1. Department of Nanotechnology for Sustainable Energy, School of Science and Technology, Kwansei Gakuin University, Gakuen-Uegahara 1, Sanda 669-1330, Japan
2. National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba 305-0044, Japan
3. Center for Spintronics Research Network (CSRN), Osaka University, Toyonaka 560-8531, Japan