EFFECT OF SUBSTITUTION OF MN3- LA(0.7)A(0.3)MN(1-X)M(X)O(3) (A = CA, SR, PB M = AL, CR, FE, CO)( BY OTHER TRIVALENT CATIONS ON THE COLOSSALMAGNETORESISTANCE AND RELATED PROPERTIES OF THE MANGANATES )

Investigations of the manganates of the general formula La(0.7)A(0.3)M n(1-x)M(x)O(3) with A = Ca, Sr, or Pb and M = Al, Cr, Fe, or Co in the x range 0.00-0.20 have shown that the ferromagnetic T-c and the insul ator-metal transition temperature, T-p, generally decrease with increa se in x, accompanied by an increase in the resistivity at T-p The valu e of the saturation magnetization and, hence, the saturation moment al so decrease with increase in x. The magnitude of magnetoresistance is generally smaller in the Fe and Co substituted systems when A = Pb. Ho wever, with A Sr, we find enhanced colossal magnetoresistance in the 5 0-250 K range when x = 0.1 for M Fe and Co. Interestingly, these syste ms exhibit a nearly flat resistivity curve over this temperature range . (C) 1998 Elsevier Science Ltd.