1. a Department of Physics , University of Niigata, Faculty of Science , Niigata , 950-21 , Japan
2. b Department of Applied Physics , University of Nagoya, Faculty of Engineering , Nagoya , 464 , Japan
3. c The Oarai Branch, The Research Institute for Iron, Steel and Other Metals, Tohoku University, Oarai , Ibaraki , 311-13 , Japan