Localized Ferromagnetic Resonance in Inhomogeneous Thin Films

The effect of sample inhomogeneity on the ferromagnetic resonance linewidth is determined by diagonalization of a spin wave Hamiltonian for ferromagnetic thin films with inhomogeneities spanning a wide range of characteristic length scales. A model inhomogeneity is used that consists of size D grains and an anisotropy field H_p that varies randomly from grain to grain in a film with thickness d and magnetization M_s. The resulting linewidth agrees well with the two-magnon model for small inhomogeneity, H_pD≪πM_sd. For large inhomogeneity, H_pD≫πM_sd, the precession becomes localized and the spectrum approaches that of local precession on independent grains.