INTERGRANULAR FLUX TRAPPING EFFECTS IN YTTRIUM BARIUM CUPRATE SUPERCONDUCTORS

Abstract

Simultaneous measurements of the magnetic field dependence of the critical current density and the magnetization of yttrium barium cuprate superconductors have shown the presence of significant residual magnetic fluxes after the applied field has been reduced to zero. This trapped flux can be sufficient to leave the material in the mixed state and results in anomalous behavior of the observed electrical and magnetic properties. The flux appears to be associated with a magnetic field component threaded through the intergranular regions, whose motion is inhibited by circulating currents flowing in the granular system surrounding the field and preserved through the weak-link coupling. Once this coupling is destroyed, the field can move more freely. For a current-carrying sample in zero applied field, the Lorentz force due to the residual field causes the flux to leak from the sample, leading to the appearance of a voltage along the specimen.