AC IRREVERSIBILITY LINE OF BISMUTH-BASED HIGH-TEMPERATURE SUPERCONDUCTORS

We discuss the magnetic properties of lead doped Bi-2223 bulk samples obtained through combined magnetic melt texturing and hot pressing (MM THP). The ac complex susceptibility measurements are achieved over a b road ac field range (1 Oe < h(ac) < 100 Oe) and show highly anisotropi c properties. The intergranular coupling is improved in the direction perpendicular to the applied stress and magnetic field direction, and an intragranular loss peak is observed for the first time. A compariso n is made with other bismuth-based compounds and it is shown that the MMTHP process shifts the ac irreversibility line (ac LL) toward higher fields. It is also shown that all the ac IL's for quasi 2D bismuth-ba sed compounds show a nearly quadratic temperature dependence and devia te therefore strongly from the linear behavior observed in quasi 3D co mpounds and expected from a critical state model.