1. Synchrotron Radiation Research Unit, Japan Atomic Energy Agency, Sayo, Hyogo 679-5148
2. Institute for Materials Research, Tohoku University, Sendai 980-8577
3. ADSM, Hiroshima University, Higashihiroshima, Hiroshima 739-8530
4. Department of Physics, Faculty of Science, Tohoku University, Sendai 980-8578