1. Department of Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
2. Peter Grünberg Institut, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
3. Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
4. Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
5. Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
6. Department of Physics, National Taiwan University, Taipei 10617, Taiwan