Effect of substitution of Cr3+ in place of Mn3+ in rare-earth manganates on the magnetism and magnetoresistance: Role of superexchange interaction and lattice distortion in LnMn(1-x)Cr(x)O(3)

Magnetic and electrical properties of oxides of the formula LnMn(1-x)Cr(x)O(3) (Ln = rare earth) have been investigated to understand the importance of the Mn3+-O-Cr3+ superexchange interactions, in contrast to the Ln(1-x)A(x)MnO(3)(A = divalent cation) system, where double exchange interactions predominate. All the LnMn(1-x)Cr(x)O(3) compositions are ferromagnetic insulators and exhibit small values of negative magnetoresistance (MR) at ordinary temperatures, the highest value of MR at 6 T being similar to 20% at 120 K for some of the compositions. The results underscore the important role of double exchange, as well as lattice distortion effects, in giving rise to high values of MR in Ln(1-x)A(x)MnO(3). (C) 1996 Academic Press.