Zinc oxide-based diluted magnetic semiconductors

The current experimental situation on the occurrence or absence of ferromagnetism in diluted magnetic semiconductors based on wurtzite zinc oxide hosts is presented, focusing mainly on the many recent experiments which have been performed on bulk systems. Numerous reports have suggested that partial (typically less than 10 at.%) substitution of Zn2+ in ZnO by magnetic transition metal (tM) ions, particularly Mn2+ and Co2+, can result in samples with ferromagnetic Curie temperatures above the room temperature. Reports which cast doubt on the very existence of any kind of long range magnetic order in clean samples of Zn(1-x)tM(x)O at low transition metal (tM) concentrations are also appearing with increasing frequency. The confusing situation clearly calls for a critical, even subjective position to be taken on this topic. The experimental situation on bulk samples strongly favors the view that in cases when ferromagnetism is found, it is not intrinsic to Zn(1-x)tM(x)O. (c) 2006 Elsevier Ltd. All rights reserved.