Magnetic anisotropy in CoNi nanowire arrays: Analytical calculations and experiments

TLDR

Tuning the Co‑Ni alloy composition by varying Ni content controls the effective anisotropy axis, which balances hcp and fcc magnetocrystalline and shape anisotropies. The study reports on the structural and magnetic properties of CoₓNi₁₋ₓ nanowires, with particular emphasis on their angular dependence. CoₓNi₁₋ₓ nanowires were fabricated by template‑assisted electrodeposition into anodic aluminum oxide membranes, and their angular coercivity was modeled analytically, with experimental fitting indicating a transition from transverse crystalline anisotropy in the hcp phase to axial anisotropy in the fcc phase as Ni content increases. The nanowires shift from hcp to fcc structure as Ni increases, causing a change from transverse to axial anisotropy and markedly modifying their magnetization process and magnetic properties.

Abstract

Ordered arrays of Co${}_{x}$Ni${}_{1\ensuremath{-}x}$ nanowires ($0<x<1$) were fabricated by a template-assisted method using electrodeposition into anodic aluminum oxide membranes. Tuning of the Co-alloy composition by changing the Ni content enables control of the effective anisotropy axis, which is determined by the balance between the hcp and fcc magnetocrystalline and shape anisotropies. We report on the nanowires' structural and magnetic properties (e.g., hysteresis curves and their parameters as well as first-order reversal curve analysis), paying particular attention to their angular dependence. It is confirmed that the crystal phase of nanowires with length 2.5 $\ensuremath{\mu}$m and diameter 35 nm shifts from hcp to fcc as the Ni content increases. That results in a significant modification of the magnetization process and, accordingly, of the magnetic properties of the array. Analytical calculations of the angular dependence of the coercivity allow us to confirm that the magnetization reversal is mostly ascribed to the propagation of a transverse domain wall. Fitting of the experiment to these calculations indicates the presence of a transverse crystalline anisotropy (ascribed to the hcp phase) in Co wires, while this changes to an axial anisotropy (fcc phase) as the Ni content increases.