Grain size effects on charge-ordering, phase segregation and related properties of rare-earth manganates, Nd_0.5A_0.5MnO₃ (A=Ca or Sr)

Abstract

Grain size has marked effects on charge-ordering and other properties of Nd_0.5A_0.5MnO₃ (A=Ca or Sr). Thus, the antiferromagnetic (AFM) transition in Nd_0.5Ca_0.5MnO₃ is observed distinctly only in samples sintered at 1273 K or higher. The sample with a small grain size (sintered at 1173 K) shows evidence for greater ferromagnetic (FM) interaction at low temperatures, probably due to phase segregation. The FM transition as well as the charge-ordering transition in Nd_0.5Sr_0.5MnO₃ becomes sharper in samples sintered at 1273 K or higher. The sample sintered at 1173 K does not show the AFM-CO transition around 150 K and is FM down to low temperatures; the apparent T_c-T_co gap decreases with the increase in the grain size. The samples sintered at lower temperatures (<1673 K) show evidence for greater segregation of the AFM and FM domains.