Preparation Of Cobalt-dysprosium Ferrite Magnetic Nanocrystals By Liquid Precipitation

Magnetic nanocrystal has the special optical electromagnetic properties with a broad application prospect in various fields including medical, biological, environmental, electronic, catalytic and some other fields. It possesses a unique magnetism which is called mesoscopic magnetism with mesoscopic properties of nano material and magnetic properties of magnetic material. In recent years, there is a significant progress in preparation and characteristic analysis of magnetic nanocrystal.In the paper, the Co-Dy-ferrites were prepared by liquid precipitation method with Dy(NO3)3·xH2O, CoCl2·xH2O, FeSO4·7H2O, Fe2(SO4)3·xH2O, NH3·H2O,NaOH as raw materials and the results were studied. To avoid its agglomeration in dry state, the surface of Co-Dy-ferrite magnetic nanocrystal was modified online by using lauric acid, an organic modifier. Both NH3·H2O and NaOH were usual precipitating agents, when liquid precipitation method was used. The precipitating agent NaOH would produce Na2O, which was doped into ferrite crystal structure as a nonmagnetic constituent.This kind coexistent phase would seriously affect the magnetism of nanocrystal. In order to increase its magnetic properties by decreasing nonmagnetic components, NaOH solution was replaced with NH3·H2O as a precipitating agent. Influence of NH3·H2O contend, reaction time, stirring speed and NH3·H2O dropping speed on product output has been investigated by orthogonal test in order to determine the optimal process parameters of liquid precipitation with precipitant NH3·H2O. Effects of different precipitants on the composition, crystal configuration, particle size and related magnetic properties of Co-Dy-ferrite magnetic nanocrystals were compared. The morphology, crystal structure and magnetic properties of ferrite nanocrystals under different doping contents of Dy3+and Co2+, and influence of various magnetic particle sizes on magnetization, corcivity and remanent magnetization were investigated. The principal metal oxides and their contents of cobalt-dysprosium ferrite magnetic nanocrystals without surface modification were detected by X-ray fluorescence spectrometer(XRF); The morphology and crystal structure of cobalt-dysprosium ferrite magnetic nanocrystals were analyzed by X-ray diffraction(XRD);The surface chemical environment of Co-Dy-ferrite magnetic nanocrystals modified by lauric acid online were observed by Fourier transform infrared spectrometer(FT-IR); The magnetic properties of Co-Dy-ferrite magnetic nanocrystals prepared with different precipitating agents at room temperature were measured by Superconducting quantum interference device(SQUID);The hysteresis curves of Co-Dy-ferrite magnetic nanocrystals prepared in different cobalt-dysprosium amounts at room temperature were detected by Vibrating sample magnetometer(VSM).The XRF data show that the use of precipitant NH3·H2O significantly avoided the adverse influence of nonmagnetic particles on crystalline structure and magnetic properties of Co-Dy-ferrite magnetic nanocrystals. The magnetic nanocrystal is a mixed oxidation state compound, mainly formed by the combination of Fe2O3, Co3O4and Dy2O3. Nonmagnetic phase Na2O decresed greatly. The relative contents of each metal oxides are different with doping various amounts of Dy3+and Co2+. The XRD patterns show that Co-Dy-ferrite magnetic nanocrystal is an inverse spinel face centered cubic structure with a high degree of crystallinity and its average particle size is about6-11nm. The FT-IR spectra shows that the surface chemistry environment of Co-Dy-ferrite magnetic nanocrystals have been changed, and there is a strong chemical effect between the particles and the surfactant. The contents of Dy3+and Co2+have a certain effect on the structure of Co-Dy-ferrite magnetic nanocrystal. The SQUID photos indicate that after using NH3·H2O as a precipitating agent, the corcivity of Co-Dy-ferrite magnetic nanocrystal was decreased slightly. However the saturated magnetization was significantly increased. Constract to previous nanocrystal prepared by using NaOH as a precipitant, its magnetic properties were improved greatly. The VSM results show that the magnetic properties of Co-Dy-ferrite magnetic nanocrystal are related to the particle size, Dy3+and Co2+doped amounts. In case of the close particle size, Dy3+doped amounts can influence the magnetic properties greatly. But the effect of Co2+doped amounts is slight. With increasing Dy3+doped amounts, magnetization rises first and then decreases. When Fe3+:Dy3+≈1:0.08, the property of Co-Dy-ferrite nanocrystal gets the best.