Electronic and transport properties of a new quaternary Heusler alloy CoMnFeSi

The electronic and galvanomagnetic properties of the equiatomic quaternary Heusler alloy CoMnFeSi, which was recently synthesized and which crystallizes in the cubic LiMgPdSb structure, are studied from first principles. We concentrate on two problems: (i) the origin of the alloy disorder, which was found to exist in this alloy, and (ii) the evaluation of basic galvanomagnetic properties such as the dc conductivity a tot and the anomalous Hall conductivity(AHC) for swap defects, accompanied by a comparison of the calculated results with a recent experiment. The origin of the alloy disorder is investigated by estimating corresponding formation energies of possible swap defects which preserve the sample stoichiometry. We discuss various defects with respect to the sample half metallicity. The most favorable swap types are those for which the calculated a tot and AHC agree reasonably with the experiment. On the basis of calculated transport quantities a tot (AHC), the two most favorable swap types can be identified, namely, (i) the Co-Fe swaps, which preserve the half metallicity and have the lowest formation energy, and (ii) the Co-Mn swaps, which violate the half metallicity but have larger formation energy.