Effect of NiO impurity on the magneto-transport properties of the La0.7Ba0.3MnO3 granular manganite

Magnetoresistive, magnetic and thermoelectric properties of the La_0.7Ba_0.3MnO₃/xNiO system are studied. The x-ray diffraction shows the coexistence of the NiO and the La_0.7Ba_0.3MnO₃ phases in doped composites, revealing their interaction lack. This suggests the precipitation of the NiO at grain boundaries and on the La_0.7Ba_0.3MnO₃ surface, interrupting the conduction between grains. Hindering the direct contact between the La_0.7Ba_0.3MnO₃ grains increases the resistivity and decreases the metal-semiconductor transition temperature, leading to the spin tunneling effect. This enhances the room temperature magnetoresistance of the La_0.7Ba_0.3MnO₃ compound from -11.25% to -42.7% and -17.24% for 5% and 20% of the NiO additive amount, respectively. The pristine La_0.7Ba_0.3MnO₃ compound shows a Curie temperature value of 348 K that fluctuates negligibly with the NiO addition. However, it decreases to 332 K at the x = 0.05 composite due to a tiny diffusion of NiO in the La_0.7Ba_0.3MnO₃ lattice at this composite. The thermoelectric power properties of the La_0.7Ba_0.3MnO3 compound are changed with the NiO addition. Where the hole conduction interval increases and the peak of the Seebeck coefficient is shifted towards higher temperatures.