Electronic structure, magnetism and antisite disorder in CoFeCrGe and CoMnCrAl quaternary Heusler alloys

TL;DR

This study combines theoretical and experimental approaches to analyze the electronic structure, magnetism, and disorder in CoFeCrGe and CoMnCrAl Heusler alloys, highlighting their potential for spintronics and the effects of antisite disorder.

Contribution

It provides new insights into the structural and magnetic properties of these alloys, including the impact of antisite disorder and a predicted magnetic transition with Al excess.

Findings

Magnetization matches theoretical predictions and obeys Slater-Pauling rule.

CFCG is fully ordered; CMCA exhibits L2_1 disorder.

Antisite disorder influences magnetic properties and induces a transition from half-metallic ferromagnet to metallic antiferromagnet.

Abstract

We present a combined theoretical and experimental study of two quaternary Heusler alloys CoFeCrGe (CFCG) and CoMnCrAl (CMCA), promising candidates for spintronics applications. Magnetization measurement shows the saturation magnetization and transition temperature to be $3\; \mu_B$, $866$ K and $0.9 \; \mu_B$, $358$ K for CFCG and CMCA respectively. The magnetization values agree fairly well with our theoretical results and also obey the Slater-Pauling rule, a prerequisite for half metallicity. A striking difference between the two systems is their structure; CFCG crystallizes in fully ordered Y-type structure while CMCA has L2$_1$ disordered structure. The antisite disorder adds a somewhat unique property to the second compound, which arises due to the probabilistic mutual exchange of Al positions with Cr/Mn and such an effect is possibly expected due to comparable electronegativities of Al and Cr/Mn. {\it Ab-initio} simulation predicted a unique transition from half metallic ferromagnet to metallic antiferromagnet beyond a critical excess amount of Al in the alloy.