The transport and magnetic properties of La-Pb-Mg-Mn-O manganites at low temperatures

The structure, transport properties and the magnetoresistance behavior in the temperature interval 77-400 K of the perovskite-like lanthanum manganites La0.6Pb0.4−xMgx+yMnO3 (x=0, 0.1, 0.2 and y=0, 0.2) were investigated. Polycrystalline bulk samples were prepared by sol-gel self-combustion and subsequent heat treatment at 1000 °C for different times, 40, 80, 160 and 320 min. All manganites exhibit a peak in the resistivity around 200-250 K, below the ferromagnetic ordering temperature (320-330 K). An isotropic and negative magnetoresistance has been observed in all compounds. Magnetoresistance MR exhibits a peak in the temperature range 130-150 K, below SC-metal transition temperature. Magnitude of MR at the peaks was nearly 27% in the magnetic field of 2 T. At room temperature, a magnetoresistance of 9.5% for La0.6Pb0.2Mg0.2MnO3 composition was obtained. Longer heat treatment time enhanced the magnetorezistive properties.