Nanostructured Superconductor/Ferromagnet Bilayers

Abstract

Magnetic field can penetrate type-II superconductors in the form of vortices. Each vortex carries a magnetic flux that is an integer multiple of the flux quantum φ0. The pinning properties of the vortices determine the magnitude of the critical current density (j c ) and the magnetisation (M) of the superconductor. Advances in nanolithography have allowed the fabrication of superconducting thin films with artificial pinning arrays like antidot lattices [1, 2] or lattices of magnetic dots [3, 4, 5, 6, 7]. These pinning centres give rise to a huge enhancement of (j c ) and M and can be used to stabilize new vortex phases like multiquanta and composite vortex lattices [2]. Pronounced commensurability effects between the vortex lattice and the array of pinning sites can be observed as peaks or cusps in (j c )(H) and M(H) at specific values of the perpendicularly applied magnetic field H. We report on two different types of magnetic pinning centres with out-of- plane magnetisation. In the first type of sample, the Pb film is deposited on a square array of Co/Pt multilayer dots, the second system consists of a Pb film that is grown on a Co/Pt multilayer containing a regular array of antidots. In both systems, we will investigate how the direction of the magnetic moments in the Co/Pt multilayer influences the flux pinning in the superconducting film. These studies enable us to elucidate the pinning potential that the magnetic nanostructures impose in the superconducting film.KeywordsFlux LineMagnetic Force MicroscopyMatching EffectStray FieldMagnetic NanostructuresThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.