Range of Applicability for the Critical State Model and the Interaction between the Abrikosov and Josephson Vortices

The minimal a.c. magnetic field which is able to penetrate into the hollow ceramic Y-Ba-Cu-O cylinder was studied experimentally and theoretically as a function of the d.c. magnetic field. The critical state model predicts reversible dependence on the d.c. field in disagreement with observed irreversibility which is explained by interaction between Abrikosov vortices in grains and Josephson vortices in weak links.