钙钛矿锰氧化物(Nd_(1-x)La_x)_(0.5)Ca_(0.5)MnO_3体系中的铁磁再入现象  

OCCURRENCE OF RE-ENTRANT FERROMAGNETIC TRANSITIONS IN (Nd_ (1-x)La_ x)_ (0.5)Ca_ ( 0.5)MnO_ 3 manganeses

作　　者：王芳[1] 方军[1] 黄真[1] 田建军[1] 张勇[1] 陈治友[1] 陈敬林[1] 

机构地区：[1]中国科学院等离子体物理研究所强磁场实验室

出　　处：《低温物理学报》2006年第2期147-151,共5页Low Temperature Physical Letters

摘　　要：研究了(Nd1-xLax)0.5Ca0.5MnO3(0≤x≤0.5)体系的X射线衍射谱,Raman吸收谱和电输运特性.通过电输运性质的测量给出了金属绝缘转变温度Tm与A位离子平均半径之间的关联.结果表明,La3+离子的掺杂压制低温下的电荷有序,导致金属绝缘转变开始出现,且随掺杂浓度的增加,金属绝缘转变(MI)温度(Tm)向高温区移动,对应的峰值电阻率ρp降低.X射线衍射谱和电输运特性均表明,La3+离子的掺入使得A位平均离子半径(〈rA〉)增大,导致局部晶格畸变减小.在掺杂量0.3≤x≤0.5的区域范围内,随着x的增加,双交换作用逐渐增强,有利于低温下铁磁态的形成.但热循环实验的研究结果表明,这种铁磁态属于亚稳态,在能量上反铁磁态比铁磁态更稳定.The properties of perovskite （Nd1-xLax）0.5Ca0.5MnO3（0≤x≤0.5） compounds are systematically investigated by use of Raman spectra and resistivity measurements. It is found that the metal-insulator（M-I） transition temperature Tm is related to average ion size of A site. It is given that the La doping induces the M-I transition and the transition temperature Tm shifts to higher temperature with the increasing of the La^3＋ doping content, while the relevant resistance peak ρp sharply decreases. All the Raman spectra and resistivity results indicates that the La^3＋ doping increases the average ion size of the A site, which decreases the local distortion of the lattice. In the doping range of 0.3≤x≤〈0.5, with the increasing of x, the doping of La^3＋ cation favors the formation of ferromagnetic state which is due to the strengthen of the double exchange interaction. However, the recycling experiment reveals that the ferromagnetic state here is a metastable state and the antiferromagnetic state is favored in the energy aspect.

关 键 词：钙钛矿锰氧化物 金属-绝缘转变 离子尺寸效应 

分 类 号：O513[理学—低温物理]