Physica C-Superconductivity and its applications vol:369 issue:1-4 pages:97-105
This paper gives an overview of pinning phenomena in superconductors with artificial magnetic pinning arrays. Different ferromagnetic structures have been considered in combination with a low T-c type-II superconducting film. Magnetic force microscopy is used to characterise the magnetic patterns. The pinning properties (critical current, matching effects) are investigated by macroscopic measurements (SQUID, electrical transport) as well as by local observation using scanning Hall probe microscopy. It is shown that, besides structural and geometric modulations, the magnetic interaction of flux lines (FLs) with the ferromagnetic patterns plays an essential role in their pinning properties. The local magnetic stray field affects the order parameter and determines the pinning through the magnetic interaction with the flux lines. To understand this interaction, one should take into account fluxoid quantisation effects and the possibility of having additional induced flux quanta in the superconductor. The magnetic moments of the dots and their mutual alignment with the applied magnetic field are especially important for the asymmetric pinning by perpendicularly magnetised dot- and anticlot arrays. (C) 2001 Elsevier Science B.V. All rights reserved.