[1] Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
[2] Department of Physics, Faculty of Science, Kyoto Sangyo University, Kyoto 603-8555, Japan
[3] Low Temperature Center, Osaka University, Toyonaka, Osaka 560-0043, Japan
[4] Res. Ctr. Mat. Sci. Extreme C., Osaka University, Toyonaka, Osaka 560-8531, Japan
[5] Department of Physics, Faculty of Science, Shizuoka University, 836 Ohya, Shizuoka 422-8529, Japan
[6] Advanced Science Research Center, Japan Atom. Energy Res. Institute, Tokai, Ibaraki 319-1195, Japan