Mössbauer study of Fe-Co nanowires

Arrays of Fe_1-xCo_x (0.0 ≤ × ≤ 0.92) nanowires have been prepared by an electrochemical process, co-depositing Fe and Co atoms into the pores of anodic aluminium; their compositions were determined by atomic absorption spectroscopy. Transmission electron microscope results show that the nanowires are regularly spaced and uniform in shape with lengths of about 7.5 μm and diameters of 20 nm. The x-ray diffraction indicates a texture in the deposited nanowires. For the composition below 82 at.% cobalt, the nanowires had a body-centred-cubic structure with a [110] preferred orientation. For the 92 at.% cobalt sample, the alloy exhibited a mixture of bcc and face-centered-cubic structure. The room temperature ⁵⁷Fe Mössbauer spectra of the arrays of Fe_1-xCo_x nanowires have second and fifth absorption lines of the six-line pattern with almost zero intensity, indicating that the internal magnetic field in the nanowires lies along the long axis of the nanowire. The maximum values of the hyperfine field (B_hf = 36.6 ± 0.1 T) and isomer shift (IS = 0.06±0.01 mms^-1) occur for 44 at.% cobalt. The variations of the isomer shift and the linewidths with composition indicate that the Fe_1-xCo_x alloy nanowires around the equiatomic composition are in an atomistic disordered state.