Several experimental studies have referred to the grain boundary GB defect as the origin of ferromagnetism in zinc oxide ZnO. However, the mechanism of this hypothesis has never been confirmed. Present study investigates the atomic structure and the effect of point defects in a ZnO GB using the generalized gradient ​approximation+U approximation. The relaxed GB possesses large periodicity and channels with 8 and 10 numbered atoms having 4 and 3 fold coordination. The Zn vacancy VZn shows a tendency to be attracted to the GB, relative to the bulk-like region. Although no magnetization is obtained from point defect-free GB, VZn induces spin polarization as large as 0.68 µB/atom to the O sites at the GB. Ferromagnetic exchange energy >150 eV is obtained by increasing the concentration of VZn and by the injection of holes into the system. Electronic structure analysis indicates that the spin polarization without external dopants originates from the O 2p orbitals, a common feature of d 0 semiconducto

DOI: 10.1063/1.4936659 ​​