Electrochemical growth of CoPt nanowires of different aspect ratio and their magnetic properties

The electrodeposition process of the CoPt system into two types of gold-coated polycarbonate and alumina membranes have been studied to test the possibility of electrochemical growth of CoPt nanowires with different length and aspect ratio but fixed composition showing hcp phase with maximum Pt incorporation. The evolution of the nanowires as a function of the deposition time was analysed; nanowires from 250 nm to 8 mu m have been prepared. During the initial stages of the deposition, the formation of nanotubes in the membranes of higher porous diameter was observed, subsequently forming nanowires after continued deposition. With around 60 wt.% of Pt the CoPt nanowires show distorted hcp cobalt phase and preferred orientation conditioned by the pore's diameter of the membrane. When using polycarbonate membranes, nanowires with an aspect ratio of 0.025 or lower showed clear magnetic anisotropy and the membrane magnetises easily by applying a parallel magnetic field (magnetic field perpendicular to the nanowires axis). When the length of the nanowires was reduced, magnetic anisotropy decreased. Coercivity remains in the range between 500 and 1000 Oe. When using an alumina template, the arrays showed similar coercivity, however, a higher magnetic anisotropy was observed with respect to those of similar length in a polycarbonate membrane, probably as a consequence of the elevated density of the arrays that permits higher interaction between the wires. (C) 2012 Elsevier B.V. All rights reserved.