Ferroelectricity from iron valence ordering in rare earth ferrites?

TL;DR

This paper reviews the potential for ferroelectricity from charge ordering in rare earth ferrites, concluding recent evidence does not support this mechanism and highlighting the need for further theoretical understanding.

Contribution

It critically assesses previous claims of ferroelectricity from charge ordering in LuFe2O4 and related ferrites, emphasizing the need for additional theoretical work.

Findings

Recent experiments do not support ferroelectricity from charge ordering.

Charge and spin order origins remain unclear and require further study.

Other phenomena like geometrical frustration are briefly discussed.

Abstract

The possibility of multiferroicity arising from charge ordering in LuFe2O4 and structurally related rare earth ferrites is reviewed. Recent experimental work on macroscopic indications of ferroelectricity and microscopic determination of coupled spin and charge order indicates that this scenario does not hold. Understanding the origin of the experimentally observed charge and spin order will require further theoretical work. Other aspects of recent research in these materials, such as geometrical frustration effects, possible electric-field-induced transitions, or orbital order are also briefly treated.