  We investigated the pinning of flux lines in a superconducting film by a
regular array of magnetic antidots. The sample consists of a Co/Pt multilayer
with perpendicular magnetic anisotropy in which a regular pattern of submicron
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 polarity. This
asymmetry clearly demonstrates that the magnetic contribution dominates the
pinning potential imposed by the magnetic antidots on the superconducting film.
