1. Department of Physics, Division of Material Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602
2. Low Temperature Center, Osaka University, Toyonaka, Osaka 560-0043
3. Neutron Science Laboratory, ISSP, The University of Tokyo, 106-1 Shirakata, Tokai, Ibaraki 319-1195
4. Advanced Science Research Center, JAERI, Tokai, Ibaraki 319-1195