COMPOSITION DEPENDENCE OF GIANT MAGNETORESISTANCE IN LA1-XCAXMNO3 LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.9)

We have studied the resistivity (rho) and the magnetoresistance (MR) i n sintered samples of La1-xCaxMnO3 for 0.1 less than or equal to x les s than or equal to 0.9 in the temperature range 4.2K less than or equa l to T less than or equal to 400K in magnetic fields H less than or eq ual to 6T. We have observed giant negative magnetoresistance in the wh ole composition range, although the magnitude of MR depends on the lev el of doping,the peak in the magnitude of MR [(rho(H) - rho(0))/rho(0) ] at 6T being be as high as 90%. The magnitude of the MR generally inc reases as the temperature corresponding to the MR peak decreases. All the samples with x < 0.5 show a ferromagnetic transition with the temp erature dependence of rho showing a metallic behavior (d rho/dT > 0) b elow the Curie temperature. The sample with x = 0.9 shows insulating b ehavior over the entire temperature range but the MR shows a peak at l ow temperatures.