1. School of Physics; Huazhong University of Science and Technology; Wuhan 430074 China
2. ISIS Facility; Rutherford Appleton Laboratory; Harwell Oxford; Didcot Oxfordshire OX11 0QX UK
3. School of Engineering; University of Newcastle; New South Wales 2308 Australia
4. Department of Earth Sciences; University of Cambridge; Cambridge CB2 3EQ UK
5. Laboratory of Optical Information Technology; Wuhan Institute of Technology; Wuhan 430205 China
6. Department of Materials; Imperial College London; Royal School of Mines; London SW7 2AZ UK
7. Department of Materials Science and Metallurgy; University of Cambridge; Cambridge CB3 0FS UK