[Yi, J. B.
; Fan, H. M.
; Huang, X. L.
; Zhang, H. T.
; Ding, J.] Natl Univ Singapore, Dept Mat Sci & Engn, Singapore 119260, Singapore
; [Lim, C. C.
; Yang, K. S.
; Gao, X. Y.
; Liu, T.
; Wee, A. T. S.
; Feng, Y. P.] Natl Univ Singapore, Dept Phys, Singapore 117542, Singapore
; [Xing, G. Z.
; Huang, S. L.
; Wu, T.
; Wang, L.] Nanyang Technol Univ, Sch Phys & Math Sci, Singapore 637371, Singapore
; [Van, L. H.] Natl Univ Singapore, Nanosci & Nanotechnol Initiat, Singapore 119260, Singapore
; [Yang, K. S.] Shandong Univ, Dept Phys, Jinan 250100, Peoples R China
; [Qin, X. B.
; Wang, B. Y.] Chinese Acad Sci, Inst High Energy Phys, Key Lab Nucl Anal Tech, Beijing 100049, Peoples R China
We demonstrate, both theoretically and experimentally, that cation vacancy can be the origin of ferromagnetism in intrinsic dilute magnetic semiconductors. The vacancies can be controlled to tune the ferromagnetism. Using Li-doped ZnO as an example, we found that while Li itself is nonmagnetic, it generates holes in ZnO, and its presence reduces the formation energy of Zn vacancy, and thereby stabilizes the zinc vacancy. Room temperature ferromagnetism with p type conduction was observed in pulsed laser deposited ZnO: Li films with certain doping concentration and oxygen partial pressure.