Preparation Of The Zn_0.5Fe_2.5O₄/α-Fe₂O₃ Polycrystalline Material With Giant Tunneling Magnetoresistance

Nowadays, magnetic materials are playing a more and more important role in people's daily lives. They have been applied in various fields (?) high-tech industries. The research and development of giant magnetoresistance materials have attracted steady interests since 1988 when the giant magnetoresistance in Fe/Cr mutilayers was found by Baibich and his colleagues. It has been recognized that the mechanism of giant magnetoresistance was different from anisotropic magnetoresistance. It is closely related to the transport of spin electrons, from which a new discipline of science, so-called spintronics, has been developed.In this thesis, the research progress in giant magnetoresistance materials in recent decades has been reviewed with special attention to the magnetoresistance arising from magnetic tunneling junction in polycrystalline materials, which began to provoke great attention recent years ago. We chose a high spin polarization compound Zn_0.5Fe_2.5O₄ as a ferromagnetic phase to prepare Zn_0.5Fe_2.5O₄/α-Fe₂O₃ polycrystalline magnetoresistive materials and explored the relationship between the preparation technology and magnetoresistance performance of the Zn_0.5Fe_2.5O₄/α-Fe₂O₃ polycrystalline materials. The research area includes:1) The preparation of single phase Zn_0.5Fe_2.5O₄ nanopowders with high saturation magnetization. By comparing several different preparation methods for ultrafine powders such as solution co-precipitation, PVA dispersing sol-gel and citric acid chelating sol-gel methods, the influences of processing conditions on the phase purity, particle size and magnetic properties of ultrafine Zn_0.5Fe_2.5O₄ powders was studied to seek the best synthesis approach.2) The preparation of magnetoresistive Zn_0.5Fe_2.5O₄/α-Fe₂O₃ polycrystalline materials with magnetic tunneling junctions. To achieve magnetoresistive effect in Zn_0.5Fe_2.5O₄/α-Fe₂O₃ polycrystalline structures, two methods were used to form insulating α-Fe₂O₃ boundary layers between Zn_0.5Fe_2.5O₄ grains: a) the reactive atmosphere sintering and b) the particle-encapsulation method. By taking advantage of the Zn_0.5Fe_2.5O₄ stoichiometry associated with the temperature...