Magnetic transition in B2 Al-Cr-Co alloys

TL;DR

This study combines DFT and Monte Carlo simulations to analyze magnetic transitions in B2 Al-Cr-Co alloys, revealing how Co content influences magnetic order and Curie temperature, and predicting a spin-glass state at high Co levels.

Contribution

It provides a detailed computational analysis of magnetic behavior in Al-Cr-Co alloys, highlighting the impact of Co concentration on magnetic phases and exchange interactions.

Findings

Low Co favors antiferromagnetic order

High Co induces ferromagnetic transition

Spin-glass behavior predicted at >40% Co

Abstract

Using Density Functional Theory (DFT) calculations and Monte-Carlo (MC) simulations, we investigate the recently reported magnetic transition in B2 Al-Cr-Co alloys. The Cr sublattice is alloyed with different amounts of Co in the antiferromagnetic (AFM) B2 AlCr binary alloy and the resulting exchange interactions are analyzed within the Heisenberg Hamiltonian framework. DFT results reveal that at low Co concentrations the system favors the AFM order, while at high Co contents a transition to the ferromagnetic (FM) state is observed. Within the FM stability field, the Curie temperature (TC), obtained within the mean-field approximation, is below ~160 K and decreases with Co concentration. The calculated exchange parameters evolve systematically with Co content, and the trends are consistent with the DFT total energies. The magnetic configurations obtained from MC simulations follow the DFT results at low Cr levels but predict a spin-glass behavior for alloys containing more than 40 at.% Co on Cr sublattice. These findings provide a fundamental understanding of how the chemistry-driven changes in exchange interactions affect magnetism in the B2 Al-Cr-Co alloys.