Preparation And Magnetic Properties Of Nanocrystalline Fe_0.13[Co_xNi_100-x]_0.87 Alloy Fine Fibers

Ferromagnetic metal fibers (Fe, Ni, Co and their alloys fibers) are promising materials for applications in high performance conductive polymer-matrix composites of electromagnetic interference (EMI) shielding and electromagnetic wave absorbing technology due to their characteristics such as a high aspect ratio, anisotropy and small density.In this paper, nanocrystalline Fe_0.13[Co_xNi_100-x]_0.87 alloy fine fibres were prepared by the organic-gel thermal reduction process from raw materials of citric acid and metal salts. The structure and morphologies of the gel precursors and the fibres derived from thermal reduction of these precursors were characterized by FTIR, XRD, TG/DSC, SEM. The magnetic properties for the as-prepared alloy fibres were examined by vibrating sample magnetometer(VSM). Fe_0.13[Co_xNi_100-x]_0.87 (x=30,50,80) alloy fine fibre-epoxy resin composites were also prepared as a kind of radar absorbing materials. Reflection coefficient of one-layered absorber was numerically calculated.The results show that the diameters of the Fe_0.13[Co_xNi_100-x]_0.87 alloy fibres are in the range of 0.3μm to 2μm and these alloy fibers consist of grain sizes of about 35 nm. The crystal structures of the alloy fibers are influenced by the Co content. While the x value is lower than 30, the alloy is a nickel-based solid solution. While the value is higher than 60, it is a cobalt-based solid solution and the alloy has a FeNi₃ crystal lattice with the x value in the range from 30 to 60.The magnetic anisotropy is largely determined by the combination of magnetocrystalline anisotropy, shape anisotropy and magnetostatic interactions. The aligned nanocrystalline Fe_0.13[Co_xNi_100-x]_0.87 fibers show an obvious magnetic anisotropy. The ease axis is in the direction of the nanocrystalline fiber axis and the hard axis is perpendicular to the aligned nanocrystalline fiber. The nanocrystalline Fe_0.13[Co₅₀Ni₅₀]_0.87 fibers exhibit a very high remanence ratio of 0.48.Comparing with the other two composites, Fe_0.13[Co₅₀Ni₅₀]_0.87 alloy fine fibre-epoxy resin composite has the most excellent absorbing properties. In the frequency range of 3.01-6.82 GHz Fe_0.13[Co₅₀Ni₅₀]_)0.87 alloy fine fibre-epoxy resin composite with a thickness of 2 mm has a absorbing efficiency of -6 dB .While in the range of 3.7-5.1 GHz, it has a absorbing efficiency of -10 dB. The absorption peak reaches -11.8 dB while the frequency is 4.3 GHz.