The effect of annealing process on the physical properties of La1−xNaxMnOy

Abstract The effect of Na doping and annealing time on the structure, electrical properties, magnetoresistance and thermopower properties has been investigated in perovskite La 1− x Na x MnO y ( x =0.025, 0.075 and 0.1) systems. La 1− x Na x MnO y crystallizes in a single-phase rhombohedral structure. It is observed a simultaneous occurrence of the ferromagnetic to paramagnetic state and metallic to insulating state. In the meanwhile, a large negative magnetoresistance with low applied magnetic field is observed. In addition, ρ ( T ) curves for Na-doped samples exhibit another broad transition T ms2 below T ms . Such double peak behavior in the ρ ( T ) curve interpreted by the electronic inhomogeneity in the samples. The sign of S changes from positive to negative depending on composition. The values of Seebeck coefficient are small (in the microvolt range).