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Prestwood, D.*; 吉川 貴史; 齊藤 英治; 他15名*
Physical Review B, 113(13), p.134410_1 - 134410_12, 2026/04
We study a thin-film yttrium iron garnet sample that exhibits magnetic stripe domains due to a small perpendicular magnetic anisotropy. Using wide-field magneto-optic Kerr effect measurements we reveal the domain pattern evolution as a function of applied field and discuss the role of cubic anisotropy in the domain formation. Rich magnon spectra are observed in the stripe domain states, with a range of excitation conditions providing distinct spectra. The measurements are interpreted using micromagnetic simulations to provide the spatial profiles of each resonance mode. We further simulate domain patterns and resonance spectra accounting for the cubic anisotropy, with good correlation to experiment. This study highlights how noncollinear magnetic domain structures can host complex resonant behavior in a low-damping magnetic material, with potential use in future magnonic applications.
吉川 貴史
Nature Physics, 22, p.178 - 179, 2026/02
被引用回数：0 パーセンタイル：0.00(Physics, Multidisciplinary)Chiral phonons, quasiparticles of lattice vibrations arising from circular atomic motion, hold potential as carriers of angular momentum for next-generation technologies. Experiments show that they can generate orbital currents under thermal gradients.
Wang, C.*; Yang, Z.*; Ren, Q.*; Mo. X.*; 吉川 貴史; 大門 俊介*; Diao, D.*; 齊藤 英治
Carbon, 246, p.120909_1 - 120909_7, 2026/01
被引用回数：0 パーセンタイル：0.00(Chemistry, Physical)Disordered carbon offers untapped potential for spin caloritronics. We report a phonon-enhanced spin-dependent Seebeck effect (SDSE) in a magnetic carbon film (MCF) with graphene nano-crystallites (10 nm), interfaced with Pt. In a longitudinal setup, the transverse thermoelectric voltage (
) peaks at (
) at 220 K, driven by a thermally induced spin current via the inverse spin Hall effect. Raman spectroscopy reveals a coincident G-band redshift peak, suggesting a phonon-spin resonance unique to MCF's hybrid structure. X-ray absorption spectra confirm stable sp
states, potentially mediating this effect. A multiple-sample study in addition reveals that smaller crystallites enhance SDSE. Unlike pristine graphene or insulators, MCF's weak ferromagnetism and phonon dynamics yield an unconventional spin-thermal regime. This finding redefines carbon's role in spin caloritronics, with tunable nano-crystallite size as a design parameter.
Gu, Y.*; 吉川 貴史; Bisogni, V.*; 他12名*
Nature, 645(8082), p.900 - 905, 2025/09
被引用回数：4 パーセンタイル：82.19(Multidisciplinary Sciences)Controlling spin currents, i.e., the flow of spin angular momentum, in small magnetic devices is the principal objective of spin electronics, a main contender for future energy efficient information technologies. Surprisingly, a pure spin current has never been measured directly since the associated electric stray fields and/or shifts in the non-equilibrium spin-dependent distribution functions are too small for conventional experimental detection methods optimized for charge transport. Here we report that resonant inelastic X-ray scattering (RIXS) can bridge this gap by measuring the spin current carried by magnons - the quanta of the spin wave excitations of the magnetic order - in the presence of temperature gradients across a magnetic insulator. This is possible due to the sensitivity of the momentum- and energy-resolved RIXS intensity to minute changes in the magnon distribution under non-equilibrium conditions. We use the Boltzmann equation in the relaxation time approximation to extract transport parameters, such as the magnon lifetime at finite momentum, essential for the realization of magnon spintronics.
巻内 崇彦*; 吉川 貴史; 今井 正樹; 中堂 博之; 齊藤 英治; 他3名*
Physical Review Research (Internet), 7(3), p.033083_1 - 033083_7, 2025/09
Hybridized nuclear and electron spin excitation in a MnCO crystal, a weakly anisotropic antiferromagnet, has been investigated. In this material, the hyperfine interaction is strong enough to form a nuclear spin wave. We measure the microwave absorption induced by magnetic resonance in a bulk MnCO and observe the dispersion representing strong frequency repulsion between electron and nuclear modes due to their hybridization, the signature of nuclear spin wave. Additionally, we observe that the nuclear spin resonance enters a nonlinear regime above a certain excitation power, attributed to the excitation of finite-wavenumber nuclear spin waves.
/graphene/yttrium iron garnet quadruple heterostructuresChoi, J. W.*; 吉川 貴史; Lee, S.-K.*; 他13名*
Journal of Materials Chemistry A, 13(32), p.26690 - 26699, 2025/08
Strong spin-orbit coupling (SOC) materials and graphene have recently emerged as promising interfacial layers for tailoring spin transport in normal metal/ferromagnet heterostructures. However, spin-to-charge conversion in Pt/two-dimensional (2D) layer/graphene/yttrium iron garnet (YIG) heterostructures remains experimentally unexplored. This study investigates the effects of monolayer graphene and its interfacial coupling with a non-magnetic 2D transition metal dichalcogenide (TMDC) with relatively strong SOC on the longitudinal spin Seebeck effect (LSSE) in Pt/TiSe (or ZrSe)/graphene/YIG quadruple heterostructures. Interfacial SOC between TMDC and graphene is demonstrated to induce an additional spin-to-charge conversion channel in the Pt layer, generating a charge current opposite in direction to the conventional inverse spin Hall effect-induced current from YIG and thereby leading to a net suppression of the LSSE signal. Thus, the study highlights the potential of non-magnetic TMDC interlayers for modulating spin transport, offering new design pathways for spintronic devices.
Watzman, S. J.*; 吉川 貴史; Skinner, B.*; 内田 健一*
MRS Bulletin, 50, p.915 - 924, 2025/08
被引用回数：2 パーセンタイル：33.90(Materials Science, Multidisciplinary)The combined use of heat, charge, and spin transport gives rise to new or deeply altered thermoelectric properties from those found in conventional, nonmagnetic thermoelectric transport; these phenomena include the magneto-Seebeck, Nernst, magnon drag, and spin Seebeck effects. Here, we explore both electron-driven and magnon-driven magneto-thermoelectric effects stemming from different origins depending on if the effect is longitudinal, where the electric field and thermal gradient are collinear, or transverse, where the electric field and thermal gradient are orthogonal. We consider both a Lorentz force acting on charge carriers in nonmagnetic conductors and the spin-orbit interaction acting on spin-polarized electrons in magnetic materials. Both intrinsic and extrinsic sources of skew forces on electrons or anomalous velocities offer promising avenues for generating new functionalities and applications in the burgeoning field of magneto-thermoelectrics and transverse thermoelectrics. Adding magnetism as a design degree of freedom offers more candidate classes of materials, such as topological, metallic, and amorphous materials, for consideration in the field of thermoelectrics.
Metzger, T. W. J.*; Fischer, P.*; 吉川 貴史; 齊藤 英治*; Kimel, A. V.*; Bossini, D.*
Physical Review Letters, 135(7), p.076702_1 - 076702_9, 2025/08
被引用回数：3 パーセンタイル：79.98(Physics, Multidisciplinary)Femtosecond laser excitation of nanometer thin heterostructures comprising a heavy metal and a magnetically ordered material is known to result in the emission of terahertz radiation. However, the nature of the emitted radiation from heavy metal/antiferromagnet heterostructures has sparked debates and controversies in the literature. Here, we unambiguously separate spin and charge contributions from Pt/NiO heterostructures by introducing an unprecedented methodology combining high external magnetic fields with a symmetry analysis of the emitted terahertz polarization. We observe two distinct mechanisms of terahertz emission, which we identify as optical difference frequency generation and ultrafast laser-induced quenching of the magnetization. We emphasize the absence of spin transport effects and signatures of coherent magnons. Overall, our Letter provides a general experimental methodology to separate spin and charge contributions to the laser-induced terahertz emission from heterostructures comprising a magnetically ordered material, thus holding great potential for advancing terahertz spintronics and establishing terahertz orbitronics.
Fe
|Pt at room temperature平田 裕也*; 吉川 貴史; 有沢 洋希*; 齊藤 英治*
Applied Physics Letters, 126(25), p.252408_1 - 252408_5, 2025/06
The nonlinear Seebeck effect, nonlinear conversion of a temperature gradient into an electric current, was observed at room temperature. Based on a second-harmonic lock-in method combined with an a.c. temperature gradient, 
, we measured a nonlinear Seebeck voltage in NiFe|Pt bilayers at 300 K, the amplitude of which increases in proportion to 
. We also observed that the nonlinear Seebeck voltage increases as the sample length along the direction decreases, showing a characteristic scaling law distinct from the conventional linear Seebeck effect. We developed a phenomenological model for the nonlinear Seebeck effect incorporating the spin-current induced modulation of the Seebeck coefficient, which well reproduces the experimental results.
Huang, Y.-C.*; 吉川 貴史; 他5名*
Applied Physics Letters, 126(9), p.092403_1 - 092403_6, 2025/03
被引用回数：0 パーセンタイル：0.00(Physics, Applied)The application of spin-current volume effect (SVE) with volume magnetostriction of iron gallium (FeGa) films is examined for micro-diaphragm actuation. A silicon diaphragm measuring 1.5
1.5 mm
is coated with Pt (100-nm-thick) and FeGa (100-nm-thick) thin films. An alternating charge current passed through the FeGa/Pt/Si diaphragm under a magnetic field perpendicular to the charge current generates an alternating spin current via the spin Hall effect in the Pt film, transferring angular momentum from the Pt film to the FeGa film. The injected spin current provides energy and changes the effective temperature, thereby varying the thermal fluctuation of the magnetic moments. In a magnetic material with volume magnetostriction, the thermal fluctuation of the magnetic moments affects its volume. When the spin fluctuations change, the volume magnetostriction induces a corresponding expansion or contraction of the material. Both electrodeposited and ion-beam sputter-deposited FeGa films are investigated, and it is observed that the FeGa film exhibits SVE. The force generated by the SVE is evaluated based on the vibration amplitude at the fundamental resonant mode. This study demonstrates that the force generated by the SVE is correlated with the volume magnetostriction and the deposition process.
GeTe homojunctions小幡 玲二*; 齊藤 英治; 吉川 貴史; 他13名*
Advanced Materials, 37(8), p.2411459_1 - 2411459_11, 2025/02
被引用回数：8 パーセンタイル：93.13(Chemistry, Multidisciplinary)Twistronics, a novel engineering approach involving the alignment of van der Waals (vdW) integrated two-dimensional materials at specific angles, has recently attracted significant attention. Novel nontrivial phenomena have been demonstrated in twisted vdW junctions (the so-called magic angle), such as unconventional superconductivity, topological phases, and magnetism. However, there have been only few reports on integrated vdW layers with large twist angles 
, such as twisted interfacial Josephson junctions using high-temperature superconductors. Herein, vdW homojunctions of the thin-magnetic flakes, Fe
GeTe
(FGT), with large ranging from 0 to 90 deg, without inserting any tunnel barriers are assembled. Nevertheless, these vdW homojunctions exhibit tunnel-magnetoresistance (TMR) like behavior (pseudo-TMR (PTMR) effect) with the ratios highly sensitive to the values, revealing that the vdW gap at the junction interface between the twisted FGT layers behaves like a tunnel barrier and the serves a control parameter for PTMR by drastically varying magnitudes of the lattice-mismatch and the subsequent appearance of antiferromagnetic (AFM) spin alignment. First-principles calculations considering vacuum gaps indicate strong dependence of TMR on the driven by the sixfold screw rotational symmetry of bulk FGT. The present homojunctions hold promise as a platform for novel AFM spin-dependent phenomena and spintronic applications.
小杉 美央子*; 吉川 貴史; 齊藤 英治; 他10名*
ACS Applied Materials & Interfaces, 16(46), p.64190 - 64196, 2024/11
被引用回数：4 パーセンタイル：39.03(Nanoscience & Nanotechnology)Atom-vacancy-defects present in various materials yield numerous interesting physical phenomena, even obstructing high performance in some cases. On the other hand, their valuable applications to novel devices, such as nitrogen vacancy centers in diamond for quantum bits, have gathered significant attention. In particular, these tendencies become more substantial in two-dimensional (2D) (atomically) thin van der Waals layers. However, correlations with various kinds of atom defects are still under exploration. Herein, we find the stochastic behaviors of large hysteresis loops with strong photoresponse in the static electrical properties in few-atom layer semiconductors, molybdenum disulfide (MoS). The temperature dependence and transmission electron microscopy reveal that they arise from pairs of two neighboring in-plane S-vacancy defects, which predominantly present only around the interface at the MoS flake/substrate, with activation energies similar to 0.35 eV. The low-frequency (
) (LF) noise measurements clarify a high f shift in the two 1/ 2-dependent regimes, implying stochastic behaviors of electric charges through the S-vacancy pairs with high-speed charge(spin) transitions across low kinetic energy barriers between narrow discrete states. The shallow energy sates are formed from the highly uniform S-vacancy pairs interacting with Mo atoms, which act like quantum dots. The observed stochastic operation holds promise for various application, particularly for probabilistic neuromorphic computation in artificial intelligence.
GeTe nanomeshes小幡 玲二*; 吉川 貴史*; 齊藤 英治; 他7名*
Nanotechnology, 35(47), p.475601_1 - 475601_9, 2024/11
被引用回数：2 パーセンタイル：25.23(Nanoscience & Nanotechnology)The growth of two-dimensional van der Waals magnetic materials presents attractive opportunities for exploring new physical phenomena and valuable applications. Among these materials, FeGeTe (FGT) exhibits a variety of remarkable properties and has garnered significant attention. Herein, we have for the first time created a nanomesh structure-a honeycomb-like array of hexagonal nanopores-with the zigzag pore-edge atomic structure on thin FGT flakes with and without oxidation of the pore edges. It is revealed that the magnitude of ferromagnetism (FM) significantly increases in both samples compared with bulk flakes without nanomeshes. Critical temperature annealing results in the formation of zigzag pore edges and interpore zigzag-edge nanoribbons. We unveil that the non-oxide (O) termination of the Fe dangling bonds on these zigzag edges enhances FM behavior, while O-termination suppresses this FM by introducing antiferromagnetic behavior through edge O-Fe coupling. FGT nanomeshes hold promise for the creation of strong FM and their effective application in magnetic and spintronic systems.
substrate小幡 玲二*; 齊藤 英治; 吉川 貴史; 他7名*
Advanced Materials, 36(19), p.2311339_1 - 2311339_8, 2024/05
被引用回数：2 パーセンタイル：25.23(Chemistry, Multidisciplinary)SrTiO (STO) substrate, a perovskite oxide material known for its high dielectric constant (epsilon), facilitates the observation of various (high-temperature) quantum phenomena. A quantum Hall topological insulating (QHTI) state, comprising two copies of QH states with antiparallel two ferromagnetic edge-spin overlap protected by the U(1) axial rotation symmetry of spin polarization, has recently been achieved in low magnetic field (B) even as high as approximate to 100 K in a monolayer graphene/thin hexagonal boron nitride (hBN) spacer placed on an STO substrate, thanks to the high epsilon of STO. Despite the use of the heavy STO substrate, however, proximity-induced quantum spin Hall (QSH) states in 2D TI phases, featuring a topologically protected helical edge spin phase within time-reversal-symmetry, is not confirmed. Here, with the use of a monolayer hBN spacer, it is revealed the coexistence of QSH (at B = 0T) and QHTI (at B not equal 0) states in the same single graphene sample placed on an STO, with a crossover regime between the two at low B. It is also classified that the different symmetries of the two nontrivial helical edge spin phases in the two states lead to different interaction with electron-puddle quantum dots, caused by a local surface pocket of the STO, in the crossover regime, resulting in a spin dephasing only for the QHTI state. The results obtained using STO substrates open the doors to investigations of novel QH spin states with different symmetries and their correlations with quantum phenomena. This exploration holds value for potential applications in spintronic devices.
Fe
O
川本 陽*; 吉川 貴史; 齊藤 英治; 他9名*
Applied Physics Letters, 124(13), p.132406_1 - 132406_7, 2024/03
被引用回数：7 パーセンタイル：68.07(Physics, Applied)Magnon spin currents in the ferrimagnetic garnet TbFe
O with 4 electrons were examined through the spin-Seebeck effect and neutron scattering measurements. The compound shows a magnetic compensation, where the spin-Seebeck signal reverses above and below 
= 249.5(4) K. Unpolarized neutron scattering unveils two major magnon branches with finite energy gaps, which are well explained in the framework of spin-wave theory. Their temperature dependencies and the direction of the precession motion of magnetic moments, i.e., magnon polarization, defined using polarized neutrons, explain the reversal at and decay of the spin-Seebeck signals at low temperatures. We illustrate an example that momentum- and energy-resolved microscopic information is a prerequisite to understand the magnon spin current.
layers on SrTiO substrates小杉 美央子*; 齊藤 英治; 吉川 貴史*; 他11名*
APL Materials (Internet), 11(8), p.081106_1 - 081106_6, 2023/08
被引用回数：2 パーセンタイル：15.21(Nanoscience & Nanotechnology)Strontium titanate [SrTiO (STO)], a perovskite oxide with an extremely high gate-tunable dielectric constant (
) due to quantum paraelectric phases, is attracting considerable attention for yielding various physical phenomena when two-dimensional (2D) layers are integrated. Superconductivity is such a typical phenomenon. However, the influence of the STO substrates on enhancing transition temperatures (
) for (atomically) thin 2D flakes attached to them has been rarely investigated. Here, we report gate-tunable and gradual four-terminal resistance drops with critical onset (
) and scanning tunneling spectroscopy (STS) spectra in devices comprising thin TaS flakes attached on monolayer hexagonal boron nitride (hBN) spacer/STO substrates. Observation of STS spectra confirms the presence of local superconducting gaps. (similar to 1.5 meV) with transition (
three-times higher than previous reports of under absent pressure and strong position dependence of 
. Depending on 
on back gate voltages (
) and magnetic fields, there is a strong correlation between and the onset of superconductivity, implying an enhancement of approximately five times compared with the previous highest-onset values without pressure as the applied increases. The high onset and. are discussed based on screening of the long-range Coulomb interaction (CI) due to the high- of SrTiO, while the short-ranged CI remains strong in the 2D limit, causing the superconductivity. Using a monolayer hBN/SrTiO substrate with opens doors to enhancement in thin superconducting layers integrated on it and wide application due to the solid-state high- substrates.
吉川 貴史*; 齊藤 英治
Annual Review of Condensed Matter Physics, 14, p.129 - 151, 2023/03
被引用回数：49 パーセンタイル：63.84(Physics, Condensed Matter)The spin Seebeck effect (SSE) refers to the generation of a spin current as a result of a temperature gradient in a magnetic material, which can be detected electrically via the inverse spin Hall effect in a metallic contact. Since the discovery of the SSE in 2008, intensive studies on the SSE have been conducted to elucidate its origin. SSEs appear in a wide range of magnetic materials including ferro-, ferri-, and antiferromagnets and also paramagnets with classical or quantum spin fluctuation. SSE voltage reflects fundamental properties of a magnet, such as elementary excitation, static magnetic order, spin correlation, and spin transport. In this article, we review recent progress on the SSE in various systems, with particular emphasis on its emerging role as a probe of these magnetic properties in solids. We also briefly discuss the recently discovered nuclear SSE.
前川 禎通; 吉川 貴史*; 中堂 博之; 家田 淳一; 齊藤 英治
Journal of Applied Physics, 133(2), p.020902_1 - 020902_24, 2023/01
被引用回数：45 パーセンタイル：95.00(Physics, Applied)Along with the progress of spin science and spintronics research, the flow of electron spins, i.e., spin current, has attracted interest. New phenomena and electronic states were explained in succession using the concept of spin current. Moreover, as many of the conventionally known spintronics phenomena became well organized based on spin current, it has rapidly been recognized as an essential concept in a wide range of condensed matter physics. In this article, we focus on recent developments in the physics of spin, spin current, and their related phenomena, where the conversion between spin angular momentum and different forms of angular momentum plays an essential role. Starting with an introduction to spin current, we first discuss the recent progress in spintronic phenomena driven by spin-exchange coupling: spin pumping, topological Hall torque, and emergent inductor. We, then, extend our discussion to the interaction/interconversion of spins with heat, lattice vibrations, and charge current and address recent progress and perspectives on the spin Seebeck and Peltier effects. Next, we review the interaction between mechanical motion and electron/nuclear spins and argue the difference between the Barnett field and rotational Doppler effect. We show that the Barnett effect reveals the angular momentum compensation temperature, at which the net angular momentum is quenched in ferrimagnets.
大柳 洸一*; 高橋 三郎*; 吉川 貴史*; 齊藤 英治
Physical Review B, 107(1), p.014423_1 - 014423_8, 2023/01
被引用回数：16 パーセンタイル：79.46(Materials Science, Multidisciplinary)We have theoretically investigated the spin Seebeck effect (SSE) in a normal metal (NM)/paramagnetic insulator (PI) bilayer system. Through a linear response approach, we calculated the thermal spin pumping from PI to NM and backflow spin current from NM to PI, where the spin-flip scattering via the interfacial exchange coupling between conduction-electron spin in NM and localized spin in PI is taken into account. We found a finite spin current appears at the interface under the difference in the effective temperatures between spins in NM and PI, and its intensity increases by increasing the density of the localized spin S. Our model well reproduces the magnetic-field-induced reduction of the paramagnetic SSE in Pt/GdGaO experimentally observed when the Zeeman energy is comparable to the thermal energy, which can be interpreted as the suppression of the interfacial spin-flip scattering. The present finding provides an insight into the mechanism of paramagnetic SSEs and the thermally induced spin-current generation in magnetic materials.
Lee, O.*; 山本 慧; 埋田 真樹; Zollitsch, C. W.*; Elyasi, M.*; 吉川 貴史*; 齊藤 英治; Bauer, G. E. W.*; 紅林 秀和*
Physical Review Letters, 130(4), p.046703_1 - 046703_6, 2023/01
被引用回数：29 パーセンタイル：93.76(Physics, Multidisciplinary)We experimentally and theoretically demonstrate that nonlinear spin-wave interactions suppress the hybrid magnon-photon quasiparticle or "magnon polariton" in microwave spectra of an yttrium iron garnet film detected by an on-chip split-ring resonator. We observe a strong coupling between the Kittel and microwave cavity modes in terms of an avoided crossing as a function of magnetic fields at low microwave input powers, but a complete closing of the gap at high powers. The experimental results are well explained by a theoretical model including the three-magnon decay of the Kittel magnon into spin waves. The gap closure originates from the saturation of the ferromagnetic resonance above the Suhl instability threshold by a coherent back reaction from the spin waves.
