Study On Preparation Of High Performance SrM Ferrite Material And Related Physical Mechanism

In recent years,with the development of electronic information system in the direction of high frequency and miniaturization,the development of electronic devices such as microwave/millimeter wave isolators and circulators in the direction high frequency,miniaturization and planarization has attracted attention.The high-performance M-type hexagonal ferrite has high remanence ratio and high anisotropy field.If it is applied to microwave devices,the permanent magnets of the device can be removed to realize the planarization,miniaturization and light weight of the device.If the application of M-type hexagonal ferrite in microwave devices is to be realized,the M-type hexagonal ferrite must have high remanence ratio,high magnetocrystalline anisotropy field and low ferromagnetic resonance linewidth.According to that,this article focuses on the preparation of SrM microwave ferrite with high remanence ratio,high magnetocrystalline anisotropy field,and low ferromagnetic resonance linewidth and the related mechanisms.Aiming to increase the magnetocrystalline anisotropy field without increasing the ferromagnetic resonance linewidth of SrM ferrite,the effect of ion substitution and additives on the performance of SrM ferrite was studied,and the critical single domain size of SrM ferrite has been calculated and verified,which provided theoretical and technical guidance for performance control of high-performance SrM ferrite materials.First,the influence of the substitution amount of La,Al and Ga ions on the performance of SrM microwave ferrite has been studied.The following results are obtained for Sr_0.7-xLa_xCa_0.3Fe_11.85Co_0.15O₁₉:As the substitution amount of La ions increases,all samples show strong uniaxial anisotropy.The magnetocrystalline anisotropy field of the sample increases first,reaches the maximum when the substitution amount is 0.3,and then decreases;the ferromagnetic resonance linewidth first increases,reaches the maximum when the substitution amount is 0.2,and then decreases.When the substitution amount is 0.3,the SrM ferrite sample has the best performance（the remanence ratio M_r/M_s is 87%,the magnetocrystalline anisotropy field H_a is 23.99k Oe,and the ferromagnetic resonance linewidthΔH is 1548Oe）.The substitution amount of fixed La is 0.3.For Sr_0.4La_0.3Ca_0.3Fe_11.85-xAl_xCo_0.15O₁₉,with the increase of the Al substitution amount,the magnetocrystalline anisotropy field of the sample first increases and then decreases,reaching the maximum when the Al substitution amount is 1.2,but the resonance line width also reaches its maximum value.Taking into account the performance of the experimental samples in this group,when the Al substitution amount is 1.0,the performance of the SrM ferrite sample is the best（M_r/M_s=83%,H_a=26.6k Oe,ΔH=1631Oe）.The substitution amount of fixed La is 0.3.For Sr_0.4La_0.3Ca_0.3Fe_11.85-xGa_xCo_0.15O₁₉,as the substitution amount of Ga increases,the remanence ratio floats around 80%,and the magnetocrystalline anisotropy field of the sample shows an increasing trend.When the substitution amount of Ga is 1.4,H_areaches the maximum value,while the ferromagnetic resonance linewidthΔH of the sample shows a decreasing trend,and reaches the minimum value when the Ga substitution amount is 1.2.Considering the influence of Al and Ga on the performance and the cost of material,the main formula of Sr_0.4La_0.3Ca_0.3Fe_10.85Al_1.0Co_0.15O₁₉ is the most suitable value.Secondly,the hexagonal crystal grain model was established by OOMMF micro-magnetism simulation software,and the model energy of the two magnetization states of the uniform state and the vortex state was calculated.The calculation results show that when the model thickness is 125nm and the hexagonal side length is350-356.25nm,the whole system is the most stable.Under this condition,the grain size D=700-712.5nm,and the model size at this time is the critical single domain size of SrM hexaferrites.SrM ferrite samples were prepared,and the OOMMF simulation results were verified from the performance changes of the samples,the Lorentz transmission electron microscope and magnetic force microscope observation results.The experimental results show that the critical single domain size of SrM ferrite is very close to the calculated result,which is consistent with the simulation result of micromagnetism.Finally,the fluxing effects in material sintering of the additives to promote sintering（CuO,Bi₂O₃）and the additive to prevent sintering（Si O₂）on the performance of SrM microwave ferrite were studied separately and mixed in proportion.The results are as follows:（1）With the increase of CuO doping,the grain size of the sample gradually increases,and the uniformity of the grain size gradually decreases.As the CuO doping amount x increases from 0 to 1.2wt%,the magnetocrystalline anisotropy field first increases and then decreases.When the doping amount x=0.2wt%,H_a reaches the maximum value of 29.8k Oe,but at this timeΔH of the sample also reaches the maximum 1663Oe,and remanence ratio M_r/M_s is 81%.（2）With the increase of Bi₂O₃doping,the grain size of the sample gradually increases,and the uniformity of the grain size gradually decreases.Compared with the CuO additive experimental group,the Bi₂O₃ additive has a lower sintering effect on the sample than CuO.When the Bi₂O₃doping amount x increases from 0 to 1.2wt%,the H_a shows a trend of first decreasing and then increasing.When x=1.0wt%,H_a reaches the maximum value of 28.9k Oe,theΔH is 1578Oe,and the remanence ratio M_r/M_s is 85%.（3）When CuO and Si O₂ are mixed and doped in a 2:1 ratio,Si O₂ will alleviate the deterioration of the microscopic morphology of ferrite samples due to the increase of CuO.With the increase of CuO/Si O₂ mixed doping,the H_a shows a trend of first increasing and then decreasing.When doping amounts of CuO and Si O₂ are added in 0.2wt%and 0.1wt%respectively,H_a reaches the maximum,which is 27.8k Oe.The sample linewidthΔH is 1540Oe,and the M_r/M_s is 80%.（4）When Bi₂O₃ and Si O₂ are mixed and mixed in a ratio of 2:1,Si O₂will alleviate the deterioration of the microscopic morphology of ferrite samples due to the increase of Bi₂O₃.As the mixing amount of Bi₂O₃/Si O₂ increases,the H_a shows a trend of first increasing and then decreasing.When doping amounts of Bi₂O₃ and Si O₂are added in 0.4wt%and 0.2wt%respectively,H_a reaches the maximum,which is29.3k Oe.The sample linewidthΔH is 1617Oe,and the M_r/M_s is 83%.（5）When Bi₂O₃and Si O₂ are mixed and doped in a ratio of 1:1,Bi₂O₃ can promote grain growth and increase the average grain size,while the inhibitory effect of Si O₂ is mainly to prevent abnormal growth of grains,slows down the increase in the standard deviation of the average grain size and protects the uniformity of the grain size distribution.With the increase of the mixing amount of Bi₂O₃/Si O₂,the H_a shows a trend of first increasing and then decreasing.When doping amounts of Bi₂O₃ and Si O₂ are added in 0.3wt%,H_areaches the maximum,which is 29.5k Oe.The sample linewidthΔH is 1597Oe,and the M_r/M_s is 81%.