1. Institute of Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
2. Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka 560-0871, Japan
3. Center for Spintronics Research Network (CSRN), Osaka University, Toyonaka, Osaka 560-0831, Japan
4. Advanced Mechanical and Electronic System Research Center, Department of Engineering, Tottori University, Tottori 680-8551, Japan