Magnetization dynamics in interlayer exchange-coupled in-plane/out-of-plane anisotropy bilayers

The static and high-frequency properties of bilayer systems consisting in a single-crystal garnet film with a perpendicular anisotropy exchange coupled with a thin Permalloy film with a small in-plane anisotropy have been investigated both numerically and experimentally. The dynamic susceptibility spectra computed by means of two-dimensional micromagnetic simulations extended to stratified films reveal clearly the existence of multiple resonance lines resulting from the coupling between different magnetic area (domain walls, domains) inside the garnet film and the Permalloy film. In particular, exaltation of intensive domain wall resonances occurs within the frequency range including the uniform gyromagnetic mode of the Permalloy film. The effect of the garnet and Permalloy film thicknesses on the features of the dynamic susceptibility spectra is then studied. The experimental power absorption spectra recorded on a Permalloy/YIGBiLuAl-like bilayer exhibit well-defined resonance lines, most of them assigned to coupled modes of the bilayer nicely predicted by the micromagnetic simulations. The strong direct exchange coupling at the interface between the two layers appears as a predominant factor for this metal-oxide system.