Electronic structures and ferromagnetism in transition metals codoped ZnO

We have investigated electronic structures and magnetic properties of potential ZnO based diluted magnetic semiconductors: (Fe, Co) and (Fe, Cu) codoped ZnO. The origins of ferromagnetism are shown to be different between two. (Fe, Co) codoped ZnO does not have a tendency of Fe-O-Co ferromagnetic cluster formation, and so the double exchange mechanism will not be effective. In contrast, (Fe, Cu) codoped ZnO has a tendency of the Fe-O-Cu ferromagnetic cluster formation with the charge transfer between Fe and Cu, which would lead to the ferromagnetism through the double-exchange mechanism. The ferromagnetic and nearly half-metallic ground state is obtained for (Fe, Cu) codoped ZnO.