Sample size dependence of the AC-susceptibility of sintered YBa₂Cu₃O_7-δ superconductors

The field dependence of both the intergranular peak temperature, T_m and the intragranular peak temperature, T_g, of the imaginary component, χ″, of the AC-susceptibility has been studied for sintered YBaCuO samples having orthorhombic shape and different thicknesses. A strong systematic influence of sample thickness on the field dependence of T_m was found. The conclusion has been drawn that the "irreversibility line" defined as a relation between the χ″-peak temperature and the AC-field amplitude being sample size dependent is not an "intrinsic" property of the material alone. Following Chen's approach, the temperature dependence of the full penetration field, H_p(T), and the average intergranular critical current, J_c(T), have been deduced from the field dependence of T_m. The relation between the intergranular χ″-peak temperature T_g and the AC-field amplitude does not show a sample thickness dependence.