産総研・田丸慎吾 氏講演のお知らせ / Lecture by Dr. Shingo Tamaru, AIST

タイトル：Study of magnetostatic mode waves on metallic magnetic films by spatially resolved ferromagnetic resonance (SRFMR) MOKE microscope
講 演 者：田丸 慎吾 氏
所　　属：産業技術総合研究所　ハイブリッド機能集積研究部門
　　　　　Research Institute for Hybrid Functional Integration (HyFI-RI), National Institute of Advanced Industrial Science and Technology (AIST),
日　　時：2025/6/20th（Fri）14:00～  (JST)
場　　所：東京大学理学部1号館　913号室

In ferromagnetic materials, two high-frequency spin wave modes—magnetostatic mode waves (MSWs) and exchange mode waves—can be excited. MSWs are dominated by long-range dipole interactions, while exchange mode waves are governed by short-range exchange interactions. Theory has predicted that MSWs exhibit anisotropic propagation behaviors due to the highly anisotropic nature of dipole interaction. This is in contrast to exchange mode waves, which reflect the isotropic nature of exchange interaction.
Furthermore, MSWs should decay as they propagate in metallic magnetic material due to their much larger damping parameters than those of low-loss ferrimagnetic insulators such as YIG. Study of such spatially inhomogeneous and anisotropic propagation of MSWs clearly requires a measurement technique that can capture spatial distribution of spin precession with sufficiently high spatial resolution. Notably, such a technique was absent when I started studying the spatial nature of MSWs.
To address these problems, I developed a scanning MOKE microscope system that excites spin precession in the sample under test and captures its complex amplitude with optical diffraction limited spatial distribution, which is named as spatially resolved ferromagnetic resonance (SRFMR) MOKE microscope1,2. The key difference between SRFMR-MOKE and the conventional time-resolved (TR) MOKE microscopes lies in the excitation scheme. While TR-MOKE microscope excites spin precession with either an impulse or step pulse magnetic field having broadly spreading spectra, SRFMR-MOKE microscope excites spin precession with a continuous sinusoidal magnetic field at a single microwave frequency. This approach provides much cleaner insights into the physical nature of propagation MSWs than TR-MOKE.
In this talk, I will present various measurement results obtained by SRFMR-MOKE, as well as a fundamental theoretical framework indispensable for physically interpreting observed spatial propagation patterns, i.e., Green’s function of MSW propagation3.

References
(1) S. Tamaru et al., J. Appl. Phys. 91, 8034 (2002)
(2) S. Tamaru et al., Phys. Rev. B 70, 104416 (2004)
(3) S. Tamaru et al., Phys. Rev. B 84, 064437 (2011)