KR20170045184A - Method for manufacturing rare earth sintered magnet using low melting point elements - Google Patents

Abstract

According to the present invention, a method for preparing a sintered rare earth-based magnet according to the present invention comprises the steps of: heating an R-Fe-B based magnet powder to a predefined temperature to produce a sintered magnet, wherein R is a rare earth element or a combination of rare earth elements; coating the surface of the produced sintered magnet with a coating solution prepared by mixing a heavy rare earth powder and a melting point depression element powder in a solvent; and heat-treating the coated sintered magnet. A heavy rare earth element is efficiently diffused on the interface of the sintered magnet to improve the coercive force of the sintered magnet.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth sintered magnet,

The present invention relates to a method of manufacturing a sintered magnet, and more particularly, to a method of manufacturing a rare earth sintered magnet using a melting point lowering element.

R-Fe-B rare earth sintered magnet (here, 'R' is a combination of rare earth elements or rare earth elements such as neodymium (Nd), dysprosium (Dy) and terbium (Tb)) is Alnico, Ferrite, , Samarium-cobalt (SmCo ₅ ), etc., are widely used in all industrial fields due to their excellent magnetic properties.

In particular, among the applications of rare earth sintered magnets, the demand for hybrid / electric automobile drive motors has increased rapidly in recent years. Magnets applicable to hybrid / electric automobile drive motors driven at high temperature (200 to 220 ° C) Only high-energy R-Fe-B sintered magnets. However, the R-Fe-B sintered magnet has a low Curie temperature and a large temperature coefficient of coercive force (0.55% / ° C), which causes a significant decrease in coercive force at high temperatures. This disadvantage can be overcome by adding coarse elements such as dysprosium (Dy) or terbium (Tb), which have large anisotropic coefficients, to the coarse-grained earth element (HREE).

Therefore, studies have been actively carried out to add a heavy rare earth element to the sintered magnet, and to reduce the content of the heavy rare earth element added to the sintered magnet to a minimum, thereby achieving a high efficiency compared to the use.

Specifically, since the grain size of the R-Fe-B sintered magnet is much larger than the size of the terminal sphere and there is almost no histological change within the grain, the coercive force depends on the generation of inversion at the grain boundary and the ease of transition. That is, when the generation and transition of the inverse prism are easy, the coercive force is low, and if it is the opposite, the coercive force is high. Since the coercive force of the R-Fe-B sintered magnet is determined by the physical and histological characteristics at the interface, inhibition of inversion and transition in the spinel can improve the coercive force.

Therefore, in order to improve the coercive force of the R-Fe-B sintered magnet, a heavy rare-earth element such as dysprosium (Dy) which is essentially added is concentratedly distributed only around the grain boundary, that is, on the surface of the ferromagnetic crystal grain. If the core-shell type structure is formed, it is possible to obtain a high coercive force while greatly reducing the amount of heavy rare earth element to be distributed evenly throughout the magnet by adding the heavy rare earth element in the mother alloy melting process.

One of the methods attempted to obtain such a structure is the Grain Boundary Diffusion Process (GBDP), which utilizes the fact that the chemical reactivity at the interface between the sintered magnets is very large, Coating or coating of pure metal or compound on the surface of the magnet by sputtering or electrolytic vapor deposition and surface diffusion by evaporation of heavy rare earth element are used for interfacial diffusion along the interface by heat treatment after coating, Since the density of the sintered magnet is almost completely densified at 90% or more, it is difficult for the heavy rare earth element to diffuse to the inner center of the magnet.

As a related prior art, there is disclosed a method of manufacturing a rare earth magnet of RE-Fe-B type rare earth metal-based diffusion type RE-Fe-B system manufactured by the registered patent publication No. 10-1516567 Rare earth magnet, registered on May 15, 2015).

Disclosure of the Invention The present invention provides a method of manufacturing a rare earth sintered magnet using a melting point lowering element capable of effectively diffusing a heavy rare earth element on an interface of a sintered magnet to improve a coercive force of the sintered magnet can do.

According to the present invention, there is provided a method for manufacturing a sintered magnet, comprising the steps of: heating a R-Fe-B based magnet powder (where R is a rare earth element or a rare earth element) to a preset temperature to produce a sintered magnet; Coating a surface of the resultant sintered magnet with a coating solution prepared by mixing a heavy rare earth powder and a melting point lowering element powder into a solvent; And performing a heat treatment on the coated sintered magnet. The method for producing a rare earth sintered magnet using the melting point lowering element and the rare earth sintered magnet produced by the method.

Here, the melting point lowering element powder may be provided as a copper powder or an aluminum powder.

In the coating solution, the heavy rare earth powder was DyH ₂ And the melting point lowering element powder is provided as copper powder or aluminum powder, and the coating step may be carried out by soaking the sintered magnet in the coating solution, followed by drying.

The coating solution may comprise 20 to 60 wt% of the heavy rare earth powder and 3 to 6 wt% of the copper powder or 3 to 6 wt% of the aluminum powder based on the total weight of the coating solution.

Wherein the heat treatment step comprises: a first heat treatment step of performing a heat treatment at a first heat treatment temperature in a range of 790 to 910 占 폚; And a second heat treatment step of performing a heat treatment at a second heat treatment temperature in a range of 450 to 550 ° C after the first heat treatment step.

In the method of manufacturing a rare earth sintered magnet using the melting point lowering element according to the present invention, in applying the intergranular diffusion method in which a heavy rare earth element is coated on the surface of a sintered magnet so as to improve coercive force, It is possible to further increase the coercive force of the rare-earth sintered magnet by improving the diffusion depth of the heavy rare earth element by adding the melting point lowering element to the coating solution coated on the rare earth sintered magnet.

1 is a schematic flow chart of a method of manufacturing a rare-earth sintered magnet using a melting point lowering element according to an embodiment of the present invention.
Fig. 2 is a schematic view for explaining a step of producing the coating solution according to Fig. 1;
3 is a flow chart for explaining the step of performing the heat treatment according to FIG.
4 is a mapping image comparing before and after the addition of copper powder and aluminum powder to the coating solution according to Fig.
5 is a potato curve showing changes in coercive force of the sintered magnet depending on the temperature of the coating solution component after the first heat treatment for the coated sintered magnet.
FIG. 6 is a mapping image comparing the diffusion depth and diffusion behavior of the sintered magnet coated with the coating solution of different compositions according to FIG.
7 is a mapping image showing the internal microstructure of the sintered magnet in the state that the copper powder and the aluminum powder are added.
Fig. 8 is a time-temperature graph showing the reason that the copper powder and the aluminum powder have different diffusion depths in the sintered magnet.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and / or features of the present invention, and how to accomplish them, will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification. In the following description, well-known functions or constructions are not described in order to avoid unnecessary obscuration of the present invention.

Prior to the description, rare earth elements such as neodymium (Nd), dysprosium (Dy), and terbium (Tb) may be selectively used for the rare earth sintered magnet according to the present invention. However, in an experimental example for explaining and supporting the present invention, an Nd-Fe-B sintered magnet using neodymium (Nd) will be described as an example.

In the method for producing a rare earth sintered magnet using a melting point lowering element according to the present invention, the surface of the sintered magnet subjected to the sintering process is coated with a coating solution to which a heavy rare earth element is added, and then a method of diffusing the heavy rare earth element , And the boundary diffusion method (GBDP). Thus, a core-shell type structure is formed in which the heavy rare earth element is abundantly present on the outer periphery of the main phase on the surface of the sintered magnet.

At this time, in applying the grain boundary diffusion method to the sintered magnet, a coating solution to which a melting point lowering element for lowering the melting point on the interface of the sintered magnet is added is used in order to improve the diffusion depth of the heavy rare earth element in the sintered magnet. That is, the present invention relates to a method of coating a sintered magnet on a surface of a sintered magnet with a coating solution prepared by mixing a melting point lowering element with a heavy rare earth powder in a solvent and a solvent, and then subjecting the sintered magnet to a predetermined heat treatment step, It is possible to further improve the diffusion depth in the sintered magnet of the heavy rare earth element contained in the heavy rare earth powder by lowering the melting point.

For reference, in this specification, the grain boundary refers to a secondary phase surrounding a columnar phase (i.e., a primary phase), or an Nd-rich phase or a triple junction phase.

Accordingly, the method for producing a rare earth sintered magnet using the melting point lowering element according to the present invention is a method of uniformly diffusing a heavy rare earth element into a sintered magnet along a grain boundary to surround the ferromagnetic crystal grains with a layer having high magnetic anisotropy, And the coercive force can be increased.

Hereinafter, a method of manufacturing a rare-earth sintered magnet using the melting point lowering element according to the present invention will be described in detail with reference to FIG. 1 to FIG.

FIG. 1 is a schematic flow chart of a method of manufacturing a rare earth sintered magnet using a melting point lowering element according to an embodiment of the present invention, FIG. 2 is a schematic view for explaining a step of manufacturing a coating solution in FIG. 1, 1 is a flowchart for explaining a heat treatment step.

1, a method of manufacturing a rare-earth sintered magnet using a melting point lowering element according to the present invention is a method of manufacturing a rare earth sintered magnet using an R-Fe-B based magnet powder (where R is a rare earth element or a rare earth element combination) (S130) of coating the surface of the sintered magnet produced from the coating solution prepared by mixing the heavy rare earth powder and the melting point element powder into a solvent (S110), and coating the sintered magnet And performing a heat treatment on the magnet (S140). At this time, the present invention may further include a step (S120) of preparing a coating solution by mixing a heavy rare earth powder and a melting point lowering element powder into a solvent.

First, a step (S110) of generating a sintered magnet by heating the R-Fe-B based magnet powder to a preset temperature is performed. At this time, the R-Fe-B based magnet powder may be prepared by preparing an alloy strip, performing hydrogen treatment and dehydrogenation treatment on the alloy strip, and pulverizing the alloy strip. At this time, the magnet powder is pulverized to a predetermined size or less. The pulverizing operation may be performed by a pulverizer such as a jet mill or a ball mill. On the other hand, it is preferable that the predetermined temperature, that is, the sintering temperature is in the range of 1000 to 1100 ° C.

Next, a step (S120) of preparing a coating solution by mixing the heavy rare earth powder and the melting point lowering element powder into a solvent is performed.

The heavy rare-earth powder used in the step (S120) of preparing the coating solution of the present invention may be provided as a heavy rare earth compound or a heavy rare earth alloy powder and may optionally be used. (R = at least one kind of Dy, Tb (at least one rare earth element such as Dy, Tb and the like, X = at least one kind of H, O, N, F, B), and the heavy rare earth alloy powder is R- A rare earth element such as tungsten, TM = at least one transition metal, X = B, C). In particular, the heavy rare earth powder is preferably provided as a dysprosium hydride powder (DyH ₂ powder) in a heavy rare earth compound, but the present invention is not limited thereto.

The melting point lowering element powder is preferably provided as copper powder or aluminum powder. Herein, the melting point lowering element refers to an element that lowers the melting point of the grain boundary of the sintered magnet in order to improve the diffusion depth of the heavy rare earth element in the sintered magnet when the grain boundary diffusion method is applied to the sintered magnet. The term interfacial phase means a secondary phase which is the outer portion of the columnar phase surrounding the columnar phase (i.e., the primary phase) of the sintered magnet, and may be referred to as an Nd-rich phase in an embodiment of the present invention.

In the present invention, the melting point lowering element should be selected in consideration of the fact that the melting point is relatively low as compared with the sintered magnet, the other magnet characteristics of the sintered magnet are not adversely affected, and the solubility with the column phase. Based on this selection criterion, copper (Cu) or aluminum (Al) is considered to be most suitable as a melting point lowering element in the present invention. The present invention relates to a method for producing a sintered magnet which comprises coating a surface of a sintered magnet with a coating solution prepared by mixing such a melting point reducing element in a solvent together with a heavy rare earth powder in a solvent and then subjecting the sintered magnet to a predetermined heat treatment step, The diffusion depth in the sintered magnet of the heavy rare earth element contained in the heavy rare earth powder such as dysprosium (Dy) can be further improved.

In other words, the melting point lowering element lowers the melting point on the interface surrounding the main phase of the sintered magnet, and diffuses dysprosium (Dy) added to the middle rare earth powder to the inside of the magnet to serve as a carrier to improve the coercive force . The reason for this phenomenon is that in the heat treatment step (S140), the coating solution to which the melting point lowering element is added lowers the melting point on the interface, so that the liquid phase is formed more rapidly, and the microstructure in the sintered magnet is improved, This is because the diffusion depth of the diffusion layer can be deepened.

The solvent serves to melt and mix the heavy rare earth powder and the melting point lowering element powder. At this time, anhydrous alcohol may be used as the solvent, but it is not limited thereto. Further, the solvent mixed with the heavy rare earth powder and the melting point lowering element powder may be coated on the surface of the sintered magnet, and then dried and removed in a vacuum state.

The coating solution according to the present invention comprises 20 to 60% by weight of DyH ₂ powder and 3 to 6% by weight of copper powder, 20 to 60% by weight of DyH ₂ powder and 3 to 6% by weight of aluminum powder, . That is, in the coating solution according to the present invention, copper powder or aluminum powder is preferably added in a ratio of 0.01 to 0.04 weight with respect to DyH ₂ powder.

Next, a step (S130) of coating the surface of the sintered magnet with the coating solution prepared in the step S120 is performed. That is, in this step S130, the surface of the sintered magnet is coated with a coating solution prepared by mixing a heavy rare earth powder and a melting point lowering element powder into a solvent. For example, the surface of the sintered magnet can be coated by a dipping method in which the sintered magnet is immersed in a coating solution and then taken out and dried. However, it goes without saying that various coating methods other than the dipping method may be applied to the coating step (S130) in the present invention.

Finally, in step S130, a step of performing heat treatment on the coated sintered magnet (S140) is performed. 3, the heat treatment step S140 of the present invention includes a first heat treatment step S141 for performing a heat treatment at a first heat treatment temperature in the range of 790 to 910 占 폚 and a step 450 for performing heat treatment at a first heat treatment step S141, And a second heat treatment step (S142) for performing heat treatment at a second heat treatment temperature in the range of about 550 to about < RTI ID = 0.0 > 550 C. < / RTI >

Here, the first heat treatment step (S141) preferably has a range of 790 to 910 占 폚, and the second heat treatment step (S142) has a range of 450 to 550 占 폚. This is because the diffusion action of diffusing the heavy rare earth element contained in the heavy rare earth powder to the surface of the sintered magnet progresses smoothly in this temperature range. That is, the heat treatment step (S140) of the present invention can perform the heat treatment of the coated sintered magnet from the coating treatment step (S130).

Specifically, in the heat treatment step (S140), the coated sintered magnet is heat-treated to diffuse the heavy rare earth element, that is, dysprosium (Dy) along a large chemical reaction surface.

In the foregoing, a method of manufacturing a rare earth sintered magnet using the melting point lowering element according to the present invention has been described. The present invention can include the rare earth sintered magnet manufactured by the above-described manufacturing method.

Hereinafter, the operation and effect of the method of manufacturing the sintered magnet using the melting point lowering element according to the present embodiment will be described in detail with reference to FIGS. 4 to 8 through experimental examples. FIG. 4 is a mapping image before and after the addition of the copper powder and the aluminum powder to the coating solution according to FIG. 2, FIG. 5 is a mapping image after the primary heat treatment for the coated sintered magnet, FIG. 6 is a mapping image for comparing diffusion depth and diffusion behavior of a sintered magnet coated with a coating solution having a different composition according to FIG. 5, and FIG. 7 is a graph showing the relationship between diffusion depth and diffusion behavior of copper powder and aluminum powder FIG. 8 is a time-temperature graph showing the reason why the copper powder and the aluminum powder have different diffusion depths in the sintered magnet. FIG. 8 is a time-temperature graph showing the internal microstructure of the sintered magnet in the added state.

< Experimental Example >

(1) Experimental method

In this experimental example, an alloy of 29.00 Nd 3.00 Dy bal.Fe 0.97B 2.39M was melted and rapidly cooled through a strip caster to produce an alloy strip. The prepared alloy strips were hydrogenated at 400 캜 for 2 hours under a hydrogen pressure of 0.12 MPa and then heated in a vacuum to remove hydrogen. The hydrogen / dehydrogenated alloy strip was prepared by milling the magnet powder at 6000 rpm using a jet mill. The powder thus mixed is uniaxially magnetized under a magnetic field of 2.2 T and vacuum sintered at 1060 ° C. for 4 hours to produce a sintered magnet. Then, to the ethanol was added DyH ₂ A coating solution (Example 1) in which 1.0 g of powder and 0.01 to 0.04 g of copper powder as a melting point lowering element were mixed, 1.0 g of DyH ₂ powder and 0.01 to 0.04 g of copper powder as a melting point element were mixed in ethanol Example 2), and 1.0 g of ethanol and DyH ₂ powder were mixed to prepare a coating solution (Comparative Example 1).

The sintered magnets were immersed in the coating solutions prepared in Examples 1 and 2 and Comparative Example 1, dried, and subjected to a first heat treatment at 790 to 910 ° C for 2 hours and a second heat treatment at 500 ° C for 2 hours . At this time, the first heat treatment temperature is 850 ° C, 880 ° C, 910 ° C, and the heat treatment is performed for each of the first, second and first comparative examples.

The distribution of copper, aluminum, dysprosium (Dy) (shape and distribution of the powder produced, and microstructure of the sintered body) was observed through EPMA. The magnetic properties of the sintered body (sintered magnet) were determined by BH loop tracer -300).

Through these experiments, it has been attempted to improve the diffusion depth of dysprosium (Dy) by adding a melting point lowering element in the diffusion of the dysprosium (Dy) compound to the sintered magnet through the heat treatment, Were investigated. This will be described in detail through the following experimental data.

Example 1: A coating solution prepared by mixing 1.0 g of DyH ₂ powder and 0.01 to 0.04 g of copper powder in ethanol as a solvent

Example 2: A coating solution prepared by mixing 1.0 g of DyH ₂ powder and 0.01 to 0.04 g of aluminum powder in ethanol as a solvent

Comparative Example 1: A coating solution prepared by mixing 1.0 g of DyH ₂ powder in ethanol as a solvent

(2) Analysis of experimental results

FIG. 4 is an image mapped before and after heat treatment so that copper and aluminum elements in the Nd-Fe-B sintered magnet are immersed in a coating solution and compared. As shown in the left image of FIG. 5, it can be seen that the copper element is mainly distributed in the interface with the triple point phase (TJP). In addition, as shown in the right image of FIG. 5, in the case of the aluminum element, it is confirmed that when the aluminum element is diffused along the interface, the aluminum element is partially diffused in the outer portion of the main phase to form a core-shell type structure. The reason why the core-shell type structure is formed only for the aluminum element is that it is because the copper has no solubility with the Fe in the columnar phase and the aluminum has some solubility with the columnar phase.

As shown in FIG. 5, the potato curves showing changes in the coercive force of the sintered magnets according to the first heat treatment temperature were fixed at 850 ° C., 880 ° C., and 910 ° C., respectively, As shown.

As shown in FIG. 6, when a coated sintered magnet is subjected to a first heat treatment, a potato curve showing the change in coercive force of the sintered magnet according to the temperature of each component of the coating solution is generated do.

Referring to FIG. 5, when the first heat treatment step (S141) was performed at 880 DEG C, the best coercive force was obtained. The coercive force of 3.0 kOe was measured during the heat treatment after the coating solution of Comparative Example 1 was added to the sintered magnet subjected to the heat treatment at 880 ° C and the coercive force of 3.8 kOe during the heat treatment after the coating solution of Example 1 was added. And a coercive force of 4.7 kOe was measured at the time of heat treatment after the coating solution of Example 2 was added. It can be seen that the coercive force is further increased when the melting point reducing element is added as in the case of Example 1 and Example 2, as compared with the case where the coating solution of Comparative Example 1, that is, the melting point lowering element is not added. In particular, it can be seen that the coercive force is further increased when aluminum is added to the coating solution of Example 2, that is, copper, than that of Example 1.

Also, when the coated sintered magnet was tested at a different first heat treatment temperature, the first heat treatment temperature was 880 ° C, which was larger than that at 850 ° C or 910 ° C. The reason why the coercive force is increased when the melting point lowering element is added (Examples 1 and 2) than when the melting point lowering element is not added (Comparative Example 1) is that the melting point lowering element powder lowers the melting point of the Nd- And it is judged that the heavy rare earth element is diffused on the surface of the sintered magnet powder.

6, an image obtained by mapping the sintered magnets intergranularly diffused under the three different conditions of the components of the coating solution of Example 1, Example 2 and Comparative Example 1, that is, the coating solution, can be seen. This reveals the diffusion depth of dysprosium (Dy) under three different conditions. Specifically, in the case of the coating solution of Comparative Example 1, the diffusion depth of dysprosium (Dy) is about 90 m, the coating solution of Example 1 is 150 m, which is slightly more improved, and the coercive force This is in agreement with the above-mentioned [Table 1]. Particularly, in the case of the coating solution of Example 2, the depth of diffusion was 525 탆, which is about 6 times higher than that of Comparative Example 1.

Referring to FIG. 7, a high magnification image showing the internal microstructure of the sintered magnet to which the coating solutions of Examples 1 and 2 are added can be seen. As described above, when the copper powder is added and the aluminum powder is added, the effects are different from each other because the diffusion behavior differs in the sintered magnet as shown in Fig. 6 described above. In the case of copper, It is difficult to diffuse dysprosium (Dy) into the main phase. In the case of aluminum, since dysprosium (Dy) diffuses into the magnet due to solubility with the main phase, dysprosium (Dy) diffuses to the outer periphery of the main phase And the core-shell type structure is formed.

That is, as shown in the graph of FIG. 8, the copper powder and the aluminum powder have different diffusion depths in the sintered magnet because the copper exists in a solid phase within the primary heat treatment temperature, but aluminum has a primary heat treatment temperature In a liquid phase. Specifically, in the case of aluminum, it is present in the liquid phase within the first heat treatment temperature and reacts more actively with the Nd-rich phase to help dysprosium (Dy) diffuse deeper into the magnet. In the case of copper, It does not greatly assist in the diffusion of dysprosium (Dy) because it exists in a solid phase.

Therefore, by adding a melting point lowering element such as copper or aluminum, the heavy rare earth element is uniformly diffused into the sintered magnet along the grain boundaries, and the ferromagnetic crystal grains are surrounded by the layer having high magnetic anisotropy, have. At this time, in the case of Example 2, that is, in the case where aluminum is added rather than copper in Example 1, dysprosium Dy is deeply diffused to the inside of the completely densified magnet so that a large coercive force can be obtained.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, Modification is possible. Accordingly, the spirit of the present invention should be understood only in accordance with the claims set forth below, and all of its equivalents or equivalent variations fall within the scope of the present invention.

Claims (6)

Heating the R-Fe-B based magnet powder (where R 'is a combination of rare earth elements or rare earth elements) to a preset temperature to produce a sintered magnet;
Coating a surface of the resultant sintered magnet with a coating solution prepared by mixing a heavy rare earth powder and a melting point lowering element powder into a solvent; And
And performing heat treatment on the coated sintered magnet. The method for manufacturing a rare earth sintered magnet according to claim 1,
The method according to claim 1,
Wherein the melting point lowering element powder is provided as copper powder or aluminum powder.
3. The method of claim 2,
In the coating solution, the heavy rare earth powder was DyH ₂ And the melting point lowering element powder is provided as a copper powder or an aluminum powder,
Wherein the coating step comprises immersing the sintered magnet in the coating solution, and then removing the sintered magnet and drying the sintered magnet.
The method according to claim 1,
The coating solution may contain,
Wherein the coating solution comprises 20 to 60 wt% of the heavy rare earth powder and 3 to 6 wt% of the copper powder or 3 to 6 wt% of the aluminum powder based on the total weight of the rare earth sintered magnet &Lt; / RTI &gt;
The method according to claim 1,
The heat treatment step may include:
A first heat treatment step of performing a heat treatment at a first heat treatment temperature in a range of 790 to 910 占 폚; And
And a second heat treatment step of performing a heat treatment at a second heat treatment temperature in a range of 450 to 550 ° C after the first heat treatment step.
A rare earth sintered magnet produced by the manufacturing method according to any one of claims 1 to 5.

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