Role of metallic cobalt in room temperature dilute ferromagnetic semiconductor Zn0.95Co0.05O1-δ

Using two suitably designed thin film systems, the impact of metallic cobalt nanodots on the mechanism of ferromagnetism (FM) in ZnO thin films was studied. At a relatively higher oxygen partial pressure, Co nanodots embedded ZnO thin films no longer show FM, as compared to Co-doped ZnO dilute magnetic semiconductor (DMS). The structural and magnetic properties of these two systems support the hypothesis that (1) the FM of DMS thin films is due to bound magnetic polarons instead of cobalt nanoclusters and (2) the critical defect concentration is the key parameter which controls the FM properties in DMS thin films. (c) 2008 American Institute of Physics.