1. Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1, Yamda-oka, Suita, Osaka 565-0871, Japan
2. Center for Spintronics Research Network, Osaka University, 1-3, Machikaneyama, Toyonaka, Osaka 560-8531, Japan
3. Fukui Institute of Technology, 3-6-1, Gakuen, Fukui, Fukui 910-0028, Japan
4. Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
5. High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan