Modified self-biased hexagonal gyromagnetic ferrite material and preparation method thereof

Abstract

The application belongs to the technical field of ferrite material preparation, and particularly provides a modified self-biased hexagonal gyromagnetic ferrite material and a preparation method thereof. The modified self-biased hexagonal gyromagnetic ferrite material comprises a main component and an additive. The main component comprises 74.5 mol% to 82.8 mol% of Fe2O3, 1.3 mol% to 6.1 mol% of Cr2O3, and the rest of BaCO3. Taking the weight of the main component after pre-sintering as a calculation basis, the additive comprises 0.5 wt% to 2.0 wt% of CaCO3, 0.5 wt% to 2.0 wt% of SiO2, and 0.1 wt% to 2.0 wt% of Bi2O3. The modified self-biased hexagonal gyromagnetic ferrite material (BaM) prepared through a sintering process optimization has the characteristics of high saturation magnetization (4πM s : 3.9~4.2kGs), high remanence ratio (M r / M s : 0.6~0.8), coercivity (H c : 450~550Oe), and low ferromagnetic resonance line width (ΔH: 230~280Oe), and meets the engineering requirements of microwave devices.

Description

Technical Field

[0001] This invention belongs to the field of ferrite material preparation technology, and specifically provides a modified self-biased hexagonal gyromagnetic ferrite material and its preparation method. Background Technology

[0002] With the rapid development of next-generation microwave technologies such as 5G / 6G communication, millimeter-wave radar, and satellite communication, miniaturization, integration, and high power density of devices have become core development trends, placing stringent performance requirements on core gyromagnetic materials. Self-biased hexagonal gyromagnetic ferrites, as an important branch of microwave gyromagnetic materials, possess unique uniaxial magnetocrystalline anisotropy, high coercivity, high remanence ratio, and self-biasing characteristics. They enable microwave devices to operate normally without external magnets, significantly reducing device size and weight. They exhibit irreplaceable application advantages in microwave devices such as circulators, isolators, and phase shifters, making them a key material for achieving planar integration of devices. Among them, M-type hexagonal ferrites, as a typical example, have become one of the research hotspots in the field of microwave materials in recent years due to their excellent self-biasing potential. The core performance indicators of gyromagnetic ferrites include saturation magnetization (4πM... s ), magnetocrystalline anisotropy field (H a ), ferromagnetic resonance linewidth (ΔH) and remanence ratio (M) r / M s These parameters directly determine the operating frequency, insertion loss, power handling capability, and stability of microwave devices. For self-biased hexagonal ferrite magnets, ideal performance requires: a suitable 4πM... s With H a To match the target operating frequency band, a high remanence ratio ensures stable self-biasing characteristics, a narrow ferromagnetic resonance linewidth and low dielectric loss reduce device energy loss, while high density and structural uniformity enhance power handling capability. However, performance optimization of existing self-biased hexagonal gyratory ferrite materials faces numerous bottlenecks, particularly the significant coupling contradiction between loss control and magnetic performance improvement, severely restricting their engineering application in high-performance microwave devices. Therefore, developing modified self-biased hexagonal gyratory ferrite materials to optimize loss and magnetic performance is of great significance.

[0003] Regarding modified self-biased hexagonal ferrite materials, German researchers J. Töpfer et al. investigated the effects of simultaneous addition of CaO and SiO2 on the microstructure and magnetic properties of sintered Sr-hexaferrite in their paper "Influence of SiO2 and CaO additions on the microstructure and magnetic properties of sintered Sr-hexaferrite". Both additives significantly affected grain growth behavior and magnetic properties. The addition of CaO promoted densification, leading to an increase in remanent magnetization, but due to simultaneous grain growth, the coercivity decreased to less than 100 kA / m. The addition of SiO2 inhibited grain growth. The simultaneous addition of CaO and SiO2 was beneficial for preparing a dense microstructure with relatively small grains. The optimal CaO / SiO2 ratio was around 1, with a remanent magnetization of 430 mT and a coercivity of 300 kA / m. In his paper "The effect of SiO2 addition on structural, magnetic and electrical properties of strontium hexa-ferrites", Shahid Hussain prepared strontium hexagonal ferrites with added SiO2 (0 ~ 2.0 wt%) using a solid-state reaction method. His study found that the addition of SiO2 significantly affected the structure, morphology, magnetic and electrical properties of the strontium ferrites; due to the reduced grain size, its coercivity H... c The maximum increase in magnetization was achieved with the addition of 1.5 wt% SiO2, representing a 10% improvement compared to the absence of SiO2, while the remanent magnetization decreased accordingly. Annapureddy V of the Functional Ceramics Group at the Korea Institute for Materials Science, in her paper "Growth of self-textured barium hexaferrite ceramics by normal sintering process and their anisotropic magnetic properties," employed a simple and low-cost technique to grow highly textured hexagonal barium ferrite ceramics without the need for flux or seed crystals for grain orientation. She synthesized plate-like hexagonal barium ferrite particles using a solid-state reaction method, aligned them under a weak magnetic field, and underwent uniaxial pressing. The neatly arranged hexagonal barium ferrites formed textured grains during sintering. Sintering was performed at 1200℃ and 1300℃, respectively. The density of the sample sintered at 1300℃ was 5.17 g / cm³, while the density of the sample sintered above 1200℃ was 4.95 g / cm³. 3In the sample sintered at 1200℃, the grains were small and elongated, with a grain size between 2 and 5 μm. After sintering at a higher temperature (1300℃), the microstructure consisted of anomalously grown grains (AGG). To determine the chemical composition of the sample, EDS analysis was performed, and the measured Fe / Ba ratio was approximately 12. The XRD pattern of the sample sintered at 1300℃ showed a significant enhancement in grain orientation, resulting in higher diffraction peak intensities corresponding to the <000l> plane (c-axis orientation). This may indicate that grain growth in the hexagonal barium ferrite system is more energy- and kinetically stable, and that grain growth preferentially occurs in the hexagonal a / b plane direction. Verma S of the School of Physics and Materials Science at Tapal University prepared BaFe using screen printing in the paper "Structural and magnetic properties of CoTi substituted barium hexaferrite thick films". 12- 2x Co x Ti x O 19 For thick films (x=0~1.0), it was found that with increasing substitution amount, the grain size increased, the lattice constants a and c increased, and the coercivity decreased monotonically. Co-Ti ions occupied the 2b, 4f2, 12k, and 4f1 sites in sequence, but the 2a site was substituted the least. In the paper "35-GHz Barium Hexaferrite / PDMS Composite-Based Millimeter-WaveCirculators for 5G Applications", Bowrothu disclosed the preparation of a BaM / PDMS composite material with a resonant frequency of 46.6 GHz using screen printing under completely low temperature (70℃) conditions, and successfully used this material to prepare a self-biased circulator with an operating frequency of 35 GHz.

[0004] While the aforementioned studies investigated the effects of single-process aspects, such as the type and content of additives and the influence of single process parameters, on the loss and magnetic properties of self-biased hexagonal swirl ferrite materials, they did not systematically examine the impact of multi-stage process improvements on the loss and magnetic properties of self-biased hexagonal swirl ferrite materials. Therefore, this invention provides a modified self-biased hexagonal swirl ferrite material and its preparation method to meet the engineering requirements of low loss and wide bandwidth in microwave devices. Summary of the Invention

[0005] The purpose of this invention is to provide a modified self-biased hexagonal gyromagnetic ferrite material and its preparation method, to solve the problem that existing self-biased hexagonal gyromagnetic ferrite materials cannot meet the engineering requirements of low loss and wide bandwidth in microwave devices. This invention is based on BaM hexagonal ferrite, and by introducing additives CaCO3, Bi2O3, and SiO2, while optimizing the segmented sintering process, a BaM hexagonal gyromagnetic ferrite material suitable for self-biased circulators is prepared, exhibiting high saturation magnetization (4πM). s 3.9~4.2kGs), high remanence ratio (M r / M s (0.6~0.8) and coercivity (H) c It features low ferromagnetic resonance linewidth (ΔH: 230~280Oe) and low ferromagnetic resonance linewidth (ΔH: 450~550Oe), meeting the engineering requirements of microwave devices.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A modified self-biased hexagonal gyromagnetic ferrite material, comprising a main component and additives, characterized in that:

[0008] The main components include: 74.5 mol% to 82.8 mol% Fe2O3, 1.3 mol% to 6.1 mol% Cr2O3, and the remainder is BaCO3;

[0009] Based on the weight of the main components after pre-calcination, the additives include: 0.5 wt% to 2.0 wt% of CaCO3, 0.5 wt% to 2.0 wt% of SiO2, and 0.1 wt% to 2.0 wt% of Bi2O3.

[0010] Furthermore, the saturation magnetization of the modified self-biased hexagonal gyromagnetic ferrite material is 3.9 kGs ~ 4.2 kGs, the remanence ratio is 0.6 ~ 0.8, the coercivity is 450 Oe ~ 550 Oe, and the ferromagnetic resonance linewidth is 230 Oe ~ 280 Oe.

[0011] Furthermore, the present invention provides a method for preparing the modified self-biased hexagonal gyromagnetic ferrite material, characterized by comprising the following steps:

[0012] Step 1: Prepare the ingredients;

[0013] The raw materials are BaCO3 with a purity of 99.5%, Cr2O3 with a purity of 99.5%, and Fe2O3 with a purity of 99.3%, and are mixed in a certain proportion.

[0014] Step 2, one-time ball milling;

[0015] The ingredients obtained in step 1 are ball-milled once, then dried and sieved to obtain primary ball-milled material;

[0016] Step 3, Pre-fire;

[0017] The sieved primary ball mill material was placed in an air atmosphere for pre-firing at a temperature of 1100℃~1300℃, a holding time of 1h~4h, and a heating rate of 1℃ / min~3℃ / min to obtain BaM hexagonal ferrite pre-fired material.

[0018] Step 4, doping;

[0019] Based on the mass of the pre-burned material obtained in step 3, CaCO3, SiO2, and Bi2O3 are added as additives in proportion to obtain the doped mixed powder.

[0020] Step 5: Secondary ball milling;

[0021] The mixed powder after doping was subjected to secondary ball milling, and the average particle size of the powder after ball milling was controlled to be 0.8μm~1.2μm to obtain secondary ball milling slurry;

[0022] Step 6: Shaping;

[0023] The slurry obtained in step 5 is dehydrated, and then the dehydrated slurry is pressed into a green body under a magnetic field forming press.

[0024] Step 7: Multi-step atmosphere sintering;

[0025] The green billet obtained in step 6 is placed in a controlled atmosphere resistance furnace, and the furnace temperature is raised from room temperature to 1000℃. Then, it is kept at a negative pressure atmosphere of -0.05MPa for 2 hours to accelerate the removal of moisture from the green billet and inhibit cracking. The heating rate is 0.5℃ / min to 2℃ / min.

[0026] Then the furnace temperature is continuously increased to 1200℃~1400℃ to allow the additives to be uniformly enriched at the grain boundaries and fully encapsulate the grains; the heating rate is 1℃ / min ~ 3℃ / min.

[0027] After heating to 1200℃~1400℃, the temperature is maintained in an oxygen atmosphere of 0.04MPa~0.06MPa for 6~18 hours to eliminate closed pores and make the grains uniform and dense.

[0028] Furthermore, in step 1, the raw material ratio is: 74.5 mol% to 82.8 mol% Fe2O3, 1.3 mol% to 6.1 mol% Cr2O3, and the remainder is BaCO3.

[0029] Furthermore, in step 4, the proportions of the additives are: 0.5 wt% to 2.0 wt% of CaCO3, 0.5 wt% to 2.0 wt% of SiO2, and 0.1 wt% to 2.0 wt% of Bi2O3.

[0030] Furthermore, in step 2, the ball milling time is 9 to 15 hours.

[0031] Furthermore, in step 5, the ball milling time is 15 to 24 hours.

[0032] Furthermore, in step 6, the moisture content of the slurry after dewatering is controlled between 4.0 wt% and 6.0 wt%.

[0033] Furthermore, in step 6, the parameters for pressing the green body are: the forming magnetic field strength is 0.6T to 1.2T, the forming pressure is 80 MPa to 140 MPa, and the holding time is 80 to 140 s.

[0034] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0035] This invention provides a modified self-biased hexagonal gyromagnetic ferrite material. CaCO3 is used as an additive to refine the BaM ferrite grains and inhibit abnormal grain growth. Simultaneously, CaCO3 decomposes into CaO and CO2 at high temperatures. CaO fills the intergranular gaps, increasing material density and reducing ferromagnetic resonance linewidth caused by porosity. Furthermore, the additive Bi2O3 is a low-melting-point oxide that rapidly melts during sintering to form a liquid phase, providing channels for grain growth and material diffusion, significantly reducing the sintering activation energy, achieving low-temperature sintering, and avoiding lattice distortion and magnetic performance degradation caused by high temperatures.

[0036] Meanwhile, this invention provides a method for preparing the above-mentioned modified self-biased hexagonal gyromagnetic ferrite material, optimizing the sintering process. The negative pressure sintering in the initial sintering stage removes gaseous impurities from the material's interior and generated during sintering, increasing material density; it also inhibits excessive oxidation reactions, regulates iron ion valence states, and optimizes the crystal structure; simultaneously, it promotes uniform grain growth, reduces porosity and defects, and lowers the ferromagnetic resonance linewidth; the oxygen-enriched sintering in the subsequent sintering stage replenishes the oxygen consumed during sintering, reducing lattice oxygen vacancies and repairing lattice defects; and it promotes the complete formation of the BaM ferrite phase while inhibiting impurity phase formation.

[0037] In summary, the modified self-biased hexagonal gyromagnetic ferrite material and its preparation method provided by this invention bring the following technical effects to microwave device design: 1) High saturation magnetization (4πM s 1) 3.9~4.2kGs), which can meet the engineering requirements for widening the bandwidth of microwave devices; 2) High remanence ratio (M r / M s(0.6~0.8) and coercivity (H) c 450~550Oe), which can make the magnetic moment tend to precess in a strong anisotropic direction, forming a built-in field, completely freeing it from the constraints of external magnets, and achieving small size and light weight; 3) Low ferromagnetic resonance linewidth (ΔH: 230~280Oe), which meets the engineering requirements of low insertion loss of microwave devices. Attached Figure Description

[0038] Figure 1 The X-ray diffraction patterns are shown for the low-loss self-biased hexagonal ferrite materials in Examples 1 and 2 of this invention.

[0039] Figure 2 Scanning electron microscope images of self-biased hexagonal ferrite materials sintered in air as a comparative example.

[0040] Figure 3 This is a scanning electron microscope image of the low-loss self-biased hexagonal ferrite material that was kept in an oxygen-rich atmosphere for 9 hours in Example 1 of the present invention.

[0041] Figure 4 This is a scanning electron microscope image of the low-loss self-biased hexagonal ferrite material that was kept in an oxygen-rich atmosphere for 15 hours in Embodiment 2 of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0043] Example 1

[0044] This embodiment provides a modified self-biased hexagonal gyromagnetic ferrite material, which is prepared by the following steps:

[0045] Step 1: Prepare the ingredients;

[0046] Using 99.5% pure BaCO3, 99.5% Cr2O3, and 99.3% Fe2O3 as raw materials, the ingredients were prepared in the following proportions: 76.61 mol% Fe2O3, 5.47 mol% Cr2O3, and 17.92 mol% BaCO3.

[0047] Step 2, one-time ball milling;

[0048] The ingredients obtained in step 1 are ball-milled once for 12 hours, then dried and sieved to obtain the primary ball-milled material.

[0049] Step 3, Pre-fire;

[0050] The sieved primary ball mill material was pre-fired in an air atmosphere at a pre-fired temperature of 1240℃ for 2 hours and a heating rate of 2℃ / min to obtain BaM hexagonal ferrite pre-fired material.

[0051] Step 4, doping;

[0052] Based on the mass of the pre-calcined material obtained in step 3, 1.5 wt% CaCO3, 1.0 wt% SiO2, and 0.5 wt% Bi2O3 were added to obtain the doped mixed powder.

[0053] Step 5: Secondary ball milling;

[0054] The mixed powder obtained by doping was ball-milled for 18 hours. The average particle size of the powder after ball milling was 1.0 μm, and the secondary ball-milled material was obtained.

[0055] Step 6: Shaping;

[0056] The slurry obtained in step 5 is dehydrated to control the water content of the slurry at 5.0 wt%. Then the dehydrated slurry is pressed into a green body under a magnetic field forming press. The forming magnetic field strength is 0.8 T, the forming pressure is 100 MPa, and the holding time is 120 s.

[0057] Step 7: Multi-step atmosphere sintering;

[0058] The green billet obtained in step 6 was placed in a controlled atmosphere resistance furnace, and the furnace temperature was raised from room temperature to 1000℃. It was then held at a negative pressure atmosphere of -0.05MPa for 2 hours to accelerate the removal of moisture from the green billet and inhibit cracking. The heating rate was 1℃ / min. The comparative example was held at atmospheric pressure in air for 2 hours.

[0059] Then the furnace temperature is continuously increased to 1280℃ to allow the additives to be uniformly enriched at the grain boundaries and fully encapsulate the grains; the heating rate is 2℃ / min.

[0060] After heating to 1280℃, it was held in an oxygen-rich atmosphere of 0.05MPa for 9 hours to reduce Fe. 2+ The process generates and eliminates closed pores, making the grains uniform and dense, ultimately yielding the modified self-biased hexagonal gyromagnetic ferrite material in this embodiment.

[0061] Example 2

[0062] This embodiment provides a modified self-biased hexagonal gyromagnetic ferrite material, which differs from Embodiment 1 in that: in step 7, after heating to 1280℃, it is kept at that temperature for 15 hours in an oxygen-rich atmosphere of 0.05MPa to obtain the modified self-biased hexagonal gyromagnetic ferrite material in this embodiment.

[0063] The modified self-biased hexagonal gyromagnetic ferrite material samples prepared in Examples 1 and 2 of this invention were tested below. X-ray diffraction was used to analyze the phase composition of the samples; scanning electron microscopy was used to observe the microstructure of the samples; and a LakeShore 8604 vibrating sample magnetometer was used to measure 4πM. s 4πM r H c The CK-XW-100 high-frequency integrated measurement system was used to measure ΔH, and the anisotropic field H was measured. a It is derived from Kittel's formula.

[0064] To more intuitively illustrate the beneficial effects of the present invention, the present invention also provides a comparative example, which differs from Example 1 in that: step 7, multi-step atmosphere sintering;

[0065] The green billet obtained in step 6 was placed in a controlled atmosphere resistance furnace, and the furnace temperature was raised from room temperature to 1000℃. It was then kept at room temperature for 2 hours in an atmospheric pressure atmosphere to accelerate the removal of moisture from the green billet and inhibit cracking. The heating rate was 1℃ / min. The comparative example was kept at room temperature for 2 hours in an atmospheric pressure atmosphere.

[0066] Then the furnace temperature is continuously increased to 1280℃ to allow the additives to be uniformly enriched at the grain boundaries and fully encapsulate the grains; the heating rate is 2℃ / min.

[0067] After heating to 1280℃, the material was kept at that temperature in air at normal pressure for 15 hours to obtain a self-biased hexagonal gyromagnetic ferrite material.

[0068] Tests showed that the 4πM of the self-biased hexagonal gyromagnetic ferrite samples in Comparative Examples 1 and 2 was significantly higher than that in Examples 1 and 2. s M r / M s H c H a ΔH, P and average grain size D are shown in Table 1.

[0069] Table 1 Test Results

[0070]

[0071] Furthermore, such as Figure 1 The figures show the X-ray diffraction patterns of the self-biased hexagonal ferrite materials in Examples 1-2 and the comparative example. As can be seen from the figures, the diffraction peaks of Examples 1-2 and the comparative example match well with the standard card, and no extraneous terms are generated. Figure 2 The image shown is a scanning electron microscope image of a self-biased hexagonal ferrite material sintered in air in a comparative example. Figure 3 The image shown is a scanning electron microscope image of the low-loss self-biased hexagonal ferrite material after being kept in an oxygen-rich atmosphere for 9 hours in Embodiment 1 of the present invention. Figure 4 The image shown is a scanning electron microscope image of the low-loss self-biased hexagonal ferrite material kept in an oxygen-rich atmosphere for 15 hours in Example 2 of the present invention. As can be seen from the figure, compared with the comparative examples, the average grain size of Examples 1-2 is smaller, the grain growth is more uniform, and the porosity is lower.

[0072] In summary, this invention, based on BaM hexagonal ferrite, prepared a BaM hexagonal gyromagnetic ferrite material suitable for self-biased circulators by optimizing the segmented sintering atmosphere. Its material specifications are: saturation magnetization 4πM. s 3.9~4.2kGs, remanence ratio M r / M s 0.6~0.8, coercivity H c The results show that the remanence ratio is 450~550 Oe and the ferromagnetic resonance linewidth ΔH is 230~280 Oe. These results provide a material basis for designing miniaturized self-biased circulators based on magnetic materials. The larger remanence ratio and narrow ferromagnetic resonance linewidth improve the circulator bandwidth and insertion loss characteristics.

[0073] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A modified self-biased hexagonal gyromagnetic ferrite material, comprising a main component and additives, characterized in that: The main components include: 74.5 mol%–82.8 mol% Fe2O3, 1.3 mol%–6.1 mol% Cr2O3, with the remainder being BaCO3; Based on the weight of the main components after pre-calcination, the additives include: 0.5 wt% to 2.0 wt% of CaCO3, 0.5 wt% to 2.0 wt% of SiO2, and 0.1 wt% to 2.0 wt% of Bi2O3.

2. The modified self-biased hexagonal gyromagnetic ferrite material according to claim 1, characterized in that, The saturation magnetization of the modified self-biased hexagonal gyromagnetic ferrite material is 3.9 kGs ~ 4.2 kGs, the remanence ratio is 0.6 ~ 0.8, the coercivity is 450 Oe ~ 550 Oe, and the ferromagnetic resonance linewidth is 230 Oe ~ 280 Oe.

3. The method for preparing the modified self-biased hexagonal gyromagnetic ferrite material according to claim 1, characterized in that, Includes the following steps: Step 1: Use BaCO3, Cr2O3, and Fe2O3 as raw materials and mix them in the specified proportions; Step 2: The ingredients obtained in Step 1 are ball-milled once, then dried and sieved to obtain primary ball-milled material; Step 3: Place the sieved primary ball milling material in an air atmosphere for pre-firing at a temperature of 1100℃~1300℃, a holding time of 1h~4h, and a heating rate of 1℃ / min~3℃ / min to obtain BaM hexagonal ferrite pre-fired material. Step 4: Based on the mass of the pre-burned material obtained in Step 3, add CaCO3, SiO2, and Bi2O3 as additives in proportion to obtain the doped mixed powder. Step 5: Perform a second ball milling on the mixed powder after doping, and control the average particle size of the powder after ball milling to be 0.8μm~1.2μm to obtain a second ball milling slurry; Step 6: Dehydrate the slurry obtained in Step 5, and then press the dehydrated slurry into a green body under a magnetic field forming press. Step 7: Perform multi-stage atmosphere sintering on the green body obtained in Step 6; The sample was placed in a controlled atmosphere resistance furnace, and the furnace temperature was raised from room temperature to 1000℃. Then it was kept at a negative pressure atmosphere of -0.05MPa for 2 hours, with a heating rate of 0.5℃ / min to 2℃ / min. The furnace temperature is continuously increased to 1200℃~1400℃ at a rate of 1℃ / min~3℃ / min; After further heating to 1200℃~1400℃, the material is kept at this temperature for 6~18 hours in an oxygen atmosphere of 0.04MPa~0.06MPa to obtain a modified self-biased hexagonal gyromagnetic ferrite material.

4. The method for preparing the modified self-biased hexagonal gyromagnetic ferrite material according to claim 3, characterized in that, In step 1, the raw material ratio is: 74.5 mol% to 82.8 mol% Fe2O3, 1.3 mol% to 6.1 mol% Cr2O3, and the remainder is BaCO3.

5. The method for preparing the modified self-biased hexagonal gyromagnetic ferrite material according to claim 3, characterized in that, In step 4, the proportions of the additives are: 0.5 wt% to 2.0 wt% of CaCO3, 0.5 wt% to 2.0 wt% of SiO2, and 0.1 wt% to 2.0 wt% of Bi2O3.

6. The method for preparing the modified self-biased hexagonal gyromagnetic ferrite material according to claim 3, characterized in that, In step 2, the ball milling time is 9 to 15 hours.

7. The method for preparing the modified self-biased hexagonal gyromagnetic ferrite material according to claim 3, characterized in that, In step 5, the ball milling time is 15 to 24 hours.

8. The method for preparing the modified self-biased hexagonal gyromagnetic ferrite material according to claim 3, characterized in that, In step 6, the moisture content of the slurry after dewatering is controlled between 4.0 wt% and 6.0 wt%.

9. The method for preparing the modified self-biased hexagonal gyromagnetic ferrite material according to claim 3, characterized in that, In step 6, the parameters for pressing the green body are: the forming magnetic field strength is 0.6T to 1.2T, the forming pressure is 80 MPa to 140 MPa, and the holding time is 80 to 140 seconds.

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