Tohoku University · Physics and Astronomy
Professor Tomosato Hioki's research lab specializes in ultrafast spin dynamics and magnonics in quantum materials, focusing on the generation, manipulation, and detection of spin waves and magnons using time-resolved magneto-optical microscopy. The lab explores coherent phenomena such as magnon-phonon coupling, spin-wave refraction and reflection at domain walls, and parametric excitation of magnon states, with applications in spintronics and quantum information science. A key focus is developing advanced imaging and state tomography techniques to visualize and characterize non-equilibrium magnetization dynamics at the nanoscale.
Figures are computed from collected data and may differ slightly.
Abstract Consider observing two different waves with the same frequency and wavelength. When these waves are coupled, the amplitude alternates between the two waves periodically, a phenomenon called coherent beating oscillation. Such phenomena can be seen in familiar coupled pendulums and, on a cosmic scale, neutrino oscillations: the oscillation between different types of neutrinos. In solids, on the other hand, there are various wave excitations responsible for their thermal and electromagneti
State tomography is an essential tool for analyzing physical states in quantum science. In magnets, elementary excitation called a magnon, or a spin wave, dominates magnetization dynamics and various magnetic properties. Here, we propose and demonstrate state tomography for magnetization dynamics, enabling us to obtain a density matrix and Wigner function of the magnetization dynamics. Using the technique, we found that parametrically excited magnons can form a mixed state composed of two cohere
Abstract When a light wave is refracted at a boundary between two different media, it may split into two rays due to optical anisotropy, a phenomenon called birefringence. On the other hand, for a reflected light wave in an ordinary medium, the angle of reflection is always the same as the incident angle as expected from the law of reflection. Here, we report the observation of a split of reflected spin-waves, or bi-reflection of spin-waves, where a spin-wave refers to a wavy motion of electron
We have investigated the magnetic-field-induced suppression of the longitudinal spin Seebeck effect (LSSE) by using a time-resolved measurement technique at room temperature. The result manifested two distinctive time domains: the short-time domain where the observed voltage is insensitive to the magnetic fields, and the long-time domain where the both response time and the magnitude of the observed voltage decreased simultaneously by the magnetic fields. We estimated the magnon propagation leng
© 2020 Author(s). We report the experimental observation of the refraction and reflection of propagating magnetostatic spin waves crossing a 90° domain wall (DW). Time-resolved magneto-optical imaging was used to observe the propagation dynamics of magnetostatic spin waves. Due to the magnetization rotation across such a DW, the dispersion relation of magnetostatic spin waves rotates by 90°. This results in a change in the propagation dynamics of spin waves on both sides of the DW. We observed t
Time-resolved magneto-optical (TRMO) imaging with ultrashort laser pulses now allows direct observation of the excitation, propagation, and relaxation dynamics of magnetization, with the details of excitation still being studied. This article shows how to image the in-plane component of magnetization, modulated by propagating spin waves, via the birefringence that arises in a transverse magnetic field. The authors use this method to resolve the contribution from magnetoelastic coupling in an out
A magnon parametron is a calculating element that carries binary information by a discretized oscillating phase: 0 and π. Owing to the strong non-linearity of the magnetization dynamics, the oscillation phase flips to another stochastically, which can give a rise to unconventional computing functionalities, including probabilistic computing. Here, we investigated the stochastic dynamics of ferromagnetic-metal magnon parametron, of which the precession phase is discretized into two (0 and π) by p
In-plane standing spin-wave modes in a minute magnetic disk are directly observed by using time-resolved magneto-optical microscopy synchronized with microwaves. The time-resolved microscopy allowed us to obtain snapshots of standing spin-wave modes in a magnetic disk, which show a hourglass-like standing spin wave pattern. We found that the characteristic pattern is caused by spatially nonuniform magnetization and a strong microwave excitation in terms of finite element calculation and micromag
Precessional motion of magnetization around the magnetic field decays to thermal equilibrium due to magnetization damping after cutting of the excitation force. After the decay, the phase coherence of the precession motion of magnetization was thought to be completely lost. Here we developed state tomography technique for time-resolved magnetization dynamics in a thin disk of yttrium iron garnet (YIG). We revealed that the temporal evolution of the coherence after cutting off the driving ac magn
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