Classical dynamics of resonantly modulated large-spin systems

Abstract

We study the classical dynamics of resonantly modulated large-spin systems in a strong magnetic field, where the Zeeman energy exceeds the anisotropy energy. We show that these systems have special symmetry. It leads to characteristic nonlinear effects. They include abrupt switching between magnetization branches with varying modulating field without hysteresis and a specific pattern of switching in the presence of multistability and hysteresis. Along with steady forced vibrations, the transverse spin components can display incoherent vibrations at a combination of the Larmor frequency and a smaller frequency determined by the anisotropy constant. The analysis is based on a microscopic theory that takes into account relaxation mechanisms important for single-molecule magnets and other large-spin systems. We find how the Landau‐Lifshitz model should be modified in order to describe the classical spin dynamics. The occurrence of incoherent oscillations depends on the interrelation between the relaxation parameters.