Synthesis And Magnetiec Properties Of Co_xZn_1-xFe₂O₄and Lanthanides Dopes Co_xZn_1-xFe₂O₄Nanocrystallines Via Soft Chemistry Method

Using cheap sulfate and nitrate as raw materials, NaOH, Na2CO3and NH3· H2O as precipitation agent (reaction agent), CoxZn1-xFe2O4and CoFe2-xRexO4(Re=Dy3+,La3+) nanocrystallines with spinel structure were prepared by chemical coprecipitation method and hydrothermal method. Influence of the solution pH value, reaction temperature, reaction time, sintering temperature, composition contrast, sodium citrate and the lanthanum doping on the structure, morphology and magnetic properties of CoxZn1-xFe2O4nanocrystalline have been studied. By through XRD, FTIR, SEM and VSM measurements, the microstructures, morphology and magnetic properties of CoxZn1-xFe2O4and Lanthanides doped CoxZn1-xFe2O4nanocrystallines were investigated. The results obtained are as follows:①Using NaOH as precipitation agent, CoxZn1-xFe2O4nanocrystallines with spinel structure can be prepared through one step coprecipitation reaction for60miunutes under fixed processing conditions(i.e. the pH value of the solution is12and the reaction temperature is80℃), the particle is spherical and the mean grain size is11-15nm. The Magnetic properties of the CoxZn1-xFe2O4nanocrystallines increase with the increasing content of cobalt (i.e.x), and it gradually transforms from the paramagnetism of ZnFe2O4to the ferrimagnetism of CoFe2O4. The addition of surfactant can improve dispersion status of samples in a certain extent, but no significant effect on the crystal structure and particle size of the nanocrystalline. The particle size of sintered sample is increased. The specific saturation magnetization, residual magnetization and coercive force of the samples is also increased, and the specific saturation magnetization of sintered samples is close to that of the bulk material. The doping of a moderate amount of Dy3+does not change the crystal structure of CoFe2O4(i.e. CoFe2-xDyxO4), whereas the doping level reaches a certain value (x≧0.07), the inpure phase (i.e. DyFeO3) will appear.②The preparation of CoxZn1-xFe2O4nanocrystallines by chemical coprecipitation method with NH3· H2O as precipitant needs sintering. After being sintered at750℃for3hours (for the as prepared mixed hydroxide precursor precipitates), the spinel structure CoxZn1-xFe2O4nanocrystallines with average particle size between20-40nm were prepared. The obtained nanocrystallines exhibt spheric shape, and the grain size increase with the increasing sintering temperature. The specific saturation magnetization of the as prepared CoxZn1-xFe2O4nanocrystallines is higher than that of the CoxZn1-xFe2O4nanocrystallines directly prepared by coprecipitation method useing NaOH as precipitant whereas it is less than that of the sintered samples.③In hydrothermal synthesis of CoxZn1-xFe2O4nanocrystalline using NaOH as reaction agent, the feasible pH value of the solution is13. Under the suitable pH value, the spinel structure CoxZn1-xFe2O4nanocrystalline with the average grain size of11-17nm can be synthesized through12hours hydrothermal reaction at160℃The obtainted CoFe2O4nanocrystallines exhibt a ferromagnetic property, the saturation magnetization and the coercive force of the nanocrystalline are86.7emu/g and1010.7Oe, respectively, and these values are higher than that one of the nanocrystallines prepared by coprecipitation method. The CoDyxFe2-xO4and CoFe(2-x)LaxO4nanocrystalline with spinel structure can be prepared under the same conditions, whereas a inpure phase will be appear at the higher doping level (x≥0.07). The influence of the doping of La3+on the CoFe2O4nanocrystalline is greater than that of Dy3+, and it is more useful to enhance the magnetic properties of nanocrystallines, the specific saturation magnetization of CoFe1.98La0.02O4nanocrystalline reaches93emu/g.④In the process of hydrothermal synthesis CoFe2O4nanocrystallines using NaOH as reaction agent at pH value of13, the addtion of sodium citrate can effectively restrain the growth of CoFe2O4nanocrystallines and improve the dispersity of the nanocrystallines; whereas the excessive sodium citrate can inhibit the growth or etch some crystal face of the CoFe2O4nanocrystalline. In the above mentioned hydrothermal synthesis process, the reaction time and reaction temperature have little impact on the grain size and morphology of the CoFe2O4nanocrystallines, the amount of the added sodium citrate is the key role to the grain size and the dispersity of the nanocrystallines.⑤Using NH3· H2O as reaction agent, CoFe2O4nanocrystallines with spinel structure can be prepared through hydrothermal method under the fixed processing conditions (i.e. the pH value of solution is10), the particle is spherical and the average size is10-14nm. The reaction time has little impact on the grain size and morphology of the CoFe2O4nanocrystallines, but the increasing of the reaction temperature can promote the grain growth.⑥Using Na2CO3as reaction agent, CoFe2O4nanocrystallines with spinel structure can be prepared through hydrothermal method under the fixed processing conditions (i.e. the pH value of solution is9.5and the reaction temperature is160℃), the particle is spherical and the average size is11-13nm. The reaction time and reaction temperature have little impact on the grain size and morphology of the CoFe2O4nanocrystallines, but the dispersity of the nanocrystallines improved with the increasing reaction temperature.