COMPOSITION DEPENDENCE OF GIANT MAGNETORESISTANCE IN LA1-XCAXMNO3 (0.1-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.9)

We have studied the resistivity (rho) and the magnetoresistance (MR) in sintered samples of La1-xCaxMnO3 for 0.1 less than or equal to x less than or equal to 0.9 in the temperature range 4.2K less than or equal to T less than or equal to 400K in magnetic fields H less than or equal to 6T. We have observed giant negative magnetoresistance in the whole composition range, although the magnitude of MR depends on the level 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 increases as the temperature corresponding to the MR peak decreases. All the samples with x < 0.5 show a ferromagnetic transition with the temperature dependence of rho showing a metallic behavior (d rho/dT > 0) below the Curie temperature. The sample with x = 0.9 shows insulating behavior over the entire temperature range but the MR shows a peak at low temperatures.