Abstract :
The effect of R on the ferromagnetic Curie temperatures of two different phases of RMn0.5Co0.5O3 (R=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy) has been studied. For both high-Tc and low-Tc phases of RMn0.5Co0.5O3, Tc decreases with decreasing ionic radius of R3+ and the tolerance factor. The rate of decrease of Tc is larger for the high-Tc phases containing Mn3+ and low-spin Co3+ when compared to the low-Tc phases containing Mn4+ and Co2+, indicating that the Mn3+–O–Mn3+ superexchange interactions are more susceptible to internal pressure effect of R3+ when compared to the effect on the Mn4+–O–Co2+ superexchange interactions.
