MAGNETIC-RELAXATION, FLUX CREEP AND THE DISTRIBUTION OF PINNING POTENTIALS IN CERAMIC TL-1223 HTSC

The relaxation of the remanent magnetization of ceramic Tl-1223 HTSC has been studied in the temperature range 3.5-100 K after switching a field of 1 T on and immediately off. Because of the thermal activation of vortex lines the relaxation can be well described by a logarithmic time decay. The activation energies obtained in the single-barrier-height model show a strong temperature dependence with U(o) = 40-50 meV at T = 4 K and U(o) = 200-400 meV at T = 40-80 K. The distribution of pinning potentials has been evaluated from the relaxation data and exhibits a peak at U(o) = 38 meV and can be well described by two log-normal distribution functions with E(max, 1) = 36.6 meV and E(max, 2) = 51.4 meV. In the framework of the distribution model it is possible to obtain the dependence of the activation energies on temperature in the single-barrier-height model. The small values of most of the pinning barrier heights lead to a drastic decrease of the remanent magnetization and therefore the critical current at T greater-than-or-equal-to 20 K. The dependence of the critical current on temperature can be obtained by integrating the distribution function.