The magnetoresistance of (Tb1−x Smx)0.6Sr0.4MnO3+γ manganites

(Tb1−x Smx)0.6Sr0.4MnO3γ compounds were obtained by sol–gel method, by using oxides and acetates. The compounds were sintered in O2 atmosphere at 1200 °C. The samples contain only a perovskite phase, with orthorhombic (Pnma) structure. Dependence of the tolerance factor and of the variance vs. chemical composition of the samples was observed. An increase of Tb concentration leads to a sudden decrease of the specific magnetization of the samples, but has little influence on the Curie temperature. A typical magnetoresistance behaviour (a maximum of the resistivity vs. T) was observed for the sample without Tb. The samples containing Tb have a decrease of the resistivity (ρ) vs. the intensity of the applied magnetic field and with the increase of the temperature (dρ/dT <0, typical for a semiconductor). An increase of the activation energy of the charge transport takes place with the increase of the Tb concentration in the samples.