Synthesis, Magnetic Properties and Microstructure of Ni-Zn-Cr Ferrites Doped with Lanthanum

The precursors consisted of Ni2+, Zn2+, Cr3+, Fe3+ and La3+ ionic citrate were prepared by sol-gel process. Nanocrystalline powders of Zn0.4Ni0.6Cr0.5Fe1.5O4 and Zn0.4Ni0.6Cr0.5La0.02Fe1.48O4 were obtained at low sintering temperatures. The process that amorphous precursors translated to crystalline ferrites was researched by means of DSC-TG. The structure, morphology and magnetic properties of the obtained products were characterized by X-ray diffractometer (XRD), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). The results showed that the sintering temperature and La doping had an obvious effect on the crystallite size and magnetic properties of samples. The crystallite size of Ni-Zn-Cr ferrites varied from 14.6 to 23.1 nm in the sintering temperature range from 400 to 800 °C, and the crystallite size varied from 13.2 to 19.1 nm for La-doped Ni-Zn-Cr ferrites in the same condition. The saturation magnetization of samples increased with sintering temperature, while the variation of coercivity had a reverse trend.