Structural, electronic, and magnetic properties of bulk and (001) surfaces NaFeAs half-Heusler alloy: A first-principles study

Abstract

The electronic and magnetic properties of Heusler alloys may vary significantly from their bulk form to thin films, therefore deep insights into this variation are extremely important. In this work, we employ the full-potential linearized augmented plane-wave (FP-LAPW) method - that is implemented in WIEN2k package - to investigate the electronic and magnetic properties of new half-Heusler NaFeAs alloy in bulk form and (001) surfaces. In its bulk form, the studied alloy is a half-metallic ferromagnet with an overall magnetic moment of 4.00 ${\mu }_B$. The half-metallicity is destroyed with lattice tension from 2% and lattice contraction from −7% considering the semiconductor-to-metallic state transition in this range of external strain. Upon cleaving (001) surfaces, the electronic nature depends strongly on the kind of termination, namely FeNa-termination and As-termination. Specifically, FeNa-terminated surface is classified as a metallic material considering the metallic character of its both spin states. In this case, a total magnetic moment of 17.03 ${\mu }_B$ is obtained. Meanwhile the half-metallicity is noted for As-terminated surface with an integer overall magnetic moment of 13.00 ${\mu }_B$ and half-metallic gap of 0.43 eV (larger than that of bulk form of 0.18 eV). In all cases, transition metal Fe makes main contribution to the system magnetic moment. In addition, both considered (001) surfaces are confirmed to have an out-of-plane easy magnetization direction. Our results may evidence the promise of NaFeAs half-Heusler alloy for the emerging spintronic applications.