Ferromagnetic Resonance Study of Magnetic Anisotropy in Epitaxial Fe3O4 Thin Film

Ferromagnetic resonance (FMR) is used to investigate the magnetic anisotropy of a 25.5 nm thin Fe₃O₄ film above and below its Verwey transition temperature (TV). Epitaxial smooth film of Fe₃O₄ is deposited by oxygen-assisted molecular beam epitaxy. FMR spectra are recorded using a 9.49 GHz Brucker EMX system from 80 K to room temperature with a magnetic field applied along [100] direction. The resonance field (Hr) and linewidth (AH) are extracted by fitting the FMR line with a Lorentzian function. Temperature dependence of H_r and ΔH shows a transition at T_V. Furthermore, the data of in-plane angular dependence of H_r at 300 and 83 K indicated a change in symmetry from fourfold to twofold below TV, consistent with a transformation of Fe₃O₄ from cubic (fourfold) to monoclinic (twofold) structure with its easy axis switching from [110] to [100]. Complex symmetry pattern is found in angular dependence of ΔH below TV, which is attributed to the in-plane twinning of Fe₃O₄ lattice.