1. Department of Applied Physics and Physico-Informatics, Keio University, Yokohama 223-8522, Japan
2. Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
3. Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
4. Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
5. Keio Institute of Pure and Applied Sciences, Keio University, Yokohama 223-8522, Japan
6. Center for Spintronics Research Network, Keio University, Yokohama 223-8522, Japan