1. Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305
2. Tsukuba Magnet Laboratories, National Research Institute for Metals, Tsukuba, Ibaraki 305
3. Department of Liberal Arts and Sciences, Toyama Prefectural University, Kosugi, Toyama 939-03
4. Faculty of Science, Osaka University, Osaka 560