Metrics details Conflicting observations of the speed at which various ferromagnetic materials respond to an external femtosecond laser excitation have generated considerable controversy It is now shown that ferromagnets can be divided in two categories according to the values of specific magnetic parameters Prices may be subject to local taxes which are calculated during checkout Download references Reprints and permissions Download citation Anyone you share the following link with will be able to read this content: a shareable link is not currently available for this article Sign up for the Nature Briefing newsletter — what matters in science Please enter the e-mail address you used to register to reset your password passed away on 17 June 2022 at the age of 78 Remarkable in his scientific life was the discovery of proton radioactivity as well as the synthesis of six new superheavy chemical elements between 1981 and 1996 Sigurd was born on 15 February 1944 in Böhmisch-Kamnitz (Bohemia) and studied physics at TH Darmstadt where he received his diploma in 1969 and his doctorate in 1974 with Egbert Kankeleit he joined the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt his scientific work there occupying him for almost 50 years Accuracy and scientific exactness were important to him from the beginning He investigated fusion reactions and radioactive decays in the group of Peter Armbruster and worked with Gottfried Münzenberg Sigurd achieved international fame through the discovery of proton radioactivity from the ground state of 151Lu in 1981 he benefited from his pronounced thoroughness and scientific curiosity unambiguous identification and study of the properties of the heaviest chemical elements which were to shape his further scientific life The first highlights were the synthesis of the new elements bohrium (Bh) hassium (Hs) and meitnerium (Mt) between 1981 and 1984 with which GSI entered the international stage of this renowned research field The semiconductor detectors that Sigurd had developed specifically for these experiments were far ahead of their time and are now used worldwide to search for new chemical elements At the end of the 1990s Sigurd took over the management of the Separator for Heavy Ion Reaction Products (SHIP) group and after making instrumental improvements to detectors and electronics crowned his scientific success with the discovery of the elements darmstadtium (Ds) roentgenium (Rg) and copernicium (Cn) in the years 1994 to 1996 a strategy paper developed under his leadership in 1999 for long-term heavy-element research at GSI In 2009 he was appointed Helmholtz professor and from then on was able to devote himself entirely to scientific work again For many years he also maintained an intensive collaboration and scientific exchange with his Russian colleagues in Dubna where he co-discovered the element flerovium (Fl) in a joint experiment For his outstanding research work and findings Sigurd received a large number of renowned awards and prizes; too many he was invited to talk at countless international conferences authored a large number of review articles He also liked to present scientific results at public events he was able to develop a thrilling picture of modern physics but also of the big questions of cosmology and element synthesis in stars; he was also able to convey very clearly to the public how atoms can be made “visible” Many chapters of Sigurd’s contemporary scientific life are recorded in his 2002 book On Beyond Uranium (CRC Press) His modesty and friendly nature were remarkable accuracy and deliberateness in all work were outstanding and his persistence was one of the foundations for ground-breaking scientific achievements He was always in the office or at an experiment so you could talk to him at any time and were always rewarded with detailed answers and competent advice We are pleased that we were able to work with such an excellent scientist and colleague as well as an outstanding teacher and a great person Gottfried Münzenberg and Christoph Scheidenberger GSI Darmstadt CERN Courier is essential reading for the international high-energy physics community Highlighting the latest research and project developments from around the world CERN Courier offers a unique record of the ongoing endeavour to advance our understanding of the basic laws of nature Metrics details Magnetization manipulation is essential for basic research and applications how fast can the magnetization be reversed in nanoscale magnetic storage media the speed of the magnetization dynamics depends on the nature of the energy transfer pathway The order of the spin system can be effectively influenced through spin-flip processes mediated by hot electrons It has been predicted that as electrons drive spins into the regime close to almost total demagnetization characterized by a loss of ferromagnetic correlations near criticality a second slower demagnetization process takes place after the initial fast drop of magnetization we unravel the fundamental role of the electronic structure As the ferromagnet Fe becomes more noble in the FePt compound the electronic structure is changed and the density of states around the Fermi level is reduced thereby driving the spin correlations into the limit of critical fluctuations We demonstrate the impact of the electrons and the ferromagnetic interactions which allows a general insight into the mechanisms of spin dynamics when the ferromagnetic state is highly excited and identifies possible recording speed limits in heat-assisted magnetization reversal we calculate a different response of the electronic system to the laser pulse We can pinpoint that the quasi-equilibrium values of the electron temperature above the Curie temperature is determining the response of the spin system This is leading to the critical fluctuations and a slowing down a fundamental limit to recording speeds in heat-assisted reversal on the ultrafast timescales To enable progress in high-speed and high-capacity magnetic storage devices a fundamental understanding of these dynamic processes is required in the future Sample characteristics: schematics and sample structure of the granular FePt recording media (a) and thin film (b) as measured by transmission electron microscopy (TEM) (c) Ultrafast magnetization dynamics for both cases after femtosecond laser excitation for a small demagnetization Solid line: analytical three temperature model to obtain τM Both curves can be described with sets of identical parameters (d) The reflectivity dynamics from which the exponential decay τE and (e) the electron temperature Te are obtained (laser fluence 5 mJ/cm2) (f) Relaxation time τE for the electron temperature and τM for the ultrafast demagnetization is given as function of the pump fluence Ultrafast demagnetization dynamics of FePt: spin dynamics measured by the Kerr set-up at increasing laser fluence in steps of 5 mJ/cm2 from 5 mJ/cm2 (upper curve) to 35 mJ/cm2 (lower curve) The detail on the femtosecond timescale is shown with expanded scale on the left side For the highest fluence the demagnetization still slowly progesses after the first fast demagnetization is observed (type II material) Data is normalized to the magnetization value before the pump pulse arrives (negative delay) It scales with the magnetization as ~ m(T)1.76 The internal exchange field Hi,J results from the thermal average of atomistic spins it is responsible for keeping the magnetization magnitude constant At the same time this term is responsible for the critical behavior approaching ~ TC which can be seen in the following expression: In this expression as = 2(S + 1)2/([S +1]2 + S2) and represents the longitudinal susceptibility where λ is the microscopic relaxation parameter that couples the spin dynamics to the electron temperature T = Te(t), defined by the microscopic spin scattering rate λ and qs = 3TCme/[2(S + 1)T]. Fe minority and Pt states are given respectively In darker color the occupied states are given (c) Illustration of the microscopic interaction of the heated electrons Te and the spin system via spin flips coupled by λ for both cases (d) Ultrafast dynamics for a hypothetical material having a large density of states and FePt using a small density of states (related to γe) for a high laser fluence In both cases the same reflectivity dynamics (τE) and maximum demagnetization is calculated but the resulting ultrafast magnetization dynamics is different (e) Implementation of the micromagnetic Landau-Lifshitz-Bloch (LLB) model: the magnetization is described by the average over 900 thermal macrospins with a lateral cubic discretization of Δ = 3 nm with periodic boundary conditions Each cell represents the thermodynamic average over atomistic magnetic moments (shown schematically on the right side) The thermal ultrafast heating is taken into account within each single cell by the longitudinal relaxation M(τ) and the individual macrospin allows a rotation The lateral discretization allows the implementation of more general lateral inhomogeneous excitation (e.g Via microscopic spin scattering rate λ and the relaxation dynamics the magnetization dynamics is coupled to the electron temperature T = Te(t) as described above the electron temperature within the two temperature model (2T) is coupled to the lattice temperature Tph(t) via rate equations which determine its evolution with time t after the pump pulse arrived: Ultrafast demagnetization dynamics obtained by integration of the LLB micromagnetic model coupled to the 2T model (Fig. 4). The model data are shown with increased laser fluence from top to bottom in steps of 5 mJ/cm2 from 5 mJ/cm2 (upper curve) to 40 mJ/cm2 (lower curve). The detailed view on the femtosecond timescale is shown with expanded scale on the left side. Simulation of the electron temperature Te shown as a function of the laser pump fluence (from 5 mJ/cm2 (upper curve) to 40 mJ/cm2 (lower curve) The 2T model is based on the set of parameters presented in Table I. The parameters are extracted from the reflectivity dynamics (Fig. 1) Within the shaded area marked in the left panel the electron temperature exceeds the Curie temperature (dashed line) Ultrafast demagnetization dynamics experiment at highest fluences for 30 mJ/cm2 to 40 mJ/cm2 Here the time-resolved data is normalized to its magnetization value with blocked pump beam The hysteresis curves for 5 mJ/cm2 and 40 mJ/cm2 are shown for blocked pump-beam and negative delay of −5 ps They demonstrate the irreversible parts of the laser induced dynamics present before the new laser pulse arrives (in a time scale of 4 μs pulse repetition period) For 0.5 ps and 2 ps delay the hysteresis is scaled to the maximum demagnetization demonstrating the size of the demagnetization in total (reversible and irreversible contributions) This non-deterministic spin dynamics is responsible for a speed limitation of the magnetic response to the laser pulse Note that this is not only determined by the ultrafast optical pulse but also by the nature of the FePt's density of states at the Fermi level which defines the increase in electron temperature From our experiments we conclude that a careful adjustment between electron heating is essential while the anisotropy energy of the system does not play a crucial role for the response time We identified the nature of the electronic density of states as a tuning parameter for the strength a spin system will react to the laser power Our results open possibilities for ultrafast control of the demagnetization in FePt the most promising candidate for future magnetic recording we have shown that we are able to manipulate the degree of demagnetization and its ultrafast rates We propose that for efficient writing the degree of heating and its speed have to be balanced by varying the amount of the energy deposited To get the absolute degree of demagnetization the Kerr signal is scaled to hysteresis measurements at two states of reference; one at negative delay (θK ~ Mz,0) and the other at a time delay that shows the lowest magnetization (ΔθK,min ~ ΔMz,min) a system of 30 × 30 × 1 macrospins with periodic boundary conditions in x and y directions is used in The physics of high density magnetic recording 145 (Springer Magnetic recording at 1.5 Pb m2 using an integrated plasmonic antenna The ultimate speed of magnetic switching in granular recording media Minimum field strength in precessional magnetization reversal All-optical magnetic recording with circularly polarized light First-principles study of magnetic properties of L10-ordered MnPt and FePt alloys & Spanjaard Magnetic and electronic properties of bulk and clusters of FePt L10 Connecting the timescales in picosecond remagnetization experiments Slow recovery of the magnetisation after a sub-picosecond heat pulse Spin dynamics in CoPt3 alloy films: A magnetic phase transition in the femtosecond time scale Ultrafast spin dynamics in ferromagnetic nickel Single laser pulse induced dynamic magnetization reversal mechanism of perpendicularly magnetized L10 FePt films Coercivity dynamics and origin of time-delayed magneto-optical hysteresis loops in pump-probe Kerr spectroscopy Fast magnetization precession observed in FePt L10-FePt epitaxial thin film Ultrafast heating as a sufficient stimulus for magnetization reversal in a ferrimagnet Transient ferromagnetic-like state mediating ultrafast reversal of antiferromagnetically coupled spins Ultrafast optical demagnetization manipulates nanoscale spin structure in domain walls Nanoscale spin reversal by non-local angular momentum transfer following ultrafast laser excitation in ferrimagnetic GdFeCo Ultrafast dynamical path for the switching of a ferrimagnet after femtosecond heating Ultrafast Spin Dynamics in Multisublattice Magnets Microscopic model for ultrafast magnetization dynamics of multisublattice magnets Explaining the paradoxical diversity of ultrafast laser-induced demagnetization Evidence for thermal mechanisms in laser-induced femtosecond spin dynamics Electron-and phonon-mediated ultrafast magnetization dynamics of Gd(0001) Temperature dependence of laser-induced demagnetization in Ni: A key for identifying the underlying mechanism Superdiffusive spin transport as a mechanism of ultrafast demagnetization Ultrafast magnetization enhancement in metallic multilayers driven by superdiffusive spin current Ultrafast transport of laser-excited carriers in Au/Fe/MgO(001) Terahertz spin current pulses controlled by magnetic heterostructures Towards multiscale modeling of magnetic materials: Simulations of FePt Spin polarization in half-metals probed by femtosecond spin excitation Ultra-high coercivity small-grain FePt media for thermally assisted recording Prevention of dewetting during annealing of FePt films for bit patterned media applications Intrinsic and non-local Gilbert damping in polycrystalline nickel studied by Ti:sapphire laser fs spectroscopy Ultrafast magnetization dynamics rates within the Landau-Lifshitz-Bloch model Measurement of the magneto-optical response of Fe and CrO2 epitaxial films by pump-probe spectroscopy: Evidence for a spin-charge separation Ultrafast magneto-optical response of iron thin films Coherent ultrafast magnetism induced by femtosecond laser pulses Generalized equation of motion for a ferromagnet Dynamic approach for micromagnetics close to the Curie temperature Micromagnetic modeling of laser-induced magnetization dynamics using the Landau-Lifshitz-Bloch equation Thermal fluctuations and longitudinal relaxation of single-domain magnetic particles at elevated temperatures Thermal stability of the magnetization following thermomagnetic writing in perpendicular media Chemical-order-dependent magnetic anisotropy and exchange stiffness constant of FePt (001) epitaxial films Temperature-dependent magnetic properties of FePt: Eective spin Hamiltonian model Multiscale modeling of magnetic materials: Temperature dependence of exchange stiffness Stochastic form of the Landau-Lifshitz-Bloch equation in Thin film non-noble transition metal thermophysical properties Spin waves and small intrinsic damping in an in-plane magnetized FePt film Fast magnetization precession observed in L10-FePt epitaxial thin film Quadratic scaling of intrinsic Gilbert damping with spin-orbital coupling in L10-FePdPt films: experiments and ab initio calculations Origins of the damping in perpendicular media: Three component ferromagnetic resonance linewidth in CoCrPt alloy films Electron and lattice dynamics following optical excitation of metals Scaling and critical slowing down in random-field Ising systems Download references McCallum for providing a sample and TEM image Research at Göttingen University was supported by German Research Foundation (DFG) through Research at Göttingen University was supported by German Research Foundation (DFG) through MU 1780/ 6-1 Photo-Magnonics Research in Madrid was supported by the European Community's Seventh Framework Programme under grant agreement NNP3-SL-2012-281043 (FEMTOSPIN) and the Spanish Ministry of Science and Innovation under the grant FIS2010-20979-C02-02 We acknowledge support by the German Research Foundation and the Open Access Publication Funds of the Göttingen University Instituto de Ciencia de Materiales de Madrid Universität Greifswald Felix-Hausdorff-Straβe 6 carried out the experiments and analyzed experimental data discussed the data and anlysis and wrote the manuscript The authors declare no competing financial interests This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/ Download citation Metrics details Adrian Dingle tells the story of how the name of element 109 represents the lasting recognition that one of the greatest nuclear physicists was in danger of never receiving Lise Meitner (1878–1968) 'Mother of Nuclear Structure Physics' (GSI Download references author of The Elements: An Encyclopedic Tour of the Periodic Table Reprints and permissions Download citation Metrics details Knowledge of the spin polarization is of fundamental importance for the use of a material in spintronics applications we used femtosecond optical excitation of half-metals to distinguish between half-metallic and metallic properties Because the direct energy transfer by Elliot–Yafet scattering is blocked in a half-metal the demagnetization time is a measure for the degree of half-metallicity We propose that this characteristic enables us vice versa to establish a novel and fast characterization tool for this highly important material class used in spin-electronic devices The technique has been applied to a variety of materials where the spin polarization at the Fermi level ranges from 45 to 98%: Ni Spintronics: A spin-based electronics vision for the future Microwave oscillations of a nanomagnet driven by a spin-polarized current Simple explanation of tunneling spin-polarization of Fe Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions Giant tunnelling magnetoresistance at room temperature with MgO(100) tunnel barriers Spin-dependent tunneling conductance of Fe/MgO/Fe sandwiches Enhanced magnetotransport at high bias in quasimagnetic tunnel junctions with EuS spin-filter barriers New class of materials: Half-metallic ferromagnets in Handbook of Magnetism and Advanced Magnetic Materials Vol Half metallic ferromagnets: From band structure to many-body effects Measuring the spin polarization of a metal with a superconducting point contact How to define and calculate the degree of spin polarization in ferromagnets Origin of high transport spin polarization in La0.7Sr0.3MnO3: Direct evidence for minority spin states Superconductor-ferromagnet tunneling measurements indicate sp-spin and d-spin currents Positron-annihilation study of the half-metallic ferromagnet NiMnSb: Experiment Ultrafast spin-dynamics in half-metallic CrO2 thin films General features of photoinduced spin dynamics in ferromagnetic and ferrimagnetic compounds Simple theory for spin-lattice relaxation in metallic rare-earth ferromagnets Spin–lattice interaction in colossal magnetoresistance manganites Nonquasiparticle states in Co2MnSi evidenced through magnetic tunnel junction spectroscopy measurements Finite-temperature spin polarization in half-metallic ferromagnets Thermal collapse of spin polarization in half-metallic ferromagnets Spin-wave dispersion in ferromagnetic Ni and fcc Co Evolution of spin-wave excitations in ferromagnetic metallic manganites Adiabatic spin dynamics from spin-density-functional theory: Application to Fe Ultrafast magneto-optics in nickel: Magnetism or optics CrO2 predicted as a half-metallic ferromagnet Room-temperature observation of high-spin polarization of epitaxial CrO2(100) island films at the Fermi energy Near-complete spin polarization in atomically-smooth chromium-dioxide epitaxial films prepared using a CVD liquid precursor Spin polarization of CrO2 at and across an artificial barrier Role of structural defects on the half-metallic character of Co2MnGe and Co2MnSi Heusler alloys Giant tunneling magnetoresistance in Co2MnSi/Al–O/Co2MnSi magnetic tunnel junctions Transport properties of magnetic tunnel junctions with Co2MnSi electrodes: The influence of temperature-dependent interface magnetization and electronic band structure Tunnel magnetoresistance effect in magnetic tunnel junctions using a Co2MnSi(110) electrode Large spin polarization in epitaxial and polycrystalline Ni films Evidence for the half-metallic ferromagnetic state of Fe3O4 by spin-resolved photoelectron spectroscopy Theory of the effect of spin–orbit coupling on magnetic resonance in some semiconductors Activation of additional energy dissipation processes in the magnetization dynamics of epitaxial chromium dioxide films Femtosecond modification of electron localization and transfer of angular momentum in nickel Nonequilibrium magnetization dynamics of gadolinium studied by magnetic linear dichroism in time-resolved 4f core-level photoemission Spin-flip processes and ultrafast magnetization dynamics in Co: Unifying the microscopic and macroscopic view of femtosecond magnetism Download references Support by the Deutsche Forschungsgemeinschaft within the priority program SPP 1133 and SFB 602 is gratefully acknowledged the work is supported by NSF and ONR grants; at the University of Alabama support by a NSF MRSEC grant is gratefully acknowledged carried out research (femtosecond dynamics) main contributor to experiment execution and data analysis; G.X.M. Download citation Metrics details Understanding the transfer of spin angular momentum is essential in modern magnetism research A model case is the generation of magnons in magnetic insulators by heating an adjacent metal film we reveal the initial steps of this spin Seebeck effect with <27 fs time resolution using terahertz spectroscopy on bilayers of ferrimagnetic yttrium iron garnet and platinum Upon exciting the metal with an infrared laser pulse a spin Seebeck current js arises on the same ~100 fs time scale on which the metal electrons thermalize This observation highlights that efficient spin transfer critically relies on carrier multiplication and is driven by conduction electrons scattering off the metal–insulator interface Analytical modeling shows that the electrons’ dynamics are almost instantaneously imprinted onto js because their spins have a correlation time of only ~4 fs and deflect the ferrimagnetic moments without inertia spin-noise spectroscopy and terahertz spin pumping emerge To probe the ultimate speed of the spin Seebeck effect center photon energy 1.6 eV) is incident on a F|N bilayer made of N = Pt (thickness of d = 5 nm) on top of F = YIG (thickness 5 µm While the YIG film is transparent to the pump pulse resulting in a transient increase \({\mathrm{\Delta }}T_{\mathrm{e}}^{\mathrm{N}}\) of its electronic temperature Any ultrafast spin–current density js(t) arising in Pt is converted into a transverse charge–current density jc(t) by the inverse spin Hall effect thereby acting as a source of a THz electromagnetic pulse whose transient electric field E(t) is detected by electrooptic sampling The electron dynamics in the Pt layer is interrogated by an optical probe pulse that measures the transient sample reflectance we reveal the initial elementary steps of the longitudinal SSE by pushing its measurement to the THz regime Upon exciting the metal of a prototypical F|N bilayer structure with an infrared laser pulse the dynamics of the spin Seebeck current js versus time t are determined with a resolution better than 27 fs using the ISHE and electrooptic sampling We find that js(t) rises and decays on time scales of ~100 fs The decay directly follows the cooling dynamics of the N electrons as seen in the transient sample reflectance An analytical model shows that js(t) monitors the density of the transient electrons and holes in the metal quasi-instantaneously because their spins have a correlation time of only ~4 fs and deflect the ferrimagnetic moments without inertia Simulations consistently reveal that the rise of js(t) mirrors the thermalization process during which the photoexcited electrons approach a Fermi–Dirac distribution Our results are relevant for a large variety of optically driven spin-transfer processes spin-noise spectroscopy and THz spin pumping come into reach Typical THz electrooptic signals S versus time t for a YIG(3 μm)|Pt(5.5 nm) bilayer are displayed in Fig. 2a. The signal inverts when the in-plane sample magnetization M is reversed. Since the SSE current is expected to be odd in M, we focus on the THz-signal difference S_ = S(+M) − S(−M) in the following. Terahertz emission of photoexcited F|N bilayers a THz emission signals S(±M) from a YIG(3 µm)|Pt(5.5 nm) sample for opposite directions of the in-plane YIG magnetization M as a function of time t We focus on the difference S_ = S(M) − S(−M) odd in M b Amplitude of the THz signal S− (root-mean-square RMS) and the Faraday rotation of a continuous-wave laser beam (wavelength 532 nm) as a function of the external magnetic field Both hysteresis loops were measured under identical pump conditions at room temperature c Amplitude of S− as a function of the absorbed pump fluence d THz emission signal from a 3 µm thick YIG film capped with Pt and W e THz emission signal from a 5 µm YIG film capped with Pt(5.6 nm) or Cu(1.9 nm)|Pt(5.4 nm) The solid line is a fit proportional to \(\left( {T_{\mathrm{C}} - T_0} \right)^\alpha\) h(t) acts like a temporal derivative on js(t) b Extracted spin-current density js(t) entering the Pt layer (red line) The gray line is a Gaussian with a full-width at half maximum of 27 fs and visualizes an upper limit to the experimental time resolution (see Methods) The dashed black line is the monoexponential decay as obtained from the pump-induced sample reflectance of panel (c) c Pump-induced relative changes −ΔR(t)/R0 in the reflectance of a Pt thin film under excitation conditions similar to those used for measuring the THz emission signal of panel (a) (orange line) The dashed line is a fit of a monoexponential decay plus an offset for t  > 350 fs and yields a time constant of τe−ph = 310 fs the absorbed pump energy is deposited in the electronic system thereby inducing a nonequilibrium electron distribution Due to electron–electron and electron–phonon scattering the electrons approach a Fermi–Dirac distribution yet with a usually slower time constant \(\tau _{{\mathrm {e-ph}}}\) the hot electrons cool down by energy transfer to the phonon system This observation strongly indicates that js(t) quasi-instantaneously follows the transient changes ΔTe(t) in the electron temperature on the time scale of electron cooling It also suggests that the intrinsic response time of the SSE is significantly faster than \(\tau _{{\mathrm{e - ph}}}\) and \(\hbar {\mathbf{S}}^{\mathrm F}\) and \(\hbar {\mathbf{S}}^{\mathrm N}\) are the total electron spin angular momenta contained in an interfacial cell of dimension a3 on the F and N side with ħ denoting the reduced Planck constant Thermal spin fluctuations sF(t) in F and sN(t) in N cause stochastic effective magnetic fields and the average-induced moment ⟨ΔsF(t)⟩ vanishes because ⟨sN⟩ = 0 By integration over all first-interaction times t′ (see Methods section) we find the spin current due to N-cell fluctuations equals As this time constant is shorter than the pump-pulse duration the N-cell spin correlation function mirrors the instantaneous state of the optically excited electrons in the metal the spin current follows the dynamics of the electron distribution in the metal without delay where \(n\left( {{\it{\epsilon }},t} \right)\) is the occupation number of an electron Bloch state at energy \({\it{\epsilon }}\) \(D\left( {\it{\epsilon }} \right)\) denotes the density of Bloch states and \({\it{\epsilon }}_{\mathrm{F}}\) is the Fermi energy identify \(\tilde T_{\mathrm{e}}^{\mathrm{N}}\left( t \right)\) as a generalized electronic temperature that is applicable to arbitrary nonthermal electron distributions Using linear-response theory (see Methods) express the correlation function \(\langle s_z^{\mathrm{N}}\left( t \right)s_z^{\mathrm{N}}\left( {t\prime } \right)\rangle\) by means of \(\tilde T_{\mathrm{e}}^{\mathrm{N}}\) and the isotropic spin susceptibility χN of the N cell As the F layer remains cold at temperature T0 the spin current quasi-instantaneously follows the dynamics of the generalized electron temperature of N where \({\cal K} = {\int} {\mathrm{d}} t{\mathrm{\kappa }}^{\mathrm{N}}\left( t \right) = {\int} {\mathrm{d}} t{\mathrm{\kappa }}^{\mathrm{F}}\left( t \right)\) is the static SSE coefficient. We now put this conclusion to test by considering the rise and decay dynamics of the measured spin current js(t) (Fig. 4b) As this value is significantly smaller than the increase of the Pt electron temperature we can neglect the back-action of the heated YIG layer on the spin current we measured an ultrafast spin current in the prototypical SSE system YIG|Pt triggered by femtosecond optical excitation of the metal layer The current exhibits all the hallmarks expected from the THz SSE based on sd-like exchange-coupled YIG|Pt layers can reproduce both the magnitude and the dynamics of the measured ultrafast spin current It allows us to identify the ultrafast elementary steps leading to the formation of the initial SSE current: optically excited metal electrons impinge on the interface with the magnetic insulator They apply random torque that is rectified by two subsequent interactions thereby resulting in a net spin current from YIG into the metal The SSE response to heating of the metal layer is quasi-instantaneous for two reasons the total electron spin of a Pt unit cell at the YIG|Pt interface has a correlation time of less than 4 fs the YIG spins respond to these fluctuations without inertia We emphasize that the step-like impulse response of the YIG spins is a feature of all ferromagnetic magnons of YIG and independent of their frequencies As a consequence of these instantaneous responses the SSE current directly monitors the thermalization and cooling of the photoexcited electrons which both proceed on a sub-picosecond time scale Our insights highlight the significant role of carrier multiplication in these processes and strongly suggest that lower pump photon energies (ideally on the order of the thermal energy) will substantially shorten the rise time of the angular-momentum transfer and extend its bandwidth to tens of THz Pt and Cu layers were grown using a home-built deposition system with DC magnetron sputtering at rates of 0.7 and 0.63 Å s−1 The samples were characterized magnetooptically by the Faraday effect of a beam from a 512 nm laser diode under an angle of incidence of 45° hysteresis loops were measured by slowly varying the external magnetic field the in-plane sample magnetization was saturated by an external magnetic field of 10 mT For setting the sample temperature T0 between 300 and 600 K a resistive heating coil was attached to the sample holder onto which the sample was glued with a heat-conducting silver paste The temperature was measured with a type-K thermocouple As schematically shown in Fig. 1 the sample was excited by linearly or circularly polarized laser pulses (duration 10 fs pulse energy 2.5 nJ) from a Ti:sapphire laser oscillator (repetition rate 80 MHz) under normal incidence from the GGG/YIG side (beam diameter at sample 22 μm full-width at half-maximum of the intensity) The resulting absorbed fluence was 120 µJ cm−2 yielding an upper bound of 19 fs for the pulse duration 10 fs) from the same laser copropagate with the THz field through an electrooptic crystal The resulting signal S(t) equals twice the THz-field-induced probe ellipticity where t is the delay between the THz and probe pulse Depending on the signal strength and bandwidth required ZnTe(110) (thickness of 1 mm) and GaP(110) (250 µm) all measurements were performed at room temperature in a dry N2 atmosphere the measured electrooptic signal S(t) is related to the THz electric field E(t) directly behind the sample by the convolution Note that the DC component of h(t) is zero because a DC electric field cannot propagate away from its source We determined the missing DC component of E(t) by using the causality principle: the pump-induced charge current inside the sample and E(t) is zero before arrival of the pump pulse at t = 0 In the frequency domain, the field E(ω) is related to the spin current injected into the Pt layer by a generalized Ohm’s law17 We infer that the time resolution of the spin-current transient is better than 27 fs This value is a result of the pump-pulse duration in the Pt layer and of the low-pass filtering included in our extraction procedure which imply a temporal broadening of at most 19 and 24 fs energy conservation furthermore implies \({\mathrm{\Delta }}\dot T_{\mathrm e}\left( t \right) \propto {\mathrm{\Delta }}\dot T_{{\mathrm{ph}}}\left( t \right)\) and ΔR(t) becomes proportional to ΔTe(t) plus a constant As illustrated in Fig. 5a–d interfacial F and N layers of thickness a are coupled by nearest-neighbor sd-type exchange interaction We divide the interfacial plane in N cells of size a3 and consider the total electron spin \(\hbar {\mathbf{S}}_\alpha ^{\mathrm{F}}\) and \(\hbar {\mathbf{S}}_\alpha ^{\mathrm{N}}\) contained in an F cell and N cell with index α The expectation value of \({\mathbf{S}}_\alpha ^{\mathrm{F}}\) is related to the F magnetization by \(\langle{\mathbf{S}}_\alpha ^{\mathrm{F}}\rangle \propto a^3{\mathbf{M}}\) each \({\mathbf{S}}_\alpha ^{\mathrm{N}}\) applies the torque \({\mathbf{S}}_\alpha ^{\mathrm{F}}(t) \times J_{{\mathrm{sd}}}{\mathbf{S}}_\alpha ^{\mathrm{N}}(t)\) on the adjacent \({\mathbf{S}}_\alpha ^{\mathrm{F}}\) the total \(H_{{\mathrm{sd}}}\)-related torque exerted by N on F is given by the sum over all cells α we obtain the average spin-current density Note that the tensor of the spin-current density is given by the tensor product \({\mathbf{j}}_{\mathrm{s}} \otimes {\mathbf{n}} = {\mathbf{j}}_{\mathrm{s}}^{\,\,\,\mathrm{t}}{\mathbf{n}}\) with n being the normal unit vector of the F|N interface We now split the random observable \({\mathbf{S}}_\alpha ^{\mathrm{F}} = \langle{\mathbf{S}}_\alpha ^{\mathrm{F}}\rangle + {\mathbf{s}}_\alpha ^{\mathrm{F}} + {\mathrm{\Delta }}{\mathbf{s}}_\alpha ^{\mathrm{F}}\) in three contributions: its mean value \(\langle{\mathbf{S}}_\alpha ^{\mathrm{F}}\rangle \propto a^3{\mathbf{M}}\) and its fluctuating part \({\mathbf{s}}_\alpha ^{\mathrm{F}}\) both taken in the absence of interfacial coupling \({\mathrm{\Delta }}{\mathbf{s}}_\alpha ^{\mathrm{F}}\) quantifies the modification due to sd-coupling to the N layer By applying an analogous splitting to \({\mathbf{S}}_\alpha ^{\mathrm{N}}\) In Eq. (11), the difference of the two terms reflects the competition between the torques arising from the fluctuations of the N-cell and F-cell spins. For example, as illustrated by Fig. 5a, b the first term can be understood as follows: the fluctuating exchange field \(J_{{\mathrm{sd}}}{\mathbf{s}}^{\mathrm {N}}(t)\) due to N exerts torque on the magnetic moment \({\mathrm{\Delta }}{\boldsymbol{s}}^{\mathrm {F}}\left( t \right) = J_{{\mathrm{sd}}}{\int} {\mathrm{d}} t\prime \,\underline {\mathrm{\chi }} ^{\mathrm{F}}\left( {t - t\prime } \right){\mathbf{s}}^{\mathrm {N}}\left( {t\prime } \right)\) As this torque scales quadratically with the noise sN provided ΔsF(t) results from an earlier time t′ that lies inside the correlation window of the N-cell spin where \({\it{\epsilon }}_{xjk}\) denotes the Levi–Civita symbol. The first term of Eq. (12) quantifies the torque due to N-cell spin fluctuations and depends critically on the spin correlation function \(\langle s_j^{\mathrm N}\left( t \right)s_l^{\mathrm N}\left( {t\prime } \right)\rangle\) which typically peaks sharply around time \(t = t\prime\) Any temperature change of the N spins will lead to a (possibly delayed) modification of the spin correlation function and a spin-current response whose time dependence is determined by the spin susceptibility \(\chi _{kl}^{\mathrm{F}}\left( t \right)\) of the ferromagnet F An analogous interpretation applies to the second term we first consider thermal states and subsequently extend our treatment to nonthermal electron distributions in the N layer where Θ is the Heaviside step function. The overbar denotes time inversion, that is, \(\bar f\left( t \right) = f\left( { - t} \right)\), and * denotes convolution (see Eq. (6)) Note that strictly this equation refers to equilibrium and cannot be applied to the situation of our experiment where the temperature of N (and F) is generally time-dependent the spin fluctuations sN(t) arise from a random magnetic field rN(t) the bath applies to the spin system Assuming rN has no memory and vanishing ensemble average the intensity of the spin fluctuations is directly proportional to the instantaneous bath temperature where the constant AN quantifies how strongly the N bath and the N spins are coupled and writing out the convolution (Eq. (6)) we obtain the spin–spin correlation function for a time-dependent bath temperature TN This constraint on the spin susceptibility function can be used to determine the constant AN Completely analogous equations are obtained for the F-cell spin We now substitute Eq. (16) and its analog for F into Eq. (12) and obtain For an isotropic nonmagnetic metal N with \(\chi _{ij}^{\mathrm{N}}\left( t \right) = \delta _{ij}\chi ^{\mathrm{N}}\left( t \right)\), Eq. (19) implies the somewhat simpler relationship As seen from Eq. (21) the longitudinal spin susceptibility \(\chi _{jj}^{\mathrm{F}}\) of the F cell does not contribute to \({\mathrm{\kappa }}^{\mathrm{N}}\) The reason is that spin fluctuations along different coordinate axes are uncorrelated in the isotropic N layer the first interaction of the F layer with \(J_{{\mathrm{sd}}}s_j^{\mathrm{N}}\left( {t\prime } \right)\) would induce a change \(\propto \chi _{jj}^{\mathrm{F}}\left( {t - t\prime } \right)J_{{\mathrm{sd}}}s_j^{\mathrm{N}}\left( {t\prime } \right)\) in the F-cell spin Because \(\langle s_j^{\mathrm {N}}\left( t \right)s_l^{\mathrm {N}}\left( {t\prime } \right) \rangle\propto \delta _{jl}\) the only relevant second interaction is due to \(J_{{\mathrm{sd}}}s_j^{\mathrm{N}}\left( t \right)\) and the longitudinal \(\chi _{jj}^{\mathrm{F}}\) does not contribute to \({\mathrm{\kappa }}^{\mathrm{N}}\) This cancellation does not occur for \({\mathrm{\kappa }}^{\mathrm{F}}\) because spin fluctuations in F are correlated in different j directions we model the dynamics of the N-cell spin as where \(v_{k,z}\) is the z component of the group velocity of Bloch state k. We assume constant \(v_{k,z}\) and isotropic electronic occupation numbers \(n_k\left( t \right) = n\left( {{\it{\epsilon }}_k,t} \right)\), where \({\it{\epsilon }}_k\) denotes the band structure. Consequently, Eq. (24) simplifies to where \(\tilde T_{\mathrm{e}}^{\mathrm{N}}\left( t \right)\) is given by Eq. (3) of the main text thereby extending this fluctuation-dissipation relationship of the N layer to non-Fermi–Dirac electron distributions the spin current \({\mathbf{j}}_{\mathrm{s}}^{\mathrm{F}}\left( t \right)\) due to F-cell spin fluctuations can be expressed by the occupation numbers of all magnon modes since in our experiment the pump-induced changes of the YIG layer are negligible Our numerical calculations are based on Eqs. (21) and (22) The factor \(a^3\) is required since \(\chi _0^{\mathrm{N}}\) refers to the integrated N-cell volume whereas \(\tilde \chi _0^{\mathrm{N}}\) is given per volume The factor \(\mu _0g^2\mu _{\mathrm{B}}^2\) accounts for the different units used in the definition of \(\tilde \chi _0^{\mathrm{N}}\) and \(\chi _0^{\mathrm{N}}\) The ensemble average was obtained by averaging the product \(s_j^{\mathrm F}\left( {t - t\prime } \right)s_l^{\mathrm F}\left( 0 \right)\) over many trajectories As a cross check, we use Eq. (21) to estimate the order of magnitude of \({\cal K} = {\int} {\mathrm{d}} t{\mathrm{\kappa }}^{\mathrm{N}}\left( t \right)\). This formula can be simplified using Eq. (17) and yields the spin Seebeck coefficient All integrals take the density of states and quantum statistics of electrons and phonons of the material under study into account For the screened electron–electron and electron–lattice Coulomb interaction the screening parameter is calculated based on the instantaneous electron distribution function The data that support the findings of this study are available from the corresponding author upon reasonable request Fokker-Planck approach to the theory of the magnon-driven spin Seebeck effect Role of bulk-magnon transport in the temporal evolution of the longitudinal spin-Seebeck effect Spin Seebeck effect at microwave frequencies Theory of magnon-driven spin Seebeck effect Magnon spin-current theory for the longitudinal spin-Seebeck effect Thermal spin dynamics of yttrium iron garnet Evidence for Dyakonov-Perel-like spin relaxation in Pt Ultrafast spin-transfer torque driven by femtosecond pulsed-laser excitation Nanoscale interface confinement of ultrafast spin transfer torque driving non-uniform spin dynamics Terahertz electrical writing speed in an antiferromagnetic memory Efficient metallic spintronic emitters of ultrabroadband terahertz radiation High-performance THz emitters based on ferromagnetic/nonmagnetic heterostructures Powerful and tunable THz emitters based on the Fe/Pt magnetic heterostructure Ultrabroadband single-cycle terahertz pulses with peak fields of 300 kV cm−1 from a metallic spintronic emitter Optimized spintronic terahertz emitters based on epitaxial grown Fe/Pt layer structures Imaging magnetization structure and dynamics in ultrathin Y3Fe5O12/Pt bilayers with high sensitivity using the time-resolved longitudinal spin Seebeck effect Ultrafast optical manipulation of magnetic order Ultrafast photocurrents at the surface of the three-dimensional topological insulator Bi2Se3 Enhancement of pure spin currents in spin pumping Y3Fe5O12/Cu/metal trilayers through spin conductance matching Investigation of induced Pt magnetic polarization in Pt/Y3Fe5O12 bilayers Longitudinal spin Seebeck effect free from the proximity Nernst effect Measurement of hot electron momentum relaxation times in metals by femtosecond ellipsometry Spin Seebeck effect and spin Hall magnetoresistance at high temperatures for a Pt/yttrium iron garnet hybrid structure Quantitative temperature dependence of longitudinal spin Seebeck effect at high temperatures Time-resolved thermoreflectivity of thin gold films and its dependence on film thickness Nonlocal magnetization dynamics in ferromagnetic heterostructures Spin transfer torque on magnetic insulators Coupling between ferromagnetic and conduction-spin-resonance modes at a ferromagnetic-normal-metal interface Transmission of electrical signals by spin-wave interconversion in a magnetic insulator Inertia-driven spin switching in antiferromagnets Quantum Theory of Magnetism (Springer-Verlag Calculation of the electronic structure and related physical properties of platinum The Landau–Lifshitz equation in atomistic models Ultrafast dynamics of nonequilibrium electrons in metals under femtosecond laser irradiation Relaxation dynamics in laser-excited metals under nonequilibrium conditions Emission of spin waves by a magnetic multilayer traversed by a current Hot-electron-driven charge transfer processes on O2/Pt (111) surface probed by ultrafast extreme-ultraviolet pulses Ultra-fast dynamics of electron thermalization Spin Pumping at Ytrium Iron Garnet Interfaces In Magnonics: From Fundamentals to Applications (eds Experimental test of the spin mixing interface conductivity concept Temperature dependence of spin diffusion length and spin Hall angle in Au and Pt Evolution of the spin Hall effect in Pt nanowires: size and temperature effects T3/2 dependence of the interlayer exchange coupling in ferromagnetic multilayers Temperature variation of the interfilm exchange in magnetic multilayers: the influence of spin wave interactions Spin-wave excitations: the main source of the temperature dependence of interlayer exchange coupling in nanostructures Macrospin dynamics in antiferromagnets triggered by sub-20 femtosecond injection of nanomagnons Coherent THz transient spin currents by spin pumping Complex Terahertz and direct current inverse spin Hall effect in YIG/Cu1–xIrx bilayers across a wide concentration range Electron-magnon scattering in magnetic heterostructures far out of equilibrium Laser-induced magnetization dynamics and reversal in ferrimagnetic alloys Explaining the paradoxical diversity of ultrafast laserinduced demagnetization Competing effects at Pt/YIG interfaces: spin Hall magnetoresistance Optical properties of gadolinium gallium garnet Detectors and sources for ultrabroadband electro-optic sampling: experiment and theory Sampling of broadband terahertz pulses with thick electrooptic crystals Inverse spin Hall effect in Ni81Fe19/normal-metal bilayers Signal propagation in time-dependent spin transport Fluctuation-dissipation theorems from the generalised Langevin equation Fundamentals and applications of the Landau–Lifshitz–Bloch equation Fermi velocity and Fermi radius in platinum Calculated Electronic Properties of Metals (Pergamon Press Download references Bauer for stimulating discussions and acknowledge funding by the ERC H2020 CoG project TERAMAG/Grant No the collaborative research center SFB TRR 227 Ultrafast spin dynamics (projects B01 the collaborative research center SFB TRR 173 Spin+X (projects A01 the Marie Curie FP7 project ITN WALL/Grant No MaHoJeRo) as well as the DFG priority programs SPP 1538 SpinCaT and SPP 1666 Topological Insulators Fritz Haber Institute of the Max Planck Society Department of Physics and Research Center OPTIMAS Institut für Festkörper- und Materialphysik carried out the terahertz experiments and optical sample characterization with support from O.G The transient reflectance measurements were performed by I.R The theoretical model was developed by T.K Atomistic spin-dynamics simulations of YIG were conducted by J.B Electron-dynamics simulations of Pt were conducted by S.T.W All authors contributed to discussing the results and writing the paper The authors declare no competing Interests Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations Download citation DOI: https://doi.org/10.1038/s41467-018-05135-2 Metrics details List of discoveries shows US contributions have declined Reprints and permissions Download citation DOI: https://doi.org/10.1038/news.2011.571 Metrics details Spatially resolved measurements of the magnetization dynamics on a thin CoFeB film induced by an intense laser pump-pulse reveal that the frequencies of resulting spin-wave modes depend strongly on the distance to the pump center This can be attributed to a laser generated temperature profile We determine a shift of 0.5 GHz in the spin-wave frequency due to the spatial thermal profile induced by the femtosecond pump pulse that persists for up to one nanosecond Similar experiments are presented for a magnonic crystal composed of a CoFeB-film based antidot lattice with a Damon Eshbach mode at the Brillouin zone boundary and its consequences are discussed magnetostatic surface spin waves propagating along the stripline are trapped in the resulting potential well we address the generation of a spin-wave trap on a magnonic crystal by means of a temperature gradient induced by intense ultrashort laser pulses the technique applied in this work relies on local short wavelength spin-wave generation by a thermally induced anisotropy field pulse to start magnetic oscillations In order to saturate the 50 nm CoFeB sample an external magnetic field is applied at 20° to the sample plane Due to a strong in-plane dipolar anisotropy field the resulting magnetization will be canted 2–3° with respect to the sample plane enabling a longitudinal MOKE detection scheme Ultrashort laser pulses from a regeneratively amplified Ti:Sapphire system are used to (i) excite the magnetization dynamics (ii) probe the magnetic response of the magnonic crystal and (iii) create a spin-wave trap scenario Lateral temperature distribution for different moments in time (left) and simulated time evolution of the sample’s temperature for different depths (right) Gray shadowed area in the right panel indicates the first 100 ps While the temperature is mainly homogeneous throughout the sample depth, it changes significantly across its plane, as shown in Fig. 1 (left) The Gaussian distribution of laser intensity in the pump spot produces a temperature profile that persists longer than the lifetime of the observed coherent spin-wave modes no significant heat transport takes place on a micrometer scale and the FWHM of the lateral temperature distribution remains unchanged the temperature increase quenches the sample’s saturation magnetization which leads to a change in the spin-wave frequency spectrum Experiments were performed separating the pump and probe spots on the sample and measuring the magnetization dynamics as a function of pump-probe distance allowing us to determine the shift in magnetization oscillation frequency along the lateral temperature gradient A coherent oscillation of the magnetization is visible (center) A fast Fourier transform is performed (right) two modes are identified as the uniform precession (Kittel k = 0 mode) and perpendicular standing spin waves (PSSW) In order to determine the central frequency xc of each mode Both Kittel and PSSW modes have no wave vector components in the lateral direction i.e they do not propagate on the sample but have a rather localized character at the spot of (optical) excitation spatially resolved measurements should show no significant precession outside of the pump laser spot Experimental results on a continuous film In (left) open squares represent fitted peak positions The precession frequency observed after optical excitation is not constant across the pump spot Together with the magnetization curve shown in the inset the temperature of the spin system can be derived (right) Closed diamonds correspond to a displacement of the probe with respect to the pump spot in a direction orthogonal to the applied field Curves are offset so that the frequency dip of the Kittel mode is centered at Δx = 0 Using the dependence of Kittel mode frequency on the saturation magnetization MS only short propagation distances are expected: within a certain band width we derive group velocities of 1.3 km/s at the middle of Brillouin zone reducing further towards higher k-vector the propagation length estimated in the antidot lattice is reduced sigificantly up to 1.3 μm towards the zone boundary for the Bloch mode In addition we note that the DE spin-wave dispersion is derived for continous thin films With the lateral variation of the temperature gradient here it is a good local approximation for wavelengths much smaller than the magnetization gradient only The DE spin-wave dispersion is locally modified by a temperature dependent magnetization as well Experimental results on a magnonic crystal Bottom: Fourier-spectrum in analogy to Fig. 3(left) with the additional magnonic Damon-Eshbach (DE) Bloch mode the DE-mode is shown with an adapted color code for better visibility The Fourier amplitude for fundamental Kittel mode (squares) and dipolar DE mode (circles) is plotted as a function of the relative position between pump and probe No significant spatial widening is observed for the DE mode frequency profile Top: Scanning direction relative to the applied field and to the magnonic crystal which is somehow expected with the short propogation lenght of the DE mode and the resolution also determined by the probe spot diameter of 24 μm FWHM However their intensities interchange for the 45° configuration and the DE mode becomes larger in its Fourier amplitude The presented experiments and consequences from their analysis carry out two important points: Firstly we observe a magnetization profile that follows the intensity profile of the optical excitation and allows to modify the spin-wave spectrum observed Despite of the ultrashort character of the excitation the temperature profile remains over the range of our observation of one nanosecond This change in saturation magnetization impacts the position dependent eigenfrequency supported locally and a controlled magnetic non-uniformity can be formed by the local absorption of the femtosecond laser pulse in space and time the laser excited spin-wave excitation results in a large spin-wave density and is leading to a high probability for scattering between spin waves and a reduced mean free path an effect known from hot phonon localization spin waves traveling away from the spot of excitation would propagate towards an increasing effective saturation magnetization due to the heat gradient imposed by the pump laser so that a frequency up-conversion is needed to adopt to the local spin-wave frequency at the boundary to the cooler region This imposes additional scattering as spin waves are continuously reflected when entering a colder region with higher saturation magnetization an interesting scenario for a dynamic modification of magnetic film properties via femtosecond laser pulses has been demonstrated To simulate the thermal response of the thin film is solved in rotational symmetry for isolating sample edges and a fixed temperature at the bottom of the substrate using the material parameters listed in table 1 Ultrashort laser pulses (central wavelength pulse duration 50 fs) amplified by a Coherent RegA 9040 regenerative amplifier (250 KHz repetition rate) were used to excite and detect the magnetization dynamics in a pump-probe experiment The angle of incidence of the probe beam was 25° to the surface while the pump beam impinged the surface perpendicularly The pump and probe beams are focused to Gaussian spots with 93 and 24 μm FWHM respectively This is mainly limiting the spatial resolution The expected experimental width will be given by pump-and probe beam profiles convoluted However the width of the Gaussian can be determined with a much higher precision than that of the probe-beam’s FWHM Double-modulation technique was used to detect the time-resolved longitudinal component of magnetic precession: The pump intensity is modulated at 800 Hz by a chopper and the probe beam’s polarization is modulated at 50 kHz by a photoelastic modulator Spin torque-generated magnetic droplet solitons Spin-wave propagation and transformation in a thermal gradient Directional control of spin-wave emission by spatially shaped light Magnonic spin-wave modes in CoFeB antidot lattices Spin-wave population in nickel after femtosecond laser pulse excitation Direct excitation of propagating spin waves by focused ultrashort optical pulses High propagating velocity of spin waves and temperature dependent damping in a CoFeB thin film Spin-wave modes and band structure of rectangular CoFeB antidot lattices Spin wave wells in nonellipsoidal micrometer size magnetic elements in Handbook of optical constants of solids Optical constants of transition metals: Ti Intrinsic and nonlocal Gilbert damping parameter in all optical pump-probe experiments Seebeck effect in magnetic tunnel junctions Reflectance of evaporated ruthenium films from 300 Å to 50 μm Ferromagnetic properties of some new metallic glasses Download references M.Mansurova thanks Soham Manni for assistance during VSM measurements We thank the German Research Foundation (DFG) for funding through MU 1780/ 6-1 Photo-Magnonics Marvin von der Ehe & Markus Münzenberg analyzed and discussed experimental and modeling data performed and analyzed magnetization dynamics experiments performed COMSOL simulations and discussed the results All the authors discussed the results and contributed to the writing of the 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Please upgrade your browser and get all benefits of browsing the new JINR site You can also use the previous version of the JINR site As part of the International Year of the Periodic Table of Chemical Elements 2019, the Conference on the Chemistry and Physics of Heavy Elements (TAN) taking place in Wilhelmshaven Germany from the 25th to the 30th of August brought together the discoverers of new chemical elements in a unique historic gathering who have added new elements to the periodic table in recent years who was a member of the element 113 discovery team He was head of the discovery team of Elements 114 to 118 (flerovium tennessine and oganesson) at the Flerov Laboratory of the Joint Institute for Nuclear Research He is currently the only living person an element is named after: element 118 the Flerov Laboratory and the RIKEN Nishina Center where the respective elements were discovered A total of 120 researchers from 19 countries and 4 continents take part in the TAN conference they discussed the current results and perspectives of research on the so-called transactinides the namesakes of the TAN conference series This refers to the elements starting with the atomic number 104 which follow the subgroup of actinides Following the article on eps.org Ron Schleifer is a senior lecturer at Israel’s Ariel University and head of the Ariel Center for Defense and Communication, where he specializes in psychological and information warfare. He spoke to an April 3rd Middle East Forum Webinar (video) in an interview with Ashley Perry adviser to the Middle East Forum Israel office and former senior Israeli government adviser about the Palestinian Arab strategy used since the late 1960s in its war against Israel The following is a summary of Schleifer’s comments: Schleifer has spent forty years researching the “phenomenon” of the Palestine Liberation Organization (PLO) and its effective use of psychological warfare (“psywar,” or the use of propaganda against an enemy A central question in this regard is why Israel “is doing so poorly when it comes to propaganda.” There is considerable evidence that the Soviet Union played a significant role in setting up the PLO Indeed “the PLO is practically an invention of the Soviets but the actual setting up of the organization in itself was an initiative of the Soviets.” The communists had a long track record of using psywar and were particularly adept in this field Three communists played a role in these efforts: Lenin the chief rabbi of moving a people towards a revolution.” Willi Münzenberg established the concept of “front organizations where people are very active for a purpose they believe in and have no idea they’re serving something entirely different.” The third person in this group is General Vo Nguyen Giap who led his small nation for two decades to victory over the U.S PLO chairman Yasser Arafat learned the ‘art’ of defeating a greater military power whose doctrine held that the “real fight is not in the jungles of Vietnam but in the streets of Washington,” Yasser Arafat learned the “art” of how to defeat a greater military power He changed his “mode of strategy” from terrorism to embracing the “whole charade” of human rights advocating for the establishment of “two states,” or a “secular democratic government.” Over the decades and from European nations in a mapping campaign to “penetrate the interest map of the West.” The PLO researched its allies and its opponents By utilizing psychological warfare principles over the past half century the Palestinian strategy has succeeded in that there is a well-funded “de facto state” today that has more embassies around the world than does Israel The essential principles of psychological warfare the Palestinians use against Israel 1.Understanding the enemy culture – By sociologically marginalizing the Sephardic and Eastern Jews who came to Israel in the late 1940s and shaming them for their non-Western background Israel squandered a major strategic resource which could have been better used to try and understand Arab culture founded an institute for Israel studies to understand Israeli culture Drive a wedge in parts of the enemy society to create a schism – “In every society there are differences there are between the veterans and the newcomers There’s [a difference] between the people who came from the West and people who came from the East It’s always the religious and the not religious.” So the task of the psychological operator is to “to drive a wedge and plant and create the schism between the parts of enemy society.” Lower the enemy’s morale – The idea here “is to persuade the enemy that [he is] not right and .. and he is eventually going to lose.” There is a need to persuade the enemy that what he thought is an “asset” is in fact a “liability.” This liability can manifest itself through the exacting of cost in various forms: diplomatic Segmentation – Define the target audience and direct the message to each separate audience Guilt – This is used by Palestinians who arrange visits to refugee camps for political leaders and societal influencers (academics religious figures) as a means of manipulating public reaction By leaving the squalid state of refugee camps unaddressed and subverting any attempt by Israel to improve conditions the PLO succeeds in exploiting the misery of the refugees thereby creating the preferred image of victimhood and instilling guilt in its target audience The takeaway lesson for Israeli victory is to copy the Palestinian six-decade psywar strategy that was originally copied from Israel To cultivate the idea of Israeli victory among the enemy and follow the Soviet model a goal worth pursuing is “annexation” of “Judea and Samaria” to Israel proper By instilling the idea in a “slow process,” similar to the Palestinian strategy of “a two- stage solution,” the idea will transition from the “far periphery” and gradually move to the center the psywar principle of driving a wedge between the competing factions in Palestinian society can be adopted by promoting who the winners and losers will be Schleifer is convinced that “coexistence” with the Palestinian Arabs will come about if the settlers are open to “cultural understanding” and learn to speak Arabic to overcome the language barrier and facilitate interactions with their Arab neighbors The geographic proximity of Jews in the West Bank to Palestinians is such that the idea of living in peace with each other will become a daily practical necessity for both sides Israel needs to project the sense that the future “belongs to Israel and to no one else.” © 2025 Middle East Forum • E-mail: info@meforum.org • Tel: 1 (215) 546-5406 Metrics details Thermoelectric effects in magnetic tunnel junctions are promising to serve as the basis for logic devices or memories in a ”green” information technology up to now the readout contrast achieved with Seebeck effects was magnitudes smaller compared to the well-established tunnel magnetoresistance effect we resolve this problem by demonstrating that the tunnel magneto-Seebeck effect (TMS) in CoFeB/MgO/CoFeB tunnel junctions can be switched on to a logic “1” state and off to “0” by simply changing the magnetic state of the CoFeB electrodes This new functionality is achieved by combining a thermal gradient and an electric field Our results show that the signal crosses zero and can be adjusted by tuning a bias voltage that is applied between the electrodes of the junction; hence the name of the effect is bias-enhanced tunnel magneto-Seebeck effect (bTMS) Via the spin- and energy-dependent transmission of electrons in the junction the bTMS effect can be configured using the bias voltage with much higher control than the tunnel magnetoresistance and even completely suppressed for only one magnetic configuration our measurements are a step towards the experimental realization of high TMS ratios without additional bias voltage which are predicted for specific Co-Fe compositions Shifting the electronic bands and the measurement setup (a) Exemplary transmission functions T(E) are plotted for the parallel (P) and antiparallel (AP) configurations; the derivative of the occupation function ∂f(E T)/∂E is marked in dark color around the Fermi level zero and positive TMS values (asymmetry around the electrochemical potential μ) This result can be achieved by changing the electrode composition and a comparable effect can be realized by tuning the bias voltage (b) Electrical setup with a transimpedance amplifier that converts the AC thermocurrent into an AC voltage which is measured using the lock-in amplifier The lock-in amplifier also serves as a filter for the DC signal that is generated by the bias voltage The tunneling scheme depicts the transmission of the tunnel junction (density of states in [100] direction) in the antiparallel configuration which is formed by the Δ1 bands and the barrier we compare the currents Ion/off that are driven through the MTJ when it is heated by the laser and when the laser is switched off: In a bias voltage region where the contributions generated by ΔT and V are comparable this relationship allows to deliberately set the current ΔI in a combination of both ΔT and V we should receive an on/off switching of the measured current upon magnetization reversal we define a bias-enhanced TMS (bTMS) ratio (a) TMR ratio and the resistance of the MTJ under a changing magnetic field (b) Bias TMS ratio and measured current signal for a bias voltage of −10 mV under 150 mW laser power the resulting effect ratio reaches nearly -3000% and is much higher than the TMR ratio observed at the same MTJ (c) Dependence of the differential conductance dI/dV on the bias voltage for the heated (laser power 150 mW) and cold (laser blocked) MTJ The values for the parallel (P) state and the antiparallel (AP) state have been measured at a magnetic field of 30 mT and −7 mT which makes the detection of the MTJ's state easier and more precise the high ratio is realized by combining a bias voltage of −10 mV with a temperature gradient across the barrier which is created using a laser power of 150 mW The measured signal ΔI is the current difference between the heated and non-heated MTJ which is approximately 0 nA in the P state and −2.5 nA in the AP state of the MTJ The high effect ratio is created by this on/off behavior of the signal when the MTJ state is switched between P and AP The high readout contrast and the on/off behavior are two advantages of the bTMS compared to the TMR effect when it is used to determine the state of an MTJ Dependence of SΔT on the bias voltage and heating power Seebeck voltages that are determined according to Eq. (1) for different laser powers in P and AP states The signal rises with increasing laser power the Seebeck voltage in the AP state of the MTJ varies much more with the bias voltage which causes a crossing of the P and AP voltages this crossing is observed at −15 mV and 5 mV bias the crossing is observed at −9 mV and 5 mV this technique is a step towards the determination of the bias-voltage-dependent Seebeck coefficients in MTJs the Seebeck effect will always disturb the resistance measurement of the heated MTJ An independent determination is only possible when the temperature dependence of the resistance is determined separately This task is challenging because the temperatures of both electrodes (separated by only a 1 nm tunnel barrier) cannot yet be determined we presented the bias-enhanced tunnel magneto-Seebeck (bTMS) effect that drastically increases the magnetic readout contrast we introduced a new technique to determine the Seebeck voltages under an applied bias by applying a linear model to the experimental data which allows a better readout contrast than the commonly used TMR effect Both techniques – Fermi-level tuning and bias-enhanced TMS – provide a large contrast of a physical property in the two magnetization states This result makes them notably attractive for future applications of MTJs in logic devices and memories The layer stacks for the MTJs were produced in a UHV sputtering chamber (base pressure 10−9 mbar) The stacks were prepared on an MgO substrate and consist of Ta 10/Co25Fe55B20 2.5/MgO 1.7/Co25Fe55B20 5.4/Ta 5/Ru 3 (all thicknesses are given in nm) the stacks were annealed at 450°C for one hour in an external magnetic field of 300 mT The MTJs were patterned using e-beam lithography and subsequent Ar ion milling The Ta layer beneath the CoFeB serves as the bottom electrode SiO2 or Si3N4 is placed adjacent to the MTJs as an insulator In an additional lithography and etching step Au bond pads were patterned on top of the MTJ as the top contact so that the top electrode of the MTJ remains optically accessible which allows calculations of the Seebeck coefficients from the measured TMS current and the barrier resistance Tunneling Magnetothermopower in Magnetic Tunnel Junction Nanopillars Giant thermoelectric effect in Al2O3 magnetic tunnel junctions Parameter space for thermal spin-transfer torque Ab initio studies of the tunneling magneto-Seebeck effect: Influence of magnetic material Spin caloritronics and the thermomagnetoelectric system Thermodynamic analysis of interfacial transport and of the thermomagnetoelectric system Tunneling magneto thermocurrent in CoFeB/MgO/CoFeB based magnetic tunnel junctions Time-resolved measurement of the tunnel magneto-Seebeck effect in a single magnetic tunnel junction Temperature dependent resistance of magnetic tunnel junctions as a quality proof of the barrier Spin caloritronics in magnetic tunnel junctions: Ab initio studies Influence of the interface structure on the bias dependence of tunneling magnetoresistance Interface Magnetism and Spin Wave Scattering in Ferromagnet-Insulator-Ferromagnet Tunnel Junctions Inelastic electron tunneling spectra of MgO-based magnetic tunnel junctions with different electrode designs Tunneling spectroscopy in CoFeB/MgO/CoFeB magnetic tunnel junctions Strongly reduced bias dependence in spin–tunnel junctions obtained by ultraviolet light assisted oxidation Giant magnetothermopower of magnon-assisted transport in ferromagnetic tunnel junctions Giant intrinsic thermomagnetic effects in thin MgO magnetic tunnel junctions Voltage tuning of thermal spin current in ferromagnetic tunnel contacts to semiconductors Download references The authors gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft (DFG) in the priority program SpinCaT (TH 1399/4-1 are supported by the MIWF of the NRW state government We acknowledge support for the Article Processing Charge by the Deutsche Forschungsgemeinschaft and the Open Access Publication Fund of Bielefeld University Center for Spinelectronic Materials and Devices performed the measurements and analyzed the data; V.Z. prepared and characterized the TMR devices; A.T. invented the model to determine the Seebeck voltages under the applied bias and all other authors discussed the experiments and the manuscript Download citation Sorry, a shareable link is not currently available for this article. Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily. Tobias noted that no traces of flammable liquids or containers had been found at the site of the fire. He also exposed massive contradictions in the accounts given by a number of those close to the action and showed that after the war they had amended their accounts in order to present themselves in a good light. The book was a formidable challenge to the Communist version of events. Hett claims that Tobias worked for the intelligence service and used the information at his disposal to blackmail the Institute for Contemporary History into vindicating his own views by threatening to expose the Nazi past of the Institute’s director, Helmut Krausnick (this was no secret, and Krausnick’s many contributions to the prosecution of Nazi war criminals over the years made the fact more or less irrelevant). There should also be demonstrations in Malet Street Although I am honoured that my book Burning the Reichstag has drawn Richard Evans’s attention, his critique neglects crucial lines of my argument (LRB, 8 May) Evans makes no mention of what I present as the main flaw in the Fritz Tobias/Hans Mommsen ‘single culprit’ theory: every scientific expert I have consulted or who was called on to give an opinion in 1933 has found it ‘very difficult’ or ‘impossible’ to imagine how one man armed with nothing more than matches and firelighters could in fifteen minutes have set the fire that destroyed the Reichstag’s chamber The experts I consulted dismissed the explanations for the fire put forward by Evans’s preferred authors like Fritz Tobias and Sven Felix Kellerhoff the second major line of argument in my book: that the notion that van der Lubbe burned down the Reichstag by himself was little more than a desperate legal defence strategy on the part of war criminals Rudolf Braschwitz and Walter Zirpins had investigated the fire in 1933 After the war they maintained that they had always believed that van der Lubbe had set the fire by himself But newly available evidence shows that they worked enthusiastically to arrest frame and prosecute considerable numbers of Communists Evans claims that these men did not have to fear prosecution for the Reichstag fire after the war (and thus had no incentive to lie) and even that the statute of limitations barred prosecutions for crimes from 1933 Criminal cases arising from their work on the Reichstag fire were launched against Heisig and Braschwitz Braschwitz acknowledged that he would be in legal jeopardy were it proven that his 1933 investigations had focused on van der Lubbe while ignoring evidence against others The limitation period for most crimes from the Nazi period didn’t end until 8 May 1960 though any investigation started before that date could be continued The case against Braschwitz dragged on until March 1962 by which time Tobias’s single-culprit theory was publicly established Evans also neglects to mention that Heisig had deported Jews to Auschwitz and Theresienstadt that Braschwitz was involved in the dirty ‘anti-partisan’ war in the Soviet Union and that Zirpins had commanded the criminal police in Lodz and the Lodz Ghetto Evans is surprisingly insouciant about Tobias’s far-right connections and bad conduct as a historian He doesn’t mention that Tobias contributed a chapter to a festschrift for David Irving He downplays Tobias’s decision to republish his book with the far-right publisher Grabert Verlag although in his own writings Evans has noted Grabert’s involvement with Holocaust denial Tobias demonstrably falsified the historical record at many points even wholly inventing a substantial story about one witness to the fire in particular a letter written by the former Gestapo chief Rudolf Diels accusing a Nazi stormtrooper called Hans Georg Gewehr of being the main culprit The letter was in Tobias’s possession Evans downplays Tobias’s blackmailing of Helmut Krausnick director of the Institute for Contemporary History stating (incorrectly) that Krausnick’s Nazi Party membership was publicly known in 1962 is in this case willing to defend a man who so grossly flouted the core values of serious historical practice Evans writes: Benjamin Carter Hett’s letter contains the same non sequiturs and illogicalities as his book As far as the forensic evidence is concerned: of course ‘experts’ consulted by those peddling the theory that there was a conspiracy to burn down the Reichstag in 1933 will oblige by providing the answers they think are being sought ‘Expert’ reports from the present day about events that occurred eighty years ago are worthless The fact remains that no traces of kerosene or other incendiary liquids were found at the scene of the blaze: an impossibility if they had actually been used to light fires in locations spread across the building Braschwitz and Zirpins were arresting Communists in 1933 proves nothing in relation to the authorship of the fire: policemen were doing this all over Germany and doubtless would have done so at some stage during these months even had the Reichstag not burned Nor is the involvement of these men in war crimes of any relevance to the fire or to their alleged fear of being prosecuted in connection with it though Hett makes their supposed anxiety the principal reason for Tobias’s authorship of a 700-page book allegedly aimed at exculpating potential Nazi objects of prosecution for the fire before the statute of limitations came into effect in 1960 but in the amnesiac culture of the Federal Republic in the 1950s even major Nazi criminals had scant reason to fear arrest The few prosecutions that were launched mostly ran into the sand or ended in acquittal or scandalously lenient sentences Prosecutions begun before 1960 could be continued the ‘case against Braschwitz’ never actually came to prosecution Hett’s ignorance of the legal and political culture of West Germany in the 1950s and early 1960s is also evidenced by his attempt to blacken the name of Fritz Tobias by alluding to his ‘far-right connections’ Nobody in West Germany at the time could avoid connections with ex-Nazis To suppose that Krausnick falsified history because he was being ‘blackmailed’ by Tobias is as ludicrous as it is offensive to a historian whose role in bringing Nazi criminality to account was outstanding Hett’s point about the Grabert Verlag is already dealt with in my review to portray Tobias as an old Nazi out to protect his former comrades from prosecution is to fly in the face of the evidence of his firm Social Democratic convictions as expressed in the concluding paragraphs of his book If anything could be described as grossly flouting the core values of serious historical practice More by this contributorNot So Special: Imitating GermanyRichard J Find out more about the London Review of Books app Newsletter Preferences This site requires the use of Javascript to provide the best possible experience Please change your browser settings to allow Javascript content to run Metrics details Our findings suggest the use of chemically amenable phenalenyl-based molecules as a viable and scalable platform for building molecular-scale quantum spin memory and processors for technological development Molecular electronics emerges from molecular magnetism Robust spin crossover and memristance across a single molecule Magnetic memory of a single-molecule quantum magnet wired to a gold surface Magnetic bistability in a metal-ion cluster A quantum memory intrinsic to single nitrogen–vacancy centres in diamond Will spin-relaxation times in molecular magnets permit quantum information processing Synthetic organic spin chemistry for structurally well-defined open-shell graphene fragments Design of organic metals and superconductors Magneto-opto-electronic bistability in a phenalenyl-based neutral radical Substrate-induced magnetic ordering and switching of iron porphyrin molecules A room-temperature molecular/organic-based magnet Spin Crossover in Transition Metal Compounds I (Springer Organic tailored batteries materials using stable open-shell molecules with degenerate frontier orbitals Giant magnetoresistance in organic spin-valves Room-temperature tunnel magnetoresistance and spin-polarized tunneling through an organic semiconductor barrier Large spin diffusion length in an amorphous organic semiconductor Tunneling anisotropic magnetoresistance: a spin-valve-like tunnel magnetoresistance using a single magnetic layer Tunneling anisotropic magnetoresistance in organic spin valves Design of the local spin polarization at the organic-ferromagnetic interface Effect of molecular ordering on spin and charge injection in rubrene Molecular spintronics: The rise of spinterface science Supramolecular control of the magnetic anisotropy in two-dimensional high-spin Fe arrays at a metal interface Magnetic properties of spherical fcc clusters with radial surface anisotropy Magnetism: Nanosized Magnetic Materials (Wiley-VCH Download references were supported by the Office of Naval Research (ONR grant N00014-09-1-0177) and the National Science Foundation (grants DMR 0504158 and ULFR 09-0532-01) thanks the University of Groningen for partial financial support during his stay at MIT for performing calculations on JUROPA and JUGENE supercomputers thanks the German Science foundation for support within SFB 602 and SPP 1538 thank the Deutsche Forschungsgemeinschaft (DFG) Priority Programme 1178 and the Danish National Research Foundation (DNRF) funded Center for Materials Crystallography (CMC) for support and the Land Niedersachsen for providing a fellowship in the Catalysis for Sustainable Synthesis (CaSuS) Ph.D thank the Göttingen-Kolkata ‘Open shell systems (G-KOSS)’ initiative for supporting the collaboration Present address: Present address: IBM India Research Laboratory India (K.V.R.); Institute for Advanced Materials Kamerbeek: These authors contributed equally to this work Department of Materials Science and Engineering Indian Institute of Science Education and Research (IISER)-Kolkata Peter Grünberg Institut and Institute for Advanced Simulation designed the original research approach; A.M performed material characterization; K.V.R performed transport experiments and analysed transport and magnetic characterization; N.A. developed the organic spin-filter model; K.V.R. developed the interface magnetic anisotropy model; K.V.R provided the discussion and contributed to manuscript preparation All authors discussed the experiments and commented on the manuscript This file contains Supplementary Text and Data Supplementary Table 1 and Supplementary References Reprints and permissions Download citation Various types of molecular magnets carrying high localized spin have been studied as potential devices for information processing and storage but it remains a considerable challenge to electronically couple to these spin centres with the potential to act as an interface for the exchange of magnetic spin information in molecular spintronic devices The graphene fragment has no net spin itself but when deposited as a layer on a ferromagnet it transforms to produce a supramolecular magnetic film The resulting nanoscale magnetic molecules and the resulting device exhibits an unexpectedly large magnetoresistance of 20% near room temperature Sign up for our daily Newsletter and stay up to date with all the latest news You are receiving this pop-up because this is the first time you are visiting our site You are using software which is blocking our advertisements (adblocker) we are relying on revenues from our banners So please disable your adblocker and reload the page to continue using this site.Thanks the heated film tunnel strawberry harvest started this week "The crops are doing quite well and so far we have seen no damage We assume it will be a normal season opener," said Maximilian Reuhl of production company Wetterauer Früchtchen based in Münzenberg "The first products from unheated tunnels will be harvested in about three weeks we will finally start with the pure field strawberries The current product is of very good quality and the final selling prices are in the satisfactory range of €11-12 per kg At the moment I can not say too much about sales prices will drop again due to the increased supply," says Reuhl Great price pressureThe grower sells his fruit either directly to regional Rewe branches At this time it is mainly early variety Clery that is harvested other varieties will supplement the basic range Reuhl says a clear overall development can be observed: "When the Dutch 'autumn harvest' starts unfortunately the German market is literally flooded reasonable prices can be gotten for a good regional product and German customers are increasingly valuing these." FreshPublishers © 2005-2025 FreshPlaza.com There’s only one person who’ll be genuinely pleased with the Intelligence and Security Committee’s Russia report Russia emerges as an amorphous and formidable enemy — all the more so because the inconclusive and much-redacted report contains next to no substantiated allegations and this will spawn a thousand conspiracy theories far more corrosive and confusing to our politics than any Moscow-generated Twitter-storm or document leak Yet the government-induced delay in publication allows anyone that way inclined to imagine a cover-up Even the insistence that the state should do more to prevent Russian meddling plays into Putin’s hands The fear of Russian interference in British elections creates chaos and division — and this Russia may be reeling from a collapse in oil prices and one of the highest rates of Covid-19 infection in the world but Moscow relies on pushing the idea that it’s the West that is really in trouble racked with violent culture wars and suffering from a profound loss of faith in its own values The Kremlin’s new party line is: we may have it bad the raging divisions around the Black Lives Matter movement are also a sweet spot for Russian trolls set on fanning the flames of the West’s self-immolation — in the UK A US Senate Intelligence Committee investigation into the 2016 US presidential election concluded that a Russian fake-news campaign targeted ‘no single group… more than African-Americans’ Owen Matthews is an Associate Editor of The Spectator and the author of Overreach: The Inside Story of Putin’s war on Ukraine Be part of the conversation with other Spectator readers by getting your first three months for £3 Already a subscriber? 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