1. Department of Physical Science, Osaka Prefecture University, Sakai 599-8531, Japan
2. Center of Collaborative Research and Technology Development, Kobe University, Kobe 657-8501, Japan
3. Graduate School of Material Science, University of Hyogo, Kamigori, Hyogo 678-1297, Japan
4. Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba 277-8581, Japan
5. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan