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 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 Nd0.5Sr0.5MnO3 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 Tc−Tco 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.