Defect-induced magnetic order in pure ZnO films

Phys. Rev. B 80, 035331 (2009)

M. Khalid, M. Ziese, A. Setzer, P. Esquinazi, M. Lorenz, H. Hochmuth, M. Grundmann, D. Spemann, T. Butz, G. Brauer, W. AnwandG. Fischer, W. A. Adeagbo, W. Hergert, and A. Ernst


We have investigated the magnetic properties of pure ZnO thin films grown under N2 pressure on a-, c-, and r-plane Al2O3substrates by pulsed-laser deposition. The substrate temperature and the N2 pressure were varied from room temperature to570 °C and from 0.007 to 1.0 mbar, respectively. The magnetic properties of bare substrates 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 mbarN2 pressure. Positron annihilation spectroscopy measurements as well as density-functional theory calculations suggest that the ferromagnetism in ZnO films is related to Zn vacancies.