Ferrite powder, ferrite resin composite material, ferrite resin composite, and electromagnetic wave absorber

Abstract

The present invention provides a ferrite powder which contains 0.9% by mass to 2.5% by mass of lithium (Li), 1.0% by mass to 8.0% by mass of manganese (Mn), and 58.0% by mass to 69.5% by mass of iron (Fe), and has a crystal phase belonging to the space group P4132 and a crystal phase belonging to the space group Fd-3m. In the X-ray diffraction profile, the half width of the (311) plane of the crystal phase belonging to the space group Fd-3m is 0.09° to 0.22°, and the volume average particle diameter D50 is not less than 1 μm but less than 20 μm.

Description

[Technical Field]

[0001] The present invention relates to ferrite powder, ferrite resin composite material, ferrite resin composite, and electromagnetic wave absorber. [Background technology]

[0002] With the rapid advancement of wireless communication technology and the increasing sophistication and diversification of needs for wireless services, communication speeds have become faster and data capacity has increased (high-speed, high-capacity). In this context, commercial services for the fifth-generation mobile communication system (5G) began in the spring of 2020. 5G enables not only high speed and high capacity, but also high reliability, low latency, and massive simultaneous connections. Therefore, it is attracting great attention as an indispensable infrastructure for realizing an IoT society. For example, using 5G will enable remote robot operation and instantaneous transmission and reception of information from numerous devices. For this reason, it is considered a key technology for advancing the practical application of telemedicine and autonomous driving.

[0003] Incidentally, electromagnetic interference (EMI) is a persistent problem in communication systems. Especially with the increasing frequency of 5G, the circuit length in electronic devices and the wavelength of electromagnetic waves are close together, making the effects of EMI particularly pronounced. To prevent problems such as equipment malfunction or adverse effects on the human body caused by EMI, the use of electromagnetic wave absorbers is effective. Ferrite powder is widely used as a material for electromagnetic wave absorbers.

[0004] For example, Patent Document 1 contains Zn X Li (1-X)0.5 Fe (1-X)0.5 A Li-Zn ferrite powder for radio wave absorbers, comprising a ferrite represented by the structural formula Fe2O4 (where X is 0.1 to 0.8), is disclosed, and it is stated that this ferrite powder significantly improves the absorption performance of radio waves in the 1 to 4 GHz band (Claim 1 and

[0012] of Patent Document 1).

[0005] Furthermore, although not used for electromagnetic wave absorption applications, Patent Document 2 discloses a carrier core material for electrophotographic developers, which consists of Li ferrite, maghemite, and Fe3O4, with a portion of which is substituted with Mn, having a Li content of 1 to 2.5% by weight, a Mn content of 2 to 7.5% by weight, and further containing 25 to 10,000 ppm of silicon (Claim 1 of Patent Document 2). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2005-268368 [Patent Document 2] Japanese Patent Publication No. 2009-244571 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] While the application of ferrite powder as an electromagnetic wave absorber has been proposed for some time, conventional ferrite powders for electromagnetic wave absorbers have been insufficient in performance for use in 5G-compatible electromagnetic wave absorbers. Specifically, 5G introduces a new wireless communication method using frequencies near 28 GHz, in addition to existing frequencies below 6 GHz. Therefore, it is desirable to exhibit excellent electromagnetic wave absorption performance in the frequency range near 28 GHz, and more specifically, to show a deep electromagnetic wave absorption peak (sometimes simply called an "absorption peak") in this frequency range.

[0008] Furthermore, the frequency ranges allocated for 5G differ from country to country and from telecommunications carrier to carrier. For example, focusing on frequencies around 28GHz, Japan is allocated the 27-29.5GHz frequency range, with different frequencies within this range being distributed to each carrier. The United States is allocated 22.5-28.35GHz, Europe 24.25-27.5GHz, China 24.75-27.5GHz, and South Korea 26.5-29.5GHz. Therefore, an electromagnetic wave absorber that can be used across countries and carriers, that is, one with excellent versatility, is desirable. For this to happen, it is desirable that the absorption peak is not only deep, but also that the absorption frequency range, that is, the width of the absorption peak, is appropriately wide. However, conventional ferrite powders have not been sufficient to meet these requirements.

[0009] The inventors conducted studies in view of these problems. As a result, they found that it is important to adjust the composition and particle size of ferrite powder containing lithium (Li) and manganese (Mn), to include a crystalline phase belonging to a specific space group, and to control its XRD full width at half maximum. By controlling these factors, it was possible to obtain a ferrite powder that exhibits a moderately broad and deep absorption peak near 28 GHz, particularly in the frequency range of 21-32 GHz. They found that by using this ferrite powder, it is possible to create an electromagnetic wave absorber that has both excellent electromagnetic wave absorption performance and versatility in the 5G frequency range.

[0010] This invention was completed based on such findings, and aims to provide a ferrite powder that exhibits a moderately broad and deep absorption peak in the frequency range near 28 GHz, and that combines excellent electromagnetic wave absorption performance and versatility in the 5G compatible frequency range. Furthermore, this invention also aims to provide an electromagnetic wave absorber containing this ferrite powder. [Means for solving the problem]

[0011] The present invention encompasses the following embodiments (1) to (6). In this specification, the expression "~" includes the values ​​at both ends. That is, "X~Y" is synonymous with "X or greater and Y or less".

[0012] (1) It contains lithium (Li) at a ratio of 0.9% by mass or more and 2.5% by mass or less, manganese (Mn) at a ratio of 1.0% by mass or more and 8.0% by mass or less, and iron (Fe) at a ratio of 58.0% by mass or more and 69.5% by mass or less, It has a crystal phase belonging to the space group P4132 and a crystal phase belonging to the space group Fd-3m, In the X-ray diffraction profile, the half-value width of the (311) plane of the crystal phase belonging to the space group Fd-3m is 0.09° or more and 0.22° or less, A ferrite powder having a volume average particle diameter D50 of 1 μm or more and less than 20 μm.

[0013] (2) The above-mentioned space group Fd-3m Crystals belonging to this group The content of the phase and the above-mentioned space group P4132 Crystals belonging to this group The mass ratio of the content of the phase of the space group Fd-3m to the total content of the phase of the space group P4132 is 30% by mass or more and 98% by mass or less, the ferrite powder of (1) above. Crystals belonging to this group <00OO082> (3) The coercive force Hc is 40 Oe or more and 70 Oe or less, the ferrite powder of (1) or (2) above.

[0015] (4) A ferrite resin composite material containing the ferrite powder of (1) or (2) above and a resin.

[0016] (5) A ferrite resin composite, which is a molded body of the ferrite resin composite material of (4) above.

[0017] (6) An electromagnetic wave absorber including the ferrite resin composite of (5) above. [Effect of the Invention]

[0018] According to the present invention, there is provided a ferrite powder that shows a moderately wide and deep absorption peak in the frequency range near 28 GHz, and has excellent electromagnetic wave absorption performance and versatility in the 5G-compatible frequency range. Further, according to the present invention, there is provided an electromagnetic wave absorber containing this ferrite powder. [Brief Description of the Drawings]

[0019] [Figure 1] The evaluation results of electromagnetic wave absorption performance (frequency characteristics of the reflection coefficient (S11)) measured by the free-space method are shown. [Modes for carrying out the invention]

[0020] Specific embodiments of the present invention (hereinafter referred to as "this embodiment") will now be described. It should be noted that the present invention is not limited to the following embodiments, and various modifications are possible without altering the essence of the invention. In the present invention, a combination of two or more preferred embodiments is a more preferred embodiment.

[0021] <<1. Ferrite Powder>> The ferrite powder of this embodiment contains lithium (Li) in a proportion of 0.9% to 2.5% by mass, manganese (Mn) in a proportion of 1.0% to 8.0% by mass, and iron (Fe) in a proportion of 58.0% to 69.5% by mass. Furthermore, the ferrite powder of this embodiment has a crystalline phase belonging to space group P4132 (P4132 phase) and a crystalline phase belonging to space group Fd-3m (Fd-3m phase). In the X-ray diffraction profile, the full width at half maximum of the (311) plane of the crystalline phase belonging to space group Fd-3m is 0.09° to 0.22°, and the volume average particle size D50 is 1 μm to less than 20 μm. Ferrite is a ceramic material whose main component is iron oxide. Therefore, the ferrite powder of this embodiment consists of an oxide containing iron (Fe), lithium (Li), manganese (Mn), and oxygen (O) as essential components.

[0022] The ferrite powder of this embodiment, which has Li and Mn as essential components, contains Li ferrite and Mn ferrite. Li ferrite is (Li 1 / 2 Fe 1 / 2Li ferrite is a type of spinel ferrite having a basic composition represented by (Fe2O4). Mn ferrite is another type of spinel ferrite having a basic composition represented by (Mn,Fe)(Fe,Mn)2O4. Both Li ferrite and Mn ferrite contain trivalent iron ions (Fe 3+ It is a ferrimagnet having a spin magnetic moment based on ), and possesses ferromagnetic properties. Therefore, by including both Li ferrite and Mn ferrite, the overall magnetic properties can be improved.

[0023] Incidentally, Li ferrite belongs to space group P4132 and, on its own, has a spontaneous resonance absorption peak around 24-25 GHz. Furthermore, Li ferrite has a characteristic of having a very narrow absorption peak width compared to other spinel ferrites. In contrast, Mn ferrite belongs to space group Fd-3m and has a wider spontaneous resonance absorption peak width than Li ferrite. However, Mn ferrite, on its own, has a spontaneous resonance absorption peak in the relatively low frequency region around 5-25 GHz. Therefore, it is difficult to use Mn ferrite alone as a filler that exhibits good electromagnetic wave absorption characteristics in the desired frequency range for 5G (around 28 GHz).

[0024] Thus, it is difficult to produce ferrite powder suitable for 5G electromagnetic wave absorbers using Mn ferrite or Li ferrite alone. In contrast, by replacing a portion of the Mn ferrite with Li ferrite, specifically by intentionally substituting a portion of the highly crystalline Fd-3m phase with the less crystalline P4132 phase, it is possible to obtain ferrite powder that exhibits a moderately broad and deep absorption peak in the frequency range near 28 GHz. In other words, by appropriately combining the P4132 phase and the Fd-3m phase, it becomes possible to produce ferrite powder suitable for 5G electromagnetic wave absorbers.

[0025] The Li content is limited to 0.9% by mass or more and 2.5% by mass or less. If the Li content is less than 0.9% by mass, the proportion of Li ferrite becomes relatively small, and the crystal symmetry of Mn ferrite becomes dominant. As a result, the width of the absorption peak becomes excessively wide, making it difficult to selectively absorb electromagnetic waves in the desired frequency range when the ferrite powder is applied to an electromagnetic wave absorber. In other words, the depth of the absorption peak becomes small (shallow), reducing the electromagnetic wave absorption performance of the electromagnetic wave absorber. Also, if the Li content exceeds 2.5% by mass, the proportion of Mn ferrite becomes relatively small, and the crystal symmetry of Li ferrite becomes dominant. As the width of the electromagnetic wave absorption peak becomes excessively narrow, when the ferrite powder is applied to an electromagnetic wave absorber, the absorption performance in a specific frequency band becomes excessively high, resulting in reduced versatility. The Li content is preferably 1.0% by mass or more and 2.0% by mass or less, and more preferably 1.15% by mass or more and 1.8% by mass or less. In one preferred embodiment, the Li content is preferably 0.9% by mass or more and 2.0% by mass or less, and more preferably 0.9% by mass or more and 1.8% by mass or less. In a preferred embodiment, the Li content is preferably 1.0% by mass or more and 2.5% by mass or less, more preferably 1.0% by mass or more and 2.0% by mass or less, and even more preferably 1.0% by mass or more and 1.8% by mass or less. In one preferred embodiment, the Li content is preferably 1.15% by mass or more and 2.5% by mass or less, more preferably 1.15% by mass or more and 2.0% by mass or less, and even more preferably 1.15% by mass or more and 1.8% by mass or less.

[0026] The Mn content is limited to 1.0 mass% or more and 8.0 mass% or less. If the Mn content is less than 1.0 mass%, the proportion of Mn ferrite becomes relatively small, and the crystal symmetry of Li ferrite becomes dominant. As a result, the width of the electromagnetic wave absorption peak becomes excessively narrow, reducing the versatility of the electromagnetic wave absorber. Also, if the Mn content exceeds 8.0 mass%, the proportion of Li ferrite becomes relatively small, and the crystal symmetry of Mn ferrite becomes dominant. Because the depth of the absorption peak becomes smaller, the electromagnetic wave absorption performance of the electromagnetic wave absorber decreases. The Mn content is preferably 1.5 mass% or more and 7.0 mass% or less, and more preferably 2.0 mass% or more and 6.0 mass% or less. In one preferred embodiment, the Mn content is preferably 1.0% by mass or more and 7.0% by mass or less, and more preferably 1.0% by mass or more and 6.0% by mass or less. In one preferred embodiment, the Mn content is preferably 1.5% by mass or more and 8.0% by mass or less, more preferably 1.5% by mass or more and 7.0% by mass or less, and even more preferably 1.5% by mass or more and 6.0% by mass or less. In one preferred embodiment, the Mn content is preferably 2.0% by mass or more and 8.0% by mass or less, more preferably 2.0% by mass or more and 7.0% by mass or less, and even more preferably 2.0% by mass or more and 6.0% by mass or less.

[0027] The Fe content is limited to between 58.0% by mass and 69.5% by mass. If the Fe content falls below 58.0% by mass, the amount of Fe necessary to maintain the spinel-type crystal structure will be insufficient, and Li oxides and Mn oxides that did not ferrite during firing may remain in the ferrite powder. Li oxides and Mn oxides are nonmagnetic phases, and their presence will lead to a decrease in magnetic properties. Furthermore, Li oxides are alkaline. Therefore, if Li oxides remain, the viscosity of the material may change when kneading the ferrite powder with resin to manufacture resin molded products (electromagnetic wave absorbers), making manufacturing difficult. Also, if the Fe content exceeds 69.5% by mass, it will result in an Fe excess composition, and α-Fe2O3 and γ-Fe2O3 that did not ferrite during firing may remain in the ferrite powder. α-Fe2O3 is an antiferromagnetic material, and its presence may lead to a decrease in magnetic properties. Although γ-Fe2O3 is a ferromagnetic material, the frequency at which it shows its electromagnetic wave absorption peak is significantly different from that of Li ferrite and Mn ferrite. Therefore, if a large amount of γ-Fe2O3 is generated, it becomes difficult to selectively absorb electromagnetic waves in the desired frequency range (around 28 GHz). The Fe content is preferably 60.0% by mass or more and 68.0% by mass or less, and more preferably 61.5% by mass or more and 66.0% by mass or less. In one preferred embodiment, the Fe content is preferably 58.0% by mass to 68.0% by mass, and more preferably 58.0% by mass to 66.0% by mass. In one preferred embodiment, the Fe content is preferably 60.0% by mass or more and 69.5% by mass or less, more preferably 60.0% by mass or more and 68.0% by mass or less, and even more preferably 60.0% by mass or more and 66.0% by mass or less. In one preferred embodiment, the Fe content is preferably 61.5% by mass or more and 69.5% by mass or less, more preferably 61.5% by mass or more and 68.0% by mass or less, and even more preferably 61.5% by mass or more and 66.0% by mass or less.

[0028] The ferrite powder of this embodiment does not exclude the inclusion of other components (components other than Li, Mn, Fe, and O) as long as it satisfies the above-mentioned amounts of Li, Mn, and Fe. Examples of other components include Sr, Ca, Cu, Zn, Si, and / or Cl. However, in order to fully utilize the electromagnetic wave absorption performance based on Li ferrite and Mn ferrite, it is desirable that the amount of other components is not excessively large. The content of other components is preferably 1.0% by mass or less, 0.7% by mass or less, or 0.5% by mass or less. In particular, the silicon (Si) content is preferably less than 25 ppm, less than 10 ppm, or less than 1 ppm. Furthermore, since elements V and / or Bi, which promote sintering, can increase the hardness of ferrite particles and make grinding difficult, it is preferable that these are not included.

[0029] In this embodiment, the ferrite powder exhibits an X-ray diffraction profile in which the (311) plane of the crystalline phase (Fd-3m phase) belonging to the space group Fd-3m has a full width at half maximum (XRD FWHM) of 0.09° to 0.22°. By setting the FWHM within this range, excellent electromagnetic wave absorption performance can be obtained in the desired frequency range (around 28 GHz). A FWHM below 0.09° means that the distribution of lattice constants in the ferrite powder becomes smaller and the crystal structure becomes more uniform. Magnetic moments become more prone to rotation in response to an externally applied magnetic field, and this, combined with the influence of adjacent magnetic moments, may excessively lower the frequency of the absorption peak based on natural resonance. Furthermore, if the FWHM exceeds 0.22°, it becomes difficult to obtain excellent electromagnetic wave absorption performance. This is because a larger FWHM means that the distribution of lattice constants broadens, that is, a large number of spinel structures with different lattice constants exist. When many spinel structures with different lattice constants exist, the frequency of the spontaneous resonance changes according to the lattice constant. As a result, the width of the spontaneous resonance peak widens, but the depth of the spontaneous resonance peak decreases. Therefore, when ferrite powder is used as a filler in an electromagnetic wave absorber, the electromagnetic wave absorption performance in the desired frequency range (around 28 GHz) decreases. A full width at half maximum (FWHM) of 0.09° to 0.20° is preferable. The X-ray diffraction profile is determined by X-ray diffraction analysis using cobalt (Co) as the radiation source.

[0030] The ferrite powder of this embodiment has a volume-average particle size D50 of 1 μm or more and less than 20 μm. By setting D50 within this range, it becomes possible to manufacture resin molded bodies (electromagnetic wave absorbers) with excellent electromagnetic wave absorption performance. If D50 is less than 1 μm, the material viscosity may increase when kneading the ferrite powder with resin to manufacture the resin molded body, making manufacturing difficult. It is possible to reduce the amount of ferrite powder to lower the viscosity, but in that case, the electromagnetic wave absorption performance will decrease. Also, if D50 is 20 μm or more, the voids between the particles (ferrite particles) constituting the ferrite powder contained in the resin molded body become larger. This causes electromagnetic wave leakage and reduces the electromagnetic wave absorption performance. D50 is preferably 1.5 μm or more and 15 μm or less, more preferably 2 μm or more and 10 μm or less, and even more preferably 2 μm or more and less than 10 μm. In a preferred embodiment, D50 is preferably 1 μm or more and 15 μm or less, more preferably 1 μm or more and 10 μm or less, and even more preferably 1 μm or more and less than 10 μm. In one preferred embodiment, D50 is preferably 1.5 μm or more and less than 20 μm, more preferably 1.5 μm or more and 15 μm or less, even more preferably 1.5 μm or more and 10 μm or less, and particularly preferably 1.5 μm or more and less than 10 μm. In one preferred embodiment, D50 is preferably 2 μm or more and less than 20 μm, more preferably 2 μm or more and 15 μm or less, even more preferably 2 μm or more and 10 μm or less, and particularly preferably 2 μm or more and less than 10 μm.

[0031] Preferably, the proportion of the crystalline phase (Fd-3m phase) belonging to the space group Fd-3m is 30% by mass or more and 98% by mass or less. Here, the proportion of the Fd-3m phase is the mass ratio of the Fd-3m phase content to the total content of the Fd-3m phase and the P4132 phase in the ferrite powder. By setting the proportion of the Fd-3m phase to 30% by mass or more, the influence of the P4132 phase, which narrows the absorption peak width, can be suppressed, and as a result, the versatility of the electromagnetic wave absorber can be further increased. The proportion of the Fd-3m phase is more preferably 35% by mass or more and 98% by mass or less, and even more preferably 38% by mass or more and 90% by mass or less. In one preferred embodiment, the proportion of the Fd-3m phase is preferably 30% by mass or more and 90% by mass or less. In one preferred embodiment, the proportion of the Fd-3m phase is preferably 35% by mass or more and 98% by mass or less, and more preferably 35% by mass or more and 90% by mass or less. In one preferred embodiment, the proportion of the Fd-3m phase is preferably 38% by mass or more and 98% by mass or less, and more preferably 38% by mass or more and 90% by mass or less.

[0032] Preferably, the coercivity Hc of the ferrite powder is between 40Oe and 70Oe. Hc is related to the ferrite particle size. Ferrite powder with an Hc of 40Oe or higher tends to have a moderately small particle size. This reduces the voids between ferrite particles contained in the resin molded body (electromagnetic wave absorber), further improving the electromagnetic wave absorption performance. Furthermore, ferrite powder with an excessively high Hc may contain non-magnetic or antiferromagnetic phases (α-Fe2O3, Li oxide, and Mn oxide) that have not been ferriteized. Such non-magnetic phases may reduce the electromagnetic wave absorption performance. By keeping Hc below 70Oe, the influence of non-magnetic phases can be prevented, and the electromagnetic wave absorption performance can be further improved. Hc is more preferably between 40Oe and 68Oe, and even more preferably between 45Oe and 64Oe. In one preferred embodiment, Hc is preferably 40Oe or more and 68Oe or less, and more preferably 40Oe or more and 64Oe or less. In one preferred embodiment, Hc is preferably 45Oe to 70Oe, more preferably 45Oe to 68Oe, and even more preferably 45Oe to 64Oe. Note that "Oe" is the unit of magnetic field strength in the cgs system, and 1 Oe is equal to (1 / 4π) × 10⁻⁶ 3 This corresponds to A / m.

[0033] Preferably, the remanent magnetization σr of the ferrite powder is 3 emu / g or more and 10 emu / g or less. σr is related to the ferrite particle size. Ferrite powders with a σr of 3 emu / g or more tend to have moderately small particle sizes. This reduces the voids between ferrite particles contained in the resin molded body (electromagnetic wave absorber), further improving the electromagnetic wave absorption performance. Also, ferrite powders with excessively large σr may contain non-ferriteized phases. By keeping σr below 10 emu / g, the influence of non-ferrite phases can be prevented, further improving the electromagnetic wave absorption performance. A σr of 3.5 emu / g or more and 9.5 emu / g or less is more preferable, and 4 emu / g or more and 9 emu / g or less is even more preferable. In one preferred embodiment, σr is preferably 3 emu / g or more and 9.5 emu / g or less, and more preferably 3 emu / g or more and 9 emu / g or less. In a preferred embodiment, σr is preferably 3.5 emu / g or more and 10 emu / g or less, more preferably 3.5 emu / g or more and 9.5 emu / g or less, and even more preferably 3.5 emu / g or more and 9 emu / g or less. In a preferred embodiment, σr is preferably 4 emu / g or more and 10 emu / g or less, more preferably 4 emu / g or more and 9.5 emu / g or less, and even more preferably 4 emu / g or more and 9 emu / g or less. Note that "emu / g" is the unit of magnetic moment per unit mass in the cgs system, and 1 emu / g is equal to 1 A·m 2 This corresponds to / kg.

[0034] Preferably, the shape factor SF-1 of the ferrite powder is between 115 and 250. SF-1 is an indicator of the sphericity of the particle. For a perfect sphere, SF-1 is 100, and it increases as the particle deviates from a sphere. By moderately distorting the shape of the ferrite particles, the electromagnetic wave absorption performance is further improved. This is thought to be because the probability of particles contacting each other at multiple points rather than just one point in the resin molded body (electromagnetic wave absorber) increases, and as a result, when electromagnetic waves pass through the electromagnetic wave absorber, the magnetic field component is less likely to leak out of the ferrite particles.

[0035] Conversely, if SF-1 falls below 115, the sphericity of the particles becomes too high. Although the particle packing density in the electromagnetic wave absorber increases, the probability of particle contact decreases, potentially leading to a decline in electromagnetic wave absorption performance. Furthermore, ferrite powders with an SF-1 value exceeding 250 contain extremely irregularly shaped particles, plate-like particles, or particles with concave surfaces. With powders containing such particles, it is difficult to increase the particle packing density in the electromagnetic wave absorber. An SF-1 value of 120 to 240 is more preferable. In one preferred embodiment, SF-1 is preferably between 115 and 240. In one preferred embodiment, SF-1 is preferably 120 to 250, and more preferably 120 to 240.

[0036] Preferably, the shape factor SF-2 of the ferrite powder is between 115 and 250. SF-2 is an index of the degree of surface roughness of the particles. For a perfect sphere, SF-2 is 100, and it increases as the shape deviates from a sphere. The presence of a moderate amount of roughness on the surface of the ferrite particles allows the particles to interlock, reducing the gaps between them and thus further improving electromagnetic wave absorption performance. In the case of large particles with wide gaps between them, the electromagnetic wave absorption capacity may decrease even if SF-2 falls within the above range. However, in the ferrite powder of this embodiment, where the volume average particle size is less than 20 μm, it is possible to effectively improve the electromagnetic wave absorption capacity by limiting SF-2 to the above range.

[0037] On the other hand, when SF-2 is less than 115, the surface roughness of the particles becomes too small. Since the particles in the electromagnetic wave absorber do not mesh and the gaps between the particles become large, there is a risk that the electromagnetic wave absorption performance may deteriorate. Also, ferrite powder with SF-2 exceeding 250 contains extremely amorphous particles, plate-like particles, or particles having concave portions on the surface. In a powder containing such particles, it is difficult to increase the particle filling rate in the electromagnetic wave absorber. SF-2 is more preferably 120 or more and 230 or less. In a preferred embodiment, SF-2 is preferably 115 or more and 230 or less. In a preferred embodiment, SF-2 is preferably 120 or more and 250 or less, and more preferably 120 or more and 230 or less.

[0038] Preferably, the ferrite powder has a peak in the frequency characteristics of the reflection coefficient (S 11 ) within the range of 21 GHz or more and 32 GHz or less, more preferably within the range of 24 GHz or more and 30 GHz or less. By providing an absorption peak within this frequency range, it can be used as a filler that exhibits good electromagnetic wave absorption characteristics in the desired frequency band corresponding to 5G. Note that the reflection coefficient (S 11 ) is the S parameter representing the reflected signal and is measured by the free space method. In a preferred embodiment, the above peak preferably exists within the range of 21 GHz or more and 30 GHz or less. In a preferred embodiment, the above peak preferably exists within the range of 24 GHz or more and 32 GHz or less, and more preferably within the range of 24 GHz or more and 30 GHz or less.

[0039] Preferably, the ferrite powder has a product of the depth and width of the absorption peak of 10 GHz dB or more in the frequency characteristics of the reflection coefficient (S 11 ). Here, the depth of the absorption peak is the reflection coefficient (S 11This is the absolute value of the minimum value of (S). The peak width is the full width at half maximum of the absorption peak. In this way, by increasing the product of the depth and width of the absorption peak, it is possible to obtain ferrite powder and electromagnetic wave absorbers that have both excellent electromagnetic wave absorption performance and versatility in 5G. On the other hand, if the product of the depth and width of the absorption peak is less than 10 GHz dB, the depth of the absorption peak (S 11 The absolute value of the minimum value and / or width of the absorption peak becomes smaller. Therefore, it becomes difficult to obtain ferrite powder that exhibits a moderately broad and deep absorption peak in the desired frequency range. A higher product of the depth and width of the absorption peak is desirable. 12 GHz dB or higher is more preferable, and 15 GHz dB or higher is even more preferable.

[0040] The ferrite powder of this embodiment has the characteristic of exhibiting a moderately broad and deep absorption peak in the frequency range near 28 GHz. Therefore, by using this ferrite powder, an electromagnetic wave absorber can be obtained that has both excellent electromagnetic wave absorption performance and versatility in 5G.

[0041] <<2. Method for producing ferrite powder>> The manufacturing method of the ferrite powder in this embodiment is not limited as long as the above requirements are satisfied. However, a preferred method for manufacturing ferrite powder comprises the steps of: mixing iron (Fe), manganese (Mn), and lithium (Li) raw materials to obtain a raw material mixture (raw material mixing step); calcining the obtained mixture to obtain a calcined product (calcination step); crushing and granulating the obtained calcined product to obtain granules (granulation step); debinding the obtained granules to obtain a debinding product (debinding step); and firing the obtained debinding product to obtain a fired product (firing step). Furthermore, the debinding treatment is carried out in an atmosphere with an oxygen concentration of 18% by volume or less, and the firing is carried out at a temperature of 1050°C to 1280°C in an atmosphere with an oxygen concentration of 0.01% by volume or more and 8% by volume or less. In addition, if necessary, a step of crushing, classifying, and / or pulverizing the fired product (post-processing step) may be provided. Details of each step are described below.

[0042] <Raw material mixing process> In the raw material mixing process, iron (Fe), manganese (Mn), and lithium (Li) raw materials are mixed to obtain a raw material mixture. Known ferrite raw materials such as oxides, carbonates, hydroxides, and chlorides of Fe, Mn, and / or Li may be used as raw materials. The raw materials may contain each component (Fe, Mn, Li) individually or in combination of two or more. The proportions of Fe, Mn, and Li raw materials should be determined so that the final ferrite powder has the desired composition. The raw materials may be mixed using a known mixer such as a Henschel mixer, either dry or wet, or both.

[0043] <Calibration process> In the calcination process, the obtained mixture is calcined to obtain a calcined product. Calcination promotes the ferrite reaction of the raw material mixture, allowing for the production of a ferrite powder with a uniform composition. Calcination can be carried out by known methods. It can be done using a furnace such as a rotary kiln, continuous furnace, or batch furnace, under known conditions. For example, conditions include holding the mixture at a temperature of 700°C to 1300°C for 2 to 12 hours in an atmosphere such as air.

[0044] <Granulation process> In the granulation process, the calcined material obtained is crushed and granulated to produce granules. The crushing method is not particularly limited. Known crushing machines such as vibratory mills, ball mills, or bead mills may be used, and the process may be carried out either dry or wet, or both. The granulation method may also be a known method. For example, water and a binder, and optionally additives such as a dispersant and / or defoamer, may be added to the crushed calcined material to adjust the viscosity, and then granulation may be carried out using a granulator such as a spray dryer. As the binder, polyvinyl alcohol (PVA), polyvinylpyrrolidone, and / or acrylic resin binders may be used, and the amount added is 0.05% by mass or more and 1.0% by mass or less in terms of solid content relative to the raw material mixture.

[0045] <Binder removal process> In the debindering process, the obtained granules are debindered to obtain a debindered product. In the debindering process, the granules are heated to decompose and remove organic components such as binders. The debindering process can be carried out using a known heating furnace. The heating should be carried out under conditions that remove organic components, for example, at a temperature of 650°C to 1050°C for 0.5 hours to 12 hours.

[0046] In obtaining the ferrite powder of this embodiment, the atmosphere during the debinding treatment (heating), particularly the oxygen concentration, is important. Specifically, it is preferable to perform the debinding treatment (heating) in an atmosphere with an oxygen concentration of 18 volume% or less. Performing the debinding treatment in an atmosphere with an oxygen concentration of 18 volume% or less makes it easier for Mn ferrite to be formed at a lower firing temperature during the main firing. As a result, Mn ferrite and Li ferrite with different lattice constants can easily coexist during the main firing, which moderately broadens the full width at half maximum of the (311) plane of Fd-3m, leading to an improvement in electromagnetic wave absorption capacity. If the oxygen concentration exceeds 18 volume%, Mn ferrite will not be sufficiently formed, and the crystal symmetry of Li ferrite will become dominant. Therefore, the width of the absorption peak becomes extremely narrow, and the versatility of the electromagnetic wave absorber decreases.

[0047] <Firing Process> In the firing process, the debindered material is fired to obtain a fired product. The firing can be carried out using a known firing furnace such as a rotary kiln, a continuous furnace, or a batch furnace. However, the firing temperature is important for obtaining the ferrite powder of this embodiment. Specifically, it is preferable to perform the firing at a temperature of 1050°C to 1280°C. By firing at a temperature within this range, the crystal symmetry of Li ferrite and Mn ferrite can be controlled to an appropriate range, and as a result, it becomes possible to obtain an electromagnetic wave absorber that has excellent electromagnetic wave absorption performance in the 28 GHz band and is highly versatile.

[0048] To explain this point, the firing temperature of Mn ferrite is relatively high, usually above 1250°C. In contrast, Li ferrite is fired at a relatively low temperature of around 1100°C. If the firing temperature during ferrite powder production is below 1050°C, sufficient Mn ferrite is not formed, and the crystal symmetry of Li ferrite becomes dominant. As a result, the width of the absorption peak becomes extremely narrow, reducing the versatility of the electromagnetic wave absorber. Also, if the firing temperature exceeds 1280°C, the formation of Mn ferrite proceeds excessively, and the crystal symmetry of Mn ferrite becomes dominant. The absorption peak width becomes excessively wide, or the absorption peak appears at a position far from the target frequency, thereby reducing the electromagnetic wave absorption performance in the desired frequency range (around 28 GHz). A firing temperature of 1100°C to 1250°C is more preferable. In particular, when the firing temperature is between 1100°C and 1250°C, it becomes easier to create a state in which Li ferrite and Mn ferrite are mixed, and it is possible to have an appropriate distribution of lattice constants. In one preferred embodiment, the firing temperature is preferably 1050°C or higher and 1250°C or lower. In one preferred embodiment, the firing temperature is preferably 1100°C to 1280°C, and more preferably 1100°C to 1250°C. Furthermore, a firing and holding time of 2 hours to 24 hours is preferable.

[0049] In obtaining the ferrite powder of this embodiment, the atmosphere (oxygen concentration) during the main firing is also important. The oxygen concentration is preferably between 0.01 volume% and 8 volume%. By firing within this oxygen concentration range, the crystal symmetry of the Li ferrite produced by atmospheric firing and the Mn ferrite produced in a non-oxidizing atmosphere can be controlled to an appropriate range. As a result, it becomes possible to obtain an electromagnetic wave absorber that has excellent electromagnetic wave absorption performance in the desired frequency range (around 28 GHz) and is highly versatile. If the oxygen concentration falls below 0.01 volume%, the formation of Mn ferrite proceeds excessively, and the crystal symmetry of Mn ferrite becomes dominant, reducing the electromagnetic wave absorption performance. Conversely, if the oxygen concentration exceeds 8 volume%, the crystal symmetry of Li ferrite becomes dominant, reducing the versatility of the electromagnetic wave absorber.

[0050] <Post-processing steps> If necessary, a post-processing step of crushing, classifying, and / or pulverizing the obtained calcined material may be included. This makes it possible to adjust the particle size of the calcined material (ferrite powder). In particular, if the particle size of the ferrite powder is excessively small, the viscosity of the material may increase when kneading the ferrite powder with resin to manufacture a resin molded body (electromagnetic wave absorber), which may make manufacturing difficult. Also, if the particle size of the ferrite powder is excessively large, the voids between the ferrite particles contained in the resin molded body may become large, which may reduce the electromagnetic wave absorption performance. Therefore, in such cases, it is preferable to adjust the particle size by post-processing the calcined material. In particular, granular ferrite particles obtained by crushing may have a narrow XRD full width at half maximum even if the particle size is less than 20 μm, and sufficient electromagnetic wave absorption capacity may not be obtained. In such cases, widening the full width at half maximum by pulverization is effective in obtaining sufficient electromagnetic wave absorption capacity.

[0051] Crushing can be carried out using a crusher such as a hammer crusher. Classification can be carried out by methods such as air flow classification or sieving classification. Grinding can be carried out using known grinders such as vibratory mills, ball mills, or bead mills, either dry or wet, or both. However, if ferrite powder with the desired particle size can be obtained after the main calcination, the post-processing step is not essential.

[0052] In this way, the ferrite powder of this embodiment can be obtained.

[0053] <<3. Ferrite resin composite materials>> The ferrite resin composite material of this embodiment includes the ferrite powder and resin described above. The ferrite resin composite material is a precursor material for a resin molded body, which is a component of an electromagnetic wave absorber. That is, the resin composite material is molded to produce a resin molded body.

[0054] Examples of resins constituting the composite material include epoxy resins, urethane resins, acrylic resins, silicone resins, polyamide resins, polyimide resins, polyamide-imide resins, fluororesins, or combinations thereof. The silicone resin may be a modified silicone resin modified with acrylic, urethane, epoxy, and / or fluorine.

[0055] The composite material may contain components other than ferrite powder and resin. Examples of such components include solvents, fillers (organic fillers, inorganic fillers), plasticizers, antioxidants, dispersants, colorants such as pigments, and / or thermally conductive particles.

[0056] The proportion of ferrite powder to the total solid content in the composite material is preferably 50% to 95% by mass, and more preferably 80% to 95% by mass. The proportion of resin to the total solid content in the composite material is preferably 5% to 50% by mass, and more preferably 5% to 20% by mass. By keeping the proportions of ferrite powder and resin within the above ranges, the dispersion stability of the ferrite powder in the composite material, as well as the storage stability and moldability of the composite material, are improved, and the properties such as mechanical strength and magnetic properties of the composite (molded body) obtained by molding the composite material are also improved.

[0057] <<4. Ferrite resin composite>> The ferrite resin composite (resin molded body) of this embodiment is a molded body of the ferrite resin composition described above. That is, the composite is produced by molding the ferrite resin composition. The molding method is not particularly limited and includes, for example, compression molding, extrusion molding, injection molding, blow molding, or calendering. Alternatively, a method of forming a coating film of the composite material on a substrate may also be used.

[0058] <<5. Electromagnetic wave absorber>> The electromagnetic wave absorber of this embodiment comprises the ferrite resin composite (resin molded body) described above. The electromagnetic wave absorber may consist only of the resin molded body, or other members may be provided. For example, an impedance matching layer or a surface protection layer may be provided on the surface. A reflective member may also be provided on the back surface. An example of an impedance matching layer is a layer in which magnetic powder or dielectric powder is dispersed in resin. An example of a surface protection layer is a layer made of resin or glass. Examples of reflective members include film-like, foil-like, or mesh-like metal members.

[0059] Preferably, the electromagnetic wave absorber has a peak in the frequency characteristics of its reflection coefficient (S11) within the range of 21 GHz to 32 GHz, more preferably 24 GHz to 30 GHz. By having the absorption peak within this frequency range, it can be used as an absorber that exhibits good electromagnetic wave absorption characteristics in the desired frequency range for 5G. In one preferred embodiment, the peak is preferably between 21 GHz and 30 GHz. In one preferred embodiment, the peak is preferably between 24 GHz and 32 GHz, and more preferably between 24 GHz and 30 GHz.

[0060] Preferably, the electromagnetic wave absorber has a product of the depth and width of the absorption peak in the frequency characteristics of the reflection coefficient (S11) of 10 GHz dB or more. By increasing the product of the depth and width of the absorption peak, it can be used as an absorber that has both excellent electromagnetic wave absorption performance and versatility in 5G. A higher product of the depth and width of the absorption peak is desirable. 12 GHz dB or more is more preferable, and 15 GHz dB or more is even more preferable.

[0061] The applications of electromagnetic wave absorbers are not limited as long as their purpose is to absorb electromagnetic waves. For example, they can be used in transmission lines, high-frequency circuits, electronic components, and / or electronic devices. The electromagnetic wave absorber of this embodiment exhibits a moderately broad and deep absorption peak in the frequency range near 28 GHz, and has the advantage of combining excellent electromagnetic wave absorption performance and versatility in 5G. Therefore, it is suitable for 5G-compatible communication equipment and the transmission lines, high-frequency circuits, and / or electronic components used therein. [Examples]

[0062] The present invention will be described in more detail using the following examples and comparative examples. However, the present invention is not limited to the following examples.

[0063] (1) Preparation of ferrite powder [Examples 1-13] Using α-iron oxide (α-Fe2O3), trimanganese tetroxide (Mn3O4), and lithium carbonate (Li2CO3) as raw materials, these were weighed and mixed according to the amounts shown in Table 1 below. Next, water was added to the resulting mixture to a solid content of 50% by mass, and after grinding in a bead mill, the mixture was pre-granulated using a spray dryer. The resulting pre-granulated material was then calcined in air at 1000°C for 2 hours.

[0064] Water was added to the calcined material to achieve a solid content of 50% by mass. Then, PVA as a binder and an aliphatic polyhydric alcohol-based polyether polyol as an antifoaming agent were added, and the mixture was ground using a bead mill. The amounts of binder and antifoaming agent added were adjusted to the values ​​shown in Table 1 below. Next, the resulting slurry of ground powder was granulated using a spray dryer to obtain granules.

[0065] The obtained granules were subjected to a debinder treatment to remove organic components, and then calcined. The debinder treatment and calcination were carried out under the conditions shown in Table 1 below. Next, the obtained calcined material was crushed with a hammer crusher, and then some samples were classified and ground. In this way, ferrite powders of Examples 1 to 13 were obtained.

[0066] [Table 1]

[0067] (2) Evaluation The ferrite powders prepared in Examples 1-13 were evaluated for various properties as follows.

[0068] <Chemical analysis> The metal content of ferrite powder was determined by chemical analysis. First, 0.2 g of ferrite powder was weighed, and 60 ml of pure water, 20 ml of 1N hydrochloric acid, and 20 ml of 1N nitric acid were added to it. The mixture was then heated to prepare an aqueous solution in which the sample was completely dissolved. The resulting aqueous solution was placed in an ICP analyzer (Shimadzu Corporation, ICPS-10001V) to measure the metal content.

[0069] <Particle size distribution> The particle size distribution of ferrite powder was measured as follows. First, 10 g of ferrite powder and 80 ml of water were placed in a 100 ml beaker, and 2 drops of sodium hexametaphosphate were added as a dispersant. Next, the mixture was dispersed using an ultrasonic homogenizer (SMT Corporation, UH-150 model). The output level of the ultrasonic homogenizer was set to 4, and dispersion was performed for 20 seconds. After that, the bubbles formed on the surface of the beaker were removed, and the resulting dispersion was introduced into a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-7500nano) for measurement. The measurement conditions were a pump speed of 7, an internal ultrasonic irradiation time of 30, and a refractive index of 1.70-050i. From this measurement, the 10% diameter (D10), 50% diameter (volume-average particle size, D50), and 90% diameter (D90) in the volume particle size distribution were determined.

[0070] <Particle shape> The particle shape in the ferrite powder was evaluated as follows. First, the ferrite powder was observed using a scanning electron microscope (SEM; Hitachi High-Technologies Corporation, SU-8020). The magnification was set to 50,000x. Images were taken with 1 to 30 particles, preferably 1 to 10, in the field of view. Ten random fields of view were captured to examine the particle shape.

[0071] <Shape Factor> The shape factors (SF-1 and SF-2) of ferrite powder were determined using a particle image analyzer (Malvern Panalytical, Morphologi G3). First, the ferrite powder was analyzed using the particle image analyzer. For the analysis, image analysis was performed on each of the 1000 particles in the powder, and the circularity, perimeter, and equivalent diameter (CE Diameter) were automatically measured. In this process, a 50x magnification objective lens was used for samples with an average particle size smaller than 20 μm, and a 10x magnification objective lens was used for samples with an average particle size of 20 μm or more. The sample volume was 3 mm 3 The particles were dispersed on a glass slide using the dispersion jig attached to the apparatus under a dispersion pressure of 5 bar.

[0072] Of the obtained data, the average of the data for particles within ±5% of the volume-average particle size was determined as the average circularity, average perimeter, and average equivalent diameter (CE Diameter). Using these, SF-1 and SF-2 were calculated according to equations (1) and (2) below.

[0073]

number

number

[0074] <xrd> The ferrite powder was analyzed using X-ray diffraction (XRD). The analysis was performed under the following conditions.

[0075] - X-ray diffractometer: Panalytical X'pertMPD (including high-speed detector) - Source: Co-Kα - Tube voltage: 45kV -Tube current: 40mA - Incident divergence slit: 0.04 rad - Fixed divergence slit: 0.5° - Scatter prevention slit: 5.5 mm - Light-receiving divergence slit: 0.04 rad - Light-receiving slit: 0.15mm

[0076] Next, based on the obtained XRD profiles, the following crystal structures were assumed, and the composition ratio and full width at half maximum (FWHM) for each crystal structure were calculated. Specifically, after assuming the following crystal structures, the following parameters were optimized using analysis software (RIETAN-FP u2.83). The profile function used was a pseudo-Voigt function of Thompson, Cox, and Hasting, and the composition ratio and FWHM were determined from the results of asymmetric analysis using Howard's method.

[0077] Lithium iron rite: LiFe5O8 Crystal structure: Space group P4132(No.213) <atomic coordinates> Li:4a 3 / 8 3 / 8 3 / 8 Fe:8c xxx Fe:12d 1 / 8 y y+1 / 4 O: 8c xxx O:24e xyz

[0078] Manganese ferrite: MnFe2O4 Crystal structure: Space group Fd-3m (No.227) <atomic coordinates> Mn:8b 3 / 8 3 / 8 3 / 8 Fe:16c 0 0 0 O :32e xxx

[0079] <Magnetic Properties - Saturation Magnetization, Remanent Magnetization, and Coercivity> The magnetic properties (saturation magnetization, remanent magnetization, and coercivity) of ferrite powder were measured as follows. First, ferrite powder was packed into a cell with an inner diameter of 5 mm and a height of 2 mm, and set in a vibrating sample type magnetic measuring device (Toei Kogyo Co., Ltd., VSM-C7-10A). An applied magnetic field was swept up to 5 kOe, and then the applied magnetic field was decreased to generate a hysteresis curve. From the data of this curve, the saturation magnetization σs, remanent magnetization σr, and coercivity Hc of the ferrite powder were determined.

[0080] <Electromagnetic wave absorption performance> A resin molded body (electromagnetic wave absorber) was prepared using ferrite powder as a filler, and its electromagnetic wave absorption performance was evaluated. Specifically, a ferrite resin composite material was prepared by mixing and kneading 90 parts by mass of filler (ferrite powder) and 10 parts by mass of binder resin. Powdered fluororesin was used as the binder resin. The mixing was performed using a sample mill. Next, the obtained ferrite resin composite material was filled into a mold and heated at 180°C for 2 hours while being pressure molded in a press to produce a resin molded body. The dimensions of the obtained resin molded body are shown in Table 4 below.

[0081] Next, the reflection coefficient (S) is calculated from the amount of incident and reflected electromagnetic waves using the free-space method (FS method). 11 The frequency characteristics of the material were determined, and its electromagnetic wave absorption performance was evaluated. For the measurement, a 1 mm thick aluminum plate was attached to one side of the fabricated resin molded body, and the S-parameter (S) was calculated from the amount of attenuation when the incident electromagnetic wave passed through the resin molded body, was reflected by the aluminum plate, and returned after passing through the resin molded body again. 11 ,S 21 ) was sought.

[0082] (3) Evaluation results The evaluation results obtained for the ferrite powders in Examples 1-13 are summarized in Tables 2-4 below. Examples 1-8 are example samples, and Examples 9-13 are comparative example samples.

[0083] The ferrite powders of Examples 1 to 8, which served as example samples, satisfied the range specified in this embodiment in terms of composition (Fe content, Mn content, Li content) and volume-average particle size D50, as determined by chemical analysis (Table 2). They also contained both the P4132 phase and the Fd-3m phase, and the XRD full width at half maximum of the Fd-3m phase satisfied the range specified in this embodiment (Table 3). Furthermore, evaluation of the electromagnetic wave absorption performance revealed that the absorption peak was located in the frequency range near 28 GHz, and the product of the depth and width of the absorption peak was large, at 12.1 GHz dB or more (Table 4).

[0084] In contrast, the ferrite powders in comparative examples 9-11 had large D50 values ​​of 37.3-42.5 μm and small XRD full width at half maximum (F50) of the Fd-3m phase (0.056° or less). Consequently, the product of the depth and width of the absorption peak was small (5.9 GHz dB or less).

[0085] Furthermore, the ferrite powders in comparative examples 12 and 13 had a large XRD full width at half maximum (FMAX) of 0.223° or more for the Fd-3m phase. As a result, the product of the depth and width of the absorption peak remained below 6.4 GHz dB.

[0086] Reflectance coefficient (S) for Examples 7, 8, and 12 11 Figure 1 shows the frequency characteristics (electromagnetic wave absorption performance) of the device. In Examples 7 and 8, an absorption peak is present in the frequency range near 28 GHz, and the width of the absorption peak is moderately wide. In contrast, no clear absorption peak was observed in Example 12.

[0087] From the results above, it is understood that, according to this embodiment, a ferrite powder and an electromagnetic wave absorber can be obtained that exhibit a moderately broad and deep absorption peak in the frequency range near 28 GHz, achieving both excellent electromagnetic wave absorption performance and versatility in 5G.

[0088] [Table 2]

[0089] [Table 3]

[0090] [Table 4]

[0091] Note that "weight portion" and "mass portion" are synonymous. [Industrial applicability]

[0092] According to the present invention, a ferrite powder is provided that exhibits a moderately broad and deep absorption peak in the frequency range near 28 GHz, and that achieves both excellent electromagnetic wave absorption performance and versatility in the 5G compatible frequency range. Furthermore, according to the present invention, an electromagnetic wave absorber containing this ferrite powder is provided.

[0093] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2023-074734 filed on April 28, 2023, and its contents are incorporated herein by reference.< / xrd>

Claims

1. It contains lithium (Li) in a proportion of 0.9% to 2.5% by mass, manganese (Mn) in a proportion of 1.0% to 8.0% by mass, and iron (Fe) in a proportion of 58.0% to 69.5% by mass. Space group P4 １ It has a crystalline phase belonging to 32 and a crystalline phase belonging to space group Fd-3m, In the X-ray diffraction profile, the full width at half maximum of the (311) plane of the crystalline phase belonging to the space group Fd-3m is 0.09° or more and 0.22° or less. Ferrite powder having a volume-average particle size D50 of 1 μm or more and less than 20 μm.

2. The content of the crystalline phase belonging to the space group Fd-3m and the space group P4 １ The ferrite powder according to claim 1, wherein the mass ratio of the content of the crystalline phase belonging to space group Fd-3m to the total content of the crystalline phase belonging to 32 is 30% by mass or more and 98% by mass or less.

3. The ferrite powder according to claim 1 or 2, wherein the coercivity Hc is 40 Oe or more and 70 Oe or less.

4. A ferrite resin composite material comprising the ferrite powder and resin according to claim 1 or 2.

5. A ferrite resin composite, which is a molded article of the ferrite resin composite material according to claim 4.

6. An electromagnetic wave absorber comprising the ferrite resin composite described in claim 5.

Images