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 ${\mathrm{La}}_{\text{1−x}}{\mathrm{Na}}_x{\mathrm{MnO}}_{\mathrm{3}}$ $\text{(x=0.10,}$ 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 $\text{R3̄C.}$ 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 $\text{x⩾0.15}$ 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.