Temperature dependence of pinning potentials in grain-aligned and re-doped Hg-1223 superconductors

Effect of grain alignment and Re-doping on the flux-creep phenomena in Hg-1223 superconductors is investigated. Hg-based superconductors of HgBa2Ca2Cu3RexOy (x = 0. 15 and 0. 18) were fabricated by high vacuum sealing and sintering method using a precursor. Grain alignment was formed magnetically under external magnetic field of 10 T. Connectivity between the superconducting CuO2 layers is known to be enhanced with addition of Re. Flux creep characteristics and DC magnetizations were measured using a SQUID magnetometer at temperature range 5-150 K under magnetic fields up to 1 T. The pinning potentials U-0(*) estimated from the logarithmic time dependence of the magnetization for B parallel to ab are generally larger than those for B parallel to c. Non-linear relation of pinning barrier energy U(J) on current density J leads to apparently low energy in the high J region which is remarkable at low temperatures. Independence of the U-0(*) on the applied fields B parallel to c in this region and increase of the U-0(*) with lowering B parallel to ab indicate the difference of non-linearity. In addition, temperature dependence of the flux creep rate S is favorably compared with the Anderson-Kim model. (c) 2005 Elsevier B.V. All rights reserved.