ENHANCEMENT OF CRITICAL CURRENT-DENSITY JCM AND PINNING ENERGY-U IN MELT-TEXTURED BI2SR2CACU2O8+DELTA ON AG-TAPE BY HEAVY-ION IRRADIATION

Irradiation experiments using 502 MeV I-127 ions were performed on 2212 BSCCO melt textured layers on Ag-tape to create well defined columnar amorphous tracks (diameter: 5-10 nm). These tracks should act as very effective pinning centers, especially if they are aligned in parallel to the magnetic field. Magnetization measurements resulted in an enhancement of the magnetization current density j(cm) within the whole temperature range of 4.2 K up to 60 K. Enhancement factors up to 10(3) were obtained in a magnetic field of 2 T at 30 K after irradiation. We investigated our samples at magnetic inductions up to 12 T; the j(cm) results will be compared with critical current densities j(ct) derived from transport measurements revealing a pronounced lower j(c)-enhancement due to irradiation. The evaluation of E(j) curves gives evidence that granularity can be neglected in unirradiated samples, on the other hand, obvious limits for the intergrain currents exist after irradiation. According to relaxation measurements of the magnetic moment before and after irradiation with different doses of 502 MeV I-127 the activation energy U could only be increased from about 30 mev to 70 mev at 10 K and 0.1 T. The small increase of pinning energies is explained within the pancake vortex model and is consistent with recent results found on Bi2Sr2CaCu2O8+delta single crystals.