多晶Sr2Fe1－xAlxMoO6的晶粒内低场磁电阻效应

用传统的固相反应法合成了Fe位掺杂Al的双钙钛矿型氧化物Sr2Fe1-xAlxMoO6 (x=00，005，010，015，03)多晶材料. x射线衍射和扫描电子显微分析显示，在Fe位掺杂Al既没有引入杂相，也没有明显改变Sr2FeMoO6多晶材料的晶粒尺寸和晶界状态. 非磁性Al离子的掺杂使晶粒内部磁有序区细化成更小的区域，同时使反铁磁区内的磁耦合作用变弱. 这一方面提高了亚铁磁区磁化方向的磁场灵敏度；另一方面也降低了反铁磁区对自旋相关电子的散射；两方面的共同作用使Sr2FeMoO6的低场磁电阻效应明显增强，但这种尺寸效应也使材料的磁电阻在高温下下降得更快. 关键词： 低场磁电阻 掺杂 自旋极化电子

Large intragranular low field magnetoresistance in polycrystalline Sr2Fe1-xAlxMoO6 compounds

Polycrystalline powders of the family of compounds Sr 2Fe 1-xAl xMoO 6 (x=0, 0.05, 0.10, 0.15, 0.30) were prepared accord ing to the standard solid_state reaction . XRD patterns and SEM images show that the structure and t he grain size of these compounds were not changed and no impurity was observed b y doping with Al in Sr 2FeMoO 6. In the cationic ordered segregation, a large ferrimagnetic patch can be separate d into some smaller ones by the Al doping. So the chain of the ferrimagnetic exch ange path will be shortened and the strength of exchange will be weakened. There fore, their moments become more sensitive to external field. Furthermore, when t he Al ion replaces the Fe ion in the disordered segregation, the antiferromagnetic coupling becomes weaker. As a result, the low_field magnetoresistance is enha nced. But the smaller ferrimagnetic segregates become more sensitive to thermal agitation at high temperatures. The weakness of the Al_doped SFMO l ies in its stronger temperature dependence of the saturated moments and the low_ field magnetoresistance.