1. Institute of Multidisciplinary Research for Advanced Materials; Tohoku University; 2-1-1 Katahira Aoba Sendai 980-8577 Japan
2. Division of Applied Physics; Faculty of Pure and Applied Sciences; University of Tsukuba; 1-1-1 Tennodai Tsukuba 305-8573 Japan
3. Futaba Corporation; 1080 Yabutsuka, Chosei-mura Chosei-gun Chiba 299-4395 Japan