Growth and magnetic properties of single crystalline Ni nanowire arrays prepared by pulse DC electrodeposition

Abstract

Highly textured Ni nanowire arrays were fabricated into anodic aluminum oxide (AAO) templates by pulse DC electrodeposition. The applied voltage and pH value of electrolytes were found strongly affecting the microstructure and magnetic properties of Ni nanowire arrays. Low applied potential and pH value both prefer to form polycrystalline fcc Ni nanowires. Increasing the applied potential or pH value favors the Ni [220] texture and even eventually forms the [220] oriented single crystal Ni wires, while exorbitant potential and pH value will conversely weaken the texture of nanowires. The magnetic properties of Ni wires are closely related to the microstructure of Ni nanowire arrays and large coercivities more than 1000 Oe were achieved at single crystalline Ni nanowire arrays. The mechanisms for the effect of applied potential and pH value on the grain size, texture and magnetic properties of Ni nanowire arrays have been discussed. nanowire arrays, applied potential, pH value, microstructure, magnetic properties, electrodeposition PACS: 07.55.-w, 07.55.Jg, 07.50.-eElectrodepositing elements into anodic alumina oxide (AAO) templates provides a simple technique to obtain the highly ordered nanowire arrays [1-3]. The low-cost AAO films are thermally stable at high temperature and the pore channels they contain are of uniform size, parallel to each other and perpendicular to the film surface. Furthermore, it is also comparatively easy to control the wire dimensions and the areal density of pores by adjusting the anodizing parameters (e.g. voltage, electrolytes and temperature) [1,2]. These features have attracted considerable interests in recent years due to the potential applications in ultra-highdensity magnetic recording, catalysts, nanoscale electronic and optoelectronic devices [4,5]. However, a well-controlled growth of nanowires is necessary for the successful application in devices. Tian et al. [6] have reported that if lower overpotential is used during DC electrodeposition then single crystalline nanowires of noble metals such as Au, Ag, Cu can be grown, but it is difficult to grow single crystalline nanowires of high melting point metals such as Co, Ni, Rh. Nevertheless, Yue et al. have found [7] that the lower potential is essential for the growth of single crystalline Ni nanowire arrays. Conversely, Pan et al. [8] and Thongmee et al. [9] have indicated that a higher overpotential favors the growth of single crystalline nanowires of Ni, Zn, Cu and Co. Clearly, the formation of single crystalline nanowires is not as easily explained only by overpotential. In recent literature, Kockar et al. [10] have reported that the magnetic properties of continuous Ni films are very sensitive to the electrolyte pH value. However, up to now, there are relatively few reports [7] studying the effect of pH value on the structure and magnetic properties of Ni nanowires. In this work, we investigated the influences of both potential and pH value on the microstructure and magnetic properties of Ni nanowire arrays by pulse ...

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