Magnetism in C or N-doped MgO and ZnO: density-functional study of impurity pairs

TL;DR

This study uses density-functional theory to investigate how impurity pairs like C and N affect magnetism in MgO and ZnO, revealing that impurity pairing can hinder or promote ferromagnetism depending on the host material.

Contribution

It demonstrates that impurity pairing limits ferromagnetism in MgO but enables long-range ferromagnetic interactions in ZnO through hybrid functional calculations.

Findings

Impurity pairs form C2 and N2^{2+} dimers with antiferromagnetic interactions in MgO.

Resonance of C2 states with conduction band induces ferromagnetism in ZnO.

Impurity molecules may be a route to d0-ferromagnetism in oxide spintronics.

Abstract

It is shown that substitution of C or N for O recently proposed as a way to create ferromagnetism in otherwise nonmagnetic oxide insulators is curtailed by formation of impurity pairs, and the resultant C2 spin=1 dimers as well as the isoelectronic N2^{2+} interact antiferromagneticallly in p-type MgO. For C-doped ZnO, however, we demonstrate using the HSE hybrid functional that a resonance of the spin-polarized C2 pp\pi* states with the host conduction band results in a long-range ferromagnetic interaction. Magnetism of open-shell impurity molecules is proposed as a possible route to d0-ferromagnetism in oxide spintronic materials.