Asymmetric flux pinning in laterally nanostructured ferromagnetic/superconducting bilayers

We investigated the pinning of flux lines in a superconducting lm by a regu lar array of magnetic antidots. The sample consists of a Co/Pt multilayer w ith perpendicular magnetic anisotropy in which a regular pattern of submicr on holes is introduced and which is covered by a type-II superconducting Pb film. The resulting ferromagnetic/superconducting heterostructure shows a pronounced asymmetric magnetization curve with respect to the field polarit y. This asymmetry clearly demonstrates that the magnetic contribution domin ates the pinning potential imposed by the magnetic antidots on the supercon ducting film.