Grain size effects on charge-ordering, phase segregation and related properties of rare-earth manganates, Nd0.5A0.5MnO3 (A=Ca or Sr)

Grain size has marked effects on charge-ordering and other properties of Nd0.5A0.5MnO3 (A=Ca or Sr). Thus, the antiferromagnetic (AFM) transition in Nd0.5Ca0.5MnO3 is observed distinctly only in samples sintered at 1273K or higher. The sample with a small grain size (sintered at 1173K) 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 Nd0.5Sr0.5MnO3 becomes sharper in samples sintered at 1273K or higher. The sample sintered at 1173K does not show the AFM–CO transition around 150K 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 (<1673K) show evidence for greater segregation of the AFM and FM domains.