Magnetic and 57Fe Moessbauer study of Y(Fesub(1-c) Alsub(c))2 alloys: local environment effects

The magnetic properties of the Laves phase system Y (Fesub(1-c)Alsub(c))2 have been studied by means of bulk magnetisation measurements in fields up to 72 kOe for 0 < c <- 0.98 and by Moessbauer effect techniques for 0 < c <- 0.326. The mean magnetic moment and Curie temperatures show a rapid nonlinear decrease with increasing c values and go to zero near c = 0.25 while the high-field susceptibility shows a pronounced maximum at this concentration. The Moessbauer spectra lead to hyperfine fields whose values remain nearly constant in the concentration range investigated, correlated to iron sites with different environments. The results are well described in a local environment model where the iron atoms carry a moment if surrounded by n >= n0 = 15 iron neighbours; this moment remains constant and equal to that of YFe2 at least up to 32.6 at %Al. This model accounts for the variation with c of the spontaneous magnetisation related to the magnetic atoms, the high-field susceptibility which arises from the nonmagnetic Fe atoms, and for the hyperfine field distributions. (author)