Study On Preparation And Magnetic Properties Of AFe₂O₄ Spinel Ferrite

Room temperature magnetic refrigeration has developed fast as requirement of environment protect. The discovery of magnetocaloric effect in alloy, pervoskites have aroused many attentions recent years. The magnetocaloric (MEC) materials are all paramagnetism materials and ferromagnetism materials. The room temperature magnetic refrigeration has been investigated deeply, but ferrite magnetism materials have few research. In this thesis, the main research works focused on the effect of doping by various transition metals on the morphology and magnetic properties for the AFe₂O₄ spinel ferrite. We hope to possess some explore study in the magnetocaloric application of spinel ferrite.We choose (NiZn)Fe₂O₄, MnFe₂O₄, and CoFe₂O₄ as parent compound. Firstly, the effect on the magnetic properties of Ni²⁺ ions replaced by Cu²⁺ ions is studied in the (NiZn) spinel ferrite. It was found that theσ_s reduced continually with the addition of Cu²⁺ ions content and the Curie temperature (Tc) existed a transition at x=10. The decreasing ofσ_s can be ascribed to reduce the magnetic moment of crystal lattice induced by Cu²⁺ ions adding. Also the distortion of crystal lattice induced changing of Tc because of the addition of Cu²⁺. Farther, with doping La³⁺ ions in NiZnCu spinel ferrite, It is found both theσ_s and Tc decreased firstly and then increased and they have a transition when the x=0.03. The decreasing of net magnetic moment was the reason of decreasing ofσ_s and the secondary magnetic domain is the reason of increasing ofσ_s. The distortion of crystal lattice induced changing of Tc because of the addition of La³⁺. For the MnFe₂O₄ spinel ferrite, with the increasing of Zn²⁺ ions content, theσ_s and Tc increased firstly and then decreased. The increasing ofσ_S was due to increasing of net magnetic moment and the decreasing ofσ_s was due to addition of the non magnetic ions. The changing of Tc could be regard as change of crystal lattice type. The NiCuZn spinel ferrites were synthesized with high-quality crystal through a solid-molten salt method, and required lower temperature and shorter reaction time than the traditional solid method. It is found that the morphology of La³⁺ ions doped NiCuZn spinel ferrite looks roughness with the same method, which contributed to crystal lattice distortion and the surface of La³⁺ ions. The Cd²⁺ ions doping Co spinel ferrite samples were synthesized with perfect octahedron structure through sol-gel-molten salt method. With the addition of Cd²⁺ ions, the size of the series ferrite increased linearity, meanwhile theσ_s decreased.By calculating the magnetism entropy values, it is found the values of (NiZn),Mn spinel ferrite is less, but they have some merits such as the extensive origin, cheaper cost simple preparation and controller properties and so on, so the synthesized spinel ferrite is though of as a new magnetism refrigeration material.