1. Center for Advanced High Magnetic Field Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
2. Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
3. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
4. Low Temperature Center, Osaka University, Toyonaka, Osaka 560-0043, Japan
5. Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 270-8577, Japan