Anomalous Codeposition of fcc NiFe Nanowires with 5–55% Fe and Their Morphology, Crystal Structure and Magnetic Properties

Abstract

The electrodeposition of NiFe nanowires-with the length ∼3.0 μm and diameter 200 nm-using the porous anodized aluminum oxide (AAO) templates on the sputtered Au-back electrode (300 nm) using sulfate/chloride electrolyte solution and potential pulsed deposition. The electrode area of Au-AAO template, determined by the reversible one-electron transfer oxidation of K4Fe(CN)6, used as a probe in CV, was found to be ∼2.4 times larger than Au-thin film electrode. The anomalous codeposition phenomenon known as a „volcano” type curve-with a maximum in Fe-content in NiFe as a function of the applied potential-was observed in the literature. The observed results were explained through the limited mass transport of Fe+2 ions after the peak. This explanation is partially correct, but not complete. The electrodeposition of NiFe nanowire in this work resulted in a similar “volcano” type curve. The alternative explanation of anomalous codeposition-through the surface concentration of H+ dependent adsorption/desorption of FeOH+ and NiOH+ electroactive species-was proposed. The electrodeposition of NiFe nanowire arrays using a designed pulse potential method produced fcc NiFe nanowires with 5–55% Fe with controlled composition, length, and uniformity.The distinct decrease of parallel coercivity of NiFe nanowire arrays having the same length was observed with increase of Fe-content in NiFe, which also correlates with the increase of their magnetic saturation. The process of magnetization reversal in NiFe nanowires arrays was investigated. We have found two sets of magnetic behavior of NiFe nanowires depending on composition (Ni92Fe8 and Ni79Fe21 vs. Ni60Fe40, Ni56Fe44, and Ni45Fe55).