Two-magnon scattering in Permalloy thin films due to rippled substrates

We report on the influence of correlated substrate roughness on the two-magnon scattering in 30 nm Ni81Fe19 thin films. Using ion beam erosion periodically modulated substrates (ripple) were produced with wavelengths between 20 nm and 432 nm. This surface corrugation is adopted by magnetic layers grown on top yielding dipolar stray fields if magnetization and ripple ridges are aligned perpendicular. In case of λ ≥ 222 nm the evolving periodic field pattern trigger two-magnon scattering, which depends strongly on the direction of magnetization with respect to the ripple pattern. In-plane broadband ferromagnetic resonance reveals prominent peaks in the frequency dependent linewidth measured perpendicular to the ripple ridges. These peaks can be switched off if the magnetization is aligned along the ripple ridges.