Electrodeposition of hexagonal Co nanowires with large magnetocrystalline anisotropy

Cobalt nanowires were fabricated by electrodeposition from a sulfamate-based electrolyte into anodic aluminum oxide templates having pore size of 27 nm, 50 nm and 250 nm. The electrolyte and operating conditions were chosen with the aim of achieving hcp-Co with basal [001] preferred orientation. The type of structure and the orientation of the Co nanowires were found to depend on the pore size of the oxide template. Based on XRD and TEM analysis, nanowires formed in the 27 nm template showed the growth of oriented crystals with either prismatic or basal orientation; nanowires grown in the 50 nm template were oriented along the [001] direction, resulting in the alignment of the easy axis with the wire axis; the easy axis was perpendicular to the nanowire axis for nanowires grown in the 250 nm template with a prismatic [100] + [110] texture. According to AGFM and MFM measurements individual Co pillars with average diameter of 27 or 50 nm behaved as single magnetic domains with the magnetization axis parallel to the wire axis. Coercivity as high as 2700 Oe were measured for Co NWs having average diameter of 27 nm. The magnetostatic configuration of planar array of Co nanowires, strictly depending on the texture quality and the relative aspect ratio, is shown to be determined by the combined effect of shape and magnetocrystalline anisotropy.