Ferromagnetic resonance mode interactions in periodically perturbed films

Ferromagnetic resonance linewidth measurements are reported for thin films of Ni80Fe20 deposited on substrates with 320 nm period grooves or parallel aperiodic scratches. These films are model systems for studying the effects of inhomogeneity on ferromagnetic resonance. With the grooved substrate, the ferromagnetic resonance spectra show that interactions split the resonant frequencies of interacting modes leading to two resonances for strong interactions and broadened resonances for weak interactions. The results obtained with the scratched substrate are in agreement with the two-magnon model of linewidth, showing sharply increased linewidth when the scratches are oriented to allow coupling to degenerate spinwave modes. The results are not in agreement with a simple model of linewidth as a direct measure of the spread in local resonance fields.