HYSTERETICAL TEMPERATURE-DEPENDENCE OF AC SUSCEPTIBILITY IN GRANULAR HIGH-T-C SUPERCONDUCTORS

The AC susceptibility, chi(AC)(T), with superimposed DC magnetic field, H-a(DS), has been measured as a function of temperature in bulk sintered LaSrCuO, for zero-field cooled (ZFC) and field-cooled (FC) samples. Results are analyzed within Kim's critical-state model extended to a granular superconductor, where the role of grains is to determine the temperature-dependent effective permeability, mu(eff)(T), and the effective intergranular local field, H-j(eff)(H-a(DC), T), which depends on the applied field, H-a(DC) and the thermal and magnetic history, accounting for the observed hysteresis. A method to determine field-independent intergranular critical-state parameters (critical current at zero field and temperature-dependent density of pinning forces as well as mu(eff)(T)) and the proper scaling of H-j(eff)(H-a(DC), T) for ZFC and FC conditions is described. The calculated AC susceptibility for the whole temperature range for both magnetic conditions reproduces the main features of the experimental results.