[1] Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576, Singapore
[2] Data Storage Institute, 5 Engineering Drive 1, Singapore 117608, Singapore
[3] Institute of Materials Research and Engineering (IMRE), 3 Research Link, Singapore 117602, Singapore
[4] Department of Materials Science and Engineering, University of Michigan, H. H. Dow Building, 2300 Hayward Street, Ann Arbor, MI 48109-2136