Theory of Layered Iron Oxide on Frustrated Geometry: Electric Polarization, Magnetoelectric Effect and Orbital State

TL;DR

This paper develops a theoretical framework for layered iron oxides, explaining their charge-order driven electric polarization, magnetoelectric effects, and orbital states influenced by geometric frustration.

Contribution

It presents a novel theory of electronic structure and dielectric properties in layered iron oxides, highlighting the role of charge and spin frustration in inducing polarization and magnetic effects.

Findings

Charge frustration leads to charge imbalance without inversion symmetry.

Spin frustration enhances polar charge order through magnetic ordering.

Orbital model indicates absence of conventional long-range orbital order.

Abstract

A layered iron oxide \rfeo ($R$: rare-earth elements) is an exotic dielectric material with charge-order (CO) driven electric polarization and magnetoelectric effect caused by spin-charge coupling. In this paper, a theory of electronic structure and dielectric property in \rfeo is presented. Charge frustration in paired-triangular lattices allows a charge imbalance without inversion symmetry. Spin frustration induces reinforcement of this polar CO by a magnetic ordering. We also analyze an orbital model for the Fe ion which does not show a conventional long-range order.