Fe nanowires in nanoporous alumina: Geometric effect versus influence of pore walls

Fe nanowires were fabricated by electrodeposition into nanoporous alumina templates grown in sulfuric and oxalic acid by a pulse electrodeposition. A 42 nm diameter Fe nanowire grown in sulfuric anodized pores is essentially a single-crystalline object that grows preferentially so as to align its (110) axis along the long axis of the pore. Its coercivity is 1654 Oe and a squareness of 0.66 for axially aligned magnetic fields. For an Fe nanowire grown in oxalic anodized pores, both (110) and (200) diffraction peaks are observed, suggesting a polycrystalline object. Its coercivity and squareness are reduced to 1120 Oe and 0.47, respectively. Increasing pore diameter results in improved crystallinity for the nanowires deposited in the oxalic templates. However, their coercivities and squareness are reduced because of the decreased aspect ratio and hence shape anisotropy. We ascribe the differing crystallinity observed for nanowires grown in the two sets of templates to differences in the material properties of the barrier layer and the pore wall, where metal nucleates in the electrodeposition process likely brought about by the incorporation of anions out of the electrolyte.