Insulator-to-half metal transition and enhancement of structural distortions in text {Lu}_2 text {NiIrO}_6 double perovskite oxide via hole-doping

Abstract

Using density functional theory calculations, we found that recently high-pressure synthesized double perovskite oxide text {Lu}_2 text {NiIrO}_6 exhibits ferrimagnetic (FiM) Mott-insulating state having an energy band gap of 0.20 eV which confirms the experimental observations (Feng et al. in Inorg Chem 58:397–404, 2019). Strong antiferromagnetic superexchange interactions between high-energy half-filled text {Ni}^{+2}-e_g^2uparrow and low-energy partially filled text {Ir}^{+4},t_{2g}^3uparrow t_{2g}^2downarrow orbitals, results in a FiM spin ordering. Besides, the effect of 3d transition metal (TM = Cr, Mn, and Fe) doping with 50% concentration at Ni sites on its electronic and magnetic properties is explored. It is established that smaller size cation-doping at the B site enhances the structural distortion, which further gives strength to the FiM ordering temperature. Interestingly, our results revealed that all TM-doped structures exhibit an electronic transition from Mott-insulating to a half-metallic state with effective integral spin moments. The admixture of Ir 5d orbitals in the spin-majority channel are mainly responsible for conductivity, while the spin minority channel remains an insulator. Surprisingly, a substantial reduction and enhancement of spin moment are found on non-equivalent Ir and oxygen ions, respectively. This leads the Ir ion in a mixed-valence state of +4 and +5 in all doped systems having configurations of 5d^5 (t_{2g}^3uparrow t_{2g}^2downarrow) and 5d^4 (t_{2g}^2uparrow t_{2g}^2downarrow), respectively. Hence, the present work proposes that doping engineering with suitable impurity elements could be an effective way to tailor the physical properties of the materials for their technological potential utilization in advanced spin devices.