1. Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Nagatsuta-cho 4259, Midori-ku, Yokohama-shi, Kanagawa, 226-8502, Japan, and Corporate R & D Center, Mitsui Mining & Smelting Co. Ltd., Haraichi 1333-2, Ageo-shi, Saitama, 362-0021, Japan