Khalid, M., Ziese, M., Setzer, A., Esquinazi, P., Lorenz, M., Hochmuth, H., Grundmann, M., Spemann, D., Butz, T., Brauer, G., Anwand, W., Fischer, G., Adeagbo, W. A., Hergert, W., Ernst, A.
Physical Review B 80, (3), pp 035331/1-5 (2009)
We have investigated the magnetic properties of pure ZnO thin films grown under N2 pressure on a-, c-, and r-plane Al2O3 substates by pulsed-laser deposition. The substrate temperature and the N2 pressure were varied from room temperature to 570 °C and from 0.007 to 1.0 mbar, respectively. The magnetic properties of bare substates and ZnO films were investigated by SQUID magnetometry. ZnO films grown on c- and a-plane Al2O3 substrates did not show significant ferromagnetism. However, ZnO films grown on r-plane Al2O3 showed reproducible ferromagnetism at 300 K when grown at 300-400 °C and 0.1-1.0 mbar N2 pressure. Positron annihilation spectroscopy measurements as well as density-functional theory calculations suggest that the ferromagnetism in ZnO films is related to Zn vacancies.
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(Reference: TH-2009-23)