Magnetic and magnetodielectric coupling anomalies in the Haldane spin-chain system Nd2BaNiO5

TL;DR

This study investigates magnetic, dielectric, and magnetodielectric properties of Nd2BaNiO5, revealing multiple magnetic transitions, MDE coupling, and unique dielectric frequency dependence, highlighting complex interactions in this Haldane spin-chain system.

Contribution

It provides detailed insights into the magnetic and dielectric anomalies and their coupling in Nd2BaNiO5, a light rare-earth Haldane spin-chain compound, including the discovery of a glassy magnetic transition and field-induced effects.

Findings

Magnetic transition at 48 K and a glassy transition near 10 K.

Magnetic-field induced transition around 90 kOe.

Frequency-dependent dielectric step below T_N.

Abstract

We report the magnetic, heat-capacity, dielectric and magnetodielectric (MDE) behaviour of a Haldane spin-chain compound containing light rare-earth ion, Nd2BaNiO5, in detail, as a function of temperature (T) and magnetic field (H) down to 2 K. In addition to the well-known long range antiferromagnetic order setting in at (T_N=) 48 K as indicated in dc magnetization (M), we have observed another magnetic transition near 10 K; this transition appears to be of a glassy-type which vanishes with a marginal application of external magnetic field (even H= 100 Oe). There are corresponding anomalies in dielectric constant as well with variation of T. The isothermal M(H) curves at 2 and 5 K reveal the existence of a magnetic-field induced transition around 90 kOe; the isothermal H-dependent dielectric constant also tracks such a metamagnetic transition. These results illustrate the MDE coupling in this compound. Additionally, we observe a strong frequency dependence of a step in T-dependent dielectric constant with this feature appearing around 25-30 K for the lowest frequency of 1 kHz, far below T_N. This is attributed to interplay between crystal-field effect and exchange interaction between Nd and Ni, which establishes the sensitivity of dielectric measurements to detect such effects. Interestingly enough, the observed dispersions of the T-dependent dielectric constant curves is essentially H-independent in the entire T-range of measurement, despite the existence of MDE coupling, which is in sharp contrast with other heavy rare-earth members in this series.