Magnetic properties of magnetically textured Bi-2212 ceramics

This paper aims at reporting magnetic properties of bulk polycrystalline Bi2Sr2Ca0.8Dy0.2Cu2O8-y samples textured under a magnetic field. The microstructure of these materials is highly anisotropic and exhibits particular features needed to be taken into account in order to interpret their magnetic and electrical properties. First the AC magnetic susceptibility has been measured for several magnetic fields (H parallel to ab and H parallel to c) and compared to the electrical resistivity data. The structure of the chi'' peak is shown to be related to the chemical content distribution of the superconducting grains. Next, the magnetic flux profiles have been extracted from the magnetic measurements using the Campbell-Rollins procedure. The anisotropy of the flux profiles and their peculiar curvature behaviour for H parallel toc point out the role of both grain platelet structure and the presence of secondary phases. From these results, we conclude that the magnetic properties of such magnetically textured materials do not allow for a reliable extraction of the critical current density J(c) but essentially probe geometric effects. Such effects have to be taken into account for improving the manufacture of attractive high-T-c materials. (C) 2001 Elsevier Science B.V. All rights reserved.