Abstract
The spin density distributions in two alloys of iron and silicon (approximate compositions Fe3Si and Fe4Si) have been determined by polarized neutron diffraction. The observed data have been corrected for the effects of extinction and have been analysed by the standard Fourier method and also by expressing the density distribution in terms of spherical harmonics. The latter method of analysis indicated a non-centrosymmetric density around one of the iron sites and an explanation for this has been suggested in terms of a change of sign with distance for the s-d exchange interaction.