Helical bunching and symmetry lowering inducing multiferroicity in Fe langasites

TL;DR

This study uses neutron scattering to reveal complex magnetic structures in Fe-based langasites, linking their magnetic order to multiferroic behavior and providing insights into the microscopic mechanisms behind their electric polarization.

Contribution

It uncovers new magnetic features such as helical bunching and in-plane spin distortions, advancing understanding of multiferroicity in Fe langasites.

Findings

Helical modulation bunching along the c-axis.

In-plane distortion of Fe-spin arrangement.

Connection between magnetic order and electric polarization.

Abstract

The chiral Fe-based langasites represent model systems of triangle-based frustrated magnets with a strong potential for multiferroicity. We report neutron scattering measurements for the multichiral Ba3MFe3Si2O14 (M = Nb, Ta) langasites revealing new important features of the magnetic order of these systems: the bunching of the helical modulation along the c-axis and the in-plane distortion of the 120{\textdegree} Fe-spin arrangement. We discuss these subtle features in terms of the microscopic spin Hamiltonian, and provide the link to the magnetically-induced electric polarization observed in these systems. Thus, our findings put the multiferroicity of this attractive family of materials on solid ground.