Two-magnon scattering and viscous Gilbert damping in ultrathin ferromagnets

Abstract

Ferromagnetic resonance experiments of magnetic nanostructures over a large frequency range from $1\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}225\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$ are presented. We find unambiguous evidence for a nonlinear frequency dependence of the linewidth. The viscous Gilbert damping and two-magnon scattering are clearly separated. Both angular and frequency dependent measurements give a transverse scattering rate within the magnetic subsystem of the order of ${10}^{9}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, whereas the longitudinal Gilbert relaxation into the thermal bath is one to two orders of magnitude smaller.