Synthesis And Characterization Of CoFe₂O₄ Nanowires And Nanoparticles

Recently, much attention has been devoted to the study of magnetic nanowires. Cobalt ferrite has high coercivity, moderate saturation magnetization, high chemical stability and mechanical hardness. So it has potential application in high-density recording media. The porous anodized aluminum oxide (AAO) has been used extensively for the synthesis of nanowires, because of its advantages such as simple and low-cost fabrication, thermal stability, insulation, uniform pore size, high pore density and controllable pore diameter, etc. The sol-gel method is a common used wet chemical technique to synthesize materials. The method is quite simple, need low sintering temperature and can easily control the stoichiometry. In this work, we fabricated cobalt ferrite (CoFe2O4) nanowires in AAO templates by sol-gel process, and characterize its structure, morphology and magnetic properties by XRD, SEM and VSM.The AAO has been prepared by two-step anodization, and its morphology has been studied. The pores are uniform, compact and the pore diameter is about 60nm.CoFe2O4 nanowires were prepared in porous AAO template using sol-gel method. The XRD spectra show that the nanowires were polycrystalline. Magnetic measurements revealed that the nanowires did not show magnetic anisotropy. The reason should be that the magneto-crystalline anisotropy of CoFe2O4 nanowires is larger than its shape anisotropy. The coercivity, saturation magnetization and remanence of the nanowires are relatively low, the reason is that the content of Co2⁺ and Fe3⁺ are low in the Sol, and this results in short nanowires with much defect.We refilled the AAO with sol and studied its effect on the structure and magnetic properties of the nanowires. It's found that the coercivity, saturation magnetization and remanence of the nanowires increased obviously with the filling times. It should be due to the increase in the length of the nanowires and the decrease in the defect.We investigated the effect of annealing temperature on the nanowires. We annealed the sample in 600℃,650℃and 700℃respectively, and studied their magnetic properties. It's found that the coercivity and saturation magnetizatin of the nanowires increased obviously with annealing temperature. This indicates that a higher annealing temperature can improve the crystallization.We synthesized CoFe₂O₄ nanoparticles in 600℃and 800℃by sol-gel. The XRD and TEM results show that the size, coercivity and saturation magnetization of the nanoparticles all got bigger with the increase of annealing temperature.