A comprehensive study of ferromagnetic resonance and structural properties of iron-rich nickel ferrite (NixFe3−xO4, x≤1) films grown by chemical vapor deposition

We report a detailed study of the structural and ferromagnetic resonance properties of spinel nickel ferrite (NFO) films, grown on (100)-oriented cubic MgAl2O4 substrates by direct liquid injection chemical vapor deposition (DLI-CVD) technique. Three different compositions of NFO films (NixFe3−xO4 where x=1, 0.8, 0.6) deposited at optimized growth temperature of 600 °C are characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometry (VSM), and broadband ferromagnetic resonance (FMR) techniques. XRD confirms the growth of epitaxial, single crystalline NixFe3−xO4 films. The out-of-plane lattice constant (c) obtained for Ni0.8Fe2.2O4 film is slightly higher than the bulk value (0.833 nm), indicating only partial strain relaxation whereas for the other two compositions (x=1 and x=0.6) films exhibit complete relaxation. The in-plane and out-of-plane FMR linewidths measurements at 10 GHz give the lowest values of 458 Oe and 98 Oe, respectively, for Ni0.8Fe2.2O4 film as compared to the other two compositions. A comprehensive frequency (5-40 GHz) and temperature (10-300 K) dependent FMR study of the Ni0.8Fe2.2O4 sample for both in-lane and out-of-plane configurations reveals two magnon scattering (TMS) as the dominant in-plane relaxation mechanism. It is observed that the TMS contribution to the FMR linewidth scales with the saturation magnetization Ms. In-plane angle-dependent FMR measurements performed on the same sample show that the ferromagnetic resonance field (Hres) and the FMR linewidth (ΔH) have a four-fold symmetry that is consistent with the crystal symmetry of the spinel. SEM measurements show formation of pyramid-like microstructures at the surface of the Ni0.8Fe2.2O4 sample, which can explain the observed four-fold symmetry of the FMR linewidth.