MAGNETIC-PROPERTIES AND CRITICAL-CURRENTS IN TL-BASED HIGH-T-C SUPERCONDUCTING SINGLE-CRYSTALS

Tl2Ca2Ba2Cu3O10 (Tl-2223) and (TlPb)(SrBa)(2)Ca2Cu3O8 (Tl-1223) single crystals were investigated by superconducting quantum interference de vice magnetometry in fields up to 8 T (H parallel to c axis). The samp les were subjected to sequential reactor neutron irradiation up to a f luence of 24 x 10(21) m(-2) (E > 0.1 MeV). The superconducting transit ion temperature T-c, the magnetization, and the irreversibility Lines were measured before and after each irradiation step. Because of the w ide range of magnetic fields and temperatures, where the magnetization is totally reversible, especially in Tl-2223, the basic mixed-state p arameters, such as the critical magnetic fields and the characteristic lengths, could be evaluated. In the irreversible range, the critical current densities were calculated from the hysteresis loops using an e xtended Bean model. We find that J(c) is strongly enhanced by the radi ation-induced defects, e.g., by a factor of 52 in Tl-2223 at 40 K and 1 T. The irreversibility Lines are shifted to higher fields and temper atures, but remain always below those of unirradiated Tl-1223, even at the highest neutron fluence. In Tl-1223, the critical current densiti es are moderately enhanced. The irreversibility line is at the same po sition or even higher than that of Y-123 and is moderately shifted to higher fields and temperatures after irradiation. The experimental res ults are discussed in terms of flux pinning and dimensionality.