1. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan
2. Ichikawa Research Center, Sumitomo Metal Mining Co., Ltd., 3-18-5, Nakakokubun, Ichikawa, Chiba 272-8588, Japan