Electric and magnetic properties of non-stoichiometric (La_(0.8)Sr_(0.2))_(1-x)MnO_3 perovskite manganites

Phase structures, magnetic properties and magnetoresistance effect of the polycrystalline perovskite manganites with A site vacancy, (La_(0.8)Sr_(0.2))_(1-x)MnO_3 (0≤x≤0.30), have been studied. Experiments show that the compounds obviously consist of a magnetic perovskite phase and a non-magnetic Mn_3O_4 phase as x increases. The resistivity vs temperature curves present a duo-peak behavior. The resistivity peak in the side of higher temperature occurs near the Curie temperature, while the other one in the side of lower temperature was caused by the interaction of the perovskite grains with the metal-conductivity and the grain boundaries with the semiconductive or isolative conductivity. The zero-field resistivity ρ_o of the samples increases with increasing x. The temperature stability of the magnetoresistance ratio can be improved by a proper change of x. For x=0.30 the magnetoresistance ratio (9.1±0.5)% remains unchanged basically in a relatively wider temperature region from 175K to 328K.