Block antiferromagnetism and possible ferroelectricity in KFe$_2$Se$_2$

TL;DR

This paper predicts that KFe$_2$Se$_2$, an iron-selenide compound related to superconductors, exhibits block antiferromagnetism and potential ferroelectricity, with switchable electric phases due to its magnetic structure.

Contribution

It introduces the prediction of multiferroicity in KFe$_2$Se$_2$ driven by its unique magnetic ordering, expanding the understanding of iron-based materials.

Findings

KFe$_2$Se$_2$ exhibits block-type antiferromagnetism.

Magnetic ordering induces electric dipoles via exchange striction.

Ground state may switch between antiferroelectric and ferroelectric phases.

Abstract

Superconductors and multiferroics are two of the hottest branches in condensed matter physics. The connections between those two fields are fundamentally meaningful to unify the physical rules of correlated electrons. Recently, BaFe$_2$Se$_3$, was predicted to be multiferroic [Phys. Rev. Lett. 113, 187204 (2014)] due to its unique one-dimensional block-type antiferromagnetism. Here, another iron-selenide KFe$_2$Se$_2$, a parent state of iron-based superconductor, is predicted to be multiferroic. Its two-dimensional block-type antiferromagnetism can generate a moderate electric dipole for each Fe-Se layer via the Fe-Se-Fe exchange striction. Different stacking configurations of these magnetic blocks give closely proximate energies and thus the ground state of KFe$_2$Se$_2$ may be switchable between antiferroelectric and ferroelectric phases.