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  • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
  • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
  • H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
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  • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
  • H01F41/0266—Moulding; Pressing
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  • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
  • H01F41/0293—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets

Definitions

• the present invention relates to RTB system permanent magnets.
• Patent Document 1 describes an invention relating to an R--Fe--B based sintered magnet having a high coercive force (HcJ) at high temperatures due to its specific composition and microstructure.
• HcJ high coercive force
• Patent Document 2 describes an invention relating to an R--(Fe, Co)--B based sintered magnet having a high HcJ at room temperature and high temperature due to its specific composition and microstructure.
• JP 2017-228771 A Japanese Patent Application Laid-Open No. 2018-82040
• the present invention provides an RTB-based permanent magnet in which the residual magnetic flux density (Br) at room temperature and HcJ at high temperature are improved in a well-balanced manner, and the squareness ratio (Hk/HcJ) at room temperature is high. for the purpose.
• the RTB system permanent magnet comprises: An RTB permanent magnet containing Al, Cu, Ga and Zr, Assuming that the RTB permanent magnet is 100% by mass, The content of R is 30.00% by mass or more and 33.00% by mass or less, Co content is greater than 0.80% by mass and 3.00% by mass or less, The content of B is 0.70% by mass or more and 0.83% by mass or less, Al content is greater than 0% by mass and less than 0.20% by mass, Cu content is greater than 0.10% by mass and less than 1.50% by mass, Ga content is 0.40% by mass or more and 1.00% by mass or less, The Zr content is greater than 0.10% by mass and 1.60% by mass or less.
• the content of C may be 0.05% by mass or more and 0.30% by mass or less.
• the content of heavy rare earth elements may be 0% by mass or more and 0.30% by mass or less.
• Br L (mT) be the residual magnetic flux density of the RTB system permanent magnet at room temperature
• HcJ H (kA/m) the coercive force of the RTB system permanent magnet at 150° C.
• the squareness ratio at room temperature may be 92.0% or more.
• the RTB system permanent magnet contains Al, Cu, Ga and Zr. With the RTB system permanent magnet as 100% by mass, the content of R is 30.00% by mass or more and 33.00% by mass or less, and the content of Co is 0.80% by mass or more and 3.00% by mass.
• the content of B is 0.70% by mass or more and 0.83% by mass or less
• the content of Al is more than 0% by mass and less than 0.20% by mass
• the content of Cu is more than 0.10% by mass and 1 less than .50% by mass
• a Ga content of 0.40% by mass or more and 1.00% by mass or less a Zr content of more than 0.10% by mass and 1.60% by mass or less.
• R represents a rare earth element
• T represents an iron group element
• B represents boron
• RTB based permanent magnets are permanent magnets containing one or more rare earth elements, one or more iron group elements, and boron.
• the iron group element is a generic term for Fe, Co and Ni.
• RTB system permanent magnets contain main phase grains having an R 2 T 14 B type crystal structure.
• the content of R that is, the content of rare earth elements is 30.00% by mass or more and 33.00% by mass or less.
• the content of the rare earth element may be 30.00% by mass or more and 32.00% by mass or less.
• Br at room temperature is easily improved. Become. If the R content is too small, the HcJ at high temperatures tends to be low. If the content of R is too large, abnormal grain growth tends to occur, and Br at room temperature tends to decrease.
• the RTB system permanent magnet may contain substantially only one or more selected from Nd, Pr, Dy and Tb as rare earth elements, and substantially contain only one or more selected from Nd and Pr. may contain. It should be noted that the fact that the RTB system permanent magnet substantially contains only one or more selected from Nd, Pr, Dy and Tb as rare earth elements means that rare earth elements other than Nd, Pr, Dy and Tb are contained. It means that the total amount is 0.01% by mass or less. That the RTB permanent magnet substantially contains only one or more selected from Nd and Pr as rare earth elements means that the total content of rare earth elements other than Nd and Pr is 0.01% by mass or less. It means that it is
• the content of heavy rare earth elements may be 0% by mass or more and 0.80% by mass or less, or may be 0% by mass or more and 0.50% by mass or less, in order to reduce raw material costs. It may be 0% by mass or more and 0.30% by mass or less.
• Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu are heavy rare earth elements.
• RTB system permanent magnets contain Co as an essential element.
• the content of Co is more than 0.80% by mass and 3.00% by mass or less. 0.85 mass % or more and 3.00 mass % or less may be sufficient. If the Co content is too small, the HcJ at high temperatures is lowered and the Hk/HcJ is also lowered. If the Co content is too high, the HcJ at high temperatures will decrease.
• Ni does not have to be contained substantially. Specifically, the Ni content may be less than 0.01% by mass.
• the content of B is 0.70% by mass or more and 0.83% by mass or less. If the B content is too small, sintering tends to be insufficient. As a result, both Br at room temperature and HcJ at high temperature tend to be low. Furthermore, Hk/HcJ is likely to decrease. If the B content is too large, the HcJ at high temperatures tends to be low.
• the content of Al is greater than 0% by mass and less than 0.20% by mass. 0.02 mass % or more and 0.15 mass % or less may be sufficient, and 0.02 mass % or more and 0.07 mass % or less may be sufficient.
• HcJ at high temperature becomes low. If the Al content is too high, the Br at room temperature will be low.
• the content of Ga is 0.40% by mass or more and 1.00% by mass or less.
• the content of Ga may be 0.40% by mass or more and 0.80% by mass or less.
• the content of Zr is more than 0.10% by mass and 1.60% by mass or less. It may be 0.15% by mass or more and 1.50% by mass or less, 0.35% by mass or more and 1.30% by mass or less, or 0.35% by mass or more and 0.95% by mass or less. good too.
• the content may be 0.50% by mass or more and 1.50% by mass or less. If the Zr content is too small, the magnetic grains contained in the RTB system permanent magnet tend to grow. As a result, HcJ at high temperatures tends to decrease. If the Zr content is too large, sintering tends to be insufficient. As a result, both Br at room temperature and HcJ at high temperature tend to be low.
• the Cu content is greater than 0.10% by mass and less than 1.50% by mass. 0.15 mass % or more and 1.00 mass % or less may be sufficient, and 0.15 mass % or more and 0.30 mass % or less may be sufficient. When the Cu content is too small or too large, both Br at room temperature and HcJ at high temperature tend to be low. When the Cu content is 0.15% by mass or more and 1.00% by mass or less, it becomes easy to improve Br at room temperature and HcJ at high temperature in a well-balanced manner.
• the Cu content may be 0.15% by mass or more and 0.30% by mass or less.
• the Cu content is 0.15% by mass or more and 0.30% by mass or less, it becomes easier to improve HcJ at high temperatures compared to when the Cu content exceeds 0.30% by mass.
• the RTB system permanent magnet may contain O, N and/or C or may not contain O, N and/or C as required.
• the content of O may be 0% by mass or more and 0.20% by mass or less.
• the content of N may be 0% by mass or more and 0.10% by mass or less.
• the content of C may be 0.05% by mass or more and 0.30% by mass or less, or may be 0.13% by mass or more and 0.26% by mass or less.
• the content of C is within the above range, it becomes easier to improve Br at room temperature and HcJ at high temperature in a well-balanced manner, and also to improve Hk/HcJ.
• Making the RTB system permanent magnet 100% by mass means that the total content of all elements is 100% by mass.
• the Fe content in the RTB system permanent magnet may be the substantial remainder in the RTB system permanent magnet.
• the total content of elements other than the above elements that is, elements other than rare earth elements, Fe, Co, Ni, B, Al, Ga, Zr, Cu, O, N and C, is 0.50 % by mass or less.
• a method for manufacturing an RTB system permanent magnet (RTB system sintered magnet) according to this embodiment includes the following steps. Note that steps (g) to (i) shown below may be omitted.
• alloy preparation process First, a raw material alloy is prepared (alloy preparation step).
• the strip casting method will be described below as an example of the alloy preparation method, but the alloy preparation method is not limited to the strip casting method.
• a raw material metal corresponding to the composition of the raw material alloy is prepared, and the prepared raw material metal is melted in a vacuum or an inert gas atmosphere such as Ar gas. After that, a raw material alloy is produced by casting the melted raw material metal.
• a two-alloy method in which two alloys, a first alloy and a second alloy, are mixed to produce a raw material alloy may also be used.
• the type of raw metal there are no particular restrictions on the type of raw metal.
• rare earth metals, rare earth alloys, pure iron, pure cobalt, ferroboron, and alloys and compounds thereof can be used.
• the casting method for casting the raw material metal is not particularly limited. For example, an ingot casting method, a strip casting method, a book mold method, a centrifugal casting method, and the like can be used.
• the obtained raw material alloy may be subjected to homogenization treatment (solution treatment) as necessary when solidification segregation is present.
• the raw material alloy is pulverized (pulverization step).
• the pulverization process may be carried out in two stages: a coarse pulverization process for pulverizing to a particle size of about several hundred ⁇ m to several mm, and a fine pulverization process for pulverizing to a particle size of about several ⁇ m. It may be carried out in a single step of pulverization only.
• Coarse pulverization process The raw material alloy is coarsely pulverized to a particle size of about several hundred ⁇ m to several mm (rough pulverization step). As a result, a coarsely pulverized powder of the raw material alloy is obtained.
• Coarse pulverization may be performed, for example, by hydrogen absorption pulverization.
• Hydrogen absorption pulverization can be carried out by allowing the material alloy to absorb hydrogen and then releasing hydrogen based on the difference in the amount of hydrogen absorption between different phases, thereby causing self-collapsing pulverization.
• the release of hydrogen based on the difference in hydrogen storage capacity between different phases is called dehydrogenation.
• the conditions for dehydrogenation are not particularly limited, but dehydrogenation is performed, for example, at 300 to 650° C. in an argon flow or in vacuum.
• the method of coarse pulverization is not limited to the hydrogen absorption pulverization described above.
• coarse pulverization may be performed in an inert gas atmosphere using a coarse pulverizer such as a stamp mill, jaw crusher, or brown mill.
• the atmosphere in each step from the coarse pulverization step to the sintering step described later has a low oxygen concentration.
• the oxygen concentration is adjusted by controlling the atmosphere in each manufacturing process. If the oxygen concentration in each manufacturing process is high, the rare earth element in the alloy powder obtained by pulverizing the raw material alloy is oxidized to form an oxide of the rare earth element. The oxide of the rare earth element is not reduced during sintering, and is deposited as it is at the grain boundaries in the form of the oxide of the rare earth element. A grain boundary is a portion existing between two or more main phase grains. As a result, the Br of the obtained RTB system permanent magnet is lowered. Therefore, for example, each step (pulverization step, molding step) is preferably carried out in an atmosphere with an oxygen concentration of 100 ppm or less.
• the obtained coarsely pulverized powder of the raw material alloy is finely pulverized to an average particle size of about several ⁇ m (fine pulverization step).
• fine pulverization step After coarsely pulverizing the raw material alloy, the obtained coarsely pulverized powder of the raw material alloy is finely pulverized to an average particle size of about several ⁇ m (fine pulverization step).
• fine pulverization step As a result, a finely pulverized powder of the raw material alloy is obtained.
• a finely pulverized powder can be obtained.
• D50 of the particles contained in the finely ground powder There is no particular limitation on the D50 of the particles contained in the finely ground powder.
• D50 may be 2.0 ⁇ m or more and 4.5 ⁇ m or less, or may be 2.5 ⁇ m or more and 3.5 ⁇ m or less.
• the HcJ of the RTB system permanent magnet according to the present embodiment is more easily improved as the D50 is smaller.
• abnormal grain growth tends to occur in the sintering process, and the upper limit of the sintering temperature range is lowered.
• the larger the D50 the less likely abnormal grain growth will occur in the sintering process, and the higher the upper limit of the sintering temperature range.
• the HcJ of the RTB system permanent magnet according to this embodiment tends to decrease.
• Fine pulverization is performed by further pulverizing the coarsely pulverized powder using a fine pulverizer such as a jet mill, ball mill, vibration mill, wet attritor, etc., while appropriately adjusting conditions such as pulverization time. .
• a fine pulverizer such as a jet mill, ball mill, vibration mill, wet attritor, etc.
• the jet mill will be described below.
• a high-pressure inert gas for example, He gas, N2 gas, Ar gas
• the high-speed gas flow coarsely pulverizes the raw material alloy.
• a pulverizing aid may be added when finely pulverizing the coarsely pulverized powder of the raw material alloy.
• the type of grinding aid is not particularly limited.
• an organic lubricant or a solid lubricant may be used.
• organic lubricants include oleic acid amide, lauric acid amide, and zinc stearate.
• Solid lubricants include, for example, graphite.
• the finely pulverized powder is molded into the desired shape (molding step).
• the finely pulverized powder is filled in a mold placed in an electromagnet and pressed to shape the finely pulverized powder to obtain a compact.
• a molding aid may be added. There are no particular restrictions on the type of molding aid. The same lubricant as the grinding aid may be used. Further, the pulverization aid may also serve as the molding aid.
• the pressure during pressurization may be, for example, 30 MPa or more and 300 MPa or less.
• the applied magnetic field may be, for example, 1000 kA/m or more and 1600 kA/m or less.
• the applied magnetic field is not limited to a static magnetic field, and may be a pulsed magnetic field. Also, a static magnetic field and a pulsed magnetic field can be used together.
• the shape of the molded body obtained by molding the finely pulverized powder is not particularly limited, and may be, for example, a rectangular parallelepiped, a flat plate, a column, a ring, or the like, depending on the desired shape of the RTB permanent magnet. shape.
• the magnet is molded in a magnetic field, and the compact obtained by molding into a desired shape is sintered in a vacuum or an inert gas atmosphere to obtain an RTB permanent magnet (sintering step).
• the holding temperature and holding time during sintering must be adjusted according to various conditions such as the composition (mainly the content of B), the pulverization method, and the difference in particle size and particle size distribution.
• the holding temperature may be, for example, 1000° C. or higher and 1100° C. or lower, or 1020° C. or higher and 1060° C. or lower.
• the retention time is not particularly limited, but may be, for example, 2 hours or more and 50 hours or less, or 8 hours or more and 40 hours or less. The shorter the holding time, the better the production efficiency.
• the atmosphere during holding There are no particular restrictions on the atmosphere during holding. For example, an inert gas atmosphere, a vacuum atmosphere of less than 100 Pa, or a vacuum atmosphere of less than 10 Pa may be used.
• the heating rate up to the holding temperature By sintering, the finely pulverized powder undergoes liquid phase sintering, and the RTB system permanent magnet according to this embodiment is obtained.
• the cooling rate after sintering the molded body to obtain a sintered body the sintered body may be rapidly cooled in order to improve production efficiency. Quenching may be performed at a rate of 30° C./min or more.
• the RTB system permanent magnet After sintering the compact, the RTB system permanent magnet is subjected to aging treatment (aging treatment step). After sintering, the obtained RTB permanent magnet is subjected to aging treatment, such as by maintaining the obtained RTB permanent magnet at a temperature lower than that during sintering.
• aging treatment is divided into two stages of the first aging treatment and the second aging treatment, but only one aging treatment may be performed, or three or more stages of aging treatment may be performed. .
• the first aging treatment may be performed at a holding temperature of 800° C. or higher and 900° C. or lower for 30 minutes or more and 4 hours or less.
• the heating rate to the holding temperature may be 5° C./min or more and 50° C./min or less.
• the atmosphere during the first aging treatment may be an inert gas atmosphere (for example, He gas, Ar gas) having a pressure higher than the atmospheric pressure.
• the second aging treatment may be performed under the same conditions as the first aging treatment, except that the holding temperature may be 450° C. or higher and 550° C. or lower. Aging treatment can improve the magnetic properties of RTB permanent magnets.
• the aging treatment step may be performed after the processing step described later.
• the RTB permanent magnet After the RTB permanent magnet is subjected to aging treatment (first aging treatment or second aging treatment), the RTB permanent magnet is rapidly cooled in an inert gas atmosphere (cooling step). As a result, the RTB system permanent magnet according to this embodiment can be obtained.
• a cooling rate is not particularly limited. It is good also as 30 degree-C/min or more.
• the obtained RTB system permanent magnet may be processed into a desired shape if necessary (processing step).
• processing methods include shape processing such as cutting and grinding, and chamfering processing such as barrel polishing.
• a heavy rare earth element may be further diffused into grain boundaries of the processed RTB permanent magnet (grain boundary diffusion step).
• grain boundary diffusion step There is no particular limitation on the grain boundary diffusion method.
• a compound containing a heavy rare earth element may be adhered to the surface of the RTB permanent magnet by coating or vapor deposition, and then heat treated.
• the heat treatment may be performed on the RTB system permanent magnet in an atmosphere containing the vapor of the heavy rare earth element.
• Grain boundary diffusion can further improve the HcJ of the RTB system permanent magnet.
• the RTB permanent magnet obtained by the above steps may be subjected to surface treatment such as plating, resin coating, oxidation treatment, chemical conversion treatment (surface treatment step). Thereby, corrosion resistance can be further improved.
• the RTB system permanent magnet obtained as described above has excellent magnetic properties. That is, Br at room temperature and HcJ at high temperature are improved in a well-balanced manner, and an RTB permanent magnet with high Hk/HcJ can be obtained.
• the Br at room temperature (23° C.) of the RTB permanent magnet is Br L (mT)
• the HcJ at the high temperature (150° C.) of the RTB permanent magnet is HcJ H ( kA/m)
• Hk/HcJ is 92.0% or more.
• hot forming and hot working may be performed instead of sintering in the method of manufacturing the RTB system permanent magnet.
• Example 1 (Alloy preparation process) In the alloy preparation step, raw material alloys from which RTB system permanent magnets finally having the compositions shown in Tables 1 to 4 were obtained were prepared.
• TRE means R content.
• the contents of elements other than Fe, which are not listed in Tables 1 to 4, are all less than 0.01% by mass. That is, in each of the examples and comparative examples shown in Tables 1 to 4, Fe is the substantial balance.
• a raw material metal having a predetermined element was prepared.
• Examples of raw metals include simple substances of the elements listed in Tables 1 to 4, alloys containing the elements listed in Tables 1 to 4, and/or compounds containing the elements listed in Tables 1 to 4. Select and prepare accordingly.
• raw material metals were weighed, and a raw material alloy was prepared by the strip casting method. At that time, raw material alloys were prepared from which magnets finally having the compositions shown in Tables 1 to 4 were obtained. The carbon content in the raw material alloy was controlled by changing the proportion of pig iron used in the raw material metal.
• Pulverization process In the pulverization step, the raw material alloy obtained in the preparation step was pulverized to obtain an alloy powder. Pulverization was performed in two steps of coarse pulverization and fine pulverization. Coarse pulverization was performed by hydrogen absorption pulverization. After hydrogen was occluded in the material alloy, dehydrogenation was performed at 300 to 600° C. in an argon flow or in vacuum. Coarse pulverization yielded an alloy powder having a particle size of about several hundred ⁇ m to several mm.
• Fine pulverization was performed by adding oleic acid amide as a pulverization aid to 100 parts by mass of the alloy powder obtained by coarse pulverization, mixing the mixture, and then using a jet mill. The amount of oleic acid amide added was controlled so as to finally obtain magnets having the compositions shown in Tables 1 to 4. Nitrogen gas was used in the jet mill. Fine pulverization was performed until D50 of the alloy powder reached about 3.0 ⁇ m.
• the alloy powder obtained in the pulverizing step was compacted in a magnetic field to obtain a compact.
• the alloy powder was filled in a mold placed in an electromagnet, it was compacted by applying pressure while applying a magnetic field from the electromagnet.
• the magnitude of the applied magnetic field was set to 1200 kA/m.
• the pressure during molding was set to 40 MPa.
• the obtained compact was sintered to obtain a sintered body.
• the holding temperature and holding time during sintering were appropriately changed according to the B content. Tables 1 to 4 show the holding temperature and holding time during sintering.
• the heating rate was 8.0° C./min when raising the temperature to the holding temperature, and the cooling rate was 50° C./min when cooling from the holding temperature to room temperature.
• the atmosphere during sintering was a vacuum atmosphere or an inert gas atmosphere.
• the obtained sintered body was subjected to aging treatment to obtain an RTB system permanent magnet. Aging treatment was performed in two stages, a first aging treatment and a second aging treatment.
• the heating rate was 8.0°C/min when the temperature was raised to the holding temperature
• the holding temperature was 900°C
• the holding time was 1.0 hour
• the cooling rate was when cooling from the holding temperature to room temperature. was 50°C/min.
• the atmosphere during the first aging treatment was an Ar atmosphere.
• the heating rate was 8.0°C/min when the temperature was raised to the holding temperature
• the holding temperature was 500°C
• the holding time was 1.5 hours
• the cooling rate was when cooling from the holding temperature to room temperature. was 50°C/min.
• the atmosphere during the second aging treatment was an Ar atmosphere.
• compositions of the RTB permanent magnets finally obtained in each of the examples and comparative examples are shown in Tables 1 to 4 because of X-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry. (ICP method) and composition analysis by gas analysis.
• ICP method X-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry.
• the C content was measured by combustion in an oxygen stream-infrared absorption method.
• the content of B was measured by the ICP method.
• HcJ H 600, Br L +(HcJ H /3) ⁇ 1565, and Hk/HcJ of 92.0% or more were evaluated as good.
• Table 1 shows examples and comparative examples in which the content of B and the content of Al are mainly changed.
• Each example in which the B content is 0.70% by mass or more and 0.83% by mass or less and the Al content is greater than 0 and less than 0.20% by mass has HcJ H ⁇ 600, Br L + (HcJ H /3) ⁇ 1565 was satisfied, and Hk/HcJ was 92.0% or more.
• sintering did not proceed sufficiently in Comparative Example 3, in which the B content was too small.
• Comparative Example 3 did not satisfy Br L +(HcJ H /3) ⁇ 1565, and Hk/HcJ also decreased significantly. None of the comparative examples in which the B content was too large satisfied HcJ H ⁇ 600. None of the comparative examples with too high Al content satisfied HcJ H ⁇ 600 or Br L +(HcJ H /3) ⁇ 1565.
• Table 2 shows examples and comparative examples in which the Co content of Example 9 was mainly changed. Furthermore, for reference, there are also comparative examples in which the Co content is mainly changed when the Al content is too high, and comparative examples in which the Co content is mainly changed when the B content is too high. Indicated. Each example in which the Co content is more than 0.80% by mass and 3.00% by mass or less satisfies HcJ H ⁇ 600, Br L + (HcJ H /3) ⁇ 1565, and Hk/HcJ is 92.0 % or more.
• the comparative example in which the B content is 0.70% by mass or more and 0.83% by mass or less but the Co content is too small does not satisfy Br L + (HcJ H /3) ⁇ 1565, and Hk /HcJ also decreased significantly. Comparative examples with too high Al content did not satisfy Br L +(HcJ H /3) ⁇ 1565. Comparative examples with too much B content did not satisfy HcJ H ⁇ 600.
• Table 3 shows examples and comparative examples in which the content of R (TRE), the content of Cu, the content of Ga, or the content of Zr was mainly changed.
• HcJ H ⁇ 600 or Br L + (HcJ H /3) ⁇ 1565 was not satisfied.
• Table 4 shows Examples 9 and 12 in which the ratio of Nd and Pr is constant and part of Nd and part of Pr are replaced with Dy or Tb. Even if a portion of Nd and a portion of Pr are replaced with Dy or Tb, each example in which the content of all elements is within the predetermined range has HcJ H ⁇ 600, Br L +(HcJ H /3) ⁇ 1565, and Hk/HcJ was 92.0% or more.

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