Structural, magnetic and magnetotransport behavior of some Nd-based perovskite manganites

A systematic investigation of Neodymium based colossal magnetoresistive manganites with general formula Nd0.67A0.33MnO3, (A=Ca, Sr, Pb and Ba) has been undertaken mainly to understand their structural, magnetic as well as electrical behavior. The materials were prepared by the sol-gel route sintering at 900 °C. After usual characterization of the materials structurally by XRD, their metal-insulator transition (TP) as well as magnetic transition (TC) temperatures were determined and the reasons for the occurrence of ΔTT(TC-TP) values have been explained. X-ray data have been analyzed by using Rietveld analysis and the variations of various parameters are explained. It has been concluded that not only A-site cation radius, 〈rA〉 but also the size variance factor (σ2) influence both the metal-insulator as well as ferro to para magnetic transition temperatures. A systematic study of electrical conductivity of all the four materials was undertaken as a function of magnetic field upto 7 T mainly to understand the conduction mechanism in the presence of magnetic field. On analyzing the electrical resistivity data, it has been concluded that the metallic (ferromagnetic) part of the resistivity (ρ) (below TP) can be explained by electron-electron scattering processes (∼T2) and two magnon scattering processes (∼T4.5), while in the high temperature (T>TP) paramagnetic insulating regime, the adiabatic small polaron and variable range hopping models are found to fit well.