CRITICAL-CURRENT PROPERTIES AND VORTEX-GLASS-LIQUID TRANSITION IN AG-SHEATHED BI-2223 TAPES

The magnetic field and temperature dependence of the critical current density J(c) and the voltage-current characteristics of a Bi-2223 tape in a magnetic field parallel to the c-axis are studied. The critical current density decreases with increasing field in a power-law manner at low magnetic fields, and decreases exponentially at high fields. These field dependences suggest the validity of the brick-wall model proposed by Malozemoff, in which the critical current density is limited by the grain boundaries perpendicular to the c-axis. The magnetic field dependence of the macroscopic pinning force density, F-p = J(c)B, shows clear scaling behaviour for different temperatures. Furthermore, we investigated the temperature dependence of the voltage-current characteristics precisely, and a critical scaling analysis demonstrates the existence of a quasi-two-dimensional vortex-glass-liquid transition, which has been observed recently in Bi-2223 epitaxial films. The observed glass-liquid transition temperatures T-g were found to be much higher than those in the epitaxial films.