1. WPI Advanced Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan
2. JST, ERATO, Isobe Degenerate π-Integration Project, Bunkyo-ku, Tokyo 113-0033, Japan
3. Department of Chemistry, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
4. Center for Spintronics Research Network, Tohoku University, Aoba-ku, Sendai 980-8577, Japan
5. Konica Minolta, Ishikawa-cho, Hachioji 192-8505, Japan