1. Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502
2. Institute for Solid State Physics, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581
3. Research Reactor Institute, Kyoto University, Kumatori, Sennan, Osaka 590-0494
4. Neutron Scattering Laboratory, Institute for Solid State Physics, University of Tokyo, Shirakata 106-1, Tokai-mura, Ibaraki 319-1106