THE ONSET OF AUTOOSCILLATIONS OF PARAMETRICALLY EXCITED SPIN-WAVE PAIRS

The parallel pumping of spin waves in an yttrium iron garnet (YIG) sph ere placed in a microwave cavity has been performed by X-band microwav es. The onset and the principal frequency of auto-oscillations above t he threshold of spin-wave instability were studied at various magnetic fields. We found anomalous field dependence of auto-oscillations freq uency in the low field side of the butterfly curve. where the threshol d of parallel pumping instability exhibits no anomaly. This result sho ws that the higher order nonlinear relaxation process of parametricall y excited magnons becomes important in a nonequilibrium system.