Evidence of strong short-range order in (Fe0.2Co0.8)(75)SixB25-x amorphous alloys from EXAFS spectroscopy

Liquid-quenched metallic amorphous alloys (FeCo)(75)SiB were prepared with the aim of studying the influence of the relative metalloid concentration over the short-range order in these alloys. Room-temperature x-ray-absorption spectra have been recorded on the Fe and Co K edge at the Daresbury Laboratory. Both the extended x-ray-absorption fine structure (EXAFS) and x-ray-absorption near-edge structure (XANES) spectra present clear evidence of a very different chemical and topological short-range order around the Fe and Co atom in all the studied samples. The XANES region suggests the existence of a strong chemical short-range order characterized by a preferential coordination of B with Fe and Si with Co. This assumption has been proven by the EXAFS study. Moreover, the gradual appearance of a shoulder at around 4 Angstrom(-1) when the Si content increases, in the Fe K-edge EXAFS spectra, has been proven to be evidence of the existence of a very ordered structure involving higher-order coordination shells than the first one.