Origin of destruction of multiferroicity in Tb2BaNiO5 by Sr doping and its implications

TL;DR

This study investigates why multiferroicity is destroyed in Sr-doped Tb2BaNiO5 by analyzing magnetic canting angles, revealing that the absence of a critical canting angle prevents magnetoelectric coupling, unlike in the undoped compound.

Contribution

It demonstrates that the suppression of multiferroicity in Sr-doped Tb2BaNiO5 is due to the lack of a critical canting angle, providing insight into the role of magnetic structure in multiferroic behavior.

Findings

No significant change in canting angle in Sr-doped sample.

Critical canting angle is necessary for multiferroicity.

Sr doping prevents reaching the critical canting angle.

Abstract

The orthorhombic Haldane spin chain compound Tb2BaNiO5 (Neel order, TN1= 63 K) has been shown to be an exotic multiferroic system below (TN2) 25 K due to various fascinating features, pointing to a strong potential for the advancement of concepts in this field. In particular, the rare-earth ions play a direct decisive role unlike in many other well known multiferroic materials and there appears to be a critical canting angle, developing below TN2, subtended by Tb 4f and Ni 3d moments to trigger this cross coupling phenomenon. However, for a small replacement of Sr for Ba, viz. in Tb2Ba0.9Sr0.1NiO5, ferroelectricity was reported to get destroyed, but retaining magnetic features at (TN1) 55 K and (TN2) 14 K. In this article, we address the origin of suppression of multiferrocity in this Sr doped system through neutron diffraction studies and density functional theory calculations. We find that, unlike in Tb2BaNiO5, there is no pronounced change in the relative canting angle of the magnetic moments around TN2 and that the absolute value of this parameter down to 2 K fails to exceed the critical value noted for the parent, thereby explaining the origin of destruction of magnetoelectric coupling in the Sr doped material. This finding renders strong support to the proposal of possible existence of critical canting angle, at least in some cases, to induce multiferroicity, apart from serving as a route to engineer multiferroic materials for applications.