Abstract
The effect of Pb substitution on the structural, magnetic and transport properties of La0.7Ca0.3−xPbxMnO3 (0≤x≤0.3) manganites have been investigated. The structural characterization has revealed that these samples are single phase. The structural phase of samples transforms from orthorhombic phase (0≤x≤0.10) to monoclinic one (0.15≤x≤0.3). The temperature and magnetic-field dependences of magnetization indicated a gradual increase of the Curie temperature from 250K to 350K with increasing Pb-doping, which is thought to be originated mainly from the increase of the double–exchange interaction. It is found that the resistivity decreases and the metal–insulator transition temperature shifts monotonically towards higher temperature as increasing Pb concentration. Additionally, in applied field H=6T and at the Curie temperature, the magnetoresistance peak shifts to higher temperature as x increases. This shows that CMR can be effectively tuned in La0.7Ca0.3−xPbxMnO3 by changing Pb content. We explained the resistivity versus temperature data measured in the range of 5–400K using the phase-coexistence transport model and found that the activation barrier decreased with raising of Pb2+ ion concentration.
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