GIANT MAGNETORESISTANCE IN BULK SAMPLES OF LA(1-X)A(X)MNO(3) (A=SR OR CA)

Magnetoresistance measurements have been carried out on bulk samples of several members of the La(1-x)A(x)MnO(3) family (A = Sr and Ca) with varying x or Mn4+ content. The magnitude of magnetoresistance (MR) is highest at the insulator-metal (I-M) transition when the transition temperature is relatively low (less than or similar to 250 K). The relative MR (%MR) is essentially the same (40-50%) at 4.2 K for all the compositions showing the I-M transition, namely similar to 15% at T greater than or similar to 300 K. Insulating compositions (small or large x) show smaller %MR than the compositions that undergo the I-M transition. (C) 1995 Academic Press, Inc.