Templated Synthesis And Magnetic Properties Of CoFe₂ Nanowires And CoFe₂O₄ Nanowires

FeCo alloy, the one of important soft magnetic materals, has caught much attention due to their high saturation magnetization, low coercivity, high permeability and low magnetic anisotropy constant. Among perpendicular magnetic recording materials, CoFe₂O₄ are looked as the most candidate with large covercivity, moderate saturation magnetization and magnetocrystalline anisotropy. In this paper, we prepared cobalt-iron alloy nanowires with AAO templates through pulse electrodeposition, and obtained the hard magnetic materal CoFe₂O₄ nanowires by further thermal oxidation. The microstructure and morphology of the nanowires were also investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX); the magnetic performances of nanowires were determined by vibrating sample magnetometry (VSM). The main conclusions are obtained as follows:During pulse eletrodeposition of CoFe₂ alloy nanowire, temperature, pH value and electrical voltage are important factors of influencing the eletrodeposition rate and the component of iron-cobalt alloy. When the temperature rise or pH value ascend, the eletrodeposition rate and the content of iron in alloy increase, but the Fe2+ in the solution is apt to oxidation. The best eletrodeposition occurs in the condition that the average voltage is 2.65V, deposition temperature 40℃, pH value 4.0, and MCo/(MCo+MFe)=35%.The introduction of conducting salt and magnetic force mixing can improve the eletrodeposition, producing high-quality polycrystalline CoFe₂ nanowire arrays. Magnetic tests show the saturation magnetization and the coercivity of the magnetic hysteresis loops were 122 emu·g-1 and 870Oe, and the squareness is 0.13. These parameters are anisotropic, and this anisotropy decreases with the reduction of nanowire length.The anisotropy of CoFe₂O₄ nanowires mostly depends on magnetocrystalline anisotropy. The saturation magnetization and coercivity of CoFe₂O₄ nanowires is 16 emu·g-1 and 500Oe, less than CoFe₂ alloy nanowires, but the squareness(0.33) is higher. Namely soft magnetic materal CoFe₂ alloy nanowires has changed into magnetic materal CoFe₂O₄ ones. CoFe₂ nanowire samples were oxidated at 600℃,700℃and 800℃respectively, and their magnetic properties were studied. It's found that the coercivity and saturation magnetizatin of the nanowires increased obviously with oxidation temperature. This indicates that a higher oxidation temperature can improve the oxidation of CoFe₂ nanowires and the crystallization of resulting CoFe₂O₄, and eliminate the defect in the nanowires.