Magnetic properties of one-dimensional Ni/Cu and Ni/Al multilayered nanowires: Role of nonmagnetic spacers

Abstract

We have used density functional theory within spin-polarized local density approximation to investigate the equilibrium structure, electronic, and magnetic properties of one-dimensional Ni/Cu and Ni/Al multilayered nanowires. In particular, we look into the subtle changes in the magnetic properties of the nanowires with the change in the width of the nonmagnetic spacer. Our calculations yield the magnitude of cohesive energy in both the systems to decrease with the increase in the concentration of the nonmagnetic spacer, suggesting that Ni rich nanowires are more stable. Analysis of the magnetic moment per Ni atom $({\ensuremath{\mu}}_{\text{av}})$ in the Ni/Cu hybrid multilayered nanowire suggests that there is a steady decrease in ${\ensuremath{\mu}}_{\text{av}}$ with the increase in the number of Cu layers. In contrast, in Ni/Al multilayered nanowire, there is a nonmonotonic decrease in ${\ensuremath{\mu}}_{\text{av}}$ with the increase in Al layers. The observed difference in magnetic property between Ni/Cu and Ni/Al multilayered nanowires is attributed to the dissimilar interfacial bonding in the two cases. In the case of Ni/Al nanowire, the nonmonotonic variation in ${\ensuremath{\mu}}_{\text{av}}$ is due to the strong directional nature of the $\text{Ni}\text{ }d$ and $\text{Al}\text{ }p$ hybridization, which favors Ni to have higher coordination number. Higher coordination for Ni leads to smaller ${\ensuremath{\mu}}_{\text{av}}$ in the Ni/Al multilayered nanowire. However, the hybridization between $\text{Ni}\text{ }d$ and $\text{Cu}\text{ }s$ states is predominantly responsible for the smaller ${\ensuremath{\mu}}_{\text{av}}$ in the Ni/Cu nanowire. Furthermore, we found that in Ni/Al multilayered nanowire with two Al spacer layer, the antiferromagnetic configuration is favored over ferromagnetic configuration. In Ni/Cu multilayered nanowire, ferromagnetic configuration is favored over antiferromagnetic configuration for the same spacer length.