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

Abstract

Magnetoresistive, magnetic and thermoelectric properties of the La0.7Ba0.3MnO3/xNiO system are studied. The x-ray diffraction shows the coexistence of the NiO and the La0.7Ba0.3MnO3 phases in doped composites, revealing their interaction lack. This suggests the precipitation of the NiO at grain boundaries and on the La0.7Ba0.3MnO3 surface, interrupting the conduction between grains. Hindering the direct contact between the La0.7Ba0.3MnO3 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 La0.7Ba0.3MnO3 compound from −11.25% to −42.7% and −17.24% for 5% and 20% of the NiO additive amount, respectively. The pristine La0.7Ba0.3MnO3 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 La0.7Ba0.3MnO3 lattice at this composite. The thermoelectric power properties of the La0.7Ba0.3MnO3 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.