Magnetic properties of magnetic nanowire arrays

The arrays of NiFe and CoNiFe nanowires were grown in anodic alumina (alumite) and track etched polycarbonate (PCTE) membranes with various pore sizes by pulsed electrodeposition. Magnetic properties of the array were studied as functions of wire material, length, and diameter as well as field orientation. In PCTE membranes, as high as 0.92 of remanent squareness (S) was obtained for the array with wire diameter of 30 nm. However, for the array of nanowires in anodic membranes, anisotropy with field applied in and out of plane is very low, and the obtained S is less than 10%. For nanowires in alumite with the same wire length, CoNiFe shows a higher anisotropic field (H_k) than NiFe, leading to larger coercivity (H_c) and S and a lower saturation field. Wire-length dependence was measured for alumite membranes. As wire length increases, H_k, H_c, and S decrease, but the saturation field increases. This magnetic behavior can be qualitatively explained by considering dipolar interactions among nanowires and shape anisotropy of an individual nanowire, but it remains difficult to give a quantitative explanation.