Observation of a Strong Short Range Order in Co Rich Amorphous Alloys Prepared by Different Methods

X-ray absorption spectroscopy has been used to compare the short range order of some Fe-Co based amorphous alloys with low Fe concentration prepared by different methods : melt spinning (samples of FeCoSiB) and electrodeposition (FeCoP). Both the EXAFS and XANES analysis indicates that the chemical affinity of the metalloids Si or P for the Co atoms underlies the strong increase of the topological short range order around the Fe atoms. This ordering enhancement involves several coordination shells above the first one and results to be independent of the sample preparation procedure as well as the nature of the metalloids (Si or P). The large differences observed between the local structure around the Fe and Co atoms strongly suggest the existence of an inhomogeneous distribution of Fe, or Fe-B, in the bulk amorphous structure of the Co rich alloys, which takes places when the Si or P concentration is higher than the Fe one.