The Effect Of Pd And Ni Electroless Process On The Electric-Magneto Transport Properties In LCSMO System

Perovskite manganites have been a research focus of material science, condensed matter physics and other fields, since the discovery of the phenomenon of colossal magnetoresistance in these compounds. Although the value of magnetoresistance in such materials are great, but which occurs at very low temperatures, in a very narrow temperature range and in a large magnetic field usually, that limits the practical application of this kind of materials greatly. Therefore, many researchers are committed to change the internal microstructure of these materials with doping, interstitial and other methods , study the electro-magnetic transport and magnetic properties and expect to get a larger magnetoresistance at room in a low applied magnetic field. In this paper, La_0.7Ca_0.2Sr_0.1MnO₃ (LCSMO) /Pd composite system and La_0.7Ca_0.2Sr_0.1MnO₃ (LCSMO) /Pd/Ni composite system were prepared. The structure, morphologies, the electro-magnetic transport and magnetic properties of the composites were studied and the possible mechanisms of these characters were discussed. The dissertation consists of five chapters:The first chapter mainly introduces some theories of the manganese oxides. The research intention and significance of my thesis were put forward on the basis of the introduction.The second chapter mainly discusses some synthesis methods, including solid state reaction and electroless plating method.The third chapter mainly introduce Pd into the LCSMO matrix with electroless plating method.With the increase of Pd content, the resistivity (ρ) decreases and the metal - semiconductor transition temperature (Tp) increease, but Curie temperature (Tc) remain almost unchanged. AndσS decreases due to the doping of nonmagnetic Pd. The values of IMR are enhanced greatly for all Pd-added samples.For the sample of plating time x = 40min, the maximum MR is as large as 11% and 35% at 305K under 3kOe and 20kOe applied field. We can suggest that Pd segregated at the grain boundaries plays an important role. The existence of Pd can enhance and modify the magnet action of LCSMO grains.The chapter four, the La_0.7Ca_0.2Sr_0.1MnO₃/Pd/Ni composite system have been prepared with electroless plating method. Studies show that Ni present in the around of Pd, and which do not effect the crystal institution of LCSMO matrix almostly. With the increase in the amount of Ni-doped,ρof composites decreases, but Tp and Tc is almost unchanged. Since the incorporation of ferromagnetic Ni, the saturation magnetic moment increases. After incorporation of Ni,the MR of all sampers decreased, the reason is the strong magnetic nickel wakend the magnetic disorder at grain boundaries and increased the distance between adjacent LCSMO particles, and weakend the strong association of the adjacent LCSMO grain.The last chapter is the summary of the full test.