Gadolinium ion doped M-type strontium ferrite wave-absorbing material as well as preparation method and application thereof

Abstract

The invention discloses a gadolinium ion-doped M-type strontium ferrite wave-absorbing material as well as a preparation method and application thereof, relates to the field of electromagnetic wave absorbing materials, and solves the problems of insufficient magnetic response, unbalanced magnetoelectric matching and limited engineering suitability of traditional strontium ferrite in a Ku wave band. And the problems of difficulty in realizing collaborative optimization between frequency band broadening and magnetic performance stability, easiness in causing structure instability and magnetic performance fluctuation and complex preparation process of the existing rare earth ion doped modified strontium ferrite are solved. The chemical formula of the gadolinium ion doped M-type strontium ferrite wave-absorbing material is Sr1-xGdxFe12O19, x is greater than or equal to 0.01 and less than or equal to 0.50, and strontium carbonate, ferric oxide and gadolinium oxide are mixed, ground, pre-sintered and subjected to heat preservation according to the stoichiometric ratio; and carrying out grinding, sintering and heat preservation on the pre-sintered blocky product to obtain the gadolinium ion doped M-type strontium ferrite wave-absorbing material. The preparation method can be applied to preparation of a Ku-band electromagnetic interference protection wave-absorbing coating or preparation of a magnetic-electric synergistic loss composite wave-absorbing material.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing materials, specifically to a gadolinium ion-doped M-type strontium ferrite absorbing material and its preparation method and application. Background Technology

[0002] Against the backdrop of the rapid development of 5G communication systems, high-frequency phased array radars, and advanced electronic equipment, Ku-band (12~18 GHz) electromagnetic waves, characterized by short wavelengths, concentrated energy, and strong propagation directionality, are widely used in satellite communications, radar detection, and precision guidance. Existing M-type strontium ferrite (SrFe) 12 O 19 Due to its high magnetocrystalline anisotropy constant and excellent chemical stability, SrFe is considered a potential high-frequency magnetic loss absorbing material, but traditional SrFe... 12 O 19 The natural resonant frequency of these materials is typically located in the lower frequency band, resulting in insufficient magnetic response in the Ku band and a relatively simple magnetic loss mechanism. This makes it difficult to achieve ideal matching of permeability and dielectric constant at high frequencies, leading to limited absorption bandwidth and poor impedance matching performance. Furthermore, when the material thickness is reduced to meet lightweight requirements, its peak reflection loss often decreases significantly, limiting its engineering applicability.

[0003] To overcome these shortcomings, existing technologies often employ rare-earth ion doping to modify strontium ferrite, introducing rare-earth ions to adjust the crystal structure and magnetocrystalline anisotropy. However, in practical applications, it is difficult to precisely control the occupancy ratio of each ion in the crystal lattice during the doping process, easily leading to ion excess or deficiency, resulting in localized lattice stress concentration, uneven oxygen vacancy distribution, and Fe... 2+ / Fe 3+Fluctuations in the ratio disrupt the microstructure, leading to defects or stress distortion in the crystal phase, disordered magnetic moment arrangement, reduced saturation magnetization, and unstable coercivity. For example, the neodymium-zirconium co-substituted strontium ferrite material disclosed in Chinese patent document CN120191970A, while achieving bandwidth broadening and reducing matching thickness through the synergistic effect of two ions (neodymium and zirconium), suffers from decreased saturation magnetization and coercivity, weakened magnetocrystalline anisotropy, and a limited number of effective magnetic moments per unit volume capable of contributing to microwave magnetic loss. Furthermore, due to localized defects and uneven magnetic moment arrangement in the microstructure, the material is sensitive to external electromagnetic interference and thermal disturbances, making it difficult to maintain stable absorption performance under complex operating conditions. Therefore, it is evident that existing technologies in rare-earth ion doping modification present a significant contradiction between microstructure control and performance optimization, making it difficult to achieve a balance between bandwidth broadening and magnetic performance maintenance. For example, the praseodymium-doped strontium ferrite material disclosed in Chinese patent document CN115974542A, while improving dielectric properties to some extent, relies on the sol-gel method for precise control of morphology and particle size. This process is sensitive to parameters, has limited repeatability, and involves high raw material costs, hindering large-scale production. Furthermore, some doped systems suffer from severe lattice distortion, secondary phase formation, or abnormal particle growth. These microstructural issues further weaken the material's magnetic property consistency and engineering reliability.

[0004] Therefore, developing a Ku-band strontium ferrite absorbing material that is simple to manufacture, has excellent performance, and can effectively balance high-frequency magnetic response capability, magnetic property stability, and engineering feasibility has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of traditional strontium ferrites in terms of insufficient magnetic response in the Ku band, magnetoelectric mismatch, and limited engineering adaptability, as well as the difficulties in achieving synergistic optimization between bandwidth broadening and magnetic performance stability, the susceptibility to structural instability and magnetic performance fluctuations, and the complex fabrication processes of existing rare-earth ion-doped strontium ferrites, this invention proposes a gadolinium ion-doped M-type strontium ferrite microwave absorbing material, its preparation method, and its applications. The technical solution of this invention is as follows: A gadolinium ion-doped M-type strontium ferrite microwave absorbing material, wherein the chemical formula of the gadolinium ion-doped M-type strontium ferrite microwave absorbing material is Sr 1-x Gd x Fe 12 O 19 , where 0.01≤x≤0.50.

[0006] Furthermore, the thickness of the gadolinium ion-doped M-type strontium ferrite microwave absorbing material is 1~5 mm.

[0007] A method for preparing the above-mentioned gadolinium ion-doped M-type strontium ferrite microwave absorbing material includes the following preparation steps: According to Sr1-x Gd x Fe 12 O 19 According to the stoichiometric ratio, strontium carbonate (SrCO3), iron oxide (Fe2O3), and gadolinium oxide (Gd2O3) are mixed and ground once, pre-calcined, and kept at a certain temperature; the pre-calcined block product is then ground a second time, sintered, and kept at a certain temperature to obtain gadolinium ion-doped M-type strontium ferrite microwave absorbing material.

[0008] Furthermore, the particle size of the powder obtained by the first grinding is 1~6 µm.

[0009] Furthermore, the pre-firing temperature is 1100℃~1500℃; the pre-firing atmosphere is an air atmosphere; and the pre-firing heating rate is 5℃ / min.

[0010] Furthermore, the particle size of the powder obtained by the secondary grinding is 1~5 µm.

[0011] Furthermore, the sintering temperature is 1100℃~1500℃; the sintering atmosphere is an air atmosphere; and the sintering heating rate is 5℃ / min.

[0012] Furthermore, the pre-firing temperature is always 50°C lower than the sintering temperature; the holding time is always 2-5 hours.

[0013] An application of the above-mentioned gadolinium ion-doped M-type strontium ferrite absorbing material is applied to the preparation of absorbing coatings for Ku-band electromagnetic interference protection or to the preparation of composite absorbing materials with magneto-electric synergistic loss.

[0014] Furthermore, the absorbing coating for Ku-band electromagnetic interference protection or the composite absorbing material with magneto-electric synergistic loss is applied to the electromagnetic protection of satellite communication terminals, radar antenna systems, 5G communication equipment, or electronic equipment.

[0015] Compared with existing technologies, this invention solves the problems of insufficient magnetic response, magnetoelectric mismatch, and limited engineering adaptability of traditional strontium ferrites in the Ku band, as well as the difficulties in achieving synergistic optimization between bandwidth broadening and magnetic performance stability, the susceptibility to structural instability and magnetic performance fluctuations, and the complex preparation process of existing rare earth doped strontium ferrites. Specifically, the beneficial effects are as follows: 1. This invention achieves synergistic optimization of saturation magnetization and coercivity by combining Gd-doped strontium ferrite with directional control of magnetocrystalline anisotropy. Through precise control of the Gd doping amount x and sintering temperature, a stable process window is established, allowing the internal charge compensation mechanism of the material to shift from oxygen vacancy dominance to Fe… 3+The controlled transition dominated by reduction optimizes magnetic and dielectric parameters while maintaining the integrity of the M-type structure. At a thickness of 5 mm, the gadolinium ion-doped M-type strontium ferrite absorbing material provided by this invention achieves a peak reflection loss of -15.7 dB in the Ku band, an effective absorption bandwidth of 1.12 GHz, a saturation magnetization of 99.16 emu / g, and a coercivity of 3.47 kOe. This achieves a reasonable match between magnetic response intensity and anisotropic field, effectively covering the Ku band with the natural resonant frequency and improving electromagnetic energy dissipation efficiency. It exhibits stable magnetic properties and good chemical stability, adapting to complex electromagnetic environments and wide temperature conditions.

[0016] 2. This invention employs a high-temperature solid-state method to prepare gadolinium ion-doped M-type strontium ferrite microwave absorbing materials. The process is simple, the raw materials are readily available, and the operating conditions are controllable. It eliminates the need for complex precursor synthesis or precise morphology control, avoiding the reproducibility issues common in multi-step processes such as sol-gel. By optimizing key parameters (Gd doping amount x and sintering temperature), this invention establishes a repeatable, scalable process window with good performance consistency, facilitating mass production and cost control. This provides a reliable manufacturing path for the engineering application of high-performance Ku-band microwave absorbing materials, significantly improving industrial feasibility.

[0017] 3. The gadolinium ion-doped M-type strontium ferrite absorbing material prepared in this invention exhibits a clear Ku-band absorption response based on stable magnetic properties. It can be directly applied to the electromagnetic protection of satellite communication terminals, radar antenna systems, 5G communication equipment, or electronic equipment to suppress cavity clutter and electromagnetic interference. Furthermore, this material can be composited with carbon-based materials or polymer matrices to construct a magneto-electric synergistic loss composite absorbing system, expanding its application space in high-performance electromagnetic protection structural materials and achieving a systematic improvement in material performance, mechanism clarity, and engineering adaptability. Attached Figure Description

[0018] Figure 1 The room temperature hysteresis loop diagrams are shown for the gadolinium ion-doped M-type strontium ferrite absorbing material prepared in Example 1 and the undoped M-type strontium ferrite absorbing material prepared in Comparative Example 1. Figure 2 The graphs show the reflection loss versus frequency curves of the gadolinium ion-doped M-type strontium ferrite absorbing material prepared in Example 1 and the undoped M-type strontium ferrite absorbing material prepared in Comparative Example 1 under different thickness conditions; wherein, Figure 2 (a) is a graph showing the reflection loss of the gadolinium ion-doped M-type strontium ferrite absorbing material prepared in Example 1 as a function of frequency under different thickness conditions. Figure 2 (b) is a graph showing the reflection loss of the M-type strontium ferrite absorbing material without gadolinium ions prepared in Comparative Example 1 as a function of frequency under different thickness conditions. Detailed Implementation

[0019] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as limiting the present invention.

[0020] Example 1. According to the chemical formula Sr 0.97 Gd 0.03 Fe 12 O 19 According to the stoichiometric ratio, raw materials SrCO3 (analytical grade), Fe2O3 (analytical grade), and Gd2O3 (analytical grade) were weighed and mixed, and thoroughly ground to obtain a powder particle size of 1~2 µm. The mixed powder was placed in a high-temperature furnace and pre-fired in air atmosphere at a temperature of 1200℃, a heating rate of 5℃ / min, and a holding time of 3h. The pre-fired block product was then thoroughly ground a second time to obtain a powder particle size of 1~2 µm. Subsequently, sintering was carried out in air atmosphere at a temperature of 1250℃, a heating rate of 5℃ / min, and a holding time of 3h. The material was then cooled to room temperature in the furnace to obtain gadolinium ion-doped M-type strontium ferrite microwave absorbing material.

[0021] Example 2. The difference between this embodiment and Embodiment 1 is that, according to the chemical formula Sr 0.98 Gd 0.02 Fe 12 O 19 According to the stoichiometric ratio, raw materials SrCO3 (analytical grade), Fe2O3 (analytical grade), and Gd2O3 (analytical grade) were weighed, and the remaining preparation steps and conditions were the same to obtain gadolinium ion-doped M-type strontium ferrite microwave absorbing material.

[0022] Under Ku-band testing conditions, when the thickness of the gadolinium ion-doped M-type strontium ferrite absorbing material prepared in Example 2 is 5 mm, its minimum reflection loss (RL) is -15.7 dB, and its effective absorption bandwidth under the -10 dB criterion is 1.07 GHz, exhibiting stable microwave absorption capability. Simultaneously, the saturation magnetization of this absorbing material is 92.27 emu / g, and the coercivity is 3.21 kOe, indicating that the gadolinium ion-doped M-type strontium ferrite absorbing material prepared in Example 2 maintains the hard magnetic properties of M-type strontium ferrite while possessing a good magnetic response foundation.

[0023] Example 3. The difference between this embodiment and Embodiment 1 is that, according to the chemical formula Sr 0.90 Gd 0.10 Fe 12 O19 According to the stoichiometric ratio, raw materials SrCO3 (analytical grade), Fe2O3 (analytical grade), and Gd2O3 (analytical grade) were weighed, and the remaining preparation steps and conditions were the same to obtain gadolinium ion-doped M-type strontium ferrite microwave absorbing material.

[0024] Under Ku-band testing conditions, when the thickness of the gadolinium ion-doped M-type strontium ferrite absorbing material prepared in Example 3 is 5 mm, its minimum reflection loss (RL) is -14.5 dB, and its effective absorption bandwidth under the -10 dB criterion is 1.6 GHz, exhibiting stable microwave absorption capability. Simultaneously, the saturation magnetization of this absorbing material is 71.41 emu / g, and the coercivity is 3.45 kOe, further demonstrating that the gadolinium ion-doped M-type strontium ferrite absorbing material provided by this invention possesses a good magnetic response foundation while maintaining the hard magnetic properties of M-type strontium ferrite.

[0025] Example 4. The difference between this embodiment and Embodiment 1 is that, according to the chemical formula Sr 0.50 Gd 0.50 Fe 12 O 19 According to the stoichiometric ratio, raw materials SrCO3 (analytical grade), Fe2O3 (analytical grade), and Gd2O3 (analytical grade) were weighed, and the remaining preparation steps and conditions were the same to obtain gadolinium ion-doped M-type strontium ferrite microwave absorbing material.

[0026] Under Ku-band testing conditions, when the thickness of the gadolinium ion-doped M-type strontium ferrite absorbing material prepared in Example 4 is 5 mm, its minimum reflection loss (RL) is -13.7 dB, and its effective absorption bandwidth under the -10 dB criterion is 1.21 GHz, exhibiting stable microwave absorption capability. Simultaneously, the saturation magnetization of this absorbing material is 70.73 emu / g, and the coercivity is 3.41 kOe, further indicating that the gadolinium ion-doped M-type strontium ferrite absorbing material maintains the hard magnetic properties of M-type strontium ferrite while possessing a good magnetic response foundation.

[0027] Comparative Example 1. The difference between this comparative example and Example 1 is that Gd is not added; all other preparation steps and conditions are the same as in Example 1, resulting in M-type strontium ferrite microwave absorbing material SrFe. 12 O 19 .

[0028] like Figure 1The figures show the room-temperature hysteresis loops of the gadolinium ion-doped M-type strontium ferrite absorbing material prepared in Example 1 and the undoped M-type strontium ferrite absorbing material prepared in Comparative Example 1. Calculations from the hysteresis loops show that the saturation magnetization of the gadolinium ion-doped M-type strontium ferrite absorbing material prepared in Example 1 is 99.16 emu / g, indicating that gadolinium ion doping did not significantly weaken the Fe-O-Fe superexchange interaction, and the material still maintains stable spontaneous magnetization. The coercivity is 3.47 kOe, which is within the typical hard magnetic range of M-type strontium ferrite, reflecting that the material possesses a clear magnetic anisotropy field and a stable magnetic domain structure. The high saturation magnetization (99.16 emu / g) ensures that the material has a sufficient magnetic response basis in the microwave band, thereby enhancing the contribution of magnetic loss. The anisotropy field corresponding to the coercivity (3.47 kOe) can support natural resonance behavior under high-frequency conditions, which is beneficial to the effective utilization of magnetic loss in the Ku band. The undoped gadolinium M-type strontium ferrite absorbing material prepared in Comparative Example 1 exhibits a minimum reflection loss (RL) of -6.7 dB in the Ku band, failing to meet the -10 dB absorption criterion, corresponding to an effective absorption bandwidth of 0 GHz, indicating limited microwave attenuation capability. Magnetic performance tests show that the saturation magnetization of the undoped gadolinium M-type strontium ferrite absorbing material in Comparative Example 1 is 66.26 emu / g, and the coercivity is 2.22 kOe. This sample shows lower absorption performance and magnetic properties than Example 1, indicating significant deficiencies in magnetic response intensity and electromagnetic matching capability of the undoped gadolinium M-type strontium ferrite absorbing material.

[0029] like Figure 2 (a) and (b) are the reflection loss (RL) curves as a function of frequency for the gadolinium ion-doped M-type strontium ferrite absorbing material prepared in Example 1 and the undoped M-type strontium ferrite absorbing material prepared in Comparative Example 1, respectively, under different thickness conditions. Figure 2 As shown in (a), as the thickness increases from 1 mm to 5 mm, the absorption peak shifts from high frequency to low frequency, and the valley of reflection loss gradually deepens, exhibiting typical thickness-tuned characteristics. This indicates that the absorption behavior of gadolinium-doped M-type strontium ferrite absorbing materials is influenced by both the propagation path length of electromagnetic waves within the material and the phase matching condition. Increasing the thickness is beneficial to enhancing the attenuation effect of electromagnetic waves within the material. In the Ku band, when the thickness is 5 mm, the minimum reflection loss reaches -15.7 dB, corresponding to an electromagnetic wave absorption rate exceeding 97%. Simultaneously, the effective absorption bandwidth is 1.12 GHz under the -10 dB criterion, demonstrating strong absorption intensity and a certain bandwidth advantage. These results indicate that gadolinium-doping, while maintaining the stability of the magnetic loss mechanism of M-type strontium ferrite, achieves quantitative matching optimization between magnetic and dielectric parameters, making the material's input impedance closer to the free-space impedance, thereby improving the impedance matching degree and electromagnetic energy dissipation efficiency, and enhancing the absorption performance in the Ku band.

[0030] and Figure 2 In (b), the undoped gadolinium-ion M-type strontium ferrite prepared in Comparative Example 1, while exhibiting a certain degree of thickness dependence within the same thickness range, shows a significantly shallower overall reflection loss valley. It does not exhibit a significant absorption peak below -10 dB in the Ku band, and the absorption peak position tuning amplitude is limited, resulting in a narrow effective absorption bandwidth. This indicates insufficient matching between its magnetic and dielectric parameters, and an input impedance deviating from free-space impedance, leading to a higher reflection rate of electromagnetic waves on the material surface and limited internal dissipation capability. Therefore, the gadolinium-ion doping scheme of this invention effectively improves the electromagnetic parameter synergy of the material, significantly enhances the absorption intensity and impedance matching performance, and demonstrates superior Ku-band absorption performance compared to the undoped gadolinium-ion M-type strontium ferrite absorbing material.

[0031] In summary, this invention achieves synergistic optimization of saturation magnetization and coercivity through the directional control of magnetocrystalline anisotropy in Gd-doped strontium ferrite. By precisely controlling the Gd doping amount x and the sintering temperature, a stable process window is established, allowing the internal charge compensation mechanism of the material to shift from oxygen vacancies to Fe... 3+ The controllable transformation dominated by reduction achieves a reasonable match between magnetic response intensity and anisotropic field, effectively covering the Ku band with the natural resonant frequency and improving electromagnetic energy dissipation efficiency. It exhibits stable magnetic properties and good chemical stability. Simultaneously, this invention employs a high-temperature solid-state method to prepare gadolinium ion-doped M-type strontium ferrite absorbing materials, establishing a repeatable, scalable, and consistent process window. This facilitates mass production and cost control, enabling applications in electromagnetic protection for satellite communication terminals, radar antenna systems, 5G communication equipment, or electronic devices. Furthermore, it allows for the construction of a magnetic-electric synergistic loss composite absorbing system, expanding the application space of absorbing materials in high-performance electromagnetic protection structural materials and achieving a systematic improvement in material performance, mechanism clarity, and engineering adaptability.

[0032] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0033] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A gadolinium ion-doped M-type strontium ferrite microwave absorbing material, characterized in that, The chemical formula of the gadolinium ion-doped M-type strontium ferrite microwave absorbing material is Sr 1-x Gd x Fe 12 O 19 , where 0.01≤x≤0.

50.

2. The gadolinium ion-doped M-type strontium ferrite microwave absorbing material according to claim 1, characterized in that, The thickness of the gadolinium ion-doped M-type strontium ferrite microwave absorbing material is 1~5 mm.

3. A method for preparing a gadolinium ion-doped M-type strontium ferrite microwave absorbing material as described in claim 1 or 2, characterized in that, The preparation steps include the following: According to Sr 1-x Gd x Fe 12 O 19 By using the stoichiometric ratio of strontium carbonate, iron oxide, and gadolinium oxide, strontium carbonate, iron oxide, and gadolinium oxide are mixed and ground once, pre-calcined, and kept at a certain temperature; the pre-calcined product is then ground a second time, sintered, and kept at a certain temperature to obtain gadolinium ion-doped M-type strontium ferrite microwave absorbing material.

4. The method for preparing gadolinium ion-doped M-type strontium ferrite microwave absorbing material according to claim 3, characterized in that, The particle size of the powder obtained by the first grinding is 1~6 µm.

5. The method for preparing gadolinium ion-doped M-type strontium ferrite microwave absorbing material according to claim 3, characterized in that, The pre-firing temperature is 1100℃~1500℃; the pre-firing atmosphere is air; the pre-firing heating rate is 5℃ / min.

6. The method for preparing gadolinium ion-doped M-type strontium ferrite microwave absorbing material according to claim 3, characterized in that, The particle size of the powder obtained by the secondary grinding is 1~5 µm.

7. The method for preparing gadolinium ion-doped M-type strontium ferrite microwave absorbing material according to claim 5, characterized in that, The sintering temperature is 1100℃~1500℃; the sintering atmosphere is air; and the sintering heating rate is 5℃ / min.

8. The method for preparing gadolinium ion-doped M-type strontium ferrite microwave absorbing material according to claim 7, characterized in that, The pre-firing temperature is always 50°C lower than the sintering temperature; the holding time is always 2-5 hours.

9. The application of a gadolinium ion-doped M-type strontium ferrite microwave absorbing material as described in claim 1 or 2, or a gadolinium ion-doped M-type strontium ferrite microwave absorbing material prepared by the preparation method according to any one of claims 3-8, characterized in that, Preparation of absorbing coatings or composite absorbing materials with magneto-electric synergistic loss for Ku-band electromagnetic interference protection.

10. The application of the gadolinium ion-doped M-type strontium ferrite microwave absorbing material according to claim 9, characterized in that, The Ku-band electromagnetic interference protection absorbing coating is applied to the electromagnetic protection of satellite communication terminals, radar antenna systems, 5G communication equipment, or electronic equipment.

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