AB INITIO STUDY OF THE STRUCTURAL, MAGNETIC, ELECTRONIC AND THERMODYNAMIC PROPERTIES OF Li2MnGe HEUSLER ALLOY

In this study, the structural, elastic, electronic, magnetic, and thermodynamic properties of the Li₂MnGe alloy, which crystallizes in the XA type inverted Heusler structure, were comprehensively examined via first principles calculations on the basis of density functional theory (DFT). The atomic arrangement of the compound was constructed within the F4 ̅3m space group, and among the three possible phases previously reported in the literature, the phase that satisfies the Born mechanical stability criteria was selected for detailed investigation. All calculations were carried out via the Quantum Espresso simulation package within the generalized gradient approximation framework. The atomic positions within the unit cell were assigned as a Li (0,0,0), b Li (1/4,1/4,1/4), Ge (1/2,1/2,1/2), and Mn (3/4,3/4,3/4). Structural optimization confirmed that the alloy is mechanically stable, and the equilibrium lattice constant was determined to be 6.0443 Å. The second-order elastic constants were calculated as C₁₁ = 61.96 GPa, C₁₂ = 21.96 GPa, and C₄₄ = 58.95 GPa, all of which satisfy the Born stability conditions. The negative value of C₁₂ − C₄₄ suggests strong covalent bonding in the alloy. The moduli derived from the elastic constants were as follows: bulk modulus B = 35.29 GPa, shear modulus G = 38.26 GPa, Young’s modulus E = 84.02 GPa, and B/G ratio = 0.922. The Poisson’s ratio of 0.098 further supports the covalent nature of bonding within the structure. Electronic band structure and density-of-states analyses revealed that the alloy exhibited metallic conduction with a highly spin-polarized electronic structure and a narrow pseudogap-like feature near the Fermi level in the spin-down channel. The electronic states near the Fermi level were predominantly contributed by the Mn-3d orbitals. The total magnetic moment was 3.96 μB, which is in agreement with the Slater–Pauling rule. Thermodynamic calculations performed via the Debye model yielded a Debye temperature of 409.889 K. Overall, the calculated properties suggest that Li₂MnGe may be considered a promising candidate for future investigations related to spintronic applications.