Magnetic interactions in an ensemble of cubic nanoparticles: A Monte Carlo study

Abstract

The ensemble of spatially disordered and randomly oriented spherical monodispersed single-domain magnetic nanoparticles with cubic anisotropy was studied by the Monte Carlo method. In the presence of dipole-dipole interactions, the effect of both particle volume and interparticle separation was investigated with respect to the characteristic parameters of hysteresis loops and zero field cooled and field cooled magnetization curves. The coercive field and remanent magnetic moment were shown to depend strongly on the dimensionless parameter $\ensuremath{\beta}={k}_{B}T/({K}_{1}V)$ ($T$ temperature, $V$ particle volume, ${K}_{1}$ cubic anisotropy constant). It was revealed that strong dipole-dipole interactions suppress both the coercive field and the remanent magnetic moment of densely packed nanoparticles. Yet, the effect quickly diminishes with the increasing interparticle distances and becomes rather insignificant for separations exceeding three particle diameters. The blocking temperature was found to be weakly affected by dipolar interactions, but mainly governed via $\ensuremath{\beta}$, i.e., by the nanoparticle volume and the strength of crystalline anisotropy. The role of dipole-dipole interactions on magnetic properties of nanoparticles was further elucidated by a comparison of the simulation results for a single cluster with an infinite periodic arrangement of such clusters.