Ferroelectric Ferrimagnetic LiFe$_2$F$_6$: Charge Ordering Mediated Magnetoelectricity

TL;DR

This paper theoretically investigates LiFe$_2$F$_6$, revealing its charge-ordering driven ferroelectricity and tunable magnetism, which together enable a strong magnetoelectric effect suitable for multifunctional applications.

Contribution

It demonstrates that charge ordering in LiFe$_2$F$_6$ mediates both ferroelectricity and magnetization, and shows how strain can switch its magnetic state, offering a new pathway for multiferroic design.

Findings

Charge ordering causes improper ferroelectricity with large polarization.

Magnetic ground state can be tuned from antiferromagnetic to ferrimagnetic by strain.

Net magnetization can be switched by flipping polarization.

Abstract

Trirutile-type LiFe$_2$F$_6$ is a charge-ordered material with Fe$^{2+}$/Fe$^{3+}$ configuration. Here its physical properties, including magnetism, electronic structure, phase transition, and charge ordering, are studied theoretically. On one hand, the charge ordering leads to improper ferroelectricity with a large polarization. On the other hand, its magnetic ground state can be tuned from the antiferromagnetic to ferrimagnetic by moderate compressive strain. Thus, LiFe$_2$F$_6$ can be a rare multiferroic with both large magnetization and polarization. Most importantly, since the charge ordering is the common ingredient for both ferroelectricity and magnetization, the net magnetization may be fully switched by flipping the polarization, rendering intrinsically strong magnetoelectric effect and desirable function.