1. Materials Design and Characterization Laboratory, Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581
2. Deaprtment of Physics, Faculty of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522
3. Low Temperature Physics Department, Moscow State University, 119899 Moscow, Russia