Vortex matter in the presence of magnetic pinning centra

M. V. Milosevic, S. V. Yampolskii* and F. M. Peeters

Departement Natuurkunde, Universiteit Antwerpen (UIA), B-2610 Antwerpen, Belgium
The vortex structure of a thin mesoscopic disk is investigated within the phenomenological Ginzburg-Landau theory in the presence of a ferromagnetic disk or circulating currents in a loop near the superconductor as well as different ''model'' magnetic field profiles with zero average. It will be shown how a magnetic field can drive the system through different stable and metastable vortex states and ultimately to the normal state. The regions of existence of the multi-vortex state, giant vortex state and ring-shaped vortices are found. Furthermore, the ring vortex actively participates in forming of new type of multi-vortices. We also found a vortex state consisting of a central giant vortex surrounded by a collection of anti-vortices. The examples of unconventional re-entrant behavior and transitions between different superconducting states will be given.