Charge ordering, magnetic, electrical transport and thermal transport properties of Nd0.75Na0.25MnO3 manganite

The electron diffraction patterns of Nd0.75Na0.25MnO3 were recorded at various temperatures. Superlattice reflection spots were observed below 170 K, which provides direct evidence of an ordered arrangement of Mn3+ and Mn4+ cations in this compound at low temperature. By further analyzing the diffraction patterns, the Mn3+ and Mn4+ ions were found to form zigzag chains in the a–c plane of the orthorhombic lattice (space group Pnma). The magnetic, electrical-transport and thermal-transport properties of the compound were also studied. It is found that the specimen shows insulator-like characteristics in zero field, whereas a re-entrant ferromagnetic metal transition is observed when a strong magnetic field is applied. The ratio of the thermal conductivity to the electrical conductivity strongly deviates from the Wiedemann–Franz law, even in the ferromagnetic metallic state.