La_(1-x)Ca_xMnO_3化合物正电子湮没研究  

POSITRON ANNIHILATION STUDY OF La_(1-x)Ca_xMnO_3 COMPOUNDS

作　　者：王耘波[1] 郭冬云[1] 于军[1] 曹国辉[2] 魏龙 

机构地区：[1]华中科技大学电子科学与技术系,武汉430074 [2]北京科技大学材料物理系,北京100083 [3]中科院核分析技术开放研究实验室,北京100037

出　　处：《低温物理学报》2002年第3期198-202,共5页Low Temperature Physical Letters

基　　金：湖北省自然科学基金 (2 0 0 0J0 2 9);暨中科院核分析技术开放实验室基金 (K6 7)资助项目~~

摘　　要：本文对不同Ca含量的La1-xCaxMnO3一系列样品 (其中 0 .0 5≤x≤ 0 .8)在室温下进行了正电子寿命谱和多普勒展宽谱的测量 ,结果表明 :对应于出现巨磁阻效应的Ca成分范围(0 .3≤x≤ 0 .5 ) ,正电子的平均寿命τm 和多普勒谱S参数随Ca含量的增加而降低 ,说明在这一成分范围电子局域化程度增强 .具有CMR效应的样品La0 .7Ca0 .3MnO3正电子参数在Tc附近出现与晶格结构不稳定有关的反常变化 ,反映出电子结构与CMR效应间的关联 .The ceramic samples with nominal composition of La 1- x Ca x MnO 3 (0.05≤ x ≤0.8) were prepared by the ordinary solid state reaction method. The lifetime spectra and Doppler broadening radiation spectra of the positron at room temperature were measured. The Ca content dependence of the mean lifetime τ m and S parameter were measured. The results show that the τ m and the S parameter decrease with the x increasing in the range from 0.3 to 0.5, which is caused by localization of electrons. For the La 0.7 Ca 0.3 MnO 3 sample, an anomalous change of τ m and S parameter near T c can be observed with temperature decreasing. The results indicate the correspondence between electronic structure and CMR effect.

关 键 词：La1-xCaxMnO3 正电子湮没 电子结构 稀土锰氧化物 CMR 超大磁电阻效应 晶格结构 

分 类 号：O513[理学—低温物理]