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

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

Interpreting the conductive atomic force microscopy measured inhomogeneous nanoscale surface electrical properties of Al-doped ZnO films

“…It should be noted that the thermally induced increase in kinetic energy of the Al dopants is higher at higher T s , thus substituting higher number of Al atoms in ZnO lattice, as evidenced with an increase in micro strain ( ε ) in these AZO films with increasing T s from −1.73 × 10 −3 at T s = 303 K to −1.88 × 10 −3 at T s = 623 K (Table ). Further, the increase in Zn interstitials and oxygen vacancies in these AZO films with increasing T s can be because of the desorption of oxygen ions from its lattices induced at higher T s . The overall increase in the surface conductivity of these AZO films can also be associated with the increase in crystallite size ( D ) from 29.3 nm at T s = 303 K to 32.29 nm at T s = 623 K (Table ), reducing the overall grain boundary areas, which reduces the scattering of these charge carriers, leading an increase in the carrier mobility ( μ e ) from 2.94 cm 2 V −1 s −1 at T s = 303 K to 16.28 cm 2 V −1 s −1 at T s = 623 K (Table ).…”

Interband Electron Pairing for Superconductivity from the Breakdown of the Born‐Oppenheimer Approximation

“…[10] The first class of superconductors breaking the McMillan limit is the layered cuprates; La 2-x Ba x CuO 4 with T c = 35 K found in 1986, [9] YBa 2 Cu 3 O 7-x with T c = 93 K in 1987, [11] and HgBa 2 Ca 2 Cu 3 O 8 + x with T c = 134 K in 1993. [14] It has been generally believed that the cuprate and ferropnictide superconductors appear unconventional, namely, their electronpairing mechanisms differ from electron-phonon coupling. [13] Another class of superconductors breaking the McMillan limit is the layered ferropnictides, with the highest T c = 55 K found for SmFeAsO 1-x F x in 2008.…”

Robust superconductivity with large upper critical field in Nb2PdS5

“…Generally speaking, the decrease of T c with applied magnetic field, i.e., dT c /dH determines the upper critical field in a simple single band scenario. 13 In a type II superconductor, the upper critical field can be enhanced by both intrinsically 6,14 and extrinsically. 15 Intrinsically, the same happens in multi band systems having complicated electronic 6,14 and extrinsically by pinning the vortices in their mixed state.…”

“…13 In a type II superconductor, the upper critical field can be enhanced by both intrinsically 6,14 and extrinsically. 15 Intrinsically, the same happens in multi band systems having complicated electronic 6,14 and extrinsically by pinning the vortices in their mixed state. 15 The recently discovered superconductor, i.e., Nb 2 PdS 5 seems to be both intrinsically robust as well as pinned by inherent defects, etc.…”

“…When this is compared with the best of HTSc cuprates (3 K/10 kOe), 26 Fe pnictides (1 K/10 kOe), 6,14 pinned MgB 2 (1.5 K/10 kOe), 15 or the Fe chalcegonides (0.4 K/10 kOe) 7,8 and Chevrel phase (0.45 K/10 kOe) 27 compounds, one finds that Nb 2 PdS 5 is the most robust superconductor against magnetic field till date. Figure 5 shows the heat capacity (C P ) versus temperature (T) plots at different applied fields of 0, 10, 50, and 140 kOe in superconducting region i.e., 2-8 K for studied Nb 2 PdS 5 superconductor.…”