Two-current spin-dependent conduction in polycrystalline LaMnO[sub 3] produced under oxygen gas flow

Abstract

We have studied two-current spin-dependent conduction in polycrystalline LaMnO3 (LMO) produced under the oxygen gas flow (OGF). The polycrystalline La1−xSrxMnO3 (LSMO) samples were prepared with x = 0, 0.1, 0.125, 0.15, 0.175, 0.2 by use of a solid-state-reaction method. The LMO sample produced under the OGF showed large electrical conduction due to the self-hole-doping caused by the excess oxygen ions in it. The electrical resistivity and magnetoresistance (MR) of the LSMO samples were measured as a function of temperature (4K-300K). With increasing the temperature, we have observed that the MR ratios of the LSMO samples with x ≠ 0 have one maximum, while that of LMO sample has two maxima. The temperature at the maximum of the MR ratio corresponds to the magnetic phase transition temperature. The existence of two MR maxima for the LMO sample is considered to imply that the LMO sample has two regions with different doping levels; the one is the crystalline grain region with low doping and the other is the amorphous-like grain-boundary region with high doping.