Effect of substituting Ru4+ and other tetravalent ions in the B-site of rare earth manganates on the magneto-transport properties and charge-ordering

Substitution of Ti and Zr in the B-site of La0.7Ca0.3MnO3 lowers the T C and the temperature of insulator—metal transition. Substitution of Ru in the B-site of La0.7Ca0.3MnO3, however, does not alter the T C or T IM significantly. More importantly, the effect of substitution of Ti and Zr in the B-site of the charge-ordered Nd0.5Ca0.5MnO3 progressively destroys the charge-ordering in this insulating material. In contrast, substitution by Ru in the B-site renders the material ferromagnetic with the T C increasing with the Ru content and the material also shows insulator-metal transition. This marked effect of Ru substitution on the charge-ordering is also seen in Nd0.5Sr0.5MnO3 where the T C increases with Ru content while charge-ordering gets destroyed. The extraordinary effect of Ru in favouring the ferromagnetic metallic state and destroying the charge-ordering is attributed mainly to its unique electronic configuration (t 2 g 4 eg 0.