Department of Physics, Hebei University of Technology, Tianjin 300130, China. yhwangwz@263.net|Department of Physics, Hebei University of Technology, Tianjin 300130, China. yhwangwz@263.net|Department of Physics, Hebei University of Technology, Tianjin 300130, China. yhwangwz@263.net|Department of Physics, Hebei University of Technology, Tianjin 300130, China. yhwangwz@263.net