Inelastic neutron scattering in random binary alloys : an augmented space approach

TL;DR

This paper develops an exact augmented space formalism to separate coherent and incoherent neutron scattering in disordered alloys, including disorder in masses, force constants, and scattering lengths, and applies it to NiPd and NiPt alloys.

Contribution

It introduces a novel augmented space approach that accurately computes scattering intensities without mean-field approximations, incorporating full disorder effects.

Findings

Numerical results for NiPd and NiPt alloys show detailed scattering cross sections.

The formalism accurately separates coherent and incoherent intensities.

Comparison with CPA and experiments validates the approach.

Abstract

Combining the augmented space representation for phonons with a generalized version of Yonezawa-Matsubara diagrammatic technique, we have set up a formalism to seperate the coherent and incoherent part of the total intensity of thermal neutron scattering from disordered alloys. This is done exacly without taking any recourse to mean-field like approximation (as done previously). The formalism includes disorder in masses, force constants and scattering lengths. Implementation of the formalism to realistic situations is performed by an augmented space Block recursion which calculates entire Green matrix and self energy matrix which in turn is needed to evaluate the coherent and incoherent intensities. we apply the formalism to NiPd and NiPt alloys. Numerical results on coherent and incoherent scattering cross sections are presented along the highest symmetry directions. Finally the incoherent intensities are compared with the CPA and also with experiments.