Potentiostatically Electrodeposited Hard-Magnetic Fe–Pd-Based Nanowires

Near equiatomic Fe_52±3Pd_48±3 nanowires (NWs) with the length of 3.5 μm and diameter of ≈200 nm were potentiostatically deposited at -1.1 V for 900 s into a porous anodic aluminum oxide template. Cylindrical NWs with a consistent composition along their length were obtained after introducing two additional steps prior to the electrodeposition (ED) of the Fe-Pd NWs, i.e., template wetting and pre-ED of Au NWs. The as-deposited Fe-Pd NWs were isotropic and nanocrystalline with an fcc crystal structure and were magnetically soft. The influence on the development of the coercivity with annealing temperature and time due to the L1₀ transformation was investigated. For this purpose, the as-deposited NWs were annealed at temperatures from 400 °C to 700 °C for 1-5 h in Ar + H₂ and the phase transformation, microstructure and magnetic properties were analyzed. The coercivity was found to increase by increasing the annealing temperature, as the L1₀ ordering becomes more complete. A maximum in the coercivity of H_C|| = 267 kA/m and Mr/M_s|| = 0.85 was achieved upon annealing at 600 °C for 4 h. The high remanence is attributed to the exchange coupling between the nanosized grains and/or the coupling between the soft [α-Fe, y-(Fe,Pd), fcc-FePd] and hard L1₀ phases. The effect of the deposited Au NWs prior to the Fe-Pd NWs´ deposition on the L1₀ ordering was evaluated as well; however, the magnetic properties were significantly decreased due to the formation of soft-magnetic phases, i.e., (Au, Fe) and (Au, Pd).