Charge Order and the Origin of Giant Magnetocapacitance inLuFe2O4

The nature of the charge order in the charge frustrated compound ${\mathrm{LuFe}}_2{\mathrm{O}}_4$ 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 ${\mathrm{Fe}}_2{\mathrm{O}}_4$ layers of ${\mathrm{LuFe}}_2{\mathrm{O}}_4$, and that the ground state of ${\mathrm{LuFe}}_2{\mathrm{O}}_4$ has a ferrielectric arrangement of the ${\mathrm{Fe}}_2{\mathrm{O}}_4$ layers with $\sqrt{3}\times \sqrt{3}$ charge order. The giant magnetocapacitance effect of ${\mathrm{LuFe}}_2{\mathrm{O}}_4$ 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.