On Thursday, June 26th 2025, we have the pleasure to welcome in SPINTEC Kazuma Ogawa from the University of Tokyo. He will give us a seminar at 15:00 entitled :
Spin Texture Manipulation by Current and Light probed via Magneto-Optical Microscopy
Place : IRIG/SPINTEC, auditorium 445 CEA Building 10.05
video conference : https://univ-grenoble-alpes-fr.zoom.us/j/98769867024?pwd=dXNnT3RMeThjYStybGVQSUN0TVdJdz09
Meeting ID: 987 6986 7024
Passcode: 025918
Abstract : Controlling magnetic textures such as domain walls lies at the heart of modern spintronics, and fast, energy-efficient approaches are actively being explored. In this seminar, I present two contrasting strategies—employing either electrical or optical stimuli—to manipulate spin textures in distinct material systems, probed via magneto-optical microscopy.
In the first part, I focus on ultrafast time-resolved magneto-optical Kerr effect imaging of current-induced domain wall motion in Pt/GdFeCo wires [1]. By implementing a stroboscopic current-pump, optical-probe scheme synchronized with sub-nanosecond current pulses, we directly visualize domain wall dynamics on sub-nanosecond timescales. The observed motion exhibits a time-dependent velocity, which can be attributed to an enhanced domain wall speed near the angular momentum compensation temperature—a characteristic unique to ferrimagnetic systems.
In the second part, I turn to a ferromagnetic Weyl semimetal, Co₃Sn₂S₂, notable for its large Berry curvature. Here, we demonstrate non-volatile magnetization switching induced solely by circularly polarized femtosecond laser pulses, without the need for any applied magnetic field or current [2]. The all-optical magnetization reversal results in a robust and persistent change in the anomalous Hall effect, evidencing a chirality flip of the underlying Weyl fermions. Such optical control enables the creation of arbitrary spatial domain patterns, offering a new platform for studying domain wall physics in magnetic Weyl semimetals [3].
These studies underscore the role of magneto-optical methods as powerful probes of spin texture and dynamics, revealing the potential of light and current to manipulate magnetization in next-generation spintronic systems.
- K. Ogawa, N. Yoshikawa, M. Ishibashi, K. Yakushiji, A. Tsukamoto, M. Hayashi and R. Shimano, Phys. Rev. Res. 5, 033151 (2023).
- N. Yoshikawa†, K. Ogawa†, Y. Hirai, K. Fujiwara, J. Ikeda, A. Tsukazaki and R. Shimano, Commun Phys 5, 1 (2022).
- K. Fujiwara, K. Ogawa, N. Yoshikawa, K. Kobayashi, K. Nomura, R. Shimano and A. Tsukazaki, Commun Mater 5, 1 (2024).
Biography : Kazuma Ogawa is currently a doctoral candidate (Ph.D. student) at the Department of Physics, Graduate School of Science, the University of Tokyo. His research focuses on ultrafast light- and current-induced dynamics in magnetic materials, in particular topological semimetals. Some of his work has also involved experiments related to spin–charge current conversion, Floquet engineering, and the detection of axion electromagnetic responses.
He has experience in a variety of spectroscopic techniques, including optical and terahertz magneto-optical spectroscopy, terahertz emission spectroscopy, and scanning photocurrent microscopy, as well as ultrafast pump–probe measurements and cryogenic transport measurements.
