1. Department of Physics, Asahikawa Medical University, Asahikawa, Hokkaido 078-8510, Japan
2. Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0044, Japan
3. Division of Applied Physics, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan