Ab initio study of the half-metallic full-Heusler compounds Co$_2$ZAl [Z = Sc, Ti, V, Cr, Mn, Fe]; the role of electronic correlations

TL;DR

This study investigates the structural, electronic, and magnetic properties of Co2ZAl Heusler compounds using first-principles calculations, examining the effects of lattice variation and electronic correlations, and finds that DFT+U is generally not suitable except for Co2FeAl.

Contribution

The paper provides a comprehensive ab initio analysis of Co2ZAl compounds, highlighting the limited applicability of DFT+U and identifying Co2FeAl as an exception where correlations restore half-metallicity.

Findings

DFT+U is not justified for most Co2ZAl compounds.

Lattice parameter variation affects magnetic moments and stability.

Inclusion of correlations is beneficial only for Co2FeAl.

Abstract

We study the structural, electronic, and magnetic properties of Co$_2$ZAl compounds employing a pseudopotential electronic bandstructure method. The stability of the compounds is established through the formation and cohesive energy calculations. The effect of the lattice parameter variation on the electronic and magnetic properties of the compounds is investigated and meticulous explanation is provided for the observed behavior. The variation of the individual spin magnetic moments and the stability of the total spin magnetic moment during the expansion and contraction of the lattice parameter is observed and an attempt is made to understand the obtained behavior. Finally, we implement DFT+U to examine its consequences on the electronic and magnetic properties of the Co$_2$ZAl compounds. We find that the use of DFT+U is not justified for these compounds and in some cases like Co$_2$MnAl it produces unrealistic properties. The exception is Co2FeAl where the desired half-metallicity is restored after the inclusion of on-site correlations. We explain why the on-site correlations might be important for Co$_2$FeAl by comparing it with other Heusler alloys where the correlation was found to be meaningful to explain the observed magnetic moments.