1. Faculty of Engineering, Kanazawa University, Kanazawa 920-1192, Japan
2. Department of Physics, Kyushu University, Fukuoka 810-8560, Japan
3. Faculty of Engineering, Niigata University, Niigata 950-2181, Japan
4. Kurume Institute of Technology, Kurume, Fukuoka 830-0052, Japan
5. Department of Condensed Matter, Charles University, Ke Karlovu 5, 121 16 Prague 2, Czech Republic
6. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan