Observation of Nonlinear Coupled Photon-Magnon Oscillations in YIG

Nonequilibrium spin waves excited by the parallel pumping in an yttrium iron garnet placed in a microwave cavity was studied by means of additional weak microwave signal. The response of the probe signal represented a two-hump spectrum just above the threshold of parametric instability. It corresponds to mixed oscillations of photons and magnons and demonstrates that the parametric spin-wave pair behaves as a single-mode oscillator nonlinearly coupled with the electromagnetic mode of microwave cavity. We observed another splitting in the spectrum before the onset of auto-oscillations. It is assumed to indicate that this steady state of parametric system consists of two different parametric spin-wave pairs. Theoretical calculations which consider coupled systems of resonator mode and magnetic sample are found to be in good agreement with the experimental data.