Investigation on magnetic, electrical and thermoelectric power of Bi-substituted La_0.8Ca_0.2MnO₃ manganites

Abstract In the present work, the structural, magnetic, magneto-transport and thermoelectric properties of polycrystalline compounds of La_0.8-xBi_xCa_0.2MnO₃(0≤x≤0.1) compounds are reported. Structure refinement using Rietveld method confirms that the samples are single phased and crystallize in rhombohedral structure with R-3C space group. Magnetic studies reveal that the pristine sample exhibits T_C at 221 K and it shift towards lower temperature with Bi doping. Deviation of the temperature dependent of inverse susceptibility curves from the Curie-Weiss law confirms the existence of Griffiths-like phase. All the samples exhibit metal to insulator transition at temperature T_MI, which is found to decrease with increase in Bi doping which is consistent with the magnetic studies. Magneto-resistance MR% data shows that its peak value increases with Bi-doping. The analysis of electrical resistivity data in the metallic region (T<T_MI) suggests that the electron-electron scattering is predominant in this region whereas the insulating region (T>T_MI) is well described using Small polaron hopping (SPH) and Mott's variable range hopping (VRH) models. Analysis of thermoelectric power data in the high temperature region suggests that the SPH mechanism is operative in this regime, while the analysis of low temperature data reveals that the electron-magnon scattering is dominant in the region.