Study On The Magnetic Properties Of CoFe₂O₄, Co_xZn_1-xFe₂O₄ Nanopartilces By Solid State Synthesis At Low Heating Temperature

Cobalt ferrite has a unique physical properties, chemical properties and magnetic properties due to its high saturation magnetization, large magnetocrystalline anisotropy constant and better chemical stability. In recent years, Magneto-optical Kerr effect in short wavelength is observed in Cobalt ferrite thin film, which is important to improve magnetic recording density and access speed. Thus spinel series cobalt ferrite is considered as the next generation of potential magneto-optical storage materials, which attracted more and more attention. In addition, another study abroad found that cobalt ferrite magnetic fluid show a potential applications in the medical field. So it is very necessary to find a more convenient method of preparation of cobalt ferrite.Solid state synthesis at low temperatures has another name as solid state synthesis at room temperature. It is the Solid-phases reaction at room temperature or near room temperature (≤100℃). This method has the advantages of easy operation and control, non-use of solvents, high selectivity, high yield, less pollution, saving energy, and simple synthetic process.In this paper, CoFe₂O₄ and Co_xZn_1-xFe₂O₄ with a single phase of the spinel structure were prepared by solid state synthesis at low temperatures (90℃) with metal chloride and NaOH as the main raw materials. And more detailed performance analysis was investigated. The effect of stoichiometric composition on the magnetism of Co_xZn_1-xFe₂O₄ is discussed. The main results are as follows:(1) CoFe₂O₄ ferrite nanoparticles were synthesized by a method of solid state synthesis at low temperatures. The samples without heat-treated showes a single spinel structure, the grain size is of 11-56 nm, the samples coercivity is 1170 Oe which annealed at 600℃, saturation magnetization is up to 89 emu/g at 1000℃, and it is close to the block value. The single domain critical size is about 23 nm. The hyperfine field increases with the increase of grain size by M(?)ssbauer spectrum measurement, which can be explanation by the principle of collective magnetic excitation .(2) Co_xZn_1-xFe₂O₄ (x =0.2, 0.5, 0.8) ferrite nanoparticles were synthesized by a method of solid state synthesis at low temperatures. The samples without heat treatment showes a single spinel structure. Co_0.2Zn_0.8Fe₂O₄ particle annealed at 800℃showes superparamagnetism; The saturation magnetization of Co_0.8Zn_0.2Fe₂O₄ particle reaches 85 emu/g at 800℃, which is close to the block value. The single domain critical size is about 27 nm. We found that saturation magnetization and the coercivity of the samples can be improve by improving the amount of cobalt in the alternative, after analyzing the samples under the same annealing temperature with the different ion ratio.