Multiferroicity in a spin-chain compound, Tb2BaCoO5, with exceptionally large magnetodielectric coupling in polycrystalline form

We report the results of detailed investigations of magnetization, heat-capacity, dielectric, pyrocurrent, and magneto(di)electric measurements on Tb2BaCoO5, belonging to a hither-to-unexplored spin-chain cobaltates family, R2BaCoO5 (R= Rare-earths). The magnetic measurements reveal that this compound exhibits an antiferromagnetic transition at (T_N=) 18.8 K and there is a spin-reorientation beyond 40 kOe below T_N. Dielectric and pyrocurrent data measured as a function of temperature and magnetic-field establish that this compound is a type-II multiferroic material. The most fascinating finding which we would like to emphasize is that the observed value of the magnetodielectric effect beyond the metamagnetic transition field is the largest (close to 55%, below 10 K, for H= 100 kOe) ever reported for polycrystals of a compound in bulk form, thereby offering a hope to find a single-phase polycrystalline compound at room temperature to enable ease of applications.