LETTER TO THE EDITOR

Magnetic and electrical properties of oxides of the formulaLnMn1−xCr x O3(Ln= rare earth) have been investigated to understand the importance of the Mn3+–O–Cr3+superexchange interactions, in contrast to theLn 1−x A x MnO3(A= divalent cation) system, where double exchange interactions predominate. All theLnMn1−x Cr x O3compositions are ferromagnetic insulators and exhibit small values of negative magnetoresistance (MR) at ordinary temperatures, the highest value of MR at 6T being ∼20% at 120K 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 inLn 1−x A x MnO3.