Abstract
This report fairly underlines the magneto-transport, thermal properties characterization and bulk superconductivity in the FeAs-based SmFeAsO0.85F0.1. The phase formation and structure are confirmed by Rietveld analysis of room temperature powder X-ray diffraction (XRD) data. Electron microscopy was employed to unravel the micro structural details, such as perfection of the lattice and the grain morphology including size and boundaries. The electrical and magnetic measurements have been carried out to confirm the bulk superconductivity and understand the nature of electrical transport in the normal and superconducting state. The intra-grain critical current density (Jc) with applied magnetic field is calculated from isothermal DC magnetization (MH) plots using conventional Bean critical state model. Superconductivity is observed at transition temperature (Tc) above 55 K without HPHT (high pressure high temperature) synthesis route. The value of Jc is found to be around 5.26 × 104 A/cm2 at 5 K in zero field. The dependence of thermally activated flux flow energy (U/kB) on the applied magnetic field has been observed. AC susceptibility measurements were performed for 55 K superconducting SmFeAsO0.85F0.15 sample at various amplitude of applied AC drive field and its granular nature is confirmed. The parent compound SmFeAsO is found to be magnetic with Fe spin density wave (SDW) like order below 150 K, on the other hand the F doped SmFeAsO0.85F0.15 sample is bulk superconducting at below 55 K. Both Fe (SDW) at 150 K for SmFeAsO and 55 K superconductivity in case of SmFeAsO0.85F0.15 sample has confirmed by Specific heat [Cp(T)] measurement too. Further Sm orders anti-ferro-magnetically at 4.5 K for non-superconducting and at 3.5 K 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 55 K superconductor SmFeAsO0.85F0.15 samples is provided and discussed in the current article.
Highlights
The discovery of the new class of oxypnictide superconductors including iron-based LaFeAsO1−xFx with critical temperature Tc at 26 K1 has provided new impetus to research in the area of high-temperature superconductivity, and has resulted in unravelling of several new issues in the domain of high temperature superconductivity in materials incorporating Fe-As layers as the critical structural unit.[2,3,4,5,6,7,8] Such newfangled materials have the general formula REFeAsO, where RE2158-3226/2013/3(9)/092113/13 C Author(s) 2013092113-2 Srivastava et al.AIP Advances 3, 092113 (2013)is a rare earth element
The parent compound SmFeAsO is found to be magnetic with Fe spin density wave (SDW) like order below 150 K, on the other hand the F doped SmFeAsO0.85F0.15 sample is bulk superconducting at below 55 K
The un-doped (F free) REFeAsO compounds are non-superconducting and show a crystallographic phase transition around 150 K along with a static spin density wave (SDW) like long range ordering of the Fe spins below nearly the same temperature
Summary
The structural unit consists of alternating RE-O and Fe-As layers, rendering charge carriers and conducting planes, respectively These new systems are structurally similar to HTSc cuprates. The previous works have reported such high Tc values in excess of ∼55 K, with HPHT synthesis process.[8,17] We have studied the correlation between the micro-structural properties and superconducting characteristics such as the Tc and the critical current density (Jc) along with the flux pinning behaviour of the bulk samples synthesised at low temperature by a two-step solid state reaction route
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