Ferromagnetism induced by the charge transfer in Al-doped ZnO nanoparticles

The mechanism of ferromagnetism in Al-doped ZnO was investigated both theoretically and experimentally. The density functional theory calculations were carried out to explore the electronic structure origin of ferromagnetism. The Al dopants both doping in a bulk ZnO and absorbing on the ZnO surface are taken into account. Based on the Bader charge analysis for the clear and adsorbed ZnO surface, it is found that the ionic state of Zn decreases after Al doping. The corresponding room temperature ferromagnetism was also confirmed by experiments. Moreover, the experimental analysis rules out that the ferromagnetism results from zinc vacancy or oxygen vacancy. Thus, the physical origin of the induced magnetism was indicated originating from the charge transfer between Zn atoms and adsorbed Al atoms.