Electronic transport and magnetic studies of La1−xCax−0.08Sr0.04Ba0.04MnO3

Lanthanum based mixed valence manganite system La 1− x Ca x −0.08 Sr 0.04 Ba 0.04 MnO 3 (LCSBMO; x =0.15, 0.24 and 0.33) synthesized through the sol–gel route is systematically investigated in this paper. The electronic transport and magnetic susceptibility properties are analyzed and compared, apart from the study of unit cell structure, microstructure and composition. Second order phase transition is observed in all the samples and significant difference is observed between the insulator to metal transition temperature ( T MI ) and paramagnetic (PM) to ferromagnetic (FM) transition temperature ( T C ). In contrast to the insulating FM behaviour usually observed in La 1− x Ca x MnO 3 (LCMO) for x =0.15, a clear insulator to metal transition is observed for LCSBMO for the same percentage of lanthanum. The temperature dependent resistivity of polycrystalline pellets, when obeying the well studied law ρ = ρ o + ρ 2 T 2 for T T MI , is observed to differ significantly in the values of ρ o and ρ 2 , with the electrical conductivity increasing with x . The variable range hopping model has been found to fit resistivity data better than the small polaron model for T > T MI . AC magnetic susceptibility study of the polycrystalline powders of the manganite system shows the highest PM to FM transition of 285 K for x =0.33.