Magnetoresistance of metallic perovskite oxide LaNiO$_{3-\delta}$

We report a study of the magnetoresistance (MR) of the metallic perovskite oxide LaNiO 3 − δ as a function of the oxygen stoichiometry δ ( δ ≤ 0.14), magnetic field ( H ≤ 6 T ) and temperature (1.5K ≤ T ≤ 25K). We find a strong dependence of the nature of MR on the oxygen stoichiometry. The MR at low temperatures change from positive to negative as the sample becomes more oxygen deficient ( i.e, δ increases). Some of the samples which are more resistive, show a resistivity minima at T min ≈ 20K. We find that in these samples the MR is positive at T ¿ T min and negative for T ¡ T min . We conclude that in the absence of strong magnetic interaction, the negative MR in these oxides can arise from weak localisation effects.