We have investigated electronic structures and magnetic properties of ZnO-based potential diluted magnetic semiconductors codoped with transition metals: ${\mathrm{Zn}}_{1-x}(\mathrm{FeCo}{)}_x\mathrm{O}$ and ${\mathrm{Zn}}_{1-x}(\mathrm{FeCu}{)}_x\mathrm{O}.$ We have found that the origin of the observed ferromagnetism in ${\mathrm{Zn}}_{1-x}(\mathrm{FeCo}{)}_x\mathrm{O}$ would be different from that in ${\mathrm{Zn}}_{1-x}(\mathrm{FeCu}{)}_x\mathrm{O}.$ ${\mathrm{Zn}}_{1-x}(\mathrm{FeCo}{)}_x\mathrm{O}$ does not have a tendency to form the Fe-O-Co ferromagnetic cluster, and so the double-exchange mechanism will not be effective. In contrast, ${\mathrm{Zn}}_{1-x}(\mathrm{FeCu}{)}_x\mathrm{O}$ has a tendency to form the Fe-O-Cu ferromagnetic cluster with the charge transfer between Fe and Cu, which would lead to the ferromagnetism via a type of the double-exchange mechanism. The ferromagnetic and nearly half-metallic ground state is obtained for ${\mathrm{Zn}}_{1-x}(\mathrm{FeCu}{)}_x\mathrm{O}.$

• Received 15 July 2003

DOI:https://doi.org/10.1103/PhysRevB.68.224436