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

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.