Theoretical antiferromagnetism of ordered face-centered cubic Cr-Ni alloys

TL;DR

This paper demonstrates that Ni-rich ordered face-centered cubic Cr-Ni alloys are antiferromagnetic according to density-functional theory, influencing their formation and magnetic behavior, with implications for related alloys.

Contribution

It reveals the antiferromagnetic nature of Ni-rich Cr-Ni alloys and clarifies the role of magnetism in their formation using ab initio calculations.

Findings

Ni-rich ordered structures are antiferromagnetic under DFT.

Optimization of magnetic moments increases formation driving force.

Magnetism may influence phase stability and alloy properties.

Abstract

Contrary to prior calculations, the Ni-rich ordered structures of the Cr-Ni alloy system are found to be antiferromagnetic under semi-local density-functional theory. The optimization of local magnetic moments significantly increases the driving force for the formation of CrNi$_2$, the only experimentally observed intermetallic phase. This structure's ab initio magnetism appears well described by a Heisenberg Hamiltonian with longitudinal spin fluctuations; itinerant Cr moments are induced only by the strength of exchange interactions. The role of magnetism at temperature is less clear and several scenarios are considered based on a review of experimental literature, specifically a failure of the theory, the existence of an overlooked magnetic phase transition, and the coupling of antiferromagnetism to chemical ordering. Implications for related commercial and high-entropy alloys are discussed for each case.