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

Abstract

Extensive structural and magnetic analyses of ${\mathrm{Hf}}_{1-x}{\mathrm{Co}}_x{\mathrm{O}}_2$ thin films grown by molecular beam epitaxy are reported. Nearly cobalt cluster-free film with $x=0.04–0.1$ was obtained via $100°\mathrm{C}$ growth, and Co ions are inferred to be located at interstitial site. Ferromagnetic behavior was observed up to $300\mathrm{K}$ 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 $\mathrm{Hf}{\mathrm{O}}_2$ is more probable than Co doped ZnO, $\mathrm{Ti}{\mathrm{O}}_2$ , and $\mathrm{Sn}{\mathrm{O}}_2$ systems for doping concentrations under cation percolation threshold.