Flux pinning enhancement in ferromagnetic and superconducting thin-film multilayers

Flux pinning in high-temperature superconductors such as YBa2Cu3O7−x (YBCO) in the past has been accomplished by pinning the vortex cores. We demonstrate magnetic-domain-induced flux pinning of the magnetic flux of vortices in a ferromagnet-superconductor bilayer consisting of CoPt grown on YBCO, where the ferromagnet has uniaxial perpendicular magnetic anisotropy and a random domain structure. We observe an improvement of the critical current due to magnetic pinning at temperatures close to the transition temperature.