1. Laboratory for Materials and Structures, Tokyo Institute of Technology, Nagatsuta, Yokohama 226-8503, Japan
2. National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
3. ICT Devices Development Center, TDK Corporation, Ichikawa 272-8558, Japan
4. Department of Applied Physics, National Defence Academy Japan, Yokosuka 239-8686, Japan
5. Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan