Study On The High Gyromagnetic Ferrites And Applications On Ka-Band Phase Shifter

Both LiZn and NiCuZn ferrites are excellent microwave materials.With regard to LiZn ferrites,one have wide range of saturation magnetization?Ms?at room temperature,high Curie temperature,low sensitivity of remanence?Br?to stress,rectangular hysteresis loop and low fabrication cost.Compared with the LiZn ferrites,due to the lower magnetocrystalline constant K1 and higher density dm,NiCuZn ferrites have lower ferromagnetic resonance linewidth ?H,however,one have relative lower Curie temperature Tc.Thus,these two types of ferrites have been extensively used in various high frequency and power microwave/millimeter devices.With regard to the Ka-band ferrite phase shifter,challenge remains to meet to all requirements of low insertion loss,high temperature stability,miniaturization and lightening,which ask the ferrites applied in the phase shifters to obtain high saturation magnetization,remanence ratio,and Curie temperature and low coercivity,ferromagnetic resonance linewidth,and dielectric loss.In a word,on the one hand,this dissertation would foucus on studying the static magnetic properties,influence mechnisms of microwave loss of high gyromagntic LiZn ferrites,NiCuZn ferrites,LiZn/NiCuZn ferrites based on composite technology.On the other hand,we would carry out the simulation and fabrication of Ka-band ferrite phase shifter.Firstly,aiming at the high gyromagnetic LiZn ferrites,the influences of Zn substitution,iron deficiency and Bi₂O₃ additive to phase,micro structure,static magnetic,and microwave loss performance have been studied.The results indicate that,?1?Zn substitution is beneficial to increase the saturation magnetization Ms and remanence Br and decrease the coercivity Hc and cause the decrease the Curie temperature Tc.Based on the Néel's two-sublattice collinear model,the molecular-field coefficients ?aa,?bb,and ?ab=?ba have been calculated.With the same zinc content,the value of ?ab=?ba and ?aa are the biggest and smallest,respectively.Thus,the superexchange interaction strength between A-B sub-lattices is the strongest and that of A-A sub-lattices is the weakest.With the increase of Zn substitution,the decrease of the superexchange interaction strength results in the decrease of Curie Temperature Tc.?2?Based on the analysis of Fe2 p spectrum of XPS,iron deficiency could suppress the formation of Fe2+.Iron deficiency is beneficial to decrease the coercivity Hc,magnetocrystalline constant K1 and ferromagnetic resonance linewidth ?H and cause the decrease the Curie temperature Tc.On account of combination of the “brick wall” and the frequency spectra?f=0.01¹ MHz?of resistivity ? and dielectric constant ??,the grain and grain boundary resistivity have been calculated,and the grain and grain boundary resistivity would increase with the increase of iron deficiency content.Meanwhile,the ferromagnetic resonance linewidth ?H have been separated based on the magnetocrystalline constant K1 obtained via the law of approach to saturation.?3?Bi₂O₃ additive has the influence of promoting and preventing grain growth.When the Bi₂O₃ content is less than 0.25 wt%,Bi₂O₃ could promote the grain growth of LiZn ferrites,however,it would prevent the grain growth of LiZn ferrites when Bi₂O₃ content is more than 0.50 wt%.Optimum content of Bi₂O₃ additive could increase the denstity dm,saturation magnetization Ms and remanence Br and decrease the coercivity Hc and porosity P.Meanwhile,Bi₂O₃ additive is beneficial to decrease the porosity ferromagnetic resonance linewidth ?Hp and improve the microwave dielectric performance.Secondly,the NiCuZn ferrites have been fabricated via solid state reaction method,the influences of Zn substitution,iron deficiency and Bi₂O₃ additive to phase,micro structure,static magnetic,and microwave loss performance have been studied.The results manifest that,?1?ZnO could accelerate the grain growth via promoting the solid state reaction and increase the saturation magnetization Ms and remanence Br and decrease the coercivity Hc and cause the decrease the Curie temperature Tc.Based on Néel's two-sublattice collinear model,the relationship between Curie temperature Tc and temperature characteristics of Brillouin function for NiCuZn ferrites have been studied by nonlinear fitting calculation method.According to the tetrahedral A sites and the octahedral B sites of spinel structure model which do not only contain Fe3+ but also some other multiple magnetic ions?Ni2+and Cu2+?,molecular-field coefficients ?aa,?bb,and ?ab=?ba have been calculated,furthermore,the ferrimagnetism and paramagnetism Curie temperature Tc calculation formula have been modified,respectively.The magnetic moment versus temperature T?below the Curie temperature Tc?and the reciprocal of paramagnetism magnetic susceptibility 1/?m versus temperature T?beyond the Curie temperature Tc?have been investigated,respectively.The values of the calculated ferrimagnetism Curie temperature are very close to the values of the testing Curie temperature,and with the same zinc content,the values of paramagnetic Curie point are all bigger than that of ferrimagnetism Curie point.With regard to different zinc contents,the fitting results are coincided well with the experimental data.With the increasing of zinc content,?aa increases constantly.However,?ab=?ba shows an opposite trend and ?bb is invariant.?2?Optimum iron deficiency would increase the saturation magnetization Ms,density dm,and DC resistivity ?DC of NiCuZn ferrites.With the increase of iron deficiency,the ferromagnetic resonance linewidth ?H firstly derease and then increase,and the ferromagnetic resonance linewidth ?H have been separated based on the magnetocrystalline constant K1 obtained via the law of approach to saturation.When iron deficiency content is 0.08,the NiCuZn ferrites have low microwave loss performance with low ferromagnetic resonance linewidth ?H?9.63 kA/m?,high ???14.0?and low tan???1.74×10-4?.?3?Optimum content of Bi₂O₃ additive could increase the denstity dm,saturation magnetization Ms and remanence Br and decrease the coercivity Hc and porosity P of NiCuZn ferrites.Meanwhile,Bi₂O₃ additive is beneficial to decrease the porosity ferromagnetic resonance linewidth ?Hp and improve the microwave dielectric performance.When Bi₂O₃ content is 0.2 wt%,NiCuZn ferrites posses density dm?5.26 g/cm3?,saturation magnetization Ms?411 kA/m?,remanence Br?351 mT?,coercivity Hc?Hc=92 A/m?,DC resistivity ?DC?7.35×107 ??m?,ferromagnetic resonance linewidth ?H?10.7 kA/m?,???13.8?and tan???1.21×10-4?.In addition,the high gyromagnetic ferrites have been fabricated via composite technology of solid state reaction method,the influences of different mass ratio of LiZn and NiCuZn ferrites on phase,micro structure,static magnetic,ionic diffusion,and microwave loss performance have been studied.Simultaneously,in order to campare with the performance of gyromagnetic ferrites fabricated with composite technology,the influences of different Ni and Cu substitution on phase,micro structure,static magnetic,DC resistivity ?DC,and ferromagnetic resonance linewidth ?H performance of LiZn ferrite have been studied.The results manifest that,?1?With regard to the gyromagnetic ferrites fabricated with composite technology,with the increase mass ratio of NiCuZn ferrites,there would be an increase of density dm,saturation magnetization Ms and remanence Br and a derease of Hc,K1,and ?H,and the microwave dielectric constant ?? and dielectric loss tan?? performance would be improved,however,the Curie temperature Tcwould be decease.Meanwhile,in view of the analysis of the EDS energy spectra of Ni and Fe element,LiZn and Ni CuZn ferrites gradually inosculate as a whole homogeneous mass with the sintering temperature from 800 to 1200 ?.?2?Optimum Ni and Cu substitution could improve the density dm,saturation magnetization Ms,and remanence Br and decrease the ferromagnetic resonance linewidth ?H,but,the Ni and Cu substitution go against the decrease of coercivity Hc.In the end,the application of high gyromagnetic ferrites fabricated with the composite technology of solid state method with mass ration 60 to 40 of LiZn and NiCuZn has been done.Based on the high gyromagnetic ferrites fabricated with the composited technology,the Ka-band ferrite phase shifter with grooved waveguide has been simulated and fabricated.The results manifest that,?1?Optimization of width of centre hole,thickness of ferrite core wall,packing medium of ferrite core hole,length of ferrite core could suppress the formation of higher-order modes and improve the return loss S11,insertion loss S21,voltage standing wave ratio VSWR and phase shift.?2?In the temperature range of room temperature to 80 ?,the simulation results of Ka-band phase shifter achieve the expected design goal.?3?Ka-band ferrite phase shifter has been measured at 80 ? with the return loss |S11|??20 dB?,insertion loss |S21|??0.77 dB?,voltage standing wave ratio VSWR??1.1?,phase shift??360°?,and phase shift accuracy??2°?in the frequency range of 33.5 to 34.5 GHz.