Appl. Phys. Lett. 92, 082508 (2008)
Qingyu Xu, Heidemarie Schmidt, Shengqiang Zhou, Kay Potzger, Manfred Helm, Holger Hochmuth, Michael Lorenz, Annette Setzer, Pablo Esquinazi, Christoph Meinecke, and Marius Grundmann
Abstract
ZnO films were prepared by pulsed laser deposition on a-plane sapphire substrates under N2 atmosphere. Ferromagnetic loops were obtained with the superconducting quantum interference device at room temperature, which indicate a Curie temperature much above room temperature. No clear ferromagnetism was observed in intentionally Cu-doped ZnO films. This excludes that Cu doping into ZnO plays a key role in tuning the ferromagnetism in ZnO. 8.8% negative magnetoresistance probed at 5 K at 60 kOe on ferromagnetic ZnO proves the lack of s–d exchange interaction. Anomalous Hall effect (AHE) was observed in ferromagnetic ZnO as well as in nonferromagnetic Cu-doped ZnO films, indicating that AHE does not uniquely prove ferromagnetism. The observed ferromagnetism in ZnO is attributed to intrinsic defects.
