Conservation of the robust ferromagnetic half-conductivity in 110-surface half-Heusler NaCrAs alloy by strains and defects

Abstract

We have studied the structural, electronic and magnetic properties of non-polar 110-surface of half-Heusler NaCrAs alloy (110-SHH NaCrAs) using the density functional theory and Korringa–Kohn–Rostoker Green’s function method. Our results show that ferromagnetic half-conductivity (FHC) is exhibited by both the bulk and 110-SHH NaCrAs with a large spin-down energy gap of 2.61 eV and 1.70 eV respectively. The bulk high Curie temperature of 1223 K originates from the direct ferromagnetic exchange between nearest-neighbor (NN) Cr and As atoms as well as the Ruderman–Kittel–Kasuya–Yosida-type interaction between NN Cr atoms. Magnetic moment of 3.92 μB per formula unit was obtained for both the bulk and 110-SHH NaCrAs structures. We used biaxial strain to model the lattice mismatch between deposited thin film and the substrate. Our results reveal that FHC is retained in 110-SHH NaCrAs structure with −3% to 10% strain. Our phase diagram suggests that the 110-SHH NaCrAs composed of NaNaAs, NaCrNa, NaCrCr, CrCrAs, AsCrAs and NaAsAs can be synthesized under appropriate conditions. Additionally, electronic structure calculations show that the surface FHC is preserved only in NaNaAs, VcCrAs, CrCrAs, NaCrCr, NaVcAs and AsCrAs terminated surfaces. Overall, our results demonstrate that the half-Heusler NaCrAs alloy is a potential viable spin filter and spin source in spintronics devices.