Crystal chemistry aspects of the magnetically induced ferroelectricity in TbMn2O5 and BiMn2O5

TL;DR

This paper investigates the crystal chemistry behind magnetically induced ferroelectricity in TbMn2O5 and BiMn2O5, focusing on magnetic frustration, ion displacements, and charge ordering mechanisms.

Contribution

It provides a detailed analysis of how magnetic ordering induces ferroelectricity through specific ionic displacements and charge redistribution in these compounds.

Findings

Magnetic frustration origin identified.

Ionic displacements are non-polar but induce charge disorder.

Polar displacement of Mn2 and O ions causes ferroelectric transition.

Abstract

The origin of magnetic frustration was stated and the ions whose shift is accompanied by emerging magnetic ordering and ferroelectricity in TbMn2O5 and BiMn2O5 were determined on the basis of calculation of magnetic coupling parameters by using the structural data. The displacements accompanying the magnetic ordering are not polar, they just induce changes of bond valence (charge disordering) of Mn1 and Mn2, thus creating instability of the crystal structure. To approximate again the bond valence to the initial value (charge ordering) under magnetic ordering conditions is possible only due to polar displacement of Mn2 (or O1) and O4 ions along the b axis that is the cause of ferroelectric transition.