Abstract
The electron diffraction patterns of Nd 0.75Na 0.25MnO 3 were recorded at various temperatures. Superlattice reflection spots were observed below 170 K, which provides direct evidence of an ordered arrangement of Mn 3+ and Mn 4+ cations in this compound at low temperature. By further analyzing the diffraction patterns, the Mn 3+ and Mn 4+ 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.
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