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

Half-metallic (HM) ferromagnetic (FM)/ferrimagnetic (FIM) materials with a large energy-gap (<i>E</i> _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 <i>ab initio</i> 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 <i>E</i> _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 <i>E</i> _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 <i>μ</i> _B. In the Ir-dop. system it is 1.09/-1.39 <i>μ</i> _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 <i>m</i> _s values and FM/FIM state of the prs./Ir-dop. system holding a Curie temperature (<i>T</i> _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 <i>ZT</i>, while compressive strains illustrate a positive impact on the <i>T</i> _C value.