Influence of Nd doping on the magnetoresistance of La _0.7-x Nd _x Pb _0.3MnO ₃

This paper presents an investigation on the magnetoresistance properties of the polycrystalline manganite oxides, La _0.7-x Nd _x Pb _0.3MnO ₃ (x=0.0, 0.1, 0.5 and 0.7). We demonstrate that the magnetoresistance ratio is enhanced with the increase of Nd content due to the suppression of spin scattering in the presence of an applied magnetic field. We find that the magnetoresistance shows an increase with decreasing temperatures at low temperatures. These features have been conventionally attributed to spin-polarized tunneling at grain boundaries. The temperature dependence of the magnetoresistance can be described quite well by an expression of the type a+b/(T+c). At high temperatures the magnetoresistance ratio increases with increasing temperature and the resistivity shows the existence of the variable range hopping with Coulomb effects for x=0.5 and 0.7.