Magnetization curling in elongated heterostructure particles.

Abstract

A rigorous micromagnetic study of nucleation by use of the magnetization curling mode in an elongated particle with heterostructure is presented. We categorize the heterostructure particles into three different types depending on their growth conditions and internal structures. The coercivity of the heterostructure particles critically depends on the relative magnetic parameters of the composite materials. The physical origins of the enhanced coercivity for the three types of heterostructure particles are quite different. The initial slope of the enhanced coercivity of surface-coated particles results from the shell crystalline anisotropy, while the saturation level depends on the interfacial coupling, shell crystalline anisotropy, and shell surface anisotropy. The main contribution to the enhancement of the coercivity of surface-modified particles is the surface anisotropy of the adsorbed layer at the particle surface. The homogeneity of the doped materials within the volume-modified particles affects their coercivity and the saturation level of the coercivity is always higher than that of the other two types. Agreement between theory and experiment is reasonably good.