Magnetic excitation in weak stripe domains: Ferromagnetic resonance and Brillouin light scattering studies

Ferromagnetic films with perpendicular anisotropy and above a critical thickness exhibit weak stripe magnetic domains. The dynamic response of such systems with inhomogeneous state under moderate applied field can then be a probe of the local as of the macroscopic magnetization evolution. The static properties of Permalloy (Py) films of different thicknesses are obtained by VSM and MFM. Then the dynamic response is both investigated with a micro-stripe line device (FMR) and by Brillouin light scattering (BLS). For thick Py films three modes are observed below saturation which merge into a single one in the saturated state. Micromagnetic simulations have been performed to get the various resonance frequencies and the spatial distribution of the modulus of the dynamic magnetization for each mode. BLS spectra also show frequency multi-modes (at low q) in the non saturated state.