[1] Research Institute of Electrical Communication, Tohoku University, 980-8577, Japan
[2] Center for Science and Innovation in Spintronics, Tohoku University, 980-8577, Japan
[3] Center for Spintronics Research Network, Tohoku University, 980-8577, Japan
[4] Center for Innovative Integrated Electronic Systems, Tohoku University, 980-0845, Japan
[5] WPI-Advanced Institute for Materials Research, Tohoku University, 980-8577, Japan
[6] Department of Physics, University of Illinois Urbana-Champaign, Urbana,IL,61801, United States
[7] Materials Research Laboratory, University of Illinois Urbana-Champaign, Urbana,IL,61801, United States
[8] Institute of Physics, Johannes Gutenberg Universität Mainz, Mainz,55128, Germany