Mössbauer study of the Fe 1−x Ni x Invar alloys by monochromatic circularly polarized source

X-ray diffraction measurements and Mossbauer spectroscopy with and without external magnetic field parallel to beam direction have been performed for Fe1−xNix (x = 0.25, 0.30, 0.35) alloys. The compositions of the studied alloys were chosen in order to cover the concentration range where the fcc ↔ bcc structural transformation appears, as well as where single phase fcc Fe-Ni alloys exhibit the Invar phenomena. Spatial distribution of the iron magnetic moments is discussed. The hyperfine magnetic field (h.m.f.) distribution is analyzed within a scope of two models discussed in the literature. In the first model it is assumed that any hyperfine magnetic filed vector have the same spatial distribution (the same values of ( ). In the second, the low field component of the hyperfine magnetic field is ordered antiferomagnetically (or disordered) while the high field component is aligned by an external magnetic field. In order to determine the mean values of cosine of the angle between γ-rays direction and hyperfine field vector of iron, ( ), a monochromatic circularly polarized Mossbauer source (MCPMS) was used. The analysis of the MCPMS results show that the shapes of the measured spectra can be explained by single values of .