The Controllable Preparations And Properties Of Zn_xFe_3-xO₄ Nanoparticles And Fe₃O₄/zns Nanochains

As a typical inverse spinel structural ferrite,half metallic Fe₃O₄ has the high Curie temperature?around 858 K?,the therotically predicted 100%spin polarization at Fermi level and the compatible conductivity to the semiconductors.Those unique properites not only make it to be a promising candidate as the spin injection source for semicondctors,but also attract tremendous interests in the spintronics field.Moreover,Fe₃O₄ nanoparticles have excellent capability for microwave absorption and good biocompatibility,showing a wide range of potential applications in fields of biomedicine,catalysis,electronics,microwave absorbing functional materials,etc.Thus various approaches such as surface modification,self-assembling and nonmagnetic doping have been employed to manipulate the electrical,magnetic and microwave absorption properties of Fe₃O₄,which extend its application fields immensively.In this thesis,we focus on nanoscale Fe₃O₄ and realize the size controllable synthesis of Fe₃O₄ nanoparticles by adding inhibitor in the reaction solutuion with the solvothermal method.More importantly,we demonstrate that the morphology,structure and magnetic properties of the Fe₃O₄ nanoparticles can also be well engineered by the doping of Zn ions.In addition,one dimensional core shell structured Fe₃O₄/ZnS nanocomposites were successfully synthesized via a magnetic field induction method.The morphological,structural,magnetic and optical properties of the synthesized nanoparticles were well characterized,which verified the magnetic-photoluminescence multifunctionality.The main results are as follows:We successfully synthesize the Fe₃O₄ nanoparticles by a modifeid solvothermal method,in which we add inhibitor diethylene glycol?DEG?in the reaction solotion of ethylene glycol?EG?and change the ratio of EG:DEG to control the sizes and structures of nanoparticles.XRD measurements indicate that all the samples are spinel structure.TEM measurements show that the grain size of the synthesized nanoparticles is increasing with the increasing amount of EG.As a result,the saturation magnetization increases slightly from 68.6 to 73.7emu/g.Moreover,the crystallinity and the dispersibility of the particles are also improved.We report a facile solvothermal method for synthesizing nearly superparamagnetic Zn_xFe_3-xO₄ nanoparticles with controllable doping concentration,which the doping content x from 0 to 0.90.All samples demonstrate a typical spinel structure with small size?less than 20nm?.The Zn ion doping effects on the structure,morphology and magnetism of nanoparticles have been systematically studied by XRD,TEM,FTIR,XPS and FMR.It is found that the saturation magnetization first increases then decreases with increasing Zn doping concentration due to the different site occupation of Zn ions.In contrast,dynamic magnetic measurements demonstrate that the Lande g-factor shows a monotonic increasing trend by the increase of Zn doping concentration.We prepare the chain Fe₃O₄/ZnS nanocomposites with core shell structure and deposit the crystalline ZnS layer directly to the surface of Fe₃O₄ chains by a facile seed mediated growth method.Morphology and structure characterizations reveal the well-defined phases and direct coating of crystalline ZnS shell on Fe₃O₄ core,in spite of their large lattice mismatch.The composites show large saturation magnetization and good fluorescence properties,which might pave the way for their applications in semiconductor spintronics making it a promising candidate for spin injector,and therefore a popular material for spintronic studies.