First-principles density-functional theory calculations were used to study the magnetic properties of ZnO:Cr; with and without vacancies. The results indicated that the doping of Cr into ZnO introduced obvious spin polarization around the Fermi level and a total magnetic moment of 3.77μB. The ferromagnetism exchange interaction between Cr atoms was short-ranged and decreased with increasing Cr separation distance. It was suggested that the ferromagnetic state was not stable at low concentrations of Cr. The presence of O vacancies could make the half-metallic ferromagnetic state of the system more stable, so that higher Curie temperature ferromagnetism could be expected. Nevertheless, Zn vacancies could result in the ferromagnetism stability decreasing slightly. The calculated formation energy showed that a VZn+CrZn complex formed spontaneously under O-rich conditions. However, under Zn-rich conditions, a complex of VO+CrZn formed more easily. Thus, ZnO doped with Cr could exhibit a concentration of vacancies that influenced the magnetic properties.

Theoretical Study of the Magnetic Interaction of Cr-Doped ZnO with and Without Vacancies. Wang, F., Pang, Z., Lin, L., Fang, S., Dai, Y., Han, S.: Journal of Magnetism and Magnetic Materials, 2009, 321[19], 3067-70