Self-oscillations in spin-wave instabilities

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Abstract
An experimental and theoretical study of bifurcations leading to self-oscillations in spin-wave instabilities pumped by microwave fields is presented. The experiments were done with spheres of yttrium iron garnet of various diameters pumped by X-band microwave radiation in the parallel pumping and subsidiary resonance configurations. The results reveal a variety of bifurcations and chaos depending on the experimental parameters. Generally the frequency and threshold of the self-oscillations show a definite dependence on sample size not predicted by the existing models. On the theoretical side we show that the usual equations describing two interacting spin-wave modes predict various types of bifurcations, depending on the set of parameters. In particular we investigate Hopf bifurcations and homoclinic phenomena. We also show that the introduction of boundary conditions and momentum symmetry breaking in the spin-wave pumping in finite samples accounts for important quantitative features of the experimental observations not explained by the existing models.

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