Abstract
We investigated the crystallographic, transport and magnetic properties of a strongly electron correlated La 0.7 (Ba 1-x Pb x ) 0.3 MnO 3+δ series with x = 0-1.0. All our samples are in a rhombohedral R3̄c structure of lattice parameters a∼0.550 nm and c∼1.338 nm. We found that the addition of the larger Pb ion in La 0.7 (Ba 1-x Pb x ) 0.3 MnO 3+δ system does not apparently affect on the metal-insulating and magnetic ordering temperatures as well as the magnetoresistance (MR) ratio. However, it reduces the sintered temperature and improves the electric conductivity. The MR ratios are monotonically linear decreasing with temperature from ∼ 25% at 5 K down to ∼ 6% at 300 K for all samples. The chemical disorder effect of the Pb 2+ substitution does not change the magnetic properties at low temperatures. It can be contributed to exhibiting the constant hole concentration due to the same ratios of [Ba 2+ ] + [Pb 2+ ]/[La 3+ ] and [Mn 4+ ]/[Mn 3+ ] in these Pb doping manganese oxides. The cluster glass behavior was apparently observed, even for the parent sample of x = 0. © 2003 Elsevier Science B.V. All rights reserved.