Hole doping effect on ferromagnetism in Mn-doped ZnO nanowires

We investigate the magnetic properties of Mn-doped ZnO nanowires (NWs) using the local spin density approximation (LSDA) and the LSDA+U approach, where U represents the on-site Coulomb interaction. In carrier-free (Zn,Mn)O NWs, the majority Mn ta states are fully occupied, leading to an antiferromagnetic ground state. We examine the effect of additional p-type doping on the ferromagnetism by considering surface O dangling bonds, Zn vacancies, and N impurities. For all cases, localized hole carriers are generated in the majority ta states and promote a ferromagnetic ordering via double exchange interactions, similar to the trend of bulk (Zn,Mn)O. The ferromagnetic coupling tends to increase with increasing of the hole carrier density.