Magnetic states at the Oxygen surfaces of ZnO and Co-doped ZnO

TL;DR

This study uses first principles calculations to explore magnetic properties at the oxygen surfaces of ZnO and Co-doped ZnO, revealing surface-enhanced magnetism and the influence of Co doping.

Contribution

It demonstrates that Co doping enhances surface stability and induces robust ferromagnetism at the oxygen surface even without magnetic atoms.

Findings

Large magnetic moments develop on substitutional Co ions.

Surface spin polarization is three times larger than in bulk.

A stable ferromagnetic state exists at the oxygen surface without magnetic dopants.

Abstract

First principles calculations of the O surfaces of Co-ZnO show that substitutional Co ions develop large magnetic moments which long-range coupling depends on their mutual distance. The local spin polarization induced at the O atoms is three times larger at the surface than in the bulk, and the surface stability is considerably reinforced by Co. Moreover, a robust ferromagnetic state is predicted at the Oxygen (0001) surface even in the absence of magnetic atoms. The occurrence of surface magnetic moments correlates with the number of {\it p}-holes in the valence band of the oxide, and the distribution of the magnetic charge is, even in the absence of spin-orbit interaction, highly anisotropic.