Theoretical study of magnetic domain walls through a cobalt nanocontact

TL;DR

This paper introduces a first-principles computational method to determine the magnetic ground state of nanoparticles, applied to cobalt nanocontacts, revealing a cycloidal domain wall configuration with significant anisotropy effects.

Contribution

It develops a relativistic embedded cluster Green's function approach combined with a Newton-Raphson algorithm to accurately find magnetic ground states of nanoparticles.

Findings

Cycloidal domain wall is energetically favored over helical structure.

Uniaxial on-site anisotropy dominates the energy difference.

Enhanced orbital magnetic moment linked to anisotropy.

Abstract

To calculate the magnetic ground state of nanoparticles we present a self-consistent first principles method in terms of a fully relativistic embedded cluster multiple scattering Green's function technique. Based on the derivatives of the band energy, a Newton-Raphson algorithm is used to find the ground state configuration. The method is applied to a cobalt nanocontact that turned out to show a cycloidal domain wall configuration between oppositely magnetized leads. We found that a wall of cycloidal spin-structure is about 30 meV lower in energy than the one of helical spin-structure. A detailed analysis revealed that the uniaxial on-site anisotropy of the central atom is mainly responsible to this energy difference. This high uniaxial anisotropy energy is accompanied by a huge enhancement and anisotropy of the orbital magnetic moment of the central atom. By varying the magnetic orientation at the central atom, we identified the term related to exchange couplings (Weiss-field term), various on-site anisotropy terms, and also those due to higher order spin-interactions.