MAGNETIC-FIELD EXPULSION IN SUPERCONDUCTING GRANULAR CERAMICS AND IN POLYMER SUPERCONDUCTOR COMPOSITES/

The magnetic interaction between a permanent magnet and superconductin g ceramics such as YBa2Cu3O7-delta and Bi1,6Pb0,4Sr2Cu2Cu3O(10+delta) depend on the superconducting state of each phase and on the junctions between grains. In the case of polymer/superconductor composites, scr eening effects depend on the volume Fraction of superconductor. Measur ements of the evolution of the levitation force (F=A/d(gamma)) as a fu nction of the interaction distance d are used to characterize the effe ctive response of the ceramics or composites to the magnetic flux pene tration. Some of the abnormal variations of the exponent gamma and of the term A (in F=A/d(gamma)) could be reinterpreted in terms of a chan ge in superconducting regime. Other observed variations of gamma shoul d be due to the variation of the effective field from the cylindrical magnet.