Vortex self-organization in the presence of magnetic pinning arrays

Abstract

Lateral nanostructuring is an efficient tool to control vortex confinement in superconductors. This will be illustrated by studying pinning phenomena in type-II superconducting Pb films with a lattice of submicron magnetic dots. We consider rectangular Co dots with in-plane magnetization and circular Co/Pt dots with out-of-plane magnetization. The domain structure of the Co dots can be changed from multi- to single-domain, resulting in an enhancement of their stray field. After covering this Co dot array with a Pb film, we demonstrate the influence of the local magnetic stray field of the dots on their flux pinning efficiency. The Co/Pt dots have a single-domain structure with their magnetic moment out of plane. Depending on the magnetic history, the magnetic moment of all dots can be aligned in positive or negative direction, or a random distribution of positive and negative magnetic moments of the dots can be achieved. For a Pb film covering this Co/Pt dot array, we observe an asymmetric magnetization loop due to the magnetic interactions between the vortices and the magnetic dots.