Effect of annealing on Ni-doped ZnO nanoparticles synthesized by the co-precipitation method

Pure and Zn0.98Ni0.02O nanostructures were prepared by the co-precipitation method. The effects of annealing in Argon (Ar) and oxygen (O2) environment on the structure, dielectric, electric and magnetic properties were investigated. The structural analysis from X-ray diffraction and energy dispersive X-ray results confirmed that all the nanoparticles samples indexed to hexagonal wurtzite ZnO structure. A significant decrease was observed in the dielectric constant (εr) and dielectric loss (ε′′) resulting from the incorporation of Ni into the ZnO lattice. Higher εr and ε′′ were observed in the O2 annealed sample. Moreover, the AC electrical conductivity (αAC) of the Ni doped ZnO sample increased in comparison with that of pure ZnO sample due to the increase of available charge carriers after replacement of Zn ions with Ni ions. The 2 wt% Ni-doped ZnO sample annealed in O2 and Ar environment revealed room temperature ferromagnetism (RTFM) behavior, but higher ferromagnetic was only observed in the O2 annealed sample. The origin of RTFM may originate from the exchange interaction between Ni2+ and excess of O2 vacancy in Zn0.98Ni0.02O nanoparticles.