Structure and magnetic properties of Fe-Co nanowires in self-assembled arrays

Abstract

Arrays of ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x$ $(0.0\mathrm{}<~x<~1.0)$ nanowires have been fabricated by codepositing Fe and Co into porous anodic alumina. Transmission electron microscope results show that the nanowires are regular and uniform, about $7.5\mu \mathrm{m}$ in length and $20\mathrm{nm}$ in diameter. Structural determination by x-ray diffraction indicates that $\mathrm{bcc}\left(\alpha \right),$ $\mathrm{fcc}\left(\gamma \right),$ and $\mathrm{hcp}\left(\varepsilon \right)$ Fe-Co phases appear with variation in composition. However, the phase boundaries are different from that in bulk Fe-Co alloys. Magnetic hysteresis loops measured at temperatures ranging from $5\mathrm{K}$ to $300\mathrm{K}$ demonstrate that the arrays of nanowires exhibit uniaxial magnetic anisotropy which is dependent on the shape of each individual nanowire. With increasing Co content, the coercivity of the nanowire arrays, with the magnetic field applied parallel to the wire, first increases and then reaches a maximum value before decreasing. The behavior is interpreted using a magnetization reversal model based on “chains of spheres” and the symmetric fanning mechanism.