Irreversible low field flux penetration in sintered superconducting systems

The irreversible low field magnetic flux penetration in granular superconductors is analyzed by means of a 2D network of Josephson junctions under the conditions of strong grain coupling and non-negligible intergranular regions. Analytical results on simple systems and numerical simulations show that the first penetration critical field is determined by the shielding currents crossing through the junctions. These currents reduce the Josephson potential barriers and cause the instability of the magnetic metastable states. We show that by this approach a critical state model can be derived.