Local environment surrounding Co in MBE-grown Co-dopedHfO2thin films probed by EXAFS

Abstract

Local structure around Co impurity atoms in $\mathrm{Hf}{\mathrm{O}}_{2}:\mathrm{Co}$ thin films prepared by molecular beam epitaxy has been investigated using the extended x-ray absorption fine structure (EXAFS) technique. These films were found to be ferromagnetic at room temperature. Progressive formation of Co clusters was observed accompanied by interstitial doping of Co in samples with Co concentration of 1%--20% grown at a substrate temperature of $\ensuremath{\sim}700\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. However, films with a relatively high Co concentration of $\ensuremath{\sim}10%$ can be prepared without clustering of Co metal in a low-temperature growth mode with a substrate temperature $\ensuremath{\sim}100\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. These low-temperature-grown films were found to be thermally stable up to an annealing temperature of $\ensuremath{\sim}700\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. Our EXAFS results have therefore verified the feasibility for preparing Co-cluster-free room-temperature-ferromagnetic $\mathrm{Hf}{\mathrm{O}}_{2}:\mathrm{Co}$-diluted magnetic oxide thin films with great potential for possible spintronic applications.