1. Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, Aichi 466-8555, Japan
2. Department of Pure and Applied Physics, Kansai University, Suita, Osaka 564-8680, Japan
3. Center for Spintronics Research Network, Osaka University, Toyonaka, Osaka 560-8531, Japan
4. Information Storage Materials Laboratory, Toyota Technological Institute, Nagoya, Aichi 468-8511, Japan