LAUSR

In this paper, we have investigated the structure, transport properties and magnetoresistance of the La–Pb–Ca–Mn–O perovskite-manganite system within the temperature interval of 77–400 K and in magnetic field of 1.6 MA/m. Calcium as partial substitute for lead was introduced in the parent composition La0.6Pb0.4MnO3. Polycrystalline bulk samples were prepared by sol–gel self-combustion method and subsequent heat treatment at 1000 °C for 40–320 min. By a moderate substitution with Ca (Ca0.1), the Curie temperature increases by 10°, while for a bigger doping with Ca (Ca0.2), the Curie temperature decreases by 10° as compared with the sample without substitution. The samples exhibit a resistivity peak around 200–225 K, below the ferromagnetic ordering temperature (320–345 K). A negative and isotropic magnetoresistance has been obtained, which exhibits a peak in the temperature range 92–140 K, below electric transition temperature. By a moderate substitution with Ca (Ca0.1), the room temperature magnetoresistance increases (by 12%), while by a larger substitution with Ca (Ca0.2), the low temperature magnetoresistance increases (by 31% at 92 K).