Electrical behavior of some rare-earth-doped Nd0.33Ln0.34Sr0.33MnO3 manganites

A series of rare-earth-doped Nd–Sr–Mn–O manganites having the compositional formula Nd0.33Ln0.34Sr0.33MnO3, (where Ln=Gd, Eu, Sm, Nd and Ce) were prepared by citrate-based sol–gel route with ethylene glycol as a gelating reagent. After characterizing the samples by X-ray diffraction and scanning electron microscopy, a systematic study of magnetic susceptibility, electrical resistivity and magnetoresistance has been carried out over a temperature range 80–300 K. The variation of both electrical and magnetic transition temperatures with average ionic radii of A-site cation is explained.The electrical resistivity data were analyzed using different theoretical models and it has been concluded that at low temperatures (ferromagnetic metallic region) the resistivity may originate from grain/domain boundary, electron–electron scattering and two-magnon scattering effects, while in the paramagnetic insulating regime, the variation of resistivity with temperature may be explained by adiabatic small polaron and variable-range hopping mechanisms. The values of activation energies are found to decrease, while the density of states at the Fermi-level, N(EF) are increasing with increasing 〈rA〉. A suitable explanation for the observed behavior is given.