Regular Article

Competition of L2₁ and XA ordering in Fe₂CoAl Heusler alloy: a first-principles study^★

Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur 721302, India

^a e-mail: aquil@phy.iitkgp.ernet.in

Received: 31 December 2019
Received in final form: 24 March 2020
Published online: 25 May 2020

Abstract

The physical properties of Fe₂CoAl (FCA) Heusler alloy are systematically investigated using the first-principles calculations within generalized gradient approximation (GGA) and GGA+U. The influence of atomic ordering with respect to the Wyckoff sites on the phase stability, magnetism and half metallicity in both the conventional L2₁ and XA phases of FCA is focused in this study. Various possible hypothetical structures viz., L2₁, XA-I, and XA-II are prepared by altering atomic occupancies at their Wyckoff sites. At first, we have determined the stable phase of FCA considering various non-magnetic (or paramagnetic), ferromagnetic (FM) and antiferromagnetic (AFM) configurations. Out of these, the ferromagnetic (FM) XA-I structure is found to be energetically most stable. The total magnetic moments per cell are not in agreement with the Slater-Pauling (SP) rule in any phase; therefore, the half-metallicity is not observed in any configurations. However, FM ordered XA-I type FCA shows 78% spin polarization at the Fermi Energy (E_F). Interestingly, the results of XA-I type FCA are closely matched with the experimental results.