非正分钙钛矿锰氧化物(La_(0.8)Sr_(0.2))_(1-x)MnO_3的电磁特性

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

报道了A位缺位的钙钛矿锰氧化物(La0.8Sr0.2)1-xMnO3(0≤x≤0.30)多晶样品的相结构、磁性和磁电阻效应。实验表明,当x≥0.20时,化合物主要由磁性钙钛矿相和非磁性Mn3O4相所组成。它们的电阻率随温度的变化曲线均具有双峰特征,高温侧的电阻率峰出现在钙钛矿相的居里温度附近,低温侧的电阻率宽峰则是金属导电性的钙钛矿晶粒和高电阻率的半导体或绝缘体导电性的晶界或相界共同作用的结果。样品的零场电阻率ρo随着A位缺位量x的增大而增大。适当改变x值,可以改善磁电阻比的温度稳定性。当x=0.30时,化合物磁电阻比MR在一个相对宽的温度范围内(175～328K)基本上保持不变,即MR=(9.1±0.5)%。

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.