Effect of electron correlation in Sr(Ca)Ru1−xCrxO3: Density functional calculation

We have investigated the electronic structure of Sr(Ca)Ru1−xCrxO3 using the full potential linearized augmented plane wave method by different approximation such as LSDA and LSDA+U . The LSDA calculation suggest that Cr4+–Ru4+ hybridization is responsible for the high Curie temperature T C in SrRu1−xCrxO3, but it cannot completely describe its physical behavior. Our LSDA+U DOS results for SrRu1−xCrxO3 clearly establishes renormalization of the intra-atomic exchange strength at the Ru sites, arising from the Cr–Ru hybridization. The antiferromagnetic coupling of Cr3+ with Ru4+,5+ lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The more distorted Ca-based compounds as compared to the Sr-based systems shows that the hybridization mechanism is not relevant for these compounds. The bigger exchange splitting of Ru 4d and Cr 3d at the Fermi level with Ru4+,5+ and Cr3+,4+ orbital occupancies of CaRu0.75Cr0.25O3 in the LSDA+U calculation, compared with that of the LSDA calculation, shows that repulsion between electrons tend to keep the localized spins from overlapping. The low screening of the Ru t 2g electrons increases T C in the Ca-based systems, which is consistent with the both high Ru exchange splitting and magnetic moment. The insulating behavior of the high Cr-doped systems can be explained by considering the Ru4++Cr4+→Ru5++Cr3+