具有人工晶界的Sr2FeMoO6粉末磁电阻的温度特性

利用固相反应合成了纯相的Sr2FeMoO6多晶块体，并通过机械球磨方法引入了人工晶界，研究了具有此种晶界的Sr2FeMoO6粉末磁电阻的温度特性．X射线衍射分析表明，机械球磨过程没有改变Sr2FeMoO6的晶体结构，但却在晶粒间界处引入了SrMoO4绝缘相，其量随着球磨时间的增加而增加．不同磁场下的磁电阻测量结果表明，由于一定量SrMoO4绝缘相的存在，晶粒间的绝缘隧穿势垒得到加强，更有利于自旋极化电子在晶粒间的隧穿，从而提高了Sr2FeMoO6多晶粉末的低温磁电阻值．然而随着温度的升高，磁电阻值迅速下降，表现出较强的温度依赖关系．这种现象是由于随着温度的升高，电子在晶界局域态间的非弹性跳跃逐渐增强引起的，而晶界局域态是由在晶界附近的大量缺陷构成．分析表明，晶界状态对Sr2FeMoO6多晶粉末磁电阻的温度特性有十分重要的影响．

TEMPERATURE CHARACTERISTICS OF Sr2FeMoO6 POWDER MAGNETORESISTANCE WITH ARTIFICIAL GRAIN BOUNDARY

Sr-2FeMoO-6 polycrystalline bulk material was synthesized by the solid state reaction technique. The artificial grain boundary was introduced by using the ball milling method, and the temperature character of Sr-2FeMoO-6 powder magnetoresistance with such interfacial state was investigated. From X ray diffraction data, it was found that the crystal structure of Sr-2FeMoO-6 polycrystalline was not changed by the balling milling process, however, the SrMoO-4 insulating phase were introduced at the grain boundaries, and their quantity increased with the milling time increasing. The magnetoresistance measurement results under different magnetic fields showed that at low temperatures, the magetoresistance was enhanced by the reinforcement of the tunneling barriers at the grain boundaries. This behavior was related to the increasing quantity of the SrMoO-4 insulating phase as the tunneling barriers. The existence of the SrMoO-4 insulating phase improved the spin polarized electron inter granular tunneling. However, as the temperature increased, the magnetoresistance showed strong temperature dependence, which was due to the increasing intensity of the inelastic hopping through localized states at the grain boundaries. The study suggested that the interfacial state played an important role in the temperature character of Sr-2FeMoO-6 powder magnetoresistance.