1. Experimental Department, Max-Planck-Institut für Mikrostrukturphysik, Halle (Saale), Germany.
2. Peter Grünberg Institut (PGI-6), Forschungszentrum Jülich, Jülich, Germany.
3. College of Science, Ibaraki University, Mito, Japan.
4. Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan.