MAGNETIC-FIELD DISTRIBUTION IN SUPERCONDUCTING COMPOSITES AS REVEALEDBY ESR-PROBE AND MAGNETIZATION

The distribution of a static magnetic field in superconductor-insulato r composites consisting of BSCCO (YBCO) powder in paraffin wax is stud ied by ESR bulk probing and magnetization. The average field and field variance in the non-superconducting host are measured as function of temperature and volume fraction of superconductor. We develop a model of the field distribution in dilute magnetic and superconducting compo sites that relates the field inhomogeneity to magnetization and partic le shape. We find that this model satisfactorily describes field distr ibution in our superconducting composites in the regime of strong flux pinning, i.e. below irreversibility line. We find deviations from the model above the irreversibility line and attribute this to flux motio n. We show that the field distribution in superconducting composites i s determined not only by magnetization and particle shape, but is stro ngly affected by the flux profile within the superconducting particles . (C) 1998 Elsevier Science B.V.