Magnetization switching in single-domain ferromagnets

A model for single-domain uniaxial ferromagnetic particles with high anisotropy, the Ising model, is studied. Recent experimental observations have been made of the probability that the magnetization has not switched, P_NOT. Here an approach is described in which it is emphasized that a ferromagnetic particle in an unfavorable field is, in fact, a metastable system, and the switching is accomplished through the nucleation and subsequent growth of localized droplets. Nucleation theory is applied to finite systems to determine the coercivity as a function of particle size and to calculate P_NOT. Both of these quantities are modified by different boundary conditions, magnetostatic interactions, and quenched disorder.