| Summary: | The magnetic and transport properties of La2/3Ba 1/3(Mn1-xAlx)O3 (x50.0, 0.1, 0.2, 0.3 and 0.4) compounds, prepared by the solid state reaction, have been investigated. Samples show a metal-insulator transition excluding the sample x=0.0. With increased Al doping, the metal- insulator transition temperature Tp is shifted to lower temperatures. Grain size reduction leads to a larger resistivity and a decrease in Tp. Upon analysing the data using several theoretical models, it was found that the metallic (ferromagnetic) part of the resistivity ρ (below Tp) fits well with the equation ρ=ρ0+ρ2T2, where ρ0 is due to the importance of grain/domain boundary effects, and a second term ρ2T2 might be attributed to the electron-electron scattering. The microstructure results indicate that the porosity of the samples increased when the concentration increased. The magnetoresistance (MR) is defined as %MR5100×[ρ(H, T)-ρ(0, T)]/ρ(0, T)], where ρ(H, T) and ρ(0, T) are the resistivities at temperature T, with an applied magnetic field H and zero applied magnetic field respectively. All samples show low-field magnetoresistance and high-field magnetoresistance regions. The highest percentage of LFMR at a temperature of 100 K is ∼210% MR/Tesla, measured for the sample x=0.2. For x=0.3, the sample reveals the highest colossal magnetoresistance value among other doped compounds with 27.27% at 100 K. © W. S. Maney & Son Ltd. 2009.
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