DETAILED ANALYSIS OF MAGNETIZATION DATA AND TRANSPORT CRITICAL CURRENT MEASUREMENTS FOR AG-(BI,PB)SRCACUO COMPOSITE TAPES

Unlike traditional superconductors, bismuth-based high temperature superconductor wires are known for their complex electromagnetic behaviour arising from their crystal structure and anisotropic nature. To gain insight into their flux line pinning behaviour, it is necessary to understand the current flow and its distribution in these materials. Silver-sheathed (Bi,Pb)SrCaCuO tape samples (with nominal 2223 phase composition and T(c) values of 100 - 110 K) have been characterized by d.c. and a.c. susceptibility, magnetization, transport critical current and microstructural analysis. The transport critical current densities for these samples approach 10(4) A cm-2 at 77 K and in self-field. Detailed analysis of the d.c. magnetization as the applied field is cycled, for both transverse and parallel applied fields, has been used to investigate the critical currents and the scaling lengths at several temperatures. The correlations and discrepancies from the application of the critical state analysis to both magnetization data and transport critical current data are discussed. When applying simple versions of this analysis to high temperature superconductors (such as using the width of a magnetization loop to obtain the critical current density) serious errors may arise.