Correlated and uncorrelated nanoscale heterogeneities in L1_0 solid solutions and their signatures from local and extended probes

TL;DR

This study investigates nanoscale heterogeneities in L1_0 and disordered structures within NiMn alloys, analyzing how local and extended probes detect phase coexistence and signatures, explaining antiferromagnetism without diffraction evidence.

Contribution

It provides theoretical and numerical analysis of nanoscale phase coexistence and signatures in NiMn alloys, highlighting differences in detection by local versus extended probes.

Findings

Diffraction limits distinguish structures based on domain size

Correlated and uncorrelated domains produce different signatures

Elastic strain affects long-range structural coherence

Abstract

The phase coexistence of chemically ordered L1_0 and chemically disordered structures within binary alloys is investigated, using the NiMn system as an example. Theoretical and numerical predictions of the signatures one might expect in data from local and extended probes are presented, in an attempt to explain the presence of antiferromagnetism in NiMn when no L1_0 signatures appear in diffraction data. Two scenarios are considered, the first in which the tetragonal L1_0 structure and fcc chemically disordered structure are distributed evenly into uncorrelated domains of specified average diameter. The diffraction limit, below which the two structures can only be distinguished using a local probe, is quantified with respect to the domain diameter by applying straightforward diffraction analysis. In the second scenario, domains with chemical ordering oriented in different directions are required to maintain their atomic coherence with each other. A numerical treatment is used to illustrate the long-range strain that results from elastic energy considerations, and the effects on the structure factor (extended probe) and pair distribution function (local probe) are investigated.