1. Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
2. Hochfeld-Magnetlabor Dresden (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
3. Department of Physics, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan