Half-metallic ferromagnetism in Cu-doped ZnO: Density functional calculations

Half-metallic ferromagnetism in Cu-doped ZnO is predicted by accurate full-potential linearized augmented plane-wave and DMol(3) calculations based on density functional theory. A net magnetic moment of 1 mu(B) is found per Cu. At a Cu concentration of 12.5%, total energy calculations show that the ferromagnetic state is 43 meV lower than the antiferromagnetic state and is thus predicted to be the ground state with a T-c estimated to be about 380 K. The magnetic moments are localized within the CuO4 tetrahedron with ferromagnetic coupling between Cu and O. The electronic states near E-F are dominated by strong hybridization between O 2p and Cu 3d which implies that the Cu-O bond is quite covalent instead of purely ionic. We examine the interplay between the carrier density and the ferromagnetism with N codoping and oxygen vacancies where we find no apparent relation between them. Oxygen vacancies tend to destroy the ferromagnetism and therefore should be avoided during sample fabrication. We found no clustering tendency of the Cu atoms. Since there is no magnetic element in this compound, Cu-doped ZnO appears to be an unambiguous dilute magnetic semiconductor where ferromagnetic precipitate problems can be avoided.