1. Faculty of Science, Tokyo Metropolitan University, Minami-Osawa 1-1, Hachioji, Tokyo 192-03
2. Department of Metal Physics, Charles University, Ke Karlovu 5, 12116 Prague 2, Czech Republic
3. Faculty of Science, Osaka University, Toyonaka, Osaka 560
4. Physics Department, Hokkaido-Kyouiku University, Sapporo 022