1. Temasek Laboratories, National University of Singapore, 119077 Singapore
2. Department of Physics, University of Hong Kong, Hong Kong, P. R. China
3. York-Nanjing
Joint Center for Spintronics and Nano Engineering (YNJC), School of
Electronics Science and Engineering, Nanjing University, Nanjing 210093, China
4. School of
Physics, University College Dublin, Dublin 4, Ireland
5. School of Physical and Mathematical Sciences, Nanyang Technological University, 639798 Singapore