A systematic study of the NaMnAs half-Heusler compound from bulk to (001) surfaces as promising spintronic materials

The search for new materials for practical implementation in spintronic devices has attracted enormous attention. In this work, the electronic and magnetic properties of half-Heusler NaMnAs alloy in its bulk conformation and as (001) surfaces are investigated using the full-potential linearized augmented plane wave (FP-LAPW) method. The bulk NaMnAs compound is a ferromagnetic spin-gapless semiconductor (SGS) material, whose total magnetic moment of 5.00<i>μ</i> _B per unit cell satisfies the Slater-Pauling rule and is produced mainly by Mn atoms. The SGS nature is retained with external tensile strain, meanwhile the transition to a magnetic semiconductor (MS) nature is achieved by compressive strain up to -6%. In addition, stronger compression applied to the lattice causes material metallization. Further, (001) surfaces with MnNa- and As-termination with different thickness (5ML, 7ML, 9ML, and 11ML) are considered. It is found that both spin states of MnNa-terminated surfaces exhibit a metallic character, while half-metallicity is observed for the As-terminated surfaces. The calculated projected density of states indicates a key role of As-p and Mn-d orbitals in regulating the electronic nature of both bulk and surface counterparts. Interestingly, except for 11ML-As-terminated surfaces, the out-of-plane easy spin magnetization is demonstrated through calculating the magnetic anisotropy energy. Our results may introduce the new half-Heusler NaMnAs compound for spintronic applications, providing insights into the change of electronic and magnetic properties from the bulk state to (001) surfaces.