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 conce ntration 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 str ucture (EXAFS) and x-ray-absorption near-edge structure (XANES) spectr a 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-r ange order characterized by a preferential coordination of B with Fe a nd Si with Co. This assumption has been proven by the EXAFS study. Mor eover, the gradual appearance of a shoulder at around 4 Angstrom(-1) w hen 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 in volving higher-order coordination shells than the first one.