FLUX CREEP IN HIGH-TC SUPERCONDUCTORS

The critical current density and flux-creep rate have been measured as functions of temperature and magnetic field for a ring-shaped sample of Y-Ba-Cu-O ceramic which was specially prepared so that such measurements could be made without penetration of flux lines into the superconducting grains. The measurements were made in both the presence and the absence of a biasing magnetic field. A theoretical model is developed in which the superconducting grains are linked by junctions with a range of strengths and the model is used to describe the temperature dependence of the critical current density and low-field flux-creep rate. The results obtained from the analysis of our model are compared with those derived, less rigorously, by other workers in the case of flux creep in single crystals and epitaxial films. The application of our theory to our experimental data yields good internal consistency, and functions describing the distribution of junction strengths in our specimen with and without the bias field are obtained.