An insulating ferromagnetic (FM) phase exists in the quasi-one-dimensional iron chalcogenide Ce2O2FeSe2 but its origin is unknown. 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 second-order perturbation theory shows that large entanglements between doubly-occupied and half-filled orbitals play a key role in stabilizing the FM order in Ce2O2FeSe2. In addition, via many-body computational techniques applied to a multi-orbital Hubbard model, the phase diagram confirms the proposed FM mechanism, in agreement with experiments.
@article{arxiv.2105.09239,
title = {Origin of insulating ferromagnetism in iron oxychalcogenide Ce$_2$O$_2$FeSe$_2$},
author = {Ling-Fang Lin and Yang Zhang and Gonzalo Alvarez and Adriana Moreo and Elbio Dagotto},
journal= {arXiv preprint arXiv:2105.09239},
year = {2021}
}