Non-Arrhenius behavior in single domain particles

Thermally assisted reversal in noninteracting single domain particles is studied through the use of a micromagnetic model with a stochastic fluctuation field. The magnetization decay of these particles at high and low anisotropy fields is studied and compared to Arrhenius-Neel decay. Estimates of the attempt frequency are made by fitting to exponential decay. The attempt frequency is also examined while varying the applied field, the anisotropy field, and the temperature. Special attention is given to combinations of these variables which give a constant height of the energy barrier to reversal. It is shown that the attempt frequency can vary dramatically even for a constant height of the energy barrier. The basic scaling laws of the system are discussed, and the scaled attempt frequencies are plotted to test their universality.