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Abstract: Flux pinning behavior of c-axis-oriented MgB2 thin film has been investigated by magnetization and transporting measurements. Critical current density J c and flux pinning force density F p were calculated from magnetization hysteresis loops. Pinning energy U 0 was estimated from both magnetization relaxation and resistivity transition curves. Based on the field and temperature dependence of critical current density, flux pinning force density and pinning energy, flux pinning mechanism in MgB2 superconductor has been analyzed and discussed in detail. [Copyright &y& Elsevier]

Abstract: A novel silica gel-water adsorption chiller is developed. This chiller consists of three vacuum chambers: two adsorption/desorption (or evaporation/condensation) vacuum chambers and one heat pipe working vacuum chamber. In this chiller, only one vacuum valve is installed between the two adsorption/desorption vacuum chambers to improve its performance when it is driven by a low temperature heat source. The operational reliability of the chiller is highly improved because of fewer moving parts. In this work, the performance of the chiller is experimentally tested under a low grade heat source, such as 55–67°C. The test results show that the performance of this chiller is satisfying when it is driven by a low grade heat source, such as 65°C, and the cooling capacity (or refrigeration capacity) will reach about 5kW when the hot water temperature is 65°C, the cooling water temperature is 30.5°C and the chilled water inlet temperature is 15.1°C. The test results confirm that this kind of adsorption chiller can be effectively driven by a low grade heat source. [Copyright &y& Elsevier]

Magnetic properties of single crystalline and dense polycrystalline MgB2 prepared under high pressure have been investigated in a wide field range through local and global magnetization measurements using micro-Hall probe and SQUID magnetometer. The lower critical field, Hc1, measured by Hall probe shows a BCS-like temperature dependence and can be fitted by two-gap model. Field dependence of magnetic critical current density is quite different for single and polycrystalline samples. There is only one pinning force peak for bulk sample, whereas there are two pinning force peaks for single crystalline sample. The upper critical field, Hc2, and the irreversibility field, Hirr, have been measured with magnetic field parallel and perpendicular to the boron sheets and the anisotropy ratio of Hc2 is estimated to be about 3. [Copyright &y& Elsevier]

We report on the precise determination of the lower critical field (Hc1) of the newly discovered superconductor MgB2 measured by Hall probe. Two polycrystalline samples with different grain sizes and one single crystalline sample are compared. By setting a small criterion for the first flux penetration into the sample, Hc1 was determined. Based on our measurements, MgB2 seems more similar to borocarbides and low-Tc superconductors, which follow BCS temperature dependence, than to high-Tc superconductors. Comparison with two-gap superconductivity is also made. [Copyright &y& Elsevier]

Abstract: We have studied the anisotropic superconducting properties of Sc5Ir4Si10 single crystalline sample by magnetic measurements. The upper critical field, H c2, for H parallel to the c-axis is larger than that for H parallel to the ab-plane, with the anisotropic parameter of about 2.3, indicating that Sc5Ir4Si10 is a quasi-one-dimensional superconductor. The magnetic penetration depths are estimated as λ c(0)=840Å and λ ab (0)=2100Å. The anisotropy of H c2 is also confirmed in randomly oriented powder samples. [Copyright &y& Elsevier]

(Ba,Sr) 1- x K x Fe 2 As 2 superconductor is of great interest as a wire for practical applications. In this paper, Ba 0.6 K 0.4 Fe 2 As 2 precursor powder was prepared by high-energy ball-milling aided sintering (12 h/750 °C). The prepared precursor was drawn to powder-in-tube round wire. Partial as-drawn wires were subjected to biaxial cold pressure densification (BCPD) at 0.5 and 1.0 GPa, followed by an annealing for 1 min/770 °C. According to our results, the BCPD improved the grain connectivity of the BCPDed wires without degrading the superconductivity. A (Ba,Sr) 1- x K x Fe 2 As 2 round-wire record transport critical current density, 1.14 × 10 5 A/cm 2 (4.2 K, 2 T), was observed in our BCPDed samples. [ABSTRACT FROM AUTHOR]

Based on the high quality FeSe 1− x S x (0 ≤ x ≤ 1) single crystals synthesized via a hydrothermal method, we carried out systematic measurement of the normal state magnetoresistance and Hall effect. Through the maximum entropy mobility spectrum analysis (MEMSA), we investigate the evolution of mobility spectrum, which reflects the multi-band structures for different doping content x and temperature T. The relationships between T c and carrier properties calculated by MEMSA, as well as bond angles and anion height calculated by first-principle method are investigated. Nonlinear to linear transition of Hall resistivity(ρ xy (B)) is mainly attributed to the decreasing mobilities and merging of mobility peaks with the reductive x or increasing T. The relationship between T c and carrier density n show weak interaction for the orthogonal phases when x ≤ 0.2, but nearly positive correlation for the tetragonal phases when x > 0.2. Bond angle as well as the Se/S anion height change almost linearly with x within the tetragonal phases, and the V-shaped relationships with T c indicate that structural factors play a key role in the regulation of superconductivity. Our researches are helpful for understanding the multi-band and complex phase diagram of iron-based superconductors. • We systematically measured magnetoresistance and Hall resistivity of FeSe 1−x S x (0 ≤ x ≤ 1) single crystals. • Nonlinear to linear transition of Hall resistivity is mainly due to decreasing mobilities and merging of mobility peaks. • The bond angle and Se/S anion height both show V-shaped relationships with T c. • Structural factors play a key role in the regulation of superconductivity in iron-based superconductors. [ABSTRACT FROM AUTHOR]

Highlights: [•] Polycrystalline SmFeAsO1−xF x samples were prepared by different oxide precursors. [•] Phase formation and superconductivity of these samples were comparatively studied. [•] Results show that nano-Fe2O3 and As2O3 promote fluorine doping. [Copyright &y& Elsevier]

Abstract: Cu sheathed polycrystalline Ba0.6K0.4Fe2As2 superconducting wire was prepared by a two-step powder-in-tube method. A pressure of 2GPa was applied to a short sample before heat treatment. Magnetization and transport measurements were performed to investigate the effects of cold high pressure densification on the microstructure and superconductivity. The cold pressed sample shows an improved self-field transport critical current density of 2.8×104 A/cm2 (I c =83A) at 4.2K, which is nearly as twice as the unpressed sample. However, both samples manifest pronounced weak-link behavior, suggesting the technique need to be further optimized. The comparison of properties between pressed and unpressed sample and related mechanism was discussed. [Copyright &y& Elsevier]

Abstract: Polycrystalline iron-based superconducting NdFeAsO0.88F0.12 was prepared via solid-state reaction in ambient pressure. Small amounts of ferromagnetic impurities were detected by Scanning Electron Microscopy (SEM) analysis. To study the influence of magnetism on superconducting properties of the sample, magnetization M(T, H) measurements were performed in fields up to 1.5T and in the temperature range of 5–60K. The abnormal behavior was observed in the χ(T) curves, and the magnetization hysteresis loops (MHLs) can be described by a sum of the contributions of superconductive hysteresis, ferromagnetic hysteresis of the impurities and the paramagnetic background of the isolated Nd3+ ions. The influence of the ferromagnetic impurities and the paramagnetic background were investigated and discussed. After the corrections of the magnetism contributions, the intrinsic superconductive MHLs as well as the critical current density were obtained. [Copyright &y& Elsevier]

Abstract: Resistivities of polycrystalline iron-based NdFeAsO0.88F0.12 superconductors prepared via solid-state reaction in ambient pressure (AP) and high pressure (HP) were measured in various magnetic fields ranging from 0 to 9T. Different resistivity broadening behaviors of the AP and HP samples, which may originate from the anisotropic superconductivity, the vortex motion, or the connectivity, were investigated in detail. The effective pinning barriers of both the AP and HP samples were obtained from the Arrhenius plot of the resistivity data by two analytic methods of which one assuming the prefactor 2ρ c U/T of the thermally activated flux flow (TAFF) resistivity ρ=(2ρ c U/T)exp(−U/T) is a constant, while the other assuming the prefactor is temperature dependent. The results determined from the two methods were compared and analysed, and the true effective pinning barriers were obtained. The origin of different pinning barriers of the AP and HP samples is discussed. [Copyright &y& Elsevier]

Abstract: The superconducting properties of polycrystalline NdFeAsO0.88F0.12 oxypnictide were studied by both DC and AC magnetization measurements. The zero-field cooled (ZFC) magnetic susceptibility, χ(T), measured under the magnetic field of 0.5T shows a dramatic decrease at about 11K. The imaginary component of the first harmonics of the AC magnetic susceptibility, χ″(T), increases with the increasing DC field H dc below 11K. These results indicate the onset of robust intergranular superconductivity at low temperatures. The magnetic hysteresis loops show an anomalous double central peak effect at low temperatures, with one peak at positive fields in decreasing positive external fields. This phenomenon suggests the granular character of this system. The paramagnetism of Nd3+ ions tilts the magnetic hysteresis loops and broadens the hysteresis width ΔM. After correction for the paramagnetism, the temperature and field dependence of the average magnetization critical current density J cm was obtained. The related mechanism was discussed. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline NdFeAsO0.88F0.12 superconductors prepared by high pressure (HP) and ambient pressure (AP) methods were comparatively studied by magnetization and transport measurements. Upper critical field H c2, irreversibility field H irr and the anisotropy parameter Γ were estimated from resistance transition curves. The broadening of transition width was observed, and was ascribed to both H c2 anisotropy and superconductivity inhomogeneity of samples. Magnetic hysteresis loops (MHLs) in low fields were measured to detect the trace of weak-link behavior. The reclosed hysteresis loops in low fields indicate that there are weak links in both samples. Magnetization critical current density J cm were derived from MHLs. Sample HP shows higher J cm than sample AP. Direct transport I–V measurements show that the transport critical current density J ct are very low but persist up to 9T, suggesting intrinsic strong-link existing in both samples. [ABSTRACT FROM AUTHOR]