Electrodeposited Co93.2P6.8 nanowire arrays with core-shell microstructure and perpendicular magnetic anisotropy

We demonstrate the formation of an unusual core-shell microstructure in Co93.2P6.8 nanowires electrodeposited by alternating current (ac) in an alumina template. By means of transmission electron microscopy, it is shown that the coaxial-like nanowires contain amorphous and crystalline phases. Analysis of the magnetization data for Co-P alloy nanowires indicates that a ferromagnetic core is surrounded by a weakly ferromagnetic or non-magnetic phase, depending on the phosphor content. The nanowire arrays exhibit an easy axis of magnetization parallel to the wire axis. For this peculiar composition and structure, the coercivity values are 2380 ± 50 and 1260 ± 35 Oe, parallel and perpendicular to the plane directions of magnetization, respectively. This effect is attributed to the core-shell structure making the properties and applications of these nanowires similar to pure cobalt nanowires with an improved perpendicular anisotropy.