Vacancies and site occupation in Co-Ga-Fe alloys (Mossbauer study)

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Abstract
X-ray and bulk density measurements on ordered B2 alloys in the series Co2Ga2-xFex (x=0.05-0.20) have yielded vacancy concentrations in the range 4 to 7%. Room temperature 57Fe Mossbauer spectra of the same alloys have been obtained. A computer simulation of a lattice model in which the Fe atoms randomly occupy sites on the Ga sublattice has been used to determine major near-neighbour environments of the Fe atoms. Individual components corresponding to 0, 1 and 2 vacancies in the near-neighbour shell have then been successfully fitted to the Mossbauer spectra. Room temperature Mossbauer spectra for a second series Co2-yGa1.92+yFe0.08 (y=0.0-0.20) in which even more vacancies are forced on to the Co sublattice are also presented. Marked changes in the spectra at y=0.15 appear to be due to the occupation of vacant Co sites by Fe atoms. Mossbauer parameters for the alloys CoGa3 and FeGa3 have been measured and provide support for this interpretation.