Spin-Polarized Ground States and Ferromagnetic Order Induced by Low-Coordinated Surface Atoms and Defects in Nanoscale Magnesium Oxide

TL;DR

This study demonstrates that low-coordinated surface atoms and vacancies in MgO nanocrystals induce a spin-polarized ground state with long-range ferromagnetic order, revealed through hybrid density functional theory calculations.

Contribution

It reveals the role of low-coordinated surface atoms and vacancies in inducing ferromagnetism in MgO nanocrystals, a novel insight into defect-induced magnetism.

Findings

Mg vacancies at corners lower the energy of magnetic states by 1-2 eV.

Spin density extends to distant low-coordinated surface O atoms.

Remote Mg vacancies interact to produce long-range ferromagnetism.

Abstract

We investigate the effect of low-coordinated surface atoms on the defect-induced magnetism in MgO nanocrystallites using hybrid density functional theory calculations. It has been demonstrated that when Mg vacancies are introduced at the corners of cube-like MgO clusters, a magnetic state becomes lower in total energy than the nonmagnetic singlet state by 1-2 eV, resulting in the spin-polarized ground state. The spin density is not only located at the surrounding O atoms neighbor to the corner Mg vacancy site but is also extended to the distant (1 nm or longer) low-coordinated surface O atoms along the <110> directions. This directional spin delocalization allows a remote Mg vacancy-Mg vacancyinteraction, eventually leading to a spontaneous long-range ferromagnetic interaction.