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論文

Generation of megahertz-band spin currents using nonlinear spin pumping

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:4 パーセンタイル:64.36(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 Y$$_3$$Fe$$_5$$O$$_{12}$$. 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.

論文

One-dimensional spinon spin currents

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:46 パーセンタイル:3.41(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$$_{2}$$CuO$$_{3}$$. The results show that spin current can flow even in an atomic channel owing to long-range spin fluctuation.

論文

Generation of spin currents in the skyrmion phase of a helimagnetic insulator Cu$$_2$$OSeO$$_3$$

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:7 パーセンタイル:58.66(Physics, Applied)

We report spin-current generation related to skyrmion dynamics resonantly excited by a microwave in a helimagnetic insulator Cu$$_2$$OSeO$$_3$$. A Pt layer was fabricated on Cu$$_2$$OSeO$$_3$$ and voltage in the Pt layer was measured upon magnetic resonance of Cu$$_2$$OSeO$$_3$$ 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 Cu$$_2$$OSeO$$_3$$ as well as in the ferrimagnetic phase, which shows that magnetic skyrmions can contribute to the spin pumping effect.

論文

Effect of spin Hall magnetoresistance on spin pumping measurements in insulating magnet/metal systems

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。

論文

Effect of spin Hall magnetoresistance on spin pumping measurements in insulating magnet/metal systems

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:19 パーセンタイル:28.08(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.

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