Intrinsic and extrinsic anomalous transport properties of the Heusler ferromagnets Fe2CoAl and Fe2NiAl from first principles

Recently, Heusler ferromagnets have been found to exhibit unconventional anomalous electric, thermal, and thermoelectric transport properties. In this study, we employed first-principles density functional theory calculations to systematically investigate both intrinsic and extrinsic contributions to the anomalous Hall effect (AHE), anomalous Nernst effect (ANE), and anomalous thermal Hall effect (ATHE) in two Heusler ferromagnets: ${\mathrm{Fe}}_{2}\mathrm{CoAl}$ and ${\mathrm{Fe}}_{2}\mathrm{NiAl}$. Our analysis reveals that the extrinsic mechanism originating from disorder dominates the AHE and ATHE in ${\mathrm{Fe}}_{2}\mathrm{CoAl}$, primarily due to the steep band dispersions across the Fermi energy and corresponding high longitudinal electronic conductivity. Conversely, the intrinsic Berry phase mechanism, physically linked to nearly flat bands around the Fermi energy and gapped by spin-orbit interaction band crossings, governs the AHE and ATHE in ${\mathrm{Fe}}_{2}\mathrm{NiAl}$. With respect to ANE, both intrinsic and extrinsic mechanisms are competing in ${\mathrm{Fe}}_{2}\mathrm{CoAl}$ as well as in ${\mathrm{Fe}}_{2}\mathrm{NiAl}$. Furthermore, ${\mathrm{Fe}}_{2}\mathrm{CoAl}$ and ${\mathrm{Fe}}_{2}\mathrm{NiAl}$ exhibit tunable and remarkably pronounced anomalous transport properties. For instance, the anomalous Nernst and anomalous thermal Hall conductivities in ${\mathrm{Fe}}_{2}\mathrm{NiAl}$ attain giant values of 8.29 A/Km and 1.19 W/Km, respectively, at room temperature. To provide a useful comparison, we also thoroughly investigated the anomalous transport properties of ${\mathrm{Co}}_{2}\mathrm{MnGa}$. Our findings suggest that Heusler ferromagnets ${\mathrm{Fe}}_{2}\mathrm{CoAl}$ and ${\mathrm{Fe}}_{2}\mathrm{NiAl}$ are promising candidates for spintronics and spin caloritronics applications.