| With the development of information and wireless technology, electronic devices call for high integration, multifunction and miniaturization. In 1990 Kneller proposed exchange coupling mechanism, which mainly focused on metal permanent magnetic composites, such as Nd-Fe-B and Sm-Co. Mental permanent magnetic composites have been greatly improved its energy product BH(max) inferior to the single-phase permanent magnet materials. However, the industrial applications are seriously affected by the deficiency of high cost and impatience corrosion. Compared with the disadvantages of permanent composite magnetic metal materials, ferrite magnetic composite materials can be prepared by exchanged coupling mechanism, which have high remanence(Br), coercive force(Hc), energy product BH(max), low cost, easy preparation and excellent oxidation-corrision properties.Permanent magnetic composite powders were synthesized by a one-step sol-gel method, which consist of M type barium ferrite(Ba Fe12O19) as the hard magnetic phase, cobalt ferrite(Co Fe2O4) and yttrium iron garnet(Y3Fe5O12) respectively for soft magnetic phase. Then the permanent magnetic composite ceramics were sintered by microwave sintering method. The phase composition of the samples was detected by an X-ray diffractometer(XRD) with Cu Ka radiation. Raman spectra were measured by a Raman spectrometer. The morphology of the nanocomposite powders was analyzed using the scanning electron microscope(SEM) and the transmission electron microscopy(TEM). The dielectric and magnetic properties of the composites were investigated by precision impedance analyzer and vibrating sample magnetometer(VSM) respectively. The electromagnetic parameters were analyzed by using a vector network analyzer. Meanwhile, preparation technology and formation mechanism were also studied.(1) Ba Fe12O19/Co Fe2O4 permanent magnetic composite powders were prepared by sol-gel method and studied the influence of the calcination temperature, chelating agent, p H value and different fractions on the phase composition of permanent magnetic composite powders. Then the Ba Fe12O19/Co Fe2O4 permanent magnetic composite ceramics were sintered by microwave sintering method using above powders. The results show that homogeneous microstructures with few pores were observed in the Ba Fe12O19/Co Fe2O4 composites.Through the study of the magnetic hysteresis(M-H) loops of the Ba Fe12O19/Co Fe2O4, it can be seen that all the Ba Fe12O19/Co Fe2O4 composite powders are also characterized with very smooth hysteresis loops and showed a single-phase magnetization behavior, implying that the hard magnetic phase and soft magnetic phase are well exchange coupled. Compared with the single-phase ferrites, the saturation magnetization and remanent magnetization of the permanent magnetic composite powders are also improved. It can be found that the 0.9Ba Fe12O19/0.1Co Fe2O4 composite powders exhibit the maximum(BH)max value compared with the pure-phase of Ba Fe12O19. Hence, by using the exchange spring behavior in the Ba Fe12O19/Co Fe2O4 composite powders, an enhancement of 10% in(BH)max can be achieved. Moreover, within the scope of 13.2~18.17 GHz, the absorption peak of permanent composite magnetic powders is greater than the same fraction of pure-phase Ba Fe12O19. Meanwhile, the magnetic and dielectirc of composite ceramics were also studied. The results indicate that with the increasing of Co Fe2O4 content, the saturation magnetization and remanent magnetization are increased, but dielectric constant decresesd and dielectric loss tangent value first increased then decereased.(2) Ba Fe12O19/Y3Fe5O12 permanent magnetic composite powders were synthesized by sol-gel method and studied the influence of the calcination temperature, chelating agent, p H value and different fractions on the phase composite of permanent magnetic powders. Then the Ba Fe12O19/Y3Fe5O12 permanent magnetic composite ceramics were sintered by microwave sintering method using above composite powders. The results show that Ba Fe12O19 and Y3Fe5O12 phase can exist individually and display very good chemical compatibility.Through the study of the magnetic hysteresis(M-H) loops of the Ba Fe12O19/Y3Fe5O12, it can be found that all the Ba Fe12O19/Y3Fe5O12 composite powders are also characterized with very smooth hysteresis loops which indicate that the hard magnetic phase and soft magnetic phase are well exchange coupled. Compared with the puere-phase ferrites, the coercivity and the remanent magnetization of permanent magnetic composite powders are improved and the energy product of the 0.9Ba Fe12O19/0.1Y3Fe5O12 is enhanced 2 times inferior to the parent phase of Ba Fe12O19. Moreover, when the content of the Y3Fe5O12 reached 10%, a resonance peak at 19.66 GHz appeares the optimum reaction rate of-17.51 d B and the intensity of absorption peak is greater than-8.47 GHz peak width reaching to 4.3 GHz, which indicates that the components of the composite powders have excellent absorbing properties. Meanwhile, the magnetic and dielectirc of composite ceramics are also studied. The results indicate that with the increasing of Y3Fe5O12 content, coercivity and remanent magnetization are increased, but dielectric constant and dielectric loss tangent value decreased. |
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