Coupling of spin-wave modes in extended ferromagnetic thin film antidot arrays

The pattern-induced frequency splitting of propagating spin-wave modes of extended micron scale square antidot arrays fabricated from 15--120-nm-thick Ni₈₀Fe₂₀ films has been studied via Brillouin light scattering. The splitting of the surface and first volume mode is observed to be of the order of 2 GHz. Using a simple model which assumes that the spectral weight of the scattered light directly reflects the map of the spatially varying demagnetizing field, the peak splitting can be explained satisfactorily. We infer that the measured spectrum is the result of almost uncoupled propagating spin waves which correspond to regions of near constant demagnetizing field within the unit cell of the array. We conclude that in contrast to confinement effects seen in small isolated structures (dots, rectangles), the local magnetization and demagnetizing field principally determine the spin-wave mode character and its dispersion with wave vector rather than the edge boundary conditions of the array structure.