Transition temperature and magnetic properties of the granular Ising model in two dimensions studied by Monte Carlo simulations: Impact of intragrain spin structure

Abstract

Monte Carlo simulations are performed on a stacked square lattice model of weakly interacting magnetic grains composed of Ising spins. The role of intragrain spin structure on thermal properties are investigated in this simple representation of granular recording media. Various thermodynamic quantities are calculated using a cluster-flip algorithm which exhibit anomalies corresponding to both intragrain and intergrain ordering. In the single-layer case, the intergrain transition temperature vs intergrain exchange coupling strength exhibits a crossover to a nonlinear regime where the intragrain spin structure becomes increasingly important. Corresponding results on multilayer systems are shown to be in good agreement with scaling theory. Preliminary magnetization vs applied field $(M\text{\ensuremath{-}}H)$ loops are also calculated as a function of temperature and indicate the possible effect of the grain spin structure.