1. Division of Applied Physics, Faculty of Pure and Applied Science; University of Tsukuba; Tsukuba, Ibaraki 305-8573 Japan
2. Advanced Technology Lab. Fuji Electric Co., Ltd.; Hino, Tokyo 191-8502 Japan
3. Research Facility Center for Science and Technology; University of Tsukuba; Tsukuba, Ibaraki 305-8573 Japan
4. Nanomaterials Research Institute; National Institute of Advanced Industrial Science and Technology; Tsukuba, Ibaraki 305-8568 Japan