Crosstalk of propagating and localized spin-wave modes

The relaxation mechanisms in thin nickel films are investigated with all optical pump-probe experiments. Magnetic oscillations in the GHz range can be attributed to the uniform precession (Kittel mode) and spin waves with dipole character (Damon-Eshbach surface modes). Applying an external field changes both oscillation amplitude and frequency yielding experimental dispersions ν(Hext). On a wedge-shaped nickel sample we discuss i) the merging of Damon-Eshbach with the Kittel mode at a critical field as well as ii) the thickness dependence of the wave vector for magnetostatic surface waves. The signature of a non-linear interaction of modes is found such that the energy pumped into dipolar surface modes is transferred to the Kittel mode and the relaxation amplitude resonantly increases at mode crossings.