Charge Order and the Origin of Giant Magnetocapacitance in LuFe2O4

TL;DR

This study investigates the charge order in LuFe$_2$O$_4$ and explains its giant magnetocapacitance at room temperature as arising from charge fluctuations between two nearly degenerate charge orders, influenced by magnetic fields.

Contribution

It reveals the coexistence of two charge orders in LuFe$_2$O$_4$ and links charge fluctuations to its magnetocapacitance, supported by first-principles and Monte Carlo calculations.

Findings

Two types of charge order coexist in LuFe$_2$O$_4$.

The ground state has a ferrielectric charge order.

Magnetocapacitance arises from hindered charge fluctuations under magnetic field.

Abstract

The nature of the charge order in the charge frustrated compound LuFe$_2$O$_4$ and its effect on magnetocapacitance were examined on the basis of first-principles electronic structure calculations and Monte Carlo simulations of electrostatic energy. Our work shows that two different types of charge order of almost equal stability (i.e., $\sqrt{3}\times \sqrt{3}$ and chain types) occur in the W-layers of LuFe$_2$O$_4$, and that the ground state of LuFe$_2$O$_4$ has a ferrielectric arrangement of the W-layers with $\sqrt{3}\times \sqrt{3}$ charge order. The giant magnetocapacitance effect of LuFe$_2$O$_4$ at room temperature is accounted for in terms of charge fluctuations arising from the interconversion between the two types of charge order, that becomes hindered by an applied magnetic field.