The Onset of Auto-Oscillations of Parametrically Excited Spin-Wave Pairs

Abstract

The parallel pumping of spin waves in an yttrium iron garnet (YIG)sphere placed in a microwave cavity has been performed by X-band microwaves. The onset and the principal frequencyof auto-oscillations above the threshold of spin-wave instabilitywere studied at various magnetic fields. We found anomalous field dependence of auto-oscillations frequency in the low field side of the butterfly curve, where the threshold of parallel pumping instability exhibits no anomaly.This result shows that the higher order nonlinear relaxation process ofparametrically excited magnons becomes important in a nonequilibrium system.