Impact of Surface on the d0 Ferromagnetism of Lithium-Doped Zinc Oxide Nanowires

We present a first-principles study on the impacts of the surface on the ferromagnetism (FM) induced by non-magnetic defects (lithium substitutional dopants at zinc sites Li-Zn and zinc vacancies V-Zn) of zinc oxide (ZnO) nanowires. We show that unlike bulk ZnO structures, both Li-Zn and V-Zn are able to induce d(0) FM in ZnO nanowires. While the structural confinement at the nanowire surface is found to play a key role in the FM induced by Li-Zn, the reconstruction of the surface tunes the defect-induced FM. By suppressing the surface reconstruction, we find that a Li-Zn and a V-Zn, regardless of their position, induce the same magnetic moments of 0.71 and 2.00 mu B (mu B is the magneton Bohr), respectively. The steady correlation between the defect-induced FM, the dangling bonds introduced at these defects, and the local structural reconstruction surrounding these defects is unveiled. Finally, we discuss the saturation of the magnetic moment as the defect density increases.