[1] Tsing Hua Univ, Dept Mat Sci & Engn, Beijing 100084, Peoples R China
[2] Chinese Acad Sci, Inst Phys, State Key Lab Magnetism, Beijing 100080, Peoples R China
[3] Chinese Acad Sci, Inst Phys, Ctr Condensed Matter Phys, Beijing 100080, Peoples R China
[4] Chinese Acad Sci, San Huan Res Lab, Beijing 100080, Peoples R China