Magnetic and structural properties of half-metallic Sr$_{2}$FeMoO$_{6}$ epitaxial films fabricated by ultra-high vacuum sputtering*

Sr$_{2}$FeMoO$_{6}$, a double-perovskite half-metallic ferromagnet, has attracted much attention because of its high Tc of 420 K. However, the fabrication of Sr$_{2}$FeMoO$_{6}$ epitaxial films has been challenging due to impurity phases and disorder. Using ultrahigh vacuum off-axis RF sputtering with precisely controlled low-concentration H$_{2}$ in Ar, we have fabricated phase-pure Sr$_{2}$FeMoO$_{6}$ epitaxial films on SrTiO$_{3}$ (001) and (111) substrates. X-ray diffraction confirms pure phase with double perovskite ordering. The phase purity and magnetic moments are highly sensitive to the H$_{2}$ partial pressure. The optimal range for the H$_{2}$ concentration is 0.4{\%} to 0.6{\%} in Ar with 70 mTorr total pressure. The saturation magnetization of the Sr$_{2}$FeMoO$_{6}$ films grown in this range is 1.5 $\mu _{B}$ per formula unit at 5 K, which is a strong magnetization considering the epitaxial strain. Aberration-corrected HAADF TEM images reveal atomically sharp interface between Sr$_{2}$FeMoO$_{6}$ and SrTiO$_{3}$.