Magneto-transport and Magnetic Susceptibility of SmFeAsO1-xFx (x=0.0 and 0.20)

We report superconductivity in the SmFe AsO1-xFx for the x = 0.2 system being synthesized using the single step solid state reaction route. Rietveld analysis of room temperature X-ray diffraction (XRD) data shows the studied samples, SmFeAsO1-xFx with x = 0.0 and x = 0.2, are crystallized in a single phase tetragonal structure with space group P4/nmm. The resistivity measurement shows superconductivity for the x = 0.20 sample with T-c (onset) similar to 51.7 K. The upper critical field, [H-c2(0)] is estimated similar to 3770 kOe by Ginzburg-Landau (GL) theory. Broadening of superconducting transition in magnetotransport is studied through thermally activated flux flow in an applied field up to 130 kOe. The flux flow activation energy (U/k(B)) is estimated similar to 1215 K for 1 kOe field. Magnetic measurements exhibited bulk superconductivity with lower critical field (H-c1) of similar to 1.2 kOe at 2 K. In the normal state, the paramagnetic nature of compound confirms no trace of magnetic impurity, which orders ferromagnetically. AC susceptibility measurements have been carried out for SmFeAsO0.80F0.20 sample at various amplitude and frequencies of applied AC drive field. The intergranular critical current density (J(c)) is estimated. Specific heat [C-p(T)] measurement showed an anomaly at around 140 K due to the SDW ordering of Fe, followed by another peak at 5 K corresponding to the antiferromagnetic (AFM) ordering of Sm+3 ions in the SmFeAsO compound. Interestingly, the change in entropy (marked by the C-p transition height) at 5 K for Sm+3 AFM ordering is heavily reduced in the case of the superconducting SmFeAsO0.80F0.20 sample