Investigation on structural, magneto-transport, magnetic and thermal properties of La_0.8Ca_0.2-xBa_xMnO₃ (0 ≤ x ≤ 0.2) manganites

A systematic study on the structural, electrical, magnetic and thermo-electric properties of La_0.8Ba_xCa_0.2-xMnO₃ (0 ≤ x ≤ 0.2) manganites is carried out in the present work. The samples have been prepared using solid state reaction technique. All the samples are single phased. It is seen that Ba-doping introduces a structural phase transformation viz. from rhombohedral to cubic system. Electric and magnetic studies respectively show that the metal-insulator transition temperature, T_MI and Curie temperature, T_C increase with Ba-content. Magneto-resistance (MR) data shows that it decreases with Ba-doping. Analyses of the electrical transport data in metallic region i.e. T < T_MI shows that the electrical transport is governed predominantly by electron-electron scattering process. On the other hand, the adiabatic small polaron hopping (ASPH) model is appropriate in the high-temperature insulating range viz. T > T_MI. We have used the electrical resistivity data in the entire temperature range (50-300 K) and analyzed using the phenomenological percolation model which is based on the phase segregation mechanism. We have analyzed the Seebeck coefficient data which reveals that the small polaron hopping mechanism is operative in high temperature regime and the low temperature region is examined by taking into account the impurity, electron-magnon scattering, and spin wave fluctuation terms. It is established that the electron-magnon scattering is dominating for the thermoelectric transport below T_MI.