Direct observation of strong t2g−eg orbital hybridization and effects of f orbitals in a molecular analogue of chromium perovskite

Chromium-based perovskites have drawn plenty of attention due to their intriguing magnetic properties and potential technique applications. While a complete understanding of the microscopic magnetic mechanisms underlying their macroscopic properties presents great challenges, especially when involving t2g-eg (t-e) hybridization and rare earth (RE) f orbitals. Here, with the recently discovered molecular analogue of perovskite [Ce₂IIICeIVCr₈IIIO₈(O₂CPh)₁₈(HO₂CPh)], abbreviated as Ce₃Cr₈, we combine first-principles calculations and a superexchange model to successfully identify an anomalous ferromagnetism (FM)-dominated superexchange interaction between Cr ions originated from the t-e hybridization, which does not follow Goodenough-Kanamori rules. The great sensitivity of the t-e hybridization with respect to the angle of Cr-O-Cr can lead to a significant change in the magnetic interaction of Ce₃Cr₈ with the angle of Cr-O-Cr varying within only a few degrees, e.g., a ground-state transition from FM to antiferromagnetism. Additionally, the Ce f orbitals near the Fermi level can largely reduce this sensitivity by interacting with the Cr d orbitals via the virtual charge transfer process. Our results are strongly supported by an extended superexchange model developed with the inclusion of f orbitals within the t-e hybridization framework. These findings complete the theory of superexchange magnetism in chromium-based perovskites including RE f orbitals and in the meanwhile introduce a new avenue for fine-tuning the magnetic characteristics via modifying the transition metal d/RE f interactions at the nanoscale.