major Project (Grant No
acknowledges support from the US-NSF (DMR-2005108)
acknowledges support from the Deutsche Forschungsgemeinschaft (DFG
Collaborative Research Centre / Transregio (SFB/TRR) 227
C.W acknowledges support by the National Research Foundation of Korea (NRF) funded by the Korean Government (NRF-2023R1A2C1006050)
Work at the Molecular Foundry was supported by the Office of Science
of the US Department of Energy under contract no
National Laboratory of Solid State Microstructures
Department of Physics and Collaborative Innovation Center of Advanced Microstructures
Anhui Provincial Key Laboratory of Magnetic Functional Materials and Devices
School of Materials Science and Engineering
Max Planck Institute of Microstructure Physics
State Key Laboratory of Surface Physics and Advanced Materials Laboratory
supervised the project and SPLEEM facility
carried out the experiments and analysed the data
contributed to the imaging analysis algorithm
and G.C discussed and interpreted the results
The authors declare no competing interests
Nature Communications thanks the anonymous reviewers for their contribution to the peer review of this work
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations
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Some more help defensively is on the way to Los Angeles. Angel City FC announced today the signing of Japan Women’s National Team defender
on a one-year deal that will see her in Los Angeles through 2025
Moriya comes to Angel City via transfer from INAC Kobe Leonessa for an undisclosed transfer fee
She will occupy one of ACFC’s international spots
[image or embed]
— Angel City FC (@angelcity.com) January 31, 2025 at 8:34 AM
“I am grateful to Angel City for signing me and I can’t wait to play for the fans at BMO Stadium,” said Moriya in a statement. “I visited Los Angeles several times as a student athlete, and I am excited for this new journey. My heart breaks for what LA is going through right now, and I am grateful to become part of the community.”
“We are excited to add a defender of Miyabi’s caliber to our roster,” said ACFC Sporting Director Mark Parsons in a statement. “She is a versatile talent with incredible game intelligence which will allow our coaching staff to continue to evolve our style of play. Bringing Miyabi and her huge international experience with one of the top national teams in the world is an important addition to our team.”
Since making her professional debut in 2015, Moriya earned eight goals in 118 match appearances for INAC Kobe Leonessa of the Japanese WE League, helping the club win their first ever WE League title in 2022. In the 2023 season, Moriya was awarded 2023 WE League Valuable Player and was also named to the 2023 WE League Best XI. She made her National Team debut in the 2023 World Cup, and has since made 15 appearances and scored two goals.
Funnily enough, Moriya already comes to Los Angeles with friendly faces waiting to greet her. She arrives to play with not one, but two former classmates. Midfielder Jun Endo, and goalkeeper Hannah Stambaugh both attended grammar school with Moriya. Endo is also her teammate on the Japan National Team, while Stambaugh was her teammate at INAC back in 2016.
Thoughts on the new arrival? Leave a comment below!
After some much welcome time off, Angel City are back in action for an early…
It looks like Angel City FC are wasting little time in getting this new era…
After securing two points on the road with draws against two of the league’s best,…
Moriya Shokudo is now open in Richardson and serves ramen, curry and more. (Dustin Butler/Community Impact)
Dustin is a features reporter, and covers businesses and restaurants in Collin and Dallas counties. He joined Community Impact in June 2023 and previously covered the cities of Wylie, Sachse, Murphy and Princeton.
SRO’s Benjamin Franassovici discusses chances of Fanatec GT Asia holding a street race in Tokyo suburb of Moriya…
The Tokyo suburb of Moriya holding a Fanatec GT World Challenge Asia powered by AWS race has been acknowledged as a future possibility by SRO Motorsports Asia General Manager Benjamin Franassovici, who added such a prospect is still “far away”.
Moriya is a city of just under 70,000 inhabitants situated in Ibaraki Prefecture, Japan, and serves as a bedroom community on the edge of the wider Tokyo conurbation.
An organization known as Moriya GT Grand Prix has held a series of car-themed events on public roads in the city, the most recent of which took place last September (pictured top), and has set itself the target of eventually holding a full-blown street race.
To that end, preliminary talks have been held with SRO on multiple occasions, with Franassovici even making a trip to the city to meet with organizers and local government representatives whose blessing would be needed for a race to happen.
Franassovici confirmed the talks in a recent interview with Sportscar365 but warned there are still many hurdles to overcome for a race to be a reality.
“I went there [to Moriya] in February, just for one day,” confirmed Franassovici. “I travelled there by train from Tokyo just to get a proper feel of how long it took to get there.
“We’ve been having friendly and healthy conservations to see what is possible. It would be great to have a street race in Tokyo. It’s an interesting project, but it’s very early days.
“We are always open-minded. Bringing a Fanatec GT Asia race to the streets of Tokyo is very ambitious. I think it needs to start off as a showcase and prove to everyone that something can be done, and then maybe it can go to the next level.
“I would do a demonstration first, see how much interest it generates and take it from there. But convincing people in Japan to change things is challenging. The organizers are ambitious, but I think the locals are not quite ready.
“On top of that, a street circuit has to meet all the minimum safety standards, especially to reassure the Am drivers. It’s early days, but maybe one day.”
Franassovici added that the newly-standalone Japan Cup would make more sense than the main Fanatec GT Asia series should a race in Moriya ever come to fruition.
“If we were ever to race there, I think it would be natural for it to be a Japan Cup race,” he said. “But that’s still far away.”
The 2023 Moriya GT Grand Prix featured guests such as former Nissan SUPER GT star Jann Mardenborough and Super Taikyu racer Jake Parsons.
Another event similar to last year’s is in the works for next month, with a recent post from the organizer’s Facebook page suggesting an objective of holding a first race on the streets of Moriya as soon as 2026.
Franassovici’s trip to Moriya came shortly before Formula E held a first-ever street race in Tokyo, albeit that course was largely made of roads surrounding the Big Sight exhibition centre in the district of Ariake, outside of any residential areas.
Jamie Klein is Sportscar365's Asian editor. Japan-based Klein, who previously worked for Motorsport Network on the Motorsport.cоm and Autosport titles, covers the FIA World Endurance Championship and SUPER GT, among other series.
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announcing the signing of defender Miyabi Moriya
The Japanese star has been one of the best players in the WE League and has signed a deal through 2025
Angel City FC continue to build their roster ahead of the 2025 NWSL season
Follow MLS Multiplex on X (Twitter).
the team now has more depth in defense and even more international experience
scoring eight goals for INAC Kobe Leonessa
one of the most traditional clubs in Japanese soccer
she was selected as WE League MVP and chosen to the best XI of the season
Her influence goes beyond club soccer: in 2023
Moriya made her professional debut for the Japan women's national team
joining the team for the 2023 FIFA Women's World Cup and making an appearance in the 2-0 victory against Costa Rica
She had represented Japan in the 2016 U-20 Women's World Cup
Moriya joins Angel City bringing not only technical quality but also international experience
something that can be important to any team that wants to find its identity in the NWSL
The front office of ACFC made it clear Moriya signed to elevate the team level
According to the sporting director Mark Parsons: "She is a versatile talent with incredible game intelligence
which will allow our coaching staff to continue evolving our style of play."
This means that Moriya is not just joining as a roster addition but as an important piece in the team's defensive scheme
can provide new tactical options and strengthen the defense against the increasingly intense attacks in the league
the relationship she has with both Jun Endo and Hannah Stambaugh
three Japanese stars who have known each other since childhood
in and out of the field and in INAC Kobe Leonessa
Perhaps because of that kind of rapport with some teammates can get her across to NWSL mode pretty sooner
While Angel City have been working on strengthening their squad
the arrival of Moriya can be termed strategic
but the NWSL being one of the difficult leagues adaptation will always play an important role
having an experienced and award-winning defender will be an asset
but how useful this signing will prove only time will tell
Will the signing of Moriya turn out to be the key to a stronger team
The quicker Moriya gets adapted and sustains the level of performance that earned her the WE League MVP
the more vital she could become for the core of Angel City
It will be intriguing to see how the team fits her into the defensive system
whether this signing will be a first step toward more solidity for the team or another patch attempt to give strength to a backline that's still out of balance
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including magnetic skyrmions and antiskyrmions
are characterized by swirling spin textures with non-trivial topologies
They are featured with specific topological charges
which are of crucial importance in determining their topological properties
Owing to the invariance of the chiral nature
it is generally believed that Q is conserved in a given magnetic skyrmionic structure and is hard to alter
we experimentally realize the control of Q of magnetic skyrmionic structures at room temperature in a Dzyaloshinskii-Moriya interaction (DMI) platform with spatially alternating signs
Depending on how many times it crosses the interfaces between DMI regions with opposite signs
the magnetic skyrmionic structures possess different Q
Modifying the DMI energy landscape through chemisorbed oxygen
a magnetic topological transition is realized
This creation and manipulation of magnetic skyrmionic structures with controllable Q
in particular the DMI-stabilized thin-film antiskyrmions and high-Q skyrmionic structures
enables a new degree of freedom to control their dynamics via a novel DMI confinement effect
Our findings open up an unexplored avenue on various topological magnetic skyrmionic structures and their potential applications
The arrows present the direction of the local DMI vector
d–g Magnetic moment vector representation of Bloch-type skyrmion
h–k Top view of the Néel- and Bloch-component of the DMI energy distribution within magnetic skyrmionic structures
l–o Azimuthal-angle-dependent DMI energy density of the corresponding spin textures in (d–g) in the case of bulk-
we find that DMI-stabilized antiskyrmions can be realized when skyrmionic structures cross the boundaries between DMI regions with alternating sign twice
and high-Q skyrmionic structures are observed when such crossing occurs more than two times
We also experimentally demonstrate the switching of Q in an individual magnetic skyrmionic structure by adjusting the DMI energy landscape
we use micromagnetic simulations to demonstrate how such systems with spatially alternating DMI sign open new degrees of freedom for spin dynamics in the current-driven dynamics of magnetic skyrmionic structures
none of DMI type can stabilize a high-Q skyrmionic structure with |Q| > 1
a Sketch of the local chirality control via an inhomogeneous surface
b LEEM image of the morphology of Pd stripes grown on W(110) surface; 1 ML and 0 ML Pd regions are shown in red and blue
c Compound SPLEEM image of perpendicularly magnetized domain structures of [Ni(2.1 ML)/Co(1 ML)]2 grown on the Pd stripes with alternating thickness of 1.9 ML and 2.9 ML on W(110) substrate (Method)
where the black arrows and the color wheel highlight the spin inside the domain walls
d Derived Néel-chirality within the domain walls is highlighted by the thin
which are superimposed onto the LEEM image of Pd film thickness in (b)
e Simulated domain walls’ Néel-chirality on surfaces with DMI regions with opposite signs
Positive DMI corresponds to left-handed chirality
f Experimental statistics on the dependence of α on LDW
The inset is a schematic diagram defining α
m is the measured magnetization unit vector
mNéel is the expected magnetization unit vector in Néel DW controlled by engineered-DMI
LDW is the length of DW within the DMI region of the same sign
g Monte-Carlo simulated phase diagram in \({L}_{{{{\rm{DW}}}}}-{D}_{{ij}}\) space
where \({w}_{{{{\rm{DW}}}}}\) is the width of the domain wall
J is the strength of symmetric exchange interaction
and \({D}_{{ij}}\) is the strength of the DMI
The strength of the Bloch/Néel component is defined by the color bar
The orange dashed line represents the result of the analytical model of the boundary between alternating Néel domain walls and uniform Bloch domain walls
we define a critical length of DW in the same sign DMI region \({L}_{{{{\rm{DW}}}},{{{\rm{c}}}}}\) where the transition between the alternating Néel domain wall and the uniform Bloch domain wall occurs
which agrees well with the results of the Monte-Carlo simulations
the size of skyrmionic structures cannot be too large
This is due to the fact that the energy difference between different Q states with the same n is dependent on their size
When the skyrmionic structure is too large
the spin inside the Bloch line (BL) will rotate completely randomly
The energy difference between clockwise and counter-clockwise rotational spin configurations in BL can be estimated as:
where the J and R represent the strength of exchange interaction and the radius of skyrmionic structures, respectively (Details in Note S3).
a–h Monte-Carlo simulations of skyrmionic structures with topological charge equals +1
The DMI’s sign settings in the simulation are indicated by the light and dark in the derived Néel-chirality image
i Dependence of Q on the DMI-reversal line crossing n in Monte-Carlo simulations
j–q Derived Néel-chirality images overlapped with the morphology LEEM images and corresponding compound SPLEEM images of skyrmion (j
q) in [2 ML Ni/1 ML Co]2/2 ML & 3 ML Pd/W(110)
r Experimental statistics on the dependence of Q on the effective DMI-reversal line crossing neff
The numbers on the scatters indicate the number of events observed in the experiment for each case
as well as the irregular shape of the skyrmionic structures
a Compound SPLEEM image of a trivial bubble in the alternating-DMI system [Ni/Co]n/Pd/W(110)
b The corresponding Néel-chirality image overlayered with the morphology image
d compound SPLEEM image and derived Néel-chirality image at the same location after ~0.2 ML oxygen chemisorption
e–h Compound SPLEEM image and Néel-chirality image overlayered with morphology image of antiskyrmion transformed into skyrmion
m–p Monte-Carlo simulations of topological transition of trivial bubble and antiskyrmion to skyrmions
The DMI’s initial sign settings in the simulation are adapted from experimental LEEM images
a–c Spin-transfer-torque drives the skyrmion (a)
and high-Q skyrmionic structure (c) to move along the DMI-engineered racetrack
The dotted line marks the initial position of the magnetic skyrmionic structures
d Various skyrmionic structures’ velocity v as a function of electrical current density j
The empty symbols mean that the skyrmionic structures will annihilate at the present current density
Advanced patterning of the DMI energy landscape and precise control over the size of the skyrmionic structures will enable more accurate regulation of Q
and we anticipate that utilizing the Co/Pd/Ru(0001) system will enable tuning the topological charge of magnetic skyrmionic structures to an even number
which may induce a zero-energy Majorana-bound state in the core of such even-Q skyrmionic structures
we have successfully controlled the Néel-chirality of domain walls and the topological charge of magnetic skyrmionic structures through DMI engineering in the [Ni/Co]n/Pd/W(110) system
The results have been verified by LEEM/SPLEEM imaging and Monte-Carlo simulations
By changing the DMI energy landscape of the whole system
transitions from trivial bubbles and antiskyrmions to skyrmions are demonstrated
the current-driven motion of various magnetic skyrmionic structures on the DMI-engineered racetrack with suppression of the skyrmion Hall effect is achieved
Our findings of tunable topological charge of magnetic skyrmionic structures based on the DMI engineering further open up new vistas for topology in magnetism
The anisotropic DMI matrix in 2D system can be written as:
The operation matrix of rotating θ angle along the z-axis in 2D system can be written as:
Under the operation of rotating 45° along the z-axis the anisotropic DMI matrix is transformed to
cycles of flashing to 1850 °C were done in an oxygen background at 3 × 10−8 Torr until the surface was free of carbon
confirmed by Auger electron spectroscopy (AES)
Additional flashing removes the adsorbed oxygen from the surface
and Ni layers were deposited by molecular beam epitaxy (MBE) in the SPLEEM chamber under ultra-high vacuum (UHV) with a base pressure of ~4 × 10−11 Torr
The pressure was around ~5 × 10−10 Torr at the time of growth
The film thicknesses were calibrated via oscillations of the LEEM intensity (grow Co
Pd at room temperature with ~1.5 eV imaging electron energy) and via directly visible step-flow growth in-situ LEEM at elevated temperature (Co
Ni growth at 400 °C and Pd at 700 °C on W(110) with ~5 eV imaging electron energy)
Real-space magnetic images were observed using the Elmitec SPLEEM III
The spin-polarized electron beam was generated by photoemission from GaAs(001) activated to negative electron affinity by cycles of Cs and oxygen deposition in a “yo-yo” treatment
The magnetic contrast in SPLEEM images represents the asymmetry of the spin-dependent reflection
which is \(A=({{{{\rm{LEEM}}}}}_{{{{\rm{up}}}}}-{{{{\rm{LEEM}}}}}_{{{{\rm{down}}}}})/({{{{\rm{LEEM}}}}}_{{{{\rm{up}}}}}+{{{{\rm{LEEM}}}}}_{{{{\rm{down}}}}})\)
A is proportional to P · M where P is the spin polarization of the incident electrons (~27% in the instrument)
and M is the surface magnetization of the sample
the incident electron energy was set to 2 eV
and all SPLEEM images were measured at room temperature
and \({M}_{z}\) components of the magnetization M were imaged by aligning the spin polarization of the electron beam along W[1-10]
To get the colourized compound SPLEEM image
\({M}_{x}\) and \({M}_{y}\) components were mapped on the hue and the \({M}_{z}\) was mapped on the lightness in the hue-saturation-lightness (HSL) color space
The magnetic domains and domain walls are mapped separately to maintain low noise levels
The analysis of Néel-chirality/Bloch-chirality from SPLEEM images or simulated images was done in the following steps
the angles between the domain wall normal direction vector n or tangential direction vector t located at the center line of the domain wall and the unit direction vector ex (pointing from spin-down to spin-up domains) were calculated pixel-by-pixel:
the angle between in-plane magnetization direction m and the unit direction vector ex was determined pixel-by-pixel through:
Néel-chirality or Bloch-chirality was defined from the angle between the magnetization direction m being parallel to the geometric normal to the domain wall direction n
or parallel to the domain wall direction t
To better characterize the global chirality of in-plane magnetic domain walls in the PMA system
we multiply the angle by a factor that additionally describes the proportion of in-plane components
we calculated the strength of Néel-chirality N and Bloch-chirality B for every pixel on the SPLEEM images or the simulated images through:
The Monte-Carlo simulations were carried out using a two-dimensional model63
To study the dynamics of various magnetic skyrmionic structures on the DMI-engineered racetrack, the micromagnetic simulations were performed using MuMax364
The magnetization dynamics are described by the Landau–Lifshitz–Gilbert (LLG) eq.:
The Zhang-Li spin transfer torque takes the form:
Where \(\beta\) is the non-adiabaticity of spin-transfer-torque
\({\mu }_{{{{\rm{B}}}}}\) is the Bohr magneton
\({a}_{J}\) and \({b}_{J}\) correspond to the damping-like (Slonczewski–Berger) term and field-like term
\({\alpha }_{{{{\rm{H}}}}}\) is spin Hall angle of heavy metal
The data that support the findings of this study are available from the corresponding authors upon request
Topological effects in nanomagnetism: from superparamagnetism to chiral quantum solitons
Topological Hall effect in the A phase of MnSi
Tailoring the topology of an artificial magnetic skyrmion
Entropy-limited topological protection of skyrmions
stability and current-induced motion of isolated magnetic skyrmions in nanostructures
Nanoscale magnetic skyrmions in metallic films and multilayers: a new twist for spintronics
Beyond skyrmions: review and perspectives of alternative magnetic quasiparticles
Anisotropic superexchange interaction and weak ferromagnetism
Skyrmion fractionalization and merons in chiral magnets with easy-plane anisotropy
Zero-field skyrmions with a high topological number in itinerant magnets
Direct imaging of a zero-field target skyrmion and its polarity switch in a chiral magnetic nanodisk
Two-dimensional skyrmion bags in liquid crystals and ferromagnets
High-topological-number magnetic skyrmions and topologically protected dissipative structure
Static and dynamic properties of 1-kink skyrmion in Pt/Co/MgO trilayer
Eigenmodes of 1-kink skyrmions in cylindrical magnetic discs
Magnetic domain walls in bubble materials: advances in materials and device research (Academic Press
Dipolar skyrmions and antiskyrmions of arbitrary topological charge at room temperature
Magnetic imaging with spin-polarized low-energy electron microscopy
Hybrid chiral domain walls and skyrmions in magnetic multilayers
Stress induced stripe formation in Pd/W(110)
Ultrasensitive sub-monolayer palladium induced chirality switching and topological evolution of skyrmions
Multistep topological transitions among meron and skyrmion crystals in a centrosymmetric magnet
Evolution and competition between chiral spin textures in nanostripes with D2d symmetry
Controlled transformation of skyrmions and antiskyrmions in a non-centrosymmetric magnet
Elliptical Bloch skyrmion chiral twins in an antiskyrmion system
Current‐controlled topological magnetic transformations in a nanostructured kagome magnet
Laser-induced topological spin switching in a 2D van der Waals magnet
Topological transitions among skyrmion- and hedgehog-lattice states in cubic chiral magnets
Magneto-ionic control of interfacial magnetism
Controllable positive exchange bias via redox-driven oxygen migration
Effects of spatially engineered Dzyaloshinskii-Moriya interaction in ferromagnetic films
Simultaneous control of the Dzyaloshinskii-Moriya interaction and magnetic anisotropy in nanomagnetic trilayers
Observation of hydrogen-induced Dzyaloshinskii-Moriya interaction and reversible switching of magnetic chirality
Electric field manipulation of spin chirality and skyrmion dynamic
Band filling control of the Dzyaloshinskii-Moriya interaction in weakly ferromagnetic insulators
Magnetic domain wall substructures in Pt/Co/Ni/Ir multi-layers
Experimental observation of current-driven antiskyrmion sliding in stripe domains
Skyrmion qubits: a new class of quantum logic elements based on nanoscale magnetization
Majorana bound states in magnetic skyrmions
Stabilizing spin spirals and isolated skyrmions at low magnetic field exploiting vanishing magnetic anisotropy
Phase diagram of oxygen chemisorbed on nickel (111)
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We are grateful to Professor Tianping Ma for insightful discussions
This work has been supported by the National Key R&D Program of China (Grant Nos
and 2023YFC2410501) and the National Natural Science Foundation of China (Grants Nos
acknowledges support by the National Research Foundation of Korea (NRF) funded by the Korean Government (NRF-2021R1C1C2093113) and the Korea Institute of Science and Technology Institutional Program (2E33421)
acknowledges support by the National Research Foundation of Korea (NRF) funded by the Korean Government (NRF-2023R1A2C1006050)
carried out the experiments and analyzed the data
Nature Communications thanks Shawn Pollard
and the other anonymous reviewer(s) for their contribution to the peer review of this work
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DOI: https://doi.org/10.1038/s41467-025-58529-4
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Magnetic Tunnel Junction-based molecular spintronics devices (MTJMSDs) hold great potential for integrating paramagnetic molecules with ferromagnetic electrodes
creating a diverse array of metamaterials with novel magnetic behaviors
especially between molecules and electrode materials
we used Monte Carlo simulation (MCS) to examine the influence of Dzyaloshinskii-Moriya interaction (DMI) on the MTJMSDs
Our simulations reveal that the presence of DMI interaction significantly lowered the magnetization of the ferromagnetic (FM) electrode
This DMI effect on the FM electrode provides a potential mechanism to explain the experimental observations of losing magnetic contrast on one FM electrode of the MTJMSD
where several thousands of paramagnetic Octametallic Molecular Complexes are covalently bonded between two FM electrodes along the junction edges
exhibited loss of magnetic contrast on one ferromagnet in MFM imaging
DMI’s impact on FM electrode properties resembles the experimental observation on MTJMSD
Our MCS showed that the strong DMI induced alternating magnetic bands aligned in opposite directions on a ferromagnetic electrode
Molecule bridges transported the effect of the DMI-induced magnetic phases onto the FM electrode connected to the other end of the molecule
the direction of magnetization of the FM electrode present on the other end of the molecular channel could switch based on the nature of the DMI-induced magnetic phase present in the junction area
This study underscores the importance of antisymmetric interactions
in influencing the magnetic properties of MTJMSD systems
DMI on FM electrodes can be achieved using suitable molecule-FM interfaces or multilayer FM electrodes harnessing spin-orbit coupling
MTJMSD test bed provides excellent opportunities for creating unprecedented strong molecule-FM electrode coupling and using multilayer electrodes
Although previous MCS studies provided valuable insights
our attempts at density functional theory (DFT) modeling through collaboration faced challenges due to the prohibitive complexity of MTJMSD
we redirected our efforts to expand MCS studies in the alternative direction
a cross-junction-shaped MTJMSD consisted of two long ferromagnetic electrodes intersecting at the junction
We surmise that the antiferromagnetic coupling between electrodes at junctions impacts the ferromagnetic behavior of the electrodes away from the junction
The interplay between this antiferromagnetic interaction at the junction and the ferromagnetic nature of the extended electrodes may induce DMI
which we conjecture as a potential contributor to the observed magnetic contrast loss
we explored the role of DMI within one of the electrodes of MTJMSDs and its influence on the magnetic behavior of MTJMSDs
particularly at the molecule-electrode interfaces in cross-junction configurations where antiferromagnetic coupling is prevalent
we investigated how varying DMI strengths impact the magnetic phases of one electrode and its interaction with the molecular channel
This study offers insights into the potential mechanisms underlying magnetic contrast loss in MTJMSDs
where \(\:{\varvec{S}}_{\varvec{i}}\) and \(\:{\varvec{S}}_{\varvec{i}+1}\:\)represented the neighboring spin vectors within the electrode or at the interface between the electrode and molecule
\(\:{J}_{ml}\) and \(\:{J}_{mR}\) denote the Heisenberg exchange coupling strengths of the left
\(\:\varvec{D}\) represents the Dzyaloshinskii -Moriya vector for the left electrode
All of these parameters are unitless quantities
Schematics of Magnetic tunnel junction (MTJ) (a) Bare (b) With molecule
(c) Atomic force microscopy image of molecule treated MTJ junction (d) Magnetic force microscopy image of the same junction showing partial loss of identity of one electrode
each ferromagnetic electrode could achieve a maximum moment of 1250 for homogeneous spin alignment on each
16 molecules were present along the perimeter
allowing 16 moments when the spins were aligned in the same direction
While our MCS approach also has several limitations
it provides a practical way to investigate a wide range of well-established magnetic interactions to analyze experimental observations
we specifically investigated the role of DMI in the MTJMSD system by varying the DMI of the left electrode to analyze its influence on the system’s magnetic properties and spin configuration
The magnetic properties of MTJMSD were investigated for eight different magnitudes of the Dzyaloshinskii-Moriya interaction (DMI) parameter
We varied the D values for the left electrode along the x-direction ( D = 0
Monte Carlo simulations result investigating the effect of DMI on the MTJMSD devices
Temporal progression of magnetic moments of the left electrode
and MTJMSD at the magnitude of DMI (D) value (a) 0 (d) 0.1 (g) 1
Equilibrium states of a simulated spatial 3-D lattice model of the MTJMSD measured at KT = 0 0.1 for DMI values (b) 0
Zoomed-in a snapshot of the equilibrium state of the molecule between single layers of right and left electrode for DMI values (c) 0
Spin direction along the x-axis for the magnitude of DMI 0 and along the y-axis for both DMI values 0.1 and 0
the right electrode and the entire MTJMSD’s moments overlap
each being 1250 (blue and black data points)
We observed that the number of bands in the form of multiple domain states increases with an increase in DMI
This trend of increasing band numbers on the left electrode is quite interesting as it reveals the clear interplay between DMI and symmetric exchange coupling for a particular electrode
Total band numbers on the left electrode as a function of magnitude of DMI (D)
3-dimensional spatial lattice model at the end of simulation for DMI magnitude (D) = 0.4 for the (a) first and (b) third run
(c) and (d) are the 2-dimensional spatial correlation (SC) contour plots for the respective runs
Time evolution of left ferromagnetic electrode
right ferromagnetic electrode and MTJMSD for discrete DMI magnitudes
plotted energy (U) as a function of iteration counts: (a) Left Electrode (b) Right electrode (c) MTJMSD (d) Molecule-left electrode (e) Molecule -right electrode
(f) Dependence of spin magnetic moment (Msm) of the molecule as a function DMI magnitude (D)
(f) shows the variation of Msm as a function of iteration count at D = 0
Monte Carlo simulations have been effectively utilized to investigate Dzyaloshinskii-Moriya interaction (DMI) variation on cross-junction-shaped magnetic tunnel junction-based molecular spintronics devices
we varied the DMI values applied to the left electrode from 0 to 1
It is observed that the entire left electrode exhibited alternate bands of two oppositely coupled magnetic moments
a short-range ferromagnetic coupling between the molecule and the nearby band of the left electrode was examined
while long-range antiferromagnetic coupling was maintained with the right electrode
we analyzed the temporal evolution of energy for both electrodes
We observed that the impact of DMI on the molecule’s moment is significant
Molecules’ magnetic moment reached a value of 8.5 for the highest DMI magnitude of 1
which is ~ 50% of the maximum attainable value of 16 obtained for D < 0.2
the interaction energy between electrode and molecule also varied for different DMI values
indicating the influence of DMI on molecule-FM electrode interfaces of the MTJMSD devices
We surmise that dissimilar molecule/FM electrode couplings are responsible for producing a DMI-like effect in our experimental studies, leading to the disappearance of magnetic contrast (Fig. 1)
We hypothesize that DMI has subsequently created multiple bands of alternating magnetic phases that locally canceled the magnetic moments along the FM electrodes
Future work is necessary to conduct high spatial resolution MFM to verify the presence of alternating phases
Future work is needed to realize switchability on MTJMSD with FM electrodes showing optimum DMI
The fabrication of successful DMI-based switchable MTJMSD will also require the encapsulation of MTJMSD for reliable long-term operation
The interdependent encapsulation process and the design of FM electrode configurations for achieving DMI in MTJMSD are complex multivariable processes that need significant planning and effort and are part of our future work
The data presented in this paper are available upon reasonable request by contacting the corresponding author at: ptyagi@udc.edu
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Molecular spintronics and quantum computing
Quantum advantage in a molecular spintronic engine that harvests thermal fluctuation energy
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Kondo resonance in a single-molecule transistor
Electron transport through single mn 12 molecular magnets
Large on-off ratios and negative differential resistance in a molecular electronic device
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New mechanism of anisotropic superexchange interaction
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We acknowledge our funding sources: the National Science Foundation CREST Award
Department of Energy/ National Nuclear Security Agency (DE-FOA-0003945) and NASA MUREP Institutional Research Opportunity Grant under Cooperative Agreement #80NSSC19M0196
This research was funded by the National Science Foundation CREST Award
Center for Nanotechnology Research and Education
studied and analyzed the DMI impact on MTJMSD utilizing the Monte Carlo Simulation program developed by C.D.
in conducting simulations and analyzing the data
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations
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DOI: https://doi.org/10.1038/s41598-025-88741-7
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an unusual traffic jam was once caused by rumors of paranormal phenomena spread on prime time
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but it’s best to visit it during the day as it’s a residential neighborhood about 20 minutes away from the nearest station (Minami-Moriya)
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There is a temple purportedly founded by him
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cars seem to defy the laws of physics by rolling uphill
This rocking chair headstone is allegedly haunted by the spirit of a young girl named Pearl
Moriya Jutanugarn almost went the entire week without a bogey at the 2024 Portland Classic
but it didn’t matter as the Thai player clinched her first individual title in six years
Jutanugarn’s most recent LPGA victory came at the 2021 Dow Championship team event with younger sister Ariya
kind of been a long time since my last win.”
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two strokes ahead of a trio of players including Russia’s Nataliya Guseva
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who was in a wheelchair to start the season after breaking her left ankle
who’d previously missed four of her last five cuts
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Really good to build off to go to Europe.”
Jutanugarn is the fourth player from Thailand to win on tour this year:
She’s also the third player from Thailand to earn at least three wins on the LPGA
joining Thitikul (3) and her sister Ariya (12)
“This tournament is showing … no matter what happened
who looked downright giddy about her sister's success
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With so many top players already in France for the Olympics
the week presented an ideal time for players to make big moves toward winning for the first time
came awfully close to becoming the first Russian player to win on the LPGA
I'm kind of disappointed because I knew like I could win this thing very easily.”
A little further down the leaderboard is the intriguing story of Dewi Weber
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The Dutch player actually qualified for the Paris Olympics but was denied a spot because of additional criteria laid out by the Netherlands Olympic Committee
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because I've been on Epson this entire year.”
Weber ultimately dropped down to eighth after a rough stretch on Nos
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shot 74 on Sunday to drop to a share of ninth
The only player in the field in Portland who will be competing in Paris is India’s Aditi Ashok
The 2024 Olympic women's golf competition starts Wednesday and concludes Saturday
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Magnetic skyrmions are potential candidates for high-density storage and logic devices because of their inherent topological stability and nanoscale size
Two-dimensional (2D) Janus transition metal chalcogenides (TMDs) are widely used to induce skyrmions due to the breaking of inversion symmetry
the experimental synthesis of Janus TMDs is rare
which indicates that the Janus configuration might not be the most stable MXY structure
through machine-learning-assisted high-throughput first-principles calculations
we demonstrate that not all MXY compounds can be stabilized in Janus layered structure and a large proportion prefer to form other configurations with lower energy than the Janus configuration
these new configurations exhibit a strong Dzyaloshinskii–Moriya interaction (DMI)
which can generate and stabilize skyrmions even under a strong magnetic field
This work provides not only an efficient method for obtaining ferromagnetic materials with strong DMI but also a theoretical guidance for the synthesis of TMDs via experiments
These works highlight the possibility of tuning basic magnetic parameters and even inducing distinct spin textures in Janus magnets
while other arrangements of X and Y atoms have not yet been considered
previous theoretical works are insufficient to guide experimental synthesis
Searching for 2D Janus materials that can be synthesized requires us to clarify whether the Janus structure is the most stable structure among all the possible AXY structures at the same atomic ratio
These works suggested that machine learning methods can be used to construct surrogate models and assist in time-consuming Density Functional Theory (DFT) calculations
we constructed massive possible structures for 2D MXY TMDs and compared their energies calculated from DFT
The Janus structure has the lowest energy in only a few chemical compositions
while most other chemical compositions favor two anti-Janus structures
Although some TMDs do not possess a Janus structure
a considerable DMI still exists among them
based on the magnetic exchange parameters calculated from DFT
we obtained richer spin textures than Janus structures by spin dynamic simulation and successfully predicted skyrmions in those structures
The red vectors in (a) indicate the two spin configurations with opposite chirality used to extract the in-plane DMI parameters
d Twenty structures with the lowest energy predicted with the SVR model and their comparison with DFT calculations
The energy difference on the most stable structure is 0.00378 eV/unit cell
The energy sequence predicted by the SVR model is similar to that predicted by DFT calculations
which indicates that we have found the most stable structure of CrSeTe
b Structures of Structure II (S2) and Structure III (S3) in 1T-phase.c
TiSSe Structure I (S1) has the lowest energy
and the color maps of S2 and S3 represent the energy difference from S1)
Solid magnetic behavior is beneficial for skyrmions; thus
To explore the magnetic properties of these three structures
we calculated the parameters of the following Hamiltonian model
which describes the spins of magnetic atoms in the hexagonal structure:
The specific method used to calculate J and K is described in the Supplemental Material
ΔEsoc is dominated by the heavy chalcogen atom Te
The color map indicates the out-of-plane spin component of the Mn atoms
we present machine-learning-assisted high-throughput calculations to explore the ground-state configuration of MXY compounds and search for TMDs with strong DMIs
Not all configurations can be stabilized in the Janus layered configuration
and two anti-Janus structures (S2 and S3) can have a lower energy state
This result can be used to explain why 2D Janus TMDs materials are difficult to synthesize experimentally and to guide future works on synthetic TMDs
and the comparison of the energies of different magnetic orders indicated that all of them had ferromagnetic metallic states
The DMI coefficients are obtained via first-principles calculations
and we find that the DMI in S2 is even larger than that in the Janus configuration
Spin dynamics simulations indicate that the anti-Janus structure has a richer spin texture in the absence of an external magnetic field
and skyrmions still exist under strong external magnetic fields
The present work provides an effective way to discover 2D magnets with strong DMI and suggests two anti-Janus ferromagnetic materials that are desirable for spin-orbitronic and memory devices
The energy cutoff for plane wave expansion is set to 500 eV
and a Γ-centered 20 × 20 × 1 k-point mesh is adopted for Brillouin zone integration
All the structures are simulated by a slab model with a 20 Å vacuum layer
and the structures are fully relaxed until the Hellmann–Feynman forces on all atoms are less than 10−3 eV/Å
9 × 9 × 1 and 7 × 7 × 1 k-points are used for the 2 × 2 × 1 and 3 × 3 × 1 supercells
As a type of support vector machine (SVM), SVR was introduced by Corinna Cortes in 199545
The aim of SVR is to find a hyperplane that can minimize the total deviation between sample points and the hyperplane
and only the deviation of sample points out of the decision boundary is considered
The hyperplane in this work can be written as:
where \({\boldsymbol{x}}\) is the feature of our problem
we select the coordinates of the X or Y atoms in MXY as features
and \(f\left({\boldsymbol{x}}\right)\) is the energy of the structure
Our regression problem can be transformed into finding the minimum of:
where \(\left|\left|{\boldsymbol{\omega }}\right|\right|\) is the L2 norm of \({\boldsymbol{\omega }}\)
and \(l\) is the \(\epsilon\)-insensitive loss function
After introducing slack variables \({\xi }_{i}\) and \({\hat{\xi }}_{i}\) to Eq. (3)
\(f\left({{\boldsymbol{x}}}_{{\boldsymbol{i}}}\right)-{y}_{i}\le \epsilon +{\xi }_{i}\)
\({y}_{i}-f\left({{\boldsymbol{x}}}_{{\boldsymbol{i}}}\right)\le \epsilon +{\hat{\xi }}_{i}\)
The Lagrange multiplier coefficients are \({\alpha }_{i}\)
The formula of Lagrange function can be written as:
The partial derivatives of Lagrange function to \({\boldsymbol{\omega }}{\boldsymbol{,}}\,b\)
\({\xi }_{i}\) and \({\hat{\xi }}_{i}\) are zero
we can transfer the origin issue into a dual problem
SVR applies a kernel function to map the nonlinear regression to a higher latitude space
The SVR regression equation can be written as:
Gaussian kernel function \(K\left({x}_{i},{x}_{j}\right)=\exp \left(-\frac{{{||}{x}_{i}-{x}_{j}{||}}^{2}}{2{\sigma }^{2}}\right)\) is used
we use a 100 × 100 supercell with periodic boundary conditions
and the size of the supercell is large enough to eliminate finite-size effects
An external magnetic field is applied in the z-direction from 0 T to 10 T
The data that support the findings of the work is in the manuscript’s main text and Supplementary Information
Additional data are available from the corresponding author upon request
The central codes used in this paper are VASP and VAMPIRE. Source code of machine learning used in this work can be achieved via: https://github.com/Jingtong-Zhang/SVR-code-for-MXY-materials
Near room-temperature formation of a skyrmion crystal in thin-films of the helimagnet FeGe
Thermodynamically stable “vortices” in magnetically ordered crystals
Ferroelectrically tunable magnetic skyrmions in ultrathin oxide heterostructures
Robust formation of skyrmions and topological hall effect anomaly in epitaxial thin films of MnSi
Robust zero-field skyrmion formation in FeGe epitaxial thin films
Quantum properties and applications of 2D Janus crystals and their superlattices
A structure map for AB 2 type 2D materials using high-throughput DFT calculations
Strain-tunable ferromagnetism and chiral spin textures in two-dimensional Janus chromium dichalcogenides
Very large Dzyaloshinskii-Moriya interaction in two-dimensional Janus manganese dichalcogenides and its application to realize skyrmion states
Intrinsic skyrmions in monolayer Janus magnets
magnetic anisotropy and Dzyaloshinskii–Moriya interaction in two-dimensional intrinsic ferromagnetic Janus 2H-VSeX (X = S
Janus monolayers of transition metal dichalcogenides
Anomalous behavior of 2D Janus excitonic layers under extreme pressures
Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set
Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set
An adaptive design approach for defects distribution modeling in materials from first-principle calculations
DeepTMC: A deep learning platform to targeted design doped transition metal compounds
Crystal graph convolutional neural networks for an accurate and interpretable prediction of material properties
Machine learning for perovskite materials design and discovery
Graph networks as a universal machine learning framework for molecules and crystals
Mechanical and electronic properties of Janus monolayer transition metal dichalcogenides
Strain-tunable skyrmions in two-dimensional monolayer Janus magnets
Chemical welding on semimetallic TiS2 nanosheets for high-performance flexible n-type thermoelectric films
Computational insight of ZrS2/graphene heterobilayer as an efficient anode material
Strain effect on the electronic properties of 1T-HfS2 monolayer
Theoretical and experimental researches on NiS2 nanocubes with uniform reactive exposure facets
Not your familiar two dimensional transition metal disulfide: structural and electronic properties of the PdS 2 monolayer
Algorithm for generating irreducible site-occupancy configurations
Anatomy of dzyaloshinskii-moriya interaction at Co/Pt interfaces
Tailoring magnetic skyrmions in ultra-thin transition metal films
Ab initio analysis of magnetic properties of the prototype B20 chiral magnet FeGe
Room-temperature chiral magnetic skyrmions in ultrathin magnetic nanostructures
Tunable room-temperature magnetic skyrmions in Ir/Fe/Co/Pt multilayers
Additive interfacial chiral interaction in multilayers for stabilization of small individual skyrmions at room temperature
Ab initio molecular dynamics for liquid metals
Ab initio molecular-dynamics simulation of the liquid-metal–amorphous-semiconductor transition in germanium
Self-consistent equations including exchange and correlation effects
Generalized gradient approximation made simple
First-principles calculations of the electronic structure and spectra of strongly correlated systems: the LDA+ U method
Hybrid functionals based on a screened Coulomb potential
Atomistic spin model simulations of magnetic nanomaterials
Download references
This work was supported by the National Program on Key Basic Research Project (Grant No
2022YFB3807601) and the National Natural Science Foundation of China (Grant Nos
acknowledges the financial support from the National Natural Science Foundation of China (Grant 12102157) and computational support from the Center for Computational Science and Engineering of Lanzhou University
These authors contributed equally: Peng Han
Department of Engineering Mechanics and Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province
Research Center for New Materials Computing
Key Laboratory of Mechanics on Disaster and Environment in Western China
Department of Mechanics and Engineering Sciences
College of Civil Engineering and Mechanics
carried out the calculation and analysis of the result
All authors discussed the results and reviewed the manuscript
Supplementary Materials for Machine learning assisted screening of two dimensional chalcogenide ferromagnetic materials with Dzyaloshinskii Moriya interaction
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DOI: https://doi.org/10.1038/s41524-024-01419-y
Metrics details
Skyrmions in existing 2D van der Waals (vdW) materials have primarily been limited to cryogenic temperatures
and the underlying physical mechanism of the Dzyaloshinskii–Moriya interaction (DMI)
a crucial ingredient for stabilizing chiral skyrmions
we report the observation of Néel-type skyrmions in a vdW ferromagnet Fe3−xGaTe2 above room temperature
Contrary to previous assumptions of centrosymmetry in Fe3−xGaTe2
the atomic-resolution scanning transmission electron microscopy reveals that the off-centered FeΙΙ atoms break the spatial inversion symmetry
First-principles calculations further elucidate that the DMI primarily stems from the Te sublayers through the Fert–Lévy mechanism
the chiral skyrmion lattice in Fe3−xGaTe2 can persist up to 330 K at zero magnetic field
demonstrating superior thermal stability compared to other known skyrmion vdW magnets
This work provides valuable insights into skyrmionics and presents promising prospects for 2D material-based skyrmion devices operating beyond room temperature
opening up new avenues for 2D topological magnetism
the DMI mechanism in these 2D magnetic materials has yet to be deeply understood
We also find that the Néel skyrmion lattice phase can survive up to 330 K
which is higher than all other known skyrmion vdW magnets
a ZFC (dashed) and FC (solid) curves of bulk Fe3−xGaTe2 measured with an out-of-plane (red) and an in-plane (blue) magnetic field of 200 Oe
Inset shows the derivative of the out-of-plane FC curve
b Out-of-plane bulk isothermal magnetization
c Hall resistance of a 136 nm-thick Fe3−xGaTe2 flake
The red step curve in the device photo is the height profile and the scale bar is 10 μm
d L-TEM images of labyrinth domains (left) and field-induced skyrmions (middle and right) in a 179 nm-thick Fe3−xGaTe2 flake
The sample is ZFC from 370 to 295 K before imaging
e Intensity profile of a skyrmion under reversed tilt angles
The diversity of topological spin textures and their phase transitions reveal that Fe3−xGaTe2 is a rich platform for room-temperature skyrmionics
a–c L-TEM images of a 179 nm-thick Fe3−xGaTe2 flake under different tilt angles
the sample is FC from 370 to 295 K under an out-of-plane magnetic field of 360 Oe
the identical area in a and c is outlined by orange dashed lines
d–g Magnified images of four regions extracted from a and c
The red and blue circles outline two different types of spot domains
h Simulated L-TEM images of a small-sized (up) and a large-sized (down) Néel-type skyrmion under different tilt angles
The markers # and ∗ indicate Bloch-type skyrmion bubbles and Néel-type skyrmions
the average domain wall energy δw can be calculated as \({\delta }_{w}=\frac{w{{M}_{{{{{{\rm{s}}}}}}}}^{2}}{4{{{{{\rm{\pi }}}}}}\beta }\)
where Ms is the saturation magnetization and β is a phenomenological fitting parameter that is approximately equal to 0.31 for magnets with high magnetocrystalline anisotropy
the average domain wall energy at room temperature is estimated to be 0.22 mJ m−2
It is noteworthy that there is no noticeable difference in the skyrmion type
and density between the exposed and hBN-protected Fe3−xGaTe2
indicating that the oxide surface does not considerably enhance the DMI in the present case
the DMI should be intrinsically from Fe3−xGaTe2 itself
a HAADF-STEM image taken along the [100] zone axis
c Intensity profile of the orange dashed lines in (b)
The profile is fitted by the Voigt function (dashed curves)
The peak positions are indicated by the vertical lines
d HAADF-STEM images taken along the [001] zone axis
The dashed rectangle indicates the unit cell
The off-centered FeΙΙ reduces the crystal symmetry
The off-centered FeΙΙ atoms lower the crystal symmetry
making Fe3−xGaTe2 a polar metal that belongs to the non-centrosymmetric space group P3m1 (point group C3v)
which can be expressed as \({{{{{{\bf{D}}}}}}}_{{ij}}=\left|{{{{{\boldsymbol{\sigma }}}}}}\right|{{{{{{\boldsymbol{\sigma }}}}}}}_{i{i}^{{\prime} }}{{{{{{\boldsymbol{\sigma }}}}}}}_{j{j}^{{\prime} }}{{{{{{\bf{D}}}}}}}_{{i}^{{\prime} }{j}^{{\prime} }}\)
where σ contains all the symmetry operations contained in the specific point group
The nonzero diagonal or off-diagonal entries in the matrix determine the type of DMI
We can identify the DMI tensor of C3v point group:
with one independent nonzero off-diagonal entries D12
This essentially ensures the existence of interfacial-type DMI
while bulk-type DMI is absent under this condition
a Clockwise and counter-clockwise spin spiral models used in the DFT calculation
b Calculated microscopic and micromagnetic DMI parameters (d and D) as a function of FeΙΙ displacement
Note that the FeΙΙ displacements in the upper and lower layers are set to the same value for simplicity
c Schematic of spin structure and layer-resolved SOC energy difference ΔESOC calculated using the SCXRD-refined crystal structure
It is worth mentioning that our first-principles calculations reveal that the stoichiometric Fe3GaTe2 (without defects) is energetically more favorable to form the centrosymmetric crystal structure rather than the non-centrosymmetric one
Considering the Fe deficiency in our samples
we speculate that the observed FeΙΙ displacement might be caused by defects
such as Fe vacancies and/or interstitial Ga and Te atoms
The small unequal displacements in the two layers might be caused by the nonuniformity of local defect conditions
We would like to leave this interesting topic as an open question for future studies
here they show a significant size variation
suggesting a relatively weaker DMI in Fe3−xGaTe2
One can observe that the skyrmion size obviously changes with the flake thickness
The non-monotonic variation trend suggests the complicated thickness dependence of dipolar interaction and magnetic anisotropy
the magnetic skyrmions in Fe3−xGaTe2 should be primarily dipolar stabilized
and the DMI is essential to guarantee the Néel-type configuration
we have demonstrated a new vdW skyrmion-hosting ferromagnet Fe3−xGaTe2
isolated Néel-type skyrmions and metastable skyrmion lattices at zero magnetic field are successfully generated by tuning the magnetic field and applying a specific FC procedure
The metastable chiral skyrmion lattice exhibits remarkable thermal stability even above room temperature
which is the highest temperature among all known 2D vdW magnets
we have comprehensively investigated the physical origin of the DMI in Fe3−xGaTe2
An unexpected FeΙΙ displacement is experimentally observed
which breaks the spatial inversion symmetry and leads to the C3v point group
First-principles calculations further unveil that the DMI is dominated by the three-site Fert–Lévy mechanism
Our results provide a novel paradigm of 2D topological magnets and reveal the immense potential of Fe3−xGaTe2 for future skyrmion-based applications
High-quality Fe3−xGaTe2 single crystals were synthesized using a modified CVT method
The flake thickness was determined by atomic force microscopy (Park NX20)
The SCXRD experiment was performed on a Bruker D8 Venture diffractometer with Mo Kα radiation (λ = 0.71073 Å)
The magnetization measurements were carried out in a physical property measurement system with the VSM option (DynaCool
The Fe3−xGaTe2 Hall-bar device was fabricated by standard electron-beam lithography (Raith eLINE)
The electrical transport properties were measured in DynaCool
The L-TEM samples were exfoliated from bulk crystals using blue tapes (Ultron Systems)
Then they were transferred onto a silicon nitride TEM grid (CleanSiN) using polydimethylsiloxane
The Fe3−xGaTe2/hBN heterostructures were made by stacking another hBN flake on the top following the same transfer procedure
The exfoliation and transfer processes were carried out in a N2-filled glovebox (O2 < 0.5 ppm
The cross-sectional samples for HAADF-STEM experiments were cut from bulk crystals and thinned by the focused ion-beam milling technique on a TESCAN LYRA3 FIB-SEM system
The SAED and L-TEM images were acquired on an FEI Titan Cs Image (Spectra 300
The HAADF-STEM images were obtained on an FEI Titan Cs Probe (Titan Cubed Themis Z
Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article
The data that support the findings of this study are available from the corresponding author upon reasonable request
Spontaneous skyrmion ground states in magnetic metals
Noncentrosymmetric magnets hosting magnetic skyrmions
Current-induced reversible split of elliptically distorted skyrmions in geometrically confined Fe3Sn2 nanotrack
Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals
Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit
Gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2
Magnetism in two-dimensional van der Waals materials
Two-dimensional materials prospects for non-volatile spintronic memories
Integrated memory devices Based on 2D materials
Observation of magnetic skyrmion bubbles in a van der Waals ferromagnet Fe3GeTe2
Magnetic skyrmions with unconventional helicity polarization in a van der Waals ferromagnet
Room-temperature skyrmion lattice in a layered magnet (Fe0.5Co0.5)5GeTe2
Topological magnetic-spin textures in two-dimensional van der Waals Cr2Ge2Te6
Direct observation of magnetic bubble lattices and magnetoelastic effects in van der Waals Cr2Ge2Te6
Néel-type skyrmion in WTe2/Fe3GeTe2 van der Waals heterostructure
Characteristics and temperature-field-thickness evolutions of magnetic domain structures in van der Waals magnet Fe3GeTe2 nanolayers
Néel-type skyrmions and their current-induced motion in van der Waals ferromagnet-based heterostructures
Magnetic skyrmions in a thickness tunable 2D ferromagnet from a defect driven Dzyaloshinskii–Moriya interaction
Controllable skyrmionic phase transition between Néel skyrmions and bloch skyrmionic bubbles in van der Waals ferromagnet Fe3−δGeTe2
Creation of skyrmions in van der Waals ferromagnet Fe3GeTe2 on (Co/Pd)n superlattice
History-dependent domain and skyrmion formation in 2D van der Waals magnet Fe3GeTe2
Skyrmionic spin structures in layered Fe5GeTe2 up to room temperature
Room-temperature magnetic skyrmions and large topological hall effect in chromium telluride engineered by self-intercalation
Magnetic skyrmionic bubbles at room temperature and sign reversal of the topological hall effect in a layered ferromagnet Cr0.87Te
Magnetic stripes and skyrmions with helicity reversals
Chiral helimagnetism and one-dimensional magnetic solitons in a Cr-intercalated transition metal dichalcogenide
Asymmetric skyrmion Hall effect in systems with a hybrid Dzyaloshinskii-Moriya interaction
Intrinsic van der Waals magnetic materials from bulk to the 2D limit: new frontiers of spintronics
Observation of Néel-type skyrmions in acentric self-intercalated Cr1+δTe2
Multiferroic materials based on transition-metal dichalcogenides: Potential platform for reversible control of Dzyaloshinskii-Moriya interaction and skyrmion via electric field
Air-stable ultrathin Cr3Te4 nanosheets with thickness-dependent magnetic biskyrmions
Ordering of room-temperature magnetic skyrmions in a polar van der Waals magnet
Tuning magnetic order in the van der Waals metal Fe5GeTe2 by cobalt substitution
Coexistence of non-trivial van der Waals magnetic orders enable field-free spin-orbit torque switching at room temperature
Preprint at arXiv preprint arXiv:2308.13408
Anisotropy induced by nonmagnetic impurities in CuMn spin-glass alloys
Role of anisotropic exchange interactions in determining the properties of spin-glasses
Nearly room temperature ferromagnetism in a magnetic metal-rich van der Waals metal
Ferromagnetism near room temperature in the cleavable van der Waals cystal Fe5GeTe2
Magnetization reversal of Co/Pt multilayers: Microscopic origin of high-field magnetic irreversibility
Observation of stable Néel skyrmions in cobalt/palladium multilayers with Lorentz transmission electron microscopy
Laser-induced magnetic nanostructures with tunable topological properties
Skyrmionium - high velocity without the skyrmion Hall effect
Seeding and emergence of composite skyrmions in a van der Waals Magnet
Skyrmion and skyrmionium formation in the two-dimensional magnet Cr2Ge2Te6
Observation of robust Néel skyrmions in metallic PtMnGa
Building traps for skyrmions by the incorporation of magnetic defects into nanomagnets: Pinning and scattering traps by magnetic properties engineering
Néel-type skyrmion lattice with confined orientation in the polar magnetic semiconductor GaV4S8
Néel-type skyrmion lattice in the tetragonal polar magnet VOSe2O5
A new class of chiral materials hosting magnetic skyrmions beyond room temperature
Toggle-like current-induced Bloch point dynamics of 3D skyrmion strings in a room temperature nanowire
Chiral magnetism and high-temperature skyrmions in B20-ordered Co-Si
The role of temperature and drive current in skyrmion dynamics
Zur bestimmung der blochwandenergie von einachsigen ferromagneten
Dzyaloshinskii-Moriya interaction accounting for the orientation of magnetic domains in ultrathin films: Fe/W(110)
Above-room-temperature strong intrinsic ferromagnetism in 2D van der Waals Fe3GaTe2 with large perpendicular magnetic anisotropy
Anatomy of Dzyaloshinskii-Moriya Interaction at Co/Pt Interfaces
Creation of magnetic skyrmion bubble lattices by ultrafast laser in ultrathin films
Theory of isolated magnetic skyrmions: from fundamentals to room temperature applications
Magnetic microscopy and topological stability of homochiral Néel domain walls in a Pt/Co/AlOx trilayer
Particle-size dependent structural transformation of skyrmion lattice
Magnetic and geometric control of spin textures in the itinerant kagome magnet Fe3Sn2
Nanoscale magnetic bubbles in Nd2Fe14B at room temperature
Tunable magnetic antiskyrmion size and helical period from nanometers to micrometers in a D2d heusler compound
MALTS: a tool to simulate lorentz transmission electron microscopy from micromagnetic simulations
Download references
This research is supported by the National Research Foundation
Singapore and A*STAR under its Quantum Engineering Programme (NRF2022-QEP2-03-P13)
UParis-NUS 2023 award (Inducing magnetic chirality without heavy metals)
National Natural Science Foundation of China (nos
and 51771085); National Key Research and Development Program of China (MOST) (nos
These authors contributed equally: Chenhui Zhang
Department of Electrical and Computer Engineering
School of Materials and Energy and Electron Microscopy Centre of Lanzhou University
Collaborative Innovation Center of Advanced Microstructures
conceived the idea and designed the experiments
operated the L-TEM and HAADF-STEM experiments under the guidance of J.Z
carried out the first-principles calculations under the guidance of Hx.Y.; C.Z.
analyzed the data and wrote the manuscript
All authors contributed to the discussion of the results and the improvement of the manuscript
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DOI: https://doi.org/10.1038/s41467-024-48799-9
— Moriya Jutanugarn emerged from a tight pack late Sunday afternoon at Columbia Edgewater Country Club to win the Portland Classic
the sixth victory of her LPGA Tour career and first individual triumph in more than six years
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(AP) Moriya Jutanugarn emerged from a tight pack late Sunday afternoon at Columbia Edgewater to win the Portland Classic for her third career LPGA Tour title and first individual victory in more than six years
Three strokes behind leader Andrea Lee going into the round
Jutanugarn shot a 6-under 66 in mostly calm conditions for a two-stroke victory over three players
“Kind of been a long time since my last win,” Jutanugarn said
“To be in contention for the last few days
I feel like I haven’t been in contention for a little while
It kind of keep your on toes and exciting.”
playing the first 71 holes without a bogey
13-15 and made an 8-footer to save par on the par-3 16th
She made a short birdie putt on the par-4 17th and closed with a bogey
“When you make that putt it kind of feels a lot better and like taking a lot of the pressure off,” Jutanugarn said about the par save on 16
Nataliya Guseva (68) and Angel Yin (69) tied for second
The 21-year-old Guseva is the first Russian player with an LPGA Tour card
I’m kind of disappointed because I knew like I could win this thing very easily.”
Jutanugarn’s previous individual LPGA Tour victory came in the 2018 HUGEL-JTBC LA Open
she teamed with younger sister Ariya Jutanugarn to win the 2021 Dow Great Lakes Bay Invitational
because like I know she been waiting for so long,” said Ariya Jutanugarn
a 12-time LPGA Tour winner who closed with a 65 on Sunday to tie for ninth at 17 under
Sofia Garcia (68) and So Mi Lee (70) tied for fifth at 19 under
and second-round leader Dewi Weber (72) was another stroke back
the 2022 winner for her lone LPGA Tour title
had a 74 to finish in the group at 17 under
Weber dropped back with a double bogey on the par-4 15th and a bogey on 16
She was trying to win for the first time on the LPGA Tour and send a statement to the Dutch Olympic committee that it made a mistake by declining to send her to Paris
She qualified for the Olympics under International Golf Federation standards
but was left out because of the Netherlands’ separate standards for all sports to meet a realistic chance of a top-eight finish
no one from the top 30 in the world ranking was in the field
The lone Olympian in Portland was Aditi Ashok of India
She finished with a 72 to tie for 22nd at 14 under
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Ryotaro Taguchi has won three of his last five matches
Taguchi successfully qualified for the main draw tournament
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Taguchi failed to qualify for the main draw tournament
he is looking for a solid result to get into the top 500 in the rankings
Sho Shimabukuro has lost three of his last five matches
Sho lost in the opening round against Hassan in straight sets
The Japanese had a somewhat turbulent season so far
He had his most significant results on the Challenger Tour level
His biggest result was winning the challenger title in Shanghai earlier this season
he is looking for a solid result to cement his top 200 status
we believe Shimabukuro will fight for a top 100 place next season
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Shimabukuro covering the games handicap is a value bet
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Yoshihito Nishioka has lost three of his last five matches
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Moriya successfully qualified for the main draw tournament
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Main Photo Credit: Geoff Burke-USA TODAY Sports
Qinwen Zheng looked a shadow of herself against Anastasia Potatpova
A 6-4 6-4 loss sent the World #8 home early; a
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Kadokawa has announced the addition of two new cast members for the upcoming The Gorilla God’s Go-To Girl TV anime series
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the anime series is also hosting a collaboration with popular Japanese curry chain Go Go Curry
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Crunchyroll licensed the The Gorilla God’s Go-To Girl anime series for streaming worldwide
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Volume 8 - 2020 | https://doi.org/10.3389/fbioe.2020.00974
strains IU 180733JP01 (5-11-6-3) and 190790JP01 (5-25-4-2) from seaweeds and showed that both strains accumulate poly(3-hydroxybutyrate) [P(3HB)] homopolymer in a nitrogen-limiting mineral salt medium containing alginate as a sole carbon source
Genome sequence analysis of the isolated strains showed that they have putative genes which encode enzymes relevant to alginate assimilation and P(3HB) synthesis
and the putative alginate-assimilating genes formed a cluster
Investigation of the optimum culture conditions for high accumulation of P(3HB) showed that when the 5-11-6-3 strain was cultured in a nitrogen-limiting mineral salt medium (pH 5.0) containing 6% NaCl and 3% (w/v) alginate as a sole carbon source for 2 days
the P(3HB) content and P(3HB) production reached 62.1 ± 3.4 wt% and 3.11 ± 0.16 g/L
When the 5-25-4-2 strain was cultured in a nitrogen-limiting mineral salt medium (pH 4.0) containing 5% NaCl and 3% (w/v) alginate for 2 days
the P(3HB) content and P(3HB) production reached 56.9 ± 2.1 wt% and 2.67 ± 0.11 g/L
the 5-11-6-3 strain also produced P(3HB) in a nitrogen-limiting mineral salt medium (pH 5.0) containing 6% NaCl and freeze-dried and crushed waste Laminaria sp.
which is classified into brown algae and contains alginate abundantly
The resulting P(3HB) content and P(3HB) productivity were 13.5 ± 0.13 wt% and 3.99 ± 0.15 mg/L/h
we demonstrated the potential application of the isolated strains to a simple P(3HB) production process from seaweeds without chemical hydrolysis and enzymatic saccharification
there are few studies on PHA production from marine biomass
utilization of marine biomass can contribute to the increase in the diversity of substrates for PHA production
seaweeds that were chemically hydrolyzed and/or enzymatically saccharified were used for PHA production
One-step PHA production without those pretreatments would be important for a further practical production process
which we identified as strains of a Cobetia sp.
that are capable of utilizing alginate as a sole carbon source for P(3HB) production and growth
The optimum culture conditions were determined to reach effective accumulation of PHA from alginate
and the metabolic pathways relevant to alginate-assimilation and P(3HB)-synthesis were predicted based on the draft genome sequence of the isolated strains
we demonstrated that the isolated strains could produce P(3HB) from a Laminaria sp
without chemical hydrolysis and enzymatic saccharification treatment
With respect to the MM medium containing the waste Laminaria sp.
the lyophilized sections were crushed into small chips
the cells were harvested by centrifugation (6,400 g × 15 min
4°C) and washed three times with distilled water
was removed by a filter paper before centrifugation
and the polymer was extracted with chloroform at 70°C for 48 h in glass tubes with screw caps
Cell debris was removed by passage through a PTFE filter
The extracted polymer was subsequently subjected to nuclear magnetic resonance (NMR)
and differential scanning calorimetry (DSC) analyses
The extracted polymers were dissolved in deuterated chloroform and analyzed by NMR
The 1H-NMR spectra of the polymer were obtained using a JNM-AL400 spectrometer (400 MHz; JEOL
with tetramethylsilane as the internal reference
GPC and DSC analyses of extracted polymers were performed at Mitsui Chemical Analysis and Consulting Service (Japan)
Polymers dissolved in hexafluoroisopropyl alcohol (HFIP) were applied to an analytical GPC (Showa Denko
Japan) equipped with Shodex HFIP-G and HFIP-606 M (Showa Denko
The mobile phase was HFIP containing 0.01 mM sodium trifluoroacetate
The molecular weight was estimated using a polymethyl methacrylate standard (Showa Denko
DSC data were recorded in the temperature range of −90 to 200°C on an X-DSC7000 system (Hitachi High-Tech Science
Japan) equipped with a cooling accessory under a nitrogen flow rate of 50 mL/min
The solvent-cast films (10 mg) were encapsulated in aluminum pans and heated from −90 to 200°C at 10°C/min (first heating scan)
The melt samples were then rapidly quenched at −90°C and maintained at −90°C for 5 min
They were heated from −90 to 200°C at 10°C/min (second heating scan)
The glass-transition temperature (Tg) was taken as a midpoint of the heat capacity change
The melting temperature (Tm) was determined from the positions of the endothermic peaks
The coding genes were annotated using the NCBI nr database by BLAST
In order to calculate polymer content (weight percent) based on the dry cell weight and polymer productivity
The lyophilized cells were ground into powder
By incubating ∼30 mg of lyophilized cells with 1 mL chloroform
P(3HB) was ethanolyzed to ethyl 3-hydroxybutyrate
the esterified sample was neutralized by addition of 4 mL mixed solution (0.65 M NaOH and 0.9 M NaCl) and 2 mL solution (0.25 M Na2HPO4)
The organic phase containing ethyl 3-hydroxybutyrate was mixed with 16 μg of ethyl caproate as a standard and analyzed by GC on a GC4000 Plus system (GL Science
Japan) using an HP-5 column (0.25 mm × 30 m
The carrier gas was nitrogen at a flow rate of 1.6 mL/min
The GC conditions were as follows: an initial oven temperature of 45°C held for 1 min and increased to 80°C at a rate of 7°C/min and then to 300°C at a rate of 80°C/min
Beached seaweeds of Ofunato Bay (Iwate Prefecture
Japan) were selected as sources of microorganisms
The samples were put directly into the Zobell Marine Broth 2216E medium (pH 5.0
and liquid culture was carried out for 2–3 days
More than 300 colonies were isolated from the culture solution
All colonies were inoculated into the agar plate containing MM medium
and alginate as the sole carbon source for the growth and biosynthesis of PHA
The Nile red-stained colonies were selected as candidates for PHA-producing microorganisms
The 5-11-6-3 strain and the 5-25-4-2 strain, which grew in the MM medium that contained alginate as the sole carbon source at pH 5.0, exhibited strong staining. Thus, both these strains were examined for their ability to produce PHA from alginate at 30°C for 2 days under aerobic conditions. In the 1H-NMR spectra, the products of the 5-11-6-3 and 5-25-4-2 strains showed the resonances for P(3HB) between 5.24 and 5.28 ppm, 2.44 and 2.64 ppm, 1.27 and 1.28 ppm (Figure 1)
1H-NMR spectra of a commercial P(3HB) and P(3HB) produced from the isolated strains grown in the MM medium containing 3% (w/v) alginate at pH 5.0 and 30°C for 2 days
IU180733JP01 (5-11-6-3); (B) P(3HB) produced from Cobetia sp
IU190790JP01 (5-25-4-2); (C) commercial P(3HB)
The 5-11-6-3 strain and the 5-25-4-2 strain were identified by phylogenetic analysis and biochemical properties (Table 1)
The 16S rRNA gene sequences showed high similarity between the 5-11-6-3 strain (accession no
LC549335) and the 5-25-4-2 strain (accession no
but they were not completely identical (99% identity
we used these strains for further experiments as a different strain
The results of the 16S rRNA gene sequence of 1,411 bp from the 5-11-6-3 strain revealed a 100% identity to the partial sequence of the 16S rRNA gene of Cobetia sp
MH790205); this was followed by a 100% identity to a partial sequence of the 16S rRNA gene of Cobetia sp
strain Aga-AMLN-15-8 (1410/1410) (accession no
The third-closest identity was shown by the 16S rRNA gene of Cobetia marina strain HNS037 with 100% identity (1399/1399) (accession no
the results of the 16S rRNA sequence of 1,435 bp from the 5-25-4-2 strain revealed a 99% identity to the partial sequence of the 16S rRNA gene of Cobetia pacifica strain GPM2 (1429/1433) (accession no
CP047970); this was followed by a 99% identity to a partial sequence of the 16S rRNA gene of Cobetia sp
The third-closest identity was shown by the 16S rRNA gene of Cobetia marina strain JCM 21022 with 99% identity (1429/1433) (accession no
the 5-11-6-3 and 5-25-4-2 strains were identified as strains of Cobetia sp
according to all of the identification results
The isolates were deposited in the National Institute of Technology and Evaluation (NITE)
IU180733JP01 (5-11-6-3) (NITE P-02758) and Cobetia sp
In a phylogenetic tree of isolated strains with alginate-degrading bacteria (alginate lyase-producing bacteria) (Wong et al., 2000; Yamaguchi et al., 2019), the isolated strains closely related to C. marina and belonged to a cluster of marine bacteria (Figure 2)
there are no reports that these bacteria except Hydrogenophaga sp
UMI-18 exhibited PHA production from alginate
Phylogenetic tree of isolated strains with alginate-degrading bacteria (alginate lyase-producing bacteria)
The trees were constructed by the neighbor-joining method with MEGA-X software
was described after each microorganism name
The numbers at the branch nodes represent the levels of bootstrap support based on the analyses of 500 replicates
The assembled genome of the 5-11-6-3 strain and 5-25-4-2 strain consisted of 40 scaffolds with from 281 to 925,956 bp (accession nos
BLWJ01000001–BLWJ01000040) and 41 scaffolds with from 261 to 1,114,877 bp (accession nos
According to the results of assembly between the genome sequences of the 5-11-6-3 strain and the 5-25-4-2 strain
but the 5-11-6-3 strain and 5-25-4-2 strain were different strains
was found in scaffold 1 (925,956 bp) of the 5-11-6-3 strain and in scaffold 1 (1,114,691 bp) of the 5-25-4-2 strain
the putative gene encoding 2-keto-3-deoxy-D-gluconate (KDG) kinase
was not found in the draft genome sequences of either strain
Putative genes encoding the proteins or enzymes related to alginate assimilation and P(3HB) synthesis in the draft genome of Cobetia sp
Putative genes encoding the proteins or enzymes related to alginate assimilating and P(3HB) synthesis in the draft genome of Cobetia sp
Schematic representation of the putative gene cluster encoding enzymes relevant to alginate assimilation in Cobetia sp
Oligoalginate transporter and outer membrane porins genes: gray; alginate lyase genes
horizontal stripe; transcription regulator
Predicted biosynthetic pathway of P(3HB) from alginate in Cobetia sp
The amino acid sequences were relatively conserved around the α/β hydrolase domain
The conserved catalytic triad residues and lipase-like box residues were also found in the putative PhaC from the 5-11-6-3 and 5-25-4-2 strains
All putative genes related to alginate assimilation and P(3HB) synthesis listed in Tables 2, 3 with the exception of phaC showed over 99% identity between the 5-11-6-3 strain and 5-25-4-2 strain, while only the putative gene encoding PhaC did not show high identity between the 5-11-6-3 strain and 5-25-4-2 strain (Supplementary Figure S1)
The presence of an alginate-assimilating gene cluster and P(3HB)-synthesis genes in the genome of the 5-11-6-3 and 5-25-4-2 strains supported that the 5-11-6-3 and 5-25-4-2 strains have the ability to synthesize P(3HB) from alginate as a sole carbon source
We therefore further investigated the time course of growth and P(3HB) production of isolated strains using the MM medium containing 3% (w/v) alginate and 6% NaCl at pH 5.0 (for the 5-11-6-3 strain)
or 3% (w/v) alginate and 5% NaCl at pH 4.0 (for the 5-25-4-2 strain)
and pH on growth and P(3HB) production in Cobetia sp
(A) Effect of alginate concentration on growth
IU180733JP01 (5-11-6-3) in the MM medium containing 2% NaCl at 30°C
(B) Effect of alginate concentration on growth
IU190790JP01 (5-25-4-2) in the MM medium containing 2% NaCl at 30°C
(C) Effects of NaCl concentration on growth
IU180733JP01 (5-11-6-3) in the MM medium containing 3% (w/v) alginate at 30°C
(D) Effect of NaCl concentration on growth
IU190790JP01 (5-25-4-2) in the MM medium containing 3% (w/v) alginate at 30°C
IU180733JP01 (5-11-6-3) in the MM medium containing 3% (w/v) alginate and 6% NaCl at 30°C for 3 days
IU190790JP01 (5-25-4-2) in the MM medium containing 3% (w/v) alginate and 5% NaCl at 30°C for 2 days
Dry cell weight was measured after freeze-drying
The P(3HB) content of freeze-dried cells was determined by the weight of the produced P(3HB)
The data represent means ± S.D (n = 3)
The maximum P(3HB) content and P(3HB) production were 56.9 ± 2.1 wt% and 2.67 ± 0.11 g/L
Time profiles of growth and P(3HB) synthesis by Cobetia sp
IU180733JP01 (5-11-6-3) was cultured in the MM medium containing 3% (w/v) alginate and 6% NaCl at pH 5.0 and 30°C
IU190790JP01 (5-25-4-2) was cultured in the MM medium containing 3% (w/v) alginate and 5% NaCl at pH 4.0 and 30°C
The Tg and Tm values for P(3HB) obtained from the 5-25-4-2 were 5.1 and 176.0°C
Thermal properties and molecular weights of P(3HB) produced by Cobetia sp
Although the maximum P(3HB) production and polymer properties showed no significant differences between the 5-11-6-3 strain and the 5-25-4-2 strain
the 5-11-6-3 strain continued to exhibit high P(3HB) accumulation after 48 h of cultivation
we selected the 5-11-6-3 strain for further experiments
The utilization of low-purity substrates for P(3HB) production is advantageous for industrial application. We tried to use waste Laminaria sp. obtained from a seaweed farm in Yamada Bay (Iwate Prefecture, Japan) for P(3HB) production. The growth profile and P(3HB) accumulation of the 5-11-6-3 strain were evaluated in the MM medium containing 6% NaCl and 5%(w/v) freeze-dried and crushed Laminaria sp. at pH 5.0 for 4 days (Figure 8)
the cell growth was saturated and P(3HB) accumulation was confirmed [the P(3HB) content and P(3HB) productivity were 13.5 ± 0.13 wt% and 3.99 ± 0.15 mg/L/h
The P(3HB) content and P(3HB) productivity decreased gradually after 24 h
weight of seaweeds was decreased to approximately 45 wt% of the adding amount before cultivation
IU180733JP01 (5-11-6-3) from waste Laminaria species
IU180733JP01 (5-11-6-3) was cultured in the MM medium containing 6% NaCl and 5% (w/v) Laminaria sp
was lyophilized and crushed into small chips
There were two differences in the screening process between the previous study and our present one
The first difference was the source of the isolated microorganisms
Although in our previous screening we isolated microorganisms from shallow sea mud samples taken from Ofunato Bay
in this study we used beached seaweeds obtained from Ofunato Bay as a source of microorganisms
Another difference concerned the components of the culture medium used for microorganism isolation
the samples were inoculated directly into the MM medium containing alginate or mannitol as the sole carbon source in order to enrich target microorganisms
which is suitable for culturing marine bacteria
our finding of new microorganisms having the ability to biosynthesize P(3HB) from alginate would be due to these differences in the screening process
This predicted P(3HB) synthesis pathway from alginate in the isolated strains was similar to the predicted pathway in Hydrogenophaga sp
the putative gene encoding KDPG aldolase was not located in an alginate-assimilating gene cluster
and the putative genes encoding enzymes which catalyze conversion reactions from acetyl-CoA to P(3HB) did not form one gene cluster
Considering the rapid decrease in P(3HB) content in the stationary phase
the former would be a main cause in this experimental culture conditions
we should clarify which kinds of carbon sources of waste Laminaria sp
would be easily utilized for growth and P(3HB) production by the 5-11-6-3 strain in our future work
degradans 2–40 using the medium including untreated red algae
which was a similar value to the P(3HB) content of our isolated strain using the MM medium including Laminaria sp
without chemical hydrolysis and enzymatic saccharification
degradans 2–40 required at least 65 h of cultivation to reach 12 wt% of P(3HB) content
Our isolated strain accumulated an amount of P(3HB) almost equal to that accumulated by S
degradans 2–40 (13.5 ± 0.13 wt%) by culture of only 24 h
our isolated strain is an appropriate candidate for application to P(3HB) production from not only pure alginate extracted from seaweeds but also brown algae
In order to enhance P(3HB) productivity using the isolated strain and brown algae
it will be important to fine tune the culture conditions in our future experiments
MY designed the study and revised the manuscript
and MY wrote the manuscript with the help of MM
and YY performed the experiments with the help of MN and MM
All authors viewed and approved the manuscript and contributed significantly to the work
The work was supported by the Regional Innovation R&D Program (to MY) from Iwate Prefecture
and the Research support program of Initiative for the Implementation of the Diversity Research Environment (Traction Type) (to MY) from the MEXT
S-JK was employed by the company Toyota Boshoku Corporation
The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest
Yoshimi Sasaki (SANRIKU Bio Research Group) for supporting our sampling from Ofunato Bay
Naoshi Tamura (Iwate University) for preparing waste Laminaria sp
The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fbioe.2020.00974/full#supplementary-material
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Which Are Capable of Utilizing Alginate or Waste Laminaria sp
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The anime is also holding a collaboration with Go Go Curry, a popular Japanese restaurant chain whose logo features a gorilla face. Lead voice actress Kanna Nakamura conceived a "May You Also Be Blessed ♡ Gorilla God Face Curry" dish that five of the chain's Tokyo branches will serve from April 1 to April 30
Shugo Nakamura is performing the opening theme song "Illuminate," and Megumi Ogata is performing the ending theme song "Serendipity." The above video previews some of the opening theme song
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Thailand's Moriya Jutanugarn birdied four of her last seven holes to pull away from the field and win the Portland Classic on Sunday in Oregon
6-under-par 66 at Columbia Edgewater Country Club
with her only bogey of the entire tournament coming at the 72nd hole
Russia's Nataliya Guseva (68) and South Korea's Narin An (66)
An jumped into the lead at 21 under by acing the par-3 16th hole
She followed up the dramatic hole-in-one with only a par and a bogey
setting the clubhouse lead at 20 under before Moriya rolled past her
and like kind of been a long time since my last win," Moriya said
like to be in contention for the last few days
like I feel like I haven't been in contention for a little while."
began the day three strokes off the pace before following up her Saturday round of 64 by rocketing up the leaderboard
The final of her seven birdies came at the par-4 17th to give her some breathing room
Moriya knew she had an opportunity to complete the tournament bogey-free
but her par putt at the 18th slid just past the cup
I don't want to say I'm trying (to finish bogey-free)," Moriya said
like when you are in the momentum of like going and everything is kind of being like your way like most of the time
It is Moriya's third LPGA victory and her first time in the winner's circle at a non-team event since 2018
She also won the 2021 Dow Great Lakes Bay Invitational with her sister Ariya
Ariya shot a 65 on Sunday and wound up in a tie for ninth at 17 under; not long after
she was seen excitedly congratulating her older sister on her victory
"I would say so excited and so proud of her
because like I know she been waiting for so long," Ariya said
but like she go through up and down in her life
"She been like really struggling and this year is really hard for her
this tournament is show like she well deserve because she never give up."
said she could not see her hole-in-one from the 16th tee
and it landed on the front of the green and took a few hops before tracking straight into the hole
‘Whooo,' and then like ‘Rahhhh,' like this
So Mi Lee of South Korea (69) and Polly Mack of Germany (70) tied for fifth at 19 under
Second-round leader Dewi Weber of the Netherlands shot a 72 and placed eighth at 18 under
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Moriya in action in PortlandAFPThailand's Moriya Jutanugarn (30) won her third career LPGA title on Sunday, going bogey-free for 71 holes to capture the Portland Classic by two strokes.Moriya fired a six-under par 66 despite closing with her only bogey of the event to stand on 22-under 266 after 72 holes at Columbia Edgewater Country Club in Oregon
"Every win is special," she said
"It has kind of been a long time since my last win."
It was the first individual triumph for Moriya since the 2018 LA Open, her other LPGA victory coming at the 2021 Great Lakes Bay Invitational pairs event with sister Ariya
"I like to be in contention," Moriya said
I feel like I haven't been in contention for a little while
It keeps you on your toes and it's exciting."
Sharing second on 268 were South Korea's An Na-rin, who aced the par-3 16th, American Angel Yin and Russia's Nataliya Guseva
Germany's Polly Mack, Paraguay's Sofia Garcia and South Korea's Lee So-mi were on 269 with Dewi Weber of the Netherlands in eighth on 270
par-5 seventh and par-3 eighth holes and seized the lead by reeling off three birdies in a row at the par-5 12th
she sank a clutch nine-foot par putt at the par-3 16th to stay bogey-free for the week and keep her lead
it felt a lot better and felt like taking a lot of pressure off," Moriya said
Moriya then made a five-foot birdie putt at 17
and even though she missed an eight-foot par putt at 18
"Bogey free would be great," Moriya said
"But I think I'm in a pretty good position."
When Yin could not hole out from the fairway to force a playoff
whose excited sister Ariya greeted her just off the 18th green
"So excited and so proud of her because I know she been waiting for so long," Ariya said
"We won together in 2021 but she always say
"She has really struggled and this year was really hard for her
This shows she is well deserving because she never gives up
Weber birdied seven and eight and another birdie at the 12th lifted her within a stroke of the lead
But she found a bunker then deep rough at 15 on the way to a double bogey to fall three adrift
Metrics details
Seeking to enhance the strength of the interlayer Dzyaloshinskii-Moriya interaction (IL-DMI) through a combination of atomic and Rashba type spin-orbit coupling (SOC) we studied the strength and the thickness evolution of effective interlayer coupling in Co/Ag/Co trilayers by means of surface sensitive magneto-optical measurements that take advantage of the light penetration depth
thickness-dependent chiral interaction between ferromagnetic layers
the IL-DMI in our trilayers is orders of magnitude larger than that of known systems using heavy metals as a spacer except of recently reported −0.15 mJ/m2 in Co/Pt/Ru(t)/Pt/Co and varies between ≈ ±0.2 mJ/m2
In contrast to known multilayers Co/Ag/Co promotes in-plane chirality between magnetic layers
The strength of IL-DMI opens up new routes for design of three-dimensional chiral spin structures combining intra- and interlayer DMI and paves the way for enhancements of the DMI strength
and the IEC interaction was generalized by adding a term of the form −Jb(M1 · M2)2
These multilayers typically show collective behavior; that is
spin configurations in all layers are identical due to a strong ferromagnetic interlayer exchange and can be effectively regarded as one single layer with intralayer DMI
It is unclear so far whether the combination of Rashba- and atomic SOC can be used to strongly enhance or induce the IL-DMI
making it competitive with its intralayer counterpart and
by that means to manipulate characteristics of the IL-DMI
it is crucial to explore this possibility in order to significantly broaden the class of materials that can be utilized for the creation of three-dimensional topological systems
which are very relevant for future applications
a Schematic of the sample structure and experimental set-up
The inset contains the Ag-interlayer thickness profile
as well as the definition of the reference frame
M/M0 for the tT = 10 nm sample at tAg = 0.77 nm
allowing for the determination of the complete reflection matrix R of the sample
This permits us to extract magnetization vector information from our data
which we then utilize to distinguish coherent and non-coherent magnetization rotation processes
with the latter one being indicative of non-uniform magnetization states within each Co layer
b Field dependence of the measured reflection matrix element \({{{{\mathrm{Re}}}}}(\widetilde{\beta })\)
proportional to the transverse magnetization component my
for different Ag interlayer thicknesses in the a tT = 10 nm and b 15 nm samples
The right axis of the plots shows the deviation angle |Δ| of the top Co layer magnetization from the x-axis
illustrating the size of the coherent rotation process
Schematic of the combined optical and magnetic model
including all model parameters (see manuscript text)
A hypothetical variation of local magnetocrystalline anisotropy distributions upon changing the spacer layer thickness is also extremely unlikely
given the non-monotonic tAg dependence and its disappearance above 2.5 nm thickness
an antisymmetric exchange coupling such as the IL-DMI provides the specific mechanism that would explain the predefined helicity upon reversal that we observe in our Co/Ag/Co samples
we consider an effective IEC dominated by the IL-DMI contributions
the SOC required for the existence of IL-DMI observed in our experiments might come from the Rashba energy shift at the Co/Ag interface
it is the polycrystalline nature of our Co/Ag/Co samples that straightforwardly accomplishes the nonhomogeneous magnetization scenario within each layer as the necessary condition for macroscopic IL-DMI with in-plane chirality
A complete discrimination between these two scenarios requires extensive theoretical investigations and
in order to quantitatively map our experimental data onto the DM coupling described above
we have devised a combined optical and magnetic model
through which we attempt to mimic the magnetization reversal behavior of our samples at different tAg values by direct comparison to the extensive data sets that we have acquired
Color-coded maps of the experimentally determined reflection matrix quantities a \({{{{\mathrm{Re}}}}}(\widetilde{\alpha })\)
b \({{{{\mathrm{Re}}}}}(\widetilde{\beta })\)
and c \({\left|{\widetilde{r}}_{s}\right|}^{2}\) vs
d–f The side-by-side corresponding model fits according to the combined optical and magnetic model; g
h Thickness dependence of the interlayer DMI
tAg dependence of the DM type interlayer coupling strength D
as obtained from the fit to the combined optical and magnetic model of the multilayer system
The error bars in (g) and (h) correspond to the standard deviation of the experimental data
so that we cannot reliably distinguish between them
the data cannot be explained in the absence of D
we have limited the analysis to the determination of the effective chiral contribution
The reasons are the polycrystalline structure of our samples with a random distribution of in-plane anisotropy axes due to our fabrication procedures as well as the resulting normal orientation of the effective IL-DMI vector
The microscopic reason for such a behavior is the cumulative electron hopping corresponding to the fact that with increasing thickness of the magnetic layer
the electrons can scatter not only with the nonmagnetic atoms of a spacer layer (Ag in our case) but also with magnetic atoms (Co in our case)
we have shown the existence of a coherent magnetization rotation process with predefined helicity in the top ferromagnetic layer of polycrystalline Co/Ag/Co stacks via detailed MOKE measurements
We argued that the observed behavior unambiguously indicates the existence of an interlayer DMI
The strength of discovered IL-DMI is orders of magnitude stronger than that in known systems and promotes a scissor-like in-plane state between the magnetization vectors of the two Co layers that follows a predefined chirality
The interaction appears due to the combination of inversion symmetry breaking with strong SOC
arising either from the strong Rashba SOC at Co/Ag interfaces or from the Lévy–Fert three-site coupling via Co impurities in the Ag interlayer matrix
the atomic scale interaction can build up to an effective interlayer coupling if non-uniform magnetization states are present
the Co/Ag/Co stacking here is the first system showing in-plane chiral rotation of magnetic layers
We have also found that the sign and strength of the interaction varies in an oscillatory fashion with the spacer thickness
attenuating considerably for values above 2 nm
The type of interlayer coupling that we have found here could lead to field-free in-plane spin–orbit–torque switching of the top layer
and other new strategies for the generation and manipulation of chiral spin structures in multilayers and broaden the class of materials showing IL-DMI to lighter nonmagnetic metals with weak atomic SOC
Further studies on different materials as well as attempts for controlled placement of nonmagnetic impurities in the spacer will allow for optimization and tuning of the interaction
with the six real Bi parameters being related to the three complex numbers \({\widetilde{r}}_{s}\)
\(\widetilde{\alpha }\) and \(\widetilde{\beta }\) as
the fi are trigonometric functions of the polarizer angles φ1 and φ2
as well as the residual δI/I (difference between experiment and fit)
This is due to the different polarization symmetries possessed by the longitudinal and transverse MOKE
thus enabling the vector magnetometry capability of the GME technique
For an in-plane magnetized material such as the Co layers here
a dielectric tensor in the following form is usually assumed
for polycrystalline films one can expect that non-uniform (non-collinear) states of magnetization will occur within the same film
such that the off-diagonal tensor elements now take the form
with \(G=\sqrt{\mathop{\sum}_{i}\left({m}_{x,i}^{2}+{m}_{y,i}^{2}\right)}\) being the number of grains in the system
During the fit process to a best-match model fit
we still treat the dielectric tensor elements as the magnetization components of a single vector resulting from the sum
we would need to normalize the sums of mx,i and my,i as
where we have termed as G’ the quantity related to the modulus of the resulting magnetization vector
For systems formed by several magnetic moment vectors that add up
where inequality holds for the case in which non-uniform states of magnetization are present
Thus we now define our dielectric tensor elements to be of the form
this brings the effect of substituting the original magneto-optical coupling factor Q by an effective coupling defined as
where the effective coupling factor Qeff now is the original coupling factor times the relative reduction in magnetization as a result of non-uniform magnetization states
By comparing experimentally determined Q values at a high applied field and during reversal
we can directly estimate the reduction in magnetization as
MAX is the value of the magneto-optical coupling factor retrieved in magnetic saturation when all grains are considered to be aligned with the field and G′ = G
which we measured via spectroscopic ellipsometry on Si/SiO2 samples
we employ the refractive index N = 2.4 + 4.0i as well as the magneto-optical coupling factor Q = (2.95 − 0.96i) × 10−2 for the Co layers
which we also measured for polycrystalline Co films
It can be appreciated that while the optical model can reproduce well the linear trend of the reflection matrix parameters above 1 nm thickness
a thickness-independent approach for the refractive index of Ag does not give good results for tAg < 1 nm
quantum mechanical interference effects most probably induce modifications in the band structure
which in turn also vary the optical properties of the material
Further details of the simple macrospin model employed to understand the magnetization reversal behavior of our polycrystalline Co/Ag/Co stacks are presented (see Fig. 3 in the main manuscript text)
We consider the following macrospin systems and interactions among them:
Two ferromagnetic layers formed by Stoner–Wohlfarth grains with a distribution of easy axis orientations
each ferromagnetic layer is formed by two populations of grains
possessing anisotropy axes that are symmetric with respect to the field axis (and thus 90° away from each other)
The magnetic anisotropy energy per unit area of the top (T) and bottom (B) Co layers read as
with all grains possessing the uniaxial magnetocrystalline anisotropy energy density K
The grains in each Co layer interact via an intralayer exchange coupling mechanism
which regulates the inter-granular magnetization alignment within grains
the strength of this interaction is considered to be equal in the bottom and top Co layers
where J > 0 is the volume averaged exchange coupling energy
We have also introduced the in-plane magnetization components along the x- and y-axis for each of the spins in the Co layers
\({s}_{{ix}}^{l}=\cos {\theta }_{i}^{l}\) and \({s}_{{iy}}^{l}=\sin {\theta }_{i}^{l}\) (with i = 1
The energy per unit area of the Zeeman interaction affecting the spins is
where H is the applied magnetic field along the x-axis and M0 represents volume averaged magnetization density
DM type IEC between the resulting magnetization vectors of the two magnetic layers is added
we define a coupling vector \(\vec{D}=D\hat{k}\) which couples the resulting magnetization vectors of the top and bottom layers via
where the sign of the factor D determines the right- or left-handed helicity of the interaction
and the 1/4 factor accounts for the multiplication of 2 times 2 spins in the interaction term
through the cross product of the two interacting magnetization vectors
adds to the model the two key ingredients needed to qualitatively reproduce the outcome of our experiments
On one hand it favors the perpendicular alignment of the resulting moments of the layers
giving rise to noncollinear magnetization states
it introduces a preferred helicity of the magnetization configuration
due to the non-commutative property of the cross product
Heisenberg type interlayer exchange interaction between the resulting magnetization vectors of the two magnetic layers
where the sign of the factor JHeis–IEC determines the FM or AFM character of the interaction
Biquadratic interlayer exchange interaction between the resulting magnetization vectors of the two magnetic layers
one can now build the total energy per unit area by summing up the contributions from the different interactions
where the last three terms is the only one involving interaction of spins coming from different layers
Although the present model might be very simplistic
in particular in terms of its lateral sample structure
it captures the main ingredients of the physics that is present in our Co/Ag/Co samples
constituting a first good approximation toward a better understanding of their magnetization reversal properties
In order to solve the magnetic field dependent evolution of the magnetization configuration in this model for a given set of parameters {K
we recall that the free energy of a macrospin assembly can be expressed as \(F=-\mathop{\sum}_{i}{s}_{i}\cdot {\vec{H}}_{i}^{{eff}}\)
The effective field \({\vec{H}}_{i}^{{eff}}\) for each spin is defined as
the metastable magnetization configuration for each applied field H can be obtained self-consistently by requiring each spin to be aligned with its effective field vector
hence minimizing the free energy of the system
it is also convenient to introduce the following reduced parameters:
Reduced intralayer exchange coupling strength
my magnetization components of the top as well as bottom Co layers for intralayer coupling strengths j = 0
as well as zero DM type interlayer coupling
One of the most immediate results is the fact that the mx and my vs
h curves are identical for the top and bottom FM layers
as they act completely independently while sharing the very same magnetic properties
One can observe that while the mx component follows a field dependent hysteresis curve
the transverse component of magnetization my is zero for all field values
the spins in each layer rotate non-coherently in opposite directions
It is also worth to mention that the intralayer strength j controls the squareness and width of the mx hysteresis loops
as it has a direct consequence on the restoring force exerted by the anisotropy axes onto the spins against the action of the applied magnetic field
One can observe here that the mx components of the top and bottom layers have a very similar field dependence as for the d = 0 case
the my magnetization components of the top and bottom layer now feature a hysteretic behavior
having opposite signs with respect to each other
This means that apart from the non-coherent magnetization rotation process described before
a net coherent magnetization rotation also takes place upon lowering the field in both ferromagnetic layers
the magnetization of the top layer deviates from the x-axis on the order of few degrees
while the bottom layer magnetization is tilted by a significantly smaller but still appreciable angle in the opposite direction
This is understood in terms of the competition between the DM type interlayer coupling
promoting perpendicular alignment between the magnetization vectors of the layers
with magnetic anisotropy and intralayer interactions
While the interlayer coupling may not be capable to align both magnetizations perpendicular
the system still gains sufficient energy by partially adapting to this interaction
via deflecting the magnetizations of each layer to both sides of the applied field axis
This results into a configuration of the top and bottom layers in which the respective magnetizations are canted on the order of a few degrees
thus setting a plausible scenario for explaining our experimental observations in Co/Ag/Co films
From comparison of the d = 0.04 and 0.1 one can conclude that d determines the magnetization tilt amplitude from the x-axis
the ratio between the transverse magnetization components from the top and bottom layers is related by the thickness ratio
regardless the d value (this being true for small d values and hence small tilt angles of the layer magnetizations)
This is because the energy gain due to the partial fulfillment of the Zeeman or magnetic anisotropy energies is a factor of r = 10 times smaller for the top layer than for the bottom one
while both being equally affected by the DM type interlayer coupling despite their different thicknesses
It is worth noting that while the my components of the Co layers a show well-defined individual hysteretic behavior
the averaged transverse component of the Co/Ag/Co stack is vanishing in all cases
the field dependent my values of both layers change their sign upon inverting the sign of d
the preferred helicity set by the DM type interlayer coupling is reflected in that the angle going from the bottom layer magnetization mB to the top layer magnetization mT is the same in the two cases
but defined to be as counterclockwise for the positive d case
The measured color-coded δI/I datasets data are available at the “Methods” section
The azimuthal dependence of the reflectivity coefficients generated in this study are provided in the Supplementary Information
The codes are described in a detailed way in the “Methods” section
Layered magnetic structures: evidence for antiferromagnetic coupling of Fe layers across Cr interlayers
Observation of a magnetic antiphase domain structure with long-range order in a synthetic Gd-Y superlattice
Giant magnetoresistance of (001) Fe/(001) Cr magnetic superlattices
Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange
Oscillations in exchange coupling and magnetoresistance in metallic superlattice structures: Co/Ru
Ruderman-Kittel theory of oscillatory interlayer exchange coupling
Domain observations on Fe-Cr-Fe layered structures
evidence for a biquadratic coupling effect
Biquadratic interlayer coupling in layered magnetic systems
A thermodynamic theory of ‘weak’ ferromagnetism of antiferromagnetics
Magnetic and transport properties of metallic multilayers
Dzyaloshinsky-Moriya interactions induced by symmetry breaking at a surface
Atomic-scale spin spiral with a unique rotational sense: Mn monolayer on W(001)
Tailoring the chirality of magnetic domain walls by interface engineering
Chiral symmetry breaking in magnetic thin films and multilayers
Observation of room-temperature magnetic skyrmions and their current-driven dynamics in ultrathin metallic ferromagnets
Anisotropic Interlayer Dzyaloshinskii–Moriya interaction in synthetic ferromagnetic /antiferromagnetic sandwiches
Effect of interlayer Dzyaloshinskii-Moriya interaction on spin structure in synthetic antiferromagnetic multilayers
Spin-orbit torque switching of chiral magnetization across a synthetic antiferromagnet
“Interlayer Dzyaloshinskii-Moriya interactions”
Noncollinear interlayer exchange coupling caused by interface spin-orbit interaction
Twisted exchange interaction between localized spind embedded in one- and two-dimensional electron gas with Rashba spin-orbit coupling
Significant Dzyaloshinskii-Moriya interaction at graphene-ferromagnet interfaces due to the Rashba effect
Designing light-element materials with large effective spin-orbit coupling
Zero-field skyrmionic states and in-field edge-skyrmions induced by boundary tuning
Magnetic anisotropy and interlayer exchange coupling in the sputtered Co/Ag multilayers
and Au driven by spin accumulation and spin-orbit coupling
k-asymmetric spin splitting at the interface between transition metal ferromagnets and heavy metals
Magnetization reversal of in-plane uniaxial Co films and its dependence on epitaxial alignment
Quantitative vector magnetometry using generalized magneto-optical ellipsometry
Strain-induced magneto-optical anisotropy in epitaxial hcp Co films
Absence of detectable current-induced magneto-optical Kerr effects in Pt
Explicit solutions for the optical properties of arbitrary magneto-optic materials in generalized ellipsometry
Giant Spin Splitting through Surface Alloying
Thickness dependence of the interfacial Dzyaloshinskii–Moriya interaction in inversion symmetry broken systems
Rashba-type Dzyaloshinskii–Moriya interaction
and skyrmion states at 2D materials/Co interfaces
Asymmetric and symmetric exchange in a generalized 2D Rashba ferromagnet
Measuring and tailoring the Dzyaloshinskii-Moriya interaction in perpendicularly magnetized thin films
Interfacial Dzyaloshinskii-Moriya interaction in perpendicularly magnetized Pt/Co/AlOx ultrathin films measured by Brillouin light spectroscopy
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acknowledges Obra Social “la Caixa” for her Ph.D
Work at NanoGUNE was supported by the Spanish Ministry of Science and Innovation under the Maria de Maeztu Units of Excellence Program (Grant No
We acknowledge financial support from the Open Access Publication Fund of Universität Hamburg
Open Access funding enabled and organized by Projekt DEAL
Departamento de Física de la Materia Condensada
analyzed experimental data and performed the computational studies
This study does not include human or animal subjects
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DOI: https://doi.org/10.1038/s41467-023-42426-9
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Dzyaloshinskii–Moriya interaction (DMI) is vital to form various chiral spin textures
novel behaviors of magnons and permits their potential applications in energy-efficient spintronic devices
we realize a sizable bulk DMI in a transition metal dichalcogenide (TMD) 2H-TaS2 by intercalating Fe atoms
which form the chiral supercells with broken spatial inversion symmetry and also act as the source of magnetic orderings
Using a newly developed protonic gate technology
gate-controlled protons intercalation could further change the carrier density and intensely tune DMI via the Ruderman–Kittel–Kasuya–Yosida mechanism
The resultant giant topological Hall resistivity \({\rho }_{{xy}}^{T}\) of \(1.41{\mathrm{\mu}} \Omega \cdot {{\mathrm{cm}}}\) at \({V}_{g}=-5.2{\mathrm{V}}\) (about \(424 \%\) larger than the zero-bias value) is larger than most known chiral magnets
Theoretical analysis indicates that such a large topological Hall effect originates from the two-dimensional Bloch-type chiral spin textures stabilized by DMI
while the large anomalous Hall effect comes from the gapped Dirac nodal lines by spin–orbit interaction
Dual-intercalation in 2H-TaS2 provides a model system to reveal the nature of DMI in the large family of TMDs and a promising way of gate tuning of DMI
which further enables an electrical control of the chiral spin textures and related electromagnetic phenomena
realizing DMI in layered materials permits the manipulation of chiral spin textures and investigation of various related fascinating physics in few atomic layers
While in a large family of layered materials
SIS is respected in the natural unit cell and usually forbids DMI
demonstrate a promising way to induce sizable DMI by breaking SIS in the enlarged supercell through alternatively intercalating heavy magnetic atoms also as the source of magnetic orderings
we demonstrate that DMI can be induced and controlled in a TMD 2H-TaS2 by dual-intercalation
DMI is confirmed by the observation of THE at low temperatures
proton intercalation induced by electrical gating could further change the carrier density then largely tune DMI via the RKKY mechanism
resulting in a huge topological Hall resistivity of \(1.4{\mu }\Omega \cdot {{\mathrm{cm}}}\) at \({V}_{g}=-5.2 {\mathrm{V}}\)
Theoretical analysis shows that this large THE is attributed to the two-dimensional (2D) Bloch-type spin textures (skyrmions or chiral domain walls) stabilized by the large DMI that comes from the presence of the chiral supercells and strong SOC
Direct evaluation of the anomalous Hall conductivity (AHC) and Berry curvature reveals the origin of the large AHC in experiments
Tailoring DMI in 2H-TaS2 by dual-intercalation may reveal the universality of DMI and open up the opportunity of more investigations of chiral spin textures in a large family of TMDs
b Crystal structures of Fe1/3TaS2 of front view (a) and top view (b)
c Temperature-dependent Hall resistivity \({\rho }_{{xy}}\) in Fe0.28TaS2 nanoflakes
Topological Hall resistivity components \({\rho }_{{xy}}^{T}\) are shadowed by the light purple colour
d Temperature-dependent Topological Hall resistivity components \({\rho }_{{xy}}^{T}\)
The observation of THE in FexTaS2 is a direct transport evidence for DMI in Fe intercalated 2H-TaS2
a Temperature-dependent anomalous Hall conductivity in S1
The colours mark the spin expectation \(\left\langle {S}_{z}\right\rangle\) of the band
d Berry curvature distribution in \({k}_{z}=0\) plane
d Fermi energy \({E}_{{\mathrm{F}}}\) -dependent intrinsic AHC \({\sigma }_{{xy},{in}}^{A}\)
e Scaling relationship between anomalous Hall conductivities \({\sigma }_{{xy}}^{{{\mathrm{AHE}}}}\) and longitudinal conductivities \({\sigma }_{{xx}}\)
a A schematic of gate-induced proton intercalation
b Hall resistivity under different gate voltages
Topological Hall resistivity \({\rho }_{{xy}}^{T}\) are shadowed by the light purple colour
c Gate-dependent anomalous and topological Hall resistivity
Inset: a Hall-bar device on solid ion (proton) conductor (SIC)
but absent in Fe1/4TaS2 due to the presence of SIS
the specific magnetic structure can be effectively described by a spin model
where the indices i and j sum over the Fe atoms
\(J \;> \; 0\) is the FM exchange interaction
\({{\bf{d}}}_{{\bf{ij}}}\) is the vector of DMI
\(K \;<\; 0\) indicates PMA favouring an easy-axis
and the last term is the Zeeman energy due to the applied magnetic fields
with arbitrary coefficients \({c}_{\mathrm{1,2}}\) and reduced magnetization \({{\bf{m}}}_{{\bf{x}}{\boldsymbol{,}}{\bf{y}}{\boldsymbol{,}}{\bf{z}}}\)
a Spin configurations used to calculate DMI strength
b The electron number \({N}_{e}\) -dependent DMI strength \({{\bf{d}}}_{{\boldsymbol{\perp }}}\) (\(\propto {\triangle }_{E}^{{{\mathrm{DMI}}}}\)) for the supercell with four-spin cycle along one selected direction in (a)
\({N}_{e}=0\) represents the case of \({E}_{{\mathrm{F}}}=0\)
and \({N}_{e}=-1.5(+1)\) represents the Fermi energy around \(-80{{\mathrm{meV}}}(+50{{\mathrm{meV}}})\)
The black circles are the results of First-principles calculation and the red line is fitted from the black circles for guiding eyes
Fe1/3-δTaS2 (\({\rm{\delta }}\le 0.05\)) nanoplates exhibit large THE
demonstrating a strong transport evidence of sizable DMI and the emergence of Bloch-type spin textures (such as skyrmions and chiral domain walls)
Gate-induced proton intercalation can largely modulate the amplitudes of topological Hall resistivities by approximately \(420 \%\)
Theoretical analysis and First-principles calculations suggest that the sizable DMI dominantly comes from the intercalated Fe atoms
playing a key role in magnetic orders and the formation of the chiral supercells with broken SIS
Our discovery demonstrates that dual-intercalation (intercalation of magnetic atoms and protons) is a promising way of tailoring DMI and manipulating chiral spin textures in 2H-TaS2
greatly inspiring further investigations in a large family of TMDs
Single crystals of FexTaS2 were grown via chemical vapour transport method with iodine as the transport agent with suitable mole ratio and sealed in an evacuated quartz tube (Supplementary Section 1)
Solid protonic electrolyte was prepared by the sol-gel processes by mixing tetraethyl orthosilicate (from Alfa Aesar)
The mixed solution was stirred and annealed before use (Supplementary Section 2)
Transport measurements were performed in a commercial Physical Property Measurement System (PPMS) with magnetic field up to \(9{\mathrm{T}}\)
Protonic gating experiments were performed in commercial magnetic property measurement system (MPMS) with a maximal magnetic field of \(7{\mathrm{T}}\)
To decrease the leaking current during the gating
the sample was quickly cooled down to low temperatures for magneto-transport measurements
All data supporting the findings of this study are available from the corresponding author on request
Spin Nernst effect of magnons in collinear antiferromagnets
Thermal Hall effect induced by magnon–phonon interactions
Topological magnetoelastic excitations in noncollinear antiferromagnets
Berry phase theory of the anomalous Hall effect: application to colossal magnetoresistance manganites
Topological Hall effect and Berry phase in magnetic nanostructures
Bulk Dzyaloshinskii–Moriya interaction in amorphous ferrimagnetic alloys
Electrical and magnetic properties of some first row transition metal intercalates of niobium disulphide
3d transition-metal intercalates of the niobium and tantalum dichalcogenides
Three-state nematicity in the triangular lattice antiferromagnet Fe1/3NbS2.Nat
Chiral magnetic soliton lattice on a chiral helimagnet
Controlling the topological sector of magnetic solitons in exfoliated Cr1/3NbS2 crystals
RKKY ferromagnetism with ising-like spin states in intercalated Fe1/4TaS2
High-density carrier accumulation in ZnO field-effect transistors gated by electric double layers of ionic liquids
Tuning phase transitions in FeSe thin flakes by field-effect transistor with solid ion conductor as the gate dielectric
Ferromagnetism in metallic FexTaS2 (x ~ 0.28)
Band-structure calculations of Fe1/3TaS2 and Mn1/3TaS2
and transport and magnetic properties of Fe0.28TaS2
Very large magnetoresistance in Fe0.28TaS2 single crystals
Linear magnetization dependence of the intrinsic anomalous Hall effect
Electric-field control of anomalous and topological Hall effects in oxide bilayer thin films
Thermodynamically stable magnetic vortex states in magnetic crystals
Hall effect and transmission electron microscopy of epitaxial MnSi thin films
Anatomy of Dzyaloshinskii-Moriya interaction at Co/Pt interfaces
Skyrmion confinement in ultrathin film nanostructures in the presence of Dzyaloshinskii-Moriya interaction
Reversible manipulation of the magnetic state in SrRuO3 through electric-field controlled proton evolution
Anomalous hall effect and topological defects in antiferromagnetic weyl semimetals: Mn3Sn/Ge
Chiral domain walls of Mn3Sn and their memory
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Yusuke Masaki and Di Xiao for insightful discussions
This research was performed in part at the RMIT Micro Nano Research Facility (MNRF) in the Victorian Node of the Australian National Fabrication Facility (ANFF) and the RMIT Microscopy and Microanalysis Facility (RMMF)
Work at RMIT University was supported by the Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technologies (Project No
were supported by the NSF of China (Grants Nos
the National Key R&D Program of China (Grant Nos
was supported by Youth Innovation Promotion Association of CAS (Grant No
was supported by the 100 Talents Program of Chinese Academy of Sciences (CAS) and also partially by the High Magnetic Field Laboratory of Anhui Province
These authors contributed equally: Guolin Zheng
Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE)
Beijing Key Lab of Nanophotonics & Ultrafine Optoelectronic Systems
International Center for Quantum Materials
Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions
University of Science and Technology of China
fabricated the devices and performed the transport measurements
analysed the data and wrote the manuscript with assistance from all authors
Peer review information Nature Communications thanks Xianhui Chen and the other
reviewer(s) for their contribution to the peer review of this work
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DOI: https://doi.org/10.1038/s41467-021-23658-z
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Understanding the magnetic interactions is of fundamental importance in condensed-matter physics as well as in the application of spintronic devices
the Dzyaloshinskii–Moriya interaction (DMI) has attracted increasing attention
as it can trigger topological chiral magnetism
which is of particular interest from both fundamental and applied points of view
First-principles calculations have played an essential role in figuring out the microscopic properties of DMI and helped to search for the materials with strong DMI
we present a comprehensive and systematic survey of the first-principles-calculations methods for DMI
along with an overview of the first-principles calculations of the DMI properties of typical material systems and the DMI-induced magnetic phenomena
The Dzyaloshinskii–Moriya interaction (DMI) is a kind of antisymmetric exchange coupling that arises as a consequence of the spin–orbit coupling in the magnetic system with broken inversion symmetry
First-principles calculations of DMI can be based on the methods of mapping of total energies or mapping of energy derivatives
First-principles calculations with spin–orbit coupling for the noncollinear magnetic structure is the critical step to obtaining the DMI parameter
DMI resides in many magnetic bulk and thin-film systems with broken inversion symmetry
leading to the formation of many chiral topological magnetic structures
and has a strong impact on the spin dynamics
Prices may be subject to local taxes which are calculated during checkout
This paper is the first work that introduced DMI to explain the canting of moments in weak ferromagnets
References 2 and 3 present the first microscopic theory for the origin of DMI
New mechanisms for magnetic anisotropy in localised S-state moment materials
References 5 and 6 proposed a three-site DMI mechanism in spin glasses
which was extended to magnetic thin-film surfaces and interfaces
Weak antiferromagnetic ordering induced by Dzyaloshinskii-Moriya interaction and pure magnetic reflections in MnSi-type crystals
Measuring the Dzyaloshinskii–Moriya interaction in a weak ferromagnet
Revealing the absolute direction of the Dzyaloshinskii-Moriya interaction in prototypical weak ferromagnets by polarized neutrons
Dzyaloshinskii-Moriya interaction in the cuprates
Spin-orbit coupling-induced magnetic phase in the d-density-wave phase of La2−xBaxCuO4 superconductors
Field-induced staggered magnetization and 17O Knight shift anomaly in La2CuO4
Spin current and magnetoelectric effect in noncollinear magnets
Role of the Dzyaloshinskii-Moriya interaction in multiferroic perovskites
Multiferroics: a magnetic twist for ferroelectricity
Effects of the Dzyaloshinskii-Moriya interaction on low-energy magnetic excitations in copper benzoate
Dzyaloshinskii-Moriya interactions and adiabatic magnetization dynamics in molecular magnets
and chirality induced by Dzialoshinsky–Moriya interactions in a V3 cluster analog of multiferroics
This work presented the first example of the interfacial DMI
Writing and deleting single magnetic skyrmions
Chiral properties of structure and magnetism in Mn1−xFexGe compounds: when the left and the right are fighting
Towards control of the size and helicity of skyrmions in helimagnetic alloys by spin–orbit coupling
Observation of the magnetic flux and three-dimensional structure of skyrmion lattices by electron holography
Real-space observation of skyrmionium in a ferromagnet-magnetic topological insulator heterostructure
Room-temperature stabilization of antiferromagnetic skyrmions in synthetic antiferromagnets
Static Hopf solitons and knotted emergent fields in solid-state noncentrosymmetric magnetic nanostructures
Creation and observation of Hopfions in magnetic multilayer systems
Probing the Dzyaloshinskii-Moriya interaction in CoFeB ultrathin films using domain wall creep and Brillouin light spectroscopy
Asymmetric hysteresis for probing Dzyaloshinskii–Moriya interaction
Very large domain wall velocities in Pt/Co/GdOx and Pt/Co/Gd trilayers with Dzyaloshinskii-Moriya interaction
Tuning domain wall velocity with Dzyaloshinskii-Moriya interaction
Determination of the Dzyaloshinskii-Moriya interaction in exchange biased Au/Co/NiO systems
Quantifying the bulk and interfacial Dzyaloshinskii-Moriya interactions
Influence of the Dzyaloshinskii–Moriya interaction on the spin-wave spectra of thin films
Direct observation of the Dzyaloshinskii-Moriya interaction in a Pt/Co/Ni film
Linear relation between Heisenberg exchange and interfacial Dzyaloshinskii–Moriya interaction in metal films
All-electrical measurement of interfacial Dzyaloshinskii-Moriya interaction using collective spin-wave dynamics
Eavesdropping on spin waves inside the domain-wall nanochannel via three-magnon processes
Weak ferromagnetism in antiferromagnets: α-Fe2O3 and La2CuO4
Predicting the spin-lattice order of frustrated systems from first principles
First-principles analysis of a homochiral cycloidal magnetic structure in a monolayer Cr on W(110)
This paper presented the real-space spiral method for the DMI calculation
Dzyaloshinskii-Moriya interaction as a consequence of a Doppler shift due to spin-orbit-induced intrinsic spin current
Role of Dzyaloshinskii-Moriya interaction for magnetism in transition-metal chains at Pt step edges
Hund’s rule-driven Dzyaloshinskii-Moriya interaction at 3d–5d interfaces
Significant Dzyaloshinskii–Moriya interaction at graphene–ferromagnet interfaces due to the Rashba effect
Oxygen-enabled control of Dzyaloshinskii-Moriya Interaction in ultra-thin magnetic films
Controlling Dzyaloshinskii-Moriya interaction via chirality dependent atomic-layer stacking
Reversible control of Dzyaloshinskii-Moriya interaction at the graphene/Co interface via hydrogen absorption
Tuning Dzyaloshinskii-Moriya interactions in magnetic bilayers with a ferroelectric substrate
Tailoring Dzyaloshinskii–Moriya interaction in a transition metal dichalcogenide by dual-intercalation
Magnetic properties and energy-mapping analysis
References 64 and 78 presented the four-states method for the DMI calculation
Ab initio methodology for magnetic exchange parameters: generic four-state energy mapping onto a Heisenberg spin Hamiltonian
Constrained density functional theory for first principles spin dynamics
Towards a constrained local moment model for first principles spin dynamics
Ground states of constrained systems: application to cerium impurities
Ab initio treatment of noncollinear magnets with the full-potential linearized augmented plane wave method
Constrained spin-density functional theory for excited magnetic configurations in an adiabatic approximation
Constrained density functional for noncollinear magnetism
VASP. I_CONSTRAINED_M. https://www.vasp.at/wiki/index.php/I_CONSTRAINED_M (2022)
Helicoidal magnetic structure and ferroelectric polarization in Cu3Nb2O8
Giant ferroelectric polarization of CaMn7O12 induced by a combined effect of Dzyaloshinskii-Moriya interaction and exchange striction
Strong Dzyaloshinskii-Moriya interaction and origin of ferroelectricity in Cu2OSeO3
Frustration and Dzyaloshinsky-Moriya anisotropy in the kagome francisites Cu3Bi(SeO3)2O2X (X = Br
Predicting a ferrimagnetic phase of Zn2FeOsO6 with strong magnetoelectric coupling
Magnetic interactions in BiFeO3: a first-principles study
Topological spin texture in Janus monolayers of the chromium trihalides Cr(I
Emergence of skyrmionium in a two-dimensional CrGe(Se,Te)3 Janus monolayer
Controlling bimerons as skyrmion analogues by ferroelectric polarization in 2D van der Waals multiferroic heterostructures
Electric-field switching of magnetic topological charge in type-I multiferroics
Symmetry analysis of electronic states for crystals with spiral magnetic order
Interfacial magnetic anisotropy and Dzyaloshinskii-Moriya interaction at two-dimensional SiC/Fe4N(111) interfaces
Interfacial Dzyaloshinskii-Moriya interaction of antiferromagnetic materials
Strain-enhanced Dzyaloshinskii–Moriya interaction at Co/Pt interfaces
Perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction at an oxide/ferromagnetic metal interface
Large Dzyaloshinskii-Moriya interaction and room-temperature nanoscale skyrmions in CoFeB/MgO heterostructures
Reducing Dzyaloshinskii-Moriya interaction and field-free spin-orbit torque switching in synthetic antiferromagnets
Electric field induced reversal of spin polarization
magnetic anisotropy and tailored Dzyaloshinskii–Moriya interaction in underoxidized SrRuO3/SrTiO3 heterostructures
Tuning Dzyaloshinskii-Moriya interaction in ferrimagnetic GdCo: a first-principles approach
magnetic anisotropy and Dzyaloshinskii–Moriya interaction in Janus Cr2I3X3 (X = Br
magnetic anisotropy and Dzyaloshinskii–Moriya interaction in two-dimensional intrinsic ferromagnetic Janus 2H-VSeX (X = S
Ferroelectrically controlled topological magnetic phase in a Janus-magnet-based multiferroic heterostructure
Electrical control of topological spin textures in two-dimensional multiferroics
Electronic structure and magnetic properties of two-dimensional h-BN/Janus 2H-VSeX (X = S
magnetic anisotropy and Dzyaloshinskii-Moriya interaction of two-dimensional graphene/Janus 2H-VSeX (X = S
A new ternary pentagonal monolayer based on Bi with large intrinsic Dzyaloshinskii–Moriya interaction
Manipulation of topological spin configuration via tailoring thickness in van der Waals ferromagnetic
Multiferroic materials based on transition-metal dichalcogenides: potential platform for reversible control of Dzyaloshinskii-Moriya interaction and skyrmion via electric field
Ferroelectric control of magnetic skyrmions in two-dimensional van der Waals heterostructures
Spontaneous magnetic skyrmions in single-layer CrInX3 (X = Te
Anisotropic Dzyaloshinskii–Moriya interaction and topological magnetism in two-dimensional magnets protected by P4̅m2 crystal symmetry
Noncollinear magnetism in itinerant-electron systems: theory and applications
Magnetic Domain Walls in Ultrathin Films: Contribution of the Dzyaloshinskii-Moriya Interaction PhD thesis
Describing Dzyaloshinskii–Moriya spirals from first principles
124 and 125 presented the reciprocal-space spiral method for the DMI calculation
Electrons at the Fermi Surface (eds Springford
Bond analysis of heats of formation: application to some group VIII and IB hydrides
VASP. Spin spirals. https://www.vasp.at/wiki/index.php/Spin_spirals (2019)
Insight into the Dzyaloshinskii-Moriya interaction through first-principles study of chiral magnetic structures
Dzyaloshinskii-Moriya interaction and Hall effects in the skyrmion phase of Mn1−xFexGe
Dzyaloshinskii-Moriya interaction at an antiferromagnetic interface: first-principles study of Fe/Ir bilayers on Rh(001)
First-principles prediction of sub-10-nm skyrmions in Pd/Fe bilayers on Rh(111)
Dzyaloshinskii-Moriya interaction at disordered interfaces from ab initio theory: robustness against intermixing and tunability through dusting
Correlation of the Dzyaloshinskii–Moriya interaction with Heisenberg exchange and orbital asphericity
Competition of Dzyaloshinskii-Moriya and higher-order exchange interactions in Rh/Fe in atomic bilayers on Ir(111)
Isolated zero field sub-10 nm skyrmions in ultrathin Co films
Electric dipole moment as descriptor for interfacial Dzyaloshinskii-Moriya interaction
Stacking-dependent spin interactions in Pd/Fe bilayers on Re(0001) bilayers on Re(0001)
Material systems for FM-/AFM-coupled skyrmions in Co/Pt-based multilayers
Tuning exchange interactions in antiferromagnetic Fe/W(001) transition-metal overlayers
Dzyaloshinskii–Moriya interaction in noncentrosymmetric superlattices
Electrically switchable Rashba-type Dzyaloshinskii-Moriya interaction and skyrmion in two-dimensional magnetoelectric multiferroics
Topological spin textures in a two-dimensional MnBi2(Se
Information transfer by vector spin chirality in finite magnetic chains
Dzyaloshinskii-Moriya interaction and chiral magnetism in 3d–5d zigzag chains: tight-binding model and ab initio calculations
Local spin density functional approach to the theory of exchange interactions in ferromagnetic metals and alloys
Anisotropic exchange coupling in diluted magnetic semiconductors: ab initio spin-density functional theory
Crucial role of the lattice distortion in the magnetism of LaMnO3
First-principles calculations of magnetic interactions in correlated systems
First-principles relativistic study of spin waves in thin magnetic films
Spin-wave stiffness and micromagnetic exchange interactions expressed by means of the KKR Green function approach
Spin-spiral formalism based on the multiple-scattering Green’s function technique with applications to ultrathin magnetic films and multilayers
Exchange coupling constants at finite temperature
First-principles Dzyaloshinskii–Moriya interaction in a non-collinear framework
First-principles calculation of the Dzyaloshinskii-Moriya interaction: a Green’s function approach
Correlated band theory of spin and orbital contributions to Dzyaloshinskii-Moriya interactions
TB2J: a python package for computing magnetic interaction parameters
Calculation of magnetic exchange interactions in Mott-Hubbard systems
Connection between magnetic interactions and the spin-wave gap of the insulating phase of NaOsO3
Heisenberg and anisotropic exchange interactions in magnetic materials with correlated electronic structure and significant spin-orbit coupling
Micromagnetic description of twisted spin spirals in the B20 chiral magnet FeGe from first principles
Atomistic spin dynamics of low-dimensional magnets
Magnetic phase diagram of an Fe monolayer on W(110) and Ta(110) surfaces based on ab initio calculations
Domain-wall profiles in Co/Irn/Pt(111) ultrathin films: influence of the Dzyaloshinskii-Moriya interaction
Magnetism of a Co monolayer on Pt(111) capped by overlayers of 5d elements: a spin-model study
Comparison of first-principles methods to extract magnetic parameters in ultrathin films: Co/Pt(111)
Spin reorientation transition in an ultrathin Fe film on W(110) induced by Dzyaloshinsky-Moriya interactions
Complex magnetic textures in Ni/Irn/Pt(111) ultrathin films
Weak ferromagnetism in Mn nanochains on the CuN surface
Spin-cluster expansion: parametrization of the general adiabatic magnetic energy surface with ab initio accuracy
Parametrization of the magnetic energy at the atomic level
Atomistic spin model based on a spin-cluster expansion technique: application to the IrMn3/Co interface
Exchange bias driven by Dzyaloshinskii-Moriya interactions
Formation of magnetic skyrmions with tunable properties in PdFe bilayer deposited on Ir(111)
Thermal properties of a spin spiral: manganese on tungsten(110)
Phase-space Berry phases in chiral magnets: Dzyaloshinskii-Moriya interaction and the charge of skyrmions
Berry phase theory of Dzyaloshinskii–Moriya interaction and spin–orbit torques
Relation of the Dzyaloshinskii-Moriya interaction to spin currents and to the spin-orbit field
Accurate scheme to calculate the interatomic Dzyaloshinskii-Moriya interaction parameters
Composition-dependent magnetic response properties of Mn1−xFexGe alloys
First-principles evaluation of the Dzyaloshinskii–Moriya interaction
Control of Dzyaloshinskii-Moriya interaction in Mn1−xFexGe: a first-principles study
Anisotropic magnetic couplings and structure-driven canted to collinear transitions in Sr2IrO4 by magnetically constrained noncollinear DFT
Analysis of electrical-field-dependent Dzyaloshinskii-Moriya interaction and magnetocrystalline anisotropy in a two-dimensional ferromagnetic monolayer
Controlling the Dzyaloshinskii-Moriya interaction to alter the chiral link between structure and magnetism for Fe1−xCoxSi
Revisiting spin cycloids in multiferroic BiFeO3
First-principles study of spin spirals in the multiferroic BiFeO3
Spiral magnetic ordering in bismuth ferrite
Investigation of the unusual magnetic spiral arrangement in BiFeO3
Observation of skyrmions in a multiferroic material
Progress and prospects in low-dimensional multiferroic materials
Magnetoelectricity in two-dimensional materials
Ferroelectricity and ferromagnetism in a VOI2 monolayer: role of the Dzyaloshinskii-Moriya interaction
Chirality from interfacial spin-orbit coupling effects in magnetic bilayers
Dzyaloshinskii-Moriya interaction mediated by spin-polarized band with Rashba spin-orbit coupling
Theory of the interfacial Dzyaloshinskii-Moriya interaction in Rashba antiferromagnets
References 201–204 proposed the microscopic mechanism for the DMI induced by the Rashba effect
Interfacial Dzyaloshinskii-Moriya interaction: effect of 5d band filling and correlation with spin mixing conductance
Engineering skyrmions in transition-metal multilayers for spintronics
First-principles investigation of chiral magnetic properties in multilayers: Rh/Co/Pt and Pd/Co/Pt
The microscopic origin of DMI in magnetic bilayers and prediction of giant DMI in new bilayers
Dzyaloshinskii-Moriya interaction in symmetric epitaxial [Co/Pd(111)]N superlattices with different numbers of Co/Pd bilayers
Inducing skyrmions in ultrathin Fe films by hydrogen exposure
Tuning noncollinear magnetic states by hydrogenation
Two-dimensional magnetic crystals and emergent heterostructure devices
Dzyaloshinskii-Moriya interaction and magnetic skyrmions induced by curvature
Role of direct exchange and Dzyaloshinskii-Moriya interactions in magnetic properties of graphene derivatives: C2H and C2F
Field-dependent size and shape of single magnetic skyrmions
Current-driven dynamics of magnetic hopfions
Hopf solitons in helical and conical backgrounds of chiral magnetic solids
Mutual conversion between a magnetic Néel hopfion and a Néel toron
Static and dynamical properties of antiferromagnetic skyrmions in the presence of applied current and temperature
Three-dimensional spin structure on a two-dimensional lattice: Mn/Cu(111)
Conical spin-spiral state in an ultrathin film driven by higher-order spin interactions
Assembling diverse skyrmionic phases in Fe3GeTe2 monolayer
Effects of interfacial Dzyaloshinskii–Moriya interaction on magnetic dynamics
Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems
Spin-orbit torque driven chiral magnetization reversal in ultrathin nanostructures
Field-free spin-orbit torque switching of a perpendicular ferromagnet with Dzyaloshinskii-Moriya interaction
Field-free spin–orbit torque perpendicular magnetization switching in ultrathin nanostructures
Deterministic magnetization switching using lateral spin–orbit torque
Chiral symmetry breaking for deterministic switching of perpendicular magnetization by spin–orbit torque
Quantifying the Dzyaloshinskii-Moriya interaction induced by the bulk magnetic asymmetry
Topological honeycomb magnon Hall effect: a calculation of thermal Hall conductivity of magnetic spin excitations
Biquadratic exchange interactions in two-dimensional magnets
Topological magnons in CrI3 monolayers: an itinerant fermion description
Theory of the thermal Hall effect in quantum magnets
Theoretical prediction of a rotating magnon wave packet in ferromagnets
Topological magnon bands in a kagome lattice ferromagnet
Magnetic transitions in the topological magnon insulator Cu(1,3-bdc)
Topological magnon insulators in two-dimensional van der Waals ferromagnets CrSiTe3 and CrGeTe3: toward intrinsic gap-tunability
Topological spin excitations in honeycomb ferromagnet CrI3
Asymmetric spin-wave dispersion due to Dzyaloshinskii-Moriya interaction in an ultrathin Pt/CoFeB film
Nonreciprocity of spin waves in noncollinear magnets due to the Dzyaloshinskii-Moriya interaction
Interlayer Dzyaloshinskii-Moriya interactions
Bloch chirality induced by an interlayer Dzyaloshinskii-Moriya interaction in ferromagnetic multilayers
Large antisymmetric interlayer exchange coupling enabling perpendicular magnetization switching by an in-plane magnetic field
Field-free spin–orbit torque switching enabled by the interlayer Dzyaloshinskii–Moriya interaction
Topological computation based on direct magnetic logic communication
Yu, D. et al. Skyrmions-based logic gates in one single nanotrack completely reconstructed via chirality barrier. Nat. Sci. Rev. https://doi.org/10.1093/nsr/nwac021 (2022)
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This work was supported by National Natural Science Foundation of China (grant nos
11874059 and 12174405); Key Research Program of Frontier Sciences
Pioneer and Leading Goose R&D Program of Zhejiang Province (grant no
Ningbo Key Scientific and Technological Project (grant no
Zhejiang Provincial Natural Science Foundation (grant no
LR19A040002) and Beijing National Laboratory for Condensed Matter Physics (grant no
Ningbo Institute of Materials Technology and Engineering
Center of Materials Science and Optoelectronics Engnieering
Wenbo Mi and another anonymous reviewer for their contribution to the peer review of this work
The Berry curvature Ω encodes how the eigenstate \(|n({\bf{R}})\rangle \) evolves as a local function of parameter R and is defined as \(\varOmega ={\nabla }_{{\bf{R}}}\times {{\bf{A}}}_{n}\) with \({{\bf{A}}}_{n}=i\langle n({\bf{R}})| \frac{\partial }{\partial {\bf{R}}}| n({\bf{R}})\rangle \)
The spin spiral can be classified as Bloch-type spiral
in which the spins rotate in a helical way around an axis that is parallel or antiparallel to the propagation direction
the DMI between two magnetic atoms can be mediated by a third heavy atom
The resultant DMI parameter depends on the SOC strength of the heavy atom and the relative orientation of the three atoms involved
the free-energy expansion with respect to the order parameter η can include terms of the form ηi∂kηj
Invariant polynomials in the expansion that contain terms of this form are called Lifshitz invariants
The spin spiral can be classified as Néel-type spiral
in which the spins rotate in a cycloidal way around an axis that is perpendicular to the propagation direction
The Rashba effect is a momentum-dependent splitting of spin bands in two-dimensional condensed matter systems caused by SOC
The Rashba SOC Hamiltonian reads as \({H}_{{\rm{R}}}={\alpha }_{{\rm{R}}}(\widehat{{\bf{z}}}\times {\bf{k}})\cdot {\boldsymbol{\sigma }}\)
in which αR characterizes the strength of Rashba SOC and σ is the vector of the Pauli matrices
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DOI: https://doi.org/10.1038/s42254-022-00529-0
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The phase of the quantum-mechanical wave function can encode a topological structure with wide-ranging physical consequences
such as anomalous transport effects and the existence of edge states robust against perturbations
While this has been exhaustively demonstrated for electrons
properties associated with the elementary quasiparticles in magnetic materials are still underexplored
we show theoretically and via inelastic neutron scattering experiments that the bulk ferromagnet Mn5Ge3 hosts gapped topological Dirac magnons
Although inversion symmetry prohibits a net Dzyaloshinskii-Moriya interaction in the unit cell
it is locally allowed and is responsible for the gap opening in the magnon spectrum
This gap is predicted and experimentally verified to close by rotating the magnetization away from the c-axis with an applied magnetic field
Mn5Ge3 realizes a gapped Dirac magnon material in three dimensions
Its tunability by chemical doping or by thin film nanostructuring defines an exciting new platform to explore and design topological magnons
our experimental route to verify and control the topological character of the magnons is applicable to bulk centrosymmetric hexagonal materials
but its magnonic properties remain unexplored
we theoretically predict and experimentally confirm the existence of gapped Dirac magnons at the K-point due to the DMI
This gap can be closed by rotating the magnetization direction with an external magnetic field
thus validating the proposed gap mechanism and confirming the topological character of the magnons at the K-point
Our experimental route to verify and control the topological character of the magnons is not limited to Mn5Ge3 and should also be applicable to other bulk centrosymmetric hexagonal materials
The solid and dashed lines show the magnon bands obtained with and without the DMI
The inset indicates the location of the high-symmetry points in the hexagonal Brillouin zone
and a small uniaxial magnetic anisotropy energy (K ≈ − 0.1 meV)
so that the relevant spin Hamiltonian (with ∣Si∣ = 1) reads:
where we compare the results obtained with the experimental crystal structure parameters and with the theoretically optimized ones
In both cases there are two magnon bands in the energy range of experimental interest
with an energy gap at the K-point where otherwise a Dirac-like crossing of the bands would be expected by symmetry
This is straightforwardly verified to arise from the DMI
as omitting it from the magnon calculation leads to the closing of the gap
Centrosymmetry does ensure that the net DMI of the unit cell is zero
This means that the ferromagnetic domain walls are not chiral and that magnetic skyrmions cannot form
magnons can still be influenced by the local DMI
the spins at different sites precess with different phases and/or amplitudes
so that certain pairs of spins are noncollinear and can be affected by the torque arising from the DMI
where two magnon modes with opposite chirality cross and the degeneracy is lifted in a non-perturbative way by the DMI
We now report the experimental observation of this effect and its implications
a Representative measurements obtained at IN22 with constant-Q scans (symbols) at T = 10 K with ∣kf∣ = 2.662 Å−1 and fits used to determine the excitation energies (lines)
The purple arrows and rectangles indicate the peak positions in the corresponding (q,E) region of the dispersion
The dashed lines show the individual contributions of the various Gaussian peaks and of the linear background
The error bars indicate one standard deviation (square root of the neutron counts)
b Experimentally determined magnon bands (symbols) and fit to a simplified model described in the text (lines)
The solid and the dashed lines show the magnon bands obtained with and without the Dzyaloshinskii-Moriya interaction (DMI)
The error bars indicate the uncertainty in the peak location from least-squares fitting
At T = 10 K three peaks are seen between 8 meV and 22 meV
At T = 398 K (above TC) only a broad quasielastic signal is observed
Neutron intensity for the data at 10 K and 398 K is given on the right and left axis
b Dependence on magnetic field applied along the c-axis at T = 10 K
The field has almost no effect on the location of the two peaks
c Dependence on magnetic field applied along the a*-axis at T = 10 K
In zero field the magnetization is along the c-axis and two peaks are visible
The application of a transverse magnetic field saturates the magnetization along the a*-axis and merges the two peaks into one
demonstrating the closure of the magnon energy gap
The data shown in a were obtained at IN22 (∣kf∣ = 2.662 Å−1) and the data in b–c at IN12 (∣kf∣ = 1.971 Å−1)
the most crucial feature is observed both in theory and in experiment
that is the existence of a gap at the K-point where two magnon bands should otherwise cross
and confirm once more that the gap at the K-point is a consequence of a finite DMI
The model results also highlight a peculiarity of the measured magnon energies in the vicitiny of Γ
to which we shall briefly return in the Discussion
which were obtained by excluding the DMI from the calculations
although shifted to slightly higher energy than anticipated
The distinct response of the magnon excitation to a magnetic field applied to orthogonal crystal directions is consistent with the DMI mechanism
and so the gapped Dirac magnons at the K-point should consequently have a topological nature
Next we rule out potential alternative mechanisms to the DMI that could lead to a magnon gap opening at the K-point
Dipolar interactions are long-ranged but much weaker than the magnetic exchange interactions
so their effect is usually seen for rather small wave vectors in the vicinity of the Γ-point
Even if they did lift the magnon degeneracy at the K-point
their intrinsic weakness could not account for the observed magnitude of the gap
This set of bonds occurs four times in the unit cell
as it connects each Mn1 site to its six Mn2 neighbours
and so could have 1 meV/24 = 0.04 meV maximum Kitaev strength
The SAE obtained directly from the DFT calculations is about 0.02 meV in magnitude
and is one order of magnitude smaller than the values found for the DMI (0.57 meV for the set of bonds #2)
as expected from the theory of the magnetic exchange interactions for systems with weak SOC
Hence no phonon modes were detected in the vicinity of the K-point with an energy compatible with that of the magnons
which is a requirement for the gap opening mechanism through magnon-phonon interactions
we can assert that the only reasonable mechanism for the gap opening at the K-point is the DMI
Here we explore the expectation that if the bulk magnon band structure has some topologically non-trivial character it should be accompanied by magnon surface states
we compute the magnon band structure of slabs which are finite in one direction and periodic (i.e.
Comparing the simulations performed for the same slab with periodic and open boundary conditions along the chosen surface normal enables us to identify the energy range corresponding to the surface projection of the bulk magnon bands
Surface magnons are then expected to appear in the regions of (E
a Relation between the primitive cell and the rectangular cell used to define the slab, viewed along the c-axis, using the simplified model that fits the experimental data in Fig. 2b
The Mn1 chains are indicated by the two different shades of red
while the effective spin taken to represent the Mn2 sites is shown in blue
b Path in reciprocal space used for the magnon calculation
c Magnon bands of a 20-unit-cell-wide slab computed with periodic boundary conditions (PBC)
d Magnon bands of a 20-unit-cell-wide slab computed by changing periodic to open boundary conditions (OBC) along the \((01\bar{1}0)\) orientation
Results obtained excluding/including the Dzyaloshinskii-Moriya interaction (DMI) are shown by dashed/solid lines
The green arrow in d indicates the DMI-enabled magnon surface state
This might be due to changes in the domain state of the sample arising from the measurement history
This could modify the DMI by epitaxial strain
which would also be interesting in connection to potential magnetoelastic effects
or by quantum confinement effects if the thickness is just a few nanometers
we presented a combined theoretical and experimental study of the magnons in the centrosymmetric 3D FM Mn5Ge3
significant DMI has been theoretically identified on Mn-Mn bonds which do not contain an inversion center
This DMI is responsible for opening a gap in the magnon spectrum at the K-point
where otherwise symmetry would enforce a Dirac-like crossing of the magnon bands
INS measurements of the magnon spectrum show qualitative agreement with the main points predicted by theory
and confirm the expected gap at the K-point
We experimentally observe the closing of the gap by rotating the magnetization from the c-axis to the a*-axis with a magnetic field
This both validates the gap generation mechanism and the topological nature of the magnons at the K-point
thus establishing Mn5Ge3 as a realization of a gapped Dirac magnon material in three dimensions
The ability to control the gap at the K-point with an external magnetic field will also impact topological magnon surface states
As the macroscopic magnetic properties of Mn5Ge3 can be tuned by chemical substitution of Ge with Si or by carbon implantation
and it can also be grown as thin films in spintronics heterostructures
we foresee that the features of the newly-discovered topological magnons can be engineered and subsequently integrated in novel device concepts for magnonic applications
the physical mechanism leading to the formation of topological magnons at the K-point should be present in many other bulk centrosymmetric hexagonal materials
which opens an exciting avenue for future investigations
The DFT simulation packages Quantum Espresso and juKKR are publicly available (see Methods)
The code for the solution of the linear spin wave problem is available from the corresponding authors upon request
Quantal phase factors accompanying adiabatic changes
Quantized hall conductance in a two-dimensional periodic potential
Symmetry-based indicators of band topology in the 230 space groups
Robert-Jan Topological classification of crystalline insulators through band structure Combinatorics
Spin-wave spectrum of the quantum ferromagnet on the Pyrochlore Lattice Lu2V2O7
Topological magnon insulator in insulating ferromagnet
Edge states in topological magnon insulators
Topological magnon bands in a Kagome Lattice Ferromagnet
Magnetic field effect on topological spin excitations in CrI3
Topological magnon insulators in two-dimensional van der Waals ferromagnets CrSiTe3 and CrGeTe3: Toward intrinsic gap-tunability
Topological spin excitations in a three-dimensional antiferromagnet
Dirac Magnons in a Honeycomb Lattice Quantum XY Magnet CoTiO3
Order-by-disorder from bond-dependent exchange and intensity signature of nodal quasiparticles in a honeycomb cobaltate
An efficient material search for room-temperature topological magnons
The spatial distribution of magnetisation density in Mn5Ge3
Anisotropy of the magnetocaloric effect: Example of Mn5Ge3
Linear magnetization dependence of the intrinsic anomalous hall effect
Anomalous Nernst effect in ferromagnetic Mn5Ge3Cx thin films on insulating sapphire
Strongly enhanced Curie temperature in carbon-doped Mn5Ge3 films
Simulation of the enhanced Curie temperature in Mn5Ge3Cx compounds
Chiral asymmetry of the spin-wave spectra in ultrathin magnetic films
Asymmetric spin-wave dispersion on Fe(110): Direct evidence of the Dzyaloshinskii-Moriya interaction
Fundamental spin interactions underlying the magnetic anisotropy in the Kitaev ferromagnet CrI3
Probing of the interfacial Heisenberg and Dzyaloshinskii–Moriya exchange interaction by magnon spectroscopy
Unusual exchange couplings and intermediate temperature Weyl State in Co3Sn2S2
Spin phonon coupling in hexagonal multiferroic YMnO3
Magnon-polaron excitations in the noncollinear antiferromagnet Mn3Ge
Introduction to the Theory of Thermal Neutron Scattering (Cambridge University Press
Total interference between nuclear and magnetovibrational one-phonon scattering cross sections
Thermal hall effect induced by magnon-phonon interactions
Kyung-Jin Topological Magnon-Phonon hybrid excitations in two-dimensional ferromagnets with tunable chern numbers
Hilbertv Large topological Hall effect in the non-collinear phase of an antiferromagnet
Spin fluctuations drive the inverse magnetocaloric effect in Mn5Si3
Spin waves in the collinear antiferromagnetic phase of Mn5Si3
Complex magnetic structure and spin waves of the noncollinear antiferromagnet Mn5Si3
Magnetic-entropy change in Mn5Ge3−xSix alloys
Unveiling the atomic position of C in Mn5Ge3Cx thin films
QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials
Development of a relativistic full-potential first-principles multiple scattering Green function method applied to complex magnetic textures of nano structures at surfaces
https://jukkr.fz-juelich.de/
Spin-resolved inelastic electron scattering by spin waves in noncollinear magnets
JURECA: Data Centric and Booster Modules implementing the Modular Supercomputing Architecture at Jülich Supercomputing Centre
https://doi.org/10.5291/ILL-DATA.4-01-1682 (2021)
https://doi.org/10.5291/ILL-DATA.CRG-2853 (2021)
https://doi.org/10.5291/ILL-DATA.INTER-547 (2021)
https://doi.org/10.5291/ILL-DATA.CRG-2755 (2021)
dos Santos Dias, M. et al. Topological magnons driven by the Dzyaloshinskii-Moriya interaction in the centrosymmetric ferromagnet Mn5Ge3. Mater. Cloud Arch. 2023.170 (2023), https://doi.org/10.24435/materialscloud:98-m3
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Peter Grünberg Institut and Institute for Advanced Simulation
Theory and Simulation of Materials (THEOS)
and National Centre for Computational Design and Discovery of Novel Materials (MARVEL)
Jülich Centre for Neutron Science (JCNS-2) and Peter Grünberg Institut (PGI-4)
performed most DFT calculations and the spin-wave modelling
with additional calculations performed by F.J.d.S
performed the experimental measurements and the corresponding data analysis
were local contacts of IN12 and IN22 and provided instrument support
The theoretical aspects of the work were discussed with N.M.
All authors participated in the discussion of the results
wrote the manuscript with input from all authors
Yaohua Liu and the other anonymous reviewer(s) for their contribution to the peer review of this work
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DOI: https://doi.org/10.1038/s41467-023-43042-3
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Threats
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especially those operating in kernel space
are pieces of malware infamous for their near absolute power in the operating system
such implants have high privileges in the system
allowing them to intercept and potentially tamper with core I/O operations conducted by the underlying OS
like reading or writing to files or processing incoming and outgoing network packets
The capability to blend into the fabric of the operating system itself
is the quality that earns rootkits their notoriety for stealth and evasion
the number of Windows rootkits in the wild has decreased dramatically
with the bulk of those still active often being leveraged in high profile APT attacks
One such example came to our attention during an investigation last year
in which we uncovered a formerly unknown Windows rootkit and its underlying cluster of activity
We observed this rootkit and other tools by the threat actor behind it being used as part of a campaign we dubbed ‘TunnelSnake’
conducted against several prominent organizations in Asia and Africa
In this blog post we will focus on the following key findings that came up in our investigation:
We provided information about this operation in our threat intelligence portal in August 2020. More details and analysis are available to customers of our private APT reporting service. For more details contact: intelreports@kaspersky.com
Our investigation into the TunnelSnake campaign started from a set of alerts from our product on a detection of a unique rootkit within the targeted networks
Based on string artefacts within the malware’s binaries
This tool is a passive backdoor which allows attackers to inspect all incoming traffic to the infected machine
filter out packets that are marked as designated for the malware and respond to them
This forms a covert channel over which attackers are able to issue shell commands and receive back their outputs
The rootkit has two traits that make it particularly evasive
The packet inspection happens in kernel mode with the use of a Windows driver
allowing attackers to drop the packets of interest before they are processed by the network stack
thus ensuring they are not detected by security solutions
the fact that the rootkit waits for incoming traffic rather than initiating a connection to a server itself
avoids the need to incorporate a C&C address in the malware’s binary or to maintain a steady C&C infrastructure
This hinders analysis and makes it difficult to trace the attacker’s footprints
The figure below illustrates the structure of the rootkit’s components
They consist of a kernel mode driver and a user mode agent that deploys and controls it
In the following sections we will break down each of these components and describe how they operate to achieve the goal of tapping into the target’s network communication and blending in its traffic
The user mode component of the Moriya rootkit has two purposes
One is to deploy the kernel mode component of the malware on the machine and the other is to leverage the covert communication channel created by it to read shell commands sent from the C&C server to the compromised machine and to respond to them
Since Moriya is a passive backdoor intended to be deployed on a server accessible from the internet
it contains no hardcoded C&C address and relies solely on the driver to provide it with packets filtered from the machine’s overall incoming traffic
The first order of business for the attacker when using Moriya is to gain persistence on the targeted computer
the user mode agent’s DLL contains an export function named Install
which is intended to create a service named ZzNetSvc with the description ‘Network Services Manager’ and start it
the path to the user mode agent’s image is set to the registry key HKLM\System\CurrentControlSet\Services\ZzNetSvc\Parameters\ServiceDll so that it will be invoked from its ServiceMain export each time the service is initiated
the agent will attempt to load the rootkit’s driver into the system
Its binary is bundled as two driver images within the DLL’s resource section
corresponding to 32- and 64-bit architectures
while in reality only one of them is written to disk
the agent DLLs were compiled for 64-bit systems
dropping a 64-bit driver to the drivers directory in the system path
Code that writes the Moriya driver to disk
The agent uses a known technique whereby the VirtualBox driver (VBoxDrv.sys) is leveraged to bypass the Driver Signature Enforcement mechanism in Windows and load Moriya’s unsigned driver
DSE is an integrity mechanism mandating that drivers are properly signed with digital signatures in order for them to be loaded
which was introduced for all versions of Windows starting from Vista 64-bit
The technique used to bypass it was seen in use by other threat actors like Turla
Moriya’s user mode agent bypasses this protection with the use of an open-source code[1] named DSEFIX v1.0
The user agent dumps an embedded VBoxDrv.sys image of version 1.6.2 to disk and loads it
which is then used by the aforementioned code to map Moriya’s unsigned driver to kernel memory space and execute it from its entry point
These actions are made possible through IOCTLs implemented in VBoxDrv.sys that allow writing to kernel address space and executing code from it
the bypass code is used to locate and modify a flag in kernel space named g_CiOptions
the agent registers a special keyword that is used as a magic value
which will be sought in the first bytes of every incoming packet passed on the covert channel
This allows the rootkit to filter marked packets and block them for any application on the system other than the user mode agent
The registration of the value is done through a special IOCTL with the code 0x222004 sent to the driver
Registration of the packet magic value using a designated IOCTL
Except for its covert channel communication feature
Moriya is capable of establishing a reverse shell session using an overt channel
it waits for a special packet that consists of a message with the structure connect <c2_address> <c2_port>
The address and port are parsed and used by the agent to start a new connection to the given server
while creating a new cmd.exe process and redirecting its I/O to the connection’s socket
The handles for the newly created process and its main thread are destroyed to avoid detection
the agent attempts to read the incoming TCP payload from the driver
which will be retrieved as soon as a designated packet with a magic number and shell command is received
An attempt is made to read the data with a plain ReadFile API function as a blocking operation
reading is accomplished only once the buffer in kernel mode is populated with data from a Moriya-related packet
the agent creates a new cmd.exe process and redirects its I/O using named pipes
One pipe is used to read the retrieved shell command from the covert channel and the other is used to write the shell’s output (obtained from the stdout and stderr streams) back to it after execution
the agent uses the WriteFile API function with the driver’s handle
All traffic passed on the channel is encoded with a simple encryption scheme
XORed with the value 0x05 and then negated
to decode the incoming traffic’s payload
every byte of it should be first negated and then XORed with 0x05
The Moriya rootkit’s driver component makes use of the Windows Filtering Platform (WFP) to facilitate the covert channel between the compromised host and the C&C server
WFP provides a kernel space API that allows driver code to intercept packets in transit and intervene in their processing by the Windows TCP/IP network stack
This makes it possible to write a driver that can filter out distinct packet streams
and designate them for consumption by a specific user mode application
The driver fetches the distinct Moriya-related traffic using a filtering engine
This is the kernel mode mechanism used to inspect traffic according to rules that can be applied on various fields across several layers of a packet (namely data link
making it possible to handle matching packets with unique handlers
Such handlers are referred to as callout functions
the filtering engine is configured to intercept TCP packets
Each packet with these criteria will be inspected by a callout function that checks if its first six bytes correspond to the previously registered magic value
copies the packet contents into a special buffer that can be later read by the user mode agent
The matching packet will then be blocked in order to hide its presence from the system
while any other packet is permitted to be processed as intended by the network stack
To allow the crafting of a response back to the server
the callout function saves a special value in a global variable that identifies the received TCP stream
and is taken from the packet’s corresponding FWPS_INCOMING_METADATA_VALUES0 struct
When the user issues a response to the server via the driver
the latter would craft a new packet using the FwpsAllocateNetBufferAndNetBufferList0 function and insert the response data and target server based on the saved flowHandle to it
designates it for the flow of the corresponding incoming TCP packet and injects data written from user space into it
the driver registers several functions that are exposed to the user mode agent in order to interact with it:
Code used for registering the packet magic value from the driver side
Inspecting the systems targeted by the rootkit
we tried to understand how they got infected in the first place
Moriya was seen deployed mostly on public-facing servers within the victim organizations
we saw the attacker infect an organizational mail server with the China Chopper webshell
Moriya’s user mode agent was explicitly installed using a command line executed on the targeted server this way
This command and examples of others run on the victim machine via the webshell can be seen below
through vulnerable web servers in their networks
an older variant of Moriya named IISSpy (described below) targets IIS web servers
Our telemetry shows that it was likely deployed by exploiting CVE-2017-7269 to let the attackers gain an initial foothold on a server prior to running the malware
During our investigation we found a target in South Asia that enabled us to get a glimpse into some of the other tools that we assess were in use by the same attacker
The toolset includes programs used to scan hosts in the local network
perform lateral movement to spread to them and exfiltrate files
While most of the tools seem custom made and tailored for the attackers’ activities
we could also observe some open-source malware frequently leveraged by Chinese-speaking actors
Following is an outline of these tools based on their purpose in the infection chain
Malformed packet generated by HTTP scanner
the output will be displayed in the console
Console output with a server response displayed upon discovery of a new server in the network
The first one is an executable file named nw.tmp that decrypts an embedded payload using the RC4 algorithm and injects it into a newly spawned svchost.exe process
The injected payload is similar to one described by Mandiant in 2013
which is yet another intermediate loader that decrypts and loads an embedded BOUNCER DLL
The last stage is started by invoking the DLL’s dump export with the arguments passed via the command line
The other version was stored with the name rasauto.dll in the system directory
impersonating the Windows Remote Access Auto Connection Manager library
instead directly calling the DLL’s dump export without arguments
The decrypted library is a slightly modified BOUNCER variant that always listens on the hardcoded port 1437
Code from the second BOUNCER variant that uses the hardcoded port 1437 to listen for new packets
Based on compilation timestamps of all BOUNCER-related executables
we assess that the attacker reused old samples of the malware rather than compiled new versions of it:
Code used to create and start the service on targeted host
Termite provides additional features to download and upload files between the compromised hosts
as well as a way to spawn a remote shell to control the targeted machine
IISSpy is an older user-mode version of the Moriya rootkit that we were able to pinpoint in our telemetry
It is used to target IIS servers for establishing a backdoor in their underlying websites
unrelated to any of the attacks in the current operation
This suggests the threat actor has been active since at least that year
achieves its goals by enumerating running IIS processes on the server (i.e.
those that are executed from the image w3wp.exe)
and injecting the malware’s DLL into them to alter their behavior
The executed code in the IIS processes will then set inline hooks for several functions
The corresponding CreateFileW hook function checks if the filename argument contains the directory ‘\MORIYA\’ or ‘\moriya\’ in its path
infers that the attacker has sent a specially crafted HTTP request to the web server
the Moriya path in the URL is followed by an encoded command
After the command is decoded and processed
it is passed via a mailslot (\\.\mailslot\slot) to a separate thread
while signaling an event called Global\CommandEvent
Code of the CreateFileW hook function that looks for the ‘MORIYA’ \ ‘moriya’ directory in a request path
Should the currently handled file contain the Moriya path
the very same hook function will generate a special file on the web server to which command execution output will be written
This file’s path is created by finding the position of the ‘\MORIYA\’ or ‘\moriya\’ strings in the inspected filename argument
and replacing it with the string ‘\IISINFO.HTM’
This will then be appended to the command data passed on the mailslot
following a ‘ > ‘ character
The other thread waiting on the command event mentioned above is in charge of processing attacker data fetched from the mailslot
Any such command will be read and parsed to find the ‘ > ‘ character and the file path that follows it
in this case the one corresponding to ‘IISINFO.HTML’
the output will be written to the file in this path
allowing the attacker to read it by issuing a corresponding HTTP request where the URL path leads to this file on the server
Other functions that are hooked in the IIS process are CreateProcessAsUserW and CreateProcessW
These are used to detect if the current process spawns a new server instance
which will in turn be injected with the malware’s DLL
IISSpy will also create a monitoring thread that will periodically look for newly created httpd.exe processes
the malware will be injected to them as well
Although it is evident from both the functionality and use of the Moriya keyword by the malware that IISSpy and the Moriya rootkit are related
further evidence in the code substantiates the connection:
Packet decoding loop that follows the same logic as that used in Moriya
Code used in both variants to spawn a new shell
Comparison of Install export function CFGs between IISSpy and Moriya
Another interesting artefact found in our telemetry that could be tied to the developers of Moriya is a malware named ProcessKiller
it is intended to eliminate execution of processes
this tool is used to shut down and block initiation of AV processes from kernel space
thus allowing other attack tools to run without being detected
This malware operates through the following stages:
the connection to Moriya is based on several observations:
Unique debug message that appears in ProcessKiller and Moriya
we are not able to attribute the attack to any particular known actor
but based on the TTPs used throughout the campaign
We base this on the fact that the targeted entities were attacked in the past by Chinese-speaking actors
and are generally located in countries that are usually targeted by such an actor profile
are an additional indicator supporting our hypothesis as they have previously been used in campaigns attributed to well-known Chinese-speaking groups
Based on our telemetry the attacks were highly targeted and delivered to less than 10 victims around the world
The most prominent victims are two large regional diplomatic organizations in South-East Asia and Africa
while all the others were victims in South Asia
The TunnelSnake campaign demonstrates the activity of a sophisticated actor that invests significant resources in designing an evasive toolset and infiltrating networks of high-profile organizations
covert communications channels and proprietary malware
the group behind it maintains a considerable level of stealth
like the usage of a commodity webshell and open-source legacy code for loading unsigned drivers
may get detected and in fact were flagged by our product
giving us visibility into the group’s operation
with activity dating back to at least 2018
the threat actor behind this campaign has shown that it is able to evolve and tailor its toolset to target environments
This indicates the group conducting these attacks may well still be active and retooling for additional operations in the area of interest outlined in this publication
we continue to track this attacker and look for signs of its reappearance in the wild
Any findings and updates will be made available to customers of our Threat Intelligence Portal
[1] Today a copy of the original code can be found here: http://www.m5home.com/bbs/thread-8043-1-1.html
[2] https://www.fireeye.com/content/dam/fireeye-www/services/pdfs/mandiant-apt1-report.pdf
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Kaspersky GReAT experts uncovered a new campaign by Lazarus APT that exploits vulnerabilities in South Korean software products and uses a watering hole approach
MysterySnail RAT attributed to IronHusky APT group hasn’t been reported since 2021
Kaspersky GReAT detected new versions of this implant in government organizations in Mongolia and Russia
Kaspersky researchers analyze GOFFEE’s campaign in H2 2024: the updated infection scheme
Kaspersky GReAT experts discovered a complex APT attack on Russian organizations dubbed Operation ForumTroll
which exploits zero-day vulnerabilities in Google Chrome
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— Moriya Jutanugarn emerged from a tight pack late Sunday afternoon at Columbia Edgewater to win the Portland Classic for her third career LPGA Tour title
Guseva is the first Russian player with an LPGA Tour card
Jutanugarn also won the 2018 HUGEL-JTBC LA Open and 2021 Dow Great Lakes Bay Invitational team event with younger sister Ariya Jutanugarn
closed with a 65 on Sunday to tie for ninth at 17 under
but was left out because of the Netherlands' separate standards for all sports to meet a realistic chance of a top-eight finish
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Using group theory and first principles calculations
it is shown that an analogue of the Dzyaloshinskii–Moriya interaction that allows the antisymmetric exchange spin coupling in magnets exists in ferroelectrics
Zhao, H. J., Chen, P., Prosandeev, S., Artyukhin, S. & Bellaiche, L. Nat. Mater. https://doi.org/10.1038/s41563-020-00821-3 (2020)
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Departamento de Ciencias de la Tierra y Física de la Materia Condensada
The author declares no competing interests
Reprints and permissions
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DOI: https://doi.org/10.1038/s41563-020-00845-9
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Perpendicularly magnetized synthetic antiferromagnets (SAF)
possessing low net magnetization and high thermal stability as well as easy reading and writing characteristics
have been intensively explored to replace the ferromagnetic free layers of magnetic tunnel junctions as the kernel of spintronic devices
utilizing spin-orbit torque (SOT) to realize deterministic switching of perpendicular SAF have been reported while a large external magnetic field is typically needed to break the symmetry
combining theoretic analysis and experimental results
we report that the effective modulation of Dzyaloshinskii-Moriya interaction by the interfacial crystallinity between ferromagnets and adjacent heavy metals plays an important role in domain wall configurations
By adjusting the domain wall configuration between Bloch type and Néel type
we successfully demonstrate the field-free SOT-induced magnetization switching in [Co/Pd]/Ru/[Co/Pd] SAF devices constructed with a simple wedged structure
Our work provides a practical route for utilization of perpendicularly SAF in SOT devices and paves the way for magnetic memory devices with high density
it is still difficult to experimentally manipulate and detect antiferromagnetic storage layers reliably
field-free SOT-driven switching in SAFs remains to be demonstrated experimentally
we systematically analyzed how to realize field-free magnetization switching in SAF by SOT and successfully demonstrated the deterministic switching experimentally
We show that the strength of DMI plays an important role in the configuration of domain walls
which further affects the current-induced magnetization switching
the DMI between heavy metal and the ferromagnetic layer was greatly reduced
thereby reducing the assistive field required for SOT-induced magnetization switching
When the domain wall energy effective field is comparable with the DMI effective field
the domain walls exhibit the configuration between Bloch-type and Néel-type
making them easily manipulated by the external assistive magnetic field
to achieve the field-free SOT switching in SAF
a simple method of the wedged heavy metal structure is designed to break the symmetry
which enables the current-induced effective magnetic field
The SAF structure deposited on wedged Pt film presents uniform perpendicular magnetic anisotropy and the realization of field-free SOT switching in SAF shows stable circularity
We believe that these results represent an important step towards utilizing perpendicularly SAF as the free layer in MTJ devices and bringing functional SAF closer to potential applications
a–d Schematic illustrations of DWs in the top and bottom magnetic layers in perpendicularly magnetized SAF nanowires under an external magnetic field with HDMI much larger than HDWE (a–c) and HDMI comparable to HDWE (d)
the center moments of domain walls are rotated to different directions with Hext < HEX (a)
and Hext are the domain wall energy effective field
which give rise to \({H}_{{\rm{B}}}^{{\rm{lg}}}\)
e–j Directions of different fields and corresponding longitudinal torques \({\tau }_{{\rm{B}}}^{{\rm{lg}}}\) and \({\tau }_{{\rm{T}}}^{{\rm{lg}}}\) (e
transversal torques \({\tau }_{{\rm{B}}}^{{\rm{ts}}}\) and \({\tau }_{{\rm{T}}}^{{\rm{ts}}}\) (f
i) and exchange torques \({\tau }_{{\rm{B}}}^{{\rm{ex}}}\) and \({\tau }_{{\rm{T}}}^{{\rm{ex}}}\) (g
upper and lower diagrams correspond to TM and BM
the “↓→↑” domain wall can move under the applied current
the “↑☉↓” domain wall remains static until it is swallowed up by a domain wall further away
the whole BM domain is reversed by the current-induced SOT and the magnetization of TM is switched simultaneously through the antiferromagnetic coupling
the switching in SAF is most likely faster than its ferromagnetic counterpart
an external assistive field is needed to achieve the SOT switching; however
the current-induced SOT switching becomes easier when the HDMI is comparable to HDWE
which is consistent with the conclusions discussed earlier
a Sketch of the collective domain wall model
Φ and Ψ are the angles between the applied current and the up-to-down and down-to-up domain wall
while Φ’ and Ψ’ are corresponding angles with opposite directions
b Calculated results of SOT efficiency as a function of the external field for HDMI much larger than HDWE and HDMI comparable to HDWE in the SAF samples
d The SOT efficiency as a function of the external field for the ferromagnetic sample grown by e-beam evaporation (c) and magnetron sputtering (d)
Insets are the corresponding normalized AHE curves for the ferromagnetic sample
Hsat is the external magnetic field at which the SOT efficiency gets saturated and Hint is the initial field to generate SOT efficiency
The dashed lines are the fitting lines of SOT efficiency from Hint to Hsat
a Schematic of the studied Ta/Pt/[Co/Pd]2/Co/Ru/[Co/Pd]3/Co/Ru multilayer
The wedged Pt layer was grown through a moving baffle
b Creation of a net out-of-plane spin polarization and effective magnetic field in the studied SAF structure
\({H}_{{\rm{y}}}^{{\rm{DL}}}\) and \({H}_{{\rm{x}}}^{{\rm{FL}}}\) are the damping-like and field-like magnetic fields
\({H}_{{\rm{z}}}^{{\rm{eff}}}\) is the effective perpendicular magnetic field and m represents the unit vector of the magnetization
The wedged Pt layer allows for the generation of \({H}_{{\rm{z}}}^{{\rm{eff}}}\)
c Schematic of the Hall bar and the measurement configuration
I stands for current and V parameters voltage
d Out-of-plane field (Hz) dependent Kerr signals (θk) of the compensated SAF sample at different nominal Pt thicknesses
The antiferromagnetic coupling strength of the sample hardly depends on the thickness of the wedged layer
e RH curves of SAF sample measured when sweeping an external field along the z-direction
The inset represents the spin configuration of the two antiparallel states
a SOT switching under different external assistive magnetic fields
b Anomalous Hall effect measured at opposite current polarities
RH is the normalized anomalous Hall resistance and HZ is the applied out-of-plane magnetic field
The Pt thickness in this device is 4.43 nm
c Applied current dependent current-induced perpendicular effective magnetic field
d zero field repeatable SOT switching under successive current pulses with opposite polarities
The duration of the current pulse is 1 ms and the period is 3 s
b High-resolution TEM images of the SAF and ferromagnetic structures were grown by magnetron sputtering (a) and e-beam evaporation (b)
The scale bar in TEM images corresponds to 5 nm
and layer-resolved SOC energy difference \(\triangle {E}_{{\rm{soc}}}\) (d) of opposite chirality of Pt/Co heterostructures with increasing interfacial roughness
e–h Atomic-resolved \(\triangle {E}_{{\rm{soc}}}\) for each atom in interfacial Pt layer when intermixed with Co atoms
we have systematically demonstrated the deterministic field-free magnetization switching in the perpendicular synthetic antiferromagnetic structures
in which the tailored strength of Dzyaloshinskii–Moriya interaction plays the major role in configuring domain walls with enhanced spin–orbit torque efficiency
When the domain wall energy effective field is comparable with DMI effective field
the domain wall exhibits the configuration between Bloch type and Néel type which can be manipulated by external field easily
By depositing the [Co/Pd]/Ru/[Co/Pd]/Ru structure on the wedged SOC layer
we obtained the completely compensated SAF with uniform anisotropy and finally realized the SOT-induced magnetization switching without any external fields
which is crucial for practical applications
We have also shown that the DMI strength depends dramatically on the crystallinity of the Pt/Co interface and the intermixing interface favors weaker DMI
which is beneficial for the field-free SOT switching
The wedged Ta/Pt/[Co/Pd]2/Co/Ru/[Co/Pd]3/Co/Ru SAF films were deposited at room temperature onto 5 mm × 5 mm MgO substrate for magnetic property measurements via d.c
magnetron sputtering with a base vacuum better than 8.0 × 10−5 mTorr
and the working argon pressure was 3 mTorr
The wedged Pt layer was grown through a moving baffle during the deposition
The Ta/Pt/[Co/Pd]2/Co/Pd ferromagnetic stacks were deposited on a 5 mm × 5 mm MgO substrate via e-beam evaporation at a base pressure of 5 × 10−6 mTorr
Devices were patterned by means of standard photolithography and subsequent Ar ion milling
The anomalous Hall effect and current-induced magnetization switching were carried out by four-point measurements in a Hall cross with a channel width of 5 μm at room temperature
Magnetic domain images and hysteresis loops were captured using a MagVision Kerr Imaging System
which operates on the magneto-optical Kerr effect in the polar configuration
the out-of-plane magnetization is probed and observed as different levels of brightness in the image
Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions
A perpendicular-anisotropy CoFeB–MgO magnetic tunnel junction
Magnetically engineered spintronic sensors and memory
Conductance and exchange coupling of two ferromagnets separated by a tunneling barrier
Spin-current interaction with a monodomain magnetic body: A model study
Spin-orbit coupling induced anisotropy effects in bimetallic antiferromagnets: a route towards antiferromagnetic spintronics
Room-temperature perpendicular exchange coupling and tunneling anisotropic magnetoresistance in antiferromagnet-based tunnel junction
Electrical switching of an antiferromagnet
Writing and reading antiferromagnetic Mn2Au by Néel spin-orbit torques and large anisotropic magnetoresistance
Systematic variation of the strength and oscillation period of indirect magnetic exchange coupling through the 3d
Magnetic field direction dependent magnetization reversal in synthetic antiferromagnets
Current-induced magnetization switching in MgO barrier based magnetic tunnel junctions with CoFeB/Ru/CoFeB synthetic ferrimagnetic free layer
Enhanced thermal stability in perpendicular top-pinned magnetic tunnel junction with Synthetic antiferromagnetic free layers
Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection
Spin–orbit torque switching without an external field using interlayer exchange coupling
Anomalous spin–orbit torques in magnetic single-layer films
Observation of spin-orbit effects with spin rotation symmetry
Detection of spin-orbit torque with spin rotation symmetry
Switching of perpendicular magnetization by spin − orbit torques in the absence of external magnetic fields
Current-induced spin-orbit torque and field-free switching in Mo-based magnetic heterostructures
Magnetization switching by spin-orbit torque in an antiferromagnet-ferromagnet bilayer system
Field-free switching of perpendicular magnetization through spin-orbit torque in anti-ferromagnet/ferromagnet/oxide structures
Switching a perpendicular ferromagnetic layer by competing spin currents
Anomalous spin-orbit torque switching in synthetic antiferromagnets
Spin-orbit torque in a completely compensated synthetic antiferromagnet
Spin-orbit torque in MgO/CoFeB/Ta/CoFeB/MgO symmetric structure with interlayer antiferromagnetic coupling
Asymmetric current-driven switching of synthetic antiferromagnets with Pt insert layers
Spin-torque switching with the giant spin Hall effect of tantalum
Highly efficient spin-current g by the spin Hall effect in Au1−xPtx
Fast current-induced domain-wall motion controlled by the Rashba effect
Tilting of the spin orientation induced by Rashba effect in ferromagnetic metal layer
Domain-wall velocities of up to 750 ms−1 driven by exchange-coupling torque in synthetic antiferromagnets
Spatially and time-resolved magnetization dynamics driven by spin–orbit torques
Room-temperature spin-orbit torque switching induced by a topological insulator
et al.Asymmetric magnetic domain-wall motion by the Dzyaloshinskii-Moriya interaction
Determination of spin torque efficiencies in heterostructures with perpendicular magnetic anisotropy
Spin currents and spin–orbit torques in ferromagnetic trilayers
Deterministic spin-orbit torque switching by a light-metal insertion
Magnetic field direction dependence of topological Hall effect like features in synthetic ferromagnetic and antiferromagnetic multilayers
Realization of isolated and high-density skyrmions at room temperature in uncompensated synthetic antiferromagnets
Non-magnetic origin of spin Hall magnetoresistance-like signals in Pt films and epitaxial NiO/Pt bilayers
Interfacial Dzyaloshinskii-Moriya interaction in Pt/CoFeB films: effect of the heavy-metal thickness
Correlation hole of the spin-polarized electron gas
with exact small-wave-vector and high-density scaling
From ultrasoft pseudopotentials to the projector augmented-wave method
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This work was supported by the National Key R&D Program of China (Grant No
the National Natural Science Foundation of China (Grant Nos
the National Key R&D Program of China (2019FYB2205100)
and Natural Science Foundation of Zhejiang Province (LR19A040002)
Key Laboratory of Advanced Materials (MOE)
Key Laboratory of Microelectronic Devices and Integrated Technology
University of the Chinese Academy of Sciences
Center of Materials Science and Optoelectronics Engineering
grew the thin films and performed magnetization measurements
carried out the first-principles calculations
All authors discussed the results and prepared the manuscript
Peer review information Nature Communications thanks Christian Binek
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DOI: https://doi.org/10.1038/s41467-021-23414-3
An unknown threat actor with the capabilities to evolve and tailor its toolset to target environments infiltrated high-profile organizations in Asia and Africa with an evasive Windows rootkit since at least 2018
Called 'Moriya,' the malware is a "passive backdoor which allows attackers to inspect all incoming traffic to the infected machine
filter out packets that are marked as designated for the malware and respond to them," said Kaspersky researchers Mark Lechtik and Giampaolo Dedola in a Thursday deep-dive
The Russian cybersecurity firm termed the ongoing espionage campaign 'TunnelSnake.' Based on telemetry analysis
less than 10 victims around the world have been targeted to date
with the most prominent targets being two large diplomatic entities in Southeast Asia and Africa
All the other victims were located in South Asia
The first reports of Moriya emerged last November when Kaspersky said it discovered the stealthy implant in the networks of regional inter-governmental organizations in Asia and Africa
Malicious activity associated with the operation is said to have dated back to November 2019
with the rootkit persisting in the victim networks for several months following the initial infection
"This tool was used to control public facing servers in those organizations by establishing a covert channel with a C2 server and passing shell commands and their outputs to the C2," the company said in its APT trends report for Q3 2020
"This capability is facilitated using a Windows kernel mode driver."
Rootkits are particularly dangerous as they allow attackers to gain high privileges in the system, enabling them to intercept core input/output operations conducted by the underlying operating system and better blend with the landscape
thus making it difficult to trace the attacker's digital footprints
Microsoft, for its part, has implemented several protections into Windows over the years to prevent successful deployment and execution of rootkits
which makes Moriya all the more noteworthy
consists of both proprietary and well-known pieces of malware such as China Chopper web shell
and Termite that have been previously used by Chinese-speaking threat actors
giving an insight into the attacker's origins
and procedures (TTPs) used in the attacks also show that the targeted entities fit the victimology pattern associated with Chinese-speaking adversaries
The revelations come as advanced persistent threats (APTs) continue to ramp up highly-targeted data-stealing missions
while simultaneously going to great lengths to stay under the radar for as long as possible
"The TunnelSnake campaign demonstrates the activity of a sophisticated actor that invests significant resources in designing an evasive toolset and infiltrating networks of high-profile organizations," Lechtik and Dedola said
the group behind it maintains a considerable level of stealth."
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