[1] General RandD Laboratories, Taiyo Yuden Co, Ltd., 5607-2, Nakamuroda-machi, Takasaki, Gunma 370-3347, Japan
[2] Department of Metallurgy and Ceramics Science Graduate, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, Japan