Exploring multifunctional behavior in X₂CoGa (X = Cu, Ag, Zn, Nb) Heusler alloys via first-principles calculations

In the present work, first-principles density functional theory calculations are performed to investigate the structural, spin-polarized electronic, mechanical, and thermodynamic properties of full-Heusler alloys X₂CoGa (X = Cu, Ag, Zn, Nb). Structural optimization and total energy analysis reveal that Ag2CoGa stabilizes in the L2₁ state, whereas Cu2CoGa, Zn2CoGa, and Nb2CoGa preferentially adopt the XA state. Phonon dispersion calculations indicate that Ag2CoGa and Zn2CoGa are dynamically unstable due to the presence of imaginary phonon modes, while Cu2CoGa and Nb2CoGa are dynamically stable. Competing-phase analysis further confirms the stability of Cu2CoGa and Nb2CoGa against the considered decomposition pathways. Spin-polarized electronic properties show that both Cu2CoGa and Nb2CoGa possess metallic behavior, with a finite density of states at the Fermi level for both spin channels, accompanied by enhanced magnetization in Nb2CoGa compared to Cu2CoGa, mainly arising from Nb and Co atoms. Stoner analysis further supports the magnetic behavior of both compounds, while Bader charge and ELF analyses provide insight into their distinct charge-transfer and bonding characteristics. Elastic constant calculations reveal that both compounds satisfy the Born stability criteria and are ductile in nature. Elastic anisotropy analysis indicates that Nb2CoGa exhibits a near-isotropic behavior, consistent with an anisotropy factor close to unity (A_Z ≈ 0.95). The higher Debye temperature and lattice thermal conductivity of Nb2CoGa imply stronger interatomic bonding, highlighting its distinct lattice thermal transport behavior compared with Cu2CoGa.