Electron-Paramagnetic-Resonance Spectrum of a Spin System with Weak Exchange Couplings

Abstract

The temperature dependence of the EPR spectra is studied for a weakly exchange-coupled spin system with a single-ion anisotropy. The method of moments is generalized in order to take into account the collective motion of spins. The first two moments are calculated in the molecular-field approximation and are applied to a system with a hard-axis crystal-field anisotropy. The EPR linewidths are seriously affected by the soft-mode behavior of the collective mode immediately before the appearance of a transverse ordering.