| Recently, Diluted Magnetic Semiconductors (DMSs) doping by non-magnetic element have been gradually attracted much attention, which can be averted the origin of magnetic mechanism for DMSs doping by rare earth element or transitional element. In this thesis, we prepared non-magnetic element (K, Mg, Y) doped SnO2 nanocrystalline powders. The effect of different non-magnetic element on the structure and room-temperature ferromagnetism was investigated. Using the first-principles based on the density functional theory (DFT), we investigated the electronic structure and magnetic properties of non-magnetic element (K, Mg) doped with the aim to explain the experimental results.As a kind of Soft Magnetic Composites, Magnetic powder cores can be manufactured by conventional powder metallurgic process and described as ferromagnetic powder coating by the electrical insulating film. Magnetic powder cores, not only effectively decrease the eddy current loss, but also combine the productive advantages of powder metallurgic process, will be used in wide range of area in the future. The future investigation of Soft Magnetic Composites will be included as following:the exploitation of the new-type insulating film, the effect of different purity ferromagnetic powder in Soft Magnetic Composites property, the investigation of hyperoxidation in Magnetic powder cores. In this letter, Influence of different heat treatment and different concentration of Phosphoric acid treatment on resistivity and the frequency stability of resistivity in Magnetic powder cores.The main contents are following:The phase identification and microstructure were carried out by X-ray diffraction (XRD) and Scanning electron microstructure. All samples are completely the rutile-type tetragonal phase and no secondary phases are detected. The intensity of main peak (XRD) deteriorates with increasing dopant concentrations and vacuum annealing treatment, but strengthens with increasing annealing temperature. The average grain size of nanocrystalline powders decreases duo to the increment of dopant concentration, but increases with the increasing annealing temperature.All non-magnetic element doped-samples exhibit ferromagnetism at room temperature. The saturation magnetization of nanocrystalline powders increases with the increment of dopant concentration, but decreases with increasing annealing temperature. However, the average effective magnetic moment of per dopant atom weakens with increasing the dopant concentration. Based on the first- first-principles, the results show that the magnetic moment for K, Mg doped- SnO2 mainly originates from the unpaired 2p electrons of the O atoms around the dopant atoms. We predict that the energy required to replace Sn atom by K atom is reduce when there is an oxygen vacancy in K doped- SnO2. In Mg doped-SnO2 system, magnetic moment of system changes attributing to the coexistence of antiferromagnetic and ferromagnetic interactions. Therefore, the average effective magnetic moment of dopant atom weakens with increasing the dopant concentrations. With the annealing temperature increasing, the saturation magnetic moment decreases, which suggest that the ferromagnetism derives from the defects, confined the surface of nanocrystaline powders.Magnetic powder cores were manufactured by phosphate coating process. The results indicate that the density of Magnetic powder cores treated by high-concentration phosphoric acid becomes low. From XRD of samples, Fe phase can be detected for sample treated by low-concentration. Fe(PO4)n phases were detected for samples treated by high-concentration phosphoric acid. SEM shows that the insulated powders were surrounded by an ironic phosphate layer. The influence of annealing temperature on resistivity and the stability of resistivity with frequency characteristics is investigated. The resistivity greatly reduces when the annealing temperature above 650℃. With the increasing mass rate of phosphoric acid and iron powder, the resistivity is obviously improved. |
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