Ferrite sintered magnet

Abstract

This ferrite sintered magnet includes ferrite grains including hexagonal ferrite as main phase grains, and at least a portion of the main phase grains includes an orthoferrite phase within the grains. In a cross section of the ferrite sintered magnet, when, among 100 arbitrarily selected main phase grains, the number of main phase grains including an orthoferrite phase within the grains is denoted by m, and the number of orthoferrite phases included in grain boundaries of the ferrite sintered magnet in a 10 μm square region is denoted by g, m / (m+g) may be 0.2 or more.

Description

Ferrite Sintered Magnet

[0001] The present disclosure relates to a ferrite sintered magnet.

[0002] As a permanent magnet, BaFe １２ O １９ A ferrite sintered magnet having a hexagonal magnetoplumbite structure, with [[O]] as the basic composition, is known. In recent years, in response to demands for miniaturization and higher performance of electronic components such as motors, studies have been conducted to improve the magnetic properties of ferrite sintered magnets by substituting part of the elements at the A site with Sr and La, and part of the elements at the B site with Co. For example, in Patent Document 1, various studies have been conducted focusing on a ferrite magnet having a ferrite phase with a magnetoplumbite structure and an orthoferrite phase in order to improve the residual magnetic flux density (Br).

[0003] International Publication No. 2017 / 200092

[0004] Ferrite sintered magnets are used in, for example, motors, generators, and the like. In these technical fields, miniaturization has led to a more complicated internal structure, and there is a limited installation space for ferrite sintered magnets. To respond to such a trend, it is necessary to reduce the thickness of the ferrite sintered magnet. However, when the thickness is reduced, there is a concern that the ferrite sintered magnet may be demagnetized due to the demagnetizing field. To suppress such a phenomenon, increasing the coercive force of the ferrite sintered magnet is considered effective. Accordingly, the present disclosure provides a ferrite sintered magnet having a sufficiently high coercive force.

[0005] One aspect of the present disclosure provides a ferrite sintered magnet comprising ferrite particles containing hexagonal ferrite as main phase particles, wherein at least a part of the main phase particles contains an orthoferrite phase inside the grains.

[0006] According to the present disclosure, a ferrite sintered magnet having a sufficiently high coercive force can be provided.

[0007] It is a diagram schematically showing a part of a cross-section of a ferrite sintered magnet. It is a diagram for explaining the mechanism of improving the coercive force of a ferrite sintered magnet. It is a photograph of a cross-section of the ferrite sintered magnet of Example 1 taken with a scanning electron microscope. It is a photograph of a cross-section of the ferrite sintered magnet of Comparative Example 1 taken with a scanning electron microscope.

[0008] Hereinafter, some embodiments will be described with reference to the drawings as appropriate. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents. In the present disclosure, the numerical range indicated by "~" includes the numerical values indicated as the upper limit and the lower limit. In addition, numerical ranges in which the upper limit and lower limit of a numerical range are replaced with the values in the examples are also included in the present disclosure. When a numerical range is exemplified only with an upper limit or only a lower limit, a numerical range obtained by combining the numerical range having only the upper limit and the numerical range having only the lower limit is also included in the present disclosure. A numerical range obtained by replacing the upper limit and / or lower limit of a certain numerical range with the upper limit and / or lower limit of another numerical range is also included in the present disclosure. For a plurality of exemplified substances and materials, one type may be used alone, or two or more types arbitrarily selected may be used in combination.

[0009] In some embodiments, the ferrite sintered magnet includes ferrite particles containing hexagonal ferrite as main phase particles. Here, the "main phase" in the present specification refers to the most abundant crystal phase in the ferrite sintered magnet, and the "main phase particles" are particles containing the crystal phase. The most abundant crystal phase in the ferrite sintered magnet of the present specification is hexagonal ferrite. The "hexagonal ferrite" in the present specification is a ferrite having a hexagonal magnetoplumbite structure.

[0010] In some embodiments, at least a part of the main phase particles contained in the ferrite sintered magnet includes an orthoferrite phase inside the grain. The orthoferrite phase may be contained not only inside the grains of the main phase particles but also at grain boundaries. The orthoferrite phase may be contained only inside the grains of the main phase particles. The distribution of the orthoferrite phase can be examined, for example, by observing an image magnified 1000 to 5000 times with a scanning electron microscope (hereinafter sometimes referred to as "SEM") of a cross-section of the ferrite sintered magnet.

[0011] As shown in Figure 1, when a cross-section of a ferrite sintered magnet of one embodiment is observed under magnification using a scanning electron microscope (SEM), the ferrite sintered magnet contains ferrite particles containing hexagonal ferrite as the main phase particles 10. Some of the main phase particles 10A contain orthoferrite phase 20 within the grain. Other parts of the main phase particles 10 do not need to contain orthoferrite phase 20 within the grain. The ferrite sintered magnet contains orthoferrite phase 22 at the grain boundaries. In another embodiment, the ferrite sintered magnet does not need to contain orthoferrite phase 22 at the grain boundaries.

[0012] Referring to Figure 2, the mechanism by which the coercivity is improved by including the orthoferrite phase 20 within the main phase particles 10A is thought to be as follows. Coercivity refers to the strength of the opposing external magnetic field required to return a magnetized magnetic material to an unmagnetized state. Therefore, the greater the coercivity, the less likely demagnetization is to occur when exposed to an external magnetic field. As shown in Figure 2(A), when the main phase particles 10A are placed in an external magnetic field, the magnetic domain walls W move along the direction of the external magnetic field EM, as shown in Figures 2(A) and (B). At this time, it is presumed that the orthoferrite phase 20 contained within the main phase particles 10A functions as a pinning site, as shown in Figure 2(C), trapping the movement of the magnetic domain walls W. It is thought that by including the orthoferrite phase 20 within the particles, the magnetization reversal of the main phase particles 10A is suppressed, and the coercivity of the ferrite sintered magnet is improved.

[0013] To trap the movement of the magnetic domain wall W, it is sufficient for one or more orthoferrite phases 20 to be contained within each main phase particle 10A. The effect of trapping the movement of the magnetic domain wall W can be obtained regardless of the size of the orthoferrite phases 20 contained within each main phase particle 10A. For this reason, for example, if two ferrite sintered magnets are compared, where the total volume (area in cross-section) of the orthoferrite phases 20 contained within the particles is the same, but the number of main phase particles 10A containing orthoferrite phases 20 is different, the ferrite sintered magnet with a larger number of main phase particles 10A containing orthoferrite phases 20 is expected to have improved coercivity.

[0014] In a cross-section of a ferrite sintered magnet as shown in Figure 1, the number m of main phase particles 10A containing orthoferrite phase 20 within the particles, out of 100 arbitrarily selected main phase particles 10, may be 2 or more, 3 or more, 4 or more, 5 or more, or 6 or more. Such a ferrite sintered magnet has a sufficiently high coercivity. The number m of main phase particles 10A containing orthoferrite phase 20 within the particles, out of 100 arbitrarily selected main phase particles 10, may be 10 or less, 9 or less, 8 or less, or 7 or less. This makes it possible to sufficiently increase both coercivity and residual magnetic flux density, which are usually in a trade-off relationship.

[0015] In a cross-section of a ferrite sintered magnet as shown in Figure 1, the number of orthoferrite phases 22 contained in the grain boundaries of the main phase particles 10 in an arbitrarily selected 10 μm square region (length × width = 10 μm × 10 μm) may be 10 or less, 8 or less, 7 or less, 5 or less, or 4 or less. This allows the residual magnetic flux density of the ferrite sintered magnet to be sufficiently high. The cross-section shown in Figure 1 can be observed with sufficient accuracy using a SEM after, for example, cutting the ferrite sintered magnet with a diamond cutter and then mirror polishing it.

[0016] The value of m / (m+g), calculated using the number of main phase particles 10A m and the number of orthoferrite phase 22 g, may be 0.2 or greater, 0.3 or greater, 0.4 or greater, or 0.5 or greater. This allows for sufficiently high coercivity. The value of m / (m+g) may be 1.0 or less, less than 0.8, 0.7 or less, or less than 0.7. This allows for sufficiently high coercivity and residual magnetic flux density, which are usually in a trade-off relationship. Ferrite sintered magnets with a value of m / (m+g) between any of the above upper and lower limits can achieve sufficiently high coercivity and residual magnetic flux density, which are usually in a trade-off relationship.

[0017] The coercive force (hereinafter referred to as "HcJ") of the ferrite sintered magnet may be, for example, 5700 Oe or more, or 5800 Oe or more. The residual magnetic flux density (hereinafter referred to as "Br") of the ferrite sintered magnet may be, for example, 4500 G or more. In the present specification, the coercive force and residual magnetic flux density are values measured at 20°C using a B-H tracer.

[0018] The composition excluding oxygen atoms of the ferrite sintered magnet can be represented by the following composition formula (α), where R is at least one element selected from rare earth elements including Y (yttrium), and A is at least one element selected from the group consisting of Ca (calcium) and Ba (barium). R １－ｘ１－ｘ２ A ｘ１ Sr ｘ２ Fe ｎ－ｙ Co ｙ (α)

[0019] In the composition formula (α), "R １－ｘ１－ｘ２ A ｘ１ Sr ｘ２ " represents the ratio of elements occupying the A-site in the crystal structure of ferrite, and "Fe ｎ－ｙ Co ｙ " represents the ratio of elements occupying the B-site in the crystal structure of ferrite. This enables achieving both coercive force and residual magnetic flux density at higher levels. Specifically, x1 in the composition formula (α) represents the proportion of the A element (one or both of Ca and Ba) occupying the A-site. The A element at the A-site may be Ca. x2 represents the proportion of Sr (strontium) occupying the A-site. 1-x1-x2 represents the proportion of the rare earth element R occupying the A-site. The rare earth element R may contain La, and the rare earth element R may be La.

[0020] x1 may satisfy the following formula (1). Such a ferrite sintered magnet can achieve both coercive force and residual magnetic flux density at higher levels. From the viewpoint of adjusting the content of the orthoferrite phase to an appropriate amount, the lower limit of x1 may be 0.35, 0.40, or 0.43. From the same viewpoint, the upper limit of x1 may be 0.60 or 0.55. 0.30≦x1≦0.70 (1)

[0021] x² may satisfy the following equation (2). Such a ferrite sintered magnet can achieve both coercivity and residual magnetic flux density at an even higher level. From the viewpoint of ensuring an appropriate amount of orthoferrite phase content, the lower limit of x² may be 0.005 or 0.010. From a similar viewpoint, the upper limit of x² may be 0.043 or 0.040. 0 < x² ≤ 0.045 (2)

[0022] In compositional formula (α), y represents the proportion of Co occupying the B site. y may satisfy the following equation (3). Such ferrite sintered magnets can achieve both coercivity and residual magnetic flux density at an even higher level. From a similar viewpoint, the lower limit of y may be 0.25 or 0.30. From a similar viewpoint, the upper limit of y may be 0.50 or 0.45. 0.10 ≤ y ≤ 0.65 (3)

[0023] In the composition formula (α), n represents the ratio of the total number of elements occupying the B site to the total number of elements occupying the A site. n may satisfy the following formula (4). Such ferrite sintered magnets can achieve a higher level of both coercivity and residual magnetic flux density. From a similar viewpoint, the lower limit of n may be 4, 5, 6, or 7. From a similar viewpoint, the upper limit of n may be 13.5 or less than 13. 3 ≤ n < 14 (4)

[0024] Since the composition formula (α) represents the overall composition of the ferrite sintered magnet, it is determined not only by the hexagonal ferrite contained in the main phase particles 10, but also by the composition of the orthoferrite phase 20 contained in the main phase particles 10A, the orthoferrite phase 22 contained in the grain boundaries, and other crystalline phases. The composition formula (α) can be determined, for example, by performing X-ray fluorescence analysis of the ferrite sintered magnet.

[0025] Not only the hexagonal ferrite contained in the main phase particles 10, but also the orthoferrite phase 20 contained in the main phase particles 10A, the orthoferrite phase 22 contained in the grain boundaries, and other crystalline phases can be identified in the cross-section of the ferrite sintered magnet by elemental analysis and X-ray diffraction analysis using SEM-EDX. The number, proportion, and area of ​​each crystalline phase can also be determined based on the SEM-EDX observation image and the results of elemental analysis and X-ray diffraction analysis using SEM-EDX.

[0026] Ferrite sintered magnets may contain elements different from those included in the composition formula (α) as minor components. Examples of such elements include B (boron), Si (silicon), Al (aluminum), Cr (chromium), etc. For example, B ２ O ３ It may be included as follows. Including B makes it possible to lower the calcination temperature and sintering temperature when obtaining ferrite sintered magnets, thereby improving the productivity of ferrite sintered magnets. From the viewpoint of sufficiently increasing the magnetic properties, the amount of B relative to the total ferrite sintered magnet is B ２ O ３ The converted amount may be greater than 0% by mass, 0.4% by mass or less, 0.12 to 0.3% by mass, or 0.18 to 0.25% by mass.

[0027] Ferrite sintered magnets may also contain other minor components in the form of oxides, such as Ga (gallium), Mg (magnesium), Cu (copper), Mn (manganese), Ni (nickel), In (indium), Li (lithium), Ti (titanium), Zr (zirconium), Ge (germanium), Sn (tin), V (vanadium), Nb (niobium), Ta (tantalum), Sb (antimony), As (arsenic), W (tungsten), Mo (molybdenum), etc. The content of these materials may be 5% by mass or less of the oxides of the stoichiometric composition of each atom, including gallium oxide, magnesium oxide, copper oxide, manganese oxide, nickel oxide, indium oxide, lithium oxide, lithium oxide, titanium oxide, titanium oxide, zirconium oxide, germanium oxide, tin oxide, vanadium oxide, niobium oxide, tantalum oxide, antimony oxide, arsenic oxide, tungsten oxide, and molybdenum oxide. If multiple types of these materials are included in combination, their total content may be 5% by mass or less.

[0028] Ferrite sintered magnets can be used in a wide range of applications. For example, ferrite sintered magnets can be used in automotive motors such as those for fuel pumps, power windows, ABS (anti-lock braking systems), fans, wipers, power steering, active suspension, starters, door locks, and electric mirrors. Ferrite sintered magnets can also be used in motors for household appliances such as air conditioner compressors, refrigerator compressors, power tool drives, dryer fans, shaver drives, and electric toothbrushes. Ferrite sintered magnets can also be used in motors for factory automation equipment such as robot axes, joint drives, robot main drives, machine tool table drives, and machine tool belt drives. Ferrite sintered magnets can also be used in motorcycle generators, speaker / headphone magnets, magnetron tubes, MRI magnetic field generators, distributor sensors, ABS sensors, fuel / oil level sensors, magnetolatches, and isolators.

[0029] An example of a method for manufacturing ferrite sintered magnets is described below. The method for manufacturing ferrite sintered magnets may include the following compounding step, calcination step, crushing step, molding step, and firing step.

[0030] In the compounding process, raw materials for ferrite magnets are blended to obtain a raw material composition. First, as raw materials for ferrite sintered magnets, examples include compounds (raw material compounds) containing one or more of the elements that constitute ferrite sintered magnets. The raw material compounds may be in powder form. Examples of raw material compounds include oxides of each element, or compounds that become oxides by calcination (carbonates, hydroxides, nitrates, etc.). Examples of raw material compounds include SrCO ３ , La(OH) ３ Fe ２ O ３ BaCO ３ CaCO ３ and Co ３ O ４ The average particle size of the powdered raw material compound may be, for example, 0.1 to 2.0 μm.

[0031] The raw material powder containing the above-mentioned compounds may be compounded with other minor raw material compounds (elements, oxides, etc.) as needed. Compounding may be carried out, for example, by weighing each compound to obtain the desired ferrite magnet composition, and then mixing and grinding it for about 0.1 to 20 hours using a wet attritor, ball mill, etc. It is not necessary to compound all raw material compounds in the compounding process; some may be added after calcination, as described later.

[0032] In the calcination process, the raw material powder obtained in the blending process is calcined. Calcination can be carried out, for example, in an oxidizing atmosphere such as air. The calcination temperature may be 1200 to 1300°C. The calcination time may be 1 second to 3 hours. The calcined body obtained by calcination may contain hexagonal ferrite as the main phase. The primary particle size of the main phase may be 2 μm or less. The heating rate and cooling rate in calcination may be 10 to 50°C / min.

[0033] In the grinding step, the granular or lump-shaped calcined material obtained in the calcination step may be ground into a powder. In the grinding step, raw materials may be added in the blending step (addition of raw materials after the blending step). In the grinding step, for example, the calcined material may be ground into a coarse powder, and then further ground into a fine powder. That is, the grinding step may have multiple stages, including coarse grinding and fine grinding.

[0034] For coarse grinding, for example, a vibrating mill may be used until the average particle size is 0.5 to 5.0 μm. For fine grinding, the coarse material obtained in the coarse grinding step may be further ground using a wet attritor, ball mill, jet mill, etc. For fine grinding, water may be added and the material may be ground wet so that the average particle size of the resulting fine material is, for example, 0.1 to 1.0 μm. When raw materials are added in the grinding process, the addition may be made in either the coarse grinding or the fine grinding step, or both. The raw material compound added later may contain at least one of the raw material compounds blended in the blending step.

[0035] In fine grinding, from the viewpoint of increasing the magnetic orientation of the ferrite sintered magnet, for example, general formula C ｎ (OH) ｎ H ｎ＋２ A polyhydric alcohol represented by the formula may be added. In the general formula, n may be 4 to 100. Examples of polyhydric alcohols include sorbitol. Two or more types of polyhydric alcohols may be used in combination. In addition to polyhydric alcohols, other dispersants may be used in combination. When a polyhydric alcohol is added, the amount added may be 0.05 to 5.0% by mass relative to the material to which it is added (e.g., coarsely ground material). The polyhydric alcohol added in the fine grinding step may be removed by thermal decomposition in the calcination step described later.

[0036] In the molding process, the pulverized material (e.g., finely pulverized material) obtained in the grinding process is molded in a magnetic field to obtain a molded body. Molding may be carried out by either dry molding or wet molding. Wet molding is preferable from the viewpoint of increasing the degree of magnetic orientation. When molding by wet molding, for example, a slurry may be obtained by wet grinding as described above, and then this slurry may be concentrated to a predetermined concentration to obtain a slurry for wet molding. The slurry may be concentrated by centrifugation, filter press, etc. The slurry for wet molding may contain finely pulverized material accounting for about 30 to 80% by mass of its total volume. In the slurry, the dispersion medium for dispersing the finely pulverized material may be water. In this case, surfactants such as gluconic acid, gluconate salts, and sorbitol may be added to the slurry. A non-aqueous solvent may be used as the dispersion medium. As a non-aqueous solvent, organic solvents such as toluene or xylene may be used. In this case, surfactants such as oleic acid may be added. A slurry for wet molding may be prepared by adding a dispersion medium or the like to the finely ground material in a dried state after fine grinding.

[0037] In the case of wet molding, molding may be performed in a magnetic field using a wet molding slurry. In that case, the molding pressure should be 9.8 to 49 MPa (0.1 to 0.5 ton / cm²). ２ The applied magnetic field may be 398 to 1194 kA / m (5 to 15 kOe).

[0038] In the firing process, the molded body obtained in the molding process can be fired to obtain a ferrite sintered magnet. The firing may be carried out in an oxidizing atmosphere such as air. The sintering temperature (the maximum temperature in the firing process) may be 1120 to 1190°C from the viewpoint of suppressing excessive grain growth. From the same viewpoint, the sintering time (the time held at the sintering temperature) may be 10 minutes or less. The heating rate to the sintering temperature may be 6 to 20°C / minute.

[0039] The cooling rate from the sintering temperature to around 1100°C may be 0.10 to 0.30°C / min. This cooling rate allows the orthoferrite phase to precipitate within the grains of the main phase particles containing hexagonal ferrite. Increasing the cooling rate tends to make it more difficult for the orthoferrite phase to precipitate within the grains of the main phase particles. Thus, by adjusting the cooling rate from the sintering temperature to around 1100°C, the distribution of the orthoferrite phase in the ferrite sintered magnet can be adjusted. There are no particular restrictions on the cooling rate after the temperature has cooled to around 1100°C.

[0040] Although one example of a ferrite sintered magnet manufacturing method has been described, ferrite sintered magnets may be manufactured by other methods as long as a predetermined distribution of orthoferrite phases can be obtained.

[0041] The embodiments described above include the following [1] to [8]: [1] A ferrite sintered magnet comprising ferrite particles containing hexagonal ferrite as the main phase particles, wherein at least a portion of the main phase particles contain an orthoferrite phase within the grain. [2] The ferrite sintered magnet according to [1], wherein in a cross-section, of 100 arbitrarily selected main phase particles, the number of particles containing the orthoferrite phase within the grain is 2 or more. [3] The ferrite sintered magnet according to [1] or [2], wherein in a cross-section, the number of orthoferrite phases included in the grain boundaries of the ferrite sintered magnet in an arbitrarily selected 10 μm square region is 10 or less. [4] A ferrite sintered magnet according to any one of [1] to [3], wherein, in a cross-section, when m is the number of main phase particles containing the orthoferrite phase within the grain of 100 arbitrarily selected main phase particles, and g is the number of orthoferrite phases contained in the grain boundaries of the ferrite sintered magnet in a 10 μm square region, m / (m+g) is 0.2 or more. [5] A ferrite sintered magnet according to any one of [1] to [3], wherein R is at least one element selected from rare earth elements including Y, and A is at least one element selected from the group consisting of Ca and Ba, and the composition excluding oxygen atoms is R １－ｘ１－ｘ２ A ｘ１ Sr ｘ２ Fe ｎ－ｙ Co ｙWhen expressed as follows, x1, x2, y and n satisfy the following equations (1), (2), (3) and (4): 0.30 ≤ x1 ≤ 0.70 (1) 0 < x2 ≤ 0.045 (2) 0.10 ≤ y ≤ 0.65 (3) 3 ≤ n < 14 (4) A ferrite sintered magnet according to any one of [1] to [4]. [6] A ferrite sintered magnet according to [5], wherein R consists only of La. [7] A ferrite sintered magnet according to [5] or [6], satisfying the following equations (1)', (3)' and (4)': 0.35 ≤ x1 ≤ 0.60 (1)' 0.25 ≤ y ≤ 0.50 (3)' 7 ≤ n < 13 (4)' A ferrite sintered magnet according to [5] or [6]. [8] A ferrite sintered magnet that satisfies the following equations (1A), (3)' and (4)': 0.40 ≤ x1 ≤ 0.60 (1A) 0.25 ≤ y ≤ 0.50 (3)' 7 ≤ n < 13 (4)' as described in any one of [5] to [7].

[0042] The ferrite sintered magnets described in [1] to [8] above contain an orthoferrite phase within at least a portion of the main phase particles. When such ferrite sintered magnets are placed in an external magnetic field, it is presumed that the orthoferrite phase within the main phase particles functions as a pinning site, trapping the movement of the magnetic domain walls. This is thought to suppress the reversal of magnetization of the main phase particles, thereby improving the coercivity. Therefore, the above ferrite sintered magnets have sufficiently high coercivity.

[0043] This disclosure is not limited in any way to the embodiments described above. For example, in another embodiment, the ferrite sintered magnet may contain crystalline phases other than the hexagonal ferrite phase and the orthoferrite phase. Examples of such crystalline phases include hematite and spinel.

[0044] The contents of this disclosure will be described in more detail with reference to examples and comparative examples, but this disclosure is not limited to the following examples.

[0045] (Example 1) [Manufacturing of ferrite sintered magnets] As raw material compounds, ferric oxide (Fe ２ O ３), calcium carbonate (CaCO3) ３ ), strontium carbonate (SrCO ３ ), cobalt oxide (Co ３ O ４ ), and lanthanum hydroxide (La(OH) ３ ) was prepared. These raw materials were weighed and blended so that the composition after calcination would be as shown in the following formula (I). La ０．５ Ca ０．４６５ Sr ０．０３５ Fe ９．８４ Co ０．３６ O １９ (I)

[0046] Furthermore, boron oxide (B ２ O ３ ) is the B of B in the final ferrite sintered magnet. ２ O ３ A compound was obtained by blending the ingredients so that the converted content was 0.17% by mass. The compound obtained in this way and water were mixed and pulverized using a wet attritor to prepare a slurry. The aggregates obtained by drying this slurry were crushed to obtain raw material powder. This raw material powder was calcined in air at 1250°C for 2 hours. The heating rate and cooling rate during calcination were both set to 15°C / min.

[0047] The calcined powder obtained by calcination was coarsely ground for 10 minutes in a small rod vibrating mill. To this coarsely ground material, ferric oxide, calcium carbonate, strontium carbonate, cobalt oxide, and lanthanum hydroxide were added, respectively, so that the composition of the ferrite sintered magnet would be as shown in formula (I) above. Water was added to these mixtures and finely ground for 40 hours using a steel wet ball mill to obtain a slurry.

[0048] The slurry obtained by fine grinding was adjusted using a centrifuge to a solid content concentration of 73-75% by mass to obtain a slurry for wet molding. This slurry for wet molding was molded using a wet magnetic field molding machine in an applied magnetic field of 796 kA / m (10 kOe) to obtain a cylindrical molded body with a diameter of 30 mm and a thickness of 15 mm.

[0049] The obtained molded body was thoroughly dried in air at room temperature. Then, the molded body was heated in air at a rate of 10°C / min to 1160°C and held at the sintering temperature of 1160°C for 1 minute. After that, it was cooled to 1100°C at a rate of 0.1°C / min, and thereafter cooled to room temperature at a rate of 5°C / min. In this way, the ferrite sintered magnet of Example 1 was obtained.

[0050] [Evaluation of Ferrite Sintered Magnets] After processing the upper and lower surfaces of the obtained cylindrical ferrite sintered magnets, Br and HcJ were measured at 20°C using a B-H tracer with a maximum applied magnetic field of 955 kA / m (12 kOe). The results are shown in Table 1. X-ray diffraction of the ferrite sintered magnets confirmed that the ferrite sintered magnets contain ferrite with a hexagonal magnetoplumbite structure (hexagonal ferrite) as the main phase. In addition, it was confirmed that the magnets also contain trace amounts of orthoferrite phase (perovskite phase).

[0051] A ferrite sintered magnet was cut in the thickness direction using a precision cutting machine (BUEHLER, product name: ISOMET), and the cut surface was polished using waterproof abrasive paper with a precision surface grinding machine (JEOL, product name: HLA-2). Furthermore, the polished surface was mirror-polished using diamond paste with a diamond wrench (Maruto Co., Ltd., product name: ML-150P). The cross-section of the mirror-polished ferrite sintered magnet was analyzed using a SEM (Hitachi High-Tech Corporation, product name: SU5000) and an EDX (Horiba, Ltd., product name: EMAX Evolution) installed on the SEM. Such analytical equipment is referred to as "SEM-EDX".

[0052] SEM-EDX analysis of the cross-section confirmed that the composition of the ferrite sintered magnet was as described in Table 1. The cross-section of the ferrite sintered magnet was observed at a magnification of 5000x. Figure 3 shows a photograph of the observed cross-section. As shown in Figure 3, the ferrite sintered magnet of Example 1 contained ferrite particles including hexagonal ferrite as the main phase particles 10. In addition, some of the ferrite particles contained a white heterogeneous phase within the grains and at the grain boundaries. Elemental analysis and X-ray diffraction analysis by SEM-EDX confirmed that this heterogeneous phase was an orthoferrite phase. Specifically, some of the main phase particles 10 (main phase particles 10A) contained orthoferrite phase 20 within the grains. Orthoferrite phase 22 was also contained at the grain boundaries of the main phase particles 10. In Figure 3, the reason why each of the main phase particles 10 has a different color is because their crystal orientations perpendicular to the cross-section are different. The black particles were identified as hematite based on elemental analysis and X-ray diffraction analysis using SEM-EDX.

[0053] In the observation images shown in Figure 3, 100 main phase particles 10 were arbitrarily selected, and the number (m) of main phase particles 10A containing orthoferrite phase 20 within each particle was counted. Furthermore, in the observation images shown in Figure 3, the number (g) of orthoferrite phase 22 contained within the grain boundaries (between multiple main phase particles 10) of the ferrite sintered magnet was counted in an arbitrarily selected 10 μm square region (length × width = 10 μm × 10 μm). These results are shown in Table 1.

[0054] (Example 2, Comparative Examples 1-3) Ferrite sintered magnets were manufactured and evaluated in the same manner as in Example 1, except that the cooling rate from the sintering temperature to 1100°C was changed as shown in Table 1. The evaluation results are shown in Table 1. Analysis by SEM-EDX confirmed that the composition of each ferrite sintered magnet was as described in Table 1. The cross-section of the ferrite sintered magnet of Comparative Example 1 was observed at a magnification of 5000x using SEM-EDX, in the same manner as in Example 1. A photograph of the observed image is shown in Figure 4. As shown in Figure 4, the ferrite sintered magnet of Comparative Example 1 did not contain main phase particles 10A that contained orthoferrite phase within the grain. On the other hand, orthoferrite phase 22 was contained at the grain boundaries of the main phase particles 10.

[0055] (Examples 3-8) Ferrite sintered magnets were manufactured and evaluated in the same manner as in Example 1, except that the raw material compounds were blended and added so that the composition after calcination and the composition of the ferrite sintered magnet were as shown in the following formulas (II) to (VI), and the sintering temperature was as shown in Table 1. The formula numbers indicating the composition of each ferrite sintered magnet, the sintering conditions, and the evaluation results are shown in Table 1. Analysis by SEM-EDX confirmed that the composition of each ferrite sintered magnet was as described in Table 1.

[0056] La ０．５ Ca ０．４９５ Sr ０．００５ Fe ９．８４ Co ０．３６ O １９ (II) La ０．５ Ca ０．４８５ Sr ０．０１５ Fe ９．８４ Co ０．３６ O １９ (III) La ０．５ Ca ０．４５５ Sr ０．０４５ Fe ９．８４ Co ０．３６ O １９ (IV) La ０．４ Ca ０．５６５ Sr ０．０３５ Fe ９．８４ Co ０．３６ O １９ (V) La ０．６ Ca ０．３６５ Sr ０．０３５ Fe ９．８４ Co ０．３６ O １９ (VI)

[0057] (Comparative Examples 4-8) Ferrite sintered magnets were manufactured and evaluated in the same manner as in Comparative Example 1, except that the raw material compounds were blended and added so that the composition after calcination and the composition of the ferrite sintered magnet were as shown in the following formulas (II) to (VI), and the sintering temperature was as shown in Table 1. The formula numbers indicating the composition of each ferrite sintered magnet, the sintering conditions, and the evaluation results are shown in Table 1. Analysis by SEM-EDX confirmed that the composition of each ferrite sintered magnet was as described in Table 1.

[0058]

[0059] The cooling rates in Table 1 represent the rate of cooling from the sintering temperature to 1100°C. The cooling rate after reaching 1100°C was set to 5°C / min in all cases. As shown in Table 1 and Figure 3, the ferrite sintered magnets of Examples 1 to 8 contained main phase particles with an orthoferrite phase within the grain. All of these ferrite sintered magnets had an HcJ of 5700 Oe or higher and a Br of 4500 G or higher. Such ferrite sintered magnets can be suitably used, for example, in thin form for automotive electrical components and electrical equipment components.

[0060] 10, 10A... Main phase particles, 20, 22... Orthoferrite phase.

Claims

1. A ferrite sintered magnet comprising ferrite particles containing hexagonal ferrite as the main phase particles, wherein at least a portion of the main phase particles contains an orthoferrite phase within the grain.

2. The ferrite sintered magnet according to claim 1, wherein in cross-section, of 100 arbitrarily selected main phase particles, the number of particles containing the orthoferrite phase within the particle is 2 or more.

3. The ferrite sintered magnet according to claim 1, wherein in a cross-section, the number of orthoferrite phases contained in the grain boundaries of the ferrite sintered magnet in an arbitrarily selected 10 μm square region is 10 or less.

4. The ferrite sintered magnet according to claim 1, wherein, in a cross-section, when m is the number of main phase particles containing the orthoferrite phase within the grain of 100 arbitrarily selected main phase particles, and g is the number of orthoferrite phases contained in the grain boundaries of the ferrite sintered magnet in a 10 μm square region, m / (m+g) is 0.2 or more.

5. Let R be at least one element selected from the rare earth elements including Y, and let A be at least one element selected from the group consisting of Ca and Ba, and let R be the composition excluding oxygen atoms. １－ｘ１－ｘ２ A ｘ１ Sr ｘ２ Fe ｎ－ｙ Co ｙ When expressed as such, x1, x2, y, and n satisfy the following equations (1), (2), (3), and (4): 0.30 ≤ x1 ≤ 0.70 (1) 0 < x2 ≤ 0.045 (2) 0.10 ≤ y ≤ 0.65 (3) 3 ≤ n < 14 (4) A ferrite sintered magnet according to any one of claims 1 to 4.

6. The ferrite sintered magnet according to claim 5, wherein R consists only of La.

7. A ferrite sintered magnet according to claim 6, satisfying the following equations (1)', (3)' and (4)': 0.35 ≤ x1 ≤ 0.60 (1)' 0.25 ≤ y ≤ 0.50 (3)' 7 ≤ n < 13 (4)'

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