IRREVERSIBILITY LINE IN SUPERCONDUCTING BI-2212 SINGLE GRAIN WITH FINE NORMAL PARTICLES

The irreversibility line was obtained in terms of the imaginary a.c. susceptibility measurement for a melt-processed superconducting Bi-2212 single grain with fine non-superconducting particles. This line showed different temperature dependences in high and low temperature regions. The one in the low temperature region agrees approximately with the prediction from the flux creep theory with experimentally observed pinning parameters. On the other hand, the one in the high temperature region is close to the well known characteristics in Y-based superconductors, suggesting flux pinning by boundaries such as the surfaces of non-superconducting particles. A quantitative discussion is also given on flux bundle size.