A New Approach of Constructing Shape-controlled Nanowire Arrays

Magnetic nanowires with controlled morphology and crystallinity are enabling devices with novel functionalities. The fabrication of the nanowires with specific shapes such as standing U-shaped nanowires and helical nanowires is still challenging, especially on a rough and bumpy surface. Here we demonstrate a unique way to fabricate cobalt nanowire arrays on an arbitrarily-shaped surface by electrodeposition. When the pH of the electrolyte is around 2.3, the deposit shows monocrystalline hcp structure with the c-axis perpendicular to the long-axis of the nanowire arrays. On the other hand, when the pH is around 4.5, the deposit shows polycrystalline hcp structure. Counter intuitively, here the growth direction of nanowire is perpendicular to its longitudinal axis, and the specific geometry of nanowires can be achieved by introducing specially designed shaped substrate. The spatial separation and the width of the nanowires can be tuned by voltage, electrolyte concentration and temperature in electrodeposition. By taking cobalt nanowire array as an example, we show that head-to-head and tail-to-tail magnetic domain walls can be easily introduced and modulated in the nanowire arrays, which is enlightening to construct new devices such as domain wall racetrack memory.