Iron oxide for electromagnetic wave-absorbing magnetoplumbite type ferrite

Abstract

Provided is an iron oxide which can be used for manufacturing a ferrite having higher absorbency. The iron oxide of the present invention is an iron oxide for an electromagnetic wave-absorbing magnetoplumbite-type ferrite that contains different elements and has a coefficient of variation (Cv value) of the signal intensity of an electron probe microanalyzer (EPMA) for the different elements of 1.000 or less.

Description

Iron oxide for electromagnetic wave absorbing magnetoplumbite ferrite

[0001] The present invention relates to iron oxides used in the manufacture of electromagnetic wave absorbing magnetoplumbite ferrites.

[0002] In recent years, research into ADAS (Advanced Driver-Assistance Systems) and AD (Autonomous Driving) has progressed in relation to automobile driving. ADAS is a system that assists human driving operations in a vehicle, and AD is a technology that enables vehicles to drive automatically. Hereinafter, these technologies will be collectively referred to as "AD / ADAS." AD / ADAS is expected to reduce traffic accidents and congestion.

[0003] To realize AD / ADAS, it is necessary to acquire information such as the positions and relative distances of surrounding objects. Sensors are used to acquire this information, but because automobiles are used in a variety of environments, radar sensors (hereinafter simply referred to as "radar") that use electromagnetic waves are more suitable than optical sensors such as cameras. Among such radars, millimeter-wave radars that use electromagnetic waves called millimeter waves, which have wavelengths on the order of millimeters, have attracted particular attention.

[0004] Such radar is required to have EMC (Electromagnetic Compatibility), that is, not to be a source of electromagnetic interference, not to be affected by electromagnetic interference, or to operate normally even if affected.

[0005] However, in order to obtain information from all directions around the vehicle, it is possible that many millimeter-wave radars will be installed on a single vehicle, such as at the four corners and on the sides. As the number of millimeter-wave radars increases, interference between devices and self-poisoning (noise generated from circuits inside the radar housing can interfere with other circuits, reducing communication performance) become more likely to occur.

[0006] In order to solve or reduce such problems, an electromagnetic wave absorber has been proposed that includes a resin and powder (also called particles or filler) of a magnetic material or carbon dispersed in the resin.

[0007] For example, Patent Document 1 discloses a filler for a radio wave absorber, AFe （１２－ｘ） Al ｘ O １９ In the above publication, magnetoplumbite-type hexagonal ferrite particles are disclosed, which are represented by the formula: wherein A represents at least one metal element selected from the group consisting of Sr, Ba, Ca, and Pb, and x satisfies 1.0≦x≦2.2.

[0008] Japanese Patent Application Laid-Open No. 2007-250823

[0009] To effectively suppress electromagnetic noise, higher absorption of electromagnetic waves at frequencies that cause noise is required. An object of the present invention is to provide iron oxide that can be used to produce ferrite with higher absorption.

[0010] In order to solve the above problems, the present invention provides the following technologies. [1] Iron oxide for electromagnetic wave absorbing magnetoplumbite ferrite containing one or more different elements, wherein the coefficient of variation (Cv value) of signal intensity in EPMA (electron probe microanalyzer) for each of the different elements is 1.000 or less. [2] Iron oxide for electromagnetic wave absorbing magnetoplumbite ferrite according to [1] above, wherein the molar ratio of different elements / iron element in the iron oxide is 0.01 to 0.80. [3] Iron oxide for electromagnetic wave absorbing magnetoplumbite ferrite according to [1] or [2] above, wherein the different elements are at least one element selected from the group consisting of aluminum, titanium, manganese, zirconium, tin, nickel, zinc, cobalt, and copper.

[0011] By using the iron oxide of the present invention, ferrite exhibiting high electromagnetic wave absorption properties can be obtained.

[0012] <Iron Oxide> The iron oxide according to this embodiment contains one or more different elements, and the coefficient of variation (Cv value) of the signal intensity of EPMA (electron probe microanalyzer) for each different element is 1.000 or less. The Cv value is preferably 0.200 or less. Furthermore, the iron oxide is used to produce electromagnetic wave absorbing magnetoplumbite ferrite (hereinafter sometimes simply referred to as "ferrite").

[0013] The Cv value is a value expressed by the standard deviation / average value of the EPMA intensity of each element. When the Cv value of a different element is within the above range, it means that the different element is uniformly and finely dispersed in the iron oxide. When the iron oxide contains multiple different elements, the Cv value of each element represents the dispersion state of each element. There is no particular lower limit for the Cv value, but it can be said that the closer to zero the value is, the higher the uniformity.

[0014] When ferrite is produced using such highly uniform iron oxide, the composition of the ferrite also becomes highly uniform. Since the frequency at which ferrite can absorb electromagnetic waves shifts depending on the type and amount of different elements contained in the ferrite, ferrite powder with a uniform composition can exhibit excellent electromagnetic wave absorption properties in a specific frequency band. More specifically, since the ferrite powder contains many particles that can absorb electromagnetic waves in the same frequency band, the ferrite powder can exhibit high absorption properties in that frequency band.

[0015] The Cv value can be determined by measuring the intensity of each pixel in three fields of view for each element using EPMA under the following conditions: acceleration voltage 15 kV, beam current 100 nA, pixel size 0.5 μm × 0.5 μm, number of pixels 100 × 100, and measurement time 0.05 sec / pixel, and then calculating the average value and standard deviation of the intensities of all pixels. If the elements contained are unknown, the main elements contained can be identified by obtaining an X-ray spectrum of the ferrite powder using EPMA, and the pixel intensity can be measured at the wavelength corresponding to each element.

[0016] The iron oxide may be any one of hematite, magnetite, maghemite, and goethite, or a mixture thereof.

[0017] The content of the different element can be changed depending on the target absorption frequency band, etc. The molar ratio of the different element / iron element in the iron oxide may be, for example, 0.01 to 0.80, or 0.04 to 0.20.

[0018] The different element is at least one element selected from the group consisting of aluminum, titanium, manganese, zirconium, tin, nickel, zinc, cobalt, and copper, and more preferably at least one element selected from the group consisting of aluminum, titanium, and manganese.

[0019] The different element is preferably contained in the crystalline structure of the iron oxide. "Contained in the crystalline structure of the iron oxide" means that a portion of the iron element in the iron oxide is substituted with the different element.

[0020] The SSA (Specific Surface Area) of iron oxide is 5 to 20 m ２ When the SSA of the iron oxide is in this range, the effect of improving the reactivity in the ferritization reaction using this iron oxide can be obtained.

[0021] <Method for Producing Iron Oxide> The method for producing iron oxide includes, for example, (1) mixing a solution of a salt containing iron and a solution of a salt containing a different element with an alkaline solution, (2) heating the mixed solution obtained in (1) above while passing air through it, (3) adjusting the pH of the solution after (2) above to neutral, (4) recovering the reaction product generated in (3) above by filtration or the like, and (5) calcining the reaction product obtained. Specifically, the iron-containing salt is ferrous sulfate (FeSO ４ The salt containing the different elements may be a sulfate of the different elements, and the alkaline solution may be an aqueous solution of sodium hydroxide. The temperature during heating is about 90°C. The inventors believe that one of the factors that allows the different elements to be uniformly and finely dispersed in the iron oxide and that enables the Cv value to be reduced is that the solutions of all the iron oxide raw materials are thoroughly mixed in advance and then reacted.

[0022] Another method for producing iron oxide includes (1') reacting a solution of a salt containing iron with an alkaline solution, (2') mixing a solution of a salt containing a different element with the solution obtained in (1') above, (3') adjusting the pH of the mixed solution obtained in (2') above to neutral, (4') recovering the reaction product by filtration or the like, and (5') calcining the reaction product obtained.

[0023] Another method for producing iron oxide is to wet mix iron oxide powder that does not contain a specific foreign element with a compound that contains the foreign element, and then filter and dry the mixture.

[0024] <Use of Iron Oxide> Iron oxide can be used to produce magnetoplumbite ferrite, particularly ferrite powder, for absorbing electromagnetic waves. Magnetoplumbite ferrite can be designed to absorb at a desired frequency by adjusting the composition of the ferrite powder. Furthermore, by adjusting the content of ferrite powder in the electromagnetic wave absorber, the thickness of the electromagnetic wave absorber can be changed while achieving the desired absorption amount.

[0025] Specifically, ferrite is represented by formula (1). ｘ Fe （１２－ｙ） D ｙ O １９ (1) A: at least one element selected from the group consisting of Ba, Sr, and Ca; D: a different element contained in iron oxide; x: 0.9 or more and 1.3 or less; y: more than 0 and 2.0 or less.

[0026] An example of the ferrite is a ferrite represented by the following formula (2): ｘ Fe （１２－ｙ） Al ｙ O １９ (2) A: at least one element selected from the group consisting of Ba, Sr, and Ca; x: 0.9 or more and 1.3 or less; y: greater than 0 and 2.0 or less.

[0027] Another example of the ferrite is a ferrite represented by the following formula (3): ｘ Fe(12-(n+m))Ti ｎ Mnｍ O １９ (3) A: at least one element selected from the group consisting of Ba, Sr, and Ca; x: 0.9 or more and 1.3 or less; n: more than 0 and 1.2 or less; m: more than 0 and 1.2 or less; n+m: more than 0 and 2.0 or less.

[0028] The crystal distortion of the ferrite powder is 1.5 × 10 －４ It is preferable that the crystal distortion is within the above range. A crystal distortion within the above range indicates that the heterogeneous elements are uniformly dispersed, and uniform dispersion of the heterogeneous elements means that the composition is uniform. In other words, since the ferrite powder contains many particles that can absorb electromagnetic waves of the same frequency, the ferrite powder has high absorption properties for that frequency.

[0029] The frequency range allocated to millimeter-wave radar for automotive applications is 76 GHz to 81 GHz, with the narrow band of 76 GHz to 77 GHz being the most widely used. The absorption frequency band of the ferrite powder for automotive applications preferably includes this range.

[0030] In addition, frequencies used for other purposes such as millimeter-wave radar, high-speed, large-capacity communications, and 5G communications include the 57-64 GHz band and the 26-30 GHz band.

[0031] The absorption frequency band can be adjusted by the type of the foreign element used and the molar ratio of the foreign element to the iron element.

[0032] Regarding the composition of the ferrite powder, x in the formulas (1) to (3) may be 0.95 or more, or 1.1 or less.

[0033] For the 76 to 81 GHz band, in formula (2), x is preferably 0.95 or more and 1.1 or less, more preferably 0.97 or more and 0.99 or less, and y is preferably 1.4 or more and 1.9 or less, more preferably 1.6 or more and 1.7 or less. For the 57 to 64 GHz band, in formula (2), x is preferably 0.95 or more and 1.1 or less, more preferably 0.97 or more and 0.99 or less, and y is preferably 0.2 or more and 0.8 or less, more preferably 0.45 or more and 0.65 or less.

[0034] For the 26 to 30 GHz band, in formula (3), x is preferably 0.93 or more and 1.1 or less, more preferably 0.95 or more and 0.98 or less, n is preferably 0.50 or more and 1.0 or less, more preferably 0.84 or more and 0.88 or less, and m is preferably 0.50 or more and 1.0 or less, more preferably 0.82 or more and 0.86 or less.

[0035] The composition of the ferrite powder, that is, the elements contained therein and their ratios to the iron element, can be confirmed by a fluorescent X-ray spectrometer or the like.

[0036] The ferrite powder can also be used in an electromagnetic wave absorber, which is, for example, a molded body containing a resin and ferrite powder as a filler dispersed in the resin.

[0037] When an electromagnetic wave absorber is used in an automobile, it needs to be environmentally resistant. The inside of a vehicle is a harsh environment, with high temperatures and the like, so in order for the electromagnetic wave absorber to maintain stable electromagnetic wave absorbing performance even in such an environment, it is preferable that the electromagnetic wave absorber has mechanical strength that prevents cracking or chipping.

[0038] From this viewpoint, the ferrite powder is 1 t / cm ２ The density obtained by compressing the material at a pressure of 3.0 g / cm ３It is preferable that the above is the case. The reason why high compressed density provides strength is thought to be as follows: A high compressed density means that small particles can enter the spaces between relatively large particles. In other words, it can be said that the particle size distribution tends to be relatively large. Powders with such properties can be dispersed uniformly in resin, and a reinforcing effect by the powder can be expected.

[0039] Electromagnetic wave absorbers are often installed in narrow vehicle interiors where many parts and devices are arranged, or in inconspicuous locations on the vehicle body. Therefore, it is preferable that the resin composition containing ferrite powder has high moldability so that the molded product can be molded into a complex shape according to the installation location.

[0040] The higher the compressed density of the ferrite powder, the higher the fluidity of the mixture of molten resin and ferrite powder. When molding by injection or extrusion, the higher the fluidity of the mixture, the easier it is to process it into complex molded products. This also improves production efficiency during molding.

[0041] Furthermore, the high density can reduce the viscosity of a resin composition containing the ferrite powder when melted. In addition to the resin and filler, the electromagnetic wave absorber may contain additives as described below, and since the low viscosity when melted as described above allows the additives, which have a large effect on mechanical strength, to be micro-dispersed in the resin composition, it can be expected that the mechanical strength of the molded electromagnetic wave absorber will be improved.

[0042] The resin may be a thermoplastic resin, such as PPS or polyamide.

[0043] The electromagnetic wave absorber may further contain additives such as silane coupling agents and titanium coupling agents.

[0044] The shape of the electromagnetic wave absorber is not particularly limited, and can be changed depending on the location where it is placed, the purpose of use, and the like.

[0045] The filler content in the electromagnetic wave absorber can be set depending on the desired absorption capacity, etc., and is, for example, preferably 35% by mass or more or 50% by mass or more, and 94% by mass or less or 89% by mass or less.

[0046] The absorption frequency band and absorption peak of the electromagnetic wave absorber are the same as those of the ferrite powder.

[0047] <Method for producing ferrite powder> The method for producing ferrite powder includes: (i) a step of mixing raw materials weighed according to a target composition, i.e., heterogeneous element-containing iron oxide and a salt containing an element corresponding to A in formula (1); (ii) a step of mixing the obtained raw material mixed powder with a flux; and (iii) a step of firing the mixture in air.

[0048] The iron oxide is crushed before use in step (i). The mixing in step (i) is preferably wet mixing. It is also preferable to further filter and dry the mixture.

[0049] In the step (ii), a known flux can be used, such as BaCl ２ ・2H ２ O, SrCl ２ ・6H ２ O, CaCl ２ ・2H ２ O, etc. are preferred, and multiple compounds may be used. In particular, a compound containing an element corresponding to A in formula (1) is preferably used. The amount of flux added is preferably 0.1 to 10.0 mass %, more preferably 0.1 to 8.0 mass %, based on the raw material mixture obtained above. The obtained mixture may be formed into granules by a molding method such as extrusion molding.

[0050] The firing temperature in step (iii) is preferably 1200° C. or higher.

[0051] By firing at 1200°C or higher in the step (iii), the ferrite reaction can be sufficiently promoted, thereby achieving a high saturation magnetization σ ｓ can be extracted.

[0052] After the step (iii), a step of pulverizing the fired product may be carried out.

[0053] Furthermore, after step (iii) or any fine pulverization step, an annealing treatment may be carried out under known conditions, for example, at 500°C to 1000°C.

[0054] The obtained ferrite powder can be used to produce an electromagnetic wave absorber, which can be produced, for example, by melting a resin, adding ferrite powder and, if necessary, additives to the melted resin, mixing the mixture, and molding the mixture.

[0055] In this specification, the terms "mass," "parts by mass," and "mass %" are interchangeable with the terms "weight," "parts by weight," and "weight %."

[0056] <Production of Iron Oxide> [Example 1] Approximately 90 L of an alkaline solution containing 293 mol of sodium hydroxide was charged into a reaction vessel, and the liquid temperature was heated to 90°C. Next, approximately 60 L of a metal salt solution containing 107 mol of ferrous sulfate and 8.7 mol of aluminum sulfate was charged into the reaction vessel, and the reaction was carried out at 90°C, with the stirrer rotating at 580 rpm and 150 L of air per minute being ventilated. After completion of the reaction, the pH of the reaction solution was adjusted to 7, and the solution was filtered, washed with water, and dried. The resulting powder was calcined at 750°C and then pulverized to obtain an Al-containing hematite powder.

[0057] Example 2 An Al-containing hematite powder was obtained in the same manner as in Example 1, except that the amount of sodium hydroxide was 256 mol and the amount of aluminum sulfate was 2.4 mol.

[0058] [Example 3] Approximately 85 L of an alkaline solution containing 258 mol of sodium hydroxide was added to a reaction vessel, and the liquid temperature was heated to 90°C. Next, approximately 65 L of a metal salt solution containing 102 mol of ferrous sulfate, 8.8 mol of manganese sulfate, and 9.2 mol of titanyl sulfate was added to the reaction vessel, and the reaction was carried out at 90°C, with the stirrer rotating at 580 rpm and 150 L of air per minute being ventilated. After completion of the reaction, the pH of the reaction solution was adjusted to 7, and the solution was filtered, washed with water, and dried. The resulting powder was calcined at 750°C and then pulverized to obtain a hematite powder containing Ti and Mn.

[0059] [Example 4] Approximately 90 L of an alkaline solution containing 357 mol of sodium hydroxide was added to a reaction vessel and heated to 90 ° C. Next, approximately 60 L of a metal salt solution containing 165 mol of ferrous sulfate was added to the reaction vessel, and the reaction was carried out at 90 ° C., with the stirrer rotating at 580 rpm and 150 L of air per minute being passed through. Approximately 15 L of a metal salt solution containing 27.4 mol of aluminum sulfate was added to the solution, and the pH of the mixed solution was adjusted to 7 at approximately 60 ° C., followed by filtration, washing with water, and drying. The resulting powder was calcined at 750 ° C. and then pulverized to obtain an Al-containing hematite powder.

[0060] [Example 5] Aluminum sulfate powder and hematite powder were charged into a wet attritor and mixed for 5 minutes so that the molar ratio of Al / Fe became 0.162. The mixture was filtered and dried to obtain an Al-containing hematite powder.

[0061] [Comparative Example 1] Hematite powder and Al were mixed so that the molar ratio of Al / Fe was 0.162. ２ O ３ The powder was dry mixed in a mixer for 15 minutes.

[0062] [Comparative Example 2] Hematite powder, TiO ２ Powder and Mn ３ O ４ The powders were dry mixed in a mixer for 15 minutes.

[0063] <Evaluation> [Composition] For the samples obtained in the above examples and comparative examples, the contents of Al element, Ti element, Mn element, and Fe element were determined by quantitative measurement using an X-ray fluorescence spectrometer "ZSX Primus II" (manufactured by Rigaku Corporation), and then the contents of each element were calculated in molar terms.

[0064] [EPMA] The degree of fine dispersion of the heterogeneous element-containing iron oxide was measured using an electron probe microanalyzer (EPMA) "JXA-iSP100" (manufactured by JEOL Ltd.) under the following conditions: acceleration voltage 15 kV, beam current value 100 nA, pixel size 0.5 μm × 0.5 μm, number of pixels 100 × 100, and measurement time 0.05 sec / pixel. Intensity measurements were performed in three fields of view, and the average value and standard deviation of the intensities of all pixels in the three fields of view were determined, and the Cv value was calculated based on these values.

[0065] [Specific Surface Area: SSA] Using a specific surface area measuring device "Macsorb" (manufactured by Mountech Co., Ltd.), SSA was measured by the BET single-point method utilizing the adsorption and desorption characteristics of nitrogen gas on the sample. The evaluation results are shown in Table 1.

[0066]

[0067] <Production of Ferrite Powder> [Example 6] The Al-containing hematite powder of Example 1 and SrCO were weighed so that the resulting ferrite had the composition shown in Table 2. ３ The powder was mixed in a wet attritor for 15 minutes, filtered, and dried. 3.6 wt % of flux was added to the resulting raw material powder mixture and mixed thoroughly, after which the mixture was extrusion-molded. The resulting granules were fired in air at 1280°C. The fired material was crushed in a hammer mill, then coarsely pulverized in a wet attritor for 15 minutes, washed with water, filtered, and dried. The coarsely pulverized material was then finely pulverized in a vibration mill. The finely pulverized material was annealed in air at 900°C. The properties of the resulting ferrite powder are shown in Table 2.

[0068] Example 7 A ferrite powder was obtained in the same manner as in Example 6, except that the Al-containing hematite powder obtained in Example 2 was used.

[0069] [Example 8] The Ti and Mn-containing hematite powder obtained in Example 3 was used instead of the Al-containing hematite powder; ３ BaCO instead of powder ３ Powders were used: hematite powder and BaCO ３The powder was weighed according to the composition formula in Table 2, and a ferrite powder was obtained in the same manner as in Example 6, except that the firing temperature was changed to 1300°C.

[0070] [Example 9] A ferrite powder was obtained in the same manner as in Example 6, except that the Al-containing hematite powder of Example 4 was weighed so that the resulting ferrite had the composition shown in Table 2 and mixed for 1 minute in a wet attritor.

[0071] [Example 10] A ferrite powder was obtained in the same manner as in Example 6, except that the Al-containing hematite powder of Example 5 was weighed so that the resulting ferrite had the composition shown in Table 2 and mixed for 1 minute in a wet attritor.

[0072] Comparative Example 3 A ferrite powder was obtained in the same manner as in Example 6, except that the mixture obtained in Comparative Example 1 was used instead of the Al-containing hematite powder.

[0073] Comparative Example 4 A ferrite powder was obtained in the same manner as in Example 8, except that the mixture obtained in Comparative Example 2 was used instead of the Ti and Mn-containing hematite powder.

[0074] Comparative Example 5 A ferrite powder was obtained in the same manner as in Example 9, except that the mixed powder of alumina and hematite obtained in Comparative Example 1 was used.

[0075] <Analysis of Ferrite Powder> [Composition Analysis] With respect to the composition ratios x and y of the ferrite powder, the contents of aluminum element, strontium element, and iron element were determined by quantitative measurement using a fluorescent X-ray spectrometer "ZSX Primus II" (manufactured by Rigaku Corporation), and then the contents of aluminum element, strontium element, and iron element were calculated in molar terms.

[0076] [Crystal strain] To evaluate the crystal strain of the ferrite powder, measurements were performed using an XRD "D8 ADVANCE manufactured by Bruker Japan Co., Ltd." The measurement conditions were 2θ: 15° to 100°, measurement interval: 1 / 10 or less of the half-width of the main peak, and integration time: the time required for the peak intensity of the strongest line to reach 12,000 counts. The crystal strain was calculated from the obtained measurement data using the Williamson-Hall method using the analysis software TOPAS.

[0077] [Compressed density] The weighed ferrite powder was compressed to 1 t / cm using a hydraulic press. ２ The volume after compression was measured, and the compressed density was calculated based on the measurement results.

[0078] [Specific Surface Area: SSA] The specific surface area was measured in the same manner as in Example 1 and the like.

[0079] [Ps-b] The average particle size (Ps-b) of the ferrite powder determined by the air permeability method (Blaine method) was measured using a "constant pressure ventilation type rapid standard universal type powder specific surface area measuring device" (manufactured by Shimadzu Corporation).

[0080]

[0081] <Evaluation of absorption properties> [Examples 11 to 15, Comparative Examples 6 to 8] Each of the ferrite powders obtained in Examples 6 to 10 and Comparative Examples 3 to 5 was kneaded with EVA (ethylene vinyl acetate copolymer) resin, a polymer base material, in a quantitative ratio such that the ferrite powder content was 90 mass %. The resulting kneaded mixture was rolled to a thickness of 1 mm using a hot press to produce an electromagnetic wave absorbing sheet.

[0082] [Electromagnetic wave absorption characteristics] For the obtained electromagnetic wave absorbing sheet, the intensity of the transmitted electromagnetic wave was measured by the S21 parameter in the free space method using a free space measurement device "BD1-26.5A" (manufactured by Keycom Co., Ltd.) and a network analyzer "MS4647B" (manufactured by Anritsu Co., Ltd.). The measurement results are shown in Table 3.

[0083]

[0084] Comparing Example 11 with Comparative Example 6, Example 11 was able to attenuate electromagnetic waves more while showing the same peak frequency. Also, comparing Example 13 with Comparative Example 7, Example 13 was able to attenuate electromagnetic waves more while showing the same peak frequency. Example 12 showed good transmission attenuation at a peak frequency different from Examples 11 and 13.

Claims

1. Iron oxide for electromagnetic wave absorbing magnetoplumbite ferrite, containing one or more heterogeneous elements, wherein the coefficient of variation (Cv value) of the signal intensity of EPMA (electron probe microanalyzer) for each of the heterogeneous elements is 1.000 or less.

2. The iron oxide for electromagnetic wave absorbing magnetoplumbite ferrite according to claim 1, wherein the molar ratio of different elements to iron element in the iron oxide is 0.01 to 0.

80.

3. The iron oxide for electromagnetic wave absorbing magnetoplumbite ferrite according to claim 1 or 2, wherein the different element is at least one element selected from the group consisting of aluminum, titanium, manganese, zirconium, tin, nickel, zinc, cobalt, and copper.

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