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論文

Vortex rectenna powered by environmental fluctuations

Lustikova, J.*; 塩見 雄毅*; 横井 直人*; 壁谷 典幸*; 木村 憲彰*; 家永 紘一郎*; 金子 真一*; 大熊 哲*; 高橋 三郎*; 齊藤 英治

Nature Communications (Internet), 9, p.4922_1 - 4922_6, 2018/11

 被引用回数:1 パーセンタイル:100(Multidisciplinary Sciences)

A rectenna, standing for a rectifying antenna, is an apparatus which generates d.c. electricity from electric fluctuations. It is expected to realize wireless power transmission as well as energy harvesting from environmental radio waves. To realize such rectification, devices that are made up of internal atomic asymmetry such as an asymmetric junction have been necessary so far. Here we report a material that spontaneously generates electricity by rectifying environmental fluctuations without using atomic asymmetry. The sample is a common superconductor without lowered crystalline symmetry, but, just by putting it in an asymmetric magnetic environment, it turns into a rectifier and starts generating electricity. Superconducting vortex strings only annihilate and nucleate at surfaces, and this allows the bulk electrons to feel surface fluctuations in an asymmetric environment: a vortex rectenna. The rectification and generation can be switched on and off with only a slight change in temperature or external magnetic fields.

論文

Experimental evidence consistent with a magnon Nernst effect in the antiferromagnetic insulator MnPS$$_3$$

塩見 雄毅*; 高嶋 梨菜*; 齊藤 英治

Physical Review B, 96(13), p.134425_1 - 134425_9, 2017/10

 被引用回数:18 パーセンタイル:6.76(Materials Science, Multidisciplinary)

A magnon Nernst effect, an antiferromagnetic analog of the magnon Hall effect in ferromagnetic insulators, has been studied experimentally for the layered antiferromagnetic insulator MnPS$$_3$$ in contact with two Pt strips. Thermoelectric voltage in the Pt strips grown on MnPS$$_3$$ single crystals exhibits nonmonotonic temperature dependence at low temperatures, which is unlikely to be explained by electronic origins in Pt but can be ascribed to the inverse spin Hall voltage induced by a magnon Nernst effect. Control of antiferromagnetic domains in the MnPS$$_3$$ crystal by magnetoelectric cooling is found to modulate the low-temperature thermoelectric voltage in Pt, which is evidence consistent with the emergence of the magnon Nernst effect in Pt-MnPS$$_3$$ hybrid structures.

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:2 パーセンタイル:62.86(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

Oscillatory Nernst effect in Pt$$|$$ferrite$$|$$cuprate-superconductor trilayer films

塩見 雄毅*; Lustikova, J.*; 齊藤 英治

Scientific Reports (Internet), 7, p.5358_1 - 5358_8, 2017/07

 パーセンタイル:100(Multidisciplinary Sciences)

Although magnetism and superconductivity hardly coexist in a single material, recent advances in nanotechnology and spintronics have brought to light their interplay in magnetotransport in thin-film heterostructures. Here, we found a periodic oscillation of Nernst voltage with respect to magnetic fields in Pt$$|$$LiFe$$_5$$O$$_8$$ (Pt$$|$$LFO) bilayers grown on a cuprate superconductor YBa$$_2$$Cu$$_3$$O$$_{7-x}$$ (YBCO). At high temperatures above the superconducting transition temperature ($$T_C$$) of YBCO, spin Seebeck voltages originating in Pt$$|$$LFO layers are observed. As temperature decreases well below $$T_C$$, the spin Seebeck voltage is suppressed and unconventional periodic voltage oscillation as a function of magnetic fields appears; such an oscillation emerging along the Hall direction in the superconducting state has not been observed yet. Dynamics of superconducting vortices pinned by surface precipitates seems responsible for the oscillatory Nernst effect.

論文

Linear magnetoresistance in a topological insulator Ru$$_2$$Sn$$_3$$

塩見 雄毅*; 齊藤 英治

AIP Advances (Internet), 7(3), p.035011_1 - 035011_6, 2017/03

We have studied magnetotransport properties of a topological insulator material Ru$$_2$$Sn$$_3$$. Bulk single crystals of Ru$$_2$$Sn$$_3$$ were grown by a Bi flux method. The resistivity is semiconducting at high temperatures above 160 K, while it becomes metallic below 160 K. Nonlinear field dependence of Hall resistivity in the metallic region shows conduction of multiple carriers at low temperatures. In the high-temperature semiconducting region, magnetoresistance exhibits a conventional quadratic magnetic-field dependence. In the low-temperature metallic region, however, high-field magnetoresistance is clearly linear with magnetic fields, signaling a linear dispersion in the low-temperature electronic structure. Small changes in the magnetoresistance magnitude with respect to the magnetic field angle indicate that bulk electron carriers are responsible mainly for the observed linear magnetoresistance.

論文

Fabrication and magnetic control of Y$$_3$$Fe$$_5$$O$$_{12}$$ cantilevers

Seo, Y.-J.*; 針井 一哉; 高橋 遼*; 中堂 博之; 大柳 洸一*; Qiu, Z.*; 小野 崇人*; 塩見 雄毅*; 齊藤 英治

Applied Physics Letters, 110(13), p.132409_1 - 132409_4, 2017/03

 被引用回数:4 パーセンタイル:62.86(Physics, Applied)

フェリ磁性体であるY$$_3$$Fe$$_5$$O$$_{12}$$を用いたサブミクロンカンチレバーを収束イオンビーム法によって作成し、その振動特性を磁場によって制御した。カンチレバーは縦横2つの振動モードを示し、それぞれのモードは外部磁場の印加によって共鳴周波数が減少、増大した。この結果は磁気力の磁場変化を取り扱った数値シミュレーションでよく再現された。周波数変化は数%に及ぶことから、磁場による高効率な振動制御が行われたと結論できる。

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:24 パーセンタイル:3.42(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

Universal scaling for the spin-electricity conversion on surface states of topological insulators

山本 敬太*; 塩見 雄毅*; 瀬川 耕司*; 安藤 陽一*; 齊藤 英治

Physical Review B, 94(2), p.024404_1 - 024401_6, 2016/05

 被引用回数:7 パーセンタイル:36.25(Materials Science, Multidisciplinary)

スピンポンピング技術を用いてバルク絶縁トポロジカルインシュレータ(TI)材料の表面状態のスピン-電気変換を調べた。サンプル構造はNi-Fe/Cu/TI三層であり、TI表面上の磁気近接効果はCu層の挿入により無視できるほど小さい。スピン-電気変換によって生成される電圧信号は、より低い温度で支配的な表面輸送に沿って、観察され、温度が低下するにつれて増強される。スピン-電気変換の効率は、表面スピン-電気変換と一致して、バルク状態の抵抗率が高く、表面状態の平均自由行程が長いTIサンプルの方が大きい。

論文

Dispersion-type Hall resistance in InSb$$|$$Pt hybrid systems

塩見 雄毅*; 齊藤 英治

Scientific Reports (Internet), 6, p.22085_1 - 22085_6, 2016/02

 被引用回数:3 パーセンタイル:50.84(Multidisciplinary Sciences)

In nonmagnetic semiconductors and metals, most of Hall resistance exhibits a linear dependence with applied magnetic fields. In this work, by combining conduction in a metal and a semiconductor under external magnetic fields, we realize a dispersion-type magnetic-field dependence of Hall resistance. The dispersion-type Hall resistance appears in a broad temperature range below 150K, where quantum linear magnetoresistance is noticeable in the semiconductor substrate. This unconventional Hall response in metal$$|$$semiconductor hybrid systems is explained by a change in dominant conduction from the semiconductor to the metal with increasing magnetic field strength.

論文

Vector spectroscopy for spin pumping

Lustikova, J.*; 塩見 雄毅*; 齊藤 英治

Physical Review B, 92(22), p.224436_1 - 224436_8, 2015/12

 被引用回数:5 パーセンタイル:58.63(Materials Science, Multidisciplinary)

We propose a method to separate the inverse spin Hall effect (ISHE) from galvanomagnetic effects in spin pumping experiments on metallic bilayer systems by measuring the dc electromotive force in two orthogonal directions. Calculations of dc voltages in longitudinal and Hall directions induced in Ni$$_{81}$$Fe$$_{19}$$ and Ni$$_{81}$$Fe$$_{19}$$/Pt films at ferromagnetic resonance in a microwave cavity predict that contributions from ISHE and from the galvanomagnetic effects, i.e., the anisotropic magnetoresistance and the anomalous Hall effect. exhibit distinct signal symmetry as well as angular dependence when changing the direction of the external field with respect to the film plane. According to measurements on Ni$$_{81}$$Fe$$_{19}$$/Pt, only that dc voltage component which includes ISHE is more than five times larger than purely galvanomagnetic components. This is corroborated by results on La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_{3}$$/Pt samples, demonstrating universality of this method.

論文

Enhanced inverse spin Hall contribution at high microwave power levels in La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_3$$/SrRuO$$_3$$ epitaxial bilayers

Haidar, S. M.*; 塩見 雄毅*; Lustikova, J.*; 齊藤 英治

Applied Physics Letters, 107(15), p.152408_1 - 152408_5, 2015/10

 被引用回数:5 パーセンタイル:58.63(Physics, Applied)

We have investigated microwave power dependence of dc voltage generated upon ferromagnetic resonance in a La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_3$$/SrRuO$$_3$$ epitaxial bilayer film at room temperature. With increasing microwave power above $$sim$$75 mW, the magnitude of the voltage signal decreases as the sample temperature approaches the Curie temperature of La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_3$$ due to heating effects. By analyzing the dependence of the voltage signal on the direction of the magnetic field, we show that with increasing microwave power the contribution from the inverse spin Hall effect becomes more dominant than that from the anisotropic magnetoresistance effect.

論文

Critical suppression of spin Seebeck effect by magnetic fields

吉川 貴史*; 内田 健一*; 大門 俊介*; Qiu, Z.*; 塩見 雄毅*; 齊藤 英治

Physical Review B, 92(6), p.064413_1 - 064413_9, 2015/08

 被引用回数:84 パーセンタイル:1.86(Materials Science, Multidisciplinary)

The longitudinal spin Seebeck effect (LSSE) in Pt/Y$$_3$$Fe$$_5$$O$$_{12}$$ (YIG) junction systems has been investigated at various magnetic fields and temperatures. We found that the LSSE voltage in a Pt/YIG-slab system is suppressed by applying high magnetic fields and this suppression is critically enhanced at low temperatures. The field-induced suppression of the LSSE in the Pt/YIG-slab system is too large at around room temperature to be explained simply by considering the effect of the Zeeman gap in magnon excitation. This result requires us to introduce a magnon-frequency-dependent mechanism into the scenario of LSSE; low-frequency magnons dominantly contribute to the LSSE. The magnetic field dependence of the LSSE voltage was observed to change by changing the thickness of YIG, suggesting that the thermospin conversion by the low-frequency magnons is suppressed in thin YIG films due to the long characteristic lengths of such magnons.

論文

Anomalous hall effect with giant hysteresis loop in La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_3$$|SrRuO$$_3$$ superlattices

塩見 雄毅*; 半田 優*; 吉川 貴史*; 齊藤 英治

Physical Review B, 92(2), p.024418_1 - 024418_4, 2015/07

 被引用回数:3 パーセンタイル:73.18(Materials Science, Multidisciplinary)

We report anomalous Hall effects exhibiting a hysteresis loop as large as about 10 T in a ferromagnetic superlattice comprising La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_3$$ and SrRuO$$_3$$ layers. The superlattices grown by pulsed laser deposition exhibit a strong antiferromagnetic interlayer coupling below 110 K, where both La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_3$$ and SrRuO$$_3$$ layers show anomalous Hall effects. With increasing magnetic-field strength, the anomalous Hall resistivity in the superlattices changes its sign depending on the magnetization directions of the La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_3$$ and SrRuO$$_3$$ layers. As a consequence of competition among the antiferromagnetic interlayer coupling, the Zeeman effect, and magnetic anisotropies, the width of the hysteresis loop in the anomalous Hall resistivity in the superlattices becomes larger than 8 T at 10 K, clearly greater than those observed in La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_3$$ and SrRuO$$_3$$ single layer films.

論文

Transverse thermoelectric effect in La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_3$$|SrRuO$$_3$$ superlattices

塩見 雄毅*; 半田 優*; 吉川 貴史*; 齊藤 英治

Applied Physics Letters, 106(23), p.232403_1 - 232403_4, 2015/06

 被引用回数:18 パーセンタイル:22.6(Physics, Applied)

Transverse thermoelectric effects in response to an out-of-plane heat current have been studied in an external magnetic field for ferromagnetic superlattices consisting of La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_3$$ and SrRuO$$_3$$ layers. The superlattices were fabricated on SrTiO$$_3$$ substrates by pulsed laser deposition. We found that the sign of the transverse thermoelectric voltage for the superlattices is opposite to that for La$$_{0.67}$$Sr$$_{0.33}$$MnO$$_3$$ and SrRuO$$_3$$ single layers at 200 K, implying an important role of spin Seebeck effects inside the superlattices. At 10 K, the magnetothermoelectric curves shift from the zero field due to an antiferromagnetic coupling between layers in the superlattices.

論文

Reducing galvanomagnetic effects in spin pumping measurement with Co$$_{75}$$Fe$$_{25}$$ as a spin injector

Haidar, S. M.*; 井口 亮*; Yagmur, A.*; Lustikova, J.*; 塩見 雄毅*; 齊藤 英治

Journal of Applied Physics, 117(18), p.183906_1 - 183906_6, 2015/05

 被引用回数:5 パーセンタイル:58.63(Physics, Applied)

We have investigated dc voltage generation induced by ferromagnetic resonance in a Co$$_{75}$$Fe$$_{25}$$/Pt film. In order to reduce rectification effects of anisotropic magnetoresistance and the planar Hall effect, which may be observed simultaneously with the inverse spin Hall effect, we selected Co$$_{75}$$Fe$$_{25}$$ with extremely small anisotropic magnetoresistance as a spin injector. Using the difference in the spectral shape of voltage and in the angle dependence of in-plane magnetization among the effects, we demonstrated that the generated dc voltage is governed by the inverse spin Hall effect induced by spin pumping.

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:6 パーセンタイル:52.54(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

Spectral shape deformation in inverse spin Hall voltage in Y$$_3$$Fe$$_5$$O$$_{12}|$$Pt bilayers at high microwave power levels

Lustikova, J.*; 塩見 雄毅*; 半田 優*; 齊藤 英治

Journal of Applied Physics, 117(7), p.073901_1 - 073901_7, 2015/02

 被引用回数:5 パーセンタイル:58.63(Physics, Applied)

We report on the deformation of microwave absorption spectra and of the inverse spin Hall voltage signals in thin film bilayers of yttrium iron garnet (YIG) and platinum at high microwave power levels in a 9.45 GHz TE$$_{011}$$ cavity. As the microwave power increases from 0.15 to 200 mW, the resonance field shifts to higher values, and the initially Lorentzian spectra of the microwave absorption intensity as well as the inverse spin Hall voltage signals become asymmetric. The contributions from opening of the magnetization precession cone and heating of YIG cannot well reproduce the data. Control measurements of inverse spin Hall voltages on thin-film YIG$$|$$Pt systems with a range of line widths underscore the role of spin-wave excitations in spectral deformation.

論文

Spin-electricity conversion induced by spin injection into topological insulators

塩見 雄毅*; 野村 健太郎*; 梶原 瑛祐*; 江藤 数馬*; Novak, M.*; 瀬川 耕司*; 安藤 陽一*; 齊藤 英治

Physical Review Letters, 113(19), p.196601_1 - 196601_5, 2014/11

 被引用回数:147 パーセンタイル:0.78(Physics, Multidisciplinary)

We report successful spin injection into the surface states of topological insulators by using a spin pumping technique. By measuring the voltage that shows up across the samples as a result of spin pumping, we demonstrate that a spin-electricity conversion effect takes place in the surface states of bulk-insulating topological insulators Bi$$_{1.5}$$Sb$$_{0.5}$$Te$$_{1.7}$$Se$$_{1.3}$$ and Sn-doped Bi$$_{2}$$Te$$_{2}$$Se. In this process, the injected spins are converted into a charge current along the Hall direction due to the spin-momentum locking on the surface state.

論文

Spin current generation from sputtered Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ films

Lustikova, J.*; 塩見 雄毅*; Qiu, Z.*; 吉川 貴史*; 井口 亮*; 内田 健一*; 齊藤 英治

Journal of Applied Physics, 116(15), p.153902_1 - 053902_6, 2014/10

 被引用回数:27 パーセンタイル:12.98(Physics, Applied)

Spin current injection from sputtered yttrium iron garnet (YIG) films into an adjacent platinum layer has been investigated by means of the spin pumping and the spin Seebeck effects. Films witha thickness of 83 and 96 nanometers were fabricated by on-axis magnetron rf sputtering at room temperature and subsequent post-annealing. From the frequency dependence of the ferromagneticresonance linewidth, the damping constant has been estimated to be (7.0$$pm$$1.0) $$times$$ 10$$^{-4}$$. Magnitudes of the spin current generated by the spin pumping and the spin Seebeck effect are ofthe same order as values for YIG films prepared by liquid phase epitaxy. The efficient spin current injection can be ascribed to a good YIG/Pt interface, which is confirmed by the large spin-mixingconductance (2.0 $$pm$$ 0.2) $$times$$ 10$$^{18}$$ m$$^{-2}$$.

論文

Interface-dependent magnetotransport properties for thin Pt films on ferrimagnetic Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$

塩見 雄毅*; 大谷 隆史*; 井口 敏*; 佐々木 孝彦*; Qiu, Z.*; 中山 裕康*; 内田 健一*; 齊藤 英治

Applied Physics Letters, 104(24), p.242406_1 - 242406_5, 2014/06

 被引用回数:14 パーセンタイル:31.32(Physics, Applied)

We have studied magnetoresistance and Hall effects for 1.8-nm-thick Pt films grown on a ferrimagnetic insulator Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ in a wide temperature (0.46-300 K) and magnetic-field (-15 to 15 T) region. In the low-temperature regime where quantum corrections to conductivity are observed, weak antilocalization behavior observed in Pt films is critically suppressed when the film is attached to Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$. Hall resistance in the Pt film is also affected by Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$, and it exhibits logarithmic temperature dependence in a broad temperature range. The magnetotransport properties in the high-field range are significantly influenced by the interface between Pt and Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$.

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