(La_(1-x)Ce_x)_(2/3)Ca_(1/3)MnO_3体系的结构和输运性质研究  

Study of the structural and transport properties for (La_(1-x)Ce_x)_(2/3)Ca_(1/3)MnO_3system

作　　者：王新燕[1] 曹世勋[1] 张玉凤[1] 津幡健 崔玉建[3] 刘永生[1] 曹桂新[1] 西村克彦 森克德 敬超[1] 张金仓[1] 

机构地区：[1]上海大学物理系,上海200436 [2]富山大学工学部 [3]中国计量学院物理系,杭州310034

出　　处：《物理学报》2004年第5期1456-1462,共7页Acta Physica Sinica

基　　金：国家自然科学基金 (批准号 :10 2 740 49);上海市教育委员会科技发展基金 (批准号 :0 2AK42;0 1A16);上海市教委重点学科建设项目资助的课题~~

摘　　要：对Ce掺杂锰氧化物 (La1 -xCex) 2 3Ca1 3MnO3(x =0— 1.0 )多晶样品的结构和输运性质系统研究的结果 .实验表明 ,在低掺杂浓度下 ,样品呈现完整的正交钙钛矿结构 ;随掺杂浓度的增加 ,有少量CeO2 杂相出现 ,同时伴随有Ce3+ 和Ce4 + 离子两种价态的涨落和Mn2 + Mn3+ Mn4 + 混合价态的共存 ,Ce掺杂导致的体系无序度增加 ,使得绝缘体 -金属 (I M)和顺磁 -铁磁 (PM FM)转变温度向低温方向移动 .有趣的是 ,Ce掺杂样品的电阻率测量I M转变峰值温度TIM 较PM FM转变温度Tc 为高 ,其差值ΔT(=TIM -Tc)随Ce掺杂含量的增加而增加 ,最大差值ΔT达 5 0K .各样品的磁电阻则随温度的降低而增加 ,在Tc 附近MR达到最大值 ,且随Ce掺杂含量增加Tc 附近的MR最大值迅速增加 ,达到 10 4 %以上 ,表现出很强的庞磁电阻效应 .在x≥ 0 .7时 ,磁电阻效应则表现出反常减小 .整体上而言 ,各样品的磁特性与输运行为间有较强的关联 ,电输运特性可用双交换作用模型进行很好的解释 ,在高温区满足热激活模型 .最后 ,在Ce掺杂对Tc 和MR的影响机理方面进行了初步讨论 .The structural and transport properties of the perovskite (La 1-xCe x) 2/3Ca 1/3 MnO 3 (0<x<1.0) system are systematically investigated. It is found that the compounds with smaller Ce content show orthorhombic crystal structure, while CeO 2 impurity phase appears with increasing Ce content. The fluctuations of Ce 3+ and Ce 4+ and multiple states in Mn (Mn 2+/Mn 3+/Mn 4+) site induce disorder in this system and drive the metal-insulator transition temperature T IM and ferromagnetic-paramagnetic transition temperature T c to lower temperatures. Interestingly, it is seen that in these Ce-doped compounds, T IM is higher than T c and the difference ΔT(T IM-T c) becomes remarkable with increasing Ce content and reaches 50 K for x=0.5. All the samples show colossal magnetoresistance (CMR) effect around T c and the maximum value increases with increasing Ce content; for the sample with x0.5, it has enhanced by six orders of magnitude larger than the undoped sample (x0),but it shows an abnormal decrease for the samples of x≥0.7. On the whole, it is shown that the correlation between the magnetism and the transport properties can be well explained based on the double-exchange model and the thermal activation theory. The influence of Ce substitution for La in La 2/3Ca 1/3MnO 3 system is also discussed.

关 键 词：晶体结构 输运行为 锰氧化物 铈掺杂 庞磁电阻效应 

分 类 号：O76[理学—晶体学]