Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
松下 太樹*; 小沢 耀弘*; 荒木 康史; 藤本 純治*; 佐藤 昌利*
Physical Review B, 111(24), p.245131_1 - 245131_11, 2025/06
被引用回数：1 パーセンタイル：36.38(Materials Science, Multidisciplinary)We investigate the intrinsic spin Nernst effect (SNE), a transverse spin current induced by temperature gradients, in topological Dirac semimetals (TDSMs) and magnetic Weyl semimetals (MWSMs) with Ising spin-orbit coupling. The intrinsic SNE is described by the spin Berry curvature, which reflects the geometric nature of TDSMs and MWSMs. We clarified that the intrinsic SNE becomes significant when the Fermi energy is near, but slightly deviates from, the energy of the point nodes. In this situation, Bloch electrons with strong spin Berry curvature contribute to the SNE while avoiding carrier compensation between electrons and holes. We found that in TDSMs with small Fermi surfaces, the spin Nernst angle, which measures the efficiency of the SNE, is larger than that observed in heavy metals. This suggests that TDSMs with small Fermi surfaces can achieve efficient heat-to-spin current conversion. In MWSMs, variation in the magnitude of the exchange coupling with magnetic moments significantly changes the SNE, affecting both the direction and magnitude of the spin Nernst current. This implies that ferromagnetic transitions can be used to reverse the spin Nernst current. These results provide the fundamentals for future topological spin caloritronics.
能崎 幸雄*; 介川 裕章*; 渡邉 紳一*; 柚木 清司*; 洞口 泰輔*; 中山 颯人*; 山野井 一人*; Wen, Z.*; He, C.*; Song, J.*; et al.
Science and Technology of Advanced Materials, 26(1), p.2428153_1 - 2428153_39, 2025/02
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)We present a novel method for generating spin currents using the gyromagnetic effect, a phenomenon discovered over a century ago. This effect, crucial for understanding the origins of magnetism, enables the coupling between various macroscopic rotational motions and electron spins. While higher rotational speeds intensify the effect, conventional mechanical rotations, typically, below 10,000 RPM, produce negligible results comparable to geomagnetic fluctuations, limiting applied research. Our studies demonstrate that spin current generation comparable to that of rare metals can be achieved through atomic rotations induced by GHz- range surface acoustic waves and the rotational motion of conduction electrons in metallic thin films with nanoscale gradient modulation of electrical conductivity. These effects, termed the acoustic gyromagnetic effect and the current-vorticity gyromagnetic effect, are significant in different contexts.
山野井 一人*; 榊原 有理*; 藤本 純治*; 松尾 衛; 能崎 幸雄*
Applied Physics Express, 16(6), p.063004_1 - 063004_6, 2023/06
被引用回数：0 パーセンタイル：0.00(Physics, Applied)We report a large modulation of spin pumping using temperature-induced magnetic phase transitions in c-axis oriented single crystalline dysprosium (Dy). From the temperature variation of the magnetic susceptibility, transitions from paramagnetic (PM) to ferromagnetic (FM) phases via antiferromagnetic (AFM) phase are clearly observed in the Dy. Unlike polycrystalline Dy, the spin pumping of both PM- and AFM-Dy are strongly suppressed owing to the increased non-dissipative backflow of spin current by the long-range spin transport, although two orders of magnitude difference exist between FM- and AFM-phases.
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：6 パーセンタイル：38.78(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.
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：11 パーセンタイル：50.17(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.
藤本 純治*; 松尾 衛
Physical Review B, 102(2), p.020406_1 - 020406_5, 2020/07
被引用回数：5 パーセンタイル：17.21(Materials Science, Multidisciplinary)The interaction between spin and nanomechanical degrees of freedom attracts interest from the viewpoint of basic science and device applications. We study the magnon current induced by the torsional oscillation of ferromagnetic nanomechanical cantilever. We find that a finite Dzyaloshinskii-Moriya (DM) interaction emerges by the torsional oscillation, which is described by the spin gauge field, and the DM interaction leads to the detectably large magnon current with frequency the same as that of the torsional oscillation. Our theory paves the way for studying torsional spin-nanomechanical phenomena by using the spin gauge field.
藤本 純治*; 松尾 衛
Physical Review B, 100(22), p.220402_1 - 220402_5, 2019/12
被引用回数：1 パーセンタイル：3.40(Materials Science, Multidisciplinary)We investigate an interfacial spin-transfer torque and 
-term torque with alternating current (AC) parallel to a magnetic interface. We find that both torques are resonantly enhanced as the AC frequency approaches the exchange splitting energy. We show that this resonance allows us to estimate directly the interfacial exchange interaction strength from the domain wall motion. We also find that the term includes an unconventional contribution which is proportional to the time derivative of the current and exists even in the absence of any spin relaxation processes.
松下 太樹*; 小沢 耀弘*; 荒木 康史; 藤本 純治*; 佐藤 昌利*
no journal, ,
スピンカロリトロニクスは排熱によるスピンの制御を目的とする研究分野である。スピンゼーベック効果(温度勾配に沿った方向のスピン伝導)とスピンネルンスト効果(温度勾配に垂直な方向のスピン伝導)は、当該研究分野における中心的な現象であり、温度勾配によるスピン流の生成を可能にする。そのため、スピンゼーベック効果は様々な系で研究されてきた。一方で、スピンネルンスト効果は微視的理論が長らく不在であり、その理論研究は乏しかった。また、大きなスピンネルンスト効果を実現する条件は整理されておらず、効率的な熱流-スピン流変換の指針の提案が望まれている。最近、スピンネルンスト効果の微視的理論が提案された。この微視的理論は、ラッティンジャーの重力理論に依拠しており、低温極限でスピン流が非物理的な発散をせず、スピン流のモットの関係式を満たすなど望ましい性質を持つ。さらに、スピンネルンスト効果の内因性機構がスピンベリー曲率と呼ばれる幾何学的量により記述されることも明らかとなった。スピンベリー曲率は、ディラック点やワイル点の周りで発散的に増大する。そのため、ディラック半金属やワイル半金属の幾何学的性質が、大きなスピンネルンスト効果を実現する可能性がある。本発表においては、ディラック半金属と磁性ワイル半金属における内因性スピンネルンスト効果の理論研究の成果を報告する。はじめに、内因性スピンネルンスト効果の公式を示し、強いスピンネルンスト効果が得られる条件を整理する。その後、ディラック半金属と磁性ワイル半金属におけるスピンネルンスト効果について、点ノードのエネルギーに対する依存性を議論し、これらのトポロジカル物質の幾何学的性質が大きなスピンネルンスト効果を実現し、効率的な熱流-スピン流変換に利用できることを示す。
