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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

https://doi.org/10.1038/s41467-018-07352-1
 被引用回数：30 パーセンタイル：83.87(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

Spin pumping from nuclear spin waves

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

https://doi.org/10.1038/s41567-018-0310-x
 被引用回数：17 パーセンタイル：74.55(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$$_3$$, 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.

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

https://doi.org/10.1038/s41598-017-05747-6
 被引用回数：6 パーセンタイル：29.59(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

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

https://doi.org/10.1103/PhysRevB.92.224436
 被引用回数：14 パーセンタイル：52.39(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

https://doi.org/10.1063/1.4933379
 被引用回数：8 パーセンタイル：34.64(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

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

https://doi.org/10.1063/1.4921359
 被引用回数：5 パーセンタイル：22.94(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

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

https://doi.org/10.1063/1.4908211
 被引用回数：7 パーセンタイル：30.95(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 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

https://doi.org/10.1063/1.4898161
 被引用回数：50 パーセンタイル：86(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$$^{-2}$$.

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