[1] Lanzhou Univ, Dept Phys, Lanzhou 730000, Peoples R China
[2] Lanzhou Univ, Inst Appl Magnetism, Key Lab Magnetism & Magnet Mat, Minist Educ, Lanzhou 730000, Peoples R China
[3] Lanzhou Univ, Inst Chem & Phys, Key Lab Solid Lubricat, Lanzhou 730000, Peoples R China