SAMPLE-SIZE DEPENDENCE OF THE AC-SUSCEPTIBILITY OF SINTERED YBA2CU3O7-DELTA SUPERCONDUCTORS

The field dependence of both the intergranular peak temperature, T(m) and the intragranular peak temperature, T(g) of the imaginary component, chi", 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 chi"-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 chi"-peak temperature T(g) and the AC-field amplitude does not show a sample thickness dependence.