Locking and chaos in magnetic resonance experiments (invited)

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Abstract
Nonlinear ferromagnetic resonance in YIG and (CH2NH3)2CuCl4 has been observed by the parallel pumping technique. When pumped above the threshold power the microwave absorption displays self-oscillations. In (CH2NH3)2CuCl4 the self-oscillations have the form of relaxation oscillations with varying irregularity described by high fractal dimensions up to D=5. A typical measurement is presented and compared to the results of the classically described 2n-dimensional stroboscopic model (SM). In YIG nearly harmonic self-oscillations at 170 kHz are observed as the system has approached a limit cycle. The microwave power was modulated at variable frequencies and locked states were observed at rational ratios of self-oscillation frequency to modulation frequency. The locked states are reproduced by SM for parameter values giving a limit cycle behavior and with the addition of a time-dependent pump. Both the experiment and the SM follow the main predictions of the circle map.