1. WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
2. Centro de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS), Departamento de Química-Física, Universidade de Santiago de Compostela, Santiago de Compostela 15782, Spain
3. Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
4. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
5. Faculty of Science and Engineering, Iwate University, Morioka 020-8551, Japan
6. Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
7. Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan