Multiferroicity in an organic charge-transfer salt: Electric-dipole-driven magnetism

TL;DR

This paper reports the discovery of a new class of multiferroic organic charge-transfer salts where electronic ferroelectricity and antiferromagnetic spin order occur nearly simultaneously, driven by charge order breaking inversion symmetry.

Contribution

It provides evidence for purely electronic ferroelectricity in a two-dimensional organic salt, showing a novel mechanism where ferroelectricity drives magnetic order.

Findings

Electronic ferroelectricity observed in organic salt

Simultaneous dipolar and spin order formation

Ferroelectricity induces loss of spin frustration

Abstract

Multiferroics, showing simultaneous ordering of electrical and magnetic degrees of freedom, are remarkable materials as seen from both the academic and technological points of view. A prominent mechanism of multiferroicity is the spin-driven ferroelectricity, often found in frustrated antiferromagnets with helical spin order. There, similar to conventional ferroelectrics, the electrical dipoles arise from an off-centre displacement of ions. However, recently a different mechanism, namely purely electronic ferroelectricity, where charge order breaks inversion symmetry, has attracted considerable interest. Here we provide evidence for this exotic type of ferroelectricity, accompanied by antiferromagnetic spin order, in a two-dimensional organic charge-transfer salt, thus representing a new class of multiferroics. Quite unexpectedly for electronic ferroelectrics, dipolar and spin order arise nearly simultaneously. This can be ascribed to the loss of spin frustration induced by the ferroelectric ordering. Hence, here the spin order is driven by the ferroelectricity, in marked contrast to the spin-driven ferroelectricity in helical magnets.