Numerical simulations of chaotic and hyperchaotic signals measured in nonlinear magnetic resonance

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Abstract
Nonlinear antiferromagnetic resonance observed by the parallel pumping technique in anisotropic materials exhibits a rich temporal behavior of the absorbed microwave power. When pumped well above the instability threshold, this involves fractal dimensions up to around 5. The basic physical behavior can be described with models that account for the interaction of n excited spin-wave modes. We report on simulations based on the 2n-dimensional stroboscopic model that allows an analytic integration of the (classical) spin motion between the strobing times. For three coupled spin-wave modes (n=3) we find two positive Lyapunov exponents indicating hyperchaotic behavior. The transitions from chaos to hyperchaos, which are observed upon variation of two different control parameters, can clearly be interpreted in terms of excited modes that actively contribute to the spin dynamics. Four coupled modes yield an even stronger chaos with three positive Lyapunov exponents. Moreover, we characterize our system by calculating spectra of local expansion exponents.