Superconductors in realistic geometries: geometric edge barrier versus pinning

The magnetic response of type-II superconductors can be irreversible due to two different reasons: vortex pinning and barriers for flux penetration. Even without bulk pinning and in the absence of a microscopic Bean-Lingston surface barrier for vortex penetration, superconductors of non-ellipsoidal shape can exhibit a large geometric barrier for flux penetration. This edge barrier and the resulting irreversible magnetization loops and flux-density profiles are computed from continuum electrodynamics for superconductor strips and disks with constant thickness, both with and without bulk pinning. Expressions for the field of first flux entry H-en and for the reversibility field H-rev above which the pin-free magnetization becomes reversible, are given. Both fields are proportional to the lower critical field H-c1 and depend only on the specimen shape. These realistic results are compared with the reversible magnetic behavior of ideal superconductor ellipsoids. (C) 2000 Elsevier Science B.V. All rights reserved.