La0.7-xGdxSr0.3MnO3体系中的相分离

采用固相反应法制备了样品La0.7-xGdxSr0.3MnO3(x=0.00,0.20,0.30,0.40,0.50).通过测量样品的M～T曲线,ESR曲线,研究了La0.7-xGdxSrO0.3MnO3,体系中的相分离现象及相分离与CMR之间关系.结果表明:当x=0.30,0.40时,在PM-FM相变区产生相分离,并且磁电阻MR得到增强.研究结果表明:La0.7-xGdx Sr0.3MnO3中的相分离与Gd在A位的占位情况紧密相关,磁电阻MR的增强是在外磁场作用下,铁磁区扩大顺磁区减小引起的.     

稀土掺杂(Sm、Gd、Dy)对La0.7Sr0.3MnO3室温磁电阻效应的增强

用固相反应法制备了La0.7-xSmxSr0.3MnO3,La0.7-xGdxSr0.3MnO3和La0.7-xDyxSr0.3MnO3(x=0.00,0.10,0.20,0.30)系列样品.通过M～T曲线,ρ～T曲线,研究了用稀土离子替代La对La0.7Sr0.3MnO3居里温度Tc和磁电阻的影响.结果表明:稀土离子掺杂是改变钙钛矿锰氧化物居里温度和增强MR的有效途径;适量掺杂可以在室温附近产生大的磁电阻.     

Pr0.7Ca0.3MnO3陶瓷晶界势垒的交流特性

采用固相烧结方法制备了Pr1-xCaxMnO3(x=0.3)钙态矿结构锰氧化物陶瓷样品,对其在磁场和电场下的直、交流输运性质做了系统研究.通过测量加磁场和零场下的Ⅰ-Ⅴ曲线,得到其居里温度为150K,与VSM测试结果一致.通过测量加磁场与零场下交流的阻抗频谱,发现加磁场后样品的晶界电阻明显减小,而晶粒电阻几乎保持不变,表明Pr1-xCaxMnO3陶瓷多晶样品的CMR效应源于样品的晶界.为确定晶界处的势垒高度,测量了样品在不同频率下的阻抗温谱,根据Arrhenius定律拟合得出势垒高度为117 meV,与用直流R-T数据拟合得出的激活能一致.     

Emergent phenomena in manganites under spatial confinement

It is becoming increasingly clear that the exotic properties displayed by correlated electronic materials such as high Tc superconductivity in cuprates,colossal magnetoresistance(CMR) in manganites,and heavy-fermion compounds are intimately related to the coexistence of competing nearly degenerate states which couple simultaneously active degrees of freedom-charge,lattice,orbital,and spin states.The striking phenomena associated with these materials are due in a large part to spatial electronic inhomogeneities,or electronic phase separation(EPS).In many of these hard materials,the functionality is a result of the soft electronic component that leads to self-organization.In this paper,we review our recent work on a novel spatial confinement technique that has led to some fascinating new discoveries about the role of EPS in manganites.Using lithographic techniques to confine manganite thin films to length scales of the EPS domains that reside within them,it is possible to simultaneously probe EPS domains with different electronic states.This method allows for a much more complete view of the phases residing in a material and gives vital information on phase formation,movement,and fluctuation.Pushing this trend to its limit,we propose to control the formation process of the EPS using external local fields,which include magnetic exchange field,strain field,and electric field.We term the ability to pattern EPS "electronic nanofabrication." This method allows us to control the global physical properties of the system at a very fundamental level,and greatly enhances the potential for realizing true oxide electronics.     

自旋输运和巨磁电阻--自旋电子学的物理基础之一

介绍磁性纳米结构和锰氧化物中电子的自旋极化输运和巨磁电阻效应，它们是新近发展的自旋电子学的物理基础之一．着重讨论的是以下三方面的基本物理图像：磁多层结构的巨磁电阻，铁磁隧道结的隧穿磁电阻，掺杂锰氧化物的庞磁电阻效应．