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

The current-voltage characteristics are analysed numerically at high temperatures in terms of the one-dimensional flux creep model. A melt-processed Bi-2212 material including fine non-superconducting particles is considered as an example. A virtual critical current density in the creep-free case is assumed to approach the experimentally observed value at low temperatures, and a theoretical expression based on the flux 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 irreversibility field is obtained using a suitable criterion. The obtained irreversibility field shows different temperature dependences between low- and high-temperature regions as observed experimentally. The scaling characteristics of pinning force density are also discussed.