[1] Anyang Normal Univ, Coll Phys & Elect Engn, Anyang 455002, Peoples R China
[2] Henan Univ Urban Construct, Dept Math & Phys, Pingdingshan 467036, Peoples R China
[3] Grirem Adv Mat Co Ltd, Gen Res Inst Nonferrous Met, Natl Engn Res Cent Rare Earth Mat, Beijing 100088, Peoples R China