Effect of Internal Pressure on Charge-Ordered Rare Earth Manganates

The effect of internal pressure on charge-ordered rare earth manganates of the compositionLn 1−x A x MnO3(Ln=La, Pr, Nd andA=Ca, Sr) has been studied by varying the average radius of theAsite cations (〈r A 〉). Increasing 〈r A 〉 is generally accompanied by an increase in the ferromagnetic transition temperature and a decrease in the charge-ordering transition temperature. On increasing the size of theAsite cations by appropriate substitution, charge-ordered insulators such as Pr0.7Ca0.3MnO3and Nd0.5Ca0.5MnO3become ferromagnetic, accompanied by an insulator-metal transition. In Pr0.5Sr0.5MnO3, substitution of La in place of Pr destroys the antiferromagnetic transition and favors the ferromagnetic metallic state.