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ABSTRACT: Irondeficient LiZn ferrites with compositions of Li0.35Zn0.30Fe2.29MnxO4-δ+0.005mol%Bi2O3 and Li0.35Zn0.30Fe2.29O4-δ+0.005mol%Bi2O3+x/3mol%Mn3O4(x=0.02-0.08) were prepared by a conventional ceramic process at 920℃ and 950℃. Mn3O4 was added to the raw materials and calcined powders, respectively. Sintered at 920℃, adding optimum Mn3O4to the raw materials enhances saturation magnetization Ms and remanence Br and decreases coercivity Hc, while adding Mn3O4 to the calcined powders has little effect on Ms and Br. Both kinds of samples have high Hc resulting from incomplete solid-state reaction at 920℃, whereas Hc is much lower in the sample with Mn3O4 adding to the raw materials. Sintered at 950℃, Hc of both kinds of samples decreases remarkably, whereas Hc is higher in the sample with Mn3O4 adding to the raw materials. Resistivities ρ in both kinds of samples are enhanced by optimum Mn3O4 adding and reaches the maximum when x is 0.06. Furthermore, the resistivity is higher in the sample with Mn3O4 adding to the raw materials.
Journal of Inorganic Materials. 01/2010;
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ABSTRACT: MnZn ferrites with the chemical formula Mn<SUB>0.68</SUB>Zn<SUB>0.25</SUB>Fe<SUB>2.07</SUB>O<SUB>4</SUB> were prepared by conventional ceramic techniques. The influence of Ta<SUB>2</SUB>O<SUB>5</SUB> addition on the microstructure and magnetic properties of MnZn ferrites was investigated. When the Ta<SUB>2</SUB>O<SUB>5</SUB> addition is less than 0.04wt%, the grain size increases with the increase of Ta<SUB>2</SUB>O<SUB>5</SUB> concentration, the initial permeability, saturation magnetic flux density and DC resistivity increase, the power losses and porosity decrease. However, excessive Ta<SUB>2</SUB>O<SUB>5</SUB> addition (>0.04wt%) results in the exaggerated grain growth and porosity increase which make the initial permeability, saturation magnetic flux density and DC resistivity decrease, and the power losses increase. When the Ta<SUB>2</SUB>O<SUB>5</SUB> addition is 0.04wt%, the initial permeability, saturation magnetic flux density and DC resistivity reach the maximum, the power losses and porosity reach the minimum.
Journal of Inorganic Materials. 01/2009;
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ABSTRACT: The effects of quencher after calcination on the microstructure and magnetic properties of manganese-zinc ferrites were investigated by measuring the magnetic properties, electrical resistivity and density. The powder of Mn0.68Zn0.25Fe2.07O4 composition was prepared by adopting the conventional ceramic technique. Toroidal cores were sintered at 1350 °C for 4 h in atmosphere controlled by using the equation for equilibrium oxygen partial pressure. The fracture surface micrographs of samples were observed by scanning electron microscope. The results show that the inner stress of calcined powder increases, abnormal grains of ferrite grow up, initial permeability goes down and power losses of ferrite rise with the increase in quenching temperature, and the microstructure and magnetic properties of manganese-zinc ferrites can be improved with the gradual cooling of calcined powder to room temperature (25 °C).
Journal of Magnetism and Magnetic Materials.
