la,0.7xeu,xca,0.3mno,3與la,0.7ca,0.3mno,3(eu,2o,3),x中磁電阻效應的研究與比較

1、華中科技大學碩士學位論文LaEuCaMnO與LaCaMnO/(EuO)中磁電阻效應的研究與比較姓名：代國紅申請學位級別：碩士專業(yè)：材料物理與化學指導教師：熊曹水20060424IIAbstract Recently, there are a lot of experimental and theoretical works focused on manganites. This is mainly because these mater

2、ials can exhibit extraordinary colossal magnetoresistance in the presence of magnetic field and its potential application in industry. Moreover, manganites are typical strongly correlated electron systems, spin, charge,

3、and orbital degrees of freedom are coupling simultaneously, and the classical simplifications that neglect some interactions to study the properties of manganites do not work. Therefore, to understand the mechanism of co

4、lossal magnetoresistance in manganites is a main challenge in condensed matter physics. Though Zener’s famous double exchange theory can explain the ferromagnetism/metal --paramagnetism/insulator transition and colo

5、ssal magnetoresistance successfully, but it is only qualitatively not quantitatively due to neglecting the existence of polaron formed by lattice distortion in this theory. So the study of polaron is of great importance

6、to understand manganites. In this thesis，we fabricate the La0.7-xEuxCa0.3MnO3, x=0.01, 0.03, 0.10, 0.15 by conventional solid state reaction, and La3+ is partially substituted by Eu3+. The experimental results indicate t

7、hat with the increase of Eu3+ dopant, the average ion radius of A-site decease, and size disorder increase. In order to study the high temperature (T>TP) conduction mechanism, we have used four theoretical models to f

8、it the experimental data. We found that with the increase of dopant, the single model can not fit the data very well, so we propose that there are spin polaron and lattice polaron coexistence in these material. Meanwhile

9、, the ferromagnetism/metal-paramagnetism/insulator transition temperature decrease, and the magnitude of colossal magnetoresistance is increased. Besides, we also fabricate composite La0.7Ca0.3MnO3/(Eu2O3)x, x=2%, 3％, th