Effect of bismuth doping on the structural, magnetic, electrical, and thermopower behavior of lanthanum silver manganites

Abstract

The structural, magnetic, electrical, and thermoelectric behaviors of lanthanum silver manganite and lanthanum bismuth silver manganite were thoroughly studied in the present work. Two polycrystalline samples, viz., La0.835Ag0.165MnO3 (LAMO) and La0.67Bi0.165Ag0.165MnO3 (LBAMO) possessing almost constant ratio of Mn3+/Mn4+ were synthesized using the wet chemical method. Phase formation was identified from powder X-ray diffraction and it has been confirmed through the structural analysis of which samples crystallize into rhombohedral symmetry with R-3C space group. Apparent changes at phase transition temperature were observed in temperature-dependent resistivity, magnetization and thermoelectric power behavior for bismuth-doped samples. In addition, an enhanced magnetoresistance was observed in LBAMO samples and is attributed to the presence of both ferromagnetic and anti-ferromagnetic states. The temperature-dependent resistivity data in the temperature range (50–300 K) were analyzed using the phase separation model. Spin-dependent scattering and electron–electron interactions were considered to explain the resistivity minimum in the low temperature region (T < 50 K). The Seebeck coefficient is positive and enhances around the transition temperature by substituting bismuth into LAMO. The high-temperature thermoelectric power data were explained in the framework of small polaron hopping mechanism while magnon drag effect dominates in the low temperature region.