A low-loss oriented BaM hexagonal ferrite material covering the sub-6 GHz band and its preparation method

Abstract

The present invention discloses a low-loss oriented BaM hexagonal ferrite material covering the sub-6 GHz band and a preparation method thereof, based on Co with uniaxial anisotropy 2+ and Ru 4+ ion-combined substituted BaM hexagonal ferrite material, using goethite powder with a high aspect ratio synthesized by the hydrothermal method as a raw material to replace the iron red (Fe2O3) required in the traditional ferrite preparation process, enabling the Co 2+ / Ru 4+ ion-combined substituted BaM hexagonal ferrite to achieve oriented preferred growth, thereby greatly increasing the magnetic resonance frequency and meeting the requirements of the low-loss sub-6 GHz miniaturized antenna for a high operating frequency. Secondly, by adding low-melting-point Bi2O3, the particle size and magnetic domain width are increased, which can reduce the domain wall resonance relaxation frequency, resulting in an obvious separation between the natural resonance point and the domain wall resonance point, ensuring the low magnetic loss characteristics of this material.

Description

Technical Field

[0001] The present invention belongs to the technical field of communication device base materials, and relates to a ferrite material with high operating frequency and low magnetic / dielectric loss and a preparation method thereof. Specifically, it relates to a low-loss oriented BaM hexagonal ferrite material capable of covering the sub-6 GHz band and a preparation method thereof. Background Technique

[0002] Antennas, as the core components of communication systems, are indispensable for transmitting electromagnetic signals and are widely used in fields such as autonomous driving, photovoltaics, remote sensing radars, medical devices, and the Internet of Things. Recently, the booming development of 5G technology has generated a great demand for high-frequency miniaturized antennas. Generally speaking, using high-dielectric materials as antenna substrates can reduce the electromagnetic wave wavelength in the substrate, thereby reducing the antenna size. However, the high-dielectric materials used in this technology not only cause serious mismatch between the material impedance and the environmental impedance but also trigger surface wave excitation, and these drawbacks will deteriorate the antenna performance.

[0003] Compared with traditional high-dielectric materials, magnetodielectric materials with a permeability higher than 1 and a matching dielectric constant can significantly improve the impedance matching characteristics and achieve the miniaturization of antennas. Among many magnetodielectric materials, microwave ferrites with high resistivity, high permeability, and high cut-off frequency have received great attention in the industry. For microwave ferrites, restricted by the Snoek limit, it is necessary to make a compromise between high permeability and high magnetic resonance frequency. The figure of merit ( f 0) at the highest operating frequency ( PF ) is an important parameter to measure the high-frequency magnetic performance of microwave ferrites applied in the field of miniaturized antennas. PF The higher the

[0004] value, the lower the magnetic loss the material can obtain at higher frequencies. 3+ value is 7.2 - 8.1 GHz. PF value at 1 - 30 MHz has almost equal real parts of permeability and dielectric constant (24.0 - 27.0), and both the magnetic loss and the dielectric loss tangent are lower than 0.1.

[0005] According to the angle between the easy magnetization direction and the c-axis of the unit cell, hexagonal ferrites can be divided into uniaxial, planar, and conical types. Benefiting from the high magnetic permeability advantage, researchers usually use the method of metal ion substitution to adjust the high-frequency magnetism of planar hexagonal ferrites. For example, Patent CN106573848A uses Co 2+ and Ir 4+ ion substitution to prepare Co2Z and Co2Y type hexagonal ferrite composites. In the frequency band of 0.65 - 0.85 GHz, the real part of the magnetic permeability is 4.6 - 7.5, the real part of the dielectric constant is 6.5 - 8.1, the tangent of the magnetic loss angle is 0.07 - 0.29, and the tangent of the dielectric loss angle is 0.05 - 0.09. PF The 3+ value is 36.0 GHz. Patent US11827527B2 uses Bi 2+ and Ru 4+ ion combined substitution to prepare BaM hexagonal ferrite with planar anisotropy. In the frequency band of 1.0 - 2.0 GHz, the real part of the magnetic permeability is 2.9 - 3.3, the real part of the dielectric constant is 10.8 - 11.3, the tangent of the magnetic loss angle is 0.05 - 0.25, and the tangent of the dielectric loss angle is 0.013 - 0.04. PF The PF value is 33.7 - 53.0 GHz. Recently, researchers have discovered a new type of hexagonal ferrite crystal phase - 18H hexagonal ferrite, whose magnetic resonance frequency is much higher than that of traditional planar hexagonal ferrites, which provides the possibility to meet the application requirements of S and C band miniaturized antenna substrates. For example, Patent CN117228734B developed a low-loss CoZn-18H planar hexagonal ferrite with ultra-high magnetic resonance frequency through chemical coprecipitation method. In the frequency band of 0.82 - 4.97 GHz, the real part of the magnetic permeability is 1.38 - 2.01, the real part of the dielectric constant is 11.0 - 15.5, and the tangent of the magnetic loss angle does not exceed 0.10. Summary of the Invention

[0006] In view of this, the present invention discloses a lossy BaM hexagonal ferrite material with uniaxial anisotropy that can cover the entire sub-6 GHz frequency band and its preparation method to achieve high working frequency and low dielectric loss of the material and meet the miniaturization application requirements of sub-6 GHz antennas.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A low-loss oriented BaM hexagonal ferrite material covering the sub-6 GHz band, with the chemical formula BaCo 1.2 Ru 0.2 Fe 10.9 O 19 . The preparation method thereof includes the following steps:

[0009] 1) Weigh BaCO3, Co3O4, RuO2 and goethite powder as raw materials according to the stoichiometric ratio of each element in the chemical formula BaCo 1.2 Ru 0.2 Fe 10.9 O 19 . Then add 1-5 wt% of sintering aid Bi2O3 based on the total weight of the raw materials to the raw materials and mix evenly to form a raw material mixture;

[0010] The preparation method of the goethite powder is as follows: First, drop a NaOH solution with a concentration of 4-6 M into a ferric nitrate solution with a concentration of 0.3-0.5 M at a rate of 1-2 drops per second, and the total dropping amount is between 69-84 mL to form a mixed solution; Then heat the mixed solution to 60-150 °C and keep it warm for 64-80 h. After the reaction ends, naturally cool it to room temperature, and repeatedly wash and centrifuge the obtained product with deionized water and absolute ethanol for multiple times until the pH of the supernatant of the solution is neutral; Finally, take the centrifuged precipitate, place it in an oven at 60 °C and dry it overnight, take it out and grind it into fine powder to obtain the goethite powder.

[0011] 2) Granulate the raw material mixture in step 1) and an aqueous solution of polyvinyl alcohol according to a mass ratio of 4-9:1 to obtain coarse particles; the mass concentration of the aqueous solution of polyvinyl alcohol is 7%-9%.

[0012] 3) Use a mold to press the coarse particles obtained in step 2) into a disc or circular ring block, with a forming pressure of 1000-1540 MPa and a pressure holding time of 3-30 min to obtain a block sample;

[0013] 4) Place the block sample in step 3) in a tube furnace with oxygen passing through, with a gas passing rate of 0.1-0.3 L / min, and heat it to 900-1060 °C at a rate of 1-5 °C / min and sinter for 3-5 h to obtain the low-loss oriented BaM hexagonal ferrite material.

[0014] The present invention is based on a BaM hexagonal ferrite material jointly substituted by Co 2+ and Ru 4+ ions with uniaxial anisotropy. Using goethite powder with a high aspect ratio synthesized by the hydrothermal method as a raw material to replace the iron red (Fe2O3) required in the traditional ferrite preparation process, so that Co 2+ / Ru4+ The BaM hexagonal ferrite with ion co-substitution realizes the preferred growth in orientation, thus achieving a great increase in the magnetic resonance frequency and meeting the requirement of high operating frequency for the low-loss sub-6 GHz miniaturized antenna. Secondly, by adding low-melting-point Bi2O3, the particle size and the magnetic domain width are increased, which can reduce the resonance relaxation frequency of the domain wall, resulting in an obvious separation between the natural resonance point and the domain wall resonance point and ensuring the low magnetic loss property of this material. Therefore, the present invention is based on a BaM hexagonal ferrite with uniaxial anisotropy and co-substituted by Co 2+ and Ru 4+ ions. Through goethite powder with high shape anisotropy, the preferred growth in orientation of the BaM hexagonal ferrite co-substituted by Co 2+ / Ru 4+ ions is realized, obtaining an ultra-high magnetic resonance frequency, and by using a Bi2O3 additive, the particle size and the magnetic domain width are increased, realizing the low magnetic loss property. Description of the Drawings

[0015] Figure 1 is the preparation flow chart of the low-loss BaM hexagonal ferrite material covering the sub-6 GHz frequency band in the present invention; wherein: (a) is the schematic diagram of the preparation process of goethite powder with different length-diameter ratios (7.3 - 9.0); (b) is the schematic diagram of the preparation process of the low-loss oriented BaM hexagonal ferrite material; (c) is the schematic diagram of the oriented arrangement of goethite powder after applying uniaxial pressure.

[0016] Figure 2 Among them, (a) is the schematic diagram of the preparation of the composite sample by the rotating magnetic field orientation device; (b) is the X-ray diffraction pattern of the samples obtained in Comparative Example 1 (labeled No. 1) and Comparative Example 2 (labeled No. 6); (c) is the initial magnetization curve of the sample obtained in Comparative Example 2 (labeled No. 6) along the in-plane and out-of-plane directions.

[0017] Figure 3 is the X-ray diffraction pattern of the sample obtained in Example 1.

[0018] Figure 4 are the X-ray diffraction patterns of the samples obtained in Comparative Example 1 (labeled No. 1), Example 2 (labeled No. 2), and Example 3 (labeled No. 3).

[0019] Figure 5 are the real part, imaginary part of the complex magnetic permeability, and real part of the complex permittivity of the samples obtained in Comparative Example 1 (labeled No. 1), Example 2 (labeled No. 2), and Example 3 (labeled No. 3).

[0020] Figure 6The magnetic loss tangent and dielectric loss tangent of the samples obtained in Comparative Example 1 (labeled No. 1), Example 2 (labeled No. 2), and Example 3 (labeled No. 3).

[0021] Figure 7 The real part, imaginary part of the complex magnetic permeability, and magnetic loss tangent of Example 3 (labeled No. 3), Example 4 (labeled No. 4), and Example 5 (labeled No. 5). Detailed implementation manners

[0022] The present invention will be further explained below with reference to specific embodiments.

[0023] Example 1

[0024] Weigh 40.0 g (0.099 mol) of Fe(NO3)3∙9H2O and dissolve it in 250 mL of deionized water, and mix it evenly with a stir bar. Weigh 20.0 g (0.5 mol) of NaOH and dissolve it in 100 mL of deionized water, and mix it evenly with a stir bar. Then, use a graduated cylinder to measure 79 mL of the NaOH aqueous solution. Next, use a dropper to slowly add drop by drop the measured NaOH aqueous solution to the Fe(NO3)3∙9H2O aqueous solution. After the addition is completed, transfer the mixed solution to a 100 mL stainless steel reaction kettle with a PTFE liner, and place the reaction kettle in an oven at 60, 120, and 150 °C respectively, and keep it warm for 72 h. After the reaction is completed, cool it down to room temperature with the furnace. Then, repeatedly centrifuge and wash the obtained product with deionized water and absolute ethanol 9 times until the pH of the supernatant of the solution is 7.0. Place the centrifuged precipitate in an oven at 60 °C and dry it for 24 h, and grind it into fine powder to obtain the sample of Example 1.

[0025] Example 2

[0026] Weigh 0.82 g (0.00415 mol) of BaCO3, 0.40 g (0.00166 mol) of Co3O4, 0.11 g (0.000826 mol) of RuO2, and 4.03 g (0.0453 mol) of goethite powder prepared at 150 °C in Example 1. Put all the above raw materials into a mixer and mix for 1 h to form a raw material mixture. Then, weigh 1.6 g of the raw material mixture and 0.4 g of an 8% wt aqueous solution of polyvinyl alcohol, mix the two to granulate and obtain coarse particles. Weigh 0.25 g of the coarse particles, pour them into a mold with an outer diameter of 7.5 mm and an inner diameter of 3.0 mm, apply an axial pressure of 1270 MPa, press for 4 min and then take out to obtain an annular sample. Weigh 1.1 g of the coarse particles, pour them into a circular mold with a diameter of 15 mm, apply an axial pressure of 1270 MPa, press for 30 min and then take out to obtain a disc sample. Place the above two bulk samples in a tube-type sintering furnace with oxygen passing through, the gas flow rate is 0.1 L / min, sinter at 980 °C for 4 h, and the heating rate is 2 °C / min to obtain the sample of Example 2.

[0027] Example 3

[0028] Weigh 0.82 g (0.00415 mol) of BaCO3, 0.40 g (0.00166 mol) of Co3O4, 0.11 g (0.000826 mol) of RuO2, 4.03 g (0.0453 mol) of goethite powder prepared at 150 °C in Example 1, and 0.15 g (0.000322 mol) of Bi2O3. Put all the above raw materials into a mixer and mix for 1 h to form a raw material mixture. Then, weigh 1.6 g of the raw material mixture and 0.4 g of an 8% wt aqueous solution of polyvinyl alcohol, mix the two to granulate and obtain coarse particles. Weigh 0.25 g of the coarse particles, pour them into a mold with an outer diameter of 7.5 mm and an inner diameter of 3.0 mm, apply an axial pressure of 1270 MPa, press for 4 min and then take out to obtain an annular sample. Weigh 1.1 g of the coarse particles, pour them into a circular mold with a diameter of 15 mm, apply an axial pressure of 1270 MPa, press for 30 min and then take out to obtain a disc sample. Place the above two bulk samples in a tube-type sintering furnace with oxygen passing through, the gas flow rate is 0.1 L / min, sinter at 980 °C for 4 h, and the heating rate is 2 °C / min to obtain the sample of Example 3.

[0029] Example 4

[0030] Weigh 0.82 g (0.00415 mol) of BaCO3, 0.40 g (0.00166 mol) of Co3O4, 0.11 g (0.000826 mol) of RuO2, 4.03 g (0.0453 mol) of goethite powder prepared at 60 °C in Example 1, and 0.15 g (0.000322 mol) of Bi2O3. Put all the above raw materials into a mixer and mix for 1 h to form a raw material mixture. Then, weigh 1.6 g of the raw material mixture and 0.4 g of an 8% wt aqueous solution of polyvinyl alcohol, mix the two to granulate, and obtain coarse particles. Weigh 0.25 g of the coarse particles, pour them into a mold with an outer diameter of 7.5 mm and an inner diameter of 3.0 mm, apply an axial pressure of 1270 MPa, press for 4 min and then take out to obtain an annular sample. Weigh 1.1 g of the coarse particles, pour them into a circular mold with a diameter of 15 mm, apply an axial pressure of 1270 MPa, press for 30 min and then take out to obtain a disc sample. Place the above two samples in a tube-type sintering furnace with oxygen passing through, the gas flow rate is 0.1 L / min, sinter at 980 °C for 4 h, and the heating rate is 2 °C / min to obtain the sample of Example 4.

[0031] Example 5

[0032] Weigh 0.82 g (0.00415 mol) of BaCO3, 0.40 g (0.00166 mol) of Co3O4, 0.11 g (0.000826 mol) of RuO2, 4.03 g (0.0453 mol) of goethite powder prepared at 120 °C in Example 1, and 0.15 g (0.000322 mol) of Bi2O3. Put all the above raw materials into a mixer and mix for 1 h to form a raw material mixture. Then, weigh 1.6 g of the raw material mixture and 0.4 g of an 8% wt aqueous solution of polyvinyl alcohol, mix the two to granulate, and obtain coarse particles. Weigh 0.25 g of the coarse particles, pour them into a mold with an outer diameter of 7.5 mm and an inner diameter of 3.0 mm, apply an axial pressure of 1270 MPa, press for 4 min and then take out to obtain an annular sample. Weigh 1.1 g of the coarse particles, pour them into a circular mold with a diameter of 15 mm, apply an axial pressure of 1270 MPa, press for 30 min and then take out to obtain a disc sample. Place the above two samples in a tube-type sintering furnace with oxygen passing through, the gas flow rate is 0.1 L / min, sinter at 980 °C for 4 h, and the heating rate is 2 °C / min to obtain the sample of Example 5.

[0033] Comparative Example 1

[0034] Weigh 0.82 g (0.00415 mol) of BaCO3, 0.40 g (0.00166 mol) of Co3O4, 0.11 g (0.000826 mol) of RuO2 and 3.62 g (0.0226 mol) of Fe2O3. Place the above raw material powders in a ball mill and mix them evenly. The ball-to-material ratio is 10:1, the ball mill rotation speed is 200 r / min, and the ball milling time is 14 h to obtain the primary ball-milled slurry. Dry the slurry to obtain the primary ball-milled powder; place the primary ball-milled powder in a box-type muffle furnace and sinter it at 1100 °C for 4 h in an air atmosphere with a heating rate of 2 °C / min to obtain the pre-sintered material; then add Bi2O3 additive equivalent to 3 wt% of the mass of the pre-sintered material to the pre-sintered material, place it in a ball mill and mix it evenly. The ball-to-material ratio is 10:1, the ball mill rotation speed is 250 r / min, and the ball milling time is 14 h to obtain the secondary ball-milled slurry. Dry the slurry to obtain the secondary ball-milled powder; take 1.6 g of the secondary ball-milled powder and 0.4 g of 8% wt polyvinyl alcohol aqueous solution, mix and granulate them to obtain coarse particles. Weigh 0.25 g of the coarse particles, pour them into a mold with an outer diameter of 7.5 mm and an inner diameter of 3.0 mm, and take them out after pressing for 4 min under an axial pressure of 1270 MPa to obtain a ring-shaped sample. Weigh 1.1 g of the coarse particles, pour them into a circular mold with a diameter of 15 mm, and take them out after pressing for 30 min under an axial pressure of 1270 MPa to obtain a disc sample. Place the above two samples in a tube-type sintering furnace with oxygen passing through, the gas flow rate is 0.1 L / min, sinter at 980 °C for 4 h, and the heating rate is 2 °C / min to obtain the sample of Comparative Example 1.

[0035] Comparative Example 2

[0036] Place the secondary ball-milled powder in Comparative Example 1 in a tube-type sintering furnace with oxygen passing through, the gas flow rate is 0.1 L / min, the sintering temperature is 980 °C, the sintering time is 4 h, and the heating rate is 2 °C / min to obtain the secondary sintered powder and grind it; then weigh 0.09 g of polyurethane particles (PU) and completely dissolve them in 10 mL of acetone using an ultrasonic machine to form a mixed solution. After the PU is completely dissolved, add 0.20 g of the secondary sintered powder to the mixed solution and disperse it evenly by ultrasonic to form a suspension. When the suspension is in a semi-dry state, transfer it to a mold and place the mold in a rotating magnetic field with an external magnetic field of 2 T for orientation for 10 min, as shown in Figure 2 Figure (a); after the orientation is completed, place the sample in an oven and dry it for 24 h.

[0037] The product structure characterization and performance evaluation are as follows:

[0038] Refer to the appendix Figure 1Goethite powders with different aspect ratios (7.3 - 9.0) (Example 1) and different BaM hexaferrite material samples (Examples 2 - 5) were prepared. Meanwhile, to prove that the goethite powder prepared by the present invention can significantly increase the application frequency of BaM hexaferrite materials, a ferrite sample prepared based on the traditional ceramic method was provided (Comparative Example 1). In addition, to illustrate the uniaxial anisotropy of the formula (BaCo 1.2 Ru 0.2 Fe 10.9 O 19 ) itself, a composite sample prepared based on the traditional ceramic method was also provided (Comparative Example 2).

[0039] Figure 2 (b) shows the X-ray diffraction patterns of the samples obtained in Comparative Example 1 (labeled No. 1) and Comparative Example 2 (labeled No. 6); obviously, after the external rotating magnetic field orientation treatment, the diffraction peak intensities corresponding to the (006) and (008) crystal planes of the samples are significantly reduced, indicating that most of the hexagonal unit cell c axes perpendicular to the (00 l ) plane are arranged along the in-plane direction under the action of the magnetic field orientation. Figure 2 (c) shows the initial magnetization curves of the sample obtained in Comparative Example 2 (labeled No. 6) along the in-plane and out-of-plane directions; it can be seen that the magnetization direction is the in-plane direction, that is, the easy magnetization direction is parallel to the hexagonal unit cell c axis direction. The above results prove that the formula (BaCo 1.2 Ru 0.2 Fe 10.9 O 19 ) adopted by the present invention itself has uniaxial anisotropy.

[0040] Figure 3 is the X-ray diffraction pattern of the goethite powder obtained at different reaction temperatures in Example 1. It can be seen that the phase structures of the samples obtained at all temperatures conform to the standard goethite powder diffraction results (PDF#29 - 0713). Figure 4 shows the X-ray diffraction results of the samples obtained in Comparative Example 1, Example 2, and Example 3. It can be seen that compared with the samples prepared by the traditional ceramic method using spherical Fe2O3 powder as the raw material, the diffraction peak intensities of the (006), (008), and (0014) crystal planes of the samples prepared using goethite powder as the raw material are significantly enhanced, showing significant preferred orientation.

[0041] Figure 5 (a) and (b) are the complex permeability spectra of the samples obtained in Comparative Example 1, Example 2, and Example 3. Obviously, compared with the samples prepared by the traditional ceramic method using spherical Fe2O3 powder as the raw material, the samples prepared using goethite powder as the raw material have a higher magnetic resonance frequency. This is because after applying uniaxial pressure, the goethite particles are oriented (as Figure 1As shown in (c), after high-temperature sintering, the oriented goethite particles reacted with other raw materials to form oriented BaM hexaferrite grains, achieving oriented preferential growth. This led to an enhancement of the uniaxial magnetocrystalline anisotropy in the out-of-plane direction, significantly increasing the natural resonance frequency of the sample and significantly decreasing the magnetic loss tangent in the sub-6 GHz band, as Figure 6 shown. In addition, compared with the sample obtained in Example 2 without the additive Bi2O3, the sample obtained in Example 3 containing the additive Bi2O3 had a lower domain wall resonance relaxation frequency, which led to an obvious separation between the natural resonance frequency point and the domain wall resonance frequency point, ensuring the low magnetic loss characteristics of this material.

[0042] Figure 7 The real part, imaginary part of the complex magnetic permeability, and magnetic loss tangent of the samples obtained in Examples 3 to 5 are shown. As the reaction temperature of the synthetic goethite raw material increased, the natural resonance frequency gradually increased, which caused the magnetic loss tangent of the sample in the sub-6 GHz band to gradually decrease. This indicates that by changing the reaction temperature required for the synthetic goethite raw material, the magnetic spectrum and magnetic loss characteristics of the oriented BaM hexaferrite material can be effectively regulated.

[0043] Table 1 shows the real part of the magnetic permeability μ′, magnetic loss tangent tan δ μ , real part of the dielectric constant ε′, dielectric loss tangent tan δ ε , highest operating frequency f 0, and figure of merit PF of the samples prepared in Examples 2 to 5 and Comparative Example 1.

[0044] Table 1 Performance parameters of the samples prepared in Examples 2 - 5 and Comparative Example 1

[0045]

[0046] As can be seen from Table 1, by comparing Comparative Example 1 and Example 3, it can be seen that using goethite with a high aspect ratio can increase f 0 from 0.82 GHz to 7.5 GHz, and the PF value from 23.7 GHz to 98.2 GHz, which indicates that using goethite powder as the raw material can successfully achieve the goal of covering the entire Sub-6 GHz band with the highest operating frequency. Secondly, by comparing Example 2 and Example 3, it can be seen that f 0 increased from 4.17 GHz to 7.5 GHz, and PFThe value increased from 54.6 GHz to 98.2 GHz, indicating that the addition of the sintering aid Bi2O3 can significantly increase the maximum operating frequency and effectively suppress the magnetic loss at high frequencies. Finally, by comparing Examples 3, 4, and 5, it can be seen that as the reaction temperature of the synthetic goethite raw material increases, f 0 increased from 1.84 GHz to 7.5 GHz, PF The value increased from 32.4 GHz to 98.2 GHz, indicating that by regulating the synthesis temperature of goethite powder, the high-frequency magnetism of the oriented BaM hexaferrite material can be effectively regulated.

[0047] In summary, the present invention is based on a BaM hexaferrite material with uniaxial anisotropy jointly substituted by Co 2+ and Ru 4+ ions. Using goethite powder prepared by the hydrothermal method as the raw material and combining the low-melting-point Bi2O3 addition technology, a low-loss oriented BaM hexaferrite material with high magnetic permeability (1.3 ≤ μ′ ≤ 1.8), low dielectric constant (5.2 ≤ ε′ ≤ 6.6), and low magnetodielectric loss (tan δ μ ≤ 0.10, tan δ ε ≤ 0.026) that can cover the entire sub-6 GHz band was prepared. Its magnetodielectric loss in the entire sub-6 GHz band is lower than that of the vast majority of existing polycrystalline hexaferrites. These results demonstrate the feasibility of using goethite powder with high shape anisotropy as the raw material to prepare a low-loss oriented BaM hexaferrite with uniaxial anisotropy covering the sub-6 GHz band, providing a material basis for the design of miniaturized antennas based on magnetodielectric materials applicable to the sub-6 GHz band.

Claims

1. A preparation method of a low-loss oriented BaM hexagonal ferrite material covering the sub-6 GHz frequency band, characterized in that, It includes the following steps: 1) According to the stoichiometric ratios of the elements in the chemical formula BaCo 1.2 Ru 0.2 Fe 10.9 O 19 weigh BaCO3, Co3O4, RuO2 and goethite powder with an aspect ratio of 7.3 - 9.0 as raw materials, and then add 1 - 5 wt% of the sintering aid Bi2O3 based on the total weight of the raw materials to the raw materials and mix them evenly to form a raw material mixture; 2) Mix and granulate the raw material mixture in step 1) and the aqueous polyvinyl alcohol solution at a mass ratio of 4 - 9:1 to obtain coarse particles; 3) Use a mold to press the coarse particles obtained in step 2) into round tablets or circular blocks, with a forming pressure of 1000 - 1540 MPa and a pressure holding time of 3 - 30 min to obtain block samples; 4) Place the block samples in step 3) in a tube-type sintering furnace with oxygen passing through, at a gas passing rate of 0.1 - 0.3 L / min, heat up at a rate of 1 - 5 °C / min to 900 - 1060 °C and sinter for 3 - 5 h to obtain the low-loss oriented BaM hexagonal ferrite material; The preparation method of the goethite powder is as follows: First, drop a NaOH solution with a concentration of 4 - 6 M into a ferric nitrate solution with a concentration of 0.3 - 0.5 M at a rate of 1 - 2 drops per second, and the total dropping amount is between 69 - 84 mL to form a mixed solution; then heat the mixed solution to 60 - 150 °C and keep it warm for 64 - 80 h. After the reaction ends, cool it naturally to room temperature, and repeatedly wash and centrifuge the obtained product with deionized water and absolute ethanol for multiple times until the pH of the supernatant of the solution is neutral; finally, take the centrifuged precipitate, place it in an oven at 60 °C and dry it overnight, take it out and grind it into fine powder to obtain the goethite powder.

2. The preparation method of a low-loss oriented BaM hexagonal ferrite material covering the sub-6 GHz band as described in claim 1, characterized in that, In step 2), the mass concentration of the aqueous polyvinyl alcohol solution is 7% - 9%.

3. Application of a low-loss oriented BaM hexagonal ferrite material covering the sub-6 GHz frequency band prepared by the method according to claim 1 in an antenna substrate.

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