Bulk-like Dynamic Magnetic Properties of Nickel Ferrite Epitaxial Thin Films Grown on SrTiO$_3$(001)

Nickel ferrite (NiFe 2 O 4 , NFO) films were grown at high temperatures on SrTiO 3 (001) substrates using laser molecular beam epitaxy. A spinel lattice structure, with lattice parameters close to those of bulk NFO, was confirmed by electron and X-ray diffraction. Vibrating sample magnetometer measurements show an in-plane remanent magnetization, relatively narrow (~50 Oe) hysteresis loops, and fourfold symmetry. Soft X-ray magnetic dichroism measurements indicate an inverse spinel structure. X-band ferromagnetic resonance (FMR) measurements show a line width as low as 45-50 Oe, which corresponds to the value for bulk NFO crystals. The angular dependence of FMR on a 110 nm thick NFO film indicates cubic anisotropy close to that of bulk crystals and a substrate-induced stress anisotropy field of about 0.4 kG.