Spin-wave instabilities, auto-oscillations, and chaos in yttrium-iron-garnet

A review is presented of recent experimental results in yttrium-iron-garnet subject to three different spin-wave pumping mechanisms: parallel pumping, subsidiary resonance (first-order Suhl process), and premature saturation of the main resonance (second-order Suhl process). A theoretical model derived from first principles and leading to coupled nonlinear spin-wave equations, is used to interpret the observed spin-wave instabilities, auto-oscillations, and chaotic dynamics. It is shown that a two-mode model explains the main features of the experimental observations, both in parallel and perpendicular pumping. Improvements needed in the model are indicated.