Influence of alumina membrane on magnetic properties for thermally annealed CoPt alloy nanowires

Two dimensional (2D) arrays of CoxPt1−x alloy nanowires (NWs) with x = 0.75, 0.5, and 0.28 having wire diameter of ∼200 nm are synthesized in porous alumina membrane by electrodeposition technique. The as-deposited arrays of NWs show a distinct magnetic easy axis along their perpendicular direction with respect to the NWs axes. All the as-prepared NWs show low remanence (<0.05 Ms, Ms being the saturation magnetization) and low coercivity (<500 Oe). NWs with equiatomic composition show a change in crystal structure and a massive enhanced coercivity of ∼6.2 kOe after thermal annealing at 600 °C. The remanence also increased up to ∼0.75 Ms. Observed properties of the NWs are compared with CoPt alloy nanoparticles (NPs) prepared in miceller media with an average diameter of ∼6 nm. The experimental observations suggest that a significant difference in phase transformation temperature during annealing the alumina templated NWs and organic material coated nanoparticles.