Suppression of long-range ordering and multiferroicity in Sr-substituted Ba3−xSrxMnNb2O9 (x = 1 and 3)

Abstract

Effects of Sr substitution at A-site in ordered perovskite Ba3−xSrxMnNb2O9 (x = 1 and 3) have been investigated using X-ray diffraction, magnetization, dielectric/magnetodielectric and neutron diffraction measurements. The parent compound Ba3MnNb2O9 having a large spin (S = 5/2) is known to exhibit type-II multiferroic properties with quasi 2D triangular lattice antiferromagnetic ground state. A slight perturbation in exchange interaction due to substitution of smaller size isovalent ion at the A-site in Ba3−xSrxMnNb2O9 (x = 1 and 3) has been found to alter the ground states drastically and hence the multiferroicity. The crucial role of various fluctuations (quantum and/or thermal), weak lattice distortion induced by Sr substitution and slight imbalance between different fluctuations in determining the ground states and the multiferroicity is discussed and compared with the results of smaller spin compounds (S = 1/2 or 1).