EFFECTS OF BOUNDARY-CONDITIONS ON MAGNETIZATION SWITCHING IN KINETIC ISING-MODELS OF NANOSCALE FERROMAGNETS

Magnetization switching in highly anisotropic single-domain ferromagne ts has been previously shown to be qualitatively described by the drop let theory of metastable decay and simulations of two-dimensional kine tic Ising systems with periodic boundary conditions. In this paper we consider the effects of boundary conditions od the switching phenomena . A rich range of behaviors is predicted by droplet theory: the specif ic mechanism by which switching occurs depends on the structure of the boundary, the particle size, the temperature, and the strength of the : applied field. The theory predicts the existence of a peak in the sw itching field as a function of system size in both systems with period ic boundary conditions and in systems with boundaries. The size of the peak is strongly dependent on the boundary effects. It is generally r educed by open boundary conditions, and in some cases it disappears if the boundaries are too favorable towards nucleation. However, we also demonstrate conditions under which the peak remains discernible. This peak arises as a purely dynamic effect and is not related to the poss ible existence of multiple domains. We illustrate the predictions of d roplet theory by Monte Carlo simulations of two-dimensional Ising syst ems with various system shapes and boundary conditions.