1. Gunma University, Molecular Science Division, Faculty of Science and Technology, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan
2. JEOL Resonance Inc., Musashino, Akishima, Tokyo 196-8558, Japan
3. National Institute for Material Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan
4. Osaka University, Institute of Scientific and Industrial Research, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan