1. Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
2. Center for Spintronics Research Network (CSRN), Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
3. Department of Applied Physics, Tohoku University, Sendai 980-8579, Japan
4. ULVAC-Osaka University Joint Research Laboratory for Future Technology, Osaka University, Suita, Osaka 560-0871, Japan