Magnetoelectric coupling in the Haldane spin-chain system Dy2BaNiO5

We report the results of various measurements, namely magnetization, complex dielectric permittivity, and electric polarization ($P$), on Dy${}_{2}$BaNiO${}_{5}$ as a function of temperature ($T$) and magnetic field ($H$), apart from heat capacity ($C$), with the primary motivation of exploring the existence of magnetoelectric (ME) coupling among Haldane spin-chain systems. The $M$($T$) and $C$($T$) data establish long-range magnetic ordering at 58 K. The most noteworthy observations are: (i) Distinct anomalies are observed in the dielectric constant (\ensuremath{\epsilon}\ensuremath{'}) vs $T$ and loss (tan\ensuremath{\delta}) vs $T$ at different temperatures (i.e., 12.5, 30, 50, and 58 K); at low temperatures, three magnetic-field-induced transitions are observed in \ensuremath{\epsilon}\ensuremath{'} vs $H$ at 6, 40, and 60 kOe. These transition temperatures and critical magnetic fields track those obtained from magnetization data, establishing the existence of strong magnetoelectric coupling in this compound. (ii) Correspondingly, electric polarization could be observed as a function of $T$ and $H$ in the magnetically ordered state, thereby indicating magnetism-induced ferroelectricity in this compound; this result suggests that this compound is a possible multiferroic material among spin $=$1 (nickel-containing) compounds, with successive magnetic transitions and strong magnetoelectric coupling.