Study of the magneto transport properties at room temperature in lacunary ceramics La_0,8-x□_xNa_0,2-x□_xMnO₃ in site A

In this paper, we present the effect of lanthanum (La) and sodium (Na) vacancies in site A on the morphological, structural, magnetic, and electrical properties of La_0,8-x□_xNa_0,2-x□_xMnO₃ compounds with x = 0.00, x = 0.05, and x = 0.075 prepared with the sol–gel method. The results of the X-ray powder diffraction diagrams show that these samples crystallize in a rhombohedral structure deformed with the space group R$\overline{3}$c, while electron microscopy was carried out for the surface morphology. From the magnetic measurements, the transition from a ferromagnetic (FM) state to a paramagnetic (PM) state in the vicinity of Curie temperature T_C is detailed. Moreover, in the electrical part, we study the gap effect on the transition temperature T_MI; thus, the nature of the charge transport for the resistance behavior in the different regions (low temperature, metallic, and insulating) has been explained by different models. This work is completed by explaining the two types of magnetoresistance (MR) observed as a function of temperature and applied magnetic field: low-temperature extrinsic magnetoresistance (EMR) and high-temperature intrinsic magnetoresistance (IMR) have been found to be conserved (≈ 30 ℅) with decreasing precursor percentage at room temperature.