Synthesis, crystal structure, microstructure, transport and magnetic properties of SmFeAsO and SmFeAs(O_0.93F_0.07)

Abstract

SmFeAsO and the isostructural superconducting SmFeAs(O0.93F0.07) phase were prepared and
\ncharacterized by means of Rietveld refinement of x-ray powder diffraction data, scanning
\nelectron microscope observation, transmission electron microscope analysis, and resistivity and
\nmagnetization measurements. Sintering treatment strongly improves the grain connectivity, but,
\non the other hand, induces a competition between the thermodynamic stability of the
\noxy-pnictide and Sm2O3, thus affecting the sample purity. In the pristine sample both
\nmagnetization and resistivity measurements clearly indicate that two different sources of
\nmagnetism are present: the former related to Fe ordering at T ∼ 140 K and the latter due to the
\nSm ions that order antiferromagnetically at low temperature. The feature at 140 K disappears in
\nthe F-substituted sample, and a superconducting transition appears, at low temperatures. The
\nmagnetoresistivity curves of the F-substituted sample probably indicate very high critical field
\nvalues.