Effects of Co doping and O vacancy on the magnetism of ZnO

Abstract

Existing defect models for Co-doped ZnO with O vacancy (VO) are controversial in explaining the origin of the magnetism. To address this issue, we investigated the effects of Co doping and VO on the magnetic properties of ZnO through first-principles calculations by using generalized gradient approximation + U under the density functional theory. The total density of states of co-doping of one Co and one VO shows half-metallic behavior, which is highly beneficial when using dilute magnetic semiconductors (DMSs) as a hole injection source. The ferromagnetism for co-doping of one Co and one VO is derived from the double exchange effects among the spin polarized electrons of O–2p, Co–3d, and Zn–4s states as mediated by the electron carriers from VO, which is consistent with the mean field approximation theory and the double exchange mechanism theory. The co-doping of two Co and two VO causes the ZnO crystal undergo transition from anti-ferromagnetism (AFM) to ferromagnetism (FM) with the change of Co–Co distance. Zn34Co2O35d (the Co–Co distance is 6.136 Å) can achieve Curie temperature higher than room temperature. In the same doping mode, increased concentrations of Co and VO increase the net magnetic moments.