Low-frequency ferromagnetic resonance in CeAlSi

CeAlSi is a ferromagnetic Weyl semimetal with in-plane magnetization and a weak in-plane easy-axis magnetic anisotropy. The large domain size of CeAlSi makes it an ideal platform to study various in-plane magnetic textures. A singular angular magnetoresistance is observed in a similar compound CeAlGe recently [1], which makes CeAlSi a more interesting system to explore. We observe a ferromagnetic resonance (FMR) in CeAlSi with a novel time-resolved magneto-optical setup, which can resolve both amplitude and direction changes of magnetization based on polarimetry. The FMR frequency is as low as 200 MHz and drops with the amplitude of external out-of-plane magnetic field, which is also observed in other ferromagnets with small anisotropy in plane [2]. We also locally image the FMR induced by an AC magnetic field.

[1] T. Suzuki et al. Science 365, 377-381 (2019).
[2] S. O. Demokritov et al. Sov. Phys. JETP 68(6), 1277-1290 (1989).