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Magnetotransport and thermal properties characterization of 55 K superconductor SmFeAsO0.85F0.15

Correlation between structural/microstructural and magneto-thermal transport properties of FeAs-based SmFeAsO and SmFeAsO0.85F0.15 has been studied in detail. The Rietveld analysis of room temperature powder X-ray diffraction (XRD) data reveals that both the samples are single phase, with very small amount of rare earth impurity in the F doped compound. Electron microscopic investigations show that compounds have layered morphology and structure, with the individual grains being surrounded by amorphous layers. The average grain boundary thickness is ~5 nm. The F free material is found to be magnetic and shows the appearance of Fe spin density wave (SDW) like order at T = 150 K. The F doped compound (SmFeAsO0.85F0.15) shows the occurrence of superconductivity at Tc(R=0, H=0)- 55 K, which decreases to 42 K at magnetic field (H) of 13 kOe. The superconducting transition was also confirmed by DC magnetization and AC susceptibility measurements. The intra-grain critical current density (Jc) calculated using the Bean critical state model is found to be around 5.26 x 10^4 A/cm2 at 5 K in zero field (H=0). The dependence of thermally activated flux flow energy (U/KB) on the applied magnetic field has been observed. AC susceptibility measurements at different amplitude of applied AC drive field confirm the granular nature of the superconducting compound. is confirmed. Both Fe (SDW) at 150K for SmFeAsO and 55K superconductivity in case of SmFeAsO0.85F0.15 sample has confirmed by Specific heat [Cp(T)] measurement too. Further Sm orders anti-ferro-magnetically at 4.5K for non-superconducting and at 3.5K for superconducting samples, also the entropy change is reduced significantly for the later than the former. Summarily complete physical property characterization for both non-superconducting SmFeAsO and 55K superconductor SmFeAsO0.85F0.15 samples is provided and discussed in the current article.