Superconducting disk with magnetic coating: Re-entrant Meissner phase, novel critical and vortex phenomena

Departement Fysica, Universiteit Antwerpen - Groenenborgerlaan 171, B-2020 Antwerpen, Belgium

Corresponding author: francois.peeters@ua.ac.be

Received: 28 September 2006
Accepted: 22 November 2006

Abstract

Within the Ginzburg-Landau formalism, we study the mixed state of a superconducting disk surrounded by a magnetic ring. The stray field of the magnet, concentrated at the rim of the superconducting disk, favors ring-like arrangement of induced vortices, to the point that even a single vortex state exhibits asymmetry. A novel route for the destruction of superconductivity with increasing magnetization of the magnetic coating is found: first all vortices leave the sample, and are replaced by a re-entered Meissner phase with a full depression of the order-parameter at the sample edge; subsequently, superconductivity is then gradually suppressed from the edge inwards, contrary to the well-known surface superconductivity. When exposed to an additional homogeneous magnetic field, we find a field-polarity–dependent vortex structure in our sample —for all vorticities, only giant- or multi-vortex states are found for given polarity of the external field. In large samples, the number of vortex shells and number of flux quanta in each of them can be controlled by the parameters of the magnetic coating.