The structure and magnetic properties of Zn 1−xNi xFe 2O 4 ferrite nanoparticles prepared by sol–gel auto-combustion

Abstract

Zn 1− x Ni x Fe 2O 4 ferrite nanoparticles were prepared by sol–gel auto-combustion and then annealed at 700 °C for 4 h. The results of differential thermal analysis indicate that the thermal decomposition temperature is about 210 °C and Ni–Zn ferrite nanoparticles could be synthesized in the self-propagating combustion process. The microstructure and magnetic properties were investigated by means of X-ray diffraction, scanning electron microscope, and Vibrating sample magnetometer. It is observed that all the spherical nanoparticles with an average grain size of about 35 nm are of pure spinel cubic structure. The crystal lattice constant declines gradually with increasing x from 0.8435 nm ( x=0.20) to 0.8352 nm ( x=1.00). Different from the composition of Zn 0.5Ni 0.5Fe 2O 4 for the bulk, the maximum M s is found in the composition of Zn 0.3Ni 0.7Fe 2O 4 for nanoparticles. The H c of samples is much larger than the bulk ferrites and increases with the enlarging x. The results of Zn 0.3Ni 0.7Fe 2O 4 annealed at different temperatures indicate that the maximum M s (83.2 emu/g) appears in the sample annealed at 900 °C. The H c of Zn 0.3Ni 0.7Fe 2O 4 firstly increases slightly as the grain size increases, and presents a maximum value of 115 Oe when the grains grow up to about 30 nm, and then declines rapidly with the grains further growing. The critical diameter (under the critical diameter, the grain is of single domain) of Zn 0.3Ni 0.7Fe 2O 4 nanoparticles is found to be about 30 nm.