1. Department of Material Physics, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531
2. Department of Material Science and Technology, Faculty of Engineering, Niigata University, Niigata 950-2181
3. Department of Physics, Faculty of Science, Tohoku University, Sendai, Miyagi 980-8578
4. The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047