Ferromagnetic resonance spectra in a weak stripe domain structure

The ferromagnetic resonance (FMR) spectra in magnetic films with a nonuniform magnetization configuration are known to exhibit multiple absorption peaks. In this paper, the case of ferromagnetic films supporting a weak stripe domain structure is addressed. A two-dimensional dynamic micromagnetic model is used to investigate the high-frequency response of such a magnetic structure. In a first step, the zero-field susceptibility spectra are computed. The existence of numerous resonances resulting from the excitation of surface and volume modes is predicted. The main features of spectra (number of resonances, resonance frequencies, intensities, and linewidths) strongly depend on the equilibrium spin configuration and on the rf exciting field orientation. In a second step, the susceptibility spectra in the presence of an in-plane static magnetic field applied along the stripe direction are studied in detail. The dispersion relation, frequency versus in-plane magnetic field, is computed for each magnetic excitation. These dispersion curves reveal possible mode couplings and interchange of mode characters with increasing magnetic field. The theoretical in-plane FMR spectra are then deduced from the frequency and magnetic field dependence of the dynamic susceptibility. These theoretical results are discussed in light of available experimental FMR data obtained on thin ferromagnetic films with a moderate perpendicular anisotropy.