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廣部 大地*; 佐藤 正寛*; 萩原 雅人*; 塩見 雄毅*; 益田 隆嗣*; 齊藤 英治
Physical Review Letters, 123(11), p.117202_1 - 117202_7, 2019/09
被引用回数：17 パーセンタイル：70.71(Physics, Multidisciplinary)Investigating exotic magnetic materials with spintronic techniques is effective at advancing magnetism as well as spintronics. In this work, we report unusual field-induced suppression of the spin Seebeck effect (SSE) in a quasi-one-dimensional frustrated spin-
magnet LiCuVO
, known to exhibit spin-nematic correlation in a wide range of external magnetic field 
. The suppression takes place above 
T in spite of the -linear isothermal magnetization curves in the same range. The result can be attributed to the growth of the spin-nematic correlation while increasing . The correlation stabilizes magnon pairs carrying spin 2, thereby suppressing the interfacial spin injection of SSE by preventing the spin-1 exchange between single magnons and conduction electrons at the interface. This interpretation is supported by integrating thermodynamic measurements and theoretical analysis on the SSE.
and CrGeTe伊東 直洋*; 吉川 貴史*; Barker, J.*; 廣部 大地*; 塩見 雄毅*; 齊藤 英治
Physical Review B, 100(6), p.060402_1 - 060402_6, 2019/08
被引用回数：54 パーセンタイル：88.83(Materials Science, Multidisciplinary)We have studied the longitudinal spin Seebeck effect (LSSE) in the layered ferromagnetic insulators CrSiTe and CrGeTe covered by Pt films in the measurement configuration where spin current traverses the ferromagnetic Cr layers. The LSSE response is clearly observed in the ferromagnetic phase and, in contrast to a standard LSSE magnet YFe
O
, persists above the critical temperatures in both CrSiTe/Pt and CrGeTe/Pt samples. With the help of a numerical calculation, we attribute the LSSE signals observed in the paramagnetic regime to exchange-dominated interlayer transport of in-plane paramagnetic moments reinforced by short-range ferromagnetic correlations and strong Zeeman effects.
亀田 麻衣*; 廣部 大地*; 大門 俊介*; 塩見 雄毅*; 高橋 三郎*; 齊藤 英治
Journal of Magnetism and Magnetic Materials, 476, p.459 - 463, 2019/04
被引用回数：2 パーセンタイル：8.54(Materials Science, Multidisciplinary)Nonlinear effects of spin pumping have been investigated by numerically calculating the temporal evolution of the magnon number affected by three- and four-magnon interactions. We showed that the three-magnon interaction gives rise to the enhancement of spin-pumping spin current. We also found that the four-magnon interaction in combination with the three-magnon interaction can be responsible for the experimentally observed low-frequency oscillation of spin current.
塩見 雄毅*; Lustikova, J.*; 渡辺 真悟*; 廣部 大地*; 高橋 三郎*; 齊藤 英治
Nature Physics, 15(1), p.22 - 26, 2018/10
被引用回数：21 パーセンタイル：75.53(Physics, Multidisciplinary)Various spintronic phenomena originate from the exchange of angular momentum between the spin of electrons and other degrees of freedom in crystalline materials. Many degrees of freedom, such as magnetization and mechanical motion, have already been united into this exchange framework. However, the nuclear spin -a key angular momentum- has yet to be incorporated. Here we observe spin pumping from nuclear magnetic resonance (NMR), in which nuclear spin dynamics emits a spin current, a flow of spin angular momentum of electrons. By using the canted antiferromagnet MnCO, in which typical nuclear spin-wave formation is established due to the reinforced hyperfine coupling, we find that a spin current is generated from an NMR. Nuclear spins are indispensable for quantum information technology and are also frequently used in various sensors, such as in magnetic resonance imaging. The observed NMR spin pumping allows spin-current generation from nuclei and will enable spintronic detection of nuclear spin states.
渡辺 真悟*; 廣部 大地*; 塩見 雄毅*; 井口 亮*; 大門 俊介*; 亀田 麻衣*; 高橋 三郎*; 齊藤 英治
Scientific Reports (Internet), 7, p.4576_1 - 4576_6, 2017/07
被引用回数：7 パーセンタイル：26.22(Multidisciplinary Sciences)Spin pumping enables the generation of d.c. and gigahertz-band (GHz-band) voltages from an applied microwave via magnetization dynamics when combined with inverse spin Hall effects. However, generating such voltages in the in-between frequency region, or the megahertz (MHz) band, has been difficult since ferromagnetic resonance usually occurs in the GHz band. Here we show that in spite of GHz-band microwaves applied, MHz-band voltages can be generated by spin pumping with use of nonlinear magnetization dynamics in YFeO. The mechanism is ascribed to the MHz-band oscillation of the amplitude of the magnetization precession, which is projected onto a rectified voltage component via spin pumping. The present finding could be useful for frequency down-conversion thanks to the simple and durable structure, continuous-wave operation, and the tunability of an output frequency with low magnetic fields.
廣部 大地*; 佐藤 正寛*; 川股 隆行*; 塩見 雄毅*; 内田 健一*; 井口 亮*; 小池 洋二*; 前川 禎通; 齊藤 英治
Nature Physics, 13(1), p.30 - 34, 2017/01
被引用回数：122 パーセンタイル：96.97(Physics, Multidisciplinary)Quantum spin fluctuation in a low-dimensional or frustrated magnet breaks magnetic ordering while keeping spin correlation. Such fluctuation has been a central topic in magnetism because of its relevance to high-Tc superconductivity and topological states. However, utilizing such spin states has been quite difficult. In a one-dimensional spin-1/2 chain, a particle-like excitation called a spinon is known to be responsible for spin fluctuation in a paramagnetic state. Spinons behave as a Tomonaga-Luttinger liquid at low energy, and the spin system is often called a quantum spin chain. Here we show that a quantum spin chain generates and carries spin current, which is attributed to spinon spin current. This is demonstrated by observing an anisotropic negative spin Seebeck effect along the spin chains in Sr
CuO
. The results show that spin current can flow even in an atomic channel owing to long-range spin fluctuation.
OSeO廣部 大地*; 塩見 雄毅*; 嶋田 裕樹*; 大江 純一郎*; 齊藤 英治
Journal of Applied Physics, 117(5), p.053904_1 - 053904_6, 2015/02
被引用回数：9 パーセンタイル：35.42(Physics, Applied)We report spin-current generation related to skyrmion dynamics resonantly excited by a microwave in a helimagnetic insulator CuOSeO. A Pt layer was fabricated on CuOSeO and voltage in the Pt layer was measured upon magnetic resonance of CuOSeO to electrically detect injected spin currents via the inverse spin Hall effect (ISHE) in Pt. We found that ISHE-induced electromotive forces appear in the skyrmion phase of CuOSeO as well as in the ferrimagnetic phase, which shows that magnetic skyrmions can contribute to the spin pumping effect.
井口 亮*; 佐藤 浩司*; 廣部 大地*; 大門 俊介*; 齊藤 英治
Applied Physics Express, 7(1), p.013003_1 - 013003_4, 2014/01
磁気抵抗効果がある系では、磁化運動による交流起電力が整流されて直流電圧が生じることが知られている。本研究では、磁性絶縁体/金属複合膜で生じるスピンHall磁気抵抗効果が引き起こす整流電圧のスピンポンピングに対する影響を調べた。スピンHall磁気抵抗効果で整流された直流電圧は、薄膜面内の磁場角度変化に対して、スピンポンピングから生じる逆スピンHall起電力とは異なる角度依存性を示すことを理論的に示すと同時に、マイクロ波キャビティを用いた実験において、この電圧の影響は無視できる大きさであることを実証した。
井口 亮*; 佐藤 浩司*; 廣部 大地*; 大門 俊介*; 齊藤 英治
Applied Physics Express, 7(1), p.013003_1 - 013003_4, 2014/01
被引用回数：21 パーセンタイル：62.63(Physics, Applied)We investigate a dc rectification effect of magnetization dynamics based on spin Hall magnetoresistance (SMR) in an insulating magnet/metal system on spin pumping measurements. We theoretically find that the rectification effect by SMR has different in-plane magnetization angle dependence from that of the inverse spin Hall effect on the spin pumping. The negligible contribution from the rectification effect is experimentally confirmed in a cavity measurement.
