1. National Creative Research Initiative Center for Spin Dynamics and Spin-Wave Devices, Nanospinics Laboratory, Research Institute of Advanced Materials, Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, South Korea
2. Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, South Korea
3. Department of Materials Science and Engineering, Dong-A University, Busan 604-714, South Korea
4. Center for Emergent Matter Science (CEMS), RIKEN, Hirosawa 2-1, Wako, Saitama 351-0198, Japan
5. Hitachi, Ltd., Central Research Laboratory, Hatoyama, Saitama 350-0395, Japan
6. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan