Nonlinear spin wave resonance modes

Abstract

Nonlinear spin wave resonance modes of magnetic films are studied both theoretically and experimentally. In the theoretical analysis the normal modes with arbitrary amplitudes are studied for a film magnetized perpendicular to its plane. The film is assumed to be uniform apart from a layer close to the surfaces, where the spins may be pinned. The spin wave resonance mode of the lowest frequency (principal mode) is considered in detail for the film with arbitrary surface spin pinning. The mode profile changes with increasing amplitude trying to redistribute itself in a more uniform manner across the film thickness. The nonlinear shift of the resonance field depends critically on the pinning. In experiments, we use yttrium–iron–garnet films with a strong gradient in the anisotropy field across the film thickness. With increasing pump power, the principal mode shows a sublinear shift of the resonance field and superlinear growth in the absorption amplitude. These features are explained in terms of the spatial nonuniformity of the mode profile.