Study On The Nanocrystal Microstructure And Magnetism Of Spinel Mn_xZn_1-xFe₂O₄

At present, the spinel manganese zinc ferrite is widely used in the field of electronic industry, because of some properties, such as high permeability, low coercive force, low power loss, et al., so that researchers keep on the magnetism of spinel manganese zinc ferrite. However, by the1980s, nanometer materials have become another focus in the research community, the special properties of the nano-scale manganese zinc ferrite materials will arouse wide concern quickly.A series of different nanocrystal MnxZn1-xFe2O4powder samples(x=0, x=0.1, x=0.25, x=0.5, x=0.8, x=0.9and x=1) has been prepared successfully by chemical method, sol-gel, in this dissertation. Their nanocrystal microstructures and magnetism are analyzed. Considering the most use of the bulk material, nanometer powder is processed into difinite shape of bonded body and the magnetism can be tested. This material may be expected in practice.The main points of the work can be summarized as follows:(1) In order to study the relationship of the components, crystal size and magnetism, the microstructure and magnetism of nanometer powder samples of different components are detected. Through the XRD analysis, it is easy to cause the cell constant changing and the mixed phase α-Fe2O3for different components. The crystal size, morphology and structure of the nanometer powder are characterized with TEM and the influence of different compositions and processing conditions have effect on the microstructure of samples to provide the basis for the further research of selecting a specific sample. Then the hysteresis loop is tested for the powder samples of different components by VSM. The result shows that the component x is0.8,0.5and0.25, the crystal size D is86nm,77nm and23.3nm, respectively, correspondingly, the saturation magnetization is4.31emu/g,5.213emu/g and7.925emu/g. It can clearly be seen that the crystal size has more effect on the special saturation magnetization when the three components are x=0.25, x=0.5and x=0.8, respectively. In addition, the curie temperature Tc is related to the crystal size. But the crystal size has little influence on the curie temperature Tc. Tc and x meet the linear relationship so that it can provide the future reference for materials of oxide magnetic refrigeration and magnetic liquid at the room temperature.(2) The microstructure and magnetism of nanometer powder samples of the component x=0.25are studied in detail. Through the XRD analysis, the nanometer powder samples present good face-centered cubic spinel structure of the manganese zinc ferrite. The corresponding space group is Fd3m(227). The heat decomposition of the precursor is analyzed by means of TG-DTA, then the optimal PH value, mixing time and calcination temperature are obtained. The preparation of the powder samples with different crystal sizes is researched. The result shows that the calcination time is2h, the calcination temperature interval of600℃to650℃, the crystal size grows up rapidly along with the calcination temperature; The interval of650℃to720℃, the crystal size is almost the same, even has a tendency to small with the calcination temperature; The interval of720℃to810℃, the crystal size grows up to a maximum with the calcination temperature. The calcination temperature is750℃, the calcination time is in5.5h, the crystal size can be controlled between42.5nm and66nm. The particle, the crystal size, the morphology and structures of the nanometer powder are characterized with SEM and TEM. The sample is processed into the Φ12mm cylindrical binding body. The hysteresis loop is measured by the NIM-200C testing system of magnetic properties of magnetic materials. The crystal size D is86.6nm, the saturation magnetization Ms is1.26kGs, the residual magnetic induction intensity Br is0.341kGs, the coercive force Hcj is0.791kOe, and it can not be applied into the market temporarily, so the reason of the low magnetism is explored.