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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: 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]

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]