Spin amplitude modulation driven magnetoelectic coupling in the new multiferroic FeTe$_2$O$_5$Br

TL;DR

This study reveals that in FeTe$_2$O$_5$Br, spin amplitude modulation induces magnetoelectric coupling, with magnetic order and ferroelectricity emerging simultaneously due to lattice distortions affecting Te$^{4+}$ ions.

Contribution

It demonstrates a novel mechanism where spin amplitude modulation drives magnetoelectric coupling via lattice striction in a new multiferroic material.

Findings

Incommensurate magnetic order develops below 10.6 K.

Ferroelectric order emerges simultaneously with magnetic order.

Linear scaling observed between ferroelectric and magnetic order parameters.

Abstract

Magnetic and ferroelectric properties of layered geometrically frustrated cluster compound FeTe$_2$O$_5$Br were investigated with single-crystal neutron diffraction and dielectric measurements. Incommensurate amplitude modulated magnetic order with the wave vector $\bf{q}$=($\half$, 0.463, 0) develops below $T_N=10.6(2) {\rm K}$. Simultaneously, a ferroelectric order with the spontaneous polarization perpendicular to ${\bf q}$ and to Fe$^{3+}$ magnetic moments emerges. The observed ferroelectricity and extraordinary linear scaling of the ferroelectric and magnetic order parameter are provoked by the striction of the intercluster Fe-O-Te-O-Fe bridges leading to the shift of Te$^{4+}$ ions and polarization of their lone-pair electrons.