1. a Advanced Materials Laboratory , National Institute for Materials Science , 1-1 Namiki, Tsukuba-shi, Ibaraki , 305-0044 , Japan
2. b Research Institute of Electrical Communication , Tohoku University , Katahira 2-1-1, Aoba-ku, Sendai , 980-8577 , Japan
3. c Oxide Corporation , 9633 Kobuchisawa, Kitakoma, Yamanashi , 408-0044 , Japan