Composition dependence of giant magnetoresistance in La_1−xCa_xMnO₃ (0.1≤x≤0.9)

Abstract

We have studied the resistivity (ρ) and the magnetoresistance (MR) in sintered samples of La_1−xCa_xMnO₃ 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.