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巻内 崇彦*; 日置 友智*; 清水 祐樹*; 星 幸治郎*; Elyasi, M.*; 山本 慧; 横井 直人*; Serga, A. A.*; Hillebrands, B.*; Bauer, G. E. W.*; et al.
Nature Materials, 23(5), p.627 - 632, 2024/05
When excited, a magnetization in a magnet precesses around the field in an anticlockwise manner on a time scale governed by viscous magnetization damping, after which any information carried by the initial actuation seems to be lost. The damping appears to be a fundamental bottleneck for the use of magnets in information processing. Nevertheless, here we demonstrate recall of the magnetization-precession phase after times that far exceed the damping time scale by two orders of magnitude using dedicated two-colour microwave pump-and-probe experiments for a Y
Fe
O
microstructured film. Time- resolved magnetization state tomography confirms the magnetic persistent coherence (MPC) by revealing a double-exponential decay of the magnetization correlation. We attribute MPC to a feedback effect, viz. coherent coupling of the uniform precession with long-lived excitations at the minima of the spin-wave dispersion relation. Our finding liberates magnetic systems from the strong damping in nanostructures tyranny that limits their use in coherent information storage and processing.
堀部 聡平*; 清水 祐樹*; 星 幸治郎*; 巻内 崇彦*; 日置 友智*; 齊藤 英治
Applied Physics Express, 16(7), p.073001_1 - 073001_4, 2023/07
被引用回数：0 パーセンタイル：0(Physics, Applied)Parametric oscillation occurs when the resonance frequency of an oscillator is periodically modulated. Owing to time-reversal symmetry breaking in magnets, nonreciprocal magnons can be parametrically excited when spatial-inversion symmetry breaking is provided. This means that magnons with opposite propagation directions have different amplitudes. Here we demonstrate switching on and off the magnon parametric oscillation by reversing the external field direction applied to a Y
Fe
O micro-structured film. The result originates from the nonreciprocity of surface mode magnons, leading to field-direction dependence of the magnon accumulation under nonuniform microwave pumping. Our numericalcalculation well reproduces the experimental result.
吉川 貴史*; Reitz, D.*; 伊藤 宏陽*; 巻内 崇彦*; 杉本 宜陽*; 恒川 翔*; 大門 俊介*; 大柳 洸一*; Ramos, R.*; 高橋 三郎*; et al.
Nature Communications (Internet), 12, p.4356_1 - 4356_7, 2021/07
被引用回数：19 パーセンタイル：87.71(Multidisciplinary Sciences)Thermoelectric effects have been applied to power generators and temperature sensors that convert waste heat into electricity. The effects, however, have been limited to electrons to occur, and inevitably disappear at low temperatures due to electronic entropy quenching. Here, we report thermoelectric generation caused by nuclear spins in a solid: nuclear-spin Seebeck effect. The sample is a magnetically ordered material MnCO having a large nuclear spin 
of 
Mn nuclei and strong hyperfine coupling, with a Pt contact. In the system, we observe low-temperature thermoelectric signals down to 100 mK due to nuclear-spin excitation. Our theoretical calculation in which interfacial Korringa process is taken into consideration quantitatively reproduces the results. The nuclear thermoelectric effect demonstrated here offers a way for exploring thermoelectric science and technologies at ultralow temperatures.
Ramos, R.*; 巻内 崇彦*; 吉川 貴史*; 大門 俊介*; 大柳 洸一*; 齊藤 英治
Applied Physics Letters, 117(24), p.242402_1 - 242402_5, 2020/12
被引用回数：1 パーセンタイル：5.34(Physics, Applied)We investigated the magnetotransport properties of mesoscopic platinum nanostructures (wires and rings) with sub-100 nm lateral dimensions at very low temperatures. Despite the strong spin-orbit interaction in platinum, oscillation of the conductance as a function of the external magnetic field due to quantum interference effects was found to appear. The oscillation was decomposed into Aharonov-Bohm periodic oscillations and aperiodic fluctuations of the conductance due to a magnetic flux piercing the loop of the ring and the metal wires forming the nanostructures, respectively. We also investigated the magnetotransport under different bias currents to explore the interplay between electron phase coherence and spin accumulation effects in strong spin-orbit conductors.
