| Recently, the low dimensional materials have attracted much attention for their distinct properties and potential applications. Generally, the structure and properties change with decreasing size or dimension of material.Magnetic nanowies can be fabricated with anodic aluminium oxide (AAO) membranes by anodization technique. The aluminium oxide membranes have good stability and controllability at high temperature; The diameter and spacing between the pores in AAO membranes can be controlled by adjusting the parameter of anodic oxidation; The congruity of the nanochannels in AAO templates is fairly good, the density of the nanochannels is high. The application to high density perpendicular magnetic recording mediun is being explored.We started the fabrication of nanowires by AAO membranes rather late in September, 2003. In less than two years, we set up the equipment for chemical reaction, studied the principle of fabricating AAO template and nanowires by reeding related papers and doing various experiments. We have obtained the basic experience and made preliminary studies on the fabrication of AAO template and nanowires and their structure and properties. The main work as follows:1. Study on the fabrication technology of AAO templates.Porous aluminium oxide membranes were prepared by anodic oxidation method, the structure, morphology and formation principle were studied. Different electrolytes, different voltage and reaction time in anodic oxidation were tried in order to explore the factors which affect the porous aluminium oxide membranes.Our experiment indicated that the pore diameter of AAO templates is different with different electrolytes and different concentration; The nanowires with uniform diameter could be prepared after slow and long time anodic oxidation under certain voltage. The final technology we chose is as follows: 0.3mol/l sulphuric acid as electrolytes, the duration of anodic oxidation: 11 hour under 20VDC, foramen enlargement reagent: phosphoric acid for 85 minute. The thickness of oxidized membrane in AAO template was about 10μm, the diameter of nanochannels is about 20nm in average. Because the purity of Al plate was not sufficiently high and the limit of our preparation condition, the ordering degree of the spacial distribution of the nanowires needs further improvement.2. Study on fabrication technology of electrodeposition of nanowires and their structure and morphology.Magnetic nanowires such of iron, niclel , cobalt and Ni-Co alloy were prepared by electrodeposition into the pores of AAO templates. The diameter of the namowires we prepared was about 20nm in average, the length changes from 2μm to 5μm and 4μm in average. Near the nanowires'bottom, their distribution is very dense and regular,it is obvious that the deposition of nanowires begins from the bottom of AAO templates'nanochannels.3. Study on the magnetic properties of nanowires.Magnetic properties of of nanowires of Fe, Ni, Co and Co-Ni alloy is measured by Vibrating Sample Magnetometer (VSM), with magnetic fields perpendicular to template (parallel to nanowires) and parallel to template (perpendicular to nanowires). Their hysteresis loops , Mr/Ms and Hc show anisotropy apparently. These nanowires,with aspect ratio about 200, have an obvious shape anisotropy with easy magnetization direction parallel to the nanowire axis, namely perpendicular to the template plane.When magnetic field is along the axis of nanowires, the representative experimental data show: for Ni nanowires, Hc =1040 Oe, Mr/Ms=0.97;for Co nanowires, Hc = 1653Oe, Mr/Ms=0.45, approximate, near to the data in recent literature. For Fe nanowires, the value of Hc as high as 2410Oe was obtained, which is larger than the reported value, and Mr/Ms=0.87. Comparing with the values perpendicular to the nanowires, the esay magnetization directions of Fe and Ni are along the axis, while Co does not show apparent anisotropy. We presume that crystalline anisotropy counterbalance shape anisotropy in some extent.The influence of electrodeposition frequency on the nanowires'properties was explored. It showed that with high electrodeposition frequency, the nanowires were more compact. We speculate that the process of electrodeposition is discontinuous, deposition takes place only in negative half cycles, the nanowires might grow up into stucture of bead chain. So higher deposition frequency makes nanowires more compact. This needs further experimental study.Preliminary study on changing the composition of Ni-Co alloy nanowires. Ni-Co alloy nanowires were also prepared by AAO templates method. In this study, effort were made to alter the composition of Ni-Co alloy nanowires by changing the Ni-Co atom proportion in electrolyte. It was shown that the Ni-Co atom proportion in nanowires was not equal to the atom proportion in electrolyte, since the electrodeposition rates of Ni and Co are different. In order to prepare high Ni content alloy nanowires, the concentration of Ni in electrolyte should be much higher than Co.
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