Magnetoplumbite-type hexagonal ferrite magnetic powder and method for producing the same, as well as radio wave absorber and method for producing the same

Abstract

To provide a magnetoplumbite-type hexagonal ferrite magnetic powder having electromagnetic wave absorbing capability in a 50 to 70 GHz band including a 60 GHz band, and having a small change in peak frequency of transmission attenuation over a wide temperature range, and a method for producing the same, and to provide an electromagnetic wave absorber using the magnetic powder and a method for producing the same.SOLUTION: This invention relates to a magnetoplumbite-type hexagonal ferrite magnetic powder, wherein a metallic element satisfies the general formula: A(1-x)RExFe(n-y-z)AlyCoz, indicating an atomic ratio (in the formula, A is one or more selected from the group consisting of Sr, Ba and Ca; RE is one or more of rare earth elements; 0.05≤x≤0.70; 0.01≤y<1.00; 0.00≤z≤1.00; 11.00≤n≤12.50).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to magnetoplanbite-type hexagonal ferrite magnetic powder and a method for producing the same, and also to an electromagnetic wave absorber containing magnetoplanbite-type hexagonal ferrite magnetic powder and a method for producing the same. [Background technology]

[0002] In recent years, with the advancement of information and communication technology, radio waves in the GHz band have come to be used for a variety of applications. Examples of applications using such high-frequency technology include mobile phones, wireless LANs, satellite broadcasting, intelligent transportation systems, nonstop automatic toll collection systems (ETC), and automotive assistive system systems (AHS). As the forms of radio wave utilization in the high-frequency range diversify in this way, concerns arise about failures, malfunctions, and failures due to interference between electronic components, making electromagnetic compatibility (EMC) countermeasures important. One effective method is to use radio wave absorbers to absorb unwanted radio waves and prevent reflection and intrusion of radio waves.

[0003] As such a magnetic powder for radio wave absorbers, Patent Document 1 describes a composition formula BaFe (12-x) Al x O 19 A radio wave absorber using a magnetoplumbite-type hexagonal ferrite powder represented by x=0.6 is disclosed, and it is disclosed that it absorbs radio waves at frequencies of 50 GHz to 54 GHz. Furthermore, in the embodiment, it is disclosed that when Al is used in the above composition formula, the ferromagnetic resonance frequency can be set to approximately 50 GHz to 100 GHz. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-354972 [Overview of the project] [Problems that the invention aims to solve]

[0005] As described above, frequency bands are allocated according to various applications, and radio wave absorbers corresponding to each frequency band have been developed. In addition, radio wave absorbers for absorbing radio waves (millimeter waves) in the 50-70 GHz band including the 60 GHz band are being considered for practical use in high-speed wireless communication applications called WiGig (Wireless Gigabit) and human presence detection radar applications. However, in the practical use of radio wave absorbers, it is necessary to function even when used for communication base stations outdoors, etc. Therefore, it is required to stably exhibit radio wave absorption ability in a wide temperature range from normal temperature to 80 °C or higher. Generally, the radio wave absorption ability has a maximum value in a certain frequency range, and the absorption amount gradually decreases as it deviates from that frequency range. Therefore, in order to exhibit stable radio wave absorption ability in a wide temperature range, it is desirable that the change width of the maximum value of the frequency with respect to temperature is small.

[0006] In this regard, the magnetoplumbite-type hexagonal ferrite magnetic powder of Patent Document 1 is a material having radio wave absorption ability in the 50 GHz to 100 GHz range, but has a problem that the peak frequency deviates greatly from normal temperature in the high temperature range. An object of the present invention is to provide a magnetoplumbite-type hexagonal ferrite magnetic powder having radio wave absorption ability in the 50-70 GHz band including the 60 GHz band, with a small change in peak frequency in a wide temperature range, a method for producing the same, a radio wave absorber using the magnetic powder, and a method for producing the same.

Means for Solving the Problems

[0007] In order to solve the above problems, the present inventors have intensively studied. The resonance frequency of a radio wave absorber is a value inherent to the composition, and even in magnetoplumbite-type hexagonal ferrite magnetic powder, different resonance frequencies are shown depending on each substitution element and substitution ratio. The metal elements contained in the single-phase crystal of the magnetoplumbite-type hexagonal ferrite magnetic powder are represented by the general formula showing the atomic ratio, A (1-x) RE x Fe (n-y-z) Al y Co z(Here, A is one or more selected from the group consisting of Sr, Ba, and Ca, RE is one or more rare earth elements selected from the group consisting of La, Ce, Pr, Nd, Y, Sm, Tb, and Dy, 0.05 ≦ x ≦ 0.70, 0.01 ≦ y < 1.00, 0.00 ≦ z ≦ 1.00, 11.00 ≦ n ≦ 12.50). In the magnetoplumbite-type hexagonal ferrite magnetic powder, it was confirmed that the change in the peak frequency is small in a wide temperature range. That is, the gist configuration of the present invention is as follows.

[0008] (1) Magnetoplumbite-type hexagonal ferrite magnetic powder, wherein the metal elements contained in the crystal of the magnetoplumbite-type hexagonal ferrite magnetic powder are represented by the general formula showing the atomic ratio, A (1-x) RE x Fe (n-y-z) Al y Co z (Here, A is one or more selected from the group consisting of Sr, Ba, and Ca, RE is one or more rare earth elements selected from the group consisting of La, Ce, Pr, Nd, Y, Sm, Tb, and Dy, 0.05 ≦ x ≦ 0.70, 0.01 ≦ y < 1.00, 0.00 ≦ z ≦ 1.00, 11.00 ≦ n ≦ 12.50). Magnetoplumbite-type hexagonal ferrite magnetic powder.

[0009] (2) The magnetoplumbite-type hexagonal ferrite magnetic powder according to (1), wherein the range of x is 0.05 ≦ x ≦ 0.60.

[0010] (3) When the peak frequencies of the transmission attenuation amounts at the respective temperatures of 30 °C, 60 °C, and 90 °C are X 30 , X 60 and X 90 , X 30 , X 60 and X 90A magnetoplanbite-type hexagonal ferrite magnetic powder according to (1) or (2), wherein the frequency range R, which is the difference between the maximum and minimum values, is 1.0 GHz or less.

[0011] (4) A magnetoplanbite-type hexagonal ferrite magnetic powder according to any one of (1) to (3), wherein the frequency range R is 0.7 GHz or less.

[0012] (5) The magnetoplanbite-type hexagonal ferrite magnetic powder according to any one of (1) to (4), wherein the metal element A is Sr.

[0013] (6) The rare earth element RE is one or more rare earth elements selected from the group consisting of La, Ce, and Pr, as described in any one of (1) to (5).

[0014] (7) The magnetoplanbite-type hexagonal ferrite magnetic powder according to any one of (1) to (6), wherein the range of n is 11.00 ≤ n < 12.00.

[0015] (8) A radio wave absorber comprising magnetoprumbite-type hexagonal ferrite magnetic powder and resin as described in any one of items (1) to (7).

[0016] (9) A raw material mixing step to obtain a raw material mixture by mixing powders that will be used as raw materials for magnetoplumbite-type hexagonal ferrite magnetic powder, A firing process in which the raw material mixture is fired to obtain a fired product, The process includes a grinding step of grinding the aforementioned fired product to obtain the magnetoplumbite-type hexagonal ferrite magnetic powder, The metal elements contained in the crystal of the magnetoplumbite-type hexagonal ferrite magnetic powder are expressed by the general formula of atomic ratio, A (1-x) RE x Fe (n-y-z) Al y Co z (Here, A is one or more elements selected from the group consisting of Sr, Ba, and Ca. RE is one or more rare earth elements selected from the group consisting of La, Ce, Pr, Nd, Y, Sm, Tb, and Dy. 0.05 ≤ x ≤ 0.70, 0.01≦y<1.00, 0.00 ≤ z ≤ 1.00, (11.00 ≤ n ≤ 12.50) A method for producing magnetoprumbite-type hexagonal ferrite magnetic powder.

[0017] (10) The method for producing magnetoplanbite-type hexagonal ferrite magnetic powder according to (9), wherein the range of x is 0.05 ≤ x ≤ 0.60.

[0018] (11) A method for producing magnetoplanbite-type hexagonal ferrite magnetic powder according to (9) or (10), further comprising a heat treatment step after the grinding step.

[0019] (12) A method for manufacturing an electromagnetic wave absorber, comprising the step of kneading a magnetoplanbite-type hexagonal ferrite magnetic powder obtained by the manufacturing method described in any one of (9) to (11) with a resin and then molding it. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a magnetoplanbite-type hexagonal ferrite magnetic powder having radio wave absorption capability in the 50-70 GHz band including the 60 GHz band, and exhibiting small changes in peak frequency over a wide temperature range, as well as a method for producing the same, and a radio wave absorber using the magnetic powder and a method for producing the same. [Brief explanation of the drawing]

[0021] [Figure 1] This diagram illustrates the manufacturing flow according to one embodiment of the present invention. [Figure 2] This graph shows the X-ray diffraction pattern of the magnetoplanbite-type hexagonal ferrite magnetic powder obtained in Example 1. [Modes for carrying out the invention]

[0022] (Magnetoplumbite-type hexagonal ferrite magnetic powder) The magnetoplumbite-type hexagonal ferrite magnetic powder of the present invention has a general formula, A, which shows the atomic ratio of the metal elements contained in the crystal of the magnetoplumbite-type hexagonal ferrite magnetic powder. (1-x) RE x Fe (n-y-z) Al y Co z This is a magnetic powder that satisfies the following conditions. The composition and other aspects of the magnetoplanbite-type hexagonal ferrite magnetic powder of the present invention will be described below.

[0023] [Atomic ratio] The magnetoplanbite-type hexagonal ferrite magnetic powder of the present invention is general formula, A (1-x) RE x Fe (n-y-z) Al y Co z The magnetic powder is such that each variable shown is 0.05≦x≦0.70, 0.01≦y<1.00, 0.00≦z≦1.00, and 11.00≦n≦12.50. Here, metal element A is one or more selected from the group consisting of Sr, Ba, and Ca, and is preferably one or more selected from Sr and Ba. Rare earth element RE is one or more rare earth elements selected from the group consisting of La, Ce, Pr, Nd, Y, Sm, Tb, and Dy, and is preferably one or more selected from La, Ce, and Pr. Also, in this specification, the general formula, AFe 12 O 19 In the crystal structure of magnetoprumbite-type hexagonal ferrite represented by , the sites occupied by element A are called A sites, and the sites occupied by element Fe are called Fe sites. In this invention, it is considered that the A sites are substituted with one or more rare earth elements, and the Fe sites are substituted with Al alone or Al and Co.

[0024] According to the present invention, a magnetoplumbite-type crystal structure is used as the framework for the commonly known strontium ferrite (SrFe 12 O19 Taking the above example, the effects of substitution by each element shown in the general formula can be explained as follows. First, the absorption frequency can be adjusted by substituting the Fe site with Al. Here, while Al substitution alone causes the absorption frequency to shift to the higher frequency side with increasing temperature, further substituting the A site (in this case, the Sr site) with a rare earth element selected from the group consisting of La, Ce, Pr, Nd, Y, Sm, Tb, and Dy reduces the temperature dependence of the adjusted absorption frequency. Furthermore, substituting the A site with these rare earth elements and further substituting the Fe site with Co also reduces the temperature dependence. In other words, if the A site is substituted with a rare earth element, the temperature dependence can be reduced whether or not the Fe site is substituted with Co, and Co does not hinder the effect of reducing temperature dependence. Based on this principle, a magnetoplanbite-type hexagonal ferrite magnetic powder can be obtained that has radio wave absorption capability in the 50-70 GHz band, including the 60 GHz band, and exhibits small changes in peak frequency over a wide temperature range.

[0025] To reduce the temperature dependence of the peak frequency, in the general formula showing the atomic ratios, the value of x is set to 0.05 or more and 0.70 or less with respect to the substitution of rare earth elements. Furthermore, to control the peak frequency, in the general formula showing the atomic ratios, the value of y is set to 0.01 or more and less than 1.00 with respect to the amount of Al substitution. And, in order to obtain a magnetoplumbite-type ferrite crystal structure, the value of z is set to 0 or more and 1.00 or less with respect to Co substitution.

[0026] The numerical range of x is preferably 0.05 or more and 0.60 or less, and more preferably 0.07 or more and 0.50 or less.

[0027] The numerical range of y is preferably 0.05 or greater, more preferably 0.10 or greater, and even more preferably 0.20 or greater. Furthermore, the numerical range of y is preferably 0.99 or less, more preferably 0.95 or less, and even more preferably 0.90 or less.

[0028] The numerical range of z is preferably 0.00 or more and 0.50 or less, and more preferably 0.00 or more and 0.40 or less.

[0029] To obtain hexagonal ferrite magnetic powder having a magnetoplumbite-type crystal structure, the value of n in the above atomic ratio is set to 11.00 or more and 12.50 or less. From the viewpoint of suppressing the amount of unreacted material remaining after calcination, the value of n is preferably 11.00 or more and 12.00 or less, and more preferably 11.20 or more and 11.80 or less.

[0030] The absorption frequency of a radio wave absorber depends on the composition of the magnetic powder that makes up the absorber. The elemental ratios shown by the compositional formula do not refer to the elemental ratios of the mixture as a whole. If each metal element mixed as a raw material does not substitute into each site of the magnetoprumbite-type hexagonal ferrite, but remains outside in another form (e.g., Al2O3), the resulting magnetic powder mixture will have a frequency far outside the desired absorption frequency range.

[0031] The magnetoplumbite-type hexagonal ferrite magnetic powder of the present invention may contain unavoidable components such as impurities in the raw materials and impurities originating from the manufacturing equipment. Examples of such components include oxides of Mn, etc. It is preferable to suppress the content of these components to 0.40% by mass or less. The atomic ratios of the above metal elements are the atomic ratios excluding unavoidable components.

[0032] [Transmission Attenuation] The magnetoplanbite-type hexagonal ferrite magnetic powder of the present invention has radio wave absorption capacity in the 50-70 GHz band, including the 60 GHz band, as a compacted powder, and can be used as a radio wave absorber with little change in peak frequency over a wide temperature range. Here, the radio wave absorption capacity is measured by mixing 0.28 g of magnetoplanbite-type hexagonal ferrite magnetic powder and 0.84 g of microcrystalline cellulose to obtain a mixed powder, which is then compressed at 151 MPa to produce a compacted powder with a diameter of 13 mm, and measured using terahertz wave time-domain spectroscopy. The peak frequencies of the transmission attenuation measured at 30°C, 60°C, and 90°C are then specified as X 30 , X60 and X 90 Let X 30 , X 60 , and X 90 When the difference between the maximum and minimum values ​​is defined as the frequency range R, the frequency range R is preferably 1.0 GHz or less, and more preferably 0.9 GHz or less. The compacted material made of magnetoplumbite-type hexagonal ferrite magnetic powder of the present invention is mainly used as a radio wave absorber in the 50-70 GHz band, including the 60 GHz band, and therefore stable radio wave absorption characteristics are required over a wide range. Furthermore, since it is used as a radio wave absorber, it is preferable that the transmission attenuation at all peak frequencies measured under these conditions be 6 dB or more.

[0033] (Fabrication and evaluation of radio wave absorbers) Furthermore, a radio wave absorber can be manufactured by kneading the magnetoplanbite-type hexagonal ferrite magnetic powder of the above-described embodiment with a resin. This radio wave absorber can be made into various shapes depending on the application, but when manufacturing a sheet-shaped radio wave absorber (radio wave absorber sheet), the radio wave absorber material (kneaded product) obtained by kneading the magnetoplanbite-type hexagonal ferrite magnetic powder with a resin can be rolled to the desired thickness (preferably 0.1 to 4.0 mm, more preferably 0.2 to 2.5 mm) using a rolling mill or the like. In addition, the content of magnetoplanbite-type hexagonal ferrite magnetic powder in the radio wave absorber material (kneaded product) is preferably 70 to 95% by mass in order to obtain a radio wave absorber having radio wave absorption ability in the 50 to 70 GHz band, including the 60 GHz band. In addition, the content of resin in the radio wave absorber material (kneaded product) is preferably 5 to 30% by mass in order to sufficiently disperse the magnetoplanbite-type hexagonal ferrite magnetic powder in the radio wave absorber material (kneaded product). Furthermore, it is preferable that the total content of magnetoplanbite-type hexagonal ferrite magnetic powder and resin in the radio wave absorbing material (compound) be 99% by mass or more.

[0034] (Method for producing magnetoplanvite-type hexagonal ferrite magnetic powder) The present invention provides a method for producing magnetoplumbite-type hexagonal ferrite magnetic powder, comprising at least a raw material mixing step of mixing raw material powders to obtain a raw material mixture, a firing step of firing the raw material mixture to obtain a fired product, and a pulverization step of pulverizing the fired product to obtain magnetoplumbite-type hexagonal ferrite magnetic powder, wherein the metal elements contained in the crystal of the magnetoplumbite-type hexagonal ferrite magnetic powder are expressed by the general formula, A (1-x) RE x Fe (n-y-z) Al y Co z (Here, A is one or more elements selected from the group consisting of Sr, Ba, and Ca, RE is one or more rare earth elements, and satisfies 0.05≦x≦0.70, 0.01≦y<1.00, 0.00≦z≦1.00, and 11.00≦n≦12.50).

[0035] Referring to Figure 1, each step of the method for producing magnetoplumbite-type hexagonal ferrite magnetic powder according to the present invention will be described in detail below.

[0036] [Raw material mixing process] First, in the raw material mixing process, the metal elements are mixed according to the general formula that shows the atomic ratio, A (1-x) RE x Fe (n-y-z) Al y Co z A raw material mixture is obtained by mixing powders that are the raw materials for magnetoplumbite-type hexagonal ferrite magnetic powder, satisfying the following conditions: (where A is one or more selected from the group consisting of Sr, Ba, and Ca, RE is one or more rare earth elements selected from the group consisting of La, Ce, Pr, Nd, Y, Sm, Tb, and Dy, and 0.05≦x≦0.70, 0.01≦y<1.00, 0.00≦z≦1.00, 11.00≦n≦12.50). In this case, it is preferable that x be between 0.05 and 0.60. The raw material powders are not particularly limited, but include SrCO3, BaCO3, BaCl2·2H2O, CaCO3, La2O3, La(OH)3, CeO2, and Pr2O. 3、Carbonates, oxides, or hydroxides of Fe2O3, Al2O3, and Co3O4 can be used, and other organic salts such as nitrates, chlorides, oxalates, and alkoxides may also be used. Furthermore, the method of mixing the raw material powders is not particularly limited, and mixing can be carried out using known mixing equipment such as a Henschel mixer.

[0037] Furthermore, a step may be included in which the obtained raw material mixture is granulated to obtain a molded body. The granulation method is not particularly limited, and it can be formed into pellets by any method. If the granulated molded body contains moisture, a further drying step may be included afterward.

[0038] [Firing process] Next, the obtained raw material mixture is fired in a firing process to obtain a fired product. Firing is preferably carried out in any firing furnace at a temperature of 1150°C to 1400°C, more preferably 1170°C to 1350°C, and even more preferably 1200°C to 1300°C. For example, when using a box-type firing furnace, the raw materials can be filled into a firing container. The atmosphere during firing is preferably an oxidizing atmosphere, and the oxidizing atmosphere is preferably an atmosphere such as air, oxygen, a mixture of oxygen and nitrogen, or a mixture of oxygen and a rare gas.

[0039] [Grinding process] Next, the obtained calcined product is crushed in a grinding process to obtain magnetoplanbite-type hexagonal ferrite magnetic powder. In the grinding process, coarse grinding and fine grinding may be performed. Coarse grinding means crushing the calcined product, and any grinding method such as impact grinding with a hammer mill can be used. Fine grinding means further reducing the calcined product after coarse grinding to a finer state, and any method such as wet grinding with an attritor can be used. The slurry after wet grinding can be subjected to solid-liquid separation and drying by any method to obtain magnetoplanbite-type hexagonal ferrite magnetic powder.

[0040] Furthermore, the magnetoplanbite-type hexagonal ferrite magnetic powder obtained in the pulverization process can be heat-treated using any heat treatment method in the heat treatment process. The heat treatment temperature is preferably 850°C to 1000°C, and more preferably 870°C to 930°C. In addition, an oxidizing atmosphere is preferred during the heat treatment, and an air atmosphere is more preferred. By applying heat treatment, the minute magnetoplanbite-type hexagonal ferrite magnetic powder is sintered and the specific surface area is reduced, so it is expected that the magnetoplanbite-type hexagonal ferrite magnetic powder will be uniformly dispersed in the resin or rubber when manufacturing the radio wave absorber. Although the direct effect on the absorption frequency is not known, heat treatment removes the crystal distortion generated in the pulverization process, and magnetic properties such as coercivity Hc are restored.

[0041] (Fabrication of radio wave absorbers) Furthermore, the obtained magnetoplanbite-type hexagonal ferrite magnetic powder can be mixed with a resin to produce a radio wave absorber. This radio wave absorber can be made into various shapes depending on the application, but when producing a sheet-shaped radio wave absorber (radio wave absorber sheet), the radio wave absorber material (mixture) obtained by mixing the magnetoplanbite-type hexagonal ferrite magnetic powder with a resin can be rolled to the desired thickness (preferably 0.1 to 4.0 mm, more preferably 0.2 to 2.5 mm) using a rolling mill or the like. [Examples]

[0042] The magnetoprumbite-type hexagonal ferrite magnetic powder (hereinafter simply referred to as "magnetic powder") and its manufacturing method according to the present invention will be described in detail below with reference to examples. The evaluations in the examples were performed as follows.

[0043] [Particle size distribution and cumulative 50% particle size] The particle size distribution of the magnetic powder was measured using a laser diffraction particle size distribution analyzer (HELOS&RODOS, manufactured by JEOL Ltd.) with a focal length of 200 mm and a dispersion pressure of 1.7 bar, by dry dispersion. From the obtained measurement results, the cumulative 50% particle size (D) based on volume was calculated. 50) was sought.

[0044] [Specific surface area measurement] The specific surface area of ​​the magnetic powder was measured using a specific surface area measuring device (Macsorb model-1210 manufactured by Mountec Co., Ltd.) with the BET single-point method.

[0045] [Composition analysis] Compositional analysis was performed using an ICP(720-ES) high-frequency induction plasma emission spectrometer manufactured by Agilent Technologies, Inc.

[0046] [Crystal structure] X-ray diffraction measurements of magnetic powder were performed using a powder X-ray diffractometer (Ultima IV horizontal multi-purpose X-ray diffractometer manufactured by Rigaku Corporation), with the radiation source set to CuKα rays, the tube voltage to 40kV, the tube current to 40mA, and the measurement range to 2θ = 10° to 70°, using the powder X-ray diffraction (XRD) method.

[0047] [Measurement of radio wave absorption characteristics] A mixed powder was obtained by mixing 0.28 g of magnetic powder and 0.84 g of microcrystalline cellulose, and the resulting mixture was compressed at 151 MPa to obtain a compact with a diameter of 13 mm. The transmission attenuation of the obtained compact was measured using terahertz wave time-domain spectroscopy, and the peak frequency of the transmission attenuation of the compact was determined. Specifically, measurements were performed using the Advantest TAS7400SL terahertz spectroscopy system, with the compact placed in a sample holder and as a blank. Using the Advantest TAS1030 temperature control module, the compact was heated to 30°C, 60°C, and 90°C, and the transmission attenuation was measured at each temperature. The frequency (frequency peak value, in GHz) showing the maximum transmission attenuation in the 50-100 GHz range was determined. The conditions used are listed below. • Sample holder diameter: φ10mm ·MeasurementMode:Transmission • Frequency Resolution: 1.9GHz • Vertical axis: Absorbance ·Horizontalaxis:Frequency[THz] ·CumulatedNumber(Sample):2048 ·CumulatedNumber(Background):2048

[0048] The observed sample signal waveform and the blank reference waveform were extended to 8448 ps and subjected to Fourier transform. The ratio (Ssig / Sref) of the resulting Fourier spectra (denoted as Ssig and Sref, respectively) was determined, and the transmission attenuation of the compacted powder placed in the sample holder was calculated.

[0049] (Example 1) First, 99% pure SrCO3, 99.9% pure Al2O3, 99% pure Fe2O3, and 99.99% pure La(OH)3 were weighed out as raw material powders so that the molar ratio of Sr, La, Fe, and Al was Sr:La:Fe:Al = 0.80:0.20:10.98:0.78. These raw material powders were mixed using a Henschel mixer, and then further mixed using a dry method with a vibrating mill. The resulting mixed powder was granulated into pellets to obtain a 2 kg molded body. Next, the 2 kg molded body was filled into a firing sieve, and this firing sieve was placed in a box-type firing furnace and fired in air at 1260°C for 4 hours. The calcined body obtained by this calcination was coarsely ground in a hammer mill, and the resulting coarse powder was wet-ground for 70 minutes using an attritor with water as the solvent. The resulting slurry was then separated into solid and liquid components, and the resulting cake was dried and crushed to obtain magnetic powder.

[0050] The magnetic powder obtained in this manner was first subjected to compositional analysis to evaluate its physical properties, followed by X-ray diffraction (XRD) measurements. Then, after measuring the magnetic properties and the transmission attenuation of the compacted powder, the frequency range R was determined. The XRD measurements confirmed that the magnetic powder obtained in this example has a magnetoplanbite-type crystal structure, and no other crystalline phases were observed. The obtained X-ray diffraction pattern is shown in Figure 2. Similar results were obtained for Examples 2 to 7 below. Table 1 shows the evaluation results and radio wave absorption characteristic measurement results for the magnetic powder obtained in Example 1.

[0051] Furthermore, regarding the evaluation of particle size distribution, the cumulative 50% particle size (D50) based on volume and the cumulative 50% particle size (d50) based on number were determined from the measurement results obtained for the magnetic powder in Example 1. Similarly, the cumulative 10% particle size (D10 and d10) and the cumulative 90% particle size (D90 and d90) were determined, and the mode was also confirmed. On the other hand, as a measure of the magnetic properties of the magnetic powder, a vibrating sample magnetometer (VSM) (VSM-5HSC manufactured by Toei Kogyo Co., Ltd.) was used to measure the BH curve at an applied magnetic field of 3976 kA / m (50 kOe), and the coercivity Hc, saturation magnetization σs, square aspect ratio SQ, and coercivity distribution SFD were determined. The evaluation results for the magnetic powder obtained in Example 1 are shown in Table 2.

[0052] (Example 2) The raw material powder was weighed so that the molar ratio of Sr, La, Fe, and Al was Sr:La:Fe:Al = 0.80:0.20:11.37:0.39. The magnetic powder was prepared under the same conditions as in Example 1. For the magnetic powder obtained in this way, a compositional analysis was first performed to evaluate its physical properties, followed by X-ray diffraction (XRD) measurement. Then, after measuring the magnetic properties and the transmission attenuation of the compacted powder, the frequency range R was determined.

[0053] (Example 3) The raw material powders were weighed so that the molar ratio of Sr, La, Fe, and Al was Sr:La:Fe:Al = 0.80:0.20:11.18:0.59. The magnetic powder was prepared under the same conditions as in Example 1 and evaluated under the same conditions as in Example 2.

[0054] (Example 4) The raw material powders were weighed so that the molar ratio of Sr, La, Fe, and Al in the raw material powder was Sr:La:Fe:Al = 0.90:0.10:10.98:0.78. The magnetic powder was prepared under the same conditions as in Example 1 and evaluated under the same conditions as in Example 2.

[0055] (Example 5) The raw material powder was weighed so that the molar ratio of Sr, La, Fe, and Al in the raw material powder was Sr:La:Fe:Al = 0.60:0.40:10.98:0.78. The magnetic powder was prepared under the same conditions as in Example 1 and evaluated under the same conditions as in Example 2.

[0056] (Example 6) As raw material powders, 99% by mass SrCO3, 99.9% by mass Al2O3 g, 99% by mass Fe2O3, and 99.99% by mass CeO3 were weighed so that the molar ratio of Sr, Y, Fe, and Al was Sr:Ce:Fe:Al = 0.80:0.20:10.98:0.78. The magnetic powder was prepared under the same conditions as in Example 1 and evaluated under the same conditions as in Example 2.

[0057] (Example 7) As raw material powders, 99% by mass SrCO3, 99.9% by mass Al2O3, 99% by mass Fe2O3, and 99.99% by mass Pr2O3 were weighed so that the molar ratio of Sr, Pr, Fe, and Al was Sr:Pr:Fe:Al = 0.80:0.20:10.98:0.78. Magnetic powder was prepared under the same conditions as in Example 1 and evaluated under the same conditions as in Example 2.

[0058] (Comparative Example 1) Magnetic powder was prepared under the same conditions as in Example 1, except that rare earth elements were not used and the molar ratio of Sr, Fe, and Al in the raw material powder was weighed to be Sr:Fe:Al = 1.00:10.98:0.78. It was then evaluated under the same conditions as in Example 2.

[0059] Table 1 shows the manufacturing conditions, evaluation results of the magnetic powder, and measurement results of the radio wave absorption characteristics for the above examples and comparative examples. Note that slight discrepancies between the molar ratios in the raw material powders shown in each example and comparative example and the molar ratios in the compositional formulas shown in the evaluation results of the magnetic powder in Table 1 are due to the unavoidable inclusion of impurities during the manufacturing process; these are essentially the same.

[0060] [Table 1]

[0061] [Table 2]

[0062] From the results in Table 1, comparing Examples 1-7 with Comparative Example 1, it can be seen that even a small amount of substitution of Sr with a rare earth element can reduce the frequency range R of the compacted powder, making it possible to set the frequency range R to 1.0 GHz or less. Furthermore, from the results of Examples 1-3, it can be seen that the frequency peak can be controlled by substitution with Al. According to Examples 1-5, when the rare earth element substituted for Sr is La, it can be seen that the frequency range R can be set to 0.7 GHz or less.

[0063] Thus, from the results of Examples 1 to 7, it was found that the frequency range R of the compacted powder can be suppressed to 1.0 GHz or less by controlling the frequency peak by substituting Al and by substituting rare earth elements. Furthermore, it was found that the frequency range R of the compacted powder can be suppressed to 0.7 GHz or less by limiting the type of rare earth element to be substituted. [Industrial applicability]

[0064] According to the present invention, by adjusting the substitution amounts of rare earth elements, Al, and Co, it is possible to provide a magnetoplanbite-type hexagonal ferrite magnetic powder having radio wave absorption capacity in the 50-70 GHz band, including the 60 GHz band, and exhibiting small changes in the peak frequency of transmission attenuation over a wide temperature range, as well as a method for producing the same, and a radio wave absorber using the magnetic powder and a method for producing the same.

Claims

1. Magnetoplumbite-type hexagonal ferrite magnetic powder, The metal elements contained in the crystal of the magnetoplumbite-type hexagonal ferrite magnetic powder are given by a general formula that shows the atomic ratio of the metal elements, A （１－ｘ） RE ｘ Fe （ｎ－ｙ－ｚ） Al ｙ Co ｚ (Here, A is one or more elements selected from the group consisting of Sr, Ba, and Ca. RE is one or more rare earth elements selected from the group consisting of La, Ce, Pr, Nd, Y, Sm, Tb, and Dy. 0.05 ≤ x ≤ 0.70, 0.01 ≤ y < 1.00, 0.00 ≤ z ≤ 1.00, (11.00 ≤ n ≤ 12.50) Magnetoplumbite-type hexagonal ferrite magnetic powder.

2. The magnetoplanbite-type hexagonal ferrite magnetic powder according to claim 1, wherein the range of x is 0.05 ≤ x ≤ 0.

60.

3. Let the peak frequencies of the transmission attenuation amounts at 30°C, 60°C, and 90°C be X ３０ , X ６０ , and X ９０ . When they are so, the frequency range R, which is the difference between the maximum value and the minimum value of X ３０ , X ６０ , and X ９０ , is 1.0 GHz or less. The magnetoplumbite-type hexagonal ferrite magnetic powder according to claim 1

4. The magnetoplanbite-type hexagonal ferrite magnetic powder according to claim 3, wherein the frequency range R is 0.7 GHz or less.

5. The magnetoplanbite-type hexagonal ferrite magnetic powder according to claim 1, wherein the metal element A is Sr.

6. The magnetoplanbite-type hexagonal ferrite magnetic powder according to claim 1, wherein the rare earth element RE is one or more rare earth elements selected from the group consisting of La, Ce, and Pr.

7. The magnetoplanbite-type hexagonal ferrite magnetic powder according to claim 1, wherein the range of n is 11.00 ≤ n < 12.

00.

8. A radio wave absorber comprising magnetoprumbite-type hexagonal ferrite magnetic powder and resin according to any one of claims 1 to 7.

9. A raw material mixing step to obtain a raw material mixture by mixing powders that will be used as raw materials for magnetoplumbite-type hexagonal ferrite magnetic powder, A firing step in which the raw material mixture is fired to obtain a fired product, The process includes a grinding step of grinding the aforementioned fired product to obtain the magnetoplumbite-type hexagonal ferrite magnetic powder, The metal elements contained in the crystal of the magnetoplumbite-type hexagonal ferrite magnetic powder are expressed by the general formula of atomic ratio, A （１－ｘ） RE ｘ Fe （ｎ-ｙ-ｚ） Al ｙ Co ｚ (Here, A is one or more elements selected from the group consisting of Sr, Ba, and Ca. RE is one or more rare earth elements selected from the group consisting of La, Ce, Pr, Nd, Y, Sm, Tb, and Dy. 0.05 ≤ x ≤ 0.70, 0.01 ≤ y < 1.00, 0.00 ≤ z ≤ 1.00, (11.00 ≤ n ≤ 12.50) A method for producing magnetoprumbite-type hexagonal ferrite magnetic powder.

10. A method for producing magnetoplanbite-type hexagonal ferrite magnetic powder according to claim 9, wherein the range of x is 0.05 ≤ x ≤ 0.

60.

11. A method for producing magnetoplanbite-type hexagonal ferrite magnetic powder according to claim 9, further comprising a heat treatment step after the grinding step.

12. A method for manufacturing an electromagnetic wave absorber, comprising the step of kneading a magnetoplanbite-type hexagonal ferrite magnetic powder obtained by the manufacturing method described in claims 9 to 11 with a resin, and then molding the mixture.

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