Correlation between ferromagnetism and dopant 3d metal-oxygen hybridized state lying at the bottom of conduction band in ZnO-based diluted magnetic semiconductor system

We systematically investigate the unoccupied electronic states, crystal structure, and magnetism of V- and Mn-doped ZnO nanocrystals (NCs). Post-annealing treatment at 300 °C converts diamagnetic V5+ into magnetic high-spin V3+ ions, which leads to room-temperature ferromagnetism for the V-doped NCs. In contrast, ferromagnetism does not occur for the Mn-doped NCs. Oxygen 1s x-ray absorption spectroscopy reveals that the unoccupied metal-oxygen hybridized state lies near the bottom of the conduction band for the V-doped NCs but lies far above it for the Mn-doped NCs. Therefore, the ferromagnetism in a ZnO-based diluted magnetic semiconductor system can be understood within the framework of the n-type carrier-mediated ferromagnetism model.