Field-enhanced critical parameters in magnetically nanostructured superconductors

Departement Fysica, Universiteit Antwerpen (Campus Middelheim) Groenenborgerlaan 171, B-2020 Antwerpen, Belgium

Received: 7 March 2005
Accepted: 13 April 2005

Abstract

Within the phenomenological Ginzburg-Landau theory, we demonstrate the enhancement of superconductivity in a superconducting film, when nanostructured by a lattice of magnetic particles. Arrays of out-of-plane magnetized dots (MDs) extend the critical magnetic field and critical current the sample can sustain, due to the interaction of the vortex-antivortex pairs and surrounding supercurrents induced by the dots and the external flux lines. Depending on the stability of the vortex-antivortex lattice, a peak in the H_ext-T boundary is found for applied integer and rational matching fields, which agrees with recent experiments (Lange M. et al. , Phys. Rev. Lett., 90 (2003) 197006). Due to compensation of MDs- and H_ext-induced currents, we predict the field-shifted j_c-H_ext characteristics, as was actually realized in previous experiment but not commented on (Morgan D. J. and Ketterson J. B., Phys. Rev. Lett., 80 (1998) 3614).