Evidence for strain control of magnetic anisotropy in epitaxial nickel ferrite thin films grown on strontium titanate substrates

摘要

This report is on strain control of magnetic order parameters in 50 nm epitaxial NiFe2O4 (NFO) films grown on (001), (110), and (111) SrTiO3 (STO) single-crystal substrates by pulsed laser deposition. The related in-plane strains for NFO films on (001), (110), and (111) STO substrates are found to be -1.36 %, 1.35 %, and 1.52 %, respectively, where the lattice mismatch between film and substrate is as high as 6.7 %. Our analysis of magnetization and ferromagnetic resonance on all the NFO films reveals the presence of a uniaxial anisotropy field, which is perpendicular to the film plane. The anisotropy field decreases with the increase of strain in NFO films. Specifically, NFO films on STO (111) and STO (001) have the lowest and highest uniaxial anisotropy fileds of 1.4 kOe and 6.1 kOe, respectively. These experimental values of anisotropy field are a factor of 5-10 times smaller than those of the calculated ones due to the film defects induced by the high lattice mismatch. The studies of magnetic anisotropy of spinel ferrite films are of interest for spintronics and microwave devices.