Thermally Activated Magnetisation Reversal at High Frequencies

A computational model of thermally activated magnetisation reversal in particulate materials is described. The model allows the study of the detailed relaxation behaviour of isolated (non-interacting) particles. Computed results show non-exponential relaxation over small energy barriers attributable to the absence of a unique relaxation time. The coercivity shows a rapid increase at very short measurement time which is important as regards ultimate switching speeds in recording. The effects of interparticle dipolar magnetic interactions are also introduced into the model. These have the effect of increasing the spread of relaxation times via the inevitable dispersion in the magnitude and direction of the local field.