CHAOS IN MAGNETIC RESONANCE EXPERIMENTS

Non linear antiferromagnetic resonance was observed by parallel pumping (PP) with continuous waves in (NH3CH2)2 CuCl4. This system is unique in its low threshold for PP and its strong anisotropy. The absorbed microwave power displays self spiking. As a function of power the irregularity of periods between the spikes changes. Reproducible transitions from nearly regular to irregular spiking are found (RI-transitions) with information dimensions DI in the range 2.5 ≤ Dr ≤ 5. For certain parameter settings a hierarchy of RI transitions with different amplitudes is observed. The measurements are compared to the results of the 2n-dimensional stroboscopic model (SM), which describes the dynamics of n non-linear coupled spin wave modes. The SM simulates the mentioned behaviour for n = 2 and for strong anisotropy. Certain measurements with large DI were more readily modeled by the three mode SM