[1] Tohoku Univ, Inst Mat Res, Sendai, Miyagi 980, Japan
[2] Japan Sci & Technol Agcy, PRESTO, Kawaguchi, Saitama, Japan
[3] Japan Atom Energy Agcy, Adv Sci Res Ctr, Tokai, Ibaraki, Japan
[4] Japan Sci & Technol Agcy, CREST, Tokyo, Japan
[5] Tohoku Univ, WPI Adv Inst Mat Res, Sendai, Miyagi 980, Japan