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論文

Magnetic and fermi surface properties of semimetals EuAs$$_3$$ and Eu(As$$_{1-x}$$P$$_x$$)$$_3$$

大貫 惇睦*; 軽部 皓介*; 青木 大*; 仲村 愛*; 本間 佳哉*; 松田 達磨*; 芳賀 芳範; 竹内 徹也*

Journal of the Physical Society of Japan, 92(11), p.114703_1 - 114703_12, 2023/11

https://doi.org/10.7566/JPSJ.92.114703
 被引用回数：1 パーセンタイル：22.15(Physics, Multidisciplinary)

Single crystal samples of a series of semimetallic magnet Eu(As$$_{1-x}$$P$$_x$$)$$_3$$ have successfully grown. By measuring magnetization, Hall resistivity and de Haas-van Alphen oscillations, large anomalous Hall resistivity arising from peculiar magnetic phase diagram was identified.

論文

Intercorrelated anomalous Hall and spin Hall effect in kagome-lattice Co$$_{3}$$Sn$$_{2}$$S$$_{2}$$-based shandite films

Lau, Y.-C.*; 池田 絢哉*; 藤原 宏平*; 小沢 耀弘*; Zheng, J.*; 関 剛斎*; 野村 健太郎*; Du, L.*; Wu, Q.*; 塚崎 敦*; et al.

Physical Review B, 108(6), p.064429_1 - 064429_11, 2023/08

https://doi.org/10.1103/PhysRevB.108.064429
 被引用回数：11 パーセンタイル：72.60(Materials Science, Multidisciplinary)

Magnetic Weyl semimetals (mWSMs) are characterized by linearly dispersive bands with chiral Weyl node pairs associated with broken time-reversal symmetry. One of the hallmarks of mWSMs is the emergence of large intrinsic anomalous Hall effect. On heating the mWSM above its Curie temperature, the magnetism vanishes while exchange-split Weyl point pairs collapse into doubly degenerate gapped Dirac states. Here, we reveal the attractive potential of these Dirac nodes in paramagnetic state for efficient spin current generation at room temperature via the spin Hall effect. Ni and In are introduced to separately substitute Co and Sn in a prototypal mWSM Co$$_{3}$$Sn$$_{2}$$S$$_{2}$$ shandite film and tune the Fermi level. Composition dependence of spin Hall conductivity for paramagnetic shandite at room temperature resembles that of anomalous Hall conductivity for ferromagnetic shandite at low temperature; exhibiting peak-like dependence centering around the Ni-substituted Co$$_{3}$$Ni$$_{1}$$Sn$$_{2}$$S$$_{2}$$ and undoped Co$$_{3}$$Sn$$_{2}$$S$$_{2}$$ compositions, respectively. The observed spin Hall and anomalous Hall conductivity maxima at different compositions reflect optimum Fermi-level positioning relative to the paramagnetic Dirac and magnetic Weyl states, suggesting the common origin and intercorrelation between the two Hall effects. Our findings highlight a strategy for the quest of spin Hall materials, guided by the abundant experimental anomalous Hall-effect data of ferromagnets in the literature.

論文

Spontaneous topological Hall effect induced by non-coplanar antiferromagnetic order in intercalated van der Waals materials

高木 寛貴*; 高木 里奈*; 見波 将*; 野本 拓也*; 大石 一城*; 鈴木 通人*; 柳 有起*; 平山 元昭*; Khanh, N.*; 軽部 皓介*; et al.

Nature Physics, 19(7), p.961 - 968, 2023/07

https://doi.org/10.1038/s41567-023-02017-3
 被引用回数：55 パーセンタイル：99.13(Physics, Multidisciplinary)

In ferromagnets, electric current generally induces a transverse Hall voltage in proportion to the internal magnetization. This effect is frequently used for electrical readout of the spin up and down states. While these properties are usually not expected in antiferromagnets, recent theoretical studies predicted that non-coplanar antiferromagnetic order with finite scalar spin chirality - meaning a solid angle spanned by neighboring spins - can induce a large spontaneous Hall effect even without net magnetization or external magnetic field. This phenomenon, the spontaneous topological Hall effect, can potentially be used for the efficient electrical readout of the antiferromagnetic states, but it has not been experimentally verified due to a lack of appropriate materials hosting such magnetism. Here, we report the discovery of all-in-all-out type non-coplanar antiferromagnetic order in triangular lattice compounds CoTa$$_{3}$$S$$_{6}$$ and CoNb$$_{3}$$S$$_{6}$$. These compounds are reported to host unconventionally large spontaneous Hall effect despite their vanishingly small net magnetization, and our analysis reveals that it can be explained in terms of the topological Hall effect that originates from the fictitious magnetic field associated with scalar spin chirality. These results indicate that the scalar spin chirality mechanism offers a promising route to the realisation of giant spontaneous Hall response even in compensated antiferromagnets, and highlight intercalated van der Waals magnets as a promising quasi-two-dimensional material platform to enable various nontrivial ways of electrical reading and possible writing of non-coplanar antiferromagnetic domains.

論文

Skew scattering from correlated systems; Impurities and collective excitations in the spin Hall effect

Ziman, T.*; Gu, B.; 前川 禎通

Journal of the Physical Society of Japan, 86(1), p.011005_1 - 011005_8, 2017/01

https://doi.org/10.7566/JPSJ.86.011005
 被引用回数：1 パーセンタイル：11.01(Physics, Multidisciplinary)

We examine the enhancement of the spin Hall effect due to resonant skew scattering induced by electron correlations. For single-impurity scattering, local Coulomb correlations may significantly change the observed spin Hall angle. There may be additional effects because of the special atomic environment close to a surface: extra degeneracies compared to the bulk, enhanced correlations that move the relative $$d$$- or $$f$$-levels, and interference effects coming from the lower local dimension. Our results may explain the very large spin Hall angle observed in CuBi alloys. We discuss the impact on the spin Hall effect from cooperative effects, firstly in an itinerant ferromagnet where there is an anomaly near the Curie temperature originating from high-order spin fluctuations. The second case considered is a metallic spin glass, where exchange via slowly fluctuating magnetic moments may lead to the precession of an injected spin current.

口頭

Spin mechatronics; Mechanical generation of spin current

前川 禎通

no journal, , 

We introduce mechanical effects in spintronics and propose a variety of novel spintronics phenomena. The mechanical generation of spin and spin current opens a door from "Spintronics" to "Spin-Mechatronics."

口頭

Spin dependent transport in ferromagnetic high-entropy-alloy thin films

高梨 弘毅

no journal, , 

High-entropy alloys (HEAs) have attracted considerable attention, however, most of studies have been conducted using bulk magnets, and the spin-dependent transport in ferromagnetic HEA thin films have not been well investigated. In this study, we focus on FeCoNiCuPd HEAs, which exhibit a Curie temperature higher than room temperature and contain a heavy element (Pd) with relatively large spin-orbit interaction. The thin-film samples with different composition ratios of Cu and Pd under the same amount of FeCoNi, Fe$$_{20}$$Ni$$_{20}$$Co$$_{20}$$Cu$$_{X}$$Pd$$_{Y}$$ (0$$<$$X+Y$$<$$40), were prepared on thermally oxidized Si substrates at an ambient temperature by an ultrahigh vacuum sputtering system. All the films exhibited ferromagnetic hysteresis curves with soft magnetic behavior at room temperature. The saturation magnetization increased linearly with the Pd concentration, which might be attributed mainly to the induced Pd moment. Anisotropic magnetoresistance effect (AMR) and anomalous Hall effect (AHE) were measured for Hall-bar devices fabricated by conventional photolithography and Ar milling process. The MR ratio and the anomalous Hall conductivity showed a smooth, simple increase with the Pd concentration, suggesting that the spin-orbit interaction of constituent elements plays a significant role on the AMR and the AHE in ferromagnetic HEAs.

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