Abstract
Extensive structural and magnetic analyses of Hf1-x Cox O2 thin films grown by molecular beam epitaxy are reported. Nearly cobalt cluster-free film with x=0.04-0.1 was obtained via 100 °C growth, and Co ions are inferred to be located at interstitial site. Ferromagnetic behavior was observed up to 300 K in both magnetization curves and temperature dependence of the moment. Via post-oxygen-annealing studies, a qualitative correlation between saturation magnetization and oxygen vacancy concentration is established, consistent with the impurity-band exchange model, and that the occurrence of ferromagnetic insulator behavior in the Co doped Hf O2 is more probable than Co doped ZnO, Ti O2, and Sn O2 systems for doping concentrations under cation percolation threshold. © 2007 American Institute of Physics.