Structure And Magnetic Properties Of 1-D Magnetic Nanotube And Nanowire Arrays Fabricated By AAO Templates Method

In recent years, the low dimensional materials have attracted much attention for their distinctive properties and potential application. Especially, a lot of researches are focused on the nanowires, nanotubes and nanofilms.In particular, hollow nanotubes and nanowires have attracted a great deal of attention in both fundamental and industrial studies. They possess unique properties that impart them potential applications in such fields as electronics, optics, advanced catalysis, and ultra-high-density magnetic recording media. Therefore, the fabrication techniques of magnetic nanotubes and heterogeneous alloys nanowires have been developed to fit the application requirements.Tubelike nickel ferrite nanocrystallines in the pores of porous anodic aluminum oxide (AAO) templates were successfully synthesized through a simple wetting chemical deposition process in a mixed solution of Ni and Fe nitrate and a heat treatment procedure. By varying the deposition conditions and the parameters of the templates, we could tailor the lengths and the outer as well as the inner diameters of the tubes. Owing to its versatility, this approach should be a promising route towards functionalized oxide nanotubes.The morphology, structure and magnetic properties of the samples annealed at 400°C, 500°C and 600°C have been studied. Transmission electron microscopy (TEM) images reveal that the nanotubes are uniform and well isolated. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns demonstrate that the as-obtained nanotubes can be indexed to polycrystalline cubic spinel. The Mossbauer spectra (MS) of NiFe₂O₄ tubes at room temperature and 80 K show that the magnetic hyperfine field is reduced with the decrease of metrical temperature. Simultaneously, with the increasing of the annealling temperature, the size of the nanoparticles in the tubes increases and the magnetic hyperfine field is enhanced. No obvious magnetic anisotropy is observed in this tubular material.Based on the porous AAO templates, Co_xCu1_-x(0.2≤x≤0.85) nanowire arrays with an uniform diameter of about 70 nm and a length of 4μm were fabricated by electro-deposition method in Co and Cu sulfate solution. The results of XRD reveal that Co-Cu solid solutions are formed. VSM measurements show that the nanowire arrays have obvious magnetic anisotropy.After the samples were heated at varied temperatures, distinct phase separation and structure change happened in the nanowires. When increase the annealed temperature, the coercivity of as-deposited sample increases (with a field applied parallel to the long axis of the wires). And the coercivity improves rapidly at 650℃corresponding to the point of phase separation of as-deposited sample.