1. Department of Physics, Gakushuin University, Toshima, Tokyo 171-8588, Japan
2. Grenoble High Magnetic Field Laboratory, BP166, 38042 Grenoble, Cedex 9, France
3. National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
4. National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8561, Japan
5. Department of Humanities and Sciences, Nihon University, Setagaya, Tokyo 156-8550, Japan