The Electro-magnetic Properties In Bulks And Films Of La_0.7Ca_0.3MnO₃/Cu Composites

Manganese peroveskite oxides exhibit colossal magnetoresistace (CMR) effect, meanwhile they are also an ideal laboratory for studying the physics of strongly correlated electronic systems due to the complex interaction among electrons,lattices and spins, so they have been the subject of intense study in recent years. As an ideal material for the sensing devices and the reading/writing sliders, it shows a great application potential in the future. However, because the CMR effect can be observed only at low temperature and high applied magnetic field, and its value decreases dramatically when the temperature increases, it is hard for this oxide to apply practically. In order to obtain the high MR value at the room temperature in a low applied magnetic field, several methods have been employed to modify the structure of the compounds, such as introducing the substituting ions or the interstitial atoms into this manganite matrix. In this thesis we synthesized the bulk and film form of the La_0.7Ca_0.3MnO₃ /Cu composites by different method, including the traditional solid-state reaction method and the magnetron sputtering technique, and investigated their the electro-magnetic properties and the CMR effect. There are six chapters in this thesis as follows:In chapter one, the research process and a summary of the structure, properties and magnetoresistance in the manganese oxides has been introduced. Then the intention and signification of our work in this thesis have been pointed out.In chapter two, the prepare methods of the CMR material which includes solid state reaction, stream condensation and magnetron sputtering method and the measurement technique have been described.In chapter three, we studied the Cu powder doping effects on the structure and electro-magnetic properties of La_0.7Ca_0.3MnO₃ and pointed out there are two factors contributed to the CMR effect of the samples, including substitution effect and the grain boundary effect.In chapter four, the structure and electric properties of La_0.7Ca_0.3MnO₃/Cu granular films have been studied. The influences of different substrates are compared.The Cu contentation increase inclined to modify the granular structure of the films and magnify the MR value at low temperature.In chapter five, the structure of La_0.7Ca_0.3MnO₃ /Cu trilayer films on different substrates have been studied. The electric properties and MR behavior of films with different thickness of Cu layer has been compared with each other.The last chapter is the conclusion.