1. Institute for Materials Research, Tohoku
University, Sendai 980-8577, Japan
2. Center for Spintronics Research Network, Tohoku
University, Sendai 980-8577, Japan
3. PRESTO, Japan Science and Technology
Agency, Saitama 322-0012, Japan
4. National Institute for Materials
Science, Tsukuba 305-0047, Japan
5. WPI-AIMR, Tohoku University, Sendai
980-8577, Japan
6. Advanced Science Research Center, Japan Atomic
Energy Agency, Tokai 319-1195, Japan