Magnetic Properties and Microstructures of Polyethylene Glycol (PEG)-Coated Cobalt Ferrite (CoFe_2O_4) Nanoparticles Synthesized by Coprecipitation Method

摘要

Magnetic nanoparticles of cobalt ferrite (CoFe_2O_4) have been synthesized by coprecipitation method with various synthesis temperatures, concentration of NaOH and stirring duration. The results showed that nanoparticles have well crystallized structure with various grain sizes which depend on synthesis parameters. The grain size increased with the increase of the synthesis temperature, the decrease of the concentration of NaOH, and the decrease of the stirring duration. Magnetic characterization of CoFe_2O_4 nanoparticles was measured by Vibrating Sample Magnetometer (VSM). The results showed that coercive field decreased with the decrease of the particle size. The saturation and remanent magnetization showed increasing when crystallinity increased. However, it also depends on presence of a-Fe_2O_3 phases and their grain size. Based on magnetic characterization analysis, sample with parameter of synthesis temperature 80 C, concentration of NaOH 5 M and stirring duration 120 minutes have been selected to be modified using polyethylene glycol (PEG)-4000. XRD and TEM analysis showed that surface modification with PEG-4000 could increase the crystallinity of nanoparticles, decrease agglomeration and control the shape to more spherical. VSM analysis showed that modification PEG-4000 caused the decrease of the saturation magnetization which is due to the existence of a-FeO(OH) and γ-FeO(OH) phases from bonds at interface of CoFe_2O_4 as confirmed by XRD and Fourier Transform Infrared (FTIR) analysis.