Pressure-induced anomalies in the magnetic transitions of the exotic multiferroic material, Tb2BaNiO5

TL;DR

This study investigates how external pressure affects the magnetic transitions of the multiferroic compound Tb2BaNiO5, revealing opposite shifts in transition temperatures and highlighting the role of local distortions and doping.

Contribution

It provides new insights into pressure effects on magnetic and ferroelectric transitions in Tb2BaNiO5, combining experimental and chemical pressure studies to understand local structural influences.

Findings

External pressure raises TN1 and lowers TN2.

Chemical pressure via doping reduces both TN1 and TN2.

Pressure and doping differently influence magnetic coupling and local hybridization.

Abstract

We have studied the influence of external pressure up to 1 GPa on the magnetic transitions of the orthorhombic Haldane-spin chain compound Tb2BaNiO5 an exotic multiferroic material. This parent compound is known to undergo N\'eel ordering at TN1= 63 K and another magnetic transition at TN2= 25K at which ferroelectricity sets in, however, without any change in the magnetic symmetry, but with only a sharp change in the canting angle of Tb 4f and Ni 3d magnetic moments. There is a subtle difference in the antiferromagnetic state above and below TN2, which is supported by the fact that there is a metamagnetic transition below TN2only (for 5 K, at about 60 kOe). We report here that, with the application of external pressure, there is an upward shift of TN1, while TN2 shifts towards lower temperatures. It is interesting that the two magnetic transitions in the same compound behave differently under pressure and the opposite behavior at TN2 is attributed to local distortion leading to ferroelectricity. The results are augmented by temperature dependent x-ray diffraction and positive chemical pressure studies. The chemical pressure caused by the isoelectronic doping at Ba site by Sr reduces both the transition temperatures. Clearly, the external pressure favors antiferromagnetic coupling (that is, leading to TN1 enhancement), whereas the chemical pressure reduces TN1, suggesting important role of the changes in local hybridization induced by doping on magnetism in this material.