Affiliation: | a Department of Applied Physics, Faculty of Engineering, Shizuoka University, Hamamatsu 432-8561, Japan b Institut für Festkörperforschung, Forschungszentrum Jülich, Postfach 1913, D-52545 Jülich, Germany c University of Athens, Section of Solid State Physics, Panepistimioupolis GR-15784, Athens, Greece |