Ferrite sintered magnet

Abstract

To provide a novel ferrite sintered magnet that can be made to have a high coercive force without much reduction in residual flux density.SOLUTION: A ferrite sintered magnet 100 includes magnetoplumbite-type ferrite crystal particles 4 and a two-particle grain boundary 6a interposed between the ferrite crystal particles 4. The two-particle grain boundary contains Ca and La. The Ca / La atomic ratio in the two-particle grain boundary is 0.3 to 3.0.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to ferrite sintered magnets. [Background technology]

[0002] As magnetic materials used in ferrite sintered magnets, hexagonal crystal structures such as Ba ferrite, Sr ferrite, and Ca ferrite are known (see, for example, Patent Documents 1-3). Known crystal structures of such ferrites include magnetoplumbite type (M-type) and W-type. Among these, magnetoplumbite type (M-type) ferrite is mainly used as a magnet material for motors and the like. M-type ferrite is usually AFe 12 O 19 It can be expressed by the general formula. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2006-206360 (Japanese Patent No. 4591684) [Patent Document 2] Japanese Patent Publication No. 2005-45167 [Patent Document 3] WO2017 / 200091 (Patent No. 6769482) Publication [Overview of the project] [Problems that the invention aims to solve]

[0004] In M-type ferrite sintered magnets, there is often a trade-off relationship between remanent magnetic flux density (Br) and coercivity (HcJ). Therefore, conventional attempts have been made to increase both remanent magnetic flux density (Br) and coercivity (HcJ) by adding oxides of Si or Ca. However, in M-type ferrite sintered magnets, increasing coercivity tends to significantly decrease the remanent magnetic flux density.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a novel ferrite sintered magnet capable of increasing the coercive force without significantly reducing the residual magnetic flux density.

Means for Solving the Problems

[0006] One aspect of the ferrite sintered magnet includes magnetoplumbite-type ferrite crystal particles and a two-particle grain boundary interposed between the ferrite crystal particles. The two-particle grain boundary contains Ca and La, and the Ca / La atomic ratio in the two-particle grain boundary is 0.3 to 3.0.

[0007] The Ca / La atomic ratio in the two-particle grain boundary can be 0.4 or more.

[0008] The two-particle grain boundary further contains Si, and the Si / La atomic ratio in the two-particle grain boundary can be 0.02 to 2.0.

Effects of the Invention

[0009] According to the present invention, a novel ferrite sintered magnet capable of increasing the coercive force without significantly reducing the residual magnetic flux density is provided.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of a ferrite sintered magnet.

Modes for Carrying Out the Invention

[0011] Embodiments of the present invention will be described in detail below. (Ferrite Sintered Magnet) As shown in FIG. 1, a ferrite sintered magnet 100 according to an embodiment of the present invention has M-type ferrite crystal particles 4 having a magnetoplumbite-type (M-type) crystal structure and a grain boundary phase 6 existing between the M-type ferrite crystal particles 4.

[0012] (M-Type Ferrite Crystal Particles) The magnetoplumbite-type crystal structure belongs to the hexagonal system. The composition of the M-type ferrite crystal particles 4 is not particularly limited as long as it is an oxide having a magnetoplumbite-type crystal structure.

[0013] The magnetoplumbite-type crystal structure can be represented by the following formula (III). QX 12 O 19 (III) Here, the Q (A site) contains the metal element A 1 , and a part of the metal element R. The X (B site) contains Fe, the metal element M, and the remaining metal element R. In addition, since the atomic ratios of Q (A site) and X (B site) to O in the above formula (III) actually show values slightly deviated from the above ranges, they may deviate slightly, for example, by about 10% from the above numerical values.

[0014] The M-type ferrite crystal particles 4 can contain at least one metal element A selected from the group consisting of Ca, Sr, Ba, and Pb 1 , and Fe. The M-type ferrite crystal particles 4 can further contain at least one metal element R selected from the group consisting of Bi and rare earth elements, and / or at least one metal element M selected from the group consisting of Zn (zinc), Cu (copper), Mn (manganese), Al (aluminum), Co (cobalt), Ni (nickel), and Cr (chromium). The rare earth elements are Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0015] For example, the composition of the M-type ferrite crystal particles may be represented by the formula (1). A 1 Fe 12 O 19 (1) A part of Fe may be substituted with the metal element M. The atomic ratio of Fe may be 50% or more.

[0016] The ferrite crystal particles are A1 It can be a sr ferrite in which Sr accounts for 34 at% or more, A 1 It can be a Ba ferrite in which Ba accounts for 34 at% or more, A 1 It can be a Ca ferrite in which Ca accounts for 34 at% or more of A1, and it may be a Pb ferrite in which Pb accounts for 34 at% or more of A1. Sr ferrite, Ba ferrite, Ca ferrite, and Pb ferrite are A 1 In terms of atomic ratios, Sr, Ba, Ca, and Pb can each be the most abundant component.

[0017] The ferrite crystal grains may contain Ca, metallic elements R, Fe, and metallic element M. The metallic composition of M-type ferrite may be, for example, the following general formula (5). Ca a A 2 b R c Fe d M e (5) In the above formula (5), A 2 a is at least one selected from the group consisting of Sr, Ba, and Pb. a is, for example, 0.15 or more and 0.7 or less, b is, for example, 0 to 0.5, c is, for example, 0.3 or more and 0.85 or less, d may be greater than 9.35 and less than 11.90, and e may be between 0.1 and 0.5. a + b + c = 1.

[0018] In equation (5), a may be 0.20 or greater, or 0.30 or greater. a may be 0.0.65 or less, or 0.60 or less.

[0019] In equation (5), b may be 0.01 or greater, 0.02 or greater, or 0.03 or greater, as this reduces the ratio of different phases and further improves Br, HcJ, and prismaticity. Similarly, it may be 0.40 or less, or 0.45 or less.

[0020] In equation (5), c may be 0.35 or higher, or 0.40 or higher, since Br is further improved and low-temperature demagnetization of coercivity tends to be suppressed. From a similar viewpoint, it may be 0.80 or lower, or 0.75 or lower.

[0021] In equation (5), d may be 9.50 or higher, or 9.70 or higher, from the viewpoint of increasing magnetization and further reducing heterogeneity, and may be 11.80 or lower, or 11.78 or lower, as this further improves Br, HcJ and prismaticity.

[0022] (5) In equation (5), e may be 0.15 or greater, 0.20 or greater, or 0.25 or greater, from the viewpoint of increasing magnetization and coercivity and further reducing the difference in phases. (1) In equation (1), m may be 0.48 or less, or 0.47 or less, from the same viewpoint.

[0023] In equation (5), R preferably contains at least La, and the proportion of La in R can be 50 at% or more, 70 at% or more, 80 at% or more, 90 at% or more, or 95 at% or more.

[0024] In equation (5), M preferably contains at least Co, and the proportion of Co in M ​​can be 50 at% or more, 70 at% or more, 80 at% or more, 90 at% or more, or 95 at% or more.

[0025] The mass fraction of M-type ferrite in the M-type ferrite crystal grains is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more.

[0026] In ferrite sintered magnets, the mass ratio of M-type ferrite crystal particles (main phase) to the total crystal particles is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more. By reducing the mass ratio of crystal phases other than the M-type ferrite phase (other phases), the magnetic properties can be further improved. The mass ratio (%) of the M-type ferrite phase in the total crystal particles of a ferrite sintered magnet can be confirmed by determining the abundance ratio (mol%) of the M-type ferrite phase by X-ray diffraction. The abundance ratio of the M-type ferrite phase is calculated by mixing powder samples of M-type ferrite, orthoferrite, hematite, spinel, and W-type ferrite in predetermined ratios and comparing their X-ray diffraction intensities.

[0027] The average particle size of M-type ferrite crystal particles in a ferrite sintered magnet may be, for example, 5 μm or less, 4.0 μm or less, or 0.5 to 3.0 μm. Having such an average particle size allows for high coercivity. The average particle size of ferrite crystal particles can be determined using cross-sectional observation images obtained by TEM or SEM. Specifically, the cross-sectional area of ​​each crystal particle in a cross-section of an SEM or TEM containing several hundred ferrite crystal particles is determined by image analysis, and the diameter of the circle having that cross-sectional area (equivalent circle diameter) is defined as the particle size of the crystal particle in that cross-section, and the particle size distribution is measured. From the measured particle size distribution based on the number of particles, the average particle size based on the number of particles is calculated. The average value measured in this way is taken as the average particle size of the ferrite crystal particles.

[0028] The grain boundary phase 6 is located between the M-type ferrite crystal grains 4. The main component of the grain boundary phase 6 is an oxide, containing at least La and Ca. The grain boundary phase also contains metalloid elements such as B (boron) and Si (silicon); and metallic elements A selected from the group consisting of Sr (strontium), Ba (barium), and Pb (lead). 2;Fe (iron); metal element R; may include at least one metal element M selected from the group consisting of Mn (manganese), Zn (zinc), Cr (chromium), Co (cobalt), Ni (nickel), Cu (copper), and Al (aluminum), or any combination of two or more such elements. The oxide can occupy 90% by mass or more of the grain boundary phase 6, more preferably 95% or more, and even more preferably 97% or more.

[0029] The types of metallic elements contained in the grain boundary phase 6 may be the same as the types of metallic elements contained in the M-type ferrite crystal grains 4, but they do not need to be the same.

[0030] As shown in Figure 1, the grain boundary phase 6 may have two-particle grain boundaries 6a formed between two M-type ferrite crystal particles 4, and multi-particle grain boundaries 6b surrounded by three or more M-type ferrite crystal particles 4. The presence of multi-particle grain boundaries 6b is optional.

[0031] The two-particle grain boundary 6a contains Ca and La, and the Ca / La atomic ratio at the two-particle grain boundary 6a is 0.3 to 3.0. Preferably, the Ca / La atomic ratio at the two-particle grain boundary 6a is 0.4 or higher.

[0032] It is thought that La contributes to the crystallization of the grain boundary phase, while Ca (CaO) contributes to the amorphous nature of the grain boundary phase. When the degree of amorphousness of the grain boundary phase increases, the magnetization of the grain boundary phase decreases, which improves the coercivity of the sintered magnet, but tends to decrease the remanent magnetization. On the other hand, when the degree of crystallinity of the grain boundary phase increases, the magnetization of the grain boundary phase increases, which maintains the remanent magnetization of the sintered magnet, but it is thought to become more difficult to increase the coercivity. In this embodiment, since the ratio of Ca to La in the grain boundary phase is appropriately set, it is thought that the coercivity can be increased while maintaining the remanent magnetization of the sintered magnet.

[0033] The proportion of Ca in the total metal atoms at the two-particle grain boundary 6a can be between 1.0 and 20.0 atomic percent. The proportion of La in the total metal atoms at the two-particle grain boundary 6a can be between 3.0 and 20.0 atomic percent.

[0034] The atomic ratio of Ca and La in the total metal atoms at the two-particle grain boundary 6a may be greater than, less than, or the same as the atomic ratio of Ca and La in the total metal atoms of the ferrite crystal particle 4. In addition to La and Ca, the two-particle grain boundary 6a may contain metal element R other than La, and / or metal element A other than Ca. 2 It may also contain [a specific element]. Furthermore, the two-particle grain boundary 6a may contain the metal element M.

[0035] The two-particle grain boundary can further contain Si, and it is preferable that the Si / La atomic ratio at the two-particle grain boundary 6a is 0.02 to 2.0. While the effects of this embodiment are high in a grain boundary phase containing a certain amount of Si, it is also possible to implement the embodiment with a smaller amount of Si.

[0036] When the average thickness of the two-particle grain boundary 6a of a ferrite sintered magnet is denoted as d, d can be 1 nm or less. The average thickness d can be calculated, for example, by taking measurements at the center of 10 different two-particle grain boundaries where both ends are multi-particle grain boundaries, and averaging these measurements.

[0037] In the cross-section of a ferrite sintered magnet, the area ratio of the grain boundary phase 6 to the total area of ​​the ferrite crystal particles 4 and grain boundary phase 6 can be set to 0.01 to 5%.

[0038] There are no particular limitations on the overall composition of the ferrite sintered magnet. The overall metallic composition of the ferrite sintered magnet may satisfy equation (5).

[0039] Ferrite sintered magnets can contain silicon (Si). The Si content in ferrite sintered magnets is preferably 0.01 to 1.3 mass%, more preferably 0.01 to 0.5 mass%, and even more preferably 0.01 to 0.36 mass%, in terms of SiO2. Too much SiO2 tends to decrease Br, and too little tends to decrease HcJ. By keeping the SiO2 content within the above range, an optimal grain boundary phase can be formed, making it easier to obtain high magnetic properties.

[0040] Ferrite sintered magnets may contain boron (B). The B content in ferrite sintered magnets is 0.001 to 0.9 mass% in terms of B2O3. From the viewpoint of further increasing the coercivity and square ratio (Hk / HcJ) of ferrite sintered magnets, the B content is preferably 0.01 mass% or more in terms of B2O3. Furthermore, from the viewpoint of further increasing the residual magnetic flux density (Br) of ferrite sintered magnets, the B content is preferably 0.4 mass% or less, and more preferably 0.23 mass% or less, in terms of B2O3.

[0041] In addition to these components, ferrite sintered magnets may also contain impurities in the raw materials and unavoidable components derived from the manufacturing equipment. Examples of such components include oxides of Mg (magnesium), Ti (titanium), Mo (molybdenum), and V (vanadium). The total content of these components is preferably 0.06% by mass or less.

[0042] The metal element content ratio in ferrite crystal particles and grain boundary phases can be measured by STEM-EDX, while the metal element content ratio of the entire sintered magnet can be measured by X-ray fluorescence analysis, inductively coupled plasma emission spectroscopy (ICP emission spectroscopy), etc.

[0043] There are no particular limitations on the shape of the ferrite sintered magnet; for example, it can take various shapes such as a curved arc segment (C-type) shape with an arc-shaped end face, or a flat plate shape.

[0044] Ferrite sintered magnets can be used as magnetic field generating components in rotating electrical machinery such as motors and generators, magnets for speakers and headphones, magnetron tubes, magnetic field generators for MRI, clamps for CD-ROMs, sensors for distributors, sensors for ABS, fuel and oil level sensors, magnetolats, or isolators. They can also be used as targets (pellets) when forming the magnetic layer of magnetic recording media by vapor deposition or sputtering.

[0045] (Method of manufacturing ferrite sintered magnets) Next, an example of a manufacturing method for ferrite sintered magnets will be described. The manufacturing method described below includes a compounding step, a calcination step, a grinding step, an additional powder mixing step, a molding step, and a firing step. Details of each step are described below.

[0046] (Blending process) The blending process is the process of preparing the raw material powder for calcination. The raw material powder for calcination contains the constituent elements of ferrite. That is, it contains metal elements A1 and Fe, and optionally metal elements M and R. In the blending process, it is preferable to obtain the raw material powder by mixing a mixture of powders containing each element in an attritor or ball mill for about 1 to 20 hours and then grinding it.

[0047] Examples of powders containing each element include elemental elements, oxides, hydroxides, carbonates, nitrates, silicates, and organometallic compounds. A single powder may contain two or more metallic elements, or it may contain substantially only one metallic element.

[0048] An example of a powder containing Ca is CaCO3. An example of a powder containing Sr is SrCO3. An example of a powder containing Ba is BaCO3. Examples of powders containing La are La2O3 and La(OH)3. An example of a powder containing Fe is Fe2O3. An example of a powder containing Co is Co3O4.

[0049] The ratio of each metal element in the raw material powder can be appropriately set in accordance with the composition of the ferrite crystal particles described above.

[0050] The average particle size of the raw material powder is not particularly limited, and is, for example, 0.1 to 2.0 μm.

[0051] After the blending process, it is preferable to dry the raw material composition and remove coarse particles by sieving, if necessary.

[0052] (Calibration process) In the calcination process, the raw material powder obtained in the blending process is calcined to obtain a calcined body. Calcination is preferably carried out in an oxidizing atmosphere such as air. The calcination temperature may be, for example, 1100 to 1400°C or 1100 to 1350°C. The calcination time may be, for example, 1 minute to 10 hours or 1 minute to 3 hours. The ratio of the ferrite phase (M phase) in the calcined body containing ferrite crystal particles obtained by calcination may be, for example, 70% by mass or more or 75% by mass or more. This ratio of the ferrite phase can be determined in the same way as the ratio of the ferrite phase in ferrite sintered magnets.

[0053] (Grinding process) In the grinding process, the calcined material, which has become granular or lumpy in the calcination process, is ground to obtain ferrite powder. The grinding process may be divided into two stages, for example, by grinding the calcined powder into a coarse powder (coarse grinding process) and then grinding it further to a finer consistency (fine grinding process).

[0054] Coarse grinding can be performed, for example, using a vibrating mill, until the average particle size of the calcined material is 0.1 to 5.0 μm.

[0055] In fine grinding, the coarse powder obtained in coarse grinding is further ground using a wet attritor, ball mill, jet mill, etc. In fine grinding, the average particle size of the resulting particles can be reduced to, for example, 0.08 to 2.0 μm. The specific surface area of ​​the fine powder (determined, for example, by the BET method) is, for example, 7 to 12 m². 2 The amount should be approximately / g. The suitable grinding time varies depending on the grinding method; for example, it is 30 minutes to 10 hours for wet attritors and 10 to 50 hours for wet grinding with a ball mill. The specific surface area of ​​the obtained powder can be measured using a commercially available BET specific surface area analyzer (Mountech, product name: HM Model-1210).

[0056] In the fine grinding process, in order to increase the degree of magnetic orientation of the sintered body obtained after firing, for example, general formula C n (OH) n Hn+2 A polyhydric alcohol represented by the formula may be added. In the general formula, n may be, for example, 4 to 100 or 4 to 30. Examples of polyhydric alcohols include sorbitol. Two or more polyhydric alcohols may also be used in combination. Furthermore, in addition to polyhydric alcohols, other known dispersants may be used in combination.

[0057] When adding polyhydric alcohols, the amount added may be, for example, 0.05 to 5.0% by mass or 0.1 to 3.0% by mass relative to the material to be added (e.g., coarse powder). The polyhydric alcohols added in the fine grinding process are removed by thermal decomposition in the calcination process described later.

[0058] (Additional powder mixing process) Next, the ferrite powder and the additional powder are mixed to obtain a mixed powder. The additional powder may be mixed with the ferrite powder obtained in the grinding process, but it is preferable to add the additional powder to the powder during the grinding process so that the ferrite powder and the additional powder are mixed simultaneously with the grinding of the calcined body.

[0059] The additional powder contains at least Ca and La. The atomic ratio of La and Ca in the additional powder can be appropriately adjusted according to the metal atomic ratio of the desired grain boundary phase. The additional powder may further contain metal elements other than Ca and La (for example, metal element A 2 It may contain metal elements other than La (R, M, Fe, etc.) and / or metalloid elements such as Si and B. The composition of the grain boundary phase after sintering mainly depends on the metal and metalloid components in the added powder, but since metals in the added powder may diffuse into the main phase, or metals in the main phase may diffuse into the grain boundary phase, it will not be the same as the metal and metalloid composition of the added powder.

[0060] The amount of additional powder is preferably 0.1 to 7% by mass relative to the mass of the ferrite powder.

[0061] When the calcined body is crushed in two stages, the additional powder may be added either before or after the coarse crushing process, or the additional powder may be divided into two parts and added before and after the coarse crushing.

[0062] (molding process) In the molding process, the mixed powder obtained in the additional powder mixing process (e.g., the grinding process) is molded in a magnetic field to obtain a molded body. Molding can be performed by either dry molding or wet molding. From the viewpoint of increasing the degree of magnetic orientation, wet molding is preferred.

[0063] When molding by wet molding, for example, a slurry is obtained by performing the above-described fine grinding step in a wet manner, and then this slurry is concentrated to a predetermined concentration to obtain a slurry for wet molding. Molding can be performed using this slurry for wet molding. The slurry can be concentrated by centrifugation or by a filter press, etc. The content of ferrite crystal particles in the slurry for wet molding is, for example, 30 to 80% by mass. In the slurry, water can be used as a dispersion medium to disperse the ferrite crystal particles. Surfactants such as gluconic acid, gluconate, and sorbitol may be added to the slurry. A non-aqueous solvent may be used as the dispersion medium. Organic solvents such as toluene and xylene can be used as non-aqueous solvents. In this case, surfactants such as oleic acid may be added. The slurry for wet molding may also be prepared by adding a dispersion medium to the dried ferrite crystal particles after fine grinding.

[0064] In wet molding, the wet molding slurry is then subjected to molding in a magnetic field. In this case, the molding pressure is, for example, 9.8 to 196 MPa (0.1 to 2.0 ton / cm²). The applied magnetic field is, for example, 398 to 1194 kA / m (5 to 15 kOe).

[0065] (Firing process) In the firing (main firing) process, the molded body obtained in the molding process is fired to obtain a ferrite sintered magnet. The firing of the molded body can be carried out in an oxidizing atmosphere such as air. The firing temperature may be, for example, 1050 to 1300°C or 1080 to 1290°C. The firing time (the time to hold at the firing temperature) is, for example, 0.5 to 3 hours.

[0066] In the firing process, before reaching the sintering temperature, the molded body may be heated from room temperature to approximately 100°C at a heating rate of about 0.5°C / minute. This allows the molded body to be thoroughly dried before sintering progresses. It also allows for the thorough removal of surfactants added during the molding process. These treatments may be performed at the beginning of the firing process or separately before the firing process.

[0067] Furthermore, from the viewpoint of increasing the Ca / La ratio at the two-particle grain boundary, it is preferable to set the cooling rate when lowering the temperature from the firing temperature to 1000°C to 1 to 10°C / min, and more preferably to less than 2°C / min. By slowing down the cooling rate in this way, there is a tendency for Ca to be more easily segregated into the grain boundary phase.

[0068] In this way, the above-mentioned ferrite sintered magnet can be manufactured. [Examples]

[0069] The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0070] (Comparative Examples A1-A3 and Examples A1-A11) The following powders were prepared as raw materials: barium carbonate (BaCO3), calcium carbonate (CaCO3), strontium carbonate (SrCO3), lanthanum hydroxide (La(OH)3), iron oxide (Fe2O3), and cobalt oxide (Co3O4).

[0071] These raw material powders were blended so that the metal atom ratios matched the metal composition shown in Table 1. Mixing and grinding were performed using a wet attritor and a ball mill to obtain a slurry (blending step). After drying the slurry and removing the coarse particles, calcination was performed in air at 1310°C to obtain calcined powder (calcination step).

[0072] [Table 1]

[0073] The obtained calcined powder was coarsely ground using a small rod vibrating mill to obtain coarse powder. (Coarse grinding process)

[0074] Additional powder was obtained by blending raw material powders to achieve the metal composition shown in Table 1. The additional powder was added to the above coarse powder at a concentration of 1.0% relative to the mass of the coarse powder, and then the mixed powder was finely ground using a wet ball mill to obtain a slurry containing ferrite crystal particles (grinding and additional powder mixing process).

[0075] A slurry for wet molding was obtained by adjusting the moisture content of the slurry obtained after fine grinding. 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 (molding process).

[0076] The resulting molded body was dried in air at room temperature, and then fired in air at 1280°C (firing (main firing) process). The cooling rate when lowering the temperature from the firing temperature to 1000°C was set as shown in Table 1. In this way, a cylindrical ferrite sintered magnet was obtained.

[0077] (Example B1, Examples B1, B2) Except for changing various conditions as shown in Table 2, the procedure was the same as in Example 1.

[0078] [Table 2]

[0079] (Example C1, Examples C1, C2) Except for changing various conditions as shown in Table 3, the procedure was the same as in Example 1.

[0080] [Table 3]

[0081] <Evaluation of magnetic properties> After processing the top and bottom surfaces of the ferrite sintered magnet, Br and HcJ were measured at 20°C using a BH tracer with a maximum applied magnetic field of 29 kOe.

[0082] <Composition analysis> A 100 nm thick thin section was obtained by processing a ferrite sintered magnet using the Focused Ion Beam (FIB) method with a focused ion beam apparatus. Using STEM-EDS, elemental line analysis was performed on the thin section, from one ferrite crystal grain to the other ferrite crystal grain, perpendicular to the grain boundary phase, and the concentration change along the line of metallic elements was measured. The measurement interval was 3 nm, and the metallic element concentrations at the two-particle grain boundary were obtained. This measurement was performed at five grain boundaries, and the grain boundary phase metallic element concentrations were obtained by averaging, and the atomic ratios were determined.

[0083] The results for the sintered magnets in each example and comparative example are shown in Tables 1-3.

[0084] In examples where the Ca / La atomic ratio at the grain boundaries was within a specific range, it was confirmed that the HcJ force could be increased without significantly reducing the Br, resulting in an excellent balance between Br and HcJ. In Comparative Example A2, magnetic measurement was not possible due to cracks occurring in the sintered magnet. In Comparative Example C1, neither Ca, La, nor Si could be detected at the grain boundaries. [Explanation of Symbols]

[0085] 4...ferrite crystal grains, 6...grain boundary phase, 6a...2-particle grain boundary, 6b...multi-particle grain boundary.

Claims

1. A ferrite sintered magnet comprising magnetoplumbite-type ferrite crystal particles and two-particle grain boundaries interposed between the ferrite crystal particles, The two-particle grain boundary contains Ca and La, and the Ca / La atomic ratio at the two-particle grain boundary is 0.3 to 3.

0. A ferrite sintered magnet in which the Ca / La atomic ratio is the average of values ​​obtained at multiple two-particle grain boundaries by elemental analysis using STEM-EDS.

2. The ferrite sintered magnet according to claim 1, wherein the Ca / La atomic ratio at the two-particle grain boundary is 0.4 or more.

3. The ferrite sintered magnet according to claim 1 or 2, wherein the two-particle grain boundary further contains Si, and the Si / La atomic ratio at the two-particle grain boundary is 0.02 to 2.0.

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