Magnetic nanowires in hexagonally ordered pores of alumina

Acid-anodized aluminum forms amorphous alumina with long and columnar nanopores with approximately hexagonal ordering ("alumite"). Excellent hexagonal ordering of these nanopores has been achieved by 24 hours of anodization, but with restricted domain size (2-4 /spl mu/m/sup 2/), which can be increased to 100 /spl mu/m/sup 2/ with longer anodization. We have deposited Fe in disordered pores and Co in ordered pores; we can control the average length and diameter of these nanowires, but there is still a distribution of nanowire lengths. Previously, we described Fe nanowires with diameters down to 11 nm in disordered pores. Here we focus on longer (770 nm) and shorter (64 nm) Co nanowires with diameters of 25 nm in ordered pores with 100 nm pore-to-pore separation. The longer wires have an easy axis out-of-plane, with squareness >0.9, coercivity=1900 Oe, and a fluctuation field of 5.3 Oe. The shorter wires are more isotropic, with lower coercivities (/spl ap/1300 Oe) and larger fluctuation fields /spl ap/8.4 Oe.