Monte Carlo simulation of a cluster system with strong interaction and random anisotropy

Abstract

The Monte Carlo method is used to study magnetic properties of amorphous rare-earth (RE) and transition-metal alloys, based on a model in which the magnetic units are magnetic clusters. Each cluster is assumed to possess a certain magnetic moment, which decreases with increasing temperature, and a Curie temperature Tc cluster. A random distribution is assumed for the magnetic easy directions of the clusters. Monte Carlo simulations were carried out to simulate magnetization curves after zero-field cooling and magnetic hysteresis loops at different temperatures. The simulation results showed presence of two other critical temperatures Tblock and Tc system below Tc cluster. Here Tblock is the blocking temperature due to the anisotropy energy of clusters, while Tc system is the freezing temperature due to interactions between clusters. If Tc system is lower than Tblock, the system behaves as a normal superparamagnetic material, characterized by a relatively weak effect of cluster correlation and/or dipole interaction. If Tc system is higher than Tblock, as in the case of many amorphous rare-earth and transition-metal alloys, it is possible to have three magnetic states, depending on the temperature: ferromagnetism when T