The effects of O vacancy (VO) on the electronic and magnetic properties of Co-doped ZnO were examined using first-principles total-energy calculations. The results suggested that, due to the presence of VO, O 2p states were coupled with the Co 3d states. The Co 3d empty minority states were broadened and moved up towards the Fermi level. The VO at metastable sites could induce ferromagnetic coupling between nearest-neighbour Co ions, and the atoms around the ferromagnetic-coupled nearest-neighbor Co ions were spin-polarized; leading to the long-ranged ferromagnetic coupling between Co ions. The results based upon first-principles total-energy calculations gave a possible explanation for the controversial magnetic properties of Co-doped ZnO.

O-Vacancy-Mediated Spin-Spin Interaction in Co-Doped ZnO: First-Principles Total-Energy Calculations. Liu, E.Z., Jiang, J.Z.: Journal of Applied Physics, 2010, 107[2], 023909