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

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^III ions. We investigate the complex magnetism involving both t-e hybridization and Re-f orbitals in the molecular analogue of perovskite [Ce_2^IIICe^IVCr_8^IIIO_8(O_2CPh)_18(HO_2CPh)] (Ce_3Cr_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 Ce_3Cr_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.