1. Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
2. Graduate School of Science and Technology, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan
3. Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
4. Center for Spintronics Research Network, Osaka University, Toyonaka, Osaka 560-8531, Japan