Pure ZnO and Ni-doped ZnO rods were prepared by hydrothermal method at a temperature of 120C. The morphological, structural, magnetic and optical properties of the as-prepared rods were investigated by means of field emission scanning electron microscopy, X-ray diffraction, vibrating sample magnetometer and photoluminescence. All the samples were radial-grown hexagon rods with diameter from 470 to 720nm and length of 4–6 μm. X-ray diffraction showed that the rods had single crystalline wurtzite structure without other impurity phases. The pure ZnO rods and Ni-doped ZnO rods had ferromagnetism at room temperature, and the special saturation magnetization deduces with the increasing diameter of rods. These results revealed that the saturation magnetization of the ZnO rods depended on the surface-to-volume ratio of rods rather than the Ni doping concentrations. The photoluminescence spectra studies showed the same diameter dependences of oxygen vacancies as that of magnetization, which demonstrated that oxygen vacancies at surface of rods played an important role in introducing ferromagnetism. The annealing in rich oxygen and reducing atmospheres confirmed this argument further.

Vacancy-Induced Room-Temperature Ferromagnetism in ZnO Rods Synthesized by Ni-Doped Solution and Hydrothermal Method. Z.Yu, S.Ge, Y.Zuo, G.Wang, F.Zhang: Applied Surface Science, 2010, 256[20], 5813-7