Dielectric and multiferroic behavior in a Haldane spin-chain compound Sm2BaNiO5 due to an interplay between crystal-field effect and exchange interaction

TL;DR

This study investigates Sm2BaNiO5, a Haldane spin-chain compound, revealing complex dielectric and magnetic behaviors, including a novel multiferroic state induced by crystal-field and exchange interactions, without ferroelectricity or multiglass features.

Contribution

It demonstrates that Sm2BaNiO5 exhibits multiferroicity driven by interplay between crystal-field effects and exchange interaction, distinct from other similar compounds.

Findings

Pyrocurrent peak near T_N not due to ferroelectricity

Weak dielectric peak around 22 K linked to exchange-split states

No multiglass features observed down to 2 K

Abstract

The Haldane spin-chain (S=1) insulating compound, Sm2BaNiO5, which has been proposed to order antiferromagnetically around (T_N=) 55 K, was investigated for its complex dielectric permittivity, magnetodielectric and pyrocurrent behavior as a function of temperature (T). In order to enable meaningful discussions, the results of ac and dc magnetizatioin and heat-capacity studies are also reported. We emphasize on the following findings: (i) There is a pyrocurrent peak near T_N, but it is shown not to arise from ferroelectricity, but possibly due to 'thermally stimulated depolarization current', unlike in many other members of this rare-earth series, in which case ferroelectric features were reported at or above T_N; (ii) however, the pyrocurrent measured in the presence of a bias electric field (after cooling in zero electric field) as well as dielectric constant reveal a weak peak with increasing T around 22 K - the temperature around which population of the exchange-split excited state of Kramers doublet has been known to occur. This finding suggests that this compound presents a novel situation in which multiferroicity is induced by an interplay between crystal-field effects and exchange interaction. No multiglass features could be observed down to 2 K unlike in many members of this family.