[1] Tohoku Univ, Re Inst Elect Commun, Sendai, Miyagi 9808577, Japan
[2] Tohoku Univ, Ctr Sci & Innovat Spintron, Sendai, Miyagi 9808577, Japan
[3] Tohoku Univ, Ctr Spintron Res Network, Sendai, Miyagi 9808577, Japan
[4] Tohoku Univ, Ctr Innovat Integrated Elect Syst, Sendai, Miyagi 9800845, Japan
[5] Tohoku Univ, WPI Adv Inst Mat Res, Sendai, Miyagi 9808577, Japan
[6] Univ Illinois, Dept Phys, Urbana, IL 61801 USA
[7] Univ Illinois, Mat Res Lab, Urbana, IL 61801 USA
[8] Johannes Gutenberg Univ Mainz, Inst Phys, D-55128 Mainz, Germany