1. Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
2. Low Temperature Center, Osaka University, Toyonaka, Osaka 560-0043, Japan
3. Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
4. INAC/SPSMS, CEA-Grenoble, 38054 Grenoble, France
5. Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan
6. LNCMI-G, CNRS, 325 Rue des Martyrs, 8042 Grenoble, France
7. Department of Physics, Graduate School of Science, Kobe University, Kobe 657-8501, Japan
8. Department of Physics, Faculty of Science, Kyoto Sangyo University, Kyoto 603-8555, Japan
9. Condensed Matter Science Division, Japan Atomic Energy Agency, Sayo, Hyogo 679-5148, Japan