Modelling of the magnetic behaviour of random granular superconductors by the single junction model

The magnetic measurements of the Josephson critical field and intergranular critical currents are presented for the Bi2223 compound. The investigations prove that the Josephson critical field value is mainly dependent on the intergranular critical current density. The other factors like the grain dimensions and shapes, sample porosity and density are less important. The relation between the Josephson critical field and critical current HcJ(Jc) is well described within the single junction model, Hcj∝JcλJ. The temperature dependence of HcJ can also be well fitted according to the single junction model with a critical current dependence, Jc∝(1-T/TcJ)α. The critical current density versus temperature is almost linear indicating the presence of superconductor-insulator-superconductor (SIS) type junctions.