Mesoscopic ferromagnet-superconductor junctions and the proximity effect

We have measured the electrical transport of submicron ferromagnets (Ni) in contact with a mesoscopic superconductor (Al) for a range of interface resistances. In the geometry measured, the interface and the ferromagnet are measured separately. The ferromagnet itself shows no appreciable superconducting proximity effect, but the ferromagnet/superconductor interface exhibits strong temperature, field, and current bias dependences. These effects are dependent on the local magnetic field distribution near the interface arising from the ferromagnet. We find that the temperature dependences can be qualitatively described by a modified version of the Blonder-Tinkham-Klapwijk theory for normal-superconductor transport.