Electronic structure and estimation of Curie temperature in Ca₂BIrO₆ (B= Cr, Fe) double perovskites

We investigate the electronic and magnetic properties of Ca₂CrIrO₆ and Ca₂FeIrO₆ by means of density functional theory. Upon replacement of Os by Ir in Ca₂CrOsO₆, we found the system to exhibit a stable ferrimagnetic configuration with a band gap of 0.25 eV and an effective magnetic moment of 2.58 μ_Β per unit cell. Further when chemical doping is considered by replacing Cr with Fe and Os with Ir, the material retains the insulating state but with a reduced band gap 0.13 eV and  an effective magnetic moment of 6.68  μ_Β per unit cell. These observed behaviors are noted to be the consequence of the cooperative effect of spin-orbit coupling, Coulomb correlations from Cr-3d, Fe-3d and Ir-5d electrons, and the crystal field effect of the materials. This study suggests that by chemical tuning, one can manipulate the band gap and their effective magnetic moment. To check further the suitability and applicability of Ca₂CrIrO₆ and Ca₂FeIrO₆ at higher temperatures, we estimate the Curie temperature (T_C) by calculating the spin-exchange coupling. We found that our findings are in a valid T_C trend similar to other perovskites. Our findings is expected to be useful in experimental synthesis and transport measurement for potential applications in fabrication of modern technological devices.