The study of transition on NiFe2O4 nanoparticles prepared by co-precipitation/calcination

摘要

In this study, the NiFe_2O_4 nanoparticles have been prepared by co-precipitation and calcination process. Using a vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometer of X-ray (EDX), and X-ray photoelectron spectroscopy (XPS), the samples obtained by co-precipitation and then by further calcination have been analyzed. The experimental results show that the precursor synthesized by co-precipitation is the composite of both amorphous FeOOH and Ni(OH)_2, but has no amorphous NiFe_2O _4. The results of both EDX and XPS revealed that the FeOOH species is wrapped up by Ni(OH)_2 species. In the calcination process, the amorphous composite is dehydrated and transformed gradually into crystalline NiFe_2O_4 nanoparticles, with the metal ions diffusing. The reaction is different from the one used to prepare other ferrite (e.g., CoFe_2O_4, MnFe_2O_4, Fe _3O_4, etc.) nanoparticles directly by co-precipitation. With increasing calcination temperature, the NiFe_2O_4 grains grow and the magnetization is enhanced.