Effect of Sr-doping concentration on structure and phase-separation between ferromagnetic and paramagnetic phases in lanthanum manganite oxide

The perovskite La₁Sr_xMnO₃ (LSMO) nanocrystalline compounds with the doping concentration x in the range of 0.2~0.5 have been synthesized by combustion method using the pair of citric acid and ethylene glycol as a burning fuel. It was found that the sintering temperatures at which the compounds began forming the single-phase of LSMO increased from 900 °C up to 1200 °C corresponding to the increasing of Sr-doping content. X-ray pattern investigations presented the crystalline sizes of all samples sintered at 1200 °C evidently reduced from 77.7 nm to 18.9 nm as the doping concentration x increases. The effects of Sr-doping levels on Mn⁴⁺/Mn³⁺ ratio as well as on their electrical resistivity are also studied by X-ray photoelectron spectroscopy and four-point probes method, respectively. By using a resistive approximation model, the role of the Sr-doping with respect to the phase-separation between ferromagnetic and paramagnetic phases of these compounds is discussed.