Vortex Confinement in Planar Superconductor/Ferromagnet Hybrid Structures

We use low temperature magnetic force microscopy and global magnetometry measurements to study the influence of magnetic domains on the Abrikosov vortex pinning in planar superconducting/ferromagnet bilayers. The superconducting/ferromagnet bilayers consist of a 200 nm superconducting Nb film covering a Permalloy film, with an insulating layer in between to avoid proximity effect. The periodic stripe domain in the Permalloy film produces a potential for directing vortex motion in the adjacent superconducting film. We observed an enhancement of vortex pinning by a factor of 3 that occurs in bilayers with a magnetic stripe domains w ≈ 500 nm, close to the superconducting critical temperature (T/T_c = 0.9) . At lower temperatures, when T/T_c = 0.6 the channeled vortex motion and the intrinsic pinning favor vortex avalanches.