Studies on magneto-resistance, magnetization and thermoelectric power of Cr substituted La_0.65Ca_0.35Mn_1-xCr_xO₃ (0≤x≤0.07) manganites

Abstract A systematic investigation has been carried out on effect of Cr-doping on structural, magneto-resistance, magnetic and thermoelectric power properties of La_0.65Ca_0.35Mn_1-xCr_xO₃ compounds. Samples were prepared using conventional solid state reaction method. The XRD analysis using Rietveld refinement reveals that the samples are single phased. Temperature dependent electrical resistivity measurements show the existence of the expected metal-insulator transition (T_MI) which is followed by a small hump at temperatures lower than T_MI. With the application of magnetic field, resistivity of all the samples is found to decrease and T_MI is observed to shift towards higher temperature. This is attributed to induced magnetic ordering of the localized t_2g spins and increased electron transfer integral between Mn³⁺/Mn⁴⁺ via oxygen by the application of magnetic field. MR% is observed to increase with the increasing Cr concentration. Magnetic studies show that the Curie temperature, T_C and magnetic moment decreases with Cr-content which is consistent with the electrical studies. Electrical resistivity and thermoelectric power data have been analyzed using theoretical models and both suggest that the small polaron hopping (SPH) model is operative in the high temperature insulating region for the entire series of samples.