Composition dependence of giant magnetoresistance in La1−CaMnO3 (0.1 ≤ x ≤ 0.9)

We have studied the resistivity (ϱ) and the magnetoresistance (MR) in sintered samples of La 1−x Ca x MnO 3 for 0.1 ≤ x ≤ 0.9 in the temperature range 4.2K ≤ T ≤ 400K in magnetic fields H ≤ 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 [ (ϱ(H) − ϱ(0)) ϱ(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 ϱ showing a metallic behavior ( dϱ 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.