Abstract:
The magnetic anisotropy and properties of Permalloy (Ni₈₀Fe₂₀) nanowire arrays fabricated by glancing angle deposition with substrate rotation were studied. Epitaxial Cu nanowires, with the long axis textured along the Cu[111] crystallographic direction, were used as a seed layer to grow the Ni₈₀Fe₂₀ nanowires. The nanowires exhibit a strong Ni₈₀Fe₂₀[311] texture as shown by x-ray diffraction, with a Ni₈₀Fe₂₀[111] diffraction peak uniformly distributed about the wire’s long axis normal to the substrate. Hysteresis loops taken at different angular orientations show that the magnetization saturates first along the wire’s growth direction normal to the substrate. Samples with an aspect ratio of approximately one have equal in- and out-of-plane coercivity. At low aspect ratios (∼0.5–1.5), the angular dependence of the remanence shows that the maximum remanence lies on the surface of a cone with its axis along the substrate normal. A model which contains biaxial anisotropy with a symmetry axis normal to the substrate was found to qualitatively explain the characteristics of the observed hysteresis loops. An anisotropy constant on the order of 10⁶erg/cc is necessary to explain the observed behavior, which is much larger than that of bulk Ni₈₀Fe₂₀.
