Structural, magnetotransport and thermal properties of Sm substituted La0.7−xSmxBa0.3MnO3 (0≤x≤0.2) manganites

Abstract

In the present paper we studied the structural, magnetotransport and thermopower properties of a series of polycrystalline La0.7−xSmxBa0.3MnO3 (0≤x≤0.2) compounds which were synthesized by conventional solid state reaction techniques. The Rietveld refinement of the X-ray diffraction pattern predicts the formation of single-phase compositions and doping of La3+ by Sm3+ ion converted the chemical structure form rhombohedral (R-3C) to orthorhombic (Imma) The scanning electron microscopy show clean smooth and densified structure images be a sign of good crystalline nature of the samples. The temperature dependent electrical resistivity is measured by standard four-probe method between 5 and 300K exhibits Metal–Insulator Transition MIT which shows the decreasing trend with increasing Sm doping content and metallic state (T<Tp2) that signifies importance of electron-electron, electron–phonon and electron-spin fluctuation scattering process. The metal–insulator transition temperature (Tp2) is observed which decreases with the increase in doping content when magnetic field is applied. The resistivity data in high temperature region (T>Tp2) are explained within the framework of variable range hopping (VRH) and small polaron hopping (SPH) models. The application of magnetic field suppresses the resistivity in entire temperature range and with increasing the Sm3+ content the samples showed very high magnetoresistance. The thermoelectric power (S) of the reported samples exhibit a crossover from positive to negative value and it increases in doped samples. The analysis of thermoelectric power data confirms the applicability of the small polaron hopping model in high temperature region and in low temperature fitted to an equation containing diffusion, magnon drag, phonon drag and electron-spin fluctuation term. An appropriate justification for the observed behavior is specified.