Structural stabilities, robust half-metallicity, magnetic anisotropy, and thermoelectric performance of the pristine/Ir-doped Sr2CaOsO6: strain modulations

Abstract

Half-metallic (HM) ferromagnetic (FM)/ferrimagnetic (FIM) materials with a large energy-gap (E_g) and high magnetocrystalline anisotropy energy (MAE) are receiving consideration for their potential usage in solid-state electronic devices. This study explores various traits of the pristine (prs.)/Ir-doped (dop.) Sr₂CaOsO₆ structure using ab initio calculations, where Ir is doped at the Os-site. To determine the synthesis feasibility of the structures under ambient conditions, the formation energy, elastic constants, and phonon curves are determined. The prs. structure manifests a FM semiconducting nature with an E_g of 0.048 eV. Strikingly, the Ir-dop. structure becomes HM FIM because additional electrons provided by the dopant (Ir) cause a repulsion in the Os t²_2g spin-minority channel, resulting in conductivity. Conversely, an E_g of 1.15 eV in the spin-majority channel exists, which is high enough to keep the HM state stable. The computed partial spin-moment on the Os in the prs. system is 1.19 μ_B. In the Ir-dop. system it is 1.09/−1.39 μ_B on the Os/Ir ion holding an Os⁺⁶/Ir⁺⁴ state with electronic distributions of 5d²(t²_2g↑t⁰_2g↓e⁰_g↑e⁰_g)/5d⁵(t³_2g↑t²_2g↓e⁰_g↑e⁰_g) with . Further, the spin-magnetization density isosurfaces assist in determining the m_s values and FM/FIM state of the prs./Ir-dop. system holding a Curie temperature (T_C) of 185/171 K. Besides this, we computed the thermoelectric properties of the prs./Ir-dop. motifs; the figure of merit (0.33/0.02), Seebeck coefficient (147/30 μV K⁻¹), and low thermal conductivity (0.21/0.71 × 10¹⁹ Ωm⁻¹ s⁻¹) at 300 K highlight their potential for conversion devices. Interestingly, a semiconducting-to-HM transition is predicted at a crucial compressive strain of −3% in the prs. structure. Conversely, the HM state in the dop. structure displays robustness against strain. Additionally, it is shown that an applied tensile strain can significantly improve ZT, while compressive strains illustrate a positive impact on the T_C value.