Origin of insulating ferromagnetism in iron oxychalcogenide Ce$_2$O$_2$FeSe$_2$
Ling-Fang Lin, Yang Zhang, Gonzalo Alvarez, Adriana Moreo, Elbio, Dagotto
TL;DR
This paper investigates the origin of insulating ferromagnetism in Ce$_2$O$_2$FeSe$_2$, revealing that entanglements between orbitals and many-body interactions stabilize the ferromagnetic phase, supported by theoretical and computational analysis.
Contribution
It provides a detailed theoretical and computational explanation for the ferromagnetic insulating phase in Ce$_2$O$_2$FeSe$_2$, highlighting the role of orbital entanglements and many-body effects.
Findings
Orbital entanglements are key to ferromagnetic stabilization.
Phase diagram aligns with experimental observations.
Many-body calculations confirm the proposed mechanism.
Abstract
An insulating ferromagnetic (FM) phase exists in the quasi-one-dimensional iron chalcogenide CeOFeSe 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 CeOFeSe. 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.
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