Angular dependence of GdFe and GdCo FMR spectra

The ferromagnetic resonance spectra of a series of GdFe and GdCo amorphous bubble films have been measured with the static magnetic field H→s applied at various angles to the film normal. A typical spectrum exhibits two or more peaks. The relative position of these peaks changes as the direction of H→s is changed in such a way that at some field angles, the peaks may be widely separated, while at others they strongly overlap. To analyze these results, a computer program was developed to find the best fit to these spectra by adjusting the effective anisotropy field Hk′ = Hk-4πMs and gyromagnetic ratio γ. The effective g-values obtained agree very well with the Wangness formula, especially if the spectra for H→s nearly normal to the film are excluded from the computer analysis. In these cases, spin wave excitation renders the determination of the uniform peak position difficult. The multiple-peak spectra obtained indicate the existence of sample inhomogeneities and the Hk′ and γ values deduced from our analysis throw some light on the nature of these inhomogeneities.