Growth of EuO Single Crystals at Reduced Temperatures

Single crystals of Eu$_{1-x}$Ba$_{x}$O have been grown in a barium-magnesium flux at moderate temperatures up to 1000$^{\circ}$C, producing single crystals with barium doping levels ranging from $x=0.03$ to $x=0.25$. Magnetic measurements show that the ferromagnetic Curie temperature $T_{C}$ correlates with the Ba doping levels, and a modified Heisenberg model is employed to describe the $T_{C}$ dependence on the stoichiometry. The decrease in $T_{C}$ is dominated by the Ba substitution on the Eu lattice with a small contribution arising from the lattice strain. Extrapolation of results indicates that a sample at $x=0.72$ should have a $T_{C}=0$ K, potentially producing a quantum phase transition in this material.\\ \\ This work was supported by the Department of Energy, Office of Basic Science, under contract DOE SC-0008832. This work has been performed at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation Cooperative Agreement DMR-1157490, the State of Florida, and the U.S. Department of Energy.