The Effect Of Pd Doping And Chemical Pd-plating On The Electric-magneto Transport Properties In Lcsmo System

We have investigated the effect of Pd addition LCSMO prepared by solid state reaction method, and studied systematically the effects of Pd addition LCSMO on the structure, magnetic, electric and magnetoresistant properties. And the possible mechanisms of these characters were discussed. Moreover, we have attempted to prepare LCSMO/Pd composites in electroless plating method. We hope we could get some meanful results by comparing the CMR composites prepared in these two methods. The dissertation consists of five chapters:The first chapter mainly introduces some theories of the manganese oxides and research progress. Also, the application status is also referred. The research intention and significance of this 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 pre-treatment process of ceramic powders and progress of researchare and simply introduced.In chapter three, we select LCSMO as the matrix material and introduce metal Pd phase into LCSMO matrix by conventional solid-state reaction method. Pd addition has little influence on the Curie temperature (Tc), but dramatically decreases the resistivity (ρ) and shifts the metal-insulator transition temperature (Tp) to a higher temperature. Theρin the ferromagnetic (FM) metallic regime follows an empirical relation,ρ=ρ₀+ρ_2.5T^2.5+ρ_7.5T^7.5, reflecting that the conductivity mechanism is related to electron-electron, electron-phonon, electron-magnon scattering. In the paramagnetic (PM) insulating region, theρdata fit well to the adiabatic small-polaron-hopping model. Moreover, theρversus T curves for all samples excellently fit to the phenomenological model derived from spin-polarized tunneling at grain boundaries and thermal activation. Additionally, a large enhancement of room temperature magnetoresistance (MR), defined asΔρ/ρ(H=0) over 40% and 12% can be obtained at 20kOeand 3kOe, respectively. The good agreement between the field-dependence of MR and the Brillouin function indicate that MR behavior is an intrinsic property in this composite system.In chapter four, we analyse the purpose and the feasibility of the subject and attempt to explore the preparation process of LCSMO/Pd by electroless plating method.The last chapter is the summary of the full test.