Shape-induced anisotropy in antiferromagnetic nanoparticles

TL;DR

This paper investigates how the shape and surface crystallography of antiferromagnetic nanoparticles influence their magnetic anisotropy and domain structures, providing a predictive model for their magnetic properties.

Contribution

It introduces a model that accounts for shape and surface effects on magnetic anisotropy in antiferromagnetic nanoparticles, which was previously less understood.

Findings

Shape and crystallographic orientation affect magnetic anisotropy.

Surface anisotropy contributions depend on particle volume and magnetostriction.

The model predicts domain structures based on shape and surface treatment.

Abstract

High fraction of the surface atoms considerably enhances the influence of size and shape on the magnetic and electronic properties of nanoparticles. Shape effects in ferromagnetic nanoparticles are well understood and allow to set and control the parameters of a sample that affect its magnetic anisotropy during production. In the present paper we study the shape effects in the other widely used magnetic materials -- antiferromagnets, -- which possess vanishingly small or zero macroscopic magnetization. We take into account the difference between the surface and bulk magnetic anisotropy of a nanoparticle and show that the effective magnetic anisotropy depends on the particle shape and crystallographic orientation of its faces. Corresponding shape-induced contribution to the magnetic anisotropy energy is proportional to the particle volume, depends on magnetostriction, and can cause formation of equilibrium domain structure. Crystallographic orientation of the nanoparticle surface determines the type of domain structure. The proposed model allows to predict the magnetic properties of antiferromagnetic nanoparticles depending on their shape and treatment.