Nonlinear dynamics of spin waves (invited)

Abstract

For a yttrium-iron-garnet sphere at room temperature, an experimental study is made of the first-order Suhl spin-wave instability using perpendicular pumping at 9.2 GHz with the dc field parallel to the [111] crystal axis. The dynamical behavior of the magnetization is observed with high resolution by varying two control parameters, dc field (580<H0<2100 G) and microwave pump power (1<Pin <200 mW). Within this parameter space quite varied behavior is found: (i) onset of the Suhl instability by excitation of a single spin-wave mode with very narrow linewidth (<0.5 G); (ii) when two or more modes are excited, interactions lead to collective oscillations (‘‘auto-oscillations’’) with a systematic dependence of frequency (104–106 Hz) on pump power, these oscillations displaying period-doubling to chaos; (iii) quasiperiodicity, locking, and chaos occur when three or more modes are excited; (iv) abrupt transition to wide band power spectra (i.e., turbulence), with hysteresis; (v) irregular relaxation oscillations and aperiodic spiking behavior. A theoretical model of coupled modes is numerically evaluated and found to exhibit a behavior pattern similar to those observed experimentally.