Ferromagnetism induced by defect complex in Co-doped ZnO

The effect of Al donor and O vacancy (V(O)) on the magnetic properties of Co-doped ZnO has been studied by first-principles calculations. It is found that only Al donor cannot induce ferromagnetism (FM) in Co-doped ZnO but can provide additional electrons, which results in the enhancement of Fermi level. The presence of V(O) makes the Co empty 3d-t(2g) minority state broadened, and a t(2g)-V(O) hybrid level at the conduction band minimum forms. The combination of Al donor and V(O) results in a charge transfer to the Co empty 3d-t(2g) minority states, which induces a strong carrier-mediated FM interaction. Our results give an explanation for the controversial magnetic properties of (Co, Al)-codoped ZnO reported in the literature. (C) 2008 American Institute of Physics.