Sintered ferrite magnet

Abstract

To provide a novel sintered ferrite magnet excellent in coercive force.SOLUTION: A sintered ferrite magnet includes magnetoplumbite ferrite crystal grains and a grain boundary multipoint surrounded by three or more of the magnetoplumbite ferrite crystal grains. Each magnetoplumbite ferrite crystal grain and the grain boundary multipoint contain a metal element A, La, Co and Fe. The metal element A is at least one element selected from the group consisting of Sr, Ba and Ca. An atomic ratio (A / La) of the metal element A to La at the grain boundary multipoint is 3.5-11.0. An atomic ratio (Co / Fe) of Co to Fe in the magnetoplumbite ferrite crystal grains is 0.008-0.100.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] The chemical formula for magnetoplumbite (M-type) ferrite is AFe 12 O 19 A is an alkaline earth metal with a divalent ion, Fe is a trivalent ion, and O is a divalent ion. 12 O 19 This forms a charge-balanced crystal.

[0003] AFe 12 O 19 However, it is known that the magnetic properties are improved by substituting La at the A site and Co at the Fe site (see Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-156310 A [Patent Document 2] Japanese Patent Publication No. 2023-90400 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-313617 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even conventional sintered ferrite magnets have room for improvement in coercivity.

[0006] The present invention has been made in view of the above problems, and has an object to provide a novel sintered ferrite magnet with excellent coercive force. [Means for solving the problem]

[0007] [1] A magnetoplumbite-type ferrite crystal grain and, a grain boundary multi-junction point surrounded by three or more of the magnetoplumbite-type ferrite crystal grains, the ferrite sintered magnet comprising: the magnetoplumbite-type ferrite crystal grain and the grain boundary multi-junction point each contain a metal element A, La, Co, and Fe, the metal element A is at least one element selected from the group consisting of Sr, Ba, and Ca, the atomic ratio (A / La) of the metal element A to La at the grain boundary multi-junction point is 3.5 to 11.0, the atomic ratio (Co / Fe) of Co to Fe in the magnetoplumbite-type ferrite crystal grain is 0.008 to 0.100, the ferrite sintered magnet.

[0008] [2] The metal composition of the magnetoplumbite-type ferrite crystal grain is represented by the following general formula (5), A 1-x-y La x R y (Fe 12-e-f Co e M f ) a (5) In the above formula (5), R is at least one metal element selected from the group consisting of Bi and rare earth elements (excluding La), M is at least one metal element selected from the group consisting of Zn, Cu, Mn, Al, Ni, and Cr, x > 0, 0 ≤ y < x, e > 0, 0 ≤ f < e, and, the ferrite sintered magnet according to [1], satisfying 0.800 ≤ a ≤ 1.200.

[0009] [3] The ferrite sintered magnet according to [2], satisfying x ≥ 0.05 and e ≥ 0.05.

[0010] [4] The sintered ferrite magnet according to any one of [1] to [3], wherein the atomic concentration of La relative to the total amount of metal elements and Si at the grain boundary multiple points is 9.0 mol % or less.

[0011] [5] The sintered ferrite magnet according to any one of [1] to [4], wherein the ratio of Sr to the metal element A (Sr / A) at the grain boundary multiple points is 0.30 to 0.85.

[0012] [6] The sintered ferrite magnet according to any one of [1] to [5], wherein the proportion of crystal grains having stacking faults among the magnetoplumbite ferrite crystal grains is 8 or less per 100 crystal grains. [Effects of the Invention]

[0013] According to the present invention, a novel sintered ferrite magnet capable of increasing coercive force is provided. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view of a sintered ferrite magnet. DETAILED DESCRIPTION OF THE INVENTION

[0015] Embodiments of the present invention are described in detail below.

[0016] (sintered ferrite magnet) 1, a sintered ferrite magnet 100 according to an embodiment of the present invention has a plurality of magnetoplumbite ferrite crystal grains 4 having a magnetoplumbite (M-type) crystal structure, and grain boundary multiple points 6 surrounded by three or more magnetoplumbite ferrite crystal grains 4. A grain boundary 5 is formed between two magnetoplumbite ferrite crystal grains 4.

[0017] (Magnetoplumbite ferrite grains) The magnetoplumbite ferrite crystal grains are an oxide containing a metal element A, La, Co, and Fe. The metal element A is at least one element selected from the group consisting of Sr, Ba, and Ca.

[0018] The metal composition of the magnetoplumbite ferrite crystal grains can be expressed by the following general formula (5).

[0019] A 1-x-y La x R y (Fe 12-e-f Co e M f ) a (5) In the above formula (5), A is at least one selected from the group consisting of Sr, Ba, and Ca.

[0020] R represents at least one metal element selected from the group consisting of Bi and rare earth elements (excluding La). The rare earth elements excluding La are Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0021] M is at least one metal element selected from the group consisting of Zn, Cu, Mn, Al, Ni, and Cr.

[0022] x may be any value greater than 0, for example, 0.01 or more, 0.05 or more, 0.10 or more, 0.20 or more, 0.25 or more, 0.50 or less, 0.45 or less, 0.40 or less, or 0.35 or less.

[0023] y may be smaller than x, smaller than x / 2, smaller than x / 3, smaller than x / 5, smaller than x / 10, may be 0.1 or less, may be 0.05 or less, may be 0.02 or less, may be 0.01 or less, may be 0.005 or less, may be 0.001 or less, or may be 0. y may satisfy the following formula:

[0024] 0≦y <x

[0025] e may be any value greater than 0, for example, 0.01 or more, 0.02 or more, 0.05 or more, 0.1 or more, 0.2 or more, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, or 0.4 or less.

[0026] f is smaller than e, and may be, for example, smaller than e / 2, smaller than e / 3, smaller than e / 5, or smaller than e / 10, or may be 0.1 or less, 0.05 or less, 0.02 or less, 0.01 or less, 0.005 or less, 0.0001 or less, or 0. f can satisfy the following formula:

[0027] 0≦f <e

[0028] a is 0.800 to 1.200, and may be, for example, 1.100 or less, 1.000 or less, 0.999 or less, 0.997 or less, 0.995 or less, 0.993 or less, 0.850 or more, or 0.900 or more.

[0029] Sr may account for 34 at% or more of the metal element A, Ba may account for 34 at% or more of the metal element A, or Ca may account for 34 at% or more of the metal element A. Among these, so-called Sr ferrite, in which Sr accounts for 34 at% or more of the metal element A, is preferred, and the atomic ratio of Sr to the metal element A may be 50 at% or more, 60 at% or more, 70 at% or more, 80 at% or more, 90 at% or more, 95 at% or more, 97 at% or more, 99 at% or more, or 100 at%. In this specification, atomic ratio refers to the ratio of the number of atoms and is the same as molar ratio.

[0030] The atomic ratio of Co to Fe (Co / Fe) in the magnetoplumbite ferrite crystal grains is 0.008 to 0.100. The atomic ratio (Co / Fe) may be 0.010 or more, 0.020 or more, 0.030 or more, 0.090 or less, 0.080 or less, 0.070 or less, or 0.066 or less.

[0031] The atomic ratio of Co to La (e / x) in the magnetoplumbite ferrite crystal grains may be 0.80 or more, 0.85 or more, 0.90 or more, 0.95 or more, 0.97 or more, 0.98 or more, 0.99 or more, 1.20 or less, 1.15 or less, 1.10 or less, 1.05 or less, 1.03 or less, 1.02 or less, or 1.01 or less.

[0032] The atomic ratio (A / La) of the metal element A to La in the magnetoplumbite ferrite crystal grains may be 2.5 to 11.0. The atomic ratio (A / La) in the magnetoplumbite ferrite crystal grains may be 4.0 or more, 10 or less, or 9 or less.

[0033] The mass fraction of magnetoplumbite ferrite in the magnetoplumbite ferrite crystal grains is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more.

[0034] The mass ratio of magnetoplumbite ferrite crystal grains (main phase) to all crystal grains in a sintered ferrite magnet is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more. In this way, by reducing the mass ratio of crystal phases (heterogeneous phases) different from the magnetoplumbite ferrite phase, it is possible to further improve magnetic properties. The mass ratio (%) of the M-type ferrite phase to all crystal grains of a sintered ferrite magnet can be confirmed by determining the abundance (mol %) of the magnetoplumbite ferrite phase using X-ray diffraction. The abundance ratio of the magnetoplumbite ferrite phase is calculated by mixing powder samples of magnetoplumbite ferrite, orthoferrite, hematite, spinel, and W-type ferrite in predetermined ratios and comparing their X-ray diffraction intensities.

[0035] The crystal structure of magnetoplumbite ferrite can be represented by the following formula (III).

[0036] QX 12 O 19 (III) Q is a divalent cation site (A site) and includes metal elements A, La, and R. X is a trivalent cation site (B site) and includes Fe, Co, and M. O is a divalent anion, which can balance the charge in formula (III).

[0037] In addition, the atomic ratios of Q (A site) and X (B site) to O in the above formula (III) actually show values ​​that are somewhat biased from the above range, and may therefore deviate slightly from the above numerical values, for example, by about 10%.

[0038] The average grain size of the magnetoplumbite ferrite crystal grains in the sintered ferrite 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 grain size can increase the coercive force. The average grain size of the ferrite crystal grains can be determined using a TEM or SEM image of the cross section. Specifically, the cross-sectional area of ​​each crystal grain in an SEM or TEM cross section containing several hundred ferrite crystal grains is determined by image analysis, and the diameter of a circle having that cross-sectional area (circle-equivalent diameter) is defined as the grain size of the crystal grain in that cross section, and the grain size distribution is measured. The number-based average grain size of the ferrite crystal grains is calculated from the measured number-based grain size distribution. The average value measured in this way is the average grain size of the ferrite crystal grains.

[0039] (Stacking faults in magnetoplumbite ferrite grains) Of the magnetoplumbite ferrite crystal grains, the proportion of crystal grains having stacking faults is preferably 8 or less per 100, more preferably 6 or less, more preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less.

[0040] (grain boundary multiple points) The grain boundary multiple points 6 are regions surrounded by three or more magnetoplumbite ferrite crystal grains 4. The composition of the grain boundary multiple points is an oxide containing at least the metal elements A, La, Co, and Fe.

[0041] The sintered ferrite magnet 100 may have one or more heterogeneous phases in addition to the magnetoplumbite ferrite crystal grains 4 and the grain boundary multiple points 6 surrounded by three or more magnetoplumbite ferrite crystal grains 4. The heterogeneous phases may be α-FeO ​​or LaFeO.

[0042] (Metal element A) The metal element A at the grain boundary multiple points is at least one element selected from the group consisting of Sr, Ba, and Ca.

[0043] Here, the combination of elements constituting the metal element A at the grain boundary multiple points and the combination of elements constituting the metal element A in the magnetoplumbite ferrite crystal grains may be the same as or different from each other.

[0044] There is no limitation on the atomic ratio of all metal elements at the grain boundary multiple points 6 and the metal element A in Si.

[0045] The grain boundary multiple points 6 may contain 1 mol % or more of the metal element A, 2 mol % or more, 3 mol % or more, 4 mol % or more, 5 mol % or more, 6 mol % or more, 30 mol % or less, 25 mol % or less, 20 mol % or less, 15 mol % or less, 12 mol % or less, or 10 mol % or less of the metal element A, based on all the metal elements and Si.

[0046] The metal element A contained in the grain boundary multiple points 6 preferably contains Sr. Specifically, the atomic ratio of Sr to the metal element A contained in the grain boundary multiple points (Sr / A) is preferably 0.30 to 0.85.

[0047] When Sr accounts for a certain proportion of the metal element A at the grain boundary multiple points, La and Co are more likely to diffuse from the grain boundary multiple points to the magnetoplumbite ferrite crystal grains in the solid-state reaction during sintering, and the amount of La and Co substituted in the magnetoplumbite ferrite crystal grains increases, making it easier to further improve Hcj.

[0048] The grain boundary multiple points 6 may contain 0.5 mol % or more of Sr, 1.0 mol % or more, 1.5 mol % or more, 2.0 mol % or more, 2.5 mol % or more, 3.0 mol % or more, 15 mol % or less, 13 mol % or less, 12 mol % or less, 11 mol % or less, 10 mol % or less, or 9 mol % or less of Sr among all metal elements and Si.

[0049] The grain boundary multiple points 6 may contain 0.5 mol% or more of Ca, 1.0 mol% or more, 1.5 mol% or more, 2.0 mol% or more, 2.5 mol% or more, 3.0 mol% or more, 15 mol% or less, 13 mol% or less, 12 mol% or less, 11 mol% or less, 10 mol% or less, 9 mol% or less, 8 mol% or less, or 7 mol% or less of Ca among all metal elements and Si.

[0050] (La) In this embodiment, the atomic ratio (A / La) of the metal element A to La at the grain boundary multiple points 6 is 3.5 to 11.0. This atomic ratio (A / La) may be 4.0 or more, 10 or less, or 9 or less.

[0051] At the grain boundary multiple points 6, the atomic concentration of La in all metal elements and Si may be 0.1 mol% or more, 0.2 mol% or more, 0.3 mol% or more, 0.4 mol% or more, 0.5 mol% or more, 0.6 mol% or more, 0.7 mol% or more, 0.8 mol% or more, 0.9 mol% or more, 1.0 mol% or more, 15 mol% or less, 13 mol% or less, 12 mol% or less, 11 mol% or less, 10 mol% or less, 9.0 mol% or less, 8.0 mol% or less, 7.0 mol% or less, or 6.0 mol% or less.

[0052] (metallic element R) The grain boundary multiple points 6 may contain, in addition to La, at least one metal element R selected from the group consisting of rare earth elements including Y and Bi. In the grain boundary multiple points 6, the atomic concentration of the metal element R in all metal elements and Si may be less than the concentration of La, may be ½ or less of the atomic concentration of La, may be ⅕ or less of the atomic concentration of La, may be 1 / 10 or less of the atomic concentration of La, may be 1 / 20 or less of the atomic concentration of La, or may be 0.

[0053] (Metal element Co) At the grain boundary multiple points 6, the atomic concentration of Co in all metal elements and Si may be more than 0, and may be 0.1 mol% or more, 0.2 mol% or more, 0.5 mol% or more, 0.7 mol% or more, 1.0 mol% or more, 1.2 mol% or more, 1.5 mol% or more, 10 mol% or less, 9.0 mol% or less, 8.0 mol% or less, 7.0 mol% or less, 6.0 mol% or less, 5.0 mol% or less, 4.0 mol% or less, or 3.0 mol% or less.

[0054] (metallic element Fe) At the grain boundary multiple points 6, the atomic concentration of Fe in all metal elements and Si may be more than 0, and may be 5 mol% or more, 10 mol% or more, 15 mol% or more, 20 mol% or more, 25 mol% or more, 30 mol% or more, 35 mol% or more, 80 mol% or less, 75 mol% or less, 70 mol% or less, 65 mol% or less, 60 mol% or less, 55 mol% or less, or 50 mol% or less.

[0055] (Co / Fe ratio) The atomic ratio of Co to Fe (Co / Fe) at the grain boundary multiple points is not particularly limited, but may be approximately the same as the atomic ratio of Co to Fe (Co / Fe) in the magnetoplumbite ferrite crystal grains, i.e., 0.008 to 0.100. The atomic ratio (Co / Fe) may be 0.010 or more, 0.020 or more, 0.030 or more, 0.090 or less, 0.080 or less, 0.070 or less, or 0.066 or less.

[0056] (Metal element M) The grain boundary multiple points may contain, in addition to Co, at least one metal element M selected from the group consisting of Mn, Mg, Ni, Cu, and Zn. At the grain boundary multiple points 6, the atomic concentration of the metal element M in all metal elements and Si may be less than the concentration of Co, may be ½ or less of the atomic concentration of Co, may be ⅕ or less of the atomic concentration of Co, may be 1 / 10 or less of the atomic concentration of Co, may be 1 / 20 or less of the atomic concentration of Co, or may be 0.

[0057] With respect to the number of atoms of all metal elements and Si at the grain boundary multiple points 6, the proportion of metal element A can be 6 to 14 mol %, the proportion of La can be 0.5 to 4.0 mol %, the proportion of Fe can be 5 to 80 mol %, and the proportion of Co can be 0.5 to 2.0 mol %.

[0058] In addition to the above elements, the grain boundary multiple points 6 may contain Si. The Si content may be 5 mol % or more, 10 mol % or more, 50 mol % or less, or 40 mol % or less, based on the number of all metal elements and Si atoms. The grain boundary multiple points 6 may further contain B.

[0059] In the cross section of the sintered ferrite magnet, the area ratio of the grain boundary multiple points 6 to the total area of ​​the magnetoplumbite ferrite crystal grains 4 and the grain boundary multiple points 6 can be 0.01 to 5%.

[0060] There are no particular limitations on the shape of the sintered ferrite magnet, and it can have a variety of shapes, such as an arc segment (C-shape) shape with curved end faces that form an arc, or a flat plate shape.

[0061] The content ratios of metal elements and Si in the ferrite crystal grains and grain boundary phases can be measured by STEM-EDX, and the content ratios of metal elements in the entire sintered magnet can be measured by X-ray fluorescence analysis, inductively coupled plasma atomic emission spectroscopy (ICP atomic emission spectroscopy), etc.

[0062] The content ratio of metal elements in the ferrite crystal grains and grain boundary phase can be measured by STEM-EDX, and the content ratio of metal elements in the entire sintered magnet can be measured by X-ray fluorescence analysis, inductively coupled plasma atomic emission spectroscopy (ICP atomic emission spectroscopy), etc.

[0063] There are no particular limitations on the shape of the sintered ferrite magnet, and it can have a variety of shapes, such as an arc segment (C-shape) shape with curved end faces that form an arc, or a flat plate shape.

[0064] Sintered ferrite magnets can be used as magnetic field generating components in rotating electrical machines such as motors and generators, speaker and headphone magnets, magnetron tubes, magnetic field generators for MRI, CD-ROM clampers, distributor sensors, ABS sensors, fuel and oil level sensors, magnet latches, isolators, etc. They can also be used as targets (pellets) when forming the magnetic layer of magnetic recording media by vapor deposition or sputtering methods.

[0065] (Method of manufacturing sintered ferrite magnets) Next, an example of a method for producing the above-mentioned sintered ferrite magnet will be described. The production method described below includes a first raw material preparation step, a first calcination step, a pulverization and Co addition step, a second calcination step, a sintering material preparation step, a molding step, and a sintering step. Each step will be described in detail below.

[0066] (First raw material preparation process) The first raw material is a powder containing elements other than Co among the constituent elements of magnetoplumbite ferrite crystal grains. That is, the first raw material is a powder containing metal elements A, La, and Fe, and optionally metal elements M and R. In this step, it is preferable to obtain the first raw material by mixing and pulverizing a mixture of powders containing each element in an attritor or a ball mill for about 1 to 20 hours. The first raw material does not contain Co.

[0067] Examples of powders containing each element include the simple substance, oxide, hydroxide, carbonate, nitrate, silicate, and organometallic compound of each element. One powder may contain two or more metal elements, or one powder may contain substantially only one metal element.

[0068] 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.

[0069] The ratio of each metal element in the first raw material can be appropriately set according to the target composition of ferrite crystal grains. The Fe-containing powder may be added in its entirety in this step, or may be added in two separate steps, this step and the Co-addition step described below.

[0070] The average particle size of the powder of the first raw material is not particularly limited, and is, for example, 0.1 to 2.0 μm.

[0071] After the blending step, it is preferable to dry the first raw material and remove coarse particles by sieving, if necessary.

[0072] (First calcination step) In the first calcination step, the obtained first raw material is calcined to obtain a first calcined body. The first calcination is preferably performed in an oxidizing atmosphere such as air. The temperature of the first calcination is preferably 800 to 950°C. By calcining the first raw material that does not contain Co at a relatively low temperature, a first calcined body containing AFe 12 O 19 A mixed phase compound containing a (magnetoplumbite-type) phase, an Fe2O3 phase, and an LaFeO3 (orthoferrite) phase is obtained.

[0073] The calcination time may be, for example, 1 minute to 10 hours, or 1 minute to 3 hours.

[0074] (Crushing and Co addition process) In this step, the first calcined body is pulverized, and a powder containing Co is added to the first calcined body to prepare a second raw material for the second calcination. The order of pulverizing the first calcined body and adding the powder containing Co is not limited, and the powder containing Co may be added after pulverizing the first calcined body, or before or during pulverization of the first calcined body.

[0075] Examples of powders containing Co include powders of CoFe2O4, Co(OH)2, and Co3O4. The powders containing Co may contain a metal element other than Co that constitutes the magnetoplumbite ferrite crystal grains, such as Fe. For example, when Co(OH)2 and Co3O4 are added, it is preferable to add Fe, such as Fe2O3.

[0076] (Second calcination step) In the second calcination step, the obtained second raw material is calcined to obtain a second calcined body. The second calcination is preferably carried out in an oxidizing atmosphere such as air. The temperature of the second calcination is preferably 1100 to 1200°C. The time of the second calcination may be, for example, 1 minute to 10 hours, or 1 minute to 3 hours.

[0077] As a result, a single-phase ferrite of the magnetoplumbite phase is obtained as the second calcined body. In this process, in the early stage of the second calcination, CoFe2O4 (cobalt ferrite) phase is generated by Co and Fe such as Fe2O3 in the second raw material, and then AFe 12 O 19 The magnetoplumbite ferrite (LaFeO3), orthoferrite (LaFeO3), and cobalt ferrite (CoFe2O4) phases react. In this reaction, La is released from the orthoferrite (LaFeO3) phase, and Co is released from the CoFe2O4La phase, respectively. 12 O 19 The La and Co solid-solubilized magnetoplumbite ferrite (AFe 12 O 19 ) is formed. In the magnetoplumbite ferrite crystal grains, La substitutes for the metal element A, and Co substitutes for Fe.

[0078] In this embodiment, AFe in which Co is previously dissolved 12 O 19 La is not dissolved later in the magnetoplumbite ferrite phase, but rather AFe 12 O 19 Since La and Co are both dissolved in the magnetoplumbite ferrite phase, the number of La and Co atoms is the same at the micro level, i.e., the molar ratio of these atoms is approximately the same, making it easier to dissolve uniformly. 12 O 19 It is believed that this makes it easier to achieve a charge balance in the ferrite, resulting in fewer stacking faults. Furthermore, with this manufacturing method, the ratio of element A to La (A / La) at the grain boundary multiple points of the sintered body becomes 3.5 to 11.0.

[0079] (Sintering raw material preparation process) In this step, the second calcined body that has been converted into granular or lumpy form by the second calcination step is pulverized to obtain magnetoplumbite ferrite fine powder, and a sintering aid is added as needed to obtain a molding material.

[0080] The pulverization may be carried out in two steps, for example, by pulverizing the second calcined body to a coarse powder (coarse pulverization step), and then pulverizing this into a finer powder (fine pulverization step).

[0081] Coarse pulverization can be carried out, for example, using a vibrating mill or the like until the calcined body has an average particle size of 0.1 to 5.0 μm.

[0082] In fine pulverization, the coarse powder obtained by coarse pulverization is further pulverized using a wet attritor, ball mill, jet mill, or the like. In fine pulverization, pulverization can be carried out so that the average particle size of the obtained particles becomes, for example, about 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 m 2The preferred grinding time varies depending on the grinding method; for example, it is 30 minutes to 10 hours in the case of a wet attritor, and 10 to 50 hours in the case of wet grinding using a ball mill. The specific surface area of ​​the resulting powder can be measured using a commercially available BET specific surface area measuring device (manufactured by Mountech, product name: HM Model-1210).

[0083] In the fine grinding process, in order to increase the degree of magnetic orientation of the sintered body obtained after firing, for example, n (OH) n H n+2 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 types of polyhydric alcohols may be used in combination. Furthermore, in addition to the polyhydric alcohol, other known dispersants may be used in combination.

[0084] When polyhydric alcohol is added, the amount of the polyhydric alcohol added may be, for example, 0.05 to 5.0 mass % or 0.1 to 3.0 mass % relative to the object to which it is added (e.g., coarse powder). The polyhydric alcohol added in the fine pulverization step is thermally decomposed and removed in the firing step described below.

[0085] The sintering aid may be mixed with the ferrite powder after pulverization, but it is preferable to add the sintering aid to the powder before or during pulverization, and mix the ferrite powder and sintering aid simultaneously with pulverization of the second calcined body.

[0086] Examples of sintering aids include powders containing Ca, and powders containing metalloid elements such as Si and B. Specific examples of sintering aids include powders of CaCO3, SiO2, and B2O3.

[0087] The amount of the sintering aid is preferably 0.1 to 7 mass % relative to the mass of the ferrite powder.

[0088] When the second calcined body is pulverized in two stages, the sintering aid may be added either before or after the coarse pulverization step, or the sintering aid may be added in two parts, before and after the coarse pulverization.

[0089] (molding process) In the molding step, the obtained molding raw material 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.

[0090] When forming by wet compaction, for example, a slurry is obtained by wet-pulverizing the above-mentioned powder, and then the slurry is concentrated to a predetermined concentration to obtain a slurry for wet compaction. Forming can be performed using this slurry for wet compaction. The slurry can be concentrated by centrifugation, a filter press, or the like. The content of ferrite crystal particles in the slurry for wet compaction is, for example, 30 to 80 mass %. In the slurry, a dispersion medium for dispersing the ferrite crystal particles can be, for example, water. A surfactant such as gluconic acid, a gluconate, or sorbitol may be added to the slurry. A non-aqueous solvent may be used as the dispersion medium. An organic solvent such as toluene or xylene may be used as the non-aqueous solvent. In this case, a surfactant such as oleic acid may be added. The slurry for wet compaction may be prepared by adding a dispersion medium or the like to ferrite crystal particles in a dry state after fine pulverization.

[0091] In wet compacting, the wet compacting slurry is then compacted in a magnetic field. In this case, the compacting pressure is, for example, 9.8 to 196 MPa (0.1 to 2.0 ton / cm2). The magnetic field to be applied is, for example, 398 to 1194 kA / m (5 to 15 kOe).

[0092] (Firing process) In the firing (main firing) step, the compact obtained in the compacting step is fired to obtain a sintered ferrite magnet. The compact can be fired 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 held at the firing temperature) is, for example, 0.5 to 3 hours.

[0093] In the firing step, before the sintering temperature is reached, the molded body may be heated, for example, from room temperature to about 100°C at a heating rate of about 0.5°C / min. This allows the molded body to be sufficiently dried before sintering proceeds. It also allows the surfactant added in the molding step to be sufficiently removed. These treatments may be performed at the beginning of the firing step or separately before the firing step.

[0094] In this manner, the above-mentioned sintered ferrite magnet can be produced.

[0095] (action) The sintered ferrite magnet according to this embodiment can increase the coercive force, and although the reason for this is not clear, the following circumstances are thought to be involved.

[0096] It was found that when the atomic ratio of metal element A to La (A / La) at the grain boundary multiplex points is 3.5 to 11.0 and the atomic ratio of Co to Fe (Co / Fe) in magnetoplumbite ferrite crystal grains is 0.008 to 0.100, the introduction of Co and La as substitution elements into the main phase does not increase stacking faults.

[0097] Although the mechanism behind this is unclear, it is thought that when the atomic ratio (A / La) at the grain boundary multiplex point is within a specific range and the atomic ratio (Co / Fe) of the ferrite crystal grain is also within this range, La and Co tend to dissolve uniformly within the ferrite crystal grain in a ratio that is close to equal, and the charge balance of the ferrite crystal grain is maintained at a microscopic level, resulting in few stacking faults within the ferrite crystal grain.

[0098] In the magnetoplumbite ferrite crystal grains, La substitutes for the metal element A, and Co substitutes for Fe. In this case, the substitution of equal numbers of La and Co achieves charge balance in the ferrite, reducing stacking faults.

[0099] A 2+ -> La 3+ Fe 3+ -> Co 2+ Fewer stacking faults within the ferrite grains and a larger amount of La and Co substituted in the main phase result in improved coercivity. Such magnets can also be used in the traction motors of electric vehicles.

[0100] In addition, the amount of Co added in the ferrite grains was increased to 3+ Sites with more Co 2+ Even if the Co substitution amount in the ferrite crystal grains (Co / Fe ratio in the ferrite crystal grains) is large, La and Co can be uniformly diffused into the ferrite crystal grains. [Example]

[0101] 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.

[0102] (Examples 1 to 7 and Comparative Examples 1 to 3) As raw materials, powders of barium carbonate (BaCO3), calcium carbonate (CaCO3), strontium carbonate (SrCO3), lanthanum hydroxide (La(OH)3), iron oxide (Fe2O3), and cobalt ferrite (CoFe2O4) were prepared.

[0103] These raw material powders were mixed so that the metal atomic ratio was the metal composition in the column for the main phase in Table 1 (with the exception that Co ferrite was not added), and then mixed and pulverized using a wet attritor and a ball mill to obtain a slurry. This slurry was dried, and coarse particles were removed to obtain a first raw material (first raw material preparation step).

[0104] The first raw material was subjected to first calcination in air at 900°C for 1 hour to obtain a first calcined body (first calcination step). 12 O 19 The resulting mixture was a mixture of (M phase), Fe2O3 phase, and LaFeO3 phase, and La did not dissolve in the M phase.

[0105] [Table 1]

[0106] The obtained first calcined body was coarsely pulverized using a small rod vibration mill to obtain a coarse powder. CoFe2O4 powder was blended with this coarse powder to obtain a mixed powder with the metal composition shown in Table 1. The mixed powder was finely pulverized using a wet ball mill to obtain a slurry. This slurry was dried, and coarse particles were removed to obtain a second raw material (pulverization and Co addition process).

[0107] The second raw material was calcined in air at 1150°C for 1 hour to obtain a second calcined body. 12 O 19 The result was a single-phase product (M phase).

[0108] The obtained second calcined body was coarsely pulverized in a small rod vibration mill to obtain a coarse powder. SiO2 and CaCO3 powders were blended with this coarse powder to obtain a mixed powder with the total weight composition shown in Table 1. The mixed powder was finely pulverized using a wet ball mill for 40 hours to obtain a slurry containing the raw material for sintering. The water content of the slurry obtained after fine pulverization was adjusted to obtain a wet compacting slurry containing the raw material for sintering (sintering raw material preparation step).

[0109] This wet molding slurry 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 having a diameter of 30 mm and a thickness of 15 mm (molding step).

[0110] The obtained compact was dried in the air at room temperature and then fired in the air at 1180° C. (firing (main firing) step). In this way, a cylindrical sintered ferrite magnet was obtained.

[0111] (Comparative Example 1) The same procedure as in Example 5 was carried out except that the temperature of the first calcination was set to 1300° C. In the first calcination step, La solid-solution Sr ferrite (magnetoplumbite type Sr 1-X La X Fe 12 O 19 A single phase was formed, and the La concentration at the grain boundary multiple points was low and the A / La ratio was high in the final sintered magnet.

[0112] (Comparative Example 2) The same procedures as in Example 5 were carried out except that the preparation of the first raw material and the first calcination were not carried out, and the second raw material containing all of iron oxide and strontium carbonate but not lanthanum hydroxide or cobalt ferrite was subjected to the second calcination, and then lanthanum hydroxide and cobalt ferrite were added to the raw material for sintering. In this case, the La concentration at the grain boundary multiple points increased.

[0113] (Comparative Example 3) The same procedure as in Example 5 was carried out except that the preparation of the first raw material and the first calcination were not carried out, and Co, Fe, Sr, and La were all blended in the second raw material.

[0114] Table 2 shows the conditions and the resulting grain boundary multiple points, and Table 3 shows the composition of the main phase and the evaluation of the magnet.

[0115] [Table 2]

[0116] [Table 3]

[0117] <Evaluation of magnetic properties> After processing the top and bottom surfaces of the sintered ferrite magnet, Br and HcJ were measured at 20°C using a BH tracer with a maximum applied magnetic field of 29 kOe.

[0118] <Composition analysis> A 100 nm thick flake was obtained from a sintered ferrite magnet by processing using a focused ion beam (FIB) method with a focused ion beam device. The composition of the grain boundary multipoints surrounded by three or more M phases was analyzed using STEM-EDS, and the metal element concentrations at the grain boundary multipoints were obtained. This measurement was performed at four grain boundary multipoints and averaged to obtain the grain boundary multipoint metal element concentrations and calculate the atomic ratios. Similarly, the compositions of the four M phases were analyzed using STEM-EDS, and the metal element concentrations of the M phases were obtained by averaging.

[0119] <Stacking faults> While stacking faults can be relatively easily identified using TEM or other methods, it is not practical to count the total number of crystal grains in such cases. Therefore, for example, the number of crystal grains in a certain field of view when observing a plane (a-plane) parallel to the c-axis of an anisotropic sintered magnet with a TEM is counted, and the total number of crystal grains is defined as N, and the number of crystal grains with defects found within those crystal grains is defined as n, and this number is estimated. The TEM magnification for observation is preferably 1,000 to 100,000 times, and particularly 10,000 to 20,000 times. The number of fields of view for observation is preferably two or more, particularly 2 to 10, and N is approximately 20 to 500. While the number of defects present within a crystal grain is typically around one or two, it may sometimes be three or more. Specifically, the number of crystal grains with defects found within 100 crystal grains in a certain field of view when observing a plane (a-plane) parallel to the c-axis of an anisotropic sintered magnet with a TEM is counted. [Explanation of symbols]

[0120] 4...magnetoplumbite ferrite crystal grain, 6...grain boundary multiple points, 5...grain boundary, 100...ferrite sintered magnet.

Claims

1. Magnetoplumbite ferrite grains; a grain boundary multiple point surrounded by three or more of the magnetoplumbite ferrite crystal grains, The magnetoplumbite ferrite crystal grains and the grain boundary multiple points contain metal elements A, La, Co, and Fe, respectively; The metal element A is at least one element selected from the group consisting of Sr, Ba, and Ca, the atomic ratio (A / La) of the metal element A to La at the grain boundary multiple points is 3.5 to 11.0; The sintered ferrite magnet has an atomic ratio of Co to Fe (Co / Fe) in the magnetoplumbite ferrite crystal grains of 0.008 to 0.

100.

2. The metal composition of the magnetoplumbite ferrite crystal grains is expressed by the following general formula (5): A １－ｘ－ｙ Lạ ｘ R ｙ (Fe １２－ｅ－ｆ Co ｅ M ｆ ) ａ (5) In the above formula (5), R is at least one metal element selected from the group consisting of Bi and rare earth elements (excluding La), M is at least one metal element selected from the group consisting of Zn, Cu, Mn, Al, Ni, and Cr, x>0, 0≦y<x, e>0, 0≦f<e, and The sintered ferrite magnet according to claim 1, wherein 0.800≦a≦1.

200.

3. The sintered ferrite magnet according to claim 2 , wherein x≧0.05 and e≧0.05 are satisfied.

4. 3. The sintered ferrite magnet according to claim 1, wherein the atomic concentration of La relative to the total amount of metal elements and Si at the grain boundary multiple junctions is 9.0 mol % or less.

5. 3. The sintered ferrite magnet according to claim 1, wherein the ratio of Sr to the metal element A (Sr / A) at the grain boundary multiple points is 0.30 to 0.

85.

6. 3. The sintered ferrite magnet according to claim 1, wherein the ratio of crystal grains having stacking faults among the magnetoplumbite ferrite crystal grains is 8 or less per 100 crystal grains.

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