Conductivity jumps and low-temperature magnetoresistance in the new semiconducting perovskites La1− x BixMnO3+δ

Abrupt jumps are observed on the temperature dependences of the electrical conductivity of La_{1− x} Bi_xMnO_3+δ (0.1<x<0.7) and La_0.3Bi_0.7Na_0.1MnO_3+δ ceramics. The temperatures at which the jumps take place can be reduced by several degrees by applying an external magnetic field of 15 kOe. It can be seen from the magnetization data that the poorly conducting low-temperature phase is not antiferromagnetic (it is likely ferromagnetic) and hence the real-space charge ordering mechanism is not sufficient for explaining the experimental results. An interpretation in terms of magnetic phase nonuniformity is proposed. All the samples studied exhibit high low-temperature magnetoresistance. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 250–253 (25 August 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.