1. Department of Materials Science and Metallurgy, University of Cambridge, CB3 0FS Cambridge, United Kingdom
2. Center for Spinelectronic Materials and Devices, Physics Department, Bielefeld University, D-33501 Bielefeld, Germany
3. Research Center for Magnetic and Spintronics Materials, National Institute for Materials Science (NIMS), 1-2-1, Sengen, Tsukuba, 305-0047, Japan