Magnetoelectric behavior of sodium doped lanthanum manganites

Nanocrystalline samples of sodium doped manganites with compositional formula La1−xNaxMnO3 (0.025⩽x⩽0.25) were prepared by polyvinyl alcohol assisted precursor method. After characterizing the samples by x-ray diffraction and transmission electron microscopy a systematic investigation of electrical, magnetic, and thermopower properties has been undertaken. The resistivity data were analyzed using effective medium approximation. From the analysis it has been found that the metallic fraction is increasing up to x=0.10 and remains constant with further doping. A close examination of the resistivity data clearly indicates that the sodium doped samples are slowly transformed from colossal magnetoresistance behavior to charge ordering behavior. Thermoelectric power data at low temperatures were analyzed by considering the magnon drag concept, while the high temperature data were explained by small polaron conduction mechanism.