Elucidation of orbital moment, anisotropy, and magnetic damping in epitaxial Fe3O4 films

Abstract

The size of the orbital moment in Fe3O4 has provided a long standing and contentious debate. In this paper we make use of ferromagnetic resonance (FMR) spectroscopy and x-ray magnetic circular dichroism (XMCD) to provide complementary determinations of the size of the orbital moment in "bulk-like" epitaxial Fe3O4 films grown on Yttria-stabilized zirconia (111) substrates. Annealing the 100 nm as-grown films to 1100 C in a reducing atmosphere improves the stoichiometry and microstructure of the films allowing for bulk like properties to be recovered as evidenced by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). In addition, in-plane angular FMR spectra exhibit a cross over from a 4-fold symmetry to the expected 6-fold symmetry of the (111) surface, together with an anomalous peak in the FMR linewidth at ~10 GHz; indicative of low Gilbert damping in combination with two-magnon scattering. For the bulk-like annealed sample, a spectroscopic splitting factor g ≈ 2.18 is obtained using both FMR and XMCD techniques, providing evidence for the presence of a finite orbital moment in Fe3O4.