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Lyons, T. P.*; Puebla, J.*; 山本 慧; Deacon, R. S.*; Hwang, Y.*; 石橋 幸治*; 前川 禎通*; 大谷 義近*
Physical Review Letters, 131(19), p.196701_1 - 196701_6, 2023/11
被引用回数：0Harnessing the causal relationships between mechanical and magnetic properties of van der Waals materials presents a wealth of untapped opportunity for scientific and technological advancement, from precision sensing to novel memories. This can, however, only be exploited if the means exist to efficiently interface with the magnetoelastic interaction. Here, we demonstrate acoustically-driven spin-wave resonance in a crystalline antiferromagnet, chromium trichloride, via surface acoustic wave irradiation. The resulting magnon-phonon coupling is found to depend strongly on sample temperature and external magnetic field orientation, and displays a high sensitivity to extremely weak magnetic anisotropy fields in the few mT range. Our work demonstrates a natural pairing between power-efficient strain-wave technology and the excellent mechanical properties of van der Waals materials, representing a foothold towards widespread future adoption of dynamic magneto-acoustics.
Liao, L.*; Puebla, J.*; 山本 慧; Kim, J.*; 前川 禎通*; Hwang, Y.*; Ba, Y.*; 大谷 義近*
Physical Review Letters, 131(17), p.176701_1 - 176701_6, 2023/10
被引用回数：0Phonons and magnons are engineered by periodic potential landscapes in phononic and magnonic crystals, and their combined studies may enable valley phonon transport tunable by the magnetic field. Through nonreciprocal surface acoustic wave transmission, we demonstrate valley-selective phonon-magnon scattering in magnetoelastic superlattices. The lattice symmetry and the out-of-plane magnetization component control the sign of nonreciprocity. The phonons in the valleys play a crucial role in generating nonreciprocal transmission by inducing helical strains that couple with the magnons. The transmission spectra show a nonreciprocity peak near a transmission gap, matching the phononic band structure. Our results open the way for manipulating valley phonon transport through periodically varying magnon-phonon coupling.
Chen, J.*; 山本 慧; Zhang, J.*; Ma, J.*; Wang, H.*; Sun, Y.*; Chen, M.*; Ma, J.*; Liu, S.*; Gao, P.*; et al.
Physical Review Applied (Internet), 19(2), p.024046_1 - 024046_9, 2023/02
被引用回数：4 パーセンタイル：90.23(Physics, Applied)Coherent coupling in magnon based hybrid system has many potential applications in quantum information processing. Magnons can propagate in magnetically ordered materials without any motion of electrons, offering a unique method to build low-power-consumption devices and information channels free of heat dissipation. In this article, we demonstrate the coherent propagation of hybridized modes between spin waves and Love surface acoustic waves in a multiferroic BiFeO
and ferromagnetic La
Sr
MnO based heterostructure. The magneto-elastic coupling enables a giant enhancement of strength of the hybridized mode by a factor of 26 compared to that of the pure spin waves. A short wavelength down to 250 nm is demonstrated for the hybridized mode, which is desirable for nanoscale acousto-magnonic applications. Our combined experimental and theoretical analyses represent an important step towards the coherent control in hybrid magnonics, which may inspire the study of magnon-phonon hybrid systems for coherent information processing and manipulation.
森 道康; 前川 禎通
Applied Physics Letters, 122(4), p.042202_1 - 042202_5, 2023/01
被引用回数：3 パーセンタイル：85.09(Physics, Applied)We show that ultrasound can induce the Shapiro steps (SS) in the charge-density-wave (CDW) state. When ultrasound with frequency 
and a dc voltage are applied, the SS occur at the current 
with integer 
. Even and odd multiples of SS are represented by two couplings between the CDW and ultrasound. Although an ac voltage bias with frequency induces the SS at , the ultrasound bias enhances the odd multiples more strongly than the even ones. This is the difference between the ultrasound and the ac voltage. Since the SS cause abrupt peaks in the 
, the extreme changes in the 
curve will be applied to a very sensitive ultrasound detector.
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：9 パーセンタイル：96.84(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.
山本 慧; 前川 禎通*
Annalen der Physik, 11 Pages, 2023/00
被引用回数：0 パーセンタイル：0(Physics, Multidisciplinary)We derive a general expression for the magnetostatic field generated by mechanical deformations to a ferromagnetic material in the continuum description. Linearization with respect to the displacement vector is shown to be well defined. To demonstrate the use of the formulation, we discuss two examples. Firstly, a complete derivation of the magneto-rotation coupling for a uniformly magnetized film is given. Secondly, the lowest asymmetric mode of Lamb waves propagating through a magnetic vortex is shown to induce in-plane magnetostatic field localized around the vortex core.
藤本 純治*; 船木 博志*; 小椎八重 航*; 松尾 衛; 前川 禎通*
IEEE Transactions on Magnetics, 58(8), p.1500407_1 - 1500407_7, 2022/08
被引用回数：0 パーセンタイル：0(Engineering, Electrical & Electronic)Motivated by the recent experiment done by Yu et al. [X. Z. Yu, et. al., Sci. Adv., 6, 25, eaaz9744 (2020)] on magnetic skyrmion creation and annihilation by electric currents in FeGe devices with a notch structure, we examine the interaction between the electric current vorticity near the notch and localized spins, and obtain three effects of the current vorticity on the localized spins. The first one is an effective Zeeman field induced by the current vorticity. This effective Zeeman field is responsible for skyrmion creation. The second effect is a vorticity-induced Dzyaloshinskii-Moriya (DM) interaction with the direction of the DM vector being parallel to the vorticity direction and is different from the vector of the intrinsic DM interaction. This vorticity-induced DM interaction makes the skyrmions distorted. The third effect is a spin current due to the gradient of the vorticity and the spin current drives the magnetic skyrmions far from the notch. Our theory opens a new path to design the magnetic textures by using structural settings.
K
(Zn
Mn
)
As studied by X-ray magnetic circular dichroism and resonant inelastic X-ray scattering鈴木 博人*; Zhao, G.*; 岡本 淳*; 坂本 祥哉*; Chen, Z.-Y.*; 野中 洋亮*; 芝田 悟朗; Zhao, K.*; Chen, B.*; Wu, W.-B.*; et al.
Journal of the Physical Society of Japan, 91(6), p.064710_1 - 064710_5, 2022/06
被引用回数：0 パーセンタイル：0(Physics, Multidisciplinary)The magnetic properties and the electronic excitations of the new diluted magnetic semiconductor BaK(ZnMn)As have been studied by X-ray magnetic circular dichroism (XMCD) and resonant inelastic X-ray scattering (RIXS). The sum rule analysis of the XMCD spectra indicates that the Mn atoms are in the high-spin configurations of 
, whereas the presence of competing ferromagnetic and antiferromagnetic interactions between the Mn ions reduces the net spin moment. Based on a comparison of the RIXS line shapes with those of GaMnAs, it is concluded that the ground state of Mn in BaK(ZnMn)As consists of both the 
and 
electron configurations.
Puebla, J.*; Hwang, Y.*; 前川 禎通*; 大谷 義近*
Applied Physics Letters, 120(22), p.220502_1 - 220502_9, 2022/05
被引用回数：18 パーセンタイル：92.05(Physics, Applied)Surface acoustic waves (SAWs) are elastic waves propagating on the surface of solids with the amplitude decaying into the solid. The well- established fabrication of compact SAW devices, together with well-defined resonance frequencies, places SAWs as an attractive route to manipulate the magnetization states in spintronics, all of which is made possible by the magnetostriction and magnetoelastic effects. Here, we review the basic characteristics of SAW devices and their interaction out-of-resonance and in-resonance with the magnetization in thin films. We describe our own recent results in this research field and closely related works and provide our perspectives moving forward.
山本 慧; Xu, M.*; Puebla, J.*; 大谷 義近*; 前川 禎通*
Journal of Magnetism and Magnetic Materials, 545, p.168672_1 - 168672_10, 2022/03
被引用回数：10 パーセンタイル：52.49(Materials Science, Multidisciplinary)We present a theoretical description of magnon-phonon interactions in a multi-layer structure containing a ferromagnetic thin film. The formalism is applicable to an arbitrary direction of external magnetic field and various types of acoustic waves including Rayleigh and Love surface modes. A particular attention is paid to the spatial profile of the acoustic wave modes and analytical expressions for the effective coupling coefficients are derived taking into account the degree of mode profile overlap between spin waves and acoustic waves. The results are applied to reproduce a strongly anisotropic and non-reciprocal linewidth of acoustic ferromagnetic resonance reported in a recent experiment.
/LaSrMnO heterostructuresZhang, J.*; Chen, M.*; Chen, J.*; 山本 慧; Wang, H.*; Hamdi, M.*; Sun, Y.*; Wagner, K.*; He, W.*; Zhang, Y.*; et al.
Nature Communications (Internet), 12, p.7258_1 - 7258_8, 2021/12
被引用回数：14 パーセンタイル：77.64(Multidisciplinary Sciences)Magnons can transfer information in metals and insulators without Joule heating, and therefore are promising for low-power computation. The on-chip magnonics however suffers from high losses due to limited magnon decay length. In metallic thin films, it is typically on the tens of micrometre length scale. Here, we demonstrate an ultra-long magnon decay length of up to one millimetre in multiferroic/ferromagnetic BiFeO(BFO)/LaSrMnO (LSMO) heterostructures at room temperature. This decay length is attributed to a magnon-phonon hybridization and is more than two orders of magnitude longer than that of bare metallic LSMO. The long-distance modes have high group velocities of 2.5 km
as detected by time-resolved Brillouin light scattering. Numerical simulations suggest that magnetoelastic coupling via the BFO/LSMO interface hybridizes phonons in BFO with magnons in LSMO. Our results provide a solution to the long-standing issue on magnon decay lengths in metallic magnets and advance the bourgeoning field of hybrid magnonics.
-Josephson junction森 道康; 前川 禎通
Applied Physics Express, 14(10), p.103001_1 - 103001_4, 2021/10
被引用回数：0 パーセンタイル：0(Physics, Applied)A superconducting quantum interference device (SQUID) comprising 0- and -Josephson junctions (JJs), called -SQUID, is studied by the resistively shunted junction model. The -SQUID shows half-integer Shapiro-steps (SS) under microwave irradiation at the voltage 
= 
, with angular frequency 
and half-integer /2 in addition to integer . We show that the -SQUID can be a -qubit with spontaneous loop currents by which the half-integer SS are induced. Making the 0- and -JJs equivalent is a key for the half-integer SS and realizing the -qubit.
Yao, Y.*; Cai, R.*; Yang, S.-H.*; Xing, W.*; Ma, Y.*; 森 道康; Ji, Y.*; 前川 禎通; Xie, X.-C.*; Han, W.*
Physical Review B, 104(10), p.104414_1 - 104414_6, 2021/09
被引用回数：2 パーセンタイル：7.92(Materials Science, Multidisciplinary)We report the experimental observation of half-integer Shapiro steps in the strong ferromagnetic Josephson junction (Nb-NiFe-Nb) by investigating the current-phase relation under radio-frequency microwave excitation. The half-integer Shapiro steps are robust in a wide temperature range from T = 4 to 7 K. The half-integer Shapiro steps could be attributed to co-existence of 0- and -states in the strong ferromagnetic NiFe Josephson junctions with the spatial variation of the NiFe thickness. This scenario is also supported by the high-resolution transmission electron microscopy characterization of the Nb/NiFe/Nb junction.
中堂 博之; 今井 正樹; 松尾 衛; 前川 禎通; 齊藤 英治
Journal of the Physical Society of Japan, 90(8), p.081003_1 - 081003_11, 2021/08
被引用回数：3 パーセンタイル：41.09(Physics, Multidisciplinary)We demonstrate observation of the angular momentum compensation temperature 
, at which the net angular momentum is quenched in ferrimagnets. Using the Barnett effect, in which an object is magnetized by mechanical rotation owing to spin-rotation coupling, we measure in the Ho
Dy
Fe
O
system. We determine to be 240 K in HoFeO (HoIG). We find that increases with Dy content and show that of Ho
DyFeO corresponds with room temperature. We also demonstrate that 
Fe-NMR measurements can be applied to explore domain wall dynamics in HoIG. We find that the NMR intensity exhibits a maximum at in the multi-domain state. We provide a simple model for describing this NMR signal enhancement caused by enhancement of domain-wall mobility at .
藤本 純治*; 小椎八重 航*; 松尾 衛; 前川 禎通
Physical Review B, 103(22), p.L220402_1 - L220402_5, 2021/06
被引用回数：4 パーセンタイル：36.85(Materials Science, Multidisciplinary)The Dzyaloshinskii-Moriya interaction, i.e., antisymmetric exchange interaction, combined with a Zeeman magnetic field gives rise to various magnetic states such as chiral, helical, and skyrmionic states. This interaction conventionally originates from spin-orbit coupling and thus needs somewhat heavy elements. In contrast, we here show a Dzyaloshinskii-Moriya interaction which is driven by electric current vorticity. We also find that the vorticity acts on localized spins as a Zeeman field, which may explain a recent experiment on current-driven magnetic skyrmion creation and annihilation without an external magnetic field in a device with a notch structure in FeGe. The theory explains the control of skyrmion creation and annihilation by current direction and opens different possibilities for studies of magnetic textures by using structural settings.
中堂 博之; 松尾 衛*; 前川 禎通*; 齊藤 英治
Physical Review B, 103(17), p.174308_1 - 174308_10, 2021/05
被引用回数：5 パーセンタイル：44.86(Materials Science, Multidisciplinary)We report the observation of the Barnett field, rotational Doppler effect, and Berry phase using the rotating nuclear quadrupole resonance (NQR) methods. We have developed coil-spinning techniques that enable us to systematically study the effects of rotation in setups involving rotation of the signal detector, rotation of the sample, and simultaneous rotation of both the signal detector and sample. Applying these setups to NQR measurements, we observe NQR line splittings in which the spectral structures are clearly distinct among the setups. By analyzing these structures, we clarify the origin of the NQR line splittings and discuss the relationship between the rotational Doppler effect, Barnett field effect, and Berry phase in terms of the rotational degrees of freedom, such as the relative rotation and the sample rotation itself, and the observation frame of reference. We also provide clear evidence of the difference between the rotational Doppler effect and the Barnett field, and the equivalence of the Barnett field and the Berry phase.
松岡 秀樹*; Barnes, S. E.*; 家田 淳一; 前川 禎通; Bahramy, M. S.*; Saika, B. K.*; 竹田 幸治; 和達 大樹*; Wang, Y.*; 吉田 訓*; et al.
Nano Letters, 21(4), p.1807 - 1814, 2021/02
被引用回数：13 パーセンタイル：77.64(Chemistry, Multidisciplinary)Magnetocrystalline anisotropy, a key ingredient for establishing long-range order in a magnetic material down to the two-dimensional (2D) limit, is generally associated with spin-orbit interaction (SOI) involving a finite orbital angular momentum. Here we report strong out-of-plane magnetic anisotropy without orbital angular momentum, emerging at the interface between two different van der Waals (vdW) materials, an archetypal metallic vdW material NbSe
possessing Zeeman-type SOI and an isotropic vdW ferromagnet V
Se
. We found that the Zeeman SOI in NbSe induces robust out-of-plane magnetic anisotropy in VSe
down to the 2D limit with a more than 2-fold enhancement of the transition temperature. We propose a simple model that takes into account the energy gain in NbSe in contact with a ferromagnet, which naturally explains our observations. Our results demonstrate a conceptually new magnetic proximity effect at the vdW interface, expanding the horizons of emergent phenomena achievable in vdW heterostructures.
山本 慧; Yu, W.*; Yu, T.*; Puebla, J.*; Xu, M.*; 前川 禎通*; Bauer, G.*
Journal of the Physical Society of Japan, 89(11), p.113702_1 - 113702_5, 2020/11
被引用回数：10 パーセンタイル：62.22(Physics, Multidisciplinary)We predict that surface acoustic waves are generated preferentially in one direction in a heterostructure of a thin magnetic film on a non-magnetic substrate. The non-reciprocity arises from magneto-elastic coupling and magneto-rotation coupling, the former being dominant for YIG/GGG heterostructures. For YIG films thinner than about 100 nm, the surface acoustic wave amplitude is nearly unidirectional at certain angles of the in-plane equilibrium magnetisation. We compute the full magnetic field dependence of the effect for a selected device.
栗宗 勇貴*; 松尾 衛; 前川 禎通; 能崎 幸雄*
Physical Review B, 102(17), p.174413_1 - 174413_7, 2020/11
被引用回数：16 パーセンタイル：73.04(Materials Science, Multidisciplinary)A nonuniform vorticity of lattice deformation in a surface acoustic wave (SAW) can generate a spin current (SC) in nonmagnetic metals via spin-vorticity coupling (SVC). We demonstrated a strong enhancement of SVC derived SC generated in Cu and Pt films with increasing the frequency of the SAW by observing the spin-wave resonance (SWR) in an adjacent NiFe film. The comparative amplitudes and high-order frequency variations of SWR in NiFe/Cu and NiFe/Pt bilayers imply that the amplitude of the SC generated via SVC in a SAW is robust against the strength of spin-orbit interaction in nonmagnetic metals.
中堂 博之; 松尾 衛*; 針井 一哉*; 前川 禎通*; 齊藤 英治
Applied Physics Express, 13(10), p.109102_1 - 109102_2, 2020/10
被引用回数：3 パーセンタイル：52.38(Physics, Applied)バーネット効果とは物体を回転させるとその物体が磁化する現象である。これは磁気モーメントに対して回転座標系での慣性力として磁場が働くと解釈できる。その磁場をバーネット磁場と呼ぶ。バーネット磁場は慣性力であるために、高速で回転する物体と同じ速度で回転する測定系が必要である。我々は新規にコイル回転法を独自開発し、その共振回路を用いて核磁気共鳴法(NMR)測定を行ったところ、核磁気モーメントに働くバーネット磁場によってNMRの共鳴周波数が回転数に比例してシフトするという結果を得た。この成果は2014年にApplied Physics Expressに掲載されたが、2018年の夏、Jean Jeener人物から、我々が測定したものはバーネット磁場ではなく、コイルを回転させた事による人為的な効果であるとの批判が出た。本論文はこれに対する我々の返答である。
