IRREVERSIBILITY LINE AND FLUX-PINNING PROPERTIES IN HIGH-TEMPERATURE SUPERCONDUCTORS

The current-voltage characteristics are analysed numerically at high t emperatures in terms of the one-dimensional flux creep model. A melt-p rocessed Bi-2212 material including fine non-superconducting particles is considered as an example. A virtual critical current density in th e creep-free case is assumed to approach the experimentally observed v alue at low temperatures, and a theoretical expression based on the fl ux pinning by non-superconducting particles at high temperatures where the effect of flux creep is significant. The critical current density is determined using the electric field criterion and the irreversibil ity field is obtained using a suitable criterion. The obtained irrever sibility field shows different temperature dependences between low- an d high-temperature regions as observed experimentally. The scaling cha racteristics of pinning force density are also discussed.