Independent ferroelectric contributions and rare-earth-induced polarization reversal in multiferroic TbMn2O5

TL;DR

This study separates and analyzes the different magnetic contributions to the spontaneous polarization in TbMn2O5, revealing how rare-earth magnetic order influences ferroelectricity and polarization reversal.

Contribution

It uniquely identifies and distinguishes three independent magnetic contributions to polarization in TbMn2O5 using optical second harmonic generation and Landau theory analysis.

Findings

Two contributions are related to Mn magnetic order and are field-independent.

The third contribution from Tb order decreases with magnetic field and causes polarization sign reversal.

Rare-earth order influences ferroelectricity via isotropic exchange and oxygen spin polarization.

Abstract

Three independent contributions to the magnetically induced spontaneous polarization of multiferroic TbMn2O5 are uniquely separated by optical second harmonic generation and an analysis in terms of Landau theory. Two of them are related to the magnetic Mn3+/4+ order and are independent of applied fields of up to 7 T. The third contribution is related to the long-range antiferromagnetic Tb3+ order. It shows a drastic decrease upon the application of a magnetic field and mediates the change of sign of the spontaneous electric polarization in TbMn2O5. The close relationship between the rare-earth long-range order and the non-linear optical properties points to isotropic Tb-Tb exchange and oxygen spin polarization as mechanism for this rare-earth induced ferroelectricity.