Ferromagnetic resonance study on magnetic homogeneity in spin-sprayed NiZn ferrite films highly permeable at gigahertz frequencies

Ferromagnetic resonance (FMR), including standing spin-wave resonance (SWR) modes, were measured in NiZn ferrite films, which have high permeability even up to the gigahertz range. They were prepared from an aqueous solution by spin spray ferrite plating at 90°C. The perpendicular field FMR spectra exhibited SWR modes whose line separation had linear dependence on spin wave number, deviating from the quadratic behavior. This indicated that the films have inhomogeneous distribution of magnetization perpendicular to film plane, and have different magnetic surface anisotropies between the inner and outer surfaces of the respective films. The in-plane field FMR spectra revealed no SWR mode. A possible model is proposed to explain the features not only of the FMR spectra, but also of the initial permeability spectra measured on the films.