CHAOS IN MAGNETIC RESONANCE EXPERIMENTS

Abstract
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 D_I in the range 2.5 ≤ D_r ≤ 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 D_I were more readily modeled by the three mode SM.