Magnetic field control of charge structures in the magnetically disordered phase of the multiferroic LuFe$_2$O$_4$

TL;DR

This study demonstrates that applying a magnetic field to LuFe$_2$O$_4$ influences its charge structures and enhances its magneto-electric effects, highlighting a unique coupling mechanism involving local spins rather than bulk magnetic order.

Contribution

It reveals that magnetic field effects on local spins, rather than bulk magnetic order, drive the magneto-electric coupling in LuFe$_2$O$_4$, a novel insight in multiferroic research.

Findings

Magnetic field alters charge valence order and correlation lengths.

Magnetic field influences dielectric and ferroelectric properties.

Magneto-electric effect is driven by local spin interactions.

Abstract

Using neutron diffraction, we have studied the magnetic field effect on charge structures in the charge-ordered multiferroic material LuFe$_2$O$_4$. An external magnetic field is able to change the magnitude and correlation lengths of the charge valence order even before the magnetic order sets in. This affects the dielectric and ferroelectric properties of the material and induces a giant magneto-electric effect. Our results suggest that the magneto-electric coupling in LuFe$_2$O$_4$ is likely due to magnetic field effect on local spins, in clear contrast to the case in most other known multiferroic systems where the bulk magnetic order is important.