Research On Shape-Controlled Synthesis And Magnetic Properties Of Ordered Ni Nanowire Arrays

One-dimensional magnetic nanowire arrays have potential application prospect in high-density vertical magnetic recording and the future nanodevices. Nanodevices require a controllable fabrication of nanomaterials in shape and sizes. So we fabricated Ni nanowire arrays with different shape and sizes by self-prepared anodic alumina oxide (AAO) template and then investigated the angular dependence of magnetic properties. The main research work and originalities are as follows.1. Ni nanowire arrays with different diameters (40nm、60nm、300nm) were synthesized by direct-current (DC) electrochemical deposition into AAO templates, which have the same length by adjusting the deposition time. We studied the angular (between the applied magnetic field and the wire axis) dependence of the coercivity and remanence of Ni nanowire arrays with different diameters. Investigation results demonstrate that the coercivity and remanence of Ni nanowire arrays are not only related to diameter but also to the distance between nanowires.2. We studied the angular dependence of the coercivity and remanence of Ni nanowire arrays with length of 0.85μm,4μm,9μm. For the large diameter Ni nanowire arrays with a length of about 0.85μm,the angular dependence of coercivity has a peek at middle angle and the easy magnetization direction is perpendicular to the axis of nanowires. The results show that Hc(θ) significantly depends on the nanowire length and the magnetostatic interaction reduces along with the length increasing. It is revealed that the strong magnetostatic coupling among wires not only caused the over easy axis change from parallel to perpendicular to the wire axis, but also had a great influence on the magetization reversal mechanism.3. The AAO template with Y-branched nanoporous was prepared through varying the anodic voltage by a factor of 1/(?)2 in 0.3M oxalic acid. Then, well aligned branched Ni nanowire arrays were fabricated in the as-synthesized template by direct-current (DC) electrochemical deposition method. The crystal structure of the product was characterized by high resolution transmission elecron microscopy (HRTEM), nano-beam diffraction (NBD). We firstly discussed the growth mechanism of the branched structures. Meanwhile, the angular dependence of the coercivity of Y-branched Ni nanowire arrays was also investigated.4. Large-size bud-like branched Ni nanowire arrays were synthesized by electrochemical deposition in the AAO template, which was prepared through varying the voltage by a factor of 1/(?)2 during the anodization process. The angular dependence of the coercivity and remanence of Y-branched Ni nanowire arrays was also investigated.