Enhanced coercive force of nanoparticles of special morphology in the Stoner-Wohlfarth model

Abstract

We have found an unusual effect of increasing the coercive force in the Stoner-Wohlfarth model applied to magnetic nanoparticles of a special morphology. The particles consist of a ferromagnetic single-domain core surrounding by a magnetically soft shell. We have studied thoroughly individual and collective properties of these particles both through numerical calculations and analytical analysis. Fairly accurate approximate analytical formulas have been obtained for determining magnetization, hysteresis loop, coercive force, and other magnetic properties of the particles. The physical reason of the coercivity enhancement effect is the magnetic screening of a particle core by its shell. We have found the unambiguous conditions necessary for the existence of this effect. The large magnetization and moderate magnetic anisotropy of the core favor the effect of the coercivity enhancement.