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

Abstract

A systematic investigation of Neodymium based colossal magnetoresistive manganites with general formula Nd 0.67A 0.33MnO 3, (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 ( T P) as well as magnetic transition ( T C) temperatures were determined and the reasons for the occurrence of Δ T T( T C– T P) 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, 〈 r A〉 but also the size variance factor ( σ 2) 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 T P) can be explained by electron–electron scattering processes (∼ T 2) and two magnon scattering processes (∼ T 4.5), while in the high temperature ( T> T P) paramagnetic insulating regime, the adiabatic small polaron and variable range hopping models are found to fit well.