Observation of auto‐oscillations and chaos in subsidiary absorption in yttrium iron garnet

Auto‐oscillations of the dynamic magnetization and routes to chaos for the first‐order transverse pump spin‐wave instability have been studied in single‐crystal yttrium‐iron‐garnet (YIG) films. The measurements reported here were made on a 20.8‐μm‐thick YIG film at 9.4 GHz with the static and microwave fields in the plane of the film. Auto‐oscillations at 100–400 kHz were observed in the power absorbed by the film over a relatively narrow static field range of 1100–1460 Oe, compared to the first‐order instability (FOI) range of 0–1630 Oe. The auto‐oscillation frequency and threshold microwave field amplitude were both strongly field dependent. The threshold amplitudes were about a factor of 2 larger than the FOI threshold amplitudes. At even higher power levels and for an even narrower field range of 1300–1380 Oe, the auto‐oscillations showed frequency changes indicative of chaotic behavior. Several different subharmonic bifurcation routes to chaos were observed for different fields within the chaotic region.