Co-Ru alloy nanowire arrays embedded in anodic alumina membranes: Annealing effect

The effect of annealing on the crystal structure and magnetic properties of Co95Ru5 alloy nanowires electrodeposited in anodic alumina membrane (AAM) has been investigated. Cobalt ruthenium alloy nanowires were annealed at temperatures ranging from 300 °C to 700 °C. Scanning electron microscopy showed that the nanowires have an average diameter (Ø) of 55 nm and an approximate length of 15 µm. From X-ray diffraction studies, we found that the alloy nanowires crystalize in the hcp structure, with the c-axis tending to be perpendicular to the main axis of the wires. As shown in the hysteresis loop measurements, the cobalt ruthenium alloy nanowires exhibit magnetic anisotropy with an easy axis in the direction parallel to the wire axis. Changes in saturation magnetization, squareness (Mr/Ms) and coercivity were analyzed as a function of annealing temperature (Ta). The coercivity measured parallel to the wire axis was the highest before the annealing process and varied non-monotonically during the thermal treatment, reaching the highest value at the temperature of 600 °C. The maximum (Mr/Ms) ratio attained in this study was 0.62, but during heating, it decreased monotonically to 0.35. It was found that the magnetic properties of the nanowire arrays were strongly dependent on the thermal treatment.