1. Clarendon Laboratory, Department of Physics, University of Oxford, OX1 3PU, U.K.
2. Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547, U.S.A.
3. Deaprtment of Physics, Meiji University, Tama-ku, Kawasaki 214-8571, Japan
4. Department of Applied Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
5. Department of Engineering Science, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
6. Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
7. Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
8. National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan
9. Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
10. Hochfeld-Magnetlabor Dresden, Helmholtz-Zentrum Dresden-Rossendorf, D-01314 Dresden, Germany