Research On NiCuZn Ferrite Used In Ka Band Microwave Devices

As a very important branch of microwave devices, microwave ferrite devices are widely used in various fields of today’s aviation, aerospace and electronic communications. The boom in the modern military technology and communications systems goes further in a corresponding boom in the research on microwave ferrite devices. Microwave ferrite material is the core of microwave ferrite device, the optimization of its performance has great significance to the improvement of microwave ferrite device. With the advantages of high saturation magnetic induction, good temperature stability and higher resistivity, NiCuZn microwave ferrite materials are widely used in microwave ferrite devices. In this dissertation, NiCuZn ferrite materials used in Ka-band microwave ferrite devices are prepared by solid-state reaction method. Aimed at the goal of high saturation magnetic induction, high Curie temperature, and low ferromagnetic resonance linewidth, this dissertation will investigate the impacts of the ion substitution, additives and sintering temperature on the NiCuZn ferrite microstructure and electromagnetic properties.The results show that: With the increase of ZnO content, the saturation magnetic induction Bs increases first and then decreases in the range of 17~24mol%. But the Curie temperature Tc, coercive force Hc, residual magnetic induction Br and the ferromagnetic resonance linewidth ΔH decline monotonically. When the content of ZnO is 20mol%, Bs gets maximal value 452 of mT, Tc and ΔH are 317℃ and 9.15kA/m respectively. A moderate substitution amount of Co2+ ions can significantly reduce the ΔH. In the substitution range of 0~0.015, ΔH decreases linearly along with the increase of the amount of Co2+ ions. BaTiO3 additive can refine grain of NiCuZn ferrites, slightly increase the sintering density and significantly reduce the dielectric loss. With the increase of BaTiO3 content, the dielectric loss tgδε, saturation magnetic induction Bs and residual magnetic induction Br are diminished gradually in the range of 0~1wt%, while the coercive force Hc and ferromagnetic resonance linewidth ΔH rise. Sintering temperature has significant impacts on the microstructure and magnetic properties of NiCuZn ferrite. Within the scope of 960~1080℃, the grain size increases with the rise of sintering temperature, meanwhile, the sintering density d and Bs increases first and then decreases. Bi2O3 additive can form liquid phase during sintering process and improve the sintering density. However, doping too much will cause grain growth excessively fast and deteriorate microstructure. CaO additive can restrain the grain growth effectively, refine the grain size and improve the uniformity of microstructure. Bi2O3-CaO compound addtive are using the orthogonal experimental design method. The influence of Bi2O3, CaO and sintering temperature on the properties of NiCuZn ferrite are discussed in this work. We determine the best doping formula and sintering temperature, and also get the ferrite sample with uniform microstructure and excellent electromagnetic properties afterwards. Finally, the ferrite sample which is with the primarily formula Zn0.4Ni0.505Co0.015Cu0.1Fe1.98O3.99, adding 0.15wt% of Bi2O3 and 0.12wt% of CaO before the second ball mill and sintered at 1040℃, is with uniform microstructure and excellent electromagnetic properties, meeting the demands of Ka-band microwave ferrite devices.