Medium-range order as an intrinsic property of Co-rich amorphous alloys

X-ray absorption spectroscopy has been used to study the short-range order of some Fe-Co–based amorphous alloys with low Fe concentration prepared by two different methods: melt spinning (FeCoSiB) and electrodeposition (FeCoP). A qualitative analysis of the near-edge region points clearly to the existence of a well-defined chemical affinity of the metalloids Si or P for the Co atoms. A complete EXAFS (Extended X-ray Absorption Fine Structure) analysis establishes that this chemical order induces a strong increase of the topological order in the vicinity of the Fe atoms. This ordered structure involves several coordination shells and is independent of the preparation method and of the nature of the metalloid (Si or P)