Ferromagnetism in ZnO with (Mn, Li) codoping

First-principles calculations were performed to investigate the magnetic properties of Zn(Mn, Li)O based on the Perdew-Burke-Ernzerhof form of the generalized gradient approximation. Antiferromagnetic (AFM) ordering is the ground state in Mn-doped ZnO system without the codopant of Li, while seven different geometrical configurations of Zn(Mn, Li) O prefer stable ferromagnetic (FM) ordering. We found that dopant Li can effectively change the magnetic coupling in the ZnMnO system. The Curie temperature (T-C) of FM ordering depends on the geometric configuration, and the highest T-C is about 1388 K. The FM stabilization is greatly affected by Mn-Mn distance rather than by the position of dopant Li. We propose that dopant Li mediates FM coupling through a double exchange interaction or an RKKY interaction when Li is located, respectively, near or far from Mn ions.