1. Toyota Physical and Chemical Research Institute, Yokomichi 41-1, Nagakute, Aichi 480-1192, Japan
2. Department of Engineering Science, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
3. Toyota Central R&D Labs., Inc., Yokomichi 41-1, Nagakute, Aichi 480-1192, Japan
4. Institute for Solid State Physics, The University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba, Japan
5. Department of Applied Physics, Nagoya University, Chikusa, Nagoya 464-8603, Japan