Exploring magnetic anisotropy in garnet films at low temperatures using ferromagnetic resonance

Ferromagnetic resonance is widely acknowledged as a robust tool for characterizing magnetic materials and studying physical phenomena. Low-temperature magnonics has recently garnered substantial attention; however, it lacks convenient methods for acquiring key magnetic material characteristics. In this study, we introduce a rapid and universal method to determine the temperature dependence of magnetic anisotropy constants of (111)-oriented garnet films using ferromagnetic resonance measurements, demonstrated specifically on the bismuth-substituted iron garnet film grown on a diamagnetic substrate. Our observations reveal a competitive interplay of different anisotropy types as temperature decreases. Notably, the uniaxial magnetic anisotropy constant Ku undergoes a sign change from negative to positive around 120 K, while the anisotropy type remains consistent.