Variation of microwave magnetic properties for thin films of ferromagnetic metals with the film thickness

An investigation of the dependence of magnetic properties on the thickness of ferromagnetic films was completed. The study dealt with magnetostatic and microwave measurements of single-layer films of ferromagnetic metals (Fe, Co) and was aimed at revealing reasons for the deterioration of microwave magnetic performance with an increase in film thickness. Two types of variation of microwave permeability with the film thickness were distinguished for the films under study. One exhibited a noticeable deviation from maximal values and was observed for Co. The other case involved a gradual worsening of performance, and was observed for Fe. In the first case, the resonance frequency shifted lower when the film was thicker than 0.2–0.4 μm, and Acher's coefficient fell by the factor of three. In the second case, the microwave performance worsened gradually, and a decrease of Acher's coefficient was not large, approximately by 20%. The data analysis showed that the reason for the deterioration is an increase of out-of-plane anisotropy in the first case and sufficient growth of damping factor in the second case.