Room Temperature Magnetism in Co-doped ZnO Nanorods

Zn1−xCoxO (x=0, 0.02, 0.04, 0.06, 0.08, 0.10) nanorods have been synthesized by the hydrothermal method. XRD patterns show that all samples are wurtzite structure without impurity. The magnetization measurements show that the pure ZnO is diamagnetic, while paramagnetism dominates in Zn1−xCoxO nanorods. Paramagnetism increases linearly with an increasing Co concentration. The magnetic moment calculated from the magnetic susceptibility is around 4 μB/Co, which is close to the theoretical value of Co ions with L=1.07 and S=3/2 in all Zn1−xCoxO nanorods, indicating the Co atoms are mostly isolated. All the samples exhibit weak ferromagnetism. However, the saturation magnetization of the ferromagnetic contribution in Zn1−xCoxO almost keeps constant with increasing Co concentration. We conclude that the weak ferromagnetism in Zn1−xCoxO might be due to the high concentration of defects.