Flux-line cutting in granular high-<i>T</i>_<i>c</i>and semi-reversible classical type-II superconductors

Abstract

The magnetic responses of granular (NdBa2Cu3O7-x and YBa2Cu3O7-x) and monolithic (PbIn) superconducting plates, cooled in a fixed magnetic field Hz parallel to their plane and, later, subjected to cycles of a transverse magnetic field Hy with an amplitude Hy,max>Hz, are investigated both experimentally and theoretically. Magnetization curves, generated as Hy with Hz constant applied and of the order of the full penetration field Hp, are interpreted by employing two competing models (the double critical-state model and the two-velocity hydrodynamic model) for describing flux-line cutting effects on the magnetic behaviour of superconductors. Both models qualitatively and semi-quantitatively reproduce the experimental curves. Unlike the double critical-state model, the two-velocity hydrodynamic approach predicts the appearance of zones with homogeneous magnitude of the magnetic induction B at relatively small values of Hy as |Hy| is increased. However the effect of these zones is not appreciable since they disappear when |Hy| reaches a sufficiently large value: |Hy| ≳ Hz≈Hp.