KR102438226B1 - Manufacturing method of sintered magnet and sintered magnet - Google Patents

Abstract

A method of manufacturing a sintered magnet according to an embodiment of the present invention includes preparing an additive in which an organic fluoride is coated on a surface of a rare earth hydride; and mixing the additive with a magnet powder and heating the mixture, wherein the magnet powder includes a rare earth-iron-boron-based powder.

Description

The manufacturing method of a sintered magnet, and a sintered magnet

The present invention relates to a method for manufacturing a sintered magnet and a sintered magnet. More specifically, it relates to a method for manufacturing an R-Fe-B sintered magnet and a sintered magnet manufactured by the method.

The NdFeB-based magnet is a permanent magnet having a composition of neodymium (Nd), a rare earth element, and Nd ₂ Fe ₁₄ B, a compound of iron and boron (B). After being developed in 1983, it has been used as a general-purpose permanent magnet for 30 years. These NdFeB-based magnets are used in various fields such as electronic information, automobile industry, medical equipment, energy, and transportation. In particular, it is used in products such as machine tools, electronic information devices, home appliances, mobile phones, robot motors, wind power generators, small motors for automobiles, and drive motors in line with the recent trend of light weight and miniaturization.

For the general manufacture of NdFeB-based magnets, a strip/mold casting or melt spinning method based on a metal powder metallurgy method is known. First, in the case of the strip/mold casting method, an ingot is manufactured by melting metals such as neodymium (Nd), iron (Fe), and boron (B) through heating, and grain particles are coarsely pulverized. And, it is a process of manufacturing micro-particles through a refinement process. By repeating this, a powder is obtained, and an anisotropic sintered magnet is manufactured by pressing and sintering under a magnetic field.

In addition, the melt spinning method melts metal elements, then pours them into a wheel rotating at a high speed, cools them, and after crushing the jet mill, blends them with polymers to form bonded magnets, or presses them into magnets. manufacture

In the case of obtaining a sintered magnet by sintering the magnet powder, sintering is performed in a temperature range of 1000 to 1250 degrees Celsius to densify it to obtain true density. When sintering in the temperature range is necessarily accompanied by grain growth, the growth of such grains acts as a factor for reducing the coercive force. The relationship between the size of grains and the coercive force is experimentally revealed as shown in [Equation 1].

[Equation 1]

HC = a + b/D (HC: magnetic moment, a and b: constant, D: grain size)

According to Equation 1, the coercive force of the sintered magnet tends to decrease as the size of the crystal grains increases. In other words, during sintering, grain growth (more than 1.5 times the size of the initial powder) occurs and abnormal grain growth (more than twice the size of normal grains) occurs, which greatly reduces the theoretical coercive force that the initial powder can have.

Therefore, as a method to suppress the growth of grains during sintering, the HDDR (Hydrogenation, disproportionation, desorption and recombination) process, a method to reduce the size of the initial powder through jet mill grinding, and a triple point by adding an element capable of forming a secondary phase There is a method of inhibiting the movement of grain boundaries by forming in the

However, although the coercive force of the sintered magnet can be secured to some extent through the various methods described above, the process itself is very complicated and the effect on suppressing grain growth during sintering is still insufficient. In addition, the microstructure is greatly changed due to grain movement, etc., which causes another problem such as a decrease in characteristics of a sintered magnet and a decrease in magnetic characteristics due to an added element.

The problem to be solved by the embodiments of the present invention is to solve the above problems, and the embodiments of the present invention are a method for manufacturing a sintered magnet having a high coercive force by inhibiting grain growth during a sintering process, and a method for manufacturing a sintered magnet manufactured by this method To provide a sintered magnet.

In order to solve the above problems, a method of manufacturing a sintered magnet according to an embodiment of the present invention includes: preparing an additive in which an organic fluoride is coated on a surface of a rare earth hydride; and mixing the additive with a magnet powder and heating the mixture, wherein the magnet powder includes a rare earth-iron-boron-based powder.

Each of the magnet powder and the rare earth hydride may include at least one of La, Ce, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. .

The rare earth hydride is LaH ₂ , CeH ₂ , NdH ₂ , PrH ₂ , PmH ₂ , SmH ₂ , EuH ₂ , GdH ₂ , TbH ₂ , DyH ₂ , HoH ₂ , ErH ₂ , TmH ₂ , YbH ₂ , and LuH ₂ . It may include at least one or more of

The organic fluoride may include at least one of compounds having a carbon content of C6 to C17 in a perfluorinated carboxylic acid (PFCA)-based material.

The organic fluoride may include PerFluoro Octanoic Acid (PFOA).

The preparing of the additive may include mixing and drying the rare earth hydride, the organic fluoride, and an organic solvent.

The preparing of the additive may further include pulverizing the rare earth hydride, the organic fluoride, and the organic solvent.

The organic solvent may be acetone, normal hexane or methanol.

The heating may be performed in a vacuum atmosphere at a temperature of 1000 to 1100 degrees Celsius.

The method may further include coating an organic fluoride on the surface of the magnet powder.

The organic fluoride coated on the magnet powder may include at least one of compounds having a carbon content of C6 to C17 in a perfluorinated carboxylic acid (PFCA)-based material.

The organic fluoride coated on the magnet powder may include PerFluoro Octanoic Acid (PFOA).

The coating of the organic fluoride on the surface of the magnet powder may include mixing and drying the magnet powder, the organic fluoride, and an organic solvent.

The coating of the organic fluoride on the surface of the magnet powder may further include grinding the magnet powder, the organic fluoride, and the organic solvent.

A film of rare earth fluoride or rare earth oxyfluoride may be formed on the grain surface of the sintered magnet.

The average grain size of the crystal grains of the sintered magnet may be 0.5 to 10 micrometers.

The sintered magnet may be an R-Fe-B-based sintered magnet, the composition of the sintered magnet may be R ₂ Fe ₁₄ B, and R may be La, Ce, Nd, Pr, Pm, Sm, or Eu.

According to embodiments of the present invention, by adding the coated sintering aid, the grain growth of the magnet powder particles during the sintering process can be suppressed to the size level of the initial powder, and the particle surface of the magnet powder is coated in the forming process before sintering. Through the lubricating action of organic fluoride, it is possible to manufacture high-density compacts.

1 and 2 are scanning electron micrographs of a fracture surface of a sintered magnet prepared according to Example 1. Referring to FIG.
3 and 4 are scanning electron micrographs of the fracture surface of the sintered magnet prepared according to Example 2. Referring to FIG.
5 and 6 are scanning electron micrographs of the fracture surface of the sintered magnet prepared according to Comparative Example 1.

Hereinafter, with reference to the accompanying drawings, various embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In addition, throughout the specification, when a part "includes" a certain component, this means that other components may be further included rather than excluding other components unless otherwise stated.

A method of manufacturing a sintered magnet according to an embodiment of the present invention includes preparing an additive in which an organic fluoride is coated on a surface of a rare earth hydride; and mixing the additive with a magnet powder and heating the mixture, wherein the magnet powder includes a rare earth-iron-boron-based powder.

Now, a method of manufacturing a sintered magnet according to an embodiment of the present invention will be described in detail.

Conventional rare-earth hydride is a sintering aid, which is mixed with rare-earth-iron-boron powder and then heat-treated and sintered to form R-rich and By forming the RO _X phase, the sinterability of the produced sintered magnet is improved and columnar decomposition is suppressed. That is, in order to manufacture a high-density sintered permanent magnet having an R-rich phase, sintering is performed after adding a rare earth hydride.

The surface of the rare earth hydride according to an embodiment of the present invention is coated with an organic fluoride. The step of coating the organic fluoride may include mixing the rare-earth hydride and the organic fluoride with an organic solvent and drying them, and specifically, may further include pulverizing the rare-earth hydride, the organic fluoride and the organic solvent. .

The organic fluoride is a perfluorinated compound (PFC) and includes at least one of compounds having a carbon content of C6 to C17 among perfluorinated carboxylic acid (PFCA)-based materials, among which, in particular, It is preferred to include PerFluoro Octanoic Acid (PFOA).

The compound having a carbon content of C6 to C17 among the perfluorinated carboxylic acid (PFCA)-based materials is Perfluorohexanoic Acid (PFHxA, C6), Perfluoroheptanoic Acid (PFHpA, C7), Perfluorooctanoic Acid (PFOA, C8) , Perfluorononanoic Acid (PFNA, C9), Perfluorodecanoic Acid (PFDA, C10), Perfluoroundecanoic Acid (PFUnDA, C11), Perfluorododecanoic Acid (PFDoDA, C12), Perfluorotridecnoic Acid (PFTrDA, C13), Perfluorotetradecanoic Acid (PFTeDA, C14), Perfluorotetradecanoic Acid (PFTeDA, C14) Acid (PFHxDA, C16) and Perfluoroheptadecanoic Acid (PFHpDA, 17).

The type of the organic solvent is not particularly limited as long as the organic fluoride can be dissolved in the organic solvent, but is preferably acetone, normal hexane or methanol.

If the magnet powder includes a rare earth-iron-boron-based powder, a manufacturing method is not particularly limited. Therefore, the magnet powder may be manufactured by mechanically pulverizing or hydrogen pulverizing a magnet alloy, or by a strip casting method, but a reduction-diffusion method It is preferably prepared by

When the rare earth-iron-boron-based powder is formed by the reduction-diffusion method, a separate grinding process such as coarse grinding, hydrogen fracturing, or jet milling or surface treatment is not required.

The synthesis of the rare earth-iron-boron-based powder according to the reduction-diffusion method includes a step of synthesizing from a raw material and a step of washing. In the step of synthesizing from the raw material, a rare earth oxide such as neodymium oxide, a raw material such as boron and iron, and a reducing agent such as Ca are uniformly mixed, and then heated to form a rare earth-iron-boron-based powder by reduction and diffusion of the raw materials. way to do it

Specifically, when the powder is prepared using a mixture of rare earth oxide, boron, and iron, the molar ratio of the rare earth oxide, boron and iron may be between 1:14:1 and 1.5:14:1. Rare earth oxide, boron and iron are raw materials for manufacturing R ₂ Fe ₁₄ B magnet powder, and when the molar ratio is satisfied, R ₂ Fe ₁₄ B magnet powder can be manufactured with high yield. If the molar ratio is 1:14:1 or less, there is a problem in that the composition of the R ₂ Fe ₁₄ B main phase is not formed and the R-rich grain boundary phase is not formed. There may be a problem in that the reduced rare earth element remains, and the remaining rare earth element is changed to R(OH) ₃ or RH ₂ .

The heating may be performed in an inert gas atmosphere at a temperature of 800 degrees Celsius to 1100 degrees Celsius for 10 minutes to 6 hours. When the heating time is 10 minutes or less, the powder cannot be sufficiently synthesized, and when the heating time is 6 hours or more, the size of the powder becomes coarse and there may be a problem that the primary particles are agglomerated.

When the magnet powder is manufactured by the reduction-diffusion method, oxides of alkali metals or oxides of alkaline earth metals, which are by-products generated in the manufacturing process, are formed, and a cleaning step for removing these by-products may be performed. The washing step may further include removing by-products using a quaternary ammonium-based methanol solution, and washing the powder from which the by-products are removed with a solvent.

The magnet powder thus prepared may have an average particle size of 0.5 to 10 micrometers.

The method of manufacturing a sintered magnet according to another embodiment of the present invention may further include coating an organic fluoride on the surface of the magnet powder. The coating of the organic fluoride on the surface of the magnet powder may be performed in the same or similar manner to the coating of the organic fluoride on the surface of the rare earth hydride.

The step of coating the organic fluoride on the surface of the magnet powder may include mixing the magnet powder and the organic fluoride with an organic solvent and drying them, and specifically, further comprising pulverizing the magnet powder, the organic fluoride and the organic solvent. can do.

The organic fluoride coated on the magnet powder is a perfluorinated compound (PFC) and contains at least one of compounds having a carbon content of C6 to C17 among perfluorinated carboxylic acid (PFCA)-based materials. , in particular, it is preferable to include perfluorooctanoic acid (PFOA: PerFluoro Octanoic Acid).

The compound having a carbon content of C6 to C17 among the perfluorinated carboxylic acid (PFCA)-based materials is Perfluorohexanoic Acid (PFHxA, C6), Perfluoroheptanoic Acid (PFHpA, C7), Perfluorooctanoic Acid (PFOA, C8) , Perfluorononanoic Acid (PFNA, C9), Perfluorodecanoic Acid (PFDA, C10), Perfluoroundecanoic Acid (PFUnDA, C11), Perfluorododecanoic Acid (PFDoDA, C12), Perfluorotridecnoic Acid (PFTrDA, C13), Perfluorotetradecanoic Acid (PFTeDA, C14), Perfluorotetradecanoic Acid (PFTeDA, C14) Acid (PFHxDA, C16) and Perfluoroheptadecanoic Acid (PFHpDA, 17).

The type of the organic solvent is not particularly limited as long as the organic fluoride can be dissolved in the organic solvent, but is preferably acetone, normal hexane or methanol.

Each of the magnet powder and the rare earth hydride may include at least one of La, Ce, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. .

The magnet powder is a rare earth-iron-boron-based powder, and has a composition of R ₂ Fe ₁₄ B, and R may be La, Ce, Nd, Pr, Pm, Sm, or Eu.

The rare earth hydride is LaH ₂ , CeH ₂ , NdH ₂ , PrH ₂ , PmH ₂ , SmH ₂ , EuH ₂ , GdH ₂ , TbH ₂ , DyH ₂ , HoH ₂ , ErH ₂ , TmH ₂ , YbH ₂ , and LuH ₂ . It may include at least one or more of

As mentioned above, the rare earth hydride forms R-rich and RO _X phases in the grain boundary region inside the sintered magnet or in the grain boundary region of the sintered magnetic columnar grains, thereby improving the sinterability of the produced sintered magnet and suppressing columnar decomposition. Since it is added, the magnet powder and the rare earth hydride preferably contain the same rare earth element, and more preferably contain Nd. In addition, in order to improve the coercive force by increasing magnetic anisotropy, a hydride containing heavy rare earth elements such as Dy and Tb may be added.

Meanwhile, in the present invention, a Ball-Mill, Turbula mixer, Spex mill, etc. may be used for mixing or pulverizing each component.

Next, a sintering step of mixing and heating the magnet powder and the additive is performed. According to an embodiment of the present invention, the additive is a rare-earth hydride having a surface coated with an organic fluoride, and the magnet powder includes an uncoated rare-earth-iron-boron-based powder. According to another embodiment of the present invention, both the additive and the magnet powder may be coated with an organic fluoride.

The mixture of the magnet powder and the additive may be heated to a temperature of 1000°C to 1100°C for sintering. The heating may be performed for 30 minutes to 4 hours. Specifically, the mixture of the magnet powder and the additive is put into a graphite mold, compressed, and oriented by applying a pulsed magnetic field to manufacture a molded body for a sintered magnet. The sintered magnet is manufactured by heating the molded body for a sintered magnet to a temperature of 1000 to 1100 degrees Celsius in a vacuum atmosphere.

When sintering proceeds, grain growth is necessarily accompanied, and such grain growth acts as a factor to reduce the coercive force.

Fluoride powder can be mixed with the magnet powder to suppress the grain growth that occurs during the sintering process, but if the fluoride is not evenly distributed in the magnet powder and the diffusion of fluoride does not occur sufficiently during heating, the grain growth during the sintering process is prevented. may not be sufficiently restrained. However, in embodiments of the present invention, an organic fluoride is dissolved in an organic solvent and mixed with a rare earth hydride instead of dry mixing of the fluoride, and in another embodiment of the present invention, not only the rare earth hydride but also the rare earth-iron-boron The system powder is mixed with the organic fluoride through an organic solvent. Since it is mixed through an organic solvent, the coating of organic fluoride is distributed more evenly, effectively suppressing material diffusion, so that grain growth in the sintering process can be limited to the size of the initial magnet powder, compared to the case where it is not. As a result, the reduction in the coercive force of the sintered magnet can be minimized by limiting the grain growth.

The average grain size of the crystal grains of the sintered magnet may be 0.5 to 10 micrometers.

In addition, after coating the rare earth hydride using an organic solvent, the residue may be washed with the same organic solvent and dried, and may be sintered by coating as much as desired. That is, the degree of coating can be more easily controlled, and a desired effect of limiting grain growth can be obtained while reducing the residual impurity content compared to dry mixing in which fluoride powder or the like is added.

In addition, a lubricating action is possible by the organic fluoride and the organic solvent. Through the lubrication action, it is possible to manufacture a compact for sintered magnets having high density, and by heating the compact for sintered magnets, it is possible to manufacture high-density and high-performance NdFeB sintered magnets.

Meanwhile, during heating for sintering, the magnet powder or rare-earth hydride may react with the organic fluoride to form a chemically stable coating of rare-earth fluoride or rare-earth oxyfluoride on the grain interface of the sintered magnet. Since the rare earth oxyfluoride is formed by reacting with oxygen on the surface of the magnet powder, diffusion of oxygen into the magnet powder can be minimized. Therefore, since the new oxidation reaction of the magnet particles is limited, the corrosion resistance of the sintered magnet is improved, and the rare earth element is suppressed unnecessarily to produce an oxide, so that a high-density rare earth sintered magnet can be manufactured.

Hereinafter, a method for manufacturing a sintered magnet according to the present disclosure will be described with reference to specific examples and comparative examples.

Example 1: Rare Earth Hydride PFOA Coating

34.35 g of Nd ₂ O ₃ , 69.50 g of Fe, 1.05 g of B, 0.0309 g of Cu, 0.262 g of Al and 18.412 g of Ca are uniformly mixed together with alkali metals Na and K in a sealed plastic vat, and then stainless steel of any shape It was evenly placed in a steel container and pressed, and reacted in an inert gas (Ar) atmosphere at a temperature of 920 to 950 degrees Celsius for 30 minutes to 6 hours in a tube electric furnace. After pulverizing the reactants with an automatic grinder, residual calcium compounds were removed using an organic solvent such as ethanol or methanol and ammonium nitrate. Thereafter, 10 g of the pulverized reactant, 0.375 g of ammonium nitrate, 125 ml of methanol, and 50 g of zirconia balls are mixed, pulverized and dried for 1 to 2 hours using a turbula mixer. In this way, Nd-Fe-B powder having an average particle size of 0.5 to 10 micrometers was prepared.

10 g of NdH ₂ powder, 0.05 g to 0.1 g of PFOA and 50 g of steel balls are mixed with 10 ml to 20 ml of acetone, ground coated using a spex mill and dried.

100 g of the prepared Nd-Fe-B powder and 10 g of PFOA-coated NdH ₂ were mixed to prepare a mixture. The mixture is put into a graphite mold and compressed, and the powder is oriented by applying a pulse magnetic field of 5T or more to prepare a molded body for a sintered magnet. Nd-Fe-B sintered magnets were manufactured by heating the molded body for sintered magnets in a vacuum atmosphere at a temperature of 1030 to 1070 degrees Celsius for 1 to 2 hours.

Example 2: Rare Earth Hydride and Magnet Powder PFOA Coating

Nd-Fe-B powder having an average particle size of 0.5 to 10 micrometers was prepared in the same manner as in Example 1. After removing ammonium nitrate and methanol, 0.05 g to 0.10 g of PFOA and 125 ml of methanol are added again, followed by pulverization and coating for 1 hour with a turbula mixer.

10 g of NdH ₂ powder, 0.05 g to 0.1 g of PFOA and 10 g of steel balls are mixed with 10 ml to 20 ml of acetone, ground coated using a spex mill and dried.

100 g of the prepared PFOA-coated Nd-Fe-B powder and 10 g of PFOA-coated NdH ₂ were mixed to prepare a mixture. The mixture is put into a graphite mold and compressed, and the powder is oriented by applying a pulse magnetic field of 5T or more to prepare a molded body for a sintered magnet. Nd-Fe-B sintered magnets were manufactured by heating the molded body for sintered magnets in a vacuum atmosphere at a temperature of 1030 to 1070 degrees Celsius for 1 to 2 hours.

Comparative Example 1: No PFOA coating

Nd-Fe-B powder having an average particle size of 0.5 to 10 micrometers was prepared in the same manner as in Example 1.

10 g of NdH ₂ powder, 10 to 20 ml of hexane and 50 g of steel balls are mixed, ground coated using a spex mill, and dried.

100 g of the Nd-Fe-B powder and 10 g of NdH ₂ were mixed to prepare a mixture. The mixture is put into a graphite mold and compressed, and the powder is oriented by applying a pulse magnetic field of 5T or more to prepare a molded body for a sintered magnet. Nd-Fe-B sintered magnets were manufactured by heating the molded body for sintered magnets in a vacuum atmosphere at a temperature of 1030 to 1070 degrees Celsius for 1 to 2 hours.

Evaluation Example 1: Scanning Transfer Microscopy Image

The scanning electron micrograph of the fracture surface of the sintered magnet prepared according to Example 1 is shown in FIGS. 1 and 2, and the scanning electron microscope photograph of the fracture surface of the sintered magnet prepared according to Example 2 is shown in FIG. 3 and It is shown in FIG. 4, and scanning electron micrographs of the fracture surface of the sintered magnet prepared according to Comparative Example 1 are shown in FIGS. 5 and 6 .

5 and 6, grain growth is observed in the sintered magnet when the PFOA is not coated, whereas in FIGS. 1 to 4, when the PFOA is coated, the sintered magnet grows as in FIGS. 5 and 6 This is not observed.

Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

Claims (18)

preparing an additive in which an organic fluoride is coated on a surface of a rare earth hydride;
preparing a molded body by mixing the additive with the magnetic powder, putting it into a mold, and applying a magnetic field; and
Comprising the step of heating the compact in a vacuum atmosphere to a temperature of 1000 degrees Celsius to 1100 degrees Celsius for sintering,
The magnet powder includes a rare earth-iron-boron-based powder,
The preparing of the additive comprises mixing and drying the rare earth hydride, the organic fluoride, and an organic solvent,
The method for manufacturing a sintered magnet, wherein the organic fluoride includes at least one of compounds having a carbon content corresponding to C6 to C17 in a perfluorinated carboxylic acid (PFCA)-based material. In claim 1,
Each of the magnet powder and the rare earth hydride comprises a sintered magnet comprising at least one of La, Ce, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. manufacturing method. In claim 1,
The rare earth hydride is LaH ₂ , CeH ₂ , NdH ₂ , PrH ₂ , PmH ₂ , SmH ₂ , EuH ₂ , GdH ₂ , TbH ₂ , DyH ₂ , HoH ₂ , ErH ₂ , TmH ₂ , YbH ₂ , and LuH ₂ . A method of manufacturing a sintered magnet comprising at least one of. delete In claim 1,
The method for manufacturing a sintered magnet, wherein the organic fluoride includes PerFluoro Octanoic Acid (PFOA). delete In claim 1,
The preparing of the additive further comprises pulverizing the rare earth hydride, the organic fluoride, and the organic solvent. In claim 1,
The organic solvent is acetone, normal hexane or methanol. delete In claim 1,
The method of manufacturing a sintered magnet further comprising the step of coating an organic fluoride on the surface of the magnet powder. In claim 10,
The method for manufacturing a sintered magnet, wherein the organic fluoride coated on the magnet powder includes at least one of compounds having a carbon content of C6 to C17 in a perfluorinated carboxylic acid (PFCA)-based material. In claim 10,
The method for manufacturing a sintered magnet, wherein the organic fluoride coated on the magnet powder includes PerFluoro Octanoic Acid (PFOA). In claim 10,
The coating of the organic fluoride on the surface of the magnet powder includes mixing the magnet powder, the organic fluoride, and an organic solvent and drying the mixture. In claim 13,
The coating of the organic fluoride on the surface of the magnet powder may further include pulverizing the magnet powder, the organic fluoride, and the organic solvent. In claim 1,
A method of manufacturing a sintered magnet, wherein a film of rare earth fluoride or rare earth oxyfluoride is formed on the crystal grain surface of the sintered magnet. In claim 1,
The average grain size of the crystal grains of the sintered magnet is 0.5 to 10 micrometers manufacturing method of the sintered magnet. In claim 1,
The sintered magnet is an R-Fe-B-based sintered magnet,
The composition of the sintered magnet is R ₂ Fe ₁₄ B,
wherein R is La, Ce, Nd, Pr, Pm, Sm or Eu. A sintered magnet manufactured by the method of claim 1 .

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