Synthesis Of Magnetite And Its Ordered Structure Under Magnetic Field

Driven by the promising applications in high-density magnetic data storage media, ferrofluids, and biomedicine, an important research effort has been directed towards the study on the synthesis of nanoscale magnetic materials. Moreover, ordered functional structures of magnetic nanomaterials have some brand-new properties resulted from the spatial orientation and arrangement of the building blocks and can be viewed as the foundation for the formation of novel miniaturized nanodevices. So research on the assembly of nanoscale magnetic materials is very important from the point of view of science and applications.The objective of this dissertation is to study the self-assembly of magnetic ordered materials under magnetic field, and investigate the essence of self-assembly under magnetic field, and develop some simple and effective technologies to build highly ordered magnetic functional structures. The main parts of the results are summarized below:1. Fe3O4 with different morphologies were synthesized throught a mild hydrothermal/solvothermal process, especially Fe3O4 octahedrons. Their magnetic properties were studied. Self-assemble of octahedral magnetite under an external magnetic field was studied. Fe3O4 have two easy-magnetic axes, the <111> direction and the <110> direction. The study shows that the micro-scale octahedral magnetite formed chains along with the <111> direction in a great measure by face-to-face connection, and along with the <110> direction in small quantity by edge-to-edge connection. On the basis of the results, the other factors except the easy-magnetic axis were discussed. Base on our experimental results, an ideal grow model was introduced to explain the phenomena. Both the direction of easy-magnetic axis and morphology of magnetic particle determine how magnetic particles connect in chain when there is more than one easy-magnetic axe. On the basis of the works reported, this work further shows the essence of self-assemble under magnetic field.2. A series of magnetite were synthesized under different magnetic field through a hydrothermal method. The powder X-ray diffraction results show that those Fe3O4 have same crystal structure. The magnetic measure indicates that the Fe3O4 prepared under different magnetic field has different magnetic properties. The local structure of those Fe3O4 was investigated by X-ray absorption fine structure (XAFS). The XAFS results quantitative indicate that the bond length of Fe3O4 is changed by magnetic field. The Fe-O bond length is shortened with the increasing of intensity of magnetic field. The result indicates that the magnetic filed can change the local structure of magnetic material, it result in the change of magnetic properties.3. We have a try to obtain high ordered 2D magnetic array by magnetic filed induced magnetic particles filled in pores of AAO template. Our aim is a magnetic particle fill in a pore of AAO template. When every Fe3O4 nanoparticle has a single domain structure, the 2D magnetic array shows great potential for further application in magnetic memory media. The results of experiment show that a large of particles filling in the pores of AAO template and there is a large of defects in the array, meaning it is significative to improve the method. Base on our experimental results, defects with different type wrer discussed and corresponding improved project were introduced. This experiment provides some help experimental and theoretic for the further preparation of 2D magnetic array.