Distinct transport behaviors and electronic structures in Heusler alloys CoFeCrGa and CoFeCrAl

Abstract

As one of desirable spin-gapless semiconductors, Heusler alloy CoFeCrGa is a potential candidate for semiconductor spintronic applications. However, the absence of explicit investigation on transport properties opens a great way for our theoretical research. In this study, we report on the spin-Seebeck coefficient of quaternary Heusler alloy CoFeCrGa and CoFeCrAl from ab initio density functional theory and Boltzmann transport calculations. Interestingly, CoFeCrGa is a spin-gapless semiconductor while CoFeCrAl acts as a half-metallic ferrimagnet. These two effects produce different spin-Seebeck coefficients of 6.76 μV/K and −0.57 μV/K at room temperature, respectively. By modulating chemical potential and temperature, the spin-Seebeck coefficient can be boosted to −11.7 μV/K under µ = −0.15 eV for CoFeCrGa, and −16.2 μV/K with µ = 0.13 eV for CoFeCrAl, both at 400 K. We demonstrate that the mechanism of the variation of the Seebeck coefficient depending upon the chemical potential and temperature is related to bond lengths, electronic structures, magnetic properties, and transmission. These characteristics of CoFeCrGa and CoFeCrAl offer perspectives for their spin-transport devices.