Effect of L21 and XA ordering on phase stability, half-metallicity and magnetism of Co2FeAl Heusler Alloy: GGA and GGA+U approach

TL;DR

This study investigates how L21 and XA atomic orderings influence phase stability, electronic structure, and magnetism in Co2FeAl Heusler alloys using GGA and GGA+U calculations, revealing the importance of electronic correlations.

Contribution

It demonstrates that the electronic and magnetic properties of Co2FeAl are significantly affected by atomic ordering and the inclusion of Hubbard U, highlighting the need for GGA+U in accurate predictions.

Findings

XA-II phase is most stable energetically.

GGA predicts only L21-1 as half-metallic.

GGA+U converts some metallic states into half-metallic.

Abstract

The generalized gradient approximation (GGA) scheme in the first-principles calculations are used to study the effect of L21 and XA ordering on the phase stability, half-metallicity and magnetism of Co2FeAl (CFA) Heusler alloy. Various possible hypothetical structures: L21-I, L21-II, XA-I, and XA-II were prepared under the conventional L21 and inverse XA phases by altering the atomic occupancies at their Wyckoff sites. It is found that the XA-II phase of CFA is the most stable phase energetically among all the structures. The electronic structure calculations without U show the presence of half-metallic (HM) ground state only in L21-1 structure and the other structures are found to be metallic. However, the electronic structures of CFA are significantly modified in the presence of U, although the total magnetic moments per cell remained the same and consistent with the Slater-Pauling (SP) rule. The metallic ground states of CFA in L21-II and XA-II structures are converted into the half-metallic ground states in presence of U but remained the same (metallic) in XA-I structure. The results indicate that the electronic structures are not only dependent on the L21 and XA ordering of the atoms but also depend on the choice of U values. So experiments may only verify the superiority of GGA+U to GGA.