Hysteretical temperature dependence of AC susceptibility in granular high- Tc superconductors

Abstract

The AC susceptibility, χ AC( T), with superimposed DC magnetic field, H DS a, 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, μ eff( T), and the effective intergranular local field, H eff j ( H DC a, T), which depends on the applied field, H DC a 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 μ eff( T)) and the proper scaling of H eff j ( H DC a, 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.