High-pressure growth of fluorine-free SmFeAsO1-x superconducting single crystals

Fluorine-free SmFeAsO1-x single crystals of a nominal composition with x = 0.15 were grown under the pressure of 3.3 GPa and at 1350-1450C by using the self-flux method. Plate-shaped crystals of a few-200 mu m in lateral size were obtained. The resistively determined superconducting transition of a single crystal was at about 53.5 K, with a narrow resistive transition width of 0.5 K. The detailed crystal structure was analyzed by using synchrotron-irradiated x-ray diffractometry and high-resolution scanning transmission electron microscopy. A sharp transition, a low residual resistivity, and a large residual resistivity ratio indicate the high quality of our single crystals. The temperature and magnetic field dependences of the magnetization also confirmed the absence of extrinsic impurity phases.