1. Corporate Research and Development Center, Toshiba Corporation, Kawasaki 212-8582, Japan
2. Japan Synchrotron Radiation Research Institute, Sayo 679-5198, Japan
3. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan
4. Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan