Preparation method of nickel-plated soft magnetic composite material, soft magnetic composite material and application thereof
By constructing a single-phase continuous solid solution gradient of Fe-Ni in the γ-Fe phase region, the problems of high-frequency eddy current loss and permeability reduction in the prior art are solved, realizing a soft magnetic composite material with high frequency, low loss and high permeability, which is suitable for high-frequency power inductors and electromagnetic shielding devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NBTM NEW MATERIALS GRP
- Filing Date
- 2026-05-09
- Publication Date
- 2026-07-03
AI Technical Summary
Existing technologies struggle to achieve a continuous and coordinated gradient between high surface resistance and high core permeability in single-phase iron-based systems, leading to increased high-frequency eddy current losses and decreased permeability, failing to meet the requirements of high-frequency low loss and high permeability.
A single-phase interfaceless continuous solid solution gradient is constructed by limited diffusion in the γ-Fe phase region, forming a continuous concentration gradient with nickel-rich surface and iron-rich core. By utilizing the infinite mutual solubility of Fe and Ni in the γ-phase region, the annealing temperature and time are controlled to form a moderately conductive-magnetic network, suppressing eddy currents and maintaining high permeability.
It achieves low loss and high permeability in the frequency range of 1 to 10 MHz, improves corrosion resistance, is suitable for high reliability scenarios, extends device service life, ensures smooth magnetic domain movement, and significantly reduces hysteresis loss.
Smart Images
Figure CN122337809A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of soft magnetic materials technology, specifically to a method for preparing a nickel-plated soft magnetic composite material, the soft magnetic composite material, and its applications. Background Technology
[0002] With the development of 5G communication, new energy vehicles, and consumer electronics towards higher frequencies and smaller sizes, the operating frequency of soft magnetic cores has increased to the 1-10MHz band. The core problem brought about by higher frequencies is the sharp increase in eddy current losses. The most common way to suppress eddy current losses is to construct high-resistivity interfaces between powder particles.
[0003] Existing technologies mainly employ two approaches to address interparticle insulation: one is to coat the powder surface with a continuous insulating layer, such as phosphate insulation or ferrite coating; the other is to form a high-resistivity phase through alloying, as illustrated in Chinese invention patent application CN201911196153.7 (publication number CN110899692A), which discloses a method for preparing iron-based alloy powder. This method uses a high-temperature homogenization annealing process to ensure that nickel is fully diffused and uniformly distributed, forming a homogeneous alloy phase. However, this approach has the following drawbacks: 1) While using a non-magnetic insulating layer can cut off eddy current paths, it disrupts the continuity of the magnetic circuit, leading to a significant decrease in effective permeability and an increase in the demagnetizing field; 2) Using electroless nickel plating and high-temperature homogenization annealing to ensure that nickel is fully diffused to a uniform composition does not result in a gradient structure, making it difficult to balance high surface resistance with high core permeability; 3) When the annealing temperature is below 912℃, the solid solubility of nickel in α-Fe is limited, easily leading to the precipitation of intermetallic compounds such as FeNi3, causing magnetic domain wall pinning and increased losses.
[0004] In recent years, some researchers have proposed methods to construct gradient structures through electroless nickel plating and high-temperature annealing. For example, the Chinese invention patent application CN202311091542.X (publication number CN117328048A) discloses a "Reinforcing Layer Plating Solution for Surface Treatment of Iron-Based Parts, Preparation Method for Treated Iron-Based Parts, and Iron-Based Parts." This method is mainly applied to the surface strengthening of iron-based structural parts, focusing on wear resistance and hardness, without addressing the optimization of high-frequency magnetic properties of soft magnetic materials. Furthermore, existing plating solution systems mostly use a single nickel source, resulting in a single gradient layer composition, making it difficult to simultaneously meet the requirements of high frequency, low loss, and high permeability.
[0005] In summary, existing technologies either use non-magnetic insulating coatings to disrupt magnetic continuity, or employ high-temperature homogenization annealing to eliminate gradients, or use them for structural reinforcement rather than soft magnetic property optimization. None of these methods can achieve a continuous and synergistic gradient of "high surface resistance and high core permeability" within a single-phase iron-based system. High-frequency, low-loss, and high-stability applications face insurmountable technical bottlenecks. Summary of the Invention
[0006] The first technical problem to be solved by this invention is to provide a method for preparing nickel-plated soft magnetic composite materials in light of the current state of the technology. This invention abandons the traditional approach of homogenization annealing and non-magnetic coating, and constructs a single-phase interfaceless continuous solid solution gradient through limited diffusion in the γ-Fe phase region. This achieves spatial functional decoupling within the same particle, and solves the industry's physical contradiction of the incompatibility between high resistance and high permeability in high-frequency soft magnetic materials from the structural root.
[0007] The second technical problem to be solved by the present invention is to provide a soft magnetic composite material prepared by the above-mentioned preparation method, in view of the current state of the prior art.
[0008] The third technical problem to be solved by the present invention is to provide an application of the above-mentioned soft magnetic composite material in light of the current state of the prior art.
[0009] The technical solution adopted by the present invention to solve the first technical problem mentioned above is as follows: A method for preparing a nickel-plated soft magnetic composite material includes the following steps:
[0010] (1) Prepare iron-based soft magnetic powder;
[0011] (2) Preparation of nickel plating solution: The nickel plating solution includes the following components and contents: nickel source, concentration of 20-35 g / L; reducing agent, concentration of 0.5-5 g / L; complexing agent, concentration of 20 g / L-40 g / L; stabilizer, concentration of 0.01 g / L-1 g / L; pH adjuster to maintain the pH value of the nickel plating solution at 7-12; the balance is deionized water;
[0012] The order of steps (2) and (1) is not important;
[0013] (3) Chemical plating: Under the condition of 70-100℃, the iron-based soft magnetic powder in step (1) and the nickel plating solution in step (2) are stirred and mixed evenly. The mass ratio of the nickel plating solution to the iron-based soft magnetic powder is (1-20):1. After the nickel plating solution adheres (preferably evenly) to the surface of the iron-based soft magnetic powder to form a coating, solid-liquid separation is performed. Then the solid material is rinsed with deionized water until the cleaning solution is neutral to obtain solid powder.
[0014] (4) Drying: Dry the powder from step (3) until the moisture content is ≤1%;
[0015] (5) Annealing: In a vacuum or reducing atmosphere, the dried powder in step (4) is annealed at 912-1200℃ for 5-120 minutes to obtain the soft magnetic composite material.
[0016] Preferably, in step (1), the iron-based soft magnetic powder is soaked in a dilute acid solution to remove the oxide layer, and then the iron-based soft magnetic powder is rinsed with deionized water to avoid impurities remaining. The treated iron-based soft magnetic powder is placed in an activation solution, which can form catalytic points on the surface of the iron-based soft magnetic powder that can trigger subsequent reactions. Then, the residual activation solution is washed away with deionized water.
[0017] Preferably, in step (1), the iron-based soft magnetic powder is at least one of pure iron powder, iron-silicon alloy powder, iron-silicon-aluminum alloy powder, iron-aluminum alloy powder, iron-chromium alloy powder, iron-cobalt alloy powder, and iron-silicon-chromium alloy powder.
[0018] Preferably, in step (1), the iron-based soft magnetic powder has a D50 < 200 μm and a D99 < 350 μm. Maintaining a moderate particle size range for the metal particles is beneficial for the nickel plating solution to fully coat each particle, forming a continuous and uniform nickel plating layer. When the particle size is moderate, the nickel can form an effective gradient diffusion layer during annealing, avoiding uneven diffusion due to excessively large particles. This is suitable for subsequent pressing and sintering processes, improving the density and consistency of the finished product.
[0019] Preferably, in step (2), the nickel source is a water-soluble nickel salt, and is at least one of nickel sulfate, nickel chloride, nickel sulfamate, nickel nitrate, nickel acetate, nickel bromide, nickel iodide, and nickel thiocyanate; the reducing agent is sodium borohydride or dimethylamine borane; the complexing agent is at least one of citric acid, sodium citrate, tartaric acid, potassium sodium tartrate, ethylenediaminetetraacetic acid, and sodium ethylenediaminetetraacetic acid salts (such as disodium EDTA and tetrasodium EDTA); and the stabilizer is at least one of potassium iodate, potassium nitrate, trans-butenedioic acid, and thiourea.
[0020] Preferably, in step (3), stirring and mixing are performed under ultrasonic conditions. When ultrasound propagates in the plating solution, it generates a cavitation effect, producing a local high-temperature and high-pressure environment and strong shock waves, which helps to disperse powder particles, improves the mass transfer rate, promotes the reduction and deposition of metal ions on the powder surface, and also inhibits side reactions and impurity generation.
[0021] Preferably, in step (5), the reducing atmosphere is at least one of nitrogen, argon, and hydrogen.
[0022] The technical solution adopted by this invention to solve the second technical problem mentioned above is as follows: A soft magnetic composite material prepared by the above preparation method includes a core and a wrapping part surrounding the core. The core is iron-based soft magnetic powder, and the wrapping part is a Fe-Ni continuous solid solution. The nickel content of the wrapping part decreases from the outside to the inside. The gradient change in nickel concentration forms a moderately conductive-magnetic network between the powder particles. Under a high-frequency magnetic field, this network can generate beneficial eddy currents, and the reverse magnetic field generated by it forms an effective magnetic shield against external high-frequency interference, while improving the effective permeability of the magnetic core at high frequencies. The soft magnetic composite material has no phase interface, no second phase precipitation, and no insulating coating layer inside. In the frequency range of 1 to 10 MHz, the imaginary part of the complex permeability μ'' ≤ 10, and the reflection loss ≥ 30 dB. The salt spray resistance is more than twice that of pure iron powder.
[0023] The technical solution adopted by the present invention to solve the third technical problem mentioned above is: an application of the above-mentioned soft magnetic composite material, which can be used in high-frequency power inductors and electromagnetic shielding devices.
[0024] Compared with the prior art, the advantages of the present invention are as follows:
[0025] 1) Phase transformation driven diffusion enhancement: Above 912℃, the α→γ phase transformation occurs, Fe enters the γ-Fe phase region, Fe-Ni is infinitely dissolved, and the nickel diffusion ability is significantly enhanced.
[0026] 2) Limited diffusion-controlled gradient: According to Fe-Ni diffusion kinetics, the Ni atom diffusion coefficient is significantly increased in the γ-Fe phase region (above 912℃), reaching 10 at 1100℃. -10 cm 2 On the order of / s. If the holding time exceeds a certain time, Ni atoms will diffuse fully to the point of uniform composition and the gradient structure will disappear. This invention goes against industry norms by strictly controlling the holding time and deliberately not achieving uniform composition. Instead, it precisely controls the limited diffusion of nickel through temperature and time to form a continuous concentration gradient of nickel-rich surface and iron-rich core, which has the potential for large-scale industrial production.
[0027] In addition, the continuous nickel-rich solid solution layer on the surface greatly improves corrosion resistance, effectively blocking water vapor, oxygen and salt spray corrosion. Its salt spray resistance is more than twice that of pure iron powder, significantly extending the service life of powder storage and devices, and making it suitable for high-reliability scenarios such as automotive, outdoor and humid environments.
[0028] 3) Spatial functional separation: This invention achieves functional spatial separation through a radial continuous gradient change in nickel concentration. The nickel-rich surface region exhibits high resistivity, effectively suppressing high-frequency eddy currents; the iron-rich core region maintains high permeability and high saturation magnetization, ensuring magnetic circuit conductivity. Low loss can be achieved without a non-magnetic insulating layer. At 1–10 MHz, μ''≤10 and reflection loss≥30dB, it breaks through the performance ceiling of traditional materials where "high resistance inevitably reduces magnetic permeability". This enables the same soft magnetic composite material to achieve "high surface resistance suppressing eddy currents and high core magnetic permeability for magnetic circuit conduction" within the particles.
[0029] 4) Single-phase interface-free: The soft magnetic composite material prepared by this invention is uncoated, unplated, and free of a second phase, eliminating magnetic domain pinning and demagnetizing fields. This invention forms a continuous Fe-Ni single-phase solid solution gradient through limited diffusion in the γ-Fe phase region. There is no traditional coating layer and matrix phase interface inside the particles, and no precipitation of intermetallic compounds such as FeNi3. This eliminates the magnetic domain wall pinning and demagnetizing field effects from the structural root, allowing for smooth magnetic domain movement and significantly reducing hysteresis loss. This solves the common industry problem of significant permeability decay caused by traditional insulating coatings.
[0030] In summary, in view of the shortcomings of the existing technology, the present invention solves the following technical problems: 1) overcomes the problem of discontinuous magnetic circuit and decreased magnetic permeability caused by non-magnetic insulating layer; 2) overcomes the problem that homogenized alloy cannot achieve both high resistance and high magnetic permeability; 3) overcomes the problem of easy precipitation of second phase, magnetic domain pinning and increased loss due to low temperature annealing; 4) breaks the conventional homogenized annealing approach in the industry and provides a single-phase interface-free, non-uniform continuous gradient, high frequency and low loss soft magnetic composite material. Attached Figure Description
[0031] Figure 1 This is a SEM image of the original surface of the iron powder particles before activation in Example 1.
[0032] Figure 2 Here is a SEM image of the surface of the powder particles after chemical plating (step (3)) in Example 1;
[0033] Figure 3 for Figure 2 EDS analysis of nickel element distribution in powder particles within the box;
[0034] Figure 4 for Figure 2 EDS analysis of iron element distribution in powder particles within the box;
[0035] Figure 5 This is a SEM image of the cross-section of the powder particles after annealing (step (5)) in Example 1;
[0036] Figure 6 This is an EDS surface scan image of iron content in the cross-section of the powder particles after annealing (step (5)) in Example 1;
[0037] Figure 7 This is an EDS surface scan image of nickel content in the cross-section of the powder particles after annealing (step (5)) in Example 1;
[0038] Figure 8 The EDS elemental distribution spectrum of the powder particles after annealing (step (5)) in Example 1 is shown. Detailed Implementation
[0039] The present invention will be further described in detail below with reference to the accompanying drawings, embodiments, and comparative examples. Unless otherwise specified, the reagents, materials, and equipment used in the embodiments are commercially available; the embodiments are only for explaining the present invention and are not intended to limit the scope of protection of the present invention.
[0040] Example 1
[0041] The preparation method of the nickel-plated soft magnetic composite material in this embodiment includes the following steps.
[0042] (1) Preparation of iron-based soft magnetic powder; The iron-based soft magnetic powder in this embodiment is pure iron powder prepared by water atomization, purchased from Shanxi Xinsheng New Material Co., Ltd., with a loose density of 3.5 g / cm³, D50=146 μm, and D99=293 μm. The SEM morphology of the original surface of the pure iron powder is shown in the figure. Figure 1 As shown, the iron-based soft magnetic powder was soaked in an 8 vol% dilute acid solution for 5 minutes to remove the oxide layer. Then, the iron-based soft magnetic powder was rinsed with deionized water to avoid impurities. The treated iron-based soft magnetic powder was then soaked in an activation solution (50 ppm palladium chloride) that could form catalytic points on its surface that could trigger subsequent reactions for 5 minutes. After that, the residual activation solution was washed off with deionized water.
[0043] (2) Preparation of nickel plating solution: The nickel plating solution includes the following components and contents: nickel source (nickel sulfate), concentration of 35 g / L; reducing agent (sodium borohydride), concentration of 2 g / L; complexing agent (EDTA), concentration of 20 g / L; stabilizer (thiourea), concentration of 1 g / L; pH adjuster (ammonia water) to maintain the pH value of the nickel plating solution at 12; the balance is deionized water;
[0044] The order of steps (2) and (1) is not important;
[0045] (3) Chemical plating: At 80°C, the iron-based soft magnetic powder from step (1) and the nickel plating solution from step (2) are stirred for 30 minutes to mix evenly. The mass ratio of the nickel plating solution to the iron-based soft magnetic powder is 10:1. After the nickel plating solution is evenly attached to the surface of the iron-based soft magnetic powder to form a coating, solid-liquid separation is performed (the existing solid-liquid separation method is adopted, such as centrifugation, vacuum filtration, etc.). Then, the solid material is washed with deionized water until the cleaning solution is neutral to obtain solid powder. Preferably, it is mixed under ultrasonic conditions. SEM images of the surface of powder particles after chemical plating, such as... Figure 2 As shown; EDS analysis of nickel element distribution in powder particles is as follows. Figure 3 As shown, nickel is uniformly distributed on the powder surface; the surface distribution of iron in the powder particles, as determined by EDS analysis, is as follows. Figure 4 As shown, iron is the main element of the powder matrix and is co-distributed with Ni.
[0046] (4) Drying: The powder from step (3) is dried to a moisture content of ≤1% by vacuum drying at 60℃ and then passed through a 100-mesh sieve.
[0047] (5) Annealing: In a reducing atmosphere (70 vol% H2 atmosphere), or under vacuum conditions, the powder dried in step (4) is annealed at 400-1200℃ for 5-120 minutes. Specifically, the temperature is increased to 950℃ at 10℃ / min, held for 30 minutes, cooled to below 150℃ in the furnace, crushed and passed through a 100-mesh sieve to obtain the nickel-plated soft magnetic composite material. SEM images of the cross-section of the powder particles after annealing are shown below. Figure 5 As shown, the structural continuity from the surface to the core of the powder particles is clearly displayed; the EDS surface scan of the iron element in the cross-section of the powder particles after annealing is shown in the figure. Figure 6 As shown; EDS surface scan of nickel content in the cross-section of the powder particles after annealing is shown in the figure. Figure 7 As shown, the nickel concentration gradually decreases from the surface to the core; the EDS elemental distribution spectrum of the cross-section of the powder particles after annealing is shown in the figure. Figure 8 As shown.
[0048] Example 2
[0049] The difference from Example 1 is that the concentration of nickel sulfate in step (2) is changed to 20 g / L, while the other steps and parameters are the same as in Example 1.
[0050] Example 3
[0051] The difference from Example 1 is that the annealing temperature in step (5) is changed to 1100℃ and the holding time is 30min. Other steps and parameters are the same as in Example 1.
[0052] Comparative Example 1
[0053] Nickel-plated iron powder was prepared according to steps (1) to (4) of Example 1, but the annealing temperature in step (5) was changed to 200°C and held for 30 minutes (at which temperature Ni hardly diffuses). Other steps and parameters were the same as in Example 1.
[0054] Comparative Example 2
[0055] Nickel-plated iron powder was prepared according to steps (1) to (4) of Example 1. In step (5), the annealing temperature was changed to 1100℃ and the holding time was extended to 5h to ensure that Ni diffused fully and evenly and the gradient disappeared. Other steps and parameters were the same as in Example 1.
[0056] Comparative Example 3
[0057] Nickel-plated iron powder was prepared according to steps (1) to (4) of Example 1, but the annealing temperature in step (5) was changed to 860℃ (below the α→γ phase transformation point of 912℃), and the temperature was held for 30 min. Other steps and parameters were the same as in Example 1.
[0058] The nickel-plated soft magnetic composite materials obtained in each embodiment and comparative example were pressed into toroidal cores with a diameter of φ25mm×φ15mm×5mm under 1000MPa, and then subjected to performance testing after heat treatment in a nitrogen atmosphere at 650℃ for 1h.
[0059] Table 1: Sample performance test results of each embodiment and comparative example
[0060] As shown in Table 1, in Comparative Example 1, due to the lack of Ni diffusion, the coating is only a surface layer, resulting in severe eddy currents at high frequencies, high μ″, and low reflection loss. In Comparative Example 2, due to Ni homogenization and the disappearance of the gradient, μ″ is higher than that of the Example, and the reflection loss is also lower. In Comparative Example 3, because the annealing temperature is below 912℃, Ni diffuses into α-Fe to form a second phase precipitation, disrupting magnetic continuity, resulting in the lowest μ′, the highest μ″, and the worst magnetic properties. Examples 1 to 3 all achieved excellent comprehensive performance: high μ′, low μ″, high reflection loss, and significantly improved corrosion resistance due to the formation of a continuous solid solution gradient layer during annealing in the γ-phase region.
[0061] As can be seen, by controlling the annealing temperature to be higher than 912℃, this invention successfully constructs a phase-boundary-free ferromagnetic continuous gradient layer by utilizing the infinite mutual solubility of Fe-Ni in the γ phase region. This is the fundamental reason for achieving high permeability, low loss and good reflection loss at high frequencies, and it is also the essential difference from the existing technology.
[0062] All performance tests for the embodiments and comparative examples adopted unified national standards and testing methods: (1) Density: GB / T5163-2006 "Determination of density, open porosity and total porosity of permeable sintered metal materials (excluding cemented carbide)"; (2) Magnetic property testing (magnetic induction, permeability, coercivity): GB / T13012-2008 "Methods for measuring DC magnetic properties of soft magnetic materials"; (3) Complex permeability and reflection loss RL: GB / T28869.3-2023 Measurement method for magnetic cores made of soft magnetic materials - Part 3: Magnetic properties under high excitation level; (4) Salt spray test: GB / T2423.17-2024 Environmental testing - Part 2: Test methods - Test Ka: Salt spray. The failure criterion for salt spray test is the time when the sample first shows red rust under neutral salt spray conditions.
Claims
1. A method for preparing a nickel-plated soft magnetic composite material, characterized in that, Includes the following steps: (1) Prepare iron-based soft magnetic powder; (2) Preparation of nickel plating solution: The nickel plating solution includes the following components and contents: nickel source, concentration of 20-35 g / L; reducing agent, concentration of 0.5-5 g / L; complexing agent, concentration of 20 g / L-40 g / L; stabilizer, concentration of 0.01 g / L-1 g / L; pH adjuster to maintain the pH value of the nickel plating solution at 7-12; the balance is deionized water; The order of steps (2) and (1) is not important; (3) Chemical plating: Under the condition of 70-100℃, the iron-based soft magnetic powder in step (1) and the nickel plating solution in step (2) are stirred and mixed evenly. The mass ratio of the nickel plating solution to the iron-based soft magnetic powder is (1-20):
1. After the nickel plating solution adheres to the surface of the iron-based soft magnetic powder to form a coating, solid-liquid separation is performed. Then the solid material is rinsed with deionized water until the cleaning solution is neutral to obtain solid powder. (4) Drying: Dry the powder from step (3) until the moisture content is ≤1%; (5) Annealing: In a vacuum or reducing atmosphere, the dried powder in step (4) is annealed at 912-1200℃ for 5-120 minutes to obtain nickel-plated soft magnetic composite material.
2. The method for preparing the nickel-plated soft magnetic composite material according to claim 1, characterized in that: In step (1), the iron-based soft magnetic powder is soaked in a dilute acid solution to remove the oxide layer, and then the iron-based soft magnetic powder is rinsed clean with deionized water. The treated iron-based soft magnetic powder is placed in an activation solution, which allows catalytic points to be formed on the surface of the iron-based soft magnetic powder that can trigger subsequent reactions. The residual activation solution is then washed away with deionized water.
3. The method for preparing the nickel-plated soft magnetic composite material according to claim 1, characterized in that: In step (1), the iron-based soft magnetic powder is at least one of pure iron powder, iron-silicon alloy powder, iron-silicon-aluminum alloy powder, iron-aluminum alloy powder, iron-chromium alloy powder, iron-cobalt alloy powder, and iron-silicon-chromium alloy powder.
4. The method for preparing the nickel-plated soft magnetic composite material according to claim 1, characterized in that: In step (1), the iron-based soft magnetic powder has D50 < 200 μm and D99 < 350 μm.
5. The method for preparing the nickel-plated soft magnetic composite material according to claim 1, characterized in that: In step (2), the nickel source is at least one of nickel sulfate, nickel chloride, nickel sulfamate, nickel nitrate, nickel acetate, nickel bromide, nickel iodide, and nickel thiocyanate; the reducing agent is sodium borohydride or dimethylamine borane; the complexing agent is at least one of citric acid, sodium citrate, tartaric acid, potassium sodium tartrate, ethylenediaminetetraacetic acid, and sodium ethylenediaminetetraacetic acid; and the stabilizer is at least one of potassium iodate, potassium nitrate, trans-butenedioic acid, and thiourea.
6. The method for preparing the nickel-plated soft magnetic composite material according to claim 1, characterized in that: In step (3), the mixture is stirred under ultrasonic conditions.
7. The method for preparing the nickel-plated soft magnetic composite material according to claim 1, characterized in that: In step (5), the reducing atmosphere is at least one of nitrogen, argon, and hydrogen.
8. A soft magnetic composite material prepared by the preparation method according to any one of claims 1 to 7, characterized in that: It includes a core and a wrapping portion surrounding the core. The core is made of iron-based soft magnetic powder, and the wrapping portion is a Fe-Ni continuous solid solution. The nickel content of the wrapping portion decreases from the outside to the inside.
9. An application of the soft magnetic composite material according to claim 8, characterized in that: This soft magnetic composite material can be used in high-frequency power inductors and electromagnetic shielding devices.