Observation of room temperature ferromagnetic behavior in cluster-free, Co doped HfO2 films.

Extensive structural and magnetic analyses of Hf_1-xCo_xO₂ 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 HfO₂ is more probable than Co doped ZnO, TiO₂, and SnO₂ systems for doping concentrations under cation percolation threshold. [ABSTRACT FROM AUTHOR]