1. Department of Applied Physics, The University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
2. Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
3. Department of Mechanical Engineering, Aichi Institute of Technology, Toyota, Aichi 470-0392, Japan
4. SPring-8/JASRI, Sayo, Hyogo 679-5198, Japan
5. Center for Spintronics Research Network at Osaka University, Toyonaka, Osaka 560-6671, Japan