颗粒尺寸对多晶La2／3Ca1／3Mn1-xCuxO3低场磁电阻的影响

采用溶胶-凝胶法制备了不同颗粒尺寸的La2/3Ca1/33Mn1-xCuxO3(x=0.04)系列试样。X射线衍射实验说明Cu掺杂和不同温度烧结没有改变晶体的结构。电阻-温度实验曲线表明，随颗粒尺寸的减少，半导体-金属转变温度（Tp）向低温方向移动。磁电阻曲线显示，随颗粒尺寸的减少，与颗粒晶界有关的磁电阻在25K恒温、0.4T低场下由25%增加到了51%。实验结果表明，在La2/3Ca1/3MnO3中少量Cu掺杂和小颗粒尺寸可以实质性地提高与颗粒晶界有关的低场磁电阻效应。

Influence of Grain Size on Low-field Magnetoresistance of Polycrystals La2/3Ca1/3Mn1-xCuxO3

The La2/3Ca1/3Mn1-xCuxO3(x=0.04)samples with different grain size were prepared by sol-gel method. The x-ray diffraction proves that all the samples are single phase and Cu doping and different sintering temperature do not change the lattice structure. Resistance versus temperature shows that semiconductor-metal transition moves to low temperature along with grain size decreasing. The experiment show that intergrain magnetoresistance increase from 25% to 51% in 25 K and 0.4 T as grain size decrease. The result of experiment indicates that intergrain magnetoresistance effects are substantially improved by lower level Cu doping in La2/3Ca1/3MnO3 polycrystals synthesized at low temperature and by minimizing grain size.