Annealing effect on the electronic structure and magnetic properties of Mn-doped ZnO films

We report an investigation of the local electronic structure and thermal diffusion mechanism of Zn0.8Mn0.2O epitaxial films by soft x-ray spectroscopy measurements. According to experimental results and establishment of the relationship between electronic structure and magnetic properties, the majority of Mn atoms are in substitutional sites in the as-grown film and the concentration of divalent Mn ions is found to be dominant in the ferromagnetic film, while after being annealed at 400 °C for 1 h, Mn atoms diffuse out of the ZnO lattice and accumulate in Mn-related secondary phases with high valence (+3 and/or +4) Mn ions. The formation of the secondary phases is correlated with the suppressed ferromagnetism (FM). The present results suggest that Mn2+ ions play a significant role for the FM in (Zn,Mn)O. (paper)