Intrinsic magnetism of a series of Co substituted ZnO single crystals

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 μB, 1.82 μB, 1.49 μB 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