Pressure-induced charge orders and their coupling to magnetism in hexagonal multiferroic LuFe2O4

TL;DR

This study investigates how applying pressure influences charge and spin orders in hexagonal LuFe2O4, revealing phase transitions and coupling mechanisms that could enable controlled tuning of multiferroic properties.

Contribution

The paper uncovers pressure-induced phase transitions in LuFe2O4 and elucidates the coupling mechanism between charge, spin, and lattice degrees of freedom using experimental and theoretical methods.

Findings

Identification of three correlated spin-charge ordered phases under pressure.

Pressure-induced transition from ferrimagnetic to antiferromagnetic order.

Charge density redistribution driven by pressure affects spin-charge coupling.

Abstract

Hexagonal LuFe2O4 is a promising charge-order (CO) driven multiferroic material with high charge and spin ordering temperatures. The coexisting charge and spin orders on Fe3+/Fe2+ sites result in novel magnetoelectric behaviors, but the coupling mechanism between the charge and spin orders remains elusive. Here, by tuning external pressure, we reveal three correlated spin-charge ordered phases in LuFe2O4: i) a centrosymmetric incommensurate three-dimensional CO with ferrimagnetism, ii) a non-centrosymmetric incommensurate quasi-two-dimensional CO with ferrimagnetism, and iii) a centrosymmetric commensurate CO with antiferromagnetism. Experimental in-situ single-crystal X-ray diffraction and X-ray magnetic circular dichroism measurements combined with density functional theory calculations suggest that the charge density redistribution caused by pressure-induced compression in the frustrated double-layer [Fe2O4] cluster is responsible for the correlated spin-charge phase transitions. The pressure-enhanced effective Coulomb interactions among Fe-Fe bonds drive the frustrated (1/3, 1/3) CO to a less frustrated (1/4, 1/4) CO, which induces the ferrimagnetic to antiferromagnetic transition. Our results not only elucidate the coupling mechanism among charge, spin and lattice degrees of freedom in LuFe2O4 but also provide a new way to tune the spin-charge orders in a highly controlled manner.