O-vacancy-mediated spin-spin interaction in Co-doped ZnO: First-principles total-energy calculations

The effects of O vacancy (V(O)) on the electronic and magnetic properties of Co-doped ZnO are examined through first-principles total-energy calculations. Our results suggest that due to the presence of V(O), O 2p states are coupled with the Co 3d states. Co 3d empty minority states are broadened and move up towards the Fermi level. V(O) at metastable sites can induce the ferromagnetic (FM) coupling between nearest-neighbor (NN) Co ions, and the atoms around the FM-coupled NN Co ions are spin-polarized which leads to the long-ranged FM coupling between Co ions. Our results based on first-principles total-energy calculations give a possible explanation for the controversial magnetic properties of Co-doped ZnO reported in the literature.