Electrochemical fabrication and magnetic properties of highly ordered silver-nickel core-shell nanowires

Ordered silver-nickel core-shell nanowire arrays were successfully fabricated by electrodeposition. The ordered silver nanowire arrays embedded in a porous alumina template were first fabricated from an aqueous solution of Ag(NO₃)₂ and Ac(NH₃). After removing out the template, the obtained silver nanowire arrays were subsequently electrodeposited with nickel at 1.6-2.6 V and 60 °C using the electrolyte composed of NiSO₄, NiCl₂ and H₃BO₃. Transmission electron microscopy observation revealed that a ∼15 nm thick nickel film was coated on the surface of the silver nanowires with about 200 nm in diameter. It was found that the silver nanowires with nickel coating showed enhanced magnetic properties in comparison to that of pure silver nanowires. The magnetic force microscope image of silver-nickel core-shell nanowires showed magnetic domain state. In addition, the hysteresis loops of the silver-nickel nanowire arrays showed a coercive field of 180 Oe, almost independent of the applied magnetic field. However, it was observed that a larger magnetic domain was found in parallel direction than that in perpendicular direction.