Fractal Structure of Strange Attractor at the Subsidiary Resonance in Yttrium Iron Garnet

Transverse pumping at the first-order Suhl instability in YIG has been performed at a pumping frequency of 3.3 GHz at 4.2 K. Above the spin-wave instability threshold, period-doubling cascades and chaotic auto-oscillations are observed. From time-series data, return maps, fractal dimensions, phase space portraits of strange attractors, two-dimensional Poincaré sections, and singularity spectrum f(α) are obtained. The Poincaré sections of the phase space trajectories exhibit the stretching and folding which are characteristics of strange attractors. At the onset of chaos, the f(α) spectrum is consistent with the universal one.