Investigation On Self-biased Hexaferrite Gyromagnetic Material And Its Application

Motivated by the wide application of active phased array radar in modern electronic countermeasures,microwave devices possessing characteristics like high frequency,small size and low loss have become the research focus of microwave and millimeter wave technology.Microwave circulator is a necessary component in Transmit/Receive?T/R?module.However,traditional circulator needs a large size permanent magnet to provide DC bias field,so it is difficult to realize the miniaturization of the whole Transmit-Receive system.The uniaxial hexaferrite has large magnetocrystalline anisotropy and high saturation magnetization.The microwave circulator designed based on the uniaxial hexagonal ferrite possesses self-biased field,which means it does not need permanent magnet.These characteristics are of great significance to realize the miniaturization and planarization of microwave circulator and even T/R module.Aiming at the design and application of microwave self biased circulator,this dissertation studied the effects of process condition,ion substitution and sintering aids on the oriented M-type hexaferrite.The self-biased application of W-type hexaferrite was discussed,and then the microwave self-biased circulator was designed.The effect of process condition on the oriented M-type hexaferrite was studied,including the pre-sintering temperature,the second ball milling time and the sintering temperature.When the pre-sintering temperature was 1250^oC,the grain of oriented Ba M sample grew uniformly and compactly.The density?reached the maximum value of4.61 g/cm³,and the porosity p reached the minimum value of 12.7%.Meanwhile,the saturation magnetization M_s and the remanence ratio M_r/M_s reached maximum.When the ball milling time was 12 h,the average size of the pre-sintered material was 1.434?m.Most particles were in single domain state,which was conducive to the magnetic moment rotation and orientation under the external magnetic field.However,the porosity p increased and the density?decreased when the milling time further increased.When the sintering temperature was 1200^oC,the Ba M sample possessed strong densification,small porosity p,and uniform distribution of grain.Meantime,the M_s and M_r/M_s got the maximum value.As the sintering temperature further increased?1250^oC and 1300^oC?,there were oversize grains and more pores.In summary,the proper pre-sintering temperature,the proper ball milling time and the proper sintering temperature were 1250^oC,12 h and 1200^oC respectively.The effects of ion substitution on the oriented M-type hexaferrite were investigated.Substitution of Sr²⁺for Ba²⁺could effectively improve the coercivity H_c of the oriented Ba M samples.When the substitution content of Sr²⁺was x=1.0,the coercivity H_creached the maximum value of 3156 Oe,but the M_s and M_r/M_s of Ba M samples reduced due to Sr²⁺substitution.The substitution of Gd³⁺for Fe³⁺could effectively change the magnetocrystalline anisotropy field H_a of oriented Ba M.When the substitution content of Gd³⁺was x=0.1,the H_a reached the maximum value of 17869 Oe,the M_s and M_r/M_skept high values?M_s=56.23 emu/g,M_r/M_s=0.8?.The oriented Ba Gd_0.1Fe_11.9O₁₉material was potential candidate for the design of self-biased circulator operated at high microwave frequency such as Ka and U band.The substitution of Zn²⁺-Sn⁴⁺for Fe³⁺could also effectively adjust the H_a of oriented Ba M samples.When the substitution content of Zn-Sn was x=0.6,the H_a decreased to 8527 Oe.However,the M_s,M_r/M_s and H_c decreased dramatically.The effects of sintering aids on M-type hexaferrite were studied.Bi₂O₃·B₂O₃·Si O₂·Zn O?BBSZ?was added during the preparation of oriented Ba Gd_0.1Fe_11.9O₁₉and Ba Zn_0.6Sn_0.6Fe_10.8O₁₉.When the BBSZ content was 2.5 wt%,the M_s and M_r/M_s of oriented Ba Gd_0.1Fe_11.9O₁₉ were 65.05 emu/g and 0.87 respectively,which increased by 15.7%and 8.75%respectively compared with that of sample without BBSZ.The H_c was 2604 Oe,the H_a was 16975 Oe and the relative density was92%.Meanwhile,the grain distribution was uniform.This Ba Gd_0.1Fe_11.9O₁₉ material was suitable for the design of self-biased circulator at high microwave band such as Ka and U band.For Ba Zn_0.6Sn_0.6Fe_10.8O₁₉ material,the appropriate content of BBSZ was2.5 wt%.The M_s and M_r/M_s were obviously increased,but the M_r/M_s?0.65?was still low.The H_c?512 Oe?was difficult to ensure the stability of the self-biased microwave devices.The self-biased application of W-type hexaferrite was investigated.The H_c and M_r/M_s of Sr_1-xGd_xNi₂Fe₁₆O₂₇ were very low,and the magnetic properties were similar to soft magnetic materials,so it was not suitable for the design of self-biased circulator.Oriented Ba Gd_xNi₂Fe_16-xO₂₇ grains grew uniformly in the direction of easy magnetization axis?c-axis?,which was perpendicular to the sample plane.When Gd³⁺substitution was x=0.0,the M_r/M_s reached 0.90.When Gd³⁺substitution was x=0.2,the oriented Ba W possessed high M_s?M_s=58.36 emu/g,4?M_s=3792 Gs?,high H_c?1527Oe?,high M_r/M_s?0.85?,relatively low H_a?10253Oe?and low ferromagnetic resonance linewidth?H?624 Oe?simultaneously.This material was suitable for the design of self-bias circulator operated at low microwave frequency such as Ku and K band.Three impedance matching modes were used to simulate and design the self-biased microstrip circulator,and all of them realized good circular function at K-band.