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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: Magnetization curves of dense polycrystalline MgB2 have been measured by SQUID magnetometer and calculated by solving the flux creep equation numerically. Considering the anisotropic superconductivity in MgB2 and the grain orientation in polycrystalline samples as well as the flux creep, the experimental data can be fitted very well by a two-exponential model. According to our fitting results, the nonscaling behavior of flux pinning force and the rapid decrease of critical current density of polycrystalline MgB2 at medium and higher magnetic fields originate from the anisotropic superconductivity in MgB2, the dispersion of grain orientations and the flux creep. Through this way, the real dependence of critical current density on temperature and magnetic field can be extracted, and the flux pinning mechanism is discussed. A universal method is therefore proposed for studying flux pinning in polycrystalline samples with intrinsic anisotropic superconductivity. [Copyright &y& Elsevier]

Abstract: The magnetic hysteresis loops of MgB2 polycrystalline bulk sample were measured at different temperatures and calculated numerically with different models. The influence of grain orientation, grain boundary pinning, surface pinning and flux creep on the magnetic hysteresis loops of polycrystalline MgB2 was investigated carefully. A two-exponential model taking into account the grain orientation and the flux creep is found to describe the experimental data well, which may be related to the two energy gaps in MgB2. [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]

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. [ABSTRACT FROM AUTHOR]

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]

We reported a detailed study of Fe 1+ y Te 0.6 Se 0.4 single crystals annealed in the atmosphere of chalcogens (O 2 , S, Se, Te). After annealing with appropriate amount of chalcogens, Fe 1+ y Te 0.6 Se 0.4 single crystals show T c higher than 14 K with a sharp transition width ∼1 K. Critical current density J c for the annealed crystals reach a very high value ∼2–4 × 10 5 A/cm 2 under zero field, and is also robust under applied field at low temperatures. Magneto-optical imaging reveal that the J c is homogeneously distributed in the annealed crystals and isotropic in the ab -plane. Our results show that annealing in the atmosphere of chalcogens can successfully induce bulk superconductivity in Fe 1+ y Te 0.6 Se 0.4 . [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 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]