Enhanced pinning in a magnetic-superconducting bilayer

Pinning of vortices in a high-temperature superconductor by the magnetic domain structure of a highly anisotropic ferromagnet is investigated by means of magnetic measurements in nanoscale period superconductor/ferromagnet (SC/FM) heterostructures. Two different samples consisting of highly epitaxial films of YBa2Cu3O7(SC) and BaFe12O19(FM) are analyzed relative to a pure superconducting YBa2Cu3O7 film. The irreversibility line obtained in the magnetic-field-reduced-temperature phase diagram for each heterostructure is found to shift upwards when compared to the line corresponding to the pure superconducting sample. This effect is interpreted as an evidence for the enhancement of pinning of vortices in the SC layer by the magnetic domain structure in the FM layer.