1. College of General Education, Kyushu University, Ropponmatsu, Fukuoka 810
2. Graduate School of Science and Technology, Niigata University, Niigata 950-21
3. Department of Physics, Faculty of Science, Niigata University, Niigata 950-21
4. Research Institute of Mineral Dressing and Metallurgy (SENKEN), Tohoku University, Sendai 980
5. Institute for Materials Research, Tohoku University, Sendai 980