SIZE DEPENDENCE OF THE AC SUSCEPTIBILITY AND CRITICAL CURRENT DENSITIES OF CERAMIC HIGH-TC SUPERCONDUCTORS

Measurements of the AC susceptibility of HTSC ceramic samples were performed not only for different values of the AC magnetic field, but also for different sample sizes, thus obtaining information of the temperature interdependence of penetration field and penetration depth for the intergranular phase transition. To fit the experimental data, the critical state model was modified by introducing a power law to the magnetic field dependence of the critical current. While the YBCO sample showed a dependency of the critical current density on the magnetic field with an exponent of approximately 3.5, the field dependency exponent for the BSCCO sample turned out to be only 0.7. The temperature dependence of the intergranular critical current densities shows large exponents supporting flux creep dominated behavior for the samples investigated.