On the Interpretation of the Angular Dependence of the Main FMR/SWR Line in Ferromagnetic Thin Films

The reported measurements of the angular dependence of ferromagnetic resonance spectra and their theoretical interpretation lead to the observation that a discrepancy occurs between the theory and the experiment in certain ranges of the configuration angle. This disagreement cannot be eliminated within the Smit-Beljers model commonly used in the literature for the description of ferromagnetic resonance in thin films since the main ferromagnetic resonance line observed in thin films is not necessarily associated with the excitation of a uniform mode, as the Smit-Beljers model does assume for bulk samples. Instead, we associate this line with the excitation of a surface mode or the thin-film principal nonuniform mode. By taking into account the occurrence of a surface spin-pinning anisotropy, this assumption allows to obtain an agreement between the theoretical description of the ferromagnetic resonance and the experimental data in the whole range of angular configuration of the external field. As an example, on the basis of this modified ferromagnetic resonance model, we make some observations on the angular resonant dependence in uniaxial thin films.