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Spin-wave dynamics in a ferrimagnetic sphere

1988; American Institute of Physics; Volume: 38; Issue: 8 Linguagem: Inglês

10.1103/physreva.38.4223

0556-2791

Paul H. Bryant, C. D. Jeffries, Katsuhiro Nakamura,

Chaos control and synchronization

An experimental study is made of the interactions between spin-wave modes excited in a sphere of yttrium iron garnet by pumping the Suhl subsidiary absorption at 9.2 GHz with the dc field parallel to [111]. The dynamical behavior of the magnetization is observed under high resolution by varying two control parameters, dc field (580 Oe<H<2100 Oe) and microwave pump power (1 mW<P<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 auto-oscillations with a systematic dependence of frequency (${10}^{4}$--${10}^{6}$ 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 is developed from first principles, using the plane-wave approximation and including anisotropy effects, obtaining the lowest-order nonlinear interaction terms between the excited modes. Bifurcation behavior is examined, and dynamical behavior is numerically computed and compared to the experimental data, explaining a number of features. A theory is developed regarding the nature of the experimentally observed relaxation oscillations and spiking behavior based on the interaction of ``weak'' and ``strong'' modes, and this is demonstrated in the numerical simulations.