Preparation And Magnetic Properties Of CoFe₂O₄ Nanoparticles Doped By Rare Earth Ions

The research interest lies on magnetic nanoparticles materials because of their potential applications in high-density recording storage,microwave absorbing materials,separation of biological samples,magnetic resonance imaging and targeted release of drugs.In recent years, people have devoted to synthesis of varieties with mono-dispersed,size-controlled,various shapes and stable magnetic properties of nano-materials.Among magnetic materials, CoFe₂O₄ is especially interesting because of its not only high cubic magnetocrystalline anisotropy,high coercivity,moderate saturation magnetization,but also chemical properties of stability,and no side effects in the human body.Recently,cobalt ferrite nanoparticles were known to be a pHotomagnetic material,high-density magnetic recording media,spin electronic devices,and magnetic fluid hyperthermia,etc.The main researches focused on at present were controlled particle size,narrow particle size distribution and controlled magnetic properties.This paper has mainly carried on several aspect workes as follows:1.Using the sol-gel method to synthesis controlled panicle size and magnetic properties of CoFe₂O₄ nanocrystalline.Through the research of metallic ion and the citric acid mole percent added, pH,investigated the influences of them on the calcining heat and the calcining time of the CoFe₂O₄ nanocrystal structure,the appearance and magnetism performance influence,the results show that(1) the particle size,coercivity and saturation magnetization of CoFe₂O₄ nanocrystalline increased with the increasing of sintering temperature and sintering time;(2) the coercivity and saturation magnetization of CoFe₂O₄ nanocrystalline decreased with the increasing of metallic ion and the citric acid mole and pH;(3) the best synthesis condition of CoFe₂O₄nanocrystalline by sol-gel method were as follows:metal ions and citric acid molar ratio of 1:1.2,pH value of between 2 to 4,and at 400℃calcined 3 hours.When the average particle size of CoFe₂O₄ is 35 nm, the saturation magnetization is 57.5 emu/g,and coercivity is up to 3140 Oe.2.Using coprecipitation method to synthesize CoFe₂O₄ nanocrystalline,the average particle size is 15 nm,saturation magnetization is 48.73 emu/g,and coercivity is 217.8 Oe. Researching the relationship of CoFe₂O₄ between the calcination temperature on the nanostructure and magnetic properties,the results show that the particle size,coercivity and saturation magnetization of CoFe₂O₄ nanocrystalline increased with the increasing of sintering temperature and sintering time.Comparing the two kinds of preparation methods, the results showed that the nanoparticle sizes and coercivities of CoFe₂O₄ are larger with the sol-gel method than with the coprecipitation method.The particle sizes and coercivities by the sol-gel method are higher to about 30 nm and 3140 Oe,respectively.By coprecipitation method,the average particle size and coercivity are about 15 nm and 217.8 Oe,respectively.3.CoFe_2-xRE_xO₄ ferrite nanoparticles,where RE=La,Ce,and Eu,have been synthesized by sol-gel method.The effects of the substitution RE³⁺ ions for Fe³⁺ ones on the structure,the microstructure,the chemical homogeneity,and the magnetic properties of the cobalt ferrite system are studied.The results showed that doped by lanthanide ions modulates the magnetic properties of cobalt spinel ferrite nanoparticles,the rare earth ions suppress the crystal grain growth.The coercivity and saturation magnetization decreased with the increasing of doped amount,In particular cases of Ce³⁺ ions,a dramatic change in magnetic properties is observed. In the same crystallite size and doped amount,the coercivities of CoFe_1.9RE_0.1O₄ nanoparticles were lager than that of CoFe₂O₄ nanoparticles,whereas the saturation magnetizations were lower.Especially,the coercivity and saturation magnetization of CoFe_1.9Ce_0.1O₄ changed remarkablely,the coercivity increasd from 2056.8 Oe to 2447.9 Oe, but the saturation magnetization reduced from 57.6 emu/g to 39.9 emu/g.