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 TC 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 t2g electrons increases TC 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+Ru4++Cr4+→Ru5++Cr3+ charge transfer.

Graphical AbstractWe have investigated the electronic structure of Sr(Ca)Ru1−xCrxO3 using different ab-initio calculation such as LSDA and LSDA+U approximation. The antiferromagnetic hybridization of Cr3+ with Ru4+,5+ lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The LSDA+U calculation for the more distorted Cr impurity doped Ca-based ruthenate compounds as compared to the Sr-based systems shows repulsion between electrons, which tends to keep the localized spins from overlapping. Figure optionsDownload as PowerPoint slide