| With rapidly development of information technology, magnetic material-especially is ferrite material, has been widely applied with improvement of the requirement in electronic field. The development of muniaturation, muli-function of electric chips requires that the ferrites move toward more muli-performance and more widely application and higher applied frequency. M-type barium ferrite is a magnetic material with a hexagonal crystal structure. It has high coercivity(Hc=6900 Oe), high saturation magnetization(Ms=72 emu/g) and big magnetocrystalline anistotropy constant. As a traditional permanent magnetic material, M-type barium ferrite has always played an important role in this field.With development of LTCC technology and the diversification of magnetic materials, single M-type barium ferrite has not met the needs of industrialization. Hence, the modifications on barium ferrite have become a research hot point. In this dissertation, we studied the effects on structure and properties of M-type barium ferrite with different ions substitution. The aim is to get a broad coercivity, adjustable magnetocrystalline anistotropy constant, high saturation magnetization, high magnetic permeability and applied frequency.First, M-type barium ferrite was synthesiszed by Sol-gel method and solid state method, and was sintered at low temperature. The results showed the solid state method samples had a property of Ms=59.92 emu/g and Hc=4596 Oe at 1200 °C for 6 h. Adding 3wt% Bi2O3, the Ms of sample was 55.42 emu/g and the Hc was 4212.1 Oe under low temperature sintering with 3wt% Bi2O3. The grain size of sol-gel method sample was about 1 μm, and Ms=48.99 emu/g and Hc=4290 Oe.Second, we studied the structure and magnetic properties of La-substituted, La-Co substituted and La-Zn substituted M-type barium ferrite, and studied low temperature sintered process with adding 3wt% Bi2O3 additive. Ba1-xLaxFe12O19 sample had the biggest saturation magnetization at x=0.2. The coercivity increased with x from 0.0 to 0.6. Ba(La Co)xFe12-2xO19 sample, Ms decreased from 67.85 emu/g to 60.17 emu/g and Hc decreased from 3279 Oe to 1023 Oe at 1200 °C for 6 h. Ba(La Zn)xFe12-2xO19 sample, Ms increased first from 65.44 emu/g to 68.78 emu/g and then decreased and Hc decreased from 3512.8 Oe to 1507.8 Oe at 1200 °C for 6 h. The intrinsic magnetic properties of La3+, Co2+ and Zn2+ ions and their crystal occupanies were discussed.In addition, Zn-Ti and Ni-Ti substituted M-type barium ferrite were synthesized. Zn2+ ion is a non-magnetic ion, and its magnetic moment is 0 μm, and its d-configuration of electrons is d10, and its electronegativity is 1.65, hence, Zn2+ ions preferred to occupy 4f2 site when substituted Fe3+ ions. Ni2+ ion is a magnetic ion, and its magnetic moment is 2 μm, and its d-configuration of electrons is d8, and its electronegativity is 1.9, hence, Ni2+ ions preferred to occupy 2a and 12 k sites when substituted Fe3+ ions. Ti4+ ion is a non-magnetic ion, and its d-configuration of electrons is d0, and its electronegativity is 1.53, hence, Ti4+ ions preferred to occupy 2a and 4f2 sites. By discussing the properties of the ions and the occupany of the lattice, we studied the effects of Zn-Ti and Ni-Ti substitution on structure and magnetic properties, and researched on the low temperature co-firing of materials.Finally, Co-Ti equiatomic co-substitution M-type barium ferrites were synthesized by solid state method. The effect of Co-Ti substitution on microstructure and magnetic properties were investigated. When x=0.00, Ms of sample was 65.7 emu/g,and Hc=4047 Oe. When x=1.30, Ms of Ba(Co Ti)1.3Fe9.4O19 was 47.5 emu/g and Hc=180 Oe. Meanwhile, when x=1.15, the μmax=25 and f=700 MHz. Ba Fe12-2x(Co Ti)xO19, x=1.00~1.30 with step of 0.05, was synthesized. The appropriate contents of Co-Ti substitution makes the magnetocrystalline anisotropy transform from uniaxial to planar anisotropy. Due to Co-Ti substitution, the magnetocrystalline anisotropy constant decreases from a high value and reach a minimum value, and changes from positive to negative value, increases oppositely, this determines the changes of magnetic properties. In addition, we synthesized Ba(Co Ti)1.22Fe9.56O19 materials by sol-gel method and solid state method. DSC and TGA were investigated the changes in energy and weight with respect to temperatures during the sintering process- from room temperature to 1200 oC. For sol-gel sample, in a range of 0.5-11 GHz, the 3 mm thickness shows a maximum reflection loss of-35.69 d B at 10.2 GHz and the bandwidth less than-10 d B is about 3.06 GHz(from 8.9 GHz to 11.96 GHz). The solid state sample has a maximum reflection loss of-19.02 d B at 5.66 GHz and the bandwidth less than-10 d B is about 3.51 GHz(from 3.37 GHz to 6.88 GHz). |
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