The Simulation Of Electronic And Magnetic Transport Properties Of LCMO Series Materials

Colossal Magnetoresistance in doped perovskite manganites Re1-xAxMnO3 (Re = tri-valent rare earth and A = divalent metal) has important effect on science research and application, this stimulate our interests in these compounds. Since these compounds are spin, charge and orbit strongly correlated systems, many kinds of interaction exist in these compounds lead to many complex phenomena. These phenomena include insulator to metal translation and colossal magnetoresistance. Scientist have built many theory models to explain the physical essence in the electronic and magnetic transport properties of these compounds such as double exchange, but quantified simulations need more consideration including Jahn-Teller effect and so on.The electronic and magnetic transport properties in the single crystalline doped perovskite manganites have been studied more intensively. For the polycrystalline perovskite manganites, because of the grain boundary effect, the electronic and magnetic transport properties show more complex phenomena such as the metal to insulator translation temperature changing with the average grain size and low field magnetoresistance and so on, moreover, people start research more complex composites system for expecting their application now. These composites show complex electronic and magnetic transport properties which contain intrinsic properties and extrinsic properties partly. The theory models are getting more and more complex.The important contents in this paper are the theory modeling and simulation of the electronic and magnetic properties of La_2/3Ca_1/3MnO₃ systems which contain single crystal, polycrystalline samples and La_2/3Ca_1/3MnO₃/ZnO composites; we expect that we can find a widely suitable theory model for these systems. This paper contains the following aspects:In the first chapter, we give a simple introduction about the crystal structure, electronic structure, magnetism, the intrinsic electronic and magnetic transport properties, extrinsic electronic and magnetic transport properties and the theory models.The second chapter is about the development of the low temperature electronic and magnetic transport properties testing system. All of the experiment data in this paper about electronic and magnetic transport properties were obtained by this testing system.In the third chapter we discuss the microstructure and electronic transport properties of the La_2/3Ca_1/3MnO₃ polycrystalline ceramics which were synthesized by a kind of compositive method containing two steps. Strong low field magnetoresistance were found in the samples which had smaller grains.The fourth chapter is the most important part in this paper. By modeling a random resistance network, we have gained quantified simulation of the electronic and magnetic transport properties compared with the experiment data. Of course at the beginning of this chapter we introduce the basic theory about the percolation model.In the fifth chapter we give the theory simulation of the electronic and magnetic properties of La_2/3Ca_1/3MnO₃ polycrystalline samples. By changing the parameters in the random resistance network, we have obtained quantified results.In the sixth chapter we discuss the electronic and magnetic properties of the La_2/3Ca_1/3MnO₃/ZnO composites system. The resistance vs temperature curves show double peak, we give the main explanations about this effect and build a two structure phase model to simulate this property.