Persistence of large magnetodielectric coupling anomalies and multiferroicity for significant dilution of Tb sublattice by Y in Tb_2BaNiO_5

摘要

We report temperature dependence of dc magnetization, heat capacity, dielectric, magnetodielectric (MDE) coupling, and pyrocurrent on polycrystalline specimens resulting from a gradual dilution of Tb sublattice by Y in an exotic multiferroic Haldane spin-chain system, Tb2BaNiO5, viz., for the series Tb2-xYxBaNiO5 (x = 0.1, 0.2, 0.5, 1, and 1.5). Among various observations, the ones to be stressed are as follows: (i) The Neel temperature (T-N1 = 63 K) and the second magnetic feature occurring at (T-N2) 25 K get reduced to lower temperatures with increasing x in a linear fashion, with a concomitant lowering of multiferroicity onset temperature below T-N2, scaling essentially with x. This finding emphasizes that local effects due to Tb play a major role on multiferroicity. Clearly, 4f dominates to determine this phenomenon-a rare finding in this field. (ii) The magnitude of the change (Delta epsilon') in the dielectric constant surprisingly gets maximized for x = 0.1 with respect to that of the parent compound, attaining a relatively large value of about 22% at 15 K for a field of 100 kOe, thereby revealing that a delicate balance of nonmagnetic doping or defects in favorable cases can enhance MDE coupling. (iii) Nonmonotonic changes in Delta epsilon' with a magnetic field, also a changing sign for some compositions, reveal interesting metamagnetodielectric behavior. (iv) The magnetoelectric behavior of x = 1.5 composition is found to be somewhat peculiar with respect to that of other compositions. Thus, this solid solution reveals exotic magneto(di) electric coupling anomalies. Published under license by AIP Publishing.