Multiferroicity and magneto-electric effect in Gd$_2$BaNiO$_5$

TL;DR

This study reports the discovery of multiferroic behavior in Gd$_2$BaNiO$_5$, showing coupled magnetic and electric properties with field-induced transitions, driven by spin-phonon interactions.

Contribution

It provides new experimental evidence of magneto-electric effects and spin-reorientation transitions in Gd$_2$BaNiO$_5$, a Haldane chain compound, highlighting its multiferroic potential.

Findings

Electric polarization appears in the magnetically ordered state.

Magnetic and dielectric anomalies occur at two magnetic transitions.

Field-induced spin-flop and meta-electric transitions are observed.

Abstract

We report the observation of electric polarization in the magnetically ordered state of the Haldane chain compound, Gd$_2$BaNiO$_5$, with strongly correlated magnetic and dielectric properties. The results of dc magnetic susceptibility and heat capacity measurements indicate two magnetic transitions,one corresponding to the anti-ferromagnetic order at T$_N$ around 55 K and the other to spin-reorientation transition at T$_{SR}$ around 24 K. The dielectric permittivity ($\epsilon'$) and loss (tan$\delta$) also exhibit anomalies in the vicinity of T$_{SR}$ and T$_N$ respectively. Below the spin-reorientation transition, concurrently magnetic-field-induced spin-flop and the meta-electric transitions are observed at a critical magnetic field in isothermal magnetization and magneto-dielectric results respectively. Another interesting finding is that the change in dielectric constant changes its sign at the critical magnetic field. The origin of the observed magneto-electric effect is discussed on the basis of spin-phonon coupling.