Investigations of a New Diluted Magnetic Oxide with Room Temperature Ferromagnetism in Co-doped HfO$_{2}$

The structural, chemical, and magnetic properties of HfO$_{2}$ epitaxial films $\sim $100nm thick grown on YSZ at varying growth temperature have been systematically investigated. Nearly cobalt cluster-free films with RT ferromagnetic behaviors can be obtained via low T growth. \textit{In-situ} XPS analysis during growth indicated the formation of metallic cobalt at the initial growth stage under a low O$_{2}$ partial pressure $\sim $10$^{-10 }$Torr, and that the metallic cobalt can be mostly eliminated by raising the pressure to 10$^{-7}$ Torr. In conjunction with EXAFS local structural analysis and post annealing experiments, we infer that cobalt ions in low T grown films are located at interstitial site and appeared to be stable after being annealed in O$_{2}$ at 350$^{\circ}$C. Further Hall measurements are now underway to measure the carrier concentration, and to elucidate their role to the apparent ferromagnetism.