Temperature-Induced Nonlinearity at Parametrically Excited Spin Waves

Parametrically excited spin waves in magnetic spheres of yttrium iron garnet give rise to complex multistable behaviour, which occurs for special experimental conditions at room temperature, but vanishes at helium temperature. This is in contrast to what one expects from the decreasing damping of the spin waves with temperature, which should result in an even more complex multistability at low temperature. We conclude that, in addition to the well-known nonlinear dipolar couplings, a "temperature-induced" nonlinearity occurs, which is only effective at higher temperature. This novel effect in solid-state physics can be qualitatively understood from the special form of the Hamiltonian of this system.