Spin-wave auto-oscillations still in need of a good model

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Abstract
The onset of spin-wave auto-oscillations has been studied in spheres of yttrium iron garnet pumped by a microwave field parallel or perpendicular to the dc field. Data were taken for the auto-oscillation threshold field, amplitude, and frequency as a function of sample dimension, shape, and the spin-wave relaxation rate and wave vector. The behavior near the onset confirms the theoretical prediction that the auto-oscillation results from a Hopf bifurcation. However, data for the auto-oscillation frequency and threshold field are in clear disagreement with predictions. These results indicate that although the area of nonlinear spin-wave phenomena has been under investigation for over 30 years, a good model is still needed for the auto-oscillations.