Abstract
We report the observation of electric polarization in the magnetically ordered state of the Haldane chain compound, Gd2BaNiO5, 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 TN ∼ 55 K and the other to spin-reorientation transition at TSR ∼ 24 K. The dielectric permittivity (ϵr′) and loss (tanδ) also exhibit anomalies in the vicinity of TSR and TN, 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 Δϵr′ (=(ϵr′(H)−ϵr′(0))/ϵr′(0)) 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.
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