1. Advanced Products Development Center, Technology and Intellectual Property HQ, TDK Corporation, 2-15-7 Higashi-Ohwada, Ichikawa 272-8558, Japan
2. Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
3. Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8577, Japan