Effects of Heat Treatments on the Properties of $\hbox {SmFeAsO}_{1-x}\hbox {F}_{x}$ Oxypnictide Bulks Prepared via a Single-Step Route

SmFeAsO_1-xF_x type oxypnictide bulks were made via a single-step synthesis. Polycrystalline bulk samples with nominal composition SmFeAsO_1-xF_x (x=0.35 and 0.4) were synthesized by conventional solid state reaction using the starting powders SmF₃ , Sm, Fe, Fe₂O₃ , and high-purity As (specifically allotrope-gray arsenic). The weighed powders were thoroughly ground by hand with a mortar and pestle and pressed into pellets in an argon-filled glove box. The pressed pellets were sealed in an evacuated quartz ampoule and heat treated at 1100°C using different ramp rates to reach the reaction temperature. Magnetization vs. temperature measurements were made on the various specimens, where a maximum onset T_c of 55 K was achieved.