; Huang, Feng
; Lin, Zhang
; Chen, Dagui
; Li, Wei] Chinese Acad Sci, Fujian Inst Res Struct Matter, Lab Mat Chem & Phys, Natl Engn Res Ctr Optoelect Crystalline Mat, Fuzhou 350002, Peoples R China
; [Chu, Wangsheng
; Chen, Dongliang
; Wu, Ziyu] Chinese Acad Sci, Beijing Synchrotron Radiat Facil, Inst High Energy Phys, Beijing 100049, Peoples R China
Magnetic properties of a series of well-substituted Zn1-xCoxO (x = 0.018, 0.036 and 0.05) single crystals were studied. A typical paramagnetic anisotropy property, which strengthens when x decreases, was found. A magnetization step was observed at 2 K when the magnetic field is parallel to the c axis, indicating that paramagnetic anisotropy is the origin of the strong crystal field effect on Co2+ ions in ZnO lattices. The Co2+ single-ion anisotropy parameter 2D is obtained as 7.5 K. The effective moment of Co2+ takes the values 2.7 mu(B), 1.82 mu(B), 1.49 mu(B) when x = 0.018, 0.036 and 0.05, revealing that more antiferromagnetic coupling between Co2+ ions arises in the perfect crystal when x increases.