[1] Institute of Bio- and Nanosystems (IBN-1), Virtual Institute of Spin Electronics (VISel), Research Centre Jülich, 52425 Jülich, Germany
[2] Institut für Bio- and Nanosysteme (IBN 3), CNI - Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Jülich, 52425 Jülich, Germany