阅读说明：本技术 铁氧体烧结磁铁及旋转电机 (Ferrite sintered magnet and rotating electrical machine ) 是由 室屋尚吾 村川喜堂 森田启之 池田真规 于 2021-03-22 设计创作，主要内容包括：本发明得到一种铁氧体烧结磁铁,其具有高的剩余磁通密度(Br)及高的矫顽力(HcJ),制造稳定性良好,能够以更低成本进行制作。所述铁氧体烧结磁铁包含A、R、Fe及Co,并且具有能够表示为A-(1－x)R-x(Fe-(12－y)Co-y)-zO-(19)(原子数比)的六方晶M型铁氧体。A为选自Sr、Ba及Pb中的1种以上。R为选自稀土元素中的1种以上。作为R,至少包含La。满足0.14≤x≤0.22、11.60≤(12－y)z≤11.99、0.13≤yz≤0.17。在将铁氧体烧结磁铁中所含的Ca换算成氧化物时,将CaO的含量设为Mc(质量％),满足0.30≤Mc≤0.63。(The invention provides a ferrite sintered magnet which has high residual magnetic flux density (Br) and high coercive force (HcJ), has good manufacturing stability and can be manufactured at lower cost. The ferrite sintered magnet comprises A, R, Fe and Co, and has a magnetic structure represented by A 1－x R x (Fe 12－y Co y ) z O 19 Hexagonal M-type ferrite (atomic ratio). A is more than 1 selected from Sr, Ba and Pb. R is more than 1 selected from rare earth elements. R is at least La. X is more than or equal to 0.14 and less than or equal to 0.22, z is more than or equal to 11.60 and less than or equal to 11.99, and yz is more than or equal to 0.13 and less than or equal to 0.17. When Ca contained in the ferrite sintered magnet is converted into an oxide, the content of CaO satisfies 0.30 Mc 0.63 in terms of mass%.)

1. A ferrite sintered magnet, wherein,

the ferrite sintered magnet comprises A, R, Fe and Co, and has a ratio A expressed by atomic number_1－xR_x(Fe_12－yCo_y)_zO₁₉The hexagonal M-type ferrite of (1), wherein,

a is more than 1 selected from Sr, Ba and Pb,

r is 1 or more selected from rare earth elements, and R is at least La,

x is more than or equal to 0.14 and less than or equal to 0.22

11.60≤(12－y)z≤11.99

0.13≤yz≤0.17，

Wherein the content of CaO is Mc by mass% when Ca contained in the sintered ferrite magnet is converted to oxides,

mc is more than or equal to 0.30 and less than or equal to 0.63.

2. The ferrite sintered magnet according to claim 1,

converting Si contained in the ferrite sintered magnet into an oxide, SiO₂The content of (b) is set to Ms mass%,

ms is more than or equal to 0.35 and less than or equal to 0.60.

3. The ferrite sintered magnet according to claim 1 or 2,

the content of BaO is Mb mass% when Ba contained in the ferrite sintered magnet is converted into oxide,

mb is more than or equal to 0 and less than or equal to 0.15.

4. The ferrite sintered magnet according to claim 1 or 2,

converting Al contained in the ferrite sintered magnet into an oxide₂O₃The content of (c) is defined as Ma mass%,

ma is more than or equal to 0 and less than or equal to 0.90.

5. The ferrite sintered magnet according to claim 1 or 2,

converting Cr contained in the ferrite sintered magnet into an oxide₂O₃The content of (b) is defined as Mr mass%,

mr is more than or equal to 0 and less than or equal to 0.10.

6. A rotating electric machine, wherein,

the rotating electrical machine has the ferrite sintered magnet according to any one of claims 1to 5.

Technical Field

The present invention relates to a ferrite sintered magnet and a rotating electrical machine.

Background

In order to obtain a ferrite sintered magnet having excellent magnetic characteristics (high remanence Br, high coercive force HcJ), there is known a hexagonal M-type ferrite using Sr ferrite containing at least Sr.

Patent document 1 discloses Sr ferrite containing at least La as a rare earth element and having a part of Fe substituted by Co, as the Sr ferrite. By using Sr ferrite containing La and Co as essential elements, a ferrite sintered magnet having high Br and high HcJ can be obtained.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 3337990

Disclosure of Invention

Technical problem to be solved by the invention

The purpose of the present invention is to obtain a ferrite sintered magnet which has a low amount of Co, a high Br and a high HcJ, and has good production stability.

Technical solution for solving technical problem

In order to achieve the above object, the sintered ferrite magnet of the present invention comprises A, R, Fe and Co, and has a magnetic core represented by A_1－xR_x(Fe_12－yCo_y)_zO₁₉Hexagonal M-type ferrite (atomic ratio),

a is more than 1 selected from Sr, Ba and Pb,

r is 1 or more selected from rare earth elements, and R is at least La.

X is more than or equal to 0.14 and less than or equal to 0.22

11.60≤(12－y)z≤11.99

0.13≤yz≤0.17，

When the Ca contained in the sintered ferrite magnet is converted into an oxide, the content of CaO is Mc (mass%),

mc is more than or equal to 0.30 and less than or equal to 0.63.

Converting Si contained in the ferrite sintered magnet into an oxide, SiO₂Is set to Ms (mass%),

or can satisfy Ms of more than or equal to 0.35 and less than or equal to 0.60.

When Ba contained in the ferrite sintered magnet is converted into oxide, the content of BaO is Mb (mass%),

it is also possible to satisfy 0. ltoreq. Mb.ltoreq.0.15.

Converting Al contained in the ferrite sintered magnet into an oxide₂O₃The content of (C) is Ma (mass%),

ma may be 0 or more and 0.90 or less.

Converting Cr contained in the ferrite sintered magnet into an oxide₂O₃The content of (D) is Mr (% by mass),

it is also possible to satisfy 0. ltoreq. Mr.ltoreq.0.10.

The rotating electric machine of the present invention includes the above ferrite sintered magnet.

Detailed Description

The present invention will be described below based on embodiments.

The ferrite sintered magnet of the present embodiment includes A, R, Fe and Co, and has a magnetic core represented by A_1－xR_x(Fe_12－yCo_y)_zO₁₉A ferrite sintered magnet of hexagonal M-type ferrite (atomic ratio). In the present specification, the ferrite sintered magnet according to the present embodiment is sometimes referred to as a ferrite sintered magnet.

A is more than 1 selected from strontium (Sr), barium (Ba) and lead (Pb).

R is at least 1 selected from rare earth elements, and at least lanthanum (La), x, (12-y) z and yz satisfy the following formula.

0.14≤x≤0.22

11.60≤(12－y)z≤11.99

0.13≤yz≤0.17

When calcium (Ca) contained in the ferrite sintered magnet is converted into an oxide, the content of CaO is Mc (mass%),

mc is more than or equal to 0.30 and less than or equal to 0.63.

The ferrite sintered magnet has a magnetic core represented by A_1－xR_x(Fe_12－yCo_y)_zO₁₉Hexagonal M-type ferrite (atomic ratio).

Specifically, ferriteThe sintered magnet comprises a magnet represented by formula A_1－xR_x(Fe_12－yCo_y)_zO₁₉Ferrite particles (atomic ratio). The ferrite particles are crystalline particles and have a hexagonal magnetoplumbite-type crystal structure. The ferrite particles having a hexagonal magnetoplumbite type crystal structure can be confirmed by, for example, X-ray structural diffraction.

Furthermore, when Ca contained in the ferrite sintered magnet is converted into an oxide, the content of CaO satisfies 0.30 Mc 0.63 in terms of mass%.

The ferrite sintered magnet has a small Co content (yz). Since the ferrite sintered magnet has a small amount of residual Co, the generation of a heterogeneous phase is suppressed and a uniform microstructure is formed. Thus, the ferrite sintered magnet has high Br and high HcJ. The Ca content of the ferrite sintered magnet is suppressed. The variation in grain growth with respect to the variation in firing temperature becomes small. This improves the production stability of the ferrite sintered magnet. Further, the ferrite sintered magnet has a small Co content (yz), and thus can be produced at low cost.

A is at least 1 selected from Sr, Ba and Pb. The Sr content in a may be 90 at% or more, or a may be Sr alone. The content of Ba in a may be 1 at% or less.

R is 1 or more selected from rare earth elements, and R is at least La. The content of La in R may be 90 at% or more, or R may be only La.

When x is too small, Br and production stability are lowered. If x is too large, HcJ and production stability are lowered. Further, it is preferable that 0.14. ltoreq. x.ltoreq.0.18 is satisfied. The production stability means that the change in magnetic properties (particularly HcJ) is small even if the firing temperature changes.

When (12-y) z is too small, HcJ and production stability are lowered. In the case where (12-y) z is too large, Br and/or HcJ are decreased. The production stability is also liable to be lowered. Further, it is preferable that z.ltoreq.11.99 is satisfied at 11.66. ltoreq. (12-y).

If yz is too small, HcJ and production stability are lowered. When yz is too large, Br is reduced and cost is increased. Further, it is preferable that 0.14. ltoreq. yz. ltoreq.0.17 is satisfied.

When the CaO content is too small, Br decreases. When the content of CaO is too large, production stability is lowered. When 0.30. ltoreq. Mc.ltoreq.0.60 is satisfied, the production stability is more likely to be improved.

The ferrite sintered magnet may also contain silicon (Si). When Si contained in the ferrite sintered magnet is converted to an oxide, SiO is added₂Is set to Ms (mass%),

can satisfy Ms is more than or equal to 0.35 and less than or equal to 0.60, and can also satisfy Ms is more than or equal to 0.46 and less than or equal to 0.60.

By SiO₂When the content of (b) is within the above range, Br and HcJ tend to be high, and production stability tends to be good. SiO 2₂The smaller the content of (A), the more the HcJ tends to decrease. SiO 2₂The more the content of (A), the more the Br tends to decrease. Further, when Ms is 0.45. ltoreq. Ms.ltoreq.0.60, the magnetic properties are appropriately maintained and the manufacturing stability is easily improved.

The ferrite sintered magnet may contain Ba. When Ba contained in the ferrite sintered magnet is converted into oxide, the content of BaO is Mb (mass%),

mb is not less than 0 and not more than 0.15, Mb is not less than 0.03 and not more than 0.15, and Mb is not less than 0.03 and not more than 0.12.

If the content of BaO is too large, Br is liable to decrease. When 0.03. ltoreq. Mb.ltoreq.0.12 is satisfied, Br is easily increased while HcJ and production stability are maintained well.

Further, Ba may be contained in the ferrite sintered magnet as A_1－xR_x(Fe_12－yCo_y)_zO₁₉A of (2) may be contained in the ferrite sintered magnet as a component other than A_1－xR_x(Fe_12－yCo_y)_zO₁₉Other Ba compounds or Ba monomers.

The ferrite sintered magnet may contain aluminum (Al). When Al contained in the ferrite sintered magnet is converted into an oxide, Al is added₂O₃The content of (B) is Ma (% by mass)，

Ma is more than or equal to 0 and less than or equal to 0.90, Ma is more than or equal to 0.05 and less than or equal to 0.90, and Ma is more than or equal to 0.10 and less than or equal to 0.70.

If Al is present₂O₃If the content of (b) is too large, Br tends to be reduced. In addition, Al₂O₃The smaller the content of (A), the more likely the HcJ is to be reduced. When Ma is 0.10. ltoreq.0.70, Br, HcJ and production stability are easily maintained.

The ferrite sintered magnet may contain chromium (Cr). Converting Cr contained in a ferrite sintered magnet into an oxide₂O₃The content of (D) is Mr (% by mass),

mr can be more than or equal to 0 and less than or equal to 0.10, and Mr can be more than or equal to 0.05 and less than or equal to 0.10.

If Cr is present₂O₃If the content of (b) is too large, Br tends to be reduced. In addition, Cr₂O₃The smaller the content of (A), the more likely the HcJ is to be reduced. When Mr is 0.05. ltoreq.Mr.ltoreq.0.10, Br, HcJ and production stability are easily maintained satisfactorily.

The ferrite sintered magnet may also contain manganese (Mn), magnesium (Mg), copper (Cu), nickel (Ni), and/or zinc (Zn) as impurities. The content of these impurities is not particularly limited, but the total content of these impurities may be 100 mass% and 0.5 mass% or less, respectively. These impurities may be contained in a total amount of 0.7% by mass or less.

The ferrite sintered magnet may further contain elements other than the above elements, specifically, elements other than a, R, Fe, Co, O, Ca, Si, Al, Cr, Mn, Mg, Cu, Ni, and Zn as inevitable impurities. The total amount of the inevitable impurities may be 3% by mass or less, with the total amount of the ferrite sintered magnet being 100% by mass.

The method for calculating Mc will be described below. The same applies to the methods for calculating Ms, Mb, Ma, and Mr.

First, the content of Ca contained in the ferrite sintered magnet was measured by a method generally used in the art. Then, the content of Ca was converted to oxide (CaO). Sintered magnet of ferriteThe above elements other than O contained in iron, specifically, a, R, Fe, Co, Ca, Si, Ba, Al, Cr, Mn, Mg, Cu, Ni, and Zn were also measured in the same manner and converted into oxides. Specifically, conversion to AO and R₂O₃、Fe₂O₃、Co₃O₄、CaO、SiO₂、BaO、Al₂O₃、Cr₂O₃MnO, MgO, CuO, NiO, ZnO. Further, the content of the inevitable impurities is measured in the same manner and appropriately converted to oxides.

Then, Mc can be calculated by dividing the CaO content by the total content of all the oxides.

The density of the ferrite sintered magnet is not particularly limited. For example, the density measured by the Archimedes method may be 4.9g/cm³Above 5.2g/cm³The following. The pass density is in the above range, particularly 5.0g/cm³Above, Br is likely to be good.

The method for producing the sintered ferrite magnet according to the present embodiment will be described below.

In the following embodiments, an example of a method for manufacturing a ferrite sintered magnet is shown. In the present embodiment, the ferrite sintered magnet can be manufactured through a blending step, a pre-firing step, a pulverizing step, a molding step, and a firing step. The respective steps will be explained below.

< working procedure of compounding >

In the blending step, a raw material of the ferrite sintered magnet is blended to obtain a raw material mixture. As the raw material of the ferrite sintered magnet, a compound (raw material compound) containing 1 or 2 or more of the elements constituting the raw material of the ferrite sintered magnet is exemplified. The raw material compound is preferably a powdery raw material, for example.

Examples of the raw material compound include oxides of the respective elements and compounds (carbonate, hydroxide, nitrate, etc.) which become oxides by firing. For example, SrCO can be exemplified₃、BaCO₃、PbCO₃，La₂O₃、Fe₂O₃、Co₃O₄、CaCO₃、SiO₂、MgO、Al₂O₃、Cr₂O₃MnO, MgO, NiO, CuO, ZnO, etc. The average particle diameter of the powder of the raw material compound may be about 0.1to 2.0. mu.m.

For the compounding, for example, each raw material is weighed to have a desired composition of the ferrite magnetic material. Then, the mixture can be mixed and pulverized for about 0.1to 20 hours by using a wet mill, a ball mill, or the like. In this blending step, it is not necessary to mix all the raw materials, and a part of the raw materials may be added after the calcination described below.

< Pre-burning Process >

In the calcination step, the raw material mixture obtained in the blending step is calcined. The calcination can be performed in an oxidizing atmosphere such as air. The temperature of the pre-firing is preferably in the range of 1100 ℃ to 1300 ℃. The time for the calcination may be set to 1 second to 10 hours.

The calcined body obtained by the calcination may have a primary particle diameter of 10 μm or less.

< crushing Process >

In the pulverizing step, the calcined material that has been granulated or agglomerated in the calcining step is pulverized into a powder. This facilitates molding in a molding step described later. In the pulverizing step, as described above, a raw material that is not blended in the blending step (after the addition of the raw material) may be added. The pulverizing step may be performed, for example, in a 2-stage step of pulverizing the calcined body into coarse powder (coarse pulverization) and then further finely pulverizing the coarse powder (fine pulverization).

The coarse pulverization is carried out, for example, using a vibration mill until the average particle diameter becomes 0.5 to 10.0. mu.m. In the micro-pulverization, the coarsely pulverized material obtained in the coarse pulverization is further pulverized by a wet mill, a ball mill, a jet mill, or the like.

In the fine pulverization, the fine pulverization is carried out so that the average particle diameter of the obtained fine pulverized material is preferably about 0.08 μm to 1.00. mu.m. The specific surface area of the finely divided material (obtained by, for example, the BET method) can be set to 4m²/g～12m²And about/g. The crushing time is not due to the crushing methodSimilarly, for example, about 30 minutes to 20 hours can be set for a wet grinding mill, and about 1 hour to 50 hours can be set for wet grinding by a ball mill.

In the fine pulverization step, in the case of a wet method, a nonaqueous solvent such as toluene or xylene can be used as a dispersion medium in addition to an aqueous solvent such as water. The use of the nonaqueous solvent tends to result in high orientation in wet molding described later. On the other hand, when an aqueous solvent such as water is used, it is advantageous from the viewpoint of productivity.

In the fine grinding step, for example, a known polyol or dispersant may be added to improve the degree of orientation of the sintered body obtained after firing.

< Molding and firing Process >

In the molding and firing step, a molded body is obtained by molding a pulverized material (preferably a finely pulverized material) obtained after the pulverizing step, and then the molded body is fired to obtain a sintered body. The Molding can be performed by any of dry Molding, wet Molding, or Ceramic Injection Molding (CIM).

In the dry molding method, for example, a dried magnetic powder is subjected to pressure molding while applying a magnetic field to form a molded body, and then the molded body is fired. In general, dry molding methods have an advantage that the time required for the molding step is short because dry magnetic powder is press-molded in a mold.

In the wet molding method, for example, a slurry containing magnetic powder is subjected to pressure molding in the presence of a magnetic field, while removing a liquid component to form a molded body, and then the molded body is fired. In the wet molding method, there is an advantage that the magnetic powder is easily oriented by a magnetic field during molding, and the magnetic properties of the sintered magnet are good.

The molding method using CIM is a method in which dried magnetic powder is heated and kneaded together with a binder resin, pellets (beads) formed by the kneading are injection-molded in a mold to which a magnetic field is applied, a preliminary molded body is obtained, and the preliminary molded body is subjected to binder removal treatment and then fired.

The wet molding will be described in detail below.

(Wet Molding and baking)

When a ferrite sintered magnet is obtained by a wet molding method, the above-described fine pulverization step is performed in a wet manner to obtain a slurry. The slurry was concentrated to a predetermined concentration to obtain a slurry for wet molding. The molding can be performed using a slurry for wet molding.

The concentration of the slurry can be performed by centrifugal separation, a filter press, or the like. The content of the fine grinding agent in the wet molding slurry can be about 30 to 80 mass% of the total amount of the wet molding slurry.

In the slurry, water can be used as a dispersion medium for dispersing the finely divided material. In this case, a surfactant such as gluconic acid, gluconate, sorbitol or the like may be added to the slurry. Further, as the dispersion medium, a nonaqueous solvent may also be used. As the nonaqueous solvent, an organic solvent such as toluene or xylene can be used. In this case, a surfactant such as oleic acid may be added.

The wet molding slurry may be prepared by adding a dispersion medium to the finely pulverized material in a dry state after the fine pulverization.

In the wet molding, the slurry for wet molding is then molded in a magnetic field. In this case, the molding pressure can be set to 9.8MPa to 98MPa (0.1 ton/cm)²～1.0ton/cm²) Left and right. The applied magnetic field can be about 400kA/m to 1600 kA/m. The pressing direction and the magnetic field application direction during molding may be the same direction or may be orthogonal to each other.

The firing of the molded article obtained by wet molding can be performed in an oxidizing atmosphere such as air. The firing temperature can be set to 1050 to 1270 ℃. The firing time (the time for maintaining the temperature at the firing temperature) can be set to about 0.5 to 3 hours. Then, the sintered ferrite magnet is obtained by firing.

In addition, in the case of obtaining a molded article by wet molding, the molded article can be heated from room temperature to about 100 ℃ at a temperature rise rate of about 2.5 ℃/min before reaching the firing temperature. By sufficiently drying the molded article, the occurrence of cracks can be suppressed.

Further, when a surfactant (dispersant) or the like is added, these can be sufficiently removed (degreasing treatment) by heating at a temperature rise rate of about 2.0 ℃/min, for example, in a temperature range of about 100 ℃ to 500 ℃. These treatments may be performed at the initial stage of the firing step, or may be performed separately from the firing step.

Although the preferred method for producing the ferrite sintered magnet has been described above, the production method is not limited to the above, and the production conditions and the like can be changed as appropriate.

The shape of the ferrite sintered magnet of the present invention is not limited. For example, the ferrite sintered magnet may have various shapes such as an arc segment shape having anisotropy, a flat plate shape, a cylindrical shape, and a cylindrical shape. According to the sintered ferrite magnet of the present invention, high HcJ can be maintained and high Br can be obtained regardless of the shape of the magnet. Further, the ferrite sintered magnet of the present invention is excellent in production stability.

The use of the ferrite sintered magnet obtained by the present invention is not particularly limited, but the ferrite sintered magnet can be used for, for example, a rotating electrical machine. The rotating electric machine according to the present invention includes the above ferrite sintered magnet. Further, the kind of the rotating electric machine is not particularly limited. Examples thereof include a motor and a generator.

Examples

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

< working procedure of compounding >

SrCO was prepared as a starting material₃、La₂O₃、Fe₂O₃、Co₃O₄、CaCO₃、SiO₂、BaCO₃、Al₂O₃And Cr₂O₃The final compositions of the ferrite sintered magnets were weighed as shown in tables 1to 9Composition of each sample.

Removing La from the above starting material₂O₃And Co₃O₄The other raw materials were mixed and pulverized by a wet mill to obtain a slurry-like raw material mixture.

< Pre-burning Process >

This raw material mixture was dried and then subjected to a pre-firing treatment at 1200 ℃ for 2 hours in the air to obtain a pre-fired body.

< crushing Process >

The obtained calcined body was coarsely pulverized by a rod mill to obtain a coarsely pulverized material. Then, La was added₂O₃And Co₃O₄Then, the resulting mixture was finely pulverized for 28 hours by a wet ball mill to obtain a slurry. The obtained slurry is used for wet molding, and the solid content concentration of the slurry is adjusted to 70-75 mass%.

< Molding and firing Process >

Subsequently, a preliminary molded body was obtained using a wet magnetic field molding machine. The molding pressure was 50MPa, and the applied magnetic field was 800 kA/m. The pressing direction and the magnetic field application direction during molding are set to the same direction. The preliminary molded article obtained by wet molding was in the form of a disk having a diameter of 30mm and a height of 15 mm.

The green compact was fired in the air at the optimum firing temperature for 1 hour to obtain a ferrite sintered magnet as a sintered compact.

Hereinafter, a method of determining the optimum firing temperature in the present example will be described.

First, the composition of each experimental example was fired at a firing temperature of 1190 to 1230 ℃ every 10 ℃ to prepare a sintered body. That is, a total of 5 sintered bodies were prepared based on each experimental example. Then, the density of each sintered body was measured, and the sintering temperature of the sintered body having the highest density was set as the optimum sintering temperature. The density of the sintered body was measured by the archimedes method.

Quantitative fluorescent X-ray analysis was performed on each of the ferrite sintered magnets, and it was confirmed that each of the ferrite sintered magnets had the composition shown in tables 1to 9.

In addition, it was confirmed by X-ray diffraction measurement that each of the ferrite sintered magnets in tables 1to 9 had a hexagonal M-type structure.

< measurement of magnetic Properties (Br, HcJ) >

In each experimental example, after processing the upper and lower surfaces of each ferrite sintered magnet obtained by sintering at an optimum sintering temperature, the magnetic properties were measured in an atmosphere of 25 ℃ using a B-H tracer with a maximum applied magnetic field of 1989 kA/m. The results are shown in tables 1to 9.

< measurement of sintering temperature dependence (. DELTA.HcJ) >)

HcJ was measured when firing was carried out at the optimum firing temperature of-10 ℃ and the optimum firing temperature +10 ℃. Then, the difference between the maximum value and the minimum value of HcJ is set to Δ HcJ. The smaller Δ HcJ, the better the production stability, and when Δ HcJ is less than 10.0kA/m, the better the production stability.

< cost fence >

In the cost column of the present experimental example, the content (yz) of Co, which is a high-cost raw material, is determined as pass when yz is not more than 0.17, and is determined as fail when yz > 0.17.

As is clear from tables 1to 9, in each of examples in which x, (12-y) z and yz are in specific ranges and Mc is in a specific range, Br and HcJ were good, production stability was good, and cost was excellent. Specifically, all examples had Br in excess of 435 mT. In addition, all examples had HcJ exceeding 345 kA/m. On the other hand, when any of x, (12-y) z, yz and Mc is out of the specific range, Br and HcJ, production stability and/or cost are deteriorated.

In the presence of SiO₂、BaO、Al₂O₃And/or Cr₂O₃When the amounts are included in the respective preferable ranges, the magnetic properties are more easily improved.