1. Department of Physics, Faculty of Science, Shizuoka University, 836 Ohya, Shizuoka 422-8529
2. Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043
3. Tsukuba Magnet Laboratory, National Research Institute for Metals, Tsukuba, Ibaraki 305-0003
4. Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195
5. Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047