Nature of the magnetic order and origin of induced ferroelectricity in TbMnO$_3$

TL;DR

This study uses soft x-ray resonant scattering to clarify the magnetic structures in TbMnO$_3$, revealing that its ferroelectric transition occurs between two non-collinear magnetic phases rather than a collinear to non-collinear transition.

Contribution

The paper provides a new understanding of the magnetic order and ferroelectric transition in TbMnO$_3$ through detailed XRS analysis and group theory, challenging previous assumptions.

Findings

Ferroelectric transition occurs between two non-collinear magnetic structures.

XRS effectively separates contributions from Mn and Tb moments.

New magnetic structure model for TbMnO$_3$ derived from combined analysis.

Abstract

The magnetic structures which endow TbMnO$_3$ with its multiferroic properties have been reassessed on the basis of a comprehensive soft x-ray resonant scattering (XRS) study. The selectivity of XRS facilitated separation of the various contributions (Mn $L_2$ edge, Mn 3d moments; Tb M$_4$ edge, Tb 4f moments), while its variation with azimuth provided information on the moment direction of distinct Fourier components. When the data are combined with a detailed group theory analysis, a new picture emerges of the ferroelectric transition at 28 K. Instead of being driven by the transition from a collinear to a non-collinear magnetic structure, as has previously been supposed, it is shown to occur between two non-collinear structures.