1. a Department of Metallurgy , Kyoto University , Sakyo-ku, Kyoto 606, Japan
2. b National Laboratory for High Energy Physics , Oho, Tsukuba-Shi, Ibaragi , 305 , Japan
3. c Department of Physics , Tohoku University , Aobayama , Sendai , 980 , Japan
4. d Applied Superconductivity Center , University of Wisconsin-Madison , Madison , Wisconsin , 53706 , U.S.A.
5. e Central Research Laboratory , Kobe Steel Ltd. , Nada-ku , Kobe 657 , Japan