Magnetic Properties And The Local Structure Study Of Zn_xFe_3-xO₄

Recently, the researches of nano-particle materials and their properties have been drawn much attention. Preparation and structural characterization of nano-sized materials are two important aspects of nano-science and technology. It is of great significance to develop nano-sized materials with excellent properties and to clarify their structures. The nano-particle material of magnetic ferrite is a group of technologically important materials, which has been widely applied in many fields because of its exceptive magnetism and electronic structure. As a primary representation of ferrite, zinc ferrite has long been the subject of study.In this thesis, we have investigated the structure and the mechanism of the magnetic properties of the zinc ferrites. A series of nano-particle zinc ferrites were prepared by the chemical coprecipitation method. X-ray diffraction (XRD) patterns demonstrate that the samples are in cubic phases. The results measured by Vibrating Sample Magnetometer (VSM) technique show that the saturated magnetization increases for low Zn doping up to x = 1/3, on further increasing Zn content to x > 1/3, a decreasing trend in magnetism is exhibited. In order to explain this phenomenon, we studied the site occupations of the ions by the extended x-ray absorption fine structure (EXAFS) technique, because this technique has element specificity and local structure sensitivity. The atomic structural parameters, such as coordination number, bondlength and Debye-Waller factor, were obtained by fitting the EXAFS curves. The main results of this thesis are shown below:(1) The results of EXAFS indicated a small part of zinc cations had occupied B sites and a large fraction of Zn²⁺ ions resided in A sites. It seems that the fitting result of the EXAFS data is consistent with the viewpoints that Zn ions preferentially occupy the A sites and that some zinc ions may conceivably occupy B sites if thermodynamic equilibrium has not been achieved. A paper on this study was submitted and was accepted [*], another paper is in preparation.(2) According to the fitting result of EXAFS data, the Neel's two-sublattice model...