Origin of Insulating Ferromagnetism in Iron Oxychalcogenide Ce₂O₂FeSe₂

The mechanism of magnetic exchange in transition metal compounds continues attracting the attention of the condensed matter community. An insulating ferromagnetic (FM) phase exists in the quasi-one-dimensional iron oxychalcogenide Ce2O2FeSe2, but its origin is unknown [1]. To understand the FM mechanism, here a systematic investigation of this material is provided, analyzing the competition between ferromagnetic and antiferromagnetic tendencies and the interplay of hoppings, Coulomb interactions, Hund’s coupling, and crystal-field splittings. Our intuitive analysis based on density functional theory (DFT) calculations and second-order perturbation theory show that large entanglements between doubly occupied and half-filled orbitals play a key role in stabilizing the FM order in Ce2O2FeSe2. In addition, via density matrix renormalization group (DMRG) computational techniques applied to a multiorbital Hubbard model, the phase diagram confirms the proposed FM mechanism [2].

[1] E. E.McCabe, et al., Phys. Rev. B 90, 235115 (2014).

[2] L.-F. Lin, et al., Phys. Rev. Lett. 127, 077204 (2021).