EFFECT OF INTERNAL-PRESSURE ON CHARGE-ORDERED RARE-EARTH MANGANATES

The effect of internal pressure on charge-ordered rare earth manganate s of the composition Ln(1-x)A(x)MnO(3) (Ln = La, Pr, Nd and A = Ca, Sr ) has been studied by varying the average radius of the A site cations ([r(A)]). Increasing [r(A)] is generally accompanied by an increase i n the ferromagnetic transition temperature and a decrease in the charg e-ordering transition temperature. On increasing the size of the A sit e cations by appropriate substitution, charge-ordered insulators such as Pr0.7Ca0.3MnO3 and Nd0.5Ca0.5MnO3 become 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. (C) 1998 Academic Press.