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A spin-polarized state is examined under charge current at room temperature without magnetic fields in chiral disilicide crystals NbSi_{2} and TaSi_{2}. We found that a long-range spin transport occurs over ten micrometers in these inorganic crystals. A distribution of crystalline grains of different handedness is obtained via location-sensitive electrical transport measurements. The sum rule holds in the conversion coefficient in the current-voltage characteristics. A diamagnetic nature of the crystals supports that the spin polarization is not due to localized electron spins but due to itinerant electron spins. A large difference in the strength of antisymmetric spin-orbit interaction associated with 4d electrons in Nb and 5d ones in Ta is oppositely correlated with that of the spin polarization. A robust protection of the spin polarization occurs over long distances in chiral crystals.

The collective excitation modes of a magnetic chiral soliton lattice (CSL) are numerically studied. We perform micromagnetic simulations of a monoaxial chiral helimagnet with an external magnetic field that forms the CSL. Due to the repulsive interaction between solitons through a ferromagnet state, collective modes described by the coupled oscillator are excited. These modes exist at a frequency of $\ensuremath{\sim}1\phantom{\rule{0.28em}{0ex}}\mathrm{GHz}$ while the conventional ferromagnetic resonant mode exists at a frequency of $\ensuremath{\sim}10\phantom{\rule{0.28em}{0ex}}\mathrm{GHz}$ as measured in experiments [F. Goncalves et al., Phys. Rev. B 95, 104415 (2017)]. In contrast to ferromagnetic resonance, the resonant frequency of the coupled-oscillator mode decreases by increasing the magnetic field. We clarified that the coupling energy between solitons becomes weak by increasing the distance between solitons. We also investigate the resonant condition of a precessional mode of the CSL measured in experiments.

Chirality in a helimagnetic structure is determined by the sense of magnetic moment rotation. We found that the chiral information did not disappear even after the phase transition to the high-temperature ferromagnetic phase in a helimagnet MnP. The 2nd harmonic resistivity $\rho^{\rm 2f}$, which reflects the breaking down of mirror symmetry, was found to be almost unchanged after heating the sample above the ferromagnetic transition temperature and cooling it back to the helimagnetic state. The application of a magnetic field along the easy axis in the ferromagnetic state quenched the chirality-induced $\rho^{\rm 2f}$. This indicates that the chirality memory effect originated from the ferromagnetic domain walls., Comment: 8 pages, 8 figures

Chirality-induced spin transport phenomena are investigated at room temperature without magnetic fields in a monoaxial chiral dichalcogenide CrNb_{3}S_{6}. We found that spin polarization occurs in these chiral bulk crystals under a charge current flowing along the principal c axis. Such phenomena are detected as an inverse spin Hall signal which is induced on the detection electrode that absorbs polarized spin from the chiral crystal. The inverse response is observed when applying the charge current into the detection electrode. The signal sign reverses in the device with the opposite chirality. Furthermore, the spin signals are found over micrometer length scales in a nonlocal configuration. Such a robust generation and protection of the spin-polarized state is discussed based on a one-dimensional model with an antisymmetric spin-orbit coupling.

Current-induced motion of non-axisymmetric skyrmions within angular phases of polar helimagnetis with the easy plane anisotropy is studied by micromagnetic simulations.Such non-axisymmetric skyrmions consist of a circular core and a crescent-shaped domain-wall region formed with respect to the tilted surrounding state. A current-driven motion of non-axisymmetric skyrmions exhibits two distinct time regimes: initially the skyrmions rotate towards the current flow direction and subsequently move along the current with the skyrmionic crescent first. According to the Thiele equation, the asymmetric distribution of the topological charge and the dissipative force tensor play an important role for giving the different velocities for the circular and the crescent-shaped constituent parts of the skyrmion what underlies such a shuttlecock-like movement. Moreover, the current-velocity relation depends on the tilt angle of the surrounding angular phase what makes in particular the transverse velocity of skyrmions sensitive to their field-driven configurational transformation., 5 pages, 5 figures

The magnetization dynamics of nonuniform magnetic structures induce the spin-dependent force acting on the conduction electrons via the s–d coupling. This emergent electric field, the so-called spi...

Monoaxial chiral magnets exhibit a chiral conical magnetic state in a magnetic field parallel to the chiral axis. The conical spins carry the potential for nonreciprocal transport phenomena, as they break both spatial inversion and time reversal symmetries. Here we study the spin-dependent transport in the chiral conical magnetic state, using the Landauer method based on Green's functions for a one-dimensional Kondo lattice model. We show that the system exhibits nonreciprocal spin transport, which depends on the chirality, period, cone angle, and the polarization of the spin current. In particular, we find the distinct cone angle dependence between the spin textures with long and short periods. We also show that the nonreciprocity is related with the spin states of itinerant electrons near the leads. Our results indicate that the chiral cone acts as a spin-current diode, which can be flexibly controlled by a magnetic field., 5 pages, 5 figures

Chirality control of the spin structure in monoaxial helimagnets by using charge current is theoretically investigated. The classical J 1 − J 2 Heisenberg model has two degenerate helical states that are characterized by the chirality. In a recent experiment, it has been shown that the chirality of the spin structure can be controlled by applying a charge current during the field-decreasing process [Jiang et al., Nat. Commun. 11, 1601 (2020)]. We reproduced this experiment by numerical calculations based on the Landau–Lifshitz–Gilbert equation with the spin-transfer torque. We show that the damping torque and spin-transfer torque are responsible for the controllability. In addition, we theoretically propose more convenient forms of chirality control: instantaneous switching of chirality and zero-field control by using a ferromagnet junction. Such improved controllability may pave the way to spintronics based on the chirality degree of freedom.

We report the observation of a magnon Hall-like effect for the scattering of magnons at the sample edge in Y3Fe5O12 crystals. The experiments are performed under an out-of-plane magnetic field at room temperature using an infrared thermometry. When the magnons are incident into the sample edge in the unsaturated magnetic structure, appreciable transverse thermal gradient is detected. This thermal gradient could be attributed to magnon Hall effect for sample-edge scattering. We unexpectedly find that this effect is largely enhanced in the unsaturated regime, compared with the saturated regime where theoretical mechanism of magnon Hall effect due to the Berry curvature has been proposed previously.

Thermoelectric effects driven by magnetization dynamics under a temperature gradient are studied for ferromagnets with and without a skyrmion structure. We calculate charge currents in a four-terminal geometry using the adiabatic pumping formula with full account of magnetization dynamics based on the stochastic Landau–Lifshitz–Gilbert equation. The longitudinal current (Seebeck effect) is induced from the thermally driven spin waves via the spin-transfer and momentum-transfer processes, and these two processes contribute constructively (destructively) in ferromagnets having a negative (positive) s-d exchange interaction. The transverse currents (anomalous Nernst effect) arise in proportion to the number of skyrmions, whose mechanism is identified as the thermal topological Hall effect of magnons followed by the momentum-transfer drag process.

We demonstrate the inplane anisotropy of longitudinal thermal conductivities and the weak localization of magnons in a disordered screw-type spiral magnet on a square lattice. We consider a disordered spin system, described by a spin Hamiltonian for the antiferromagnetic Heisenberg interaction and the Dzyaloshinsky-Moriya interaction with the mean-field type potential of impurities. We derive longitudinal thermal conductivities for the disordered screw-type spiral magnet in the weak-localization regime by using the linear-response theory with the linear-spin-wave approximation and performing perturbation calculations. We show that the inplane longitudinal thermal conductivities are anisotropic due to the Dzyaloshinsky-Moriya interaction. This anisotropy may be useful for experimentally estimating the magnitude of a ratio of the Dzyaloshinsky-Moriya interaction to the Heisenberg interaction. We also show that the main correction term gives a logarithmic suppression with the length scale due to the critical back scattering. This suggests that the weak localization of magnons is ubiquitous for the disordered two-dimensional magnets having global time-reversal symmetry. We finally discuss several implications for further research., 16 pages, 4 figures; published version

A chiral soliton lattice stabilized in a monoaxial chiral magnet ${\mathrm{CrNb}}_{3}{\mathrm{S}}_{6}$ is a magnetic superlattice consisting of magnetic kinks with a ferromagnetic background. The magnetic kinks are considered to be topological magnetic solitons (TMSs). Changes in the TMS number yield discretized responses in magnetization and electrical conductivity, and this effect is more prominent in smaller crystals. We demonstrate that, in microprocessed ${\mathrm{CrNb}}_{3}{\mathrm{S}}_{6}$ crystals, TMSs are geometrically protected through element-selected micromagnetometry using soft x-ray magnetic circular dichroism (MCD). A series of x-ray MCD data is supported by mean-field and micromagnetic analyses. By designing the microcrystal geometry, TMS numbers can be successfully changed and fixed over a wide range of magnetic fields.

We propose the weak localization of magnons in a disordered two-dimensional antiferromagnet. We derive the longitudinal thermal conductivity $\kappa_{xx}$ for magnons of a disordered Heisenberg antiferromagnet in the linear-response theory with the linear-spin-wave approximation. We show that the back scattering of magnons is enhanced critically by the particle-particle-type multiple impurity scattering. This back scattering causes a logarithmic suppression of $\kappa_{xx}$ with the length scale in two dimensions. We also argue a possible effect of inelastic scattering on the temperature dependence of $\kappa_{xx}$. This weak localization is useful to control turning the magnon thermal current on and off., Comment: 5 pages, 2 figures; published version

We demonstrate that a weak external magnetic field can induce negative magneto-thermal-resistance for magnons in a disordered two-dimensional antiferromagnet. We study the main effect of a weak external magnetic field on the longitudinal thermal conductivity, $\kappa_{xx}$, for a disordered antiferromagnet using the weak-localization theory for magnons. We show that the weak-localization correction term of $\kappa_{xx}$ positively increases with increasing the magnetic field parallel to the ordered spins. Since this increase corresponds to a decrease of the thermal resistivity, this phenomenon is negative magneto-thermal-resistance for magnons. This negative magneto-thermal-resistance and the weak localization of magnons will be used to control the magnon thermal current in antiferromagnetic spintronics devices. We also discuss several implications for further experimental and theoretical studies for disordered magnets., Comment: 8 pages, 1 figure; published version

We examine the surface size- and shape-effects of soliton annihilation and soliton nucleation in chiral magnet CrNb3S6. We measure magnetization (M) curves of submillimeter-sized single crystals with an equal length along the c-axis (Lc = 10 μm) but with different cross sections in the ab-plane (Sab = 0.120–0.014 mm2). We find a ferromagnetic type of magnetizing (FMM) with a convex curve (d2M/dH2 < 0) near zero field (H = 0) and a major jump in M near the forced ferromagnetic state, which are more conspicuous, compared with earlier samples with submillimeter Lc [K. Tsuruta et al. J. Phys. Soc. Jpn. 85, 013707 (2016)]. A new finding is that the major jump in M occurs at lower fields in samples with the smaller Sab. We further perform numerical simulation of the magnetization process with the Landau–Lifshitz–Gilbert equation of the Langevin-type. Based on the numerical results, we attribute the FMM at small fields to rapid annihilation of soliton assisted by the reduction of Dzyaloshinskii-Moriya interaction near the surfaces. We also discuss possible penetration processes of chiral soliton through the ac-(bc-)plane as well as ab-plane, and its relation to the major jump in M. Our experimental and calculated results will contribute to understanding of the effects of topological metastability in chiral magnets.

When energy is introduced into a region of matter, it heats up and the local temperature increases. This energy spontaneously diffuses away from the heated region. In general, heat should flow from warmer to cooler regions and it is not possible to externally change the direction of heat conduction. Here we show a magnetically controllable heat flow caused by a spin-wave current. The direction of the flow can be switched by applying a magnetic field. When microwave energy is applied to a region of ferrimagnetic Y3Fe5O12, an end of the magnet far from this region is found to be heated in a controlled manner and a negative temperature gradient towards it is formed. This is due to unidirectional energy transfer by the excitation of spin-wave modes without time-reversal symmetry and to the conversion of spin waves into heat. When a Y3Fe5O12 film with low damping coefficients is used, spin waves are observed to emit heat at the sample end up to 10 mm away from the excitation source. The magnetically controlled remote heating we observe is directly applicable to the fabrication of a heat-flow controller.

Spin-polarized current through helimagnets and the conductance modulation due to the chirality mismatch are studied numerically. The one-dimensional spiral magnet structure is obtained by taking into account the Dzyaloshinskii-Moriya interaction and the ferromagnetic interaction. Although the spiral magnetic structure consists of the $y\text{\ensuremath{-}}z$ components of the magnetization, the conduction electron through the spiral magnet is polarized in the $x$ direction, and its sign depends on the chirality of the spiral structure. We also investigate charge transport through the junction system consisting of two helimagnets. Similar to the giant magnetoresistance in the uniform ferromagnet, the conductance is reduced significantly by attaching the helimagnets with different chiralities. It is possible that our proposed mechanism can make use of the chirality measuring method by using electron transport and an alternative type of magnetoresistance using a topological property.

We have been investigating the spin motive force induced by magnetization dynamics in ferromagnetic materials. Ferrimagnetic materials are expected to exhibit even larger spin motive force due to their spatially staggered magnetic structure and high frequency spin wave modes. We believe that magnetite (Fe3O4) is one of the candidates for this purpose. Here, we report magnetic resonance in Fe3O4 thin films epitaxially grown on a MgO (001) substrate. The gyromagnetic ratio and the effective saturation magnetization are estimated to be 1.71 ×1011 s-1T-1 and 364 emu/cm3, respectively. The Gilbert damping constant of 0.02 is obtained from the magnetic field dependence of the linewidth. We expect to investigate the spin motive force induced from this magnetic resonance.

We theoretically demonstrate that a rotating electric-field component of circularly polarized microwave or terahertz light can induce electron-spin polarization within a few picoseconds in a two-dimensional electron system with the Rashba spin-orbit interaction by taking advantage of the magnetoelectric coupling. The efficiency turns out to be several orders of magnitude greater than that of conventional methods, indicating high potential of this technique for future spintronics., 6 pages, 4 figures

An insulator does not conduct electricity, and so cannot in general be used to transmit an electrical signal. However, the electrons within an insulator possess spin as well as charge, so it is possible for them to transmit a signal in the form of a spin wave. Kajiwara et al. have now developed a hybrid metal–insulator–metal structure in which an electrical signal in one metal layer is directly converted to a spin wave in the insulating layer. This wave is then transmitted to the second metal layer, where the signal can be directly recovered as an electrical voltage. The observation of voltage transmission in an insulator raises the prospect of insulator-based spintronics and other novel forms of signal delivery. An insulator does not conduct electricity, and so cannot in general be used to transmit an electrical signal. But an insulator's electrons possess spin in addition to charge, and so can transmit a signal in the form of a spin wave. Here a hybrid metal–insulator–metal structure is reported, in which an electrical signal in one metal layer is directly converted to a spin wave in the insulating layer; this wave is then transmitted to the second metal layer, where the signal can be directly recovered as an electrical voltage. The energy bandgap of an insulator is large enough to prevent electron excitation and electrical conduction1. But in addition to charge, an electron also has spin2, and the collective motion of spin can propagate—and so transfer a signal—in some insulators3. This motion is called a spin wave and is usually excited using magnetic fields. Here we show that a spin wave in an insulator can be generated and detected using spin-Hall effects, which enable the direct conversion of an electric signal into a spin wave, and its subsequent transmission through (and recovery from) an insulator over macroscopic distances. First, we show evidence for the transfer of spin angular momentum between an insulator magnet Y3Fe5O12 and a platinum film. This transfer allows direct conversion of an electric current in the platinum film to a spin wave in the Y3Fe5O12 via spin-Hall effects4,5,6,7,8,9,10,11. Second, making use of the transfer in a Pt/Y3Fe5O12/Pt system, we demonstrate that an electric current in one metal film induces voltage in the other, far distant, metal film. Specifically, the applied electric current is converted into spin angular momentum owing to the spin-Hall effect7,8,10,11 in the first platinum film; the angular momentum is then carried by a spin wave in the insulating Y3Fe5O12 layer; at the distant platinum film, the spin angular momentum of the spin wave is converted back to an electric voltage. This effect can be switched on and off using a magnetic field. Weak spin damping3 in Y3Fe5O12 is responsible for its transparency for the transmission of spin angular momentum. This hybrid electrical transmission method potentially offers a means of innovative signal delivery in electrical circuits and devices.

The magnetic-field dependence of the longitudinal spin Seebeck effect (LSSE) in a $\mathrm{Pt}/{\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (YIG)-slab junction system was found to deviate from a bulk magnetization curve of the YIG slab in a low field range. In this paper, we show that the deviation originates from the difference between surface and bulk magnetization processes in the YIG slab and that it appears even when removing possible extrinsic magnetic anisotropy due to surface roughness and replacing the Pt layer with different materials. This result indicates that the anomalous field dependence of the LSSE is due to an intrinsic magnetic property of the YIG surface. Our numerical calculation based on the Landau-Lifshitz-Gilbert equation shows that the deviation between the LSSE and bulk magnetization curves is qualitatively explained by introducing easy-axis perpendicular magnetic anisotropy near the surface of YIG.

The spin motive force driven by the dynamics of the skyrmion structure formed in a nanomagnetic disk is numerically investigated. Due to the existence of the magnetic structure along the disk edge, the collective mode of the magnetization is modified from that of the bulk skyrmion lattice obtained by using the periodic boundary condition. For a single-skyrmion disk, the dynamics of the skyrmion core and the edge magnetization induce the spin motive force, and a measurable AC voltage is obtained by two probes on the disk. For a multi-skyrmions disk, the phase-locked collective mode of skyrmions is found in the lowest resonant frequency where the amplitude of the AC voltage is enhanced by the cascade effect of the spin motive force. We also investigate the effect of the Rashba spin-orbit coupling on the spin motive force.

Changing of magnetic flux induces an electromotive force, known as a Faraday’s law. Recently, it has been pointed out that the changing of non-uniform magnetic structure in a ferromagnetic metal induces the spin-dependent force acting on the conduction electrons through a spin Berry phase [1]. This spin-motive force (SMF) has been observed in many systems [2,3] that opens a new way of manipulating spins in spintronics devices. Here, we study numerically the SMF induced by the resonant motion of a magnetic domain wall (DW) by applying an oscillating magnetic field. We have simulated the dynamics of a single DW in one-dimensional Permalloy (Ni1-xFex) system by solving Landau-Lifshitz-Gilbert equation using fourth-order Runge-Kutta method. We found that spatial configuration of the resonant oscillating mode of the DW depends on the direction of the oscillating magnetic field. We show the SMF induced by each resonant DW motion and discuss the possibility of the observation in actual experiments.

A transfer-matrix method to study ac transport in harmonically driven mesoscopic electron systems has been developed. This method makes it possible to calculate, without consuming a large amount of computing time and memory space, nonlinear ac currents in nonequilibrium systems by means of transmission and reflection amplitudes of electrons through sideband states produced by the oscillating potential. We also discuss a way to take a thermal average of the ac current at a finite temperature under a finite dc-bias voltage. Simple applications of this method exhibit the efficiency of this numerical technique.

The magnetic correlation between magnetic impurities in semiconductors is investigated by performing the quantum Monte Carlo (QMC) simulation. The Anderson Hamiltonian with the realistic parameters obtained by the local density approximation (LDA) calculation is employed. The LDA calculation gives a dispersion of the host (GaAs) electron and the mixing energy between host and magnetic impurity (Mn). The mixing between host and impurity electrons generates the impurity bound state in the energy gap of semiconductors. The long range ferromagnetic coupling is observed when the Fermi energy locates between the band edge and the impurity bound state. The ferromagnetic coupling is enhanced by decreasing temperature.

Quantum transport in harmonically driven double-barrier systems has been studied quantitatively by using a transfer matrix method, especially focusing our attention on the conductance as a function...

Using a novel transfer matrix method, photon-assisted quantum transport through a quantum point contact (QPC) has been studied theoretically. Although the previous WKB theory predicts a ministep st...

Charge currents driven by the spin dynamics in the presence of the Rashba spin–orbit interaction are investigated numerically. The spin current induced by the precession of the local magnetic moment can be converted to the charge current assisted by the spin–orbit interaction. We use the recursive Green's function method and the Brouwer's formula for calculating the pumping current in multi-terminal mesoscopic systems. Our results show that the pumping charge current has both AC and DC components. The amplitude of the pumped current increases by increasing of the strength of the spin–orbit interaction. The current is realized in an out-of-equilibrium situation, and could be considered as a battery operated by magnetism.

A current-induced magnetic fluctuation state in mesoscopic systems such as a dilute magnetic semiconductors is theoretically predicted. We investigate coherent electron transport and the dynamics of the local magnetic moment of a ferromagnetic nano-pillar system where the current-induced magnetization switching is realized in macroscopic samples. The exchange coupling between the spins of the conduction electrons and the local spins is taking into account by using the numerical technique. An interference related non-uniform spin-polarized current causes a non-uniform spin transfer torque. We show that this mesoscopic spin torque generates a spatio-temporal magnetic fluctuation state in the local spin system. We propose the measurement of the time dependent conductance fluctuation for observing the magnetic fluctuation state.

A magnetostatic spin wave analog of integer quantum Hall (IQH) state is proposed in realistic patterned ferromagnetic thin films. Due to magnetic shape anisotropy, magnetic moments in a thin film lie within the plane, while all spin-wave excitations are fully gapped. Under an out-of-plane magnetic field, the film acquires a finite magnetization, where some of the gapped magnons become significantly softened near a saturation field. It is shown that, owing to a spin-orbit locking nature of the magnetic dipolar interaction, these soft spin-wave volume-mode bands become chiral volume-mode bands with finite topological Chern integers. A bulk-edge correspondence in IQH physics suggests that such volume-mode bands are accompanied by a chiral magnetostatic spin-wave edge mode. The existence of the edge mode is justified both by micromagnetic simulations and by band calculations based on a linearized Landau-Lifshitz equation. Employing intuitive physical arguments, we introduce proper tight-binding models for these soft volume-mode bands. Based on the tight-binding models, we further discuss possible applications to other systems such as magnetic ultrathin films with perpendicular magnetic anisotropy (PMA)., 20 pages, 12 figures

Topological phases have been explored in various fields in physics such as spintronics, photonics, liquid helium, correlated electron system and cold-atomic system. This leads to the recent foundation of emerging materials such as topological band insulators, topological photonic crystals and topological superconductors/superfluid. In this paper, we propose a topological magnonic crystal which provides protected chiral edge modes for magnetostatic spin waves. Based on a linearized Landau-Lifshitz equation, we show that a magnonic crystal with the dipolar interaction acquires spin-wave volume-mode band with non-zero Chern integer. We argue that such magnonic systems are accompanied by the same integer numbers of chiral spin-wave edge modes within a band gap for the volume-mode bands. In these edge modes, the spin wave propagates in a unidirectional manner without being scattered backward, which implements novel fault-tolerant spintronic devices., 12 pages, 7 figures

Based on a linearized Landau-Lifshitz equation, we show that two-dimensional periodic allay of ferromagnetic particles coupled with magnetic dipole-dipole interactions supports chiral spin-wave edge modes, when subjected under the magnetic field applied perpendicular to the plane. The mode propagates along a one-dimensional boundary of the system in a unidirectional way and it always has a chiral dispersion within a band gap for spin-wave volume modes. Contrary to the well-known Damon-Eshbach surface mode, the sense of the rotation depends not only on the direction of the field but also on the strength of the field; its chiral direction is generally determined by the sum of the so-called Chern integers defined for spin-wave volume modes below the band gap. Using simple tight-binding descriptions, we explain how the magnetic dipolar interaction endows spin-wave volume modes with non-zero Chern integers and how their values will be changed by the field., Comment: 18 pages, 16 figures, some trivial typo in equations are fixed

A change of magnetic flux through a circuit induces an electromotive force. By analogy, a recently predicted force that results from the motion of non-uniform spin structures has been termed the spin-motive force. Although recent experiments seem to confirm its presence, a direct signature of the spin-motive force has remained elusive. Here we report the observation of a real-time spin-motive force produced by the gyration of a magnetic vortex core. We find a good agreement between the experimental results, theory and micromagnetic simulations, which taken as a whole provide strong evidence in favour of a spin-motive force. The electromotive force is a well established phenomenon that is induced by a varying magnetic field. Here, Tanabeet al. report a compelling experimental confirmation of its spin-induced analogue, the spinmotive force.

The spinmotive force associated with a moving domain wall is observed directly in Permalloy nanowires using real time voltage measurements with proper subtraction of the electromotive force. Whereas the wall velocity exhibits nonlinear dependence on magnetic field, the generated voltage increases linearly with the field. We show that the sign of the voltage reverses when the wall propagation direction is altered. Numerical simulations explain quantitatively these features of spinmotive force and indicate that it scales with the field even in a field range where the wall motion is no longer associated with periodic angular rotation of the wall magnetization.

We present a theoretical discovery of an unconventional mechanism of inverse Faraday effect (IFE) which acts selectively on topological magnetic structures. The effect, topological inverse Faraday effect (TIFE), is induced by spin Berry's phase of the magnetic structure when a circularly polarized light is applied. Thus a spin-orbit interaction is not necessary unlike in the conventional IFE. We demonstrate by numerical simulation that TIFE realizes ultrafast switching of a magnetic vortex within a switching time of 150 ps without magnetic field., Comment: 11 pages, 4 figures

We study, both experimentally and theoretically, the generation of a dc spinmotive force. By exciting a ferromagnetic resonance of a comb-shaped ferromagnetic thin film, a continuous spinmotive force is generated. Experimental results are well reproduced by theoretical calculations, offering a quantitative and microscopic understanding of this spinmotive force., 4 pages, 4 figures, accepted to Physical Review Letters

We study, both analytically and numerically, a spinmotive force arising from inherent magnetic energy of a domain wall in a wedged ferromagnetic nanowire. In a spatially-nonuniform nanowire, domain walls are subjected to an effective magnetic field, resulting in spontaneous motion of the walls. The spinmotive force mechanism converts the ferromagnetic exchange and demagnetizing energy of the nanowire into the electrical energy of the conduction electrons through the domain wall motion. The calculations show that this spinmotive force can be several microvolts, which is easily detectable by experiments., 4 pages, 2 figures

We formulate a quantitative theory of an electromotive force of spin origin, i.e., spin-motive force, by the equation-of-motion approach. In a ferromagnetic metal, electrons couple to the local magnetization via the exchange interaction. Electrons feel spin dependent forces due to this interaction, and then the spin-motive force and the anomalous Hall effect appears. We have revealed that the origin of these phenomena is a misalignment between the conduction electron spin and the local magnetization., Comment: 3 pages, 3 figures

We investigate both theoretically and experimentally a gigantic enhancement of the spin Seebeck effect in a prototypical magnet LaY$_2$Fe$_5$O$_{12}$ at low temperatures. Our theoretical analysis sheds light on the important role of phonons; the spin Seebeck effect is enormously enhanced by nonequilibrium phonons that drag the low-lying spin excitations. We further argue that this scenario gives a clue to understand the observation of the spin Seebeck effect that is unaccompanied by a global spin current, and predict that the substrate condition affects the observed signal., 5 pages, 4 figures

We formulate a linear response theory of the spin Seebeck effect, i.e., a spin voltage generation from heat current flowing in a ferromagnet. Our approach focuses on the collective magnetic excitation of spins, i.e., magnons. We show that the linear-response formulation provides us with a qualitative as well as quantitative understanding of the spin Seebeck effect observed in a prototypical magnet, yttrium iron garnet., 6 pages, 3 figures. Added references and revised argument on the length scales at the end of Sec. 3

Thermoelectric generation is an essential function of future energy-saving technologies. However, this generation has been an exclusive feature of electric conductors, a situation which inflicts a heavy toll on its application; a conduction electron often becomes a nuisance in thermal design of devices. Here we report electric-voltage generation from heat flowing in an insulator. We reveal that, despite the absence of conduction electrons, a magnetic insulator LaY2Fe5O12 converts a heat flow into spin voltage. Attached Pt films transform this spin voltage into electric voltage by the inverse spin Hall effect. The experimental results require us to introduce thermally activated interface spin exchange between LaY2Fe5O12 and Pt. Our findings extend the range of potential materials for thermoelectric applications and provide a crucial piece of information for understanding the physics of the spin Seebeck effect., 19 pages, 5 figures (including supplementary information)

In two-dimensional electron gas (2DEG), spatial gradient of effective magnetic field due to spin orbit interaction yields spin dependent force. By taking this advantage, Stern-Gerlach spin filter in 2DEG has been proposed for generating spin polarized currents without any external magnetic fields and ferromagnetic materials [Phys. Rev. B 72, 041308(R) (2005)]. In order to demonstrate the spin filtering effect, detection of spin polarized electrons becomes crucial importance. Here, we propose an electrical detection of spin filtering by introducing an in-plane magnetic field in mesoscopic Stern-Gerlach spin filter. In-plane magnetic field induces spin polarized electrons due to Zeeman splitting, generating the imbalance between up-spin and down-spin currents after the spin separation. Calculated spin separation angle becomes 20o based on experimentally accessible parameters. Time evolution of wave packet shows the spin separation as well as the charge imbalance under the in-plane magnetic field. By fabricating Y-branch shaped narrow wire structure with two split gate electrodes at the junction, spin filtering effect can be detected as the magnitude difference of each branch currents. Gate bias dependence of each branch current is measured in B ex = ±15 T at T=4.2 K.