A diffuse neutron scattering study of local atomic order and pair interaction potentials in disordered FCC γ-MnNi alloys

Abstract

Polarisation analysis of neutron diffuse scattering has been used to characterise atomic short-range order in disordered FCC MnNi alloys. The diffuse scattering observed at 4.2K is shown to arise from fluctuations of the average atomic unit cell structure. The data have yielded the concentration dependence of the Cowley short-range order parameters which express the interaction of a given atom with the atoms in its immediate local environment and show that Ni atoms prefer a Mn nearest-neighbour environment. The result of a linearised mean-field model of the pair interactions which relates the pair potentials to the diffuse scattering has also been applied to the experimental data and shows the characteristic Friedel oscillations on the pair interactions which, in general, reflect some features of the disordered alloy electron spectrum.