Abstract
Room-temperature ferromagnetism (RTFM) has been achieved in rare earth (RE) element doped ZnO nanostructures, while the mechanism of RTFM is still under debate. In this work, we investigated the electronic structure and magnetic properties of Nd-doped ZnO nanowires, and the influence of oxygen vacancies by using ab initio calculations. The impurity Nd atoms prefer to substitute the surface Zn sites and be ferromagnetically coupled with a moment of ~3.0 μB per Nd in the doped ZnO nanowires, through a superexchange interaction mediated by the oxygen ions. More interestingly, the surface oxygen vacancy can greatly enhance the stability of the ferromagnetic state via the "local carriers" of Nd- and Zn-s electrons, which accounts for the room-temperature ferromagnetism in the Nd-doped ZnO nanowires. This mechanism and analysis can be applied to other rare earth element doped semiconductor nanostructures.
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