Behavior of low-temperature magnetoresistance in some LaMnO3-based compounds

Electrical, magnetic, galvanomagnetic, and electron microscopy studies of L a0.9Ce0.1MnO3+delta, LaMnO3+delta, and La0.5Na0.2Bi0.3MnO3+delta ceramics h ave been performed. It is shown that the temperature dependence of resistiv ity for La0.9Ce0.1MnO3+delta has two peaks. The peak observed at a lower te mperature does not correspond to the Curie temperature T-C and, thus, can h ardly be attributed to magnetic order in the material. Below T-C, magnetiza tion in the fields lower than 3 kOe is almost independent of temperature be cause of a strong effect of the internal demagnetizing field on the magneti zation process. It is revealed that below T-C the absolute value of magneto resistance Delta rho is almost independent of temperature. An assumption is made about the dominant contribution of the carrier scattering by fluctuat ions of the electrostatic potential at grain boundaries into the low-temper ature magnetoresistance.