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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.
Elyasi, M.*; 山本 慧; 日置 友智*; 巻内 崇彦*; 清水 祐樹*; 齊藤 英治*; Bauer, G. E. W.*
Physical Review B, 109(18), p.L180402_1 - L180402_7, 2024/05
Magnets are interesting materials for classical and quantum information technologies. However, the short decoherence and dephasing times that determine the scale and speed of information networks severely limit the appeal of employing the ferromagnetic resonance. Here we show that the lifetime and coherence of the uniform Kittel mode can be enhanced by three-magnon interaction-induced mixing with the long-lived magnons at the minima of the dispersion relation. Analytical and numerical calculations based on this model explain recent experimental results and predict experimental signatures of quantum coherence.
Lee, O.*; 山本 慧; 埋田 真樹; Zollitsch, C. W.*; Elyasi, M.*; 吉川 貴史*; 齊藤 英治; Bauer, G. E. W.*; 紅林 秀和*
Physical Review Letters, 130(4), p.046703_1 - 046703_6, 2023/01
被引用回数：6 パーセンタイル：93.39(Physics, Multidisciplinary)We experimentally and theoretically demonstrate that nonlinear spin-wave interactions suppress the hybrid magnon-photon quasiparticle or "magnon polariton" in microwave spectra of an yttrium iron garnet film detected by an on-chip split-ring resonator. We observe a strong coupling between the Kittel and microwave cavity modes in terms of an avoided crossing as a function of magnetic fields at low microwave input powers, but a complete closing of the gap at high powers. The experimental results are well explained by a theoretical model including the three-magnon decay of the Kittel magnon into spin waves. The gap closure originates from the saturation of the ferromagnetic resonance above the Suhl instability threshold by a coherent back reaction from the spin waves.
Elyasi, M.*; 齊藤 英治; Bauer, G. E. W.*
Physical Review B, 105(5), p.054403_1 - 054403_12, 2022/02
被引用回数：7 パーセンタイル：73.94(Materials Science, Multidisciplinary)Unconventional computing schemes based on bistable systems ("Ising spins") may supersede conventional computing paradigms. The "magnon parametron" is an Ising spin that forms as a result of parametric excitation of a ferromagnetic particle by microwaves beyond a certain threshold. This Ising spin becomes unstable at a second threshold power at which a high-frequency telegraph noise emerges. We explain the experimentally observed stochastic switching ("p-bit" characteristics) at room temperature by the Suhl instability of the uniform magnetization precession.
