1. Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195
2. Graduate School of Material Science, University of Hyogo, Kamigori, Hyogo 678-1297
3. Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313
4. Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043
5. KYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531
6. Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581
7. Faculty of Science, University of the Ryukyus, Saihara, Okinawa 903-0213