Chaos and energy loss of nonlinear domain wall motion

A chaotic region of domain wall motion is calculated as a function of the amplitude and frequency of the external magnetic drive field. It shows an intricate pattern composed of regular and chaotic regions. An energy loss and the Lyapunov exponent of domain wall motion are calculated. A frequency at the peak of the energy loss versus frequency curve, namely a nonlinear resonance frequency, is different from a resonance frequency in the linear theory as it shifts toward a lower frequency with increasing amplitude of the external magnetic drive field. This peak shift is explained by the effect of the higher order term in the nonlinear restoring force. The energy loss versus frequency curve becomes irregular and the energy loss decreases in the chaotic region where the Lyapunov exponent is positive. (C) 1997 American Institute of Physics.