Influence Of Electrochemical Parameters On Growth And Properties Of Magnetic Nanowire Arrays

In this dissertation, the highly ordered anodic aluminum oxide (AAO) templates were prepared by a two-step anodic anodization. Co, Fe and Fe/Pt magnetic metal nanowire arrays were fabricated in the porous alumina templates by electrodeposition. The related parameters that affect the structure and magnetic properties of nanowire arrays have been investigated and discussed.1. Highly ordered aluminum anodic oxide templates were fabricated in the oxalic acid electrolyte by two-step anodic oxidation of aluminum foils. The pore diameter of aluminum oxide templates is about60nm. The morphology of characterization has been investigated by SEM and the corresponding growth mechanisms of the anodic oxide templates have been analyzed.2. The Co nanowire arrays were deposited into AAO template with ac、dc and pulse dc electrochemical deposition. The influence of microstructure and magnetic properties on magnetic nanowire arrays of these three different deposition methods is researched. The fill rate is close to100%of nanowire through the ac and pulse dc electrochemical deposition. It is higher than the fill rate of dc deposition (～20%). All the nanowires have the effective anisotropy perpendicular to the template. The biggest coercivity is1800Oe, which is higher than that of the block, nano-film, nanoparticles. The value of coercivity is mainly determined by the shape anisotropy and magnetocrystalline anisotropy of the material. When the shape anisotropy and magnetocrystalline anisotropy are both along to the nanowire, the highest coercivity was achieved with easy axis perpendicular to the template. Our study proved that pulse dc electrochemical deposition favors the monocrystalline structrue and high fill rate in nanowire arrays.3. A series of Fe nanowire arrays were deposited into AAO templates with pulse dc electrochemical deposition. By changing the pH value of solution, we find that different structures of nanowire were deposited. In other words, pH value of solution can adjust the crystallographic orientation of Fe nanowires. Through the magnetic study we found that Fe nanowire arrays deposited by electrodeposition show obvious anisotropy with easy axis along the wire major axis (perpendicular to the template matrix). Since the easy axis is along the [110] direction for bcc Fe, in our case, both the shape anisotropy and the magnetocrystalline anisotropy are along the wire axes and the shape anisotropy have a dominant effect for the effective anisotropy.4. Highly textured Fe/Pt nanowire arrays were fabricated using anodic aluminum oxide templates by pulse DC electrodeposition. The sedimentary frequency, duty, delay time, solubility of electrolyte, and annealing conditions have strong effect on the microstructure and magnetic properties of Fe/Pt nanowire arrays. It is found that the best performance of the sample is corresponding to the sedimentary conditions with frequency of25Hz, duty of50%, no delay time, Fe2+solubility of20g/l, and after annealing in Ar (80%) and H2(20%) about lh at600℃. This sample shows a typical fcc FePt polycrystalline structure on the basis of transmission electron microscopy and X-ray diffraction study, and there is no phase change after annealing. Magnetic hysteresis measurement shows the obvious perpendicular anisotropy and the maximum coercivity along the direction of nanowire is1910Oe.The highly ordered one-dimensional nanowire arrays with uniform diameter were prepared in AAO templates by electrodeposition. All nanowire arrays exhibit obvious magnetic anisotropy along the wire growth direction, namely, the easy axis of the wire arrays is perpendicular to the matrix of the film, which is especially useful for their application in the high-density perpendicular magnetic recording media..