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-x
F
_x
type oxypnictide bulks were made via a single-step synthesis. Polycrystalline bulk samples with nominal composition SmFeAsO
_1-x
F
_x
(x=0.35 and 0.4) were synthesized by conventional solid state reaction using the starting powders SmF
₃
, Sm, Fe, Fe
₂
O
₃
, 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.