Large room-temperature magnetoresistance and phase separation in La1-xNaxMnO3 with 0.1≤x≤0.3

The structural, magnetic, and electronic properties of the polycrystalline La1-xNaxMnO3 (x=0.10, 0.15, 0.20, and 0.30) are investigated. The result of the Rietveld refinement of x-ray powder diffraction shows that these compounds crystallize in a rhombohedrally distorted structure with space group R (3) over barC. The magnetic measurement shows that Curie temperature T-C of the studied samples is near or above room temperature. The temperature dependence of resistivity shows that all samples undergo a sharp transition accompanying a paramagnetic to ferromagnetic with the decrease of temperature, however, for x greater than or equal to0.15 samples, double transition peaks with a single ferromagnetic transition is observed. In the meanwhile, a large room-temperature magnetoresistance with low applied magnetic field is observed. The co-existing ferromagnetic metallic phases and ferromagnetic insulating (FMI) phases induced by the electronic inhomogeneity as well as the additional FMI phases caused by the presence of vacancies at the A sites, are presented to account for the transport properties and large magnetoresistance in these compounds. (C) 2001 American Institute of Physics.