COMPARATIVE-STUDY OF PINNING AND CREEP IN TL2BA2CACU2O8 AND BI2SR2CACU2O8 SINGLE-CRYSTALS

We have compared the pinning and creep in two identically shaped single crystals, T12Ba2CaCu2O8 (Tl 2:2:1:2) and Bi2Sr2CaCu2O8 (Bi 2:2:1:2) using magnetometry. The critical current density, J(c), deduced from the M-H hysteresis loops is found to be the highest in Bi 2:2:1:2 at low temperatures (T < 10 K). The field dependence of J(c), in this temperature range, is similar for both crystals. At higher temperatures, J(c) is found to decrease more rapidly with magnetic field in Bi 2:2:1:2 than in Tl 2:2:1:2. The critical current also decreases more quickly with temperature in Bi 2:2:1:2 leading to a vanishing J(c) at temperatures lower than in the case of Tl 2:2:1:2. I-V characteristic curves have been obtained from measurements of magnetic-sweep-rate dependencies of the hysteresis loops. We have found that the characteristic temperature at which flux motion becomes important is significantly higher in Tl 2:2:1:2 than in Bi 2:2:1:2.