Magnetic material and magnetic material fabrication method

Abstract

The present disclosure provides a magnetic material which is a sintered body containing a plurality of metal magnetic particles having a grain boundary phase, wherein the grain boundary phase contains a metal oxide or metal nitride obtained by oxidizing or nitriding a non-magnetic metal, and the equivalent circle diameter of the metal magnetic particles is 0.29-2.33 μm.

Description

Magnetic material and method for producing the same

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to magnetic materials and methods of making magnetic materials.

[0002] Composite magnetic materials are sometimes used as magnetic materials for magnetic components, etc. Some composite magnetic materials include a resin containing dispersed soft magnetic powder or the like made of powder particles (see Patent Document 1).

[0003] JP 2016-143827 A

[0004] When a composite magnetic material contains resin, passing an electric current through a magnetic component comprising a base body containing this magnetic material and wiring can cause localized concentration of magnetic flux between the powder particles of the soft magnetic powder in the magnetic material, which can increase eddy current loss and lead to deterioration of high-frequency characteristics.

[0005] An object of the present disclosure is to provide a magnetic material capable of improving high-frequency characteristics and a method for producing the same.

[0006] In order to achieve the above object, the present disclosure provides a magnetic material that is a sintered body including a plurality of metal magnetic particles having a grain boundary phase, the grain boundary phase including a metal oxide or metal nitride of a non-magnetic metal, and the metal magnetic particles having an equivalent circle diameter of 0.29 μm or more and 2.33 μm or less.

[0007] In order to achieve the above object, the present disclosure provides a method for producing a magnetic material, which includes forming a sintered body containing a plurality of metal magnetic particles, and forming a grain boundary phase of the plurality of metal magnetic particles, which contains a metal oxide or metal nitride of a non-magnetic metal, at least at the time when sintering is completed.

[0008] According to the present disclosure, it is possible to improve high-frequency characteristics.

[0009] Fig. 3 is a partially enlarged cross-sectional view schematically showing the structure of the magnetic material of the present disclosure. Fig. 4 is a partially enlarged cross-sectional view taken between the dotted parentheses in Fig. 1. Fig. 5 is a perspective view schematically showing an electronic component including the magnetic material of the present disclosure. Fig. 6 is a schematic cross-sectional view taken between the line a-a in Fig. 3. Fig. 7 is a perspective view schematically showing an electronic component according to another embodiment.

[0010] Hereinafter, a magnetic material according to an embodiment of the present disclosure will be described with reference to the drawings. Although the description will be made with reference to the drawings as necessary, the contents shown in the drawings are merely shown as schematic examples for the purpose of understanding the present disclosure, and the appearance, dimensional ratios, etc. may differ from the actual product.

[0011] FIG. 1 is a partially enlarged cross-sectional view schematically showing the structure of the magnetic material of the present disclosure.

[0012] The inventors of the present application have conducted extensive research into and devised a new magnetic material with a different structure from conventional magnetic materials, as conventional magnetic materials in which soft magnetic powder is dispersed in resin may lead to deterioration of high-frequency characteristics.

[0013] 1, the magnetic material 11α of the present disclosure is a sintered body including a plurality of metal magnetic grains 11A having a grain boundary phase 11B. The grain boundary phase 11B can be formed at the boundary between adjacent metal magnetic grains 11A and the other metal magnetic grain 11A by arranging the plurality of metal magnetic grains 11A in close proximity to one another.

[0014] In the present disclosure, the grain boundary phase 11B contains a metal oxide or a metal nitride formed by oxidizing or nitriding a non-magnetic metal. The grain boundary phase 11B may contain an oxide of the metal magnetic grains 11A.

[0015] When the grain boundary phase 11B has the above-described form, the metal oxide or metal nitride can contact the metal magnetic grains 11A and also covers the surfaces of the metal magnetic grains 11A.

[0016] The above metal oxides or metal nitrides are formed by oxidizing or nitriding non-magnetic metals, and therefore may have higher electrical resistivity than metal magnetic particles. For example, the electrical resistivity of the metal oxides or metal nitrides may be 1×10^11 Ω·cm or more and 1×10^16 Ω·cm or less. Furthermore, the electrical resistivity of the metal magnetic particles may be 0.089 μΩ·m or more and 1.76 μΩ·m or less. Furthermore, the above metal oxides or metal nitrides may themselves be non-magnetic.

[0017] Therefore, the grain boundary phase 11B can function as a high resistance portion compared to the metal magnetic grains 11A. In terms of such improved function, it is preferable that the metal oxide or metal nitride of the grain boundary phase 11B covers the entire surface of the metal magnetic grains 11A.

[0018] As will be described later, when the base body of an electronic component includes the magnetic material 11α of the present disclosure, the high resistance portion can increase the electrical resistance of the path of eddy currents flowing in the magnetic material (corresponding to the sintered body) of the base body, thereby reducing eddy current loss. Since this eddy current loss increases as the current frequency increases, reducing eddy current loss can improve high-frequency characteristics.

[0019] Furthermore, in the present disclosure, the equivalent circle diameter of metal magnetic particles 11A is 0.29 μm or more and 2.33 μm or less. When the base body of an electronic component includes magnetic material 11α of the present disclosure, the above-mentioned 0.29 μm or more is preferable from the viewpoint of preventing the generation of oxides of the Fe component contained in metal magnetic particles 11A in the magnetic material (corresponding to a sintered body) of the base body. Furthermore, the above-mentioned 2.33 μm or less is preferable from the viewpoint of preventing the skin depth from exceeding the skin depth at 200 MHz assumed for next-generation inductors.

[0020] The metal magnetic particles contain Fe, and the metal oxide or metal nitride may be at least one selected from the group consisting of Si, Al, Cr, Ca, Mg, Ti, Mn, V, Zr, Nb, and Ta, which are elements that are more easily oxidized than Fe. In the present disclosure, Si, which is generally called a semimetal, is treated as a metallic element.

[0021] In addition, the filling rate of the multiple metal magnetic particles 11A in the magnetic material 11α of the present disclosure is preferably 66.7% or more from the viewpoint of ensuring magnetic permeability, i.e., ensuring an appropriate inductance value (L value), and is preferably 95.1% or less from the viewpoint of reducing eddy current loss.

[0022] Fig. 3 is a perspective view schematically showing an electronic component including the magnetic material of the present disclosure, and Fig. 4 is a schematic cross-sectional view taken along line aa in Fig. 3.

[0023] 3 and 4 , the electronic component 100 includes an element body 10 including the magnetic material 5 of the present disclosure, wiring 20, and external electrodes 30, 40. By including the magnetic material 5 of the present disclosure, the element body 10 includes a sintered body 11. The sintered body 11 itself has at least one magnetic metal sintered layer. As an example, the element body 10 may have a hexahedral structure. An insulating coating layer 60 may be formed to cover the surface of the element body 10 except for the external electrodes 30, 40.

[0024] In the above-mentioned sintered body 11, when metal magnetic layers of the same composition are stacked consecutively, it is difficult to distinguish the boundaries between the metal magnetic layers. Therefore, even if a sintered body has multiple metal magnetic layers stacked, it is treated as a single sintered body if the first insulating layer described below is not located between them. Also, even if multiple metal magnetic layers of different compositions are stacked and these layers can be distinguished, it is treated as a single sintered body as long as the first insulating layer described below is not located between them.

[0025] As an example, the wiring 20 may be provided within the element body 10. The wiring 20 is made of a conductive material, and may be at least one selected from the group consisting of, for example, silver, copper, aluminum, etc. As an example, the form of the wiring 20 may be straight wiring as shown in FIG. 3 . Without being limited to this, the wiring may also be coil-shaped wiring. The external electrodes 30, 40 are provided on the surface of the element body 10. These external electrodes are connected to both ends of the wiring 20, respectively, and are arranged to face each other at a distance via the element body 10.

[0026] Because the element body 10 contains the magnetic material 5 of the present disclosure, it contains a metal oxide or metal nitride with a relatively high resistance. This makes it possible to increase the electrical resistance of the path of eddy currents flowing through the sintered body 11 of the element body 10, thereby reducing eddy current loss. This eddy current loss increases as the current frequency increases, so reducing eddy current loss makes it possible to improve high-frequency characteristics.

[0027] 3 and 4 , the element body 10 can further have a first insulating layer 13 in addition to the sintered body 11. In the present disclosure, high-resistivity portions are provided in the grain boundary phase of the metal magnetic particles contained in the magnetic material that makes up the sintered body 11 of the element body 10, thereby ensuring insulation between the magnetic particles. Therefore, even without necessarily using the first insulating layer, insulation and eddy current loss can be suppressed, resulting in good high-frequency characteristics of the next-generation inductor in the 200 MHz band.

[0028] This first insulating layer 13 can be continuous in a layer form from one side to the other side of the sintered body 11 in a direction intersecting the stacking direction L. In this form, two or more sintered bodies 11 separated by the first insulating layer 13 can be provided.

[0029] In this case, the element body 10 has two or more sintered bodies 11 and a first insulating layer 13, and adjacent sintered bodies 11 and the other sintered body can be stacked with the first insulating layer 13 sandwiched between them. By providing the first insulating layer 13, a magnetic gap function can be provided compared to when the first insulating layer 13 is not provided. Furthermore, the first insulating layer 13 is preferably nonmagnetic. This makes it possible to improve the DC bias characteristics by reducing the magnetic permeability of the element body 10. However, without being limited thereto, the first insulating layer 13 can be a low-permeability insulating layer that is not nonmagnetic but has a magnetic permeability lower than that of the sintered body 11. In this case, inductance can also be improved compared to when it is nonmagnetic.

[0030] The wiring 20 may be covered with an insulator. In such a structure, the portions of the wiring 20 other than the ends connected to the external electrodes 30, 40 are directly surrounded by the insulator. This allows the insulator to function as a magnetic gap. It is also preferable that the insulator be non-magnetic.

[0031] This makes it possible to improve the DC bias characteristics by reducing the magnetic permeability of the element body 10. However, without being limited to this, the insulator can be a low-permeability insulator that is not nonmagnetic and has a magnetic permeability lower than that of the sintered body 11. In this case, it is possible to improve the inductance compared to a nonmagnetic case.

[0032] Two or more first insulating layers 13 may be provided spaced apart from each other. In the embodiment shown in FIGS. 3 and 4, the element body 10 has four sintered bodies 11. In this case, the wiring 20 is disposed between the first insulating layers 13, and the element body 10 may include three or more sintered bodies 11. Furthermore, when two or more first insulating layers 13 are provided, a layered structure can be formed in which two or more sintered bodies 11 and first insulating layers 13 are alternately stacked. The arrangement of two or more first insulating layers 13 further provides a magnetic gap function, and if each insulating layer 13 has a lower magnetic permeability than the sintered bodies 11, the DC bias characteristics can be further improved.

[0033] 3 and 4, when the element body 10 has two or more sintered bodies 11, the first external electrode 30 and the second external electrode 40 are arranged on the surfaces of different sintered bodies 11. With such an arrangement of the external electrodes 30, 40, the element body 10 can further have a second insulating layer 50.

[0034] Specifically, the first external electrode 30 and the second external electrode 40 are respectively arranged on the surfaces of adjacent sintered bodies 11, with the first external electrode 30 arranged on the surface of the sintered body 11 on one side and the second external electrode 30 arranged on the surface of the sintered body 11 on the other side. Under this configuration, a second insulating layer 50 can be arranged between one sintered body 11 on which the first external electrode 30 is arranged and the sintered body 11 on which the second external electrode 40 is arranged. By providing such a second insulating layer 50, it is possible to prevent a short circuit between the first external electrode 30 and the second external electrode 40.

[0035] In one example, the second insulating layer 50 may be a slit-shaped tangible object that has an arrangement form extending in a direction intersecting, for example, a direction perpendicular to, the extending direction of the first insulating layer 13. Note that the second insulating layer 50 is not arranged so as to penetrate into and divide the wiring located inside the element body 10.

[0036] In the present disclosure, the wiring does not necessarily have to be arranged inside the element body, and as shown in FIG. 5, the wiring 20A may be arranged in a wound state outside the element body 10A.

[0037] The method for manufacturing an electronic component according to the present disclosure will be described below.

[0038] <Metal Magnetic Particle Preparation Process> First, metal magnetic particles containing an Fe component (e.g., FeNiCo-based particles) are prepared. Next, in one embodiment, a metal alkoxide containing a non-magnetic metal element that is more easily oxidized than Fe is mixed with a solvent (water, alcohol, etc.) by a sol-gel method to produce a slurry, in which the alkoxide is hydrolyzed. The slurry is then dried to obtain metal magnetic particles whose surfaces are covered with a coating film containing an element that is more easily oxidized than Fe. At this time, a second coating film may be formed on the first coating film using a metal alkoxide containing a non-magnetic metal element different from the non-magnetic metal material used in the first coating film. The coating film may be one layer, two layers, or three or more layers.

[0039] Metal alkoxides have the chemical formula M(OR) ｘ (M: non-magnetic metal element, OR: alkoxy group). The metal species M constituting the metal alkoxide may be at least one selected from the group consisting of Si, Al, Cr, Ca, Mg, Ti, Mn, V, Zr, Nb, and Ta. Although not particularly limited, the metal alkoxide is preferably at least one alkoxide selected from the group consisting of Si, Ti, Al, and Zr. In this specification, Si, which is generally called a semimetal, is treated as a metal element.

[0040] When the metal alkoxide is at least one alkoxide selected from the group consisting of Si, Ti, Al and Zr, a metal oxide having higher strength and higher resistivity can be formed.

[0041] The alkoxy group OR constituting the metal alkoxide is not particularly limited, and may be, for example, an alkoxy group having 10 or less carbon atoms, particularly 5 or less, and more particularly 3 or less. The smaller the carbon number, the more easily the hydrolysis reaction can proceed. The alkoxy group is preferably at least one selected from the group consisting of a methoxy group, an ethoxy group, and a propoxy group.

[0042] Specifically, the metal alkoxide is preferably at least one selected from the group consisting of tetraethyl orthosilicate, titanium tetraisopropoxide, zirconium n-butoxide, and aluminum isopropoxide.

[0043] The slurry may contain a water-soluble polymer, which may be at least one selected from the group consisting of polyvinylpyrrolidone, polyvinyl alcohol, hydroxypropyl cellulose, poly(2-methyl-2-oxazoline), polyethyleneimine, polyacrylic acid, and carboxymethyl cellulose.

[0044] It should be noted that the present invention is not limited to the sol-gel method described above, and a coating film containing an element that is more easily oxidized than Fe may be formed on the surface of the metal magnetic particles. Furthermore, the metal magnetic particles themselves may further contain an element that is more easily oxidized than Fe as a composition. Furthermore, a metal nitride component may be applied to the surface of the metal magnetic particles. Furthermore, without forming a coating film containing an element that is more easily oxidized than Fe, a metal nitride component of a non-magnetic metal may be applied to the surface of the metal magnetic particles in advance. Even in this case, the sintered metal nitride component remains in the grain boundary phase and has high electrical resistivity. Naturally, metal oxides and metal nitrides of non-magnetic metals are non-magnetic.

[0045] <Metallic Magnetic Substance Paste Preparation Step> After preparing the metallic magnetic particles, the metallic magnetic particles, varnish, solvent (e.g., terpineol), etc. are mixed in a stirrer, and then dispersed in a roll mill to obtain a metallic magnetic substance paste.

[0046] <Insulator Paste Preparation Step> Non-magnetic insulator particles are prepared. Then, the insulator particles, varnish, and a solvent (e.g., terpineol) are mixed in a mixer. A dispersion process is then performed in a roll mill to obtain an insulator paste. The non-magnetic insulator used in the insulator paste may be, for example, a mixture of alumina, silica, glass, or a dielectric material such as calcium zirconate, strontium zirconate, and / or barium zirconate with borosilicate glass or the like.

[0047] <Process for preparing wiring paste> Conductive particles, varnish, a solvent (e.g., terpineol), etc. are mixed in a mixer. Then, a dispersion process is performed in a roll mill to obtain a wiring paste. The conductive particles can be selected from copper particles, silver particles, etc.

[0048] <Preparation process of unfired laminate> After preparing each paste, the above-mentioned metal magnetic paste is used to form a metal magnetic layer of a predetermined thickness by, for example, screen printing, and then dried. After drying, slit grooves of a predetermined width are formed by laser processing, and the above-mentioned insulating paste is filled into these slit grooves by screen printing or the like, and then dried. Note that the slit grooves are not limited to post-processing by laser processing, and may also be patterned in advance using a screen printing plate or the like.

[0049] After filling the slit grooves with an insulating paste and drying it, an insulating layer of a predetermined thickness is formed on the metal magnetic layer using the insulating paste by screen printing, and then dried. The insulating paste used to form the insulating layer may be of a different type from the insulating paste filled in the slit grooves.

[0050] A wiring paste is then used to form wiring in a desired shape (e.g., straight, coiled, or meandered) by screen printing. After the coil wiring is formed, an insulating layer may be further formed thereon. The formation of the metal magnetic layer and, optionally, the formation of the insulating layer are repeated to obtain an unsintered laminate.

[0051] If the L value of the resulting electronic component is higher than the desired characteristic, the number of insulating layers may be reduced or eliminated. This makes it possible to adjust the balance between the L value and the DC bias characteristic. Furthermore, while the above embodiment shows a case in which screen-printed layers formed using a screen printing method are laminated, the present invention is not limited to this, and the electronic component may also be produced by laminating separately prepared sheets.

[0052] <Single-piece and Firing Process of Unfired Laminate> The unfired laminate is cut into pieces using a dicer or the like, and the pieces are then degreased in a firing furnace in a nitrogen atmosphere. ２:3% / N ２ By firing the material in a 97% reducing atmosphere at a temperature of 900°C to 1000°C for a predetermined time (for example, 1 hour), a sintered body having a high resistance portion inside and a fired laminate of insulating layers can be obtained.

[0053] The high-resistance portion in the obtained sintered body may contain an oxide or nitride of an element that is more easily oxidized than Fe. Note that even if the element is more difficult to oxidize than Fe, it may be configured so that it is contained in the high-resistance portion after being oxidized in a separate process.

[0054] Furthermore, although the above is based on the premise that a non-magnetic insulating layer is formed, it is also possible to obtain a low-permeability insulating layer with some magnetic properties by, for example, extending the holding time at the maximum temperature during the firing step, thereby diffusing and penetrating the metal magnetic material components from the metal magnetic material layer into the non-magnetic insulating layer.

[0055] <Formation of External Electrodes> Optionally, the outer surface of the sintered body is then coated with an insulating resin or the like, and the coating is removed from the areas where the wiring and external electrodes are connected using a laser or the like. Then, a plating process is performed to form external electrodes, ultimately obtaining an electronic component according to the present disclosure. The material of the external electrodes may be, for example, silver.

[0056] Hereinafter, examples of the present disclosure will be described.

[0057] <Obtaining the Filling Rate of Metal Magnetic Particles in Sintered Body> Each sintered sample was resin-solidified, polished with a Tegramin-25 polishing machine (manufactured by Struers), and ion-milled with an IM-3000 ion milling machine (manufactured by Hitachi High-Technologies Corporation). SEM images and, optionally, element mapping images were then acquired using a field-emission scanning electron microscope SU8230 (manufactured by Hitachi High-Technologies Corporation). These acquired images were analyzed using image analysis software WinROOF2021 (manufactured by Mitani Shoji Co., Ltd.), and the filling rate of the metal magnetic particles was calculated. The average value of analytical values ​​from three arbitrary locations approximately halfway along the thickness direction of the sintered toroidal core was used. When calculating the filling rate for the final electronic component, the average value was calculated from analytical values ​​from a total of six locations: three arbitrary locations located one time the wiring thickness above the top surface of the internal wiring and three arbitrary locations located one time the wiring thickness below the bottom surface of the internal wiring. In the present disclosure, the "filling rate of metal magnetic particles in a sintered body" is represented by the ratio of the area of ​​the metal magnetic particles to the area of ​​the sintered body including voids.

[0058] <Ollendorff's Approximate Formula> The Ollendorff's approximate formula is an approximate formula for theoretically deriving the relative permeability μη when the filling rate of metal magnetic particles is η. Using the Ollendorff's approximate formula, a desirable filling rate of metal magnetic particles at 200 MHz was calculated as follows. From the Ollendorff's approximate formula, when the filling rate of metal magnetic particles is η, the relative permeability is μ, and the demagnetizing factor is N, the relative permeability μη at a filling rate η is expressed by the following formula 1.

[0059] [Formula 1]

[0060] In this study, μ of Fe10Ni20Co was set to 70, and N was set to 0.1, which corresponds to a spherical shape. It is expected that the drive frequency of DC-DC converters will increase to approximately 200 MHz in the future, and at a frequency of 200 MHz, μη should be between 15 and 50. From the above formula, the filling factor η at which this μη can be obtained is between 66.7% and 95.1%.

[0061] When actually manufacturing an electronic component using the sintered body of the present disclosure, the electronic component can be manufactured through the following steps.

[0062] Related to Examples 1-4 and Comparative Examples 1-2 <Preparation Process of Metal Magnetic Particles> First, Fe10Ni20Co particles with D50 particle sizes of 0.19 μm, 0.40 μm, 0.85 μm, 1.85 μm, 3.10 μm, and 4.80 μm were prepared. Next, Al alkoxide and a solvent (water) were mixed together using a sol-gel method to prepare a slurry, and the alkoxide was hydrolyzed in this slurry. After that, the slurry was dried to obtain metal magnetic particles whose surfaces were covered with a sol-gel coating film containing Al. The film thickness was approximately 10 nm or more and 20 nm or less.

[0063] <Metallic Magnetic Substance Paste Preparation Step> After preparing the above metallic magnetic particles, the metallic magnetic particles, varnish, and terpineol as a solvent were mixed in a stirrer, followed by a dispersion treatment in a roll mill to obtain metallic magnetic substance pastes.

[0064] <Insulator Paste Preparation Step> Non-magnetic insulator particles of alumina and borosilicate glass with a D50 particle size of approximately 0.1 to 0.5 μm were prepared. These insulator particles were then mixed with varnish and terpineol as a solvent using a stirrer. The mixture was then dispersed using a roll mill to obtain an insulator paste.

[0065] <Preparation of Wiring Paste> Copper particles with a D50 particle size of about 1 to 5 μm, varnish, and terpineol as a solvent were mixed in a stirrer, and then dispersed in a roll mill to obtain a wiring paste.

[0066] <Preparation of Unfired Laminate> After preparing each paste, the above-mentioned metal magnetic paste was used to form a metal magnetic layer of a predetermined thickness by screen printing, followed by drying. After drying, slit grooves of a predetermined width were formed by laser processing, and the above-mentioned insulating paste was filled into the slit grooves by screen printing or the like, followed by drying.

[0067] The slit grooves were filled with an insulating paste, which was then dried. An insulating layer of a predetermined thickness was then formed on the metal magnetic layer by screen printing using the insulating paste, and the layer was then dried.

[0068] Wiring paste was used to form wiring of a desired shape on the laminate by screen printing. By forming the metal magnetic material layer and the insulating layer as described above, an unfired laminate was obtained.

[0069] <Single-piece and Firing Process of Unfired Laminate> The unfired laminate is cut into pieces using a dicer or the like, and the pieces are then degreased in a firing furnace in a nitrogen atmosphere. ２ :3% / N ２ The mixture was fired at 1000°C for 90 minutes in a 97% reducing atmosphere, thereby obtaining a sintered body containing a plurality of metal magnetic particles in which high resistance portions were formed in the grain boundary phase of the particulate metal magnetic particles.

[0070] <Formation of External Electrodes> The outer surface of the sintered body was then covered with an insulating resin, and the coating at the portion where the wiring and external electrodes were connected was removed with a laser, followed by plating to form external electrodes. In this way, an electronic component was obtained. The material for the external electrodes could be, for example, silver.

[0071] Table 1 shows the measurement data and evaluation results for the sintered material actually produced by sintering the metal magnetic paste prepared in the above-mentioned <Metal Magnetic Particle Preparation Step> and <Metal Magnetic Paste Preparation Step> in the same manner as above. The target characteristics were set as evaluation criteria that no other phase other than the oxide of the metal (here, Al) used in the sol-gel coating film was generated in the grain boundary phase, and that the particle size (circle equivalent diameter) of the metal magnetic particle surrounded by the high-resistivity grain boundary phase was smaller than the skin depth at 200 MHz. Those that met these evaluation criteria were given an overall evaluation of ◯ (good).

[0072] [Table 1] Measurement results 1

[0073] The "skin depth" was calculated based on the formula [skin depth = (1 / (π × σ × f × μ × μr))^0.5]. The relative magnetic permeability μr of the Fe10Ni20Co metal magnetic particles is 70, and the electrical conductivity σ is 2.08 × 10 ６ (S / m), μ0 is the magnetic permeability of a vacuum, and f is the frequency. The calculated skin depth at 200 MHz was 2.95 μm.

[0074] The equivalent circle diameter of the metallic magnetic particles in the sintered body was calculated using the following process. Specifically, each sintered sample was resin-bound, polished using a Tegramin-25 polishing machine (manufactured by Struers), and then ion-milled using an IM-3000 ion milling machine (manufactured by Hitachi High-Technologies Corporation). SEM images and, if necessary, elemental mapping images were then obtained using a field-emission scanning electron microscope SU8230 (manufactured by Hitachi High-Technologies Corporation). The imaging magnification was adjusted in the range of 3,500 to 60,000 times.

[0075] These acquired images were analyzed and calculated using image analysis software WinROOF2021 (manufactured by Mitani Shoji Co., Ltd.). For the analysis, the sintered toroidal core was analyzed at three arbitrary locations near halfway along its thickness, with 20 particles selected per location, i.e., a total of 60 analysis values ​​were averaged. When calculating for the final electronic component, the average was calculated for a total of 120 analysis values ​​at six locations: three arbitrary locations located one time the wiring thickness above the top surface of the internal wiring and three arbitrary locations located one time the wiring thickness below the bottom surface of the internal wiring.

[0076] The following method can be used to visualize the high-resistivity grain boundary phase: Specifically, each sintered sample was hardened with resin, polished with a Tegramin-25 polishing machine (manufactured by Struers), and then processed by focused ion beam (FIB) processing into a shape suitable for subsequent SPM (scanning probe microscope) measurement, and finally cleaned by Ar flat milling.

[0077] Using such processed samples, spreading resistance was measured in the SSRM (scanning spreading resistance microscope) mode of the SPM. In the SSRM mode, a conductive probe was scanned while applying a bias voltage to the sample, and the current flowing at each point was converted into a resistance value, thereby visualizing the high-resistivity grain boundary phase. Note that the high-resistivity grain boundary phase was defined as a region having a resistance value 10^3 times or more of the maximum measured resistance value of the metal magnetic particle portion. The threshold value can be adjusted appropriately to match the position of high-resistivity materials such as oxides and nitrides, while referring to the element mapping image.

[0078] From the above results, it is understood that in Comparative Example 1, the particle size of the metal magnetic particles used was small, and the sintering shrinkage rate during firing was high, which prevented the reducing atmosphere gas from penetrating into the interior, causing iron oxide, the material of the metal magnetic particles, to form as a different phase. Also, in Comparative Example 2, the particle size of the metal magnetic particles used was large, and as described above, the skin depth at 200 MHz was greater than 2.95 μm, so the overall evaluation was × (unsuitable).

[0079] In contrast, in Examples 1 to 4, the equivalent circle diameter of the metal magnetic particles was 0.29 μm or more and 2.33 μm or less. In this case, no heterogeneous phase other than Al oxide was generated in the grain boundary phase, and the particle size (equivalent circle diameter) of the metal magnetic particles surrounded by the high-resistivity grain boundary phase was smaller than the skin depth (2.95 μm) at 200 MHz. Therefore, the overall evaluation was good (satisfactory). In this disclosure, the heterogeneous phase refers to the oxide of the metal magnetic particles. The presence of the heterogeneous phase reduces the saturation magnetic flux density of the sintered body. The "heterogeneous phase determination" of the oxide of the metal magnetic particles (such as iron oxide) was performed using the following procedure. Specifically, as shown in FIG. 2, a heterogeneous phase was determined to be present when the oxide covered the entire metal magnetic particles 11A and the minimum value of the thickness W2 (W21 + W22) of the oxide of the metal magnetic particles relative to the width W1 of the grain boundary phase between the metal magnetic particles 11A was greater than two-thirds.

[0080] The present disclosure includes, but is not limited to, the following aspects. <1> A magnetic material, which is a sintered body including a plurality of metal magnetic particles having a grain boundary phase, wherein the grain boundary phase includes a metal oxide or metal nitride formed by oxidizing or nitriding a non-magnetic metal, and wherein the metal magnetic particles have an equivalent circle diameter of 0.29 μm or more and 2.33 μm or less. <2> The magnetic material according to <1>, wherein the grain boundary phase includes an oxide of the metal magnetic particles. <3> The magnetic material according to <1> or <2>, wherein the plurality of metal magnetic particles include Fe, and the metal oxide or metal nitride is an oxide or nitride of at least one metal selected from the group consisting of Si, Al, Cr, Ca, Mg, Ti, Mn, V, Zr, Nb, and Ta, which are elements that are more easily oxidized than Fe. <4> An electronic component including a base body including the magnetic material according to any one of <1> to <3> and wiring. <5> The electronic component according to <4>, which is an inductor. <6> A method for producing a magnetic material, comprising forming a sintered body containing a plurality of metal magnetic particles, wherein at least at the time of completion of sintering, a grain boundary phase of the plurality of metal magnetic particles is formed, the grain boundary phase containing a metal oxide or metal nitride formed by oxidizing or nitriding a non-magnetic metal. <7> The method according to <6>, wherein the metal oxide or metal nitride is an oxide or nitride of at least one non-magnetic metal selected from the group consisting of Si, Al, Cr, Ca, Mg, Ti, Mn, V, Zr, Nb, and Ta, which are elements that are more easily oxidized than Fe. <8> The method according to <6> or <7>, wherein a film containing the element that is more easily oxidized than Fe is pre-coated on the surface of the metal magnetic particles before sintering, and the film-coated metal magnetic particles are sintered. <9> The method according to <8>, wherein the film is pre-coated in two or more layers on the surface of the metal magnetic particles. <10> The production method according to any one of <6> to <9>, wherein metal magnetic particles containing Fe as the metal element and an element that is more easily oxidized than Fe are used, and the metal magnetic particles are sintered.

[0081] Although one embodiment of the present disclosure has been described above, it is merely a typical example within the scope of application of the present disclosure. Therefore, it will be readily understood by those skilled in the art that the present disclosure is not limited thereto and that various modifications can be made.

[0082] The electronic component according to the present disclosure can be used as an inductor.

[0083] REFERENCE SIGNS LIST 100 Electronic component 10 Base body 11 Sintered body 11A Metal magnetic particle 11B Grain boundary phase 11α Magnetic material 13 First insulating layer 20 Wiring 30, 40 External electrode 50 Second insulating layer 60 Covering layer

Claims

1. a sintered body containing a plurality of metal magnetic particles having a grain boundary phase, the grain boundary phase contains a metal oxide or a metal nitride formed by oxidizing or nitriding a non-magnetic metal, The magnetic material, wherein the metal magnetic particles have an equivalent circle diameter of 0.29 μm or more and 2.33 μm or less.

2. The magnetic material according to claim 1 , wherein the grain boundary phase contains an oxide of the metallic magnetic particles.

3. the plurality of metal magnetic particles contain Fe, 2. The magnetic material according to claim 1, wherein the metal oxide or the metal nitride is an oxide or nitride of at least one metal selected from the group consisting of Si, Al, Cr, Ca, Mg, Ti, Mn, V, Zr, Nb, and Ta, which are elements that are more easily oxidized than Fe.

4. 2. The magnetic material according to claim 1, wherein the filling rate of the metal magnetic particles in the sintered body is 66.7% or more and 95.1% or less.

5. An electronic component comprising an element body containing the magnetic material according to any one of claims 1 to 4 and wiring.

6. The electronic component according to claim 5 , which is an inductor.

7. forming a sintered body including a plurality of metal magnetic particles; A method for producing a magnetic material, wherein at least at the time of completion of sintering, a grain boundary phase of the plurality of metal magnetic particles is formed, the grain boundary phase containing a metal oxide or metal nitride formed by oxidizing or nitriding a non-magnetic metal.

8. 8. The method according to claim 7, wherein the metal oxide or the metal nitride is an oxide or nitride of at least one non-magnetic metal selected from the group consisting of Si, Al, Cr, Ca, Mg, Ti, Mn, V, Zr, Nb, and Ta, which are elements that are more easily oxidized than Fe.

9. The method according to claim 7, wherein a film containing an element that is more easily oxidized than Fe is coated on the surface of the metal magnetic particles before sintering, and the metal magnetic particles coated with the film are then sintered.

10. The method according to claim 9 , wherein the surface of the metal magnetic particle is coated in advance with two or more layers of the film.

11. The method according to any one of claims 7 to 10, wherein metal magnetic particles containing Fe as a metal element and an element that is more easily oxidized than Fe are used, and the metal magnetic particles are sintered.