Magnetic properties of nickel nanowires : effect of deposition temperature

We have investigated the magnetic properties of electroplated nickel nanowires with very distinct nanostructures, which are obtained by simply changing the plating temperature of the electrolyte. Low temperature (40°C) resulted in larger average grain size comparable to the diameter of the wires, whereas higher temperature (60°C) revealed self-similar morphology composed of nanogranules. For low temperature samples, a two stage magnetization process is evident in the easy axis direction where grain size is comparable to wire diameter. In contrast, for high temperature samples, nanowires are formed by an agglomeration of particles with average diameter of about 22 nm. In this case each individual particle behaves as a single domain and thereby magnetization reversal occurs by the switching of an ensemble of randomly oriented particles and magnetization saturates quickly with applied field. In the present case, with the high density of disorder caused by the self-similar morphology of the nanogranules, we suggest that the switching mechanism of the magnetization occurs by localized coherent rotation, resulting in lower coercivity. This delineates first experimental evidence of three dimensional cooperative magnetic interactions among the nanogranules within self-similar morphology of nanowires in both parallel and perpendicular wire axes.