Electrical transport properties of LaXO3+δ (X = Mn, Co, Ni)

We report here the resistivity (1.8 K < T < 300 K) and magnetoresistance (0 < H < 7 Tesla) measurement of perovskite oxides LaMnO3+δ, LaCoO3+δ and LaNiO3+δ. The sample LaMnO3+δ shows a small increase in resistivity in the low temperature range below 30 K. It also shows a large resistivity peak and large negative magnetoresistance in the temperature range about 250 K which can be ascribed to the double exchange mechanism due to the presence of mixed valency of manganese (Mn3+/Mn4+) in this compound. The LaCoO3+δ sample shows a sharp fall in the resistivity near 50 K and after that a semiconducting behaviour which is due to the combined effect of spin state transition of the Co ion and the typical thermal activation of the semiconductors. The LaNiO3+δ sample shows a metal to semiconducting type of transition near 135 K which shifts towards higher temperature with the application of magnetic field. (author)