Fabrication and low temperature magnetic studies of Ni-Co core-shell nanowires

Core-shell magnetic nanowires of nickel and cobalt embedded in ion-track etched polycarbonate (PC) template were fabricated by two step etching and deposition technique. Structural investigations reveal the successful fabrication of 60 nm nickel core nanowires surrounded by ∼20 nm concentric cobalt shell. X-ray diffraction and electron microscopy studies confirmed the presence of fcc nickel and hcp cobalt at the core and shell regions, respectively. Low temperature magnetic studies performed between 5 and 300 K indicate the ferromagnetic nature of the nanowires with coercivity and magnetization that are increasing with decreasing temperature of the nanowires. Temperature dependence of coercivity can be understood in term of thermal activation over the energy barrier with m-power dependence on the field, while the saturation magnetization was found to follow the modified Bloch's law at low temperatures.