Preparation, Structure And Magnetic Property Of ZnFe₂O₄ Nanoparticles

ZnFe2O4 is a kind of traditional spinel ferrite materials and possesses excellent chemical stability. There are many physical and chemical methods to synthesize ZnFe2O4 nanoparticles. The experiment condition has a great influence on the metal ionic distribution and consequently magnetic property in ZnFe2O4 nanoparticles. So it is important to synthesize monodisperse ZnFe2O4 nanoparticles and to study its magnetic.In this thesis, FeCl3 and ZnCl2 were employed to prepare spinel ZnFe2O4 nanoparticles by chemical coprecipitation. The influences of pH, calcination temperature and cleaning solvent on the metal ionic distribution, structure and magnetic property were investigated in the ZnFe2O4 nanoparticles. The main research results are as following:1. The influence of pH value on the structure and the physical properties of ZnFe2O4 nanoparticles was clarified. Using the alkali solvent to regulate the pH, a series of ZnFe2O4 nanoparticles were prepared at 450℃and the physical properties were characterized by Thermogravimetric Analysis(TG), X-ray diffraction Analysis(XRD), Transmission Electron Microscopy Analysis(TEM), FT-IR spectroscopy Analysis(FT-IR) and Raman spectroscopy Analysis(Raman) correspondingly. The ZnFe2O4 nanoparticle size increases with the increase of pH value. Better crystallization is obtained at low pH value, and the best crystallinity is got at pH=11.6. The prepared ZnFe2O4 presents a mixed spinel structure. The reversal degree decreases with the raise of pH when the pH value is below 12.0, and oppositely it increases with the pH value further increasing to above 12.0.2. The effect of annealing temperature on the structure and the physical properties of ZnFe2O4 nanoparticles was also clarified. With the pH value set to 11.6, a series of ZnFe2O4 nanoparticles at different annealing temperature were synthesized. The size of ZnFe2O4 particle increases from 25.6 to 82.1nm and the lattice constant rises from 8.419? to 8.439?, when the annealing temperature increases from 350 oC to 850 oC. The prepared ZnFe2O4 particles show a mixed spinel structure and the reversal degree firstly increases then decreases with the increase of annealing temperature. The ferromagnetic(FM) interaction and antiferromagnetic(AFM) interaction concurrently appear in the ZnFe2O4 nanoparticles. The interaction competition makes it show spin-glass state at low temperature. The spin freezing temperature is at 41.5K.3. The effect of acetone solvent washing on the structure and the physical properties of ZnFe2O4 nanoparticles was investigated. With the pH value set to 11.6, a series of ZnFe2O4 nanoparticles washed by acetone solution were prepared when the annealing temperatures were set at 450 oC, 550 oC and 650 oC, respectively. For the particles washed by acetone solvent, the smaller particle size leads to the better crystallization and the smaller reunite degree.