Direct observation of strong t-e orbital hybridization and the effects of f orbitals

Abstract

Recent research has revealed that the Cr family perovskite ReCrO${}_3$ exhibits intriguing magnetic coupling interactions within Cr pairs, which may not follow the Goodenough-Kanamori (GK) rules due to the t-e hybridization between Cr${}^{\mathrm{III}}$ ions. We investigate the complex magnetism involving both t-e hybridization and Re-$f$ orbitals in the molecular analogue of perovskite [$\mathrm{C}{\mathrm{e}}_2^{\mathrm{III}}\mathrm{C}{\mathrm{e}}^{\mathrm{IV}}\mathrm{C}{\mathrm{r}}_8^{\mathrm{III}}{\mathrm{O}}_8({\mathrm{O}}_2\mathrm{CPh}{)}_{18}(\mathrm{H}{\mathrm{O}}_2\mathrm{CPh})$] ($\mathrm{C}{\mathrm{e}}_3\mathrm{C}{\mathrm{r}}_8$) using first-principles method. Our results have shown that distinct from the bulk ReCrO${}_3$, the superexchange via Cr-$d$ and O-$p$ orbitals can exhibit a unexpected dominate ferromagnetic (FM) Cr-O-Cr superexchange interaction in $\mathrm{C}{\mathrm{e}}_3\mathrm{C}{\mathrm{r}}_8$ due to the strong t-e hybridization originated from the distorted molecular structure. The great sensitivity of the t-e hybridization with respect to the molecular structure, e.g., the angle of Cr-O-Cr, can lead to a ground state transition from ferromagnetic to antiferromagnetic state with the changes in the angle of Cr-O-Cr. The Ce-$f$ orbitals near the Fermi level can reduce this sensitivity through interacting with the Cr-$d$ orbitals via the virtual charge transfer process. Our results are strongly supported by a modified superexchange model based on the t-e hybridization theory. These findings complete the theory of superexchange magnetism involving the t-e hybridization and $f$ orbitals, and in the meanwhile introduce a new avenue for fine-tuning the magnetic characteristics via Tm-d/Re-f interactions at nanoscale.