Effect of substitution of Mn3+ by Ni3+ and Co3+ on the charge-ordered states of the rare earth manganates, Ln0.5A0.5MnO3

Substitution of Mn3+ in Nd0.5Sr0.5MnO3 by Ni3+ and Co3+ upto 5% destroys the charge-ordered (CO) state and renders the material ferromagnetic and metallic. In Nd0.5Ca0.5MnO3, the charge-ordering transition temperature, T CO, decreases with increase in the Ni3+ or Co3+ content and the ferromagnetic metallic state occurs below T CO. Substitution of Ni3+ or Co3+ has no effect on the CO state of Y0.5Ca0.5MnO3, showing thereby that such substitution effects delineate the different types of CO states caused by differences in the average size of the A-site ions. The presence of empty eg orbitals in the substituent transition metal ion appears to be necessary for destroying the CO state in these manganates.