Ferromagnetic resonance study of magnetic anisotropy in epitaxial Fe₃O₄ thin film

Abstract

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 (ΔH) are extracted by fitting the FMR line with a Lorentzian function. Temperature dependence of (Hr) and ΔH shows a transition at TV. Furthermore, the data of in-plane angular dependence of Hr 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.