Rare earth sintered magnet, manufacturing method for rare earth sintered magnet, rotor, and rotary machine

Abstract

A rare earth sintered magnet (1) has: a main phase (10) that includes crystal grains that are based on an Nd2Fe14B crystal structure and satisfy the general formula (Nd, R)-Fe-B-M, where R is one or more rare earth elements selected from a group excluding Nd and M is one or more elements selected from the group of Ga, Al, Cu, and Co; and a subphase (20) present between the particles of the main phase (10). The subphase (20) has a crystalline first subphase (21) based on an oxide phase whose main component is represented by (Nd, R, RH)-O, where RH is one or more heavy rare earth elements selected from the group of Dy, Tb, and Ho. The first subphase (21) has a first region in which the concentration of the heavy rare-earth element RH is a first concentration, and a second region which surrounds the first region and is such that the concentration of the heavy rare-earth element RH is a second concentration higher than the first concentration.

Description

Rare earth sintered magnet, manufacturing method of rare earth sintered magnet, rotor and rotating machine

[0001] The present disclosure relates to a rare earth sintered magnet, which is a permanent magnet obtained by sintering a material containing a rare earth element, a method for manufacturing a rare earth sintered magnet, a rotor, and a rotating machine.

[0002] Tetragonal R2T 14 R-T-B system permanent magnets are known, whose main phase is a B intermetallic compound. Here, R is a rare earth element, T is a transition metal element such as Fe (iron) or Fe partially substituted with Co (cobalt), and B is boron. R-T-B system permanent magnets are used in a variety of high-value-added components, including industrial motors. In particular, Nd—Fe—B system sintered magnets, in which R is Nd (neodymium), are used in a variety of components due to their excellent magnetic properties. Furthermore, because industrial motors are often used in high-temperature environments exceeding 100°C, attempts have been made to improve coercivity by adding heavy rare earth elements such as Dy (dysprosium) and Tb (terbium) to Nd-T-B system sintered magnets.

[0003] In recent years, the production volume of Nd—Fe—B based sintered magnets has expanded, resulting in an increase in the consumption of Nd and heavy rare earth elements such as Dy and Tb. However, Nd and heavy rare earth elements are scarce resources, and there is a demand to reduce their usage.

[0004] In Patent Document 1, Nd2Fe 14 An anisotropic rare earth sintered magnet is disclosed that has a B-type crystal compound as its main phase and contains Ce (cerium). The anisotropic rare earth sintered magnet described in Patent Document 1 has main phase grains in which the Ce / R' ratio at the center of the grain is lower than the Ce / R' ratio at the outer periphery of the grain, and an R'-rich phase containing Ce and an R'(Fe, Co)2 phase containing Ce are present at the grain boundaries. Here, R' is one or more elements selected from rare earth elements, with Nd being an essential element. The technology described in Patent Document 1 allows for the production of an anisotropic rare earth sintered magnet in which part of the Nd is replaced with Ce, which is an inexpensive element with a higher concentration in the earth's crust.

[0005] In Patent Document 2, the main phase R2Fe 14Patent Document 2 discloses a rare earth sintered magnet that is a sintered body formed using an R-T-B alloy containing a B phase, a grain boundary phase containing more R than the main phase, and a grain boundary triple junction surrounded by three or more main phases. In the rare earth sintered magnet described in Patent Document 2, an R-rich phase with an atomic ratio of (Fe + Co) / (LR + HR + Fe + Co)≦0.2 exists at the grain boundary triple junction. Furthermore, in the rare earth sintered magnet described in Patent Document 2, a region exists in the R-rich phase where HR / (LR + HR)≧0.01. In other words, an R-rich phase and an HR-rich phase coexist. Here, LR is Y (yttrium) and 57 From La (Lantern) 63 Light rare earth elements up to Eu (europium), and HR is 64 From Gd (gadolinium) 71 The heavy rare earth elements are up to Lu (lutetium). The technology described in Patent Document 2 makes it possible to obtain a rare earth sintered magnet that maintains high magnetic properties while improving corrosion resistance.

[0006] JP 2023-070057 A JP 2013-138170 A

[0007] However, the technology described in Patent Document 1 has a problem in that the main phase and subphase contain a large amount of Ce, which does not have magnetic crystal anisotropy, and therefore it is not possible to form a structure with a sufficiently enhanced anisotropy field. Furthermore, since the technology described in Patent Document 1 does not contain a heavy rare earth element, it is not possible to obtain high heat resistance and high magnetic properties. The technology described in Patent Document 2 has a problem in that the grain boundary triple junction is a transition metal-rich layer, and it is difficult to achieve both a significant reduction in heavy rare earth elements and high magnetic properties simply by allowing an R-rich phase and an HR-rich phase to coexist.

[0008] The present disclosure has been made in light of the above, and aims to provide a rare earth sintered magnet that can improve heat resistance and magnetic properties while reducing the amount of heavy rare earth elements used compared to conventional magnets.

[0009] In order to solve the above-mentioned problems and achieve the object, the rare earth sintered magnet according to the present disclosure satisfies the general formula (Nd, R)-Fe-B-M, and has the structure NdFe, where R is one or more rare earth elements selected from the group consisting of Nd (gallium), Al (aluminum), Cu (copper), and Co (copper). 14 The composite material has a main phase including crystal grains based on a Nd-B crystal structure, and a subphase existing between the main phase and the main phase. The subphase has a crystalline first subphase based on an oxide phase whose main component is represented by the formula (Nd, R, RH)-O, where RH is one or more heavy rare earth elements selected from the group consisting of Dy, Tb, and Ho (holmium). The first subphase has a first region having a first concentration of the heavy rare earth element, and a second region surrounding the first region having a second concentration of the heavy rare earth element higher than the first concentration.

[0010] The rare earth sintered magnet according to the present disclosure has the effect of being able to improve heat resistance and magnetic properties while reducing the amount of heavy rare earth elements used compared to conventional magnets.

[0011] FIG. 1 is a diagram showing a schematic example of the structure of a rare earth sintered magnet in a sintered state according to embodiment 1. FIG. 2 is a diagram showing a schematic example of the structure of a rare earth sintered magnet in a sintered state according to embodiment 3. Tetragonal NdFe 144. A diagram showing atomic sites in a B crystal structure. A flowchart showing an example of the procedure for a method for producing a rare earth sintered magnet according to embodiment 4. A flowchart showing an example of the procedure for a rare earth sintered magnet alloy production process in FIG. 4. A flowchart showing an example of the procedure for a diffusion precursor production process in FIG. 4. A flowchart showing an example of the procedure for a diffusion treatment process in FIG. 4. A cross-sectional view schematically showing an example of the configuration of a rotor equipped with a rare earth sintered magnet according to embodiment 5. A cross-sectional view schematically showing an example of the configuration of a rotating machine according to embodiment 6. A cross-section of the rare earth sintered magnet according to examples 1 to 9 was analyzed using a field emission electron probe microanalyzer (FEM). Elemental mapping of Nd obtained by FE-EPMA analysis of the cross section of the rare earth sintered magnets of Examples 1 to 9; Elemental mapping of O (oxygen) obtained by FE-EPMA analysis of the cross section of the rare earth sintered magnets of Examples 1 to 9; Elemental mapping of Tb obtained by FE-EPMA analysis of the cross section of the rare earth sintered magnets of Examples 1 to 9; Elemental mapping of Co obtained by FE-EPMA analysis of the cross section of the rare earth sintered magnets of Examples 1 to 9; Elemental mapping of La obtained by FE-EPMA analysis of the cross section of the rare earth sintered magnets of Examples 1 to 9; Elemental mapping of Sm (samarium) obtained by FE-EPMA analysis of the cross section of the rare earth sintered magnets of Examples 1 to 9

[0012] Hereinafter, a rare earth sintered magnet, a method for manufacturing a rare earth sintered magnet, a rotor, and a rotating machine according to embodiments of the present disclosure will be described in detail with reference to the drawings.

[0013] 1 is a diagram showing a schematic diagram of an example of the structure of a rare earth sintered magnet in a sintered state according to embodiment 1. The rare earth sintered magnet 1 according to embodiment 1 satisfies the general formula (Nd, R)-Fe-B-M and is composed of NdFe 14The magnet has a main phase 10 containing crystal grains based on a B crystal structure, and a subphase 20 present between the main phases 10. R is one or more rare earth elements selected from the group consisting of Nd and may include a heavy rare earth element. M is one or more elements selected from the group consisting of Ga, Al, Cu, and Co. M serves to further improve the magnetic properties of the rare earth sintered magnet 1.

[0014] The average grain size of the crystal grains in main phase 10 is preferably 100 μm or less, and more preferably 0.5 μm to 50 μm to improve magnetic properties. Furthermore, by setting the grain size to approximately 1 μm to 10 μm, the grain size will differ from that of the microstructure produced by hot working, maintaining good magnetization performance and enabling the production of rare earth sintered magnet 1 with magnetic properties superior to conventional magnets.

[0015] The subphase 20 includes a crystalline phase based on an oxide phase whose main component is represented by (Nd, R, RH)—O, where RH is one or more heavy rare-earth elements selected from the group consisting of Dy, Tb, and Ho. In the example of FIG. 1 , the subphase 20 includes a first subphase 21 having a concentration gradient of the heavy rare-earth element RH in the region that becomes the subphase 20, and a second subphase 22 having no concentration gradient of the heavy rare-earth element RH.

[0016] The first subphase 21 is a crystalline phase based on an oxide phase whose main component is represented by (Nd, R, RH)—O. The first subphase 21 has a first region having a first concentration of the heavy rare-earth element RH and a second region surrounding the first region having a second concentration of the heavy rare-earth element RH higher than the first concentration. Specifically, the first subphase 21 has a core portion 211 and a shell portion 212 covering the core portion 211, and has an inverted core-shell structure in which the shell portion 212 has a higher concentration of the heavy rare-earth element RH than the core portion 211. Here, the core portion 211 corresponds to the first region, and the shell portion 212 corresponds to the second region. In FIG. 1 , hatching is used to clearly illustrate the structure of the first subphase 21.

[0017] When the concentration of the heavy rare-earth element RH in the core portion 211 is CRH and the concentration of the heavy rare-earth element RH in the shell portion 212 is SRH, the first subphase 21 satisfies the relational expression CRH<SRH. Thus, the subphase 20 includes the first subphase 21, which is a crystalline phase in which the heavy rare-earth element RH is unevenly distributed in the shell portion 212 compared to the core portion 211.

[0018] Here, the concentration difference indicated by "CRH<SRH" means that a mapping analysis using an electron probe microanalyzer (EPMA) reveals a clear difference in the detection intensity of the heavy rare-earth element RH between the core portion 211 and the shell portion 212 of the first subphase 21. Specifically, with regard to the concentration of the heavy rare-earth element RH in the shell portion 212 of the first subphase 21, the detection intensity by EPMA is higher than the average detection intensity of the heavy rare-earth element RH, and with regard to the concentration of the heavy rare-earth element RH in the core portion 211 of the first subphase 21, the detection intensity by EPMA indicates near the lower limit of the detection intensity of the heavy rare-earth element RH.

[0019] In this way, between the main phases 10, there exists a first subphase 21 in which the heavy rare earth element RH is unevenly distributed in the shell portion 212. In other words, the presence of subphase 20 containing the heavy rare earth element RH around the main phase 10 makes it possible to improve the coercive force of the rare earth sintered magnet 1 while suppressing a decrease in remanence, even when used in a high-temperature environment.

[0020] The rare earth sintered magnet 1 according to the first embodiment, that is, the rare earth sintered magnet 1 including the main phase 10 and the subphase 20, has the general formula (Nd a R b RH c ) Fe d B e M f where RH is one or more heavy rare earth elements selected from the group consisting of Dy, Tb, and Ho, R is a rare earth element other than Nd, and M is one or more elements selected from the group consisting of Ga, Al, Cu, and Co. It is desirable that a, b, c, d, e, and f satisfy the following relational expression in atomic percent:

[0021] 5≦a≦20 0<b+c<a 0<c<10 70≦d≦90 0.5≦e≦10 0≦f≦5 a+b+c+d+e+f=100at. %

[0022] In the first embodiment, the general formula (Nd, R)-Fe-B-M is satisfied, and NdFe 14 The rare earth sintered magnet 1 has a main phase 10 containing crystal grains based on a B crystal structure, and a subphase 20 present between the main phases 10. The subphase 20 includes a first subphase 21, which is a crystalline phase based on an oxide phase whose main component is expressed as (Nd, R, RH)—O. The first subphase 21 also has an inverted core-shell structure, such that CRH < SRH. This allows the rare earth sintered magnet 1 to have improved coercivity while suppressing a decrease in remanence, even in high-temperature environments exceeding 100°C, such as those used in industrial motors.

[0023] The anisotropic rare earth sintered magnet of Patent Document 1 has a structure in which the main phase and subphase contain a large amount of Ce. Ce does not have magnetic crystalline anisotropy. Therefore, the anisotropic rare earth sintered magnet of Patent Document 1 cannot form a structure with a sufficiently enhanced anisotropy magnetic field. On the other hand, in Embodiment 1, less Ce is used than in Patent Document 1, or no Ce is used at all. Therefore, it is possible to form a structure with a sufficiently enhanced anisotropy magnetic field compared to the anisotropic rare earth sintered magnet described in Patent Document 1, and to obtain superior magnetic properties compared to Patent Document 1.

[0024] In the rare earth sintered magnet of Patent Document 2, the grain boundary triple junction is a transition metal-rich phase, and the R-rich phase and the HR-rich phase simply coexist. In particular, the HR-rich phase is present throughout the grain boundary triple junction, making it difficult to achieve both a significant reduction in the heavy rare earth element RH and high magnetic properties. In contrast, in the first embodiment, the first subphase 21 of the subphase 20 has a higher concentration of the heavy rare earth element RH in the shell portion 212 than in the core portion 211. In other words, the subphase 20 includes the first subphase 21 in which the heavy rare earth element RH is unevenly distributed in the shell portion 212. In this way, in the rare earth sintered magnet 1 of Embodiment 1, the heavy rare earth element RH is unevenly distributed in the shell portion 212. Therefore, compared to the case of Patent Document 2, in which the heavy rare earth element RH is present throughout the grain boundary triple junction, the amount of heavy rare earth element RH used can be reduced, resulting in even higher magnetic properties.

[0025] As described above, according to the first embodiment, a rare earth sintered magnet 1 can be obtained that exhibits improved coercivity compared to conventional magnets and suppresses a significant decrease in remanence while using less heavy rare earth element RH. Alternatively, a rare earth sintered magnet 1 with magnetic properties equivalent to or better than conventional magnets can be obtained with a smaller amount of heavy rare earth element RH than conventional magnets. Furthermore, because the coercivity is significantly improved compared to conventional rare earth sintered magnets, the magnetic properties of the rare earth sintered magnet 1 when subjected to a thermal load are also better than conventional magnets. In other words, a rare earth sintered magnet 1 with high coercivity and high remanence can be obtained, enabling motor driving even in high-temperature environments exceeding 100°C, where industrial motors are used. In other words, the magnetic properties of the rare earth sintered magnet 1 can be improved compared to conventional magnets. Furthermore, a high-performance rare earth sintered magnet 1 can be provided by reducing the amount of neodymium and heavy rare earth elements used as raw materials, which are unstable in terms of procurement and expensive.

[0026] Embodiment 2 In embodiment 2, a detailed structure of subphase 20 will be described. Note that rare earth sintered magnet 1 according to embodiment 2 has the same structure as that shown in FIG. 1 , and has main phase 10 and subphase 20 present between main phases 10.

[0027] The subphase 20 includes a crystalline first subphase 21 primarily composed of an oxide phase represented by the formula (Nd, R, RH)-O, which contains the element M as a trace component, and a crystalline second subphase 22 primarily composed of an oxide phase represented by the formula (Nd, R, RH)-O, which contains the element M as a trace component. The crystalline subphase 20 is a collective term for the crystalline first subphase 21 and the crystalline second subphase 22. Here, (Nd, R, RH) means that a portion of the Nd is replaced by a rare earth element R other than Nd and a heavy rare earth element RH. The R of the first subphase 21 and the R of the second subphase 22 may be the same rare earth element, or may be partially different rare earth elements, or may be different rare earth elements. Note that, since the main component elements are listed in parentheses, the first subphase 21 and the second subphase 22 may contain trace amounts of other components in addition to the elements listed in parentheses. In addition, in FIG. 1, the structure of the first subphase 21 is hatched to make it easier to understand.

[0028] As described in the first embodiment, the first subphase 21 has a first region having a first concentration of the heavy rare-earth element RH and a second region having a second concentration higher than the first concentration and surrounding the first region. In the configuration of Fig. 1, the first subphase 21 has the concentrations of the heavy rare-earth element RH in the core portion 211 and the shell portion 212 satisfy the relational expression CRH<SRH.

[0029] On the other hand, the second subphase 22 has a uniform concentration of the heavy rare-earth element RH without any significant difference within the region of the second subphase 22. The third concentration, which is the concentration of the heavy rare-earth element RH in the second subphase 22, is lower than the second concentration in the second region of the first subphase 21. The third concentration, which is the concentration of the heavy rare-earth element RH in the second subphase 22, is higher than the first concentration in the first region of the first subphase 21. Specifically, the concentration of the heavy rare-earth element RH in the second subphase 22 is higher than the concentration of the heavy rare-earth element RH in the core portion 211 of the first subphase 21 and lower than the concentration of the heavy rare-earth element RH in the shell portion 212. In other words, when the concentration of the heavy rare-earth element RH in the second subphase 22 is RH2, the concentrations of the heavy rare-earth element RH in the first subphase 21 and the second subphase 22 satisfy the relation CRH<RH2<SRH.

[0030] Here, the concentration difference indicated by "CRH<RH2<SRH" means that, by mapping analysis using EPMA, the detection intensity of the heavy rare-earth element RH is higher on average in the second subphase 22 than in the core portion 211 of the first subphase 21, and the detection intensity of the heavy rare-earth element RH is higher on average in the shell portion 212 of the first subphase 21 than in the second subphase 22.

[0031] Furthermore, the subphase 20, i.e., the first subphase 21 and the second subphase 22, contain the element M as a trace component as described above. The concentration of the element M is higher in the second subphase 22 than in the first subphase 21. In other words, when the concentration of the element M in the first subphase 21 is Cs1M and the concentration of the element M in the second subphase 22 is Cs2M, the relationship Cs1M<Cs2M is satisfied.

[0032] Here, the concentration difference indicated by "Cs1M<Cs2M" means that, by mapping analysis using EPMA, the detected intensity of element M is higher on average in the second subphase 22 than in the first subphase 21. In one example, the intensity of element M detected by EPMA in the second subphase 22 is higher than the average intensity of element M detected by EPMA, and the intensity of element M detected by EPMA in the first subphase 21 is lower than the average intensity of element M detected by EPMA.

[0033] Furthermore, in the subphase 20, the element M is present in high concentration in the second subphase 22, and the second subphase 22 forms a non-magnetic phase that magnetically separates the main phases 10, thereby contributing to improving the magnetic properties. In other words, by making the concentration of the element M higher in the second subphase 22 than in the first subphase 21, high magnetic properties, particularly coercivity, can be obtained and deterioration of the magnetic properties due to temperature increase can be suppressed.

[0034] In the rare earth sintered magnet 1 according to the second embodiment, the subphase 20 includes a first subphase 21 that satisfies the relationship C<SRH and a second subphase 22 that satisfies the relationship C<RH2<SRH, and the concentration of element M is higher in the second subphase 22 than in the first subphase 21. This configuration, combined with the addition of the heavy rare earth element RH and the trace element M, makes it possible to obtain a rare earth sintered magnet 1 that has high magnetic properties, specifically coercive force, sufficient to drive a motor even in high-temperature environments exceeding 100°C, where industrial motors are used, while suppressing degradation of the magnetic properties with increasing temperature. This also makes it possible to provide a high-performance rare earth sintered magnet 1 that uses reduced amounts of neodymium and heavy rare earth elements, which are difficult to procure and expensive to procure.

[0035] Embodiment 3. Figure 2 is a diagram showing a schematic diagram of an example of the structure of a rare earth sintered magnet in a sintered state according to embodiment 3. The rare earth sintered magnet 1 according to embodiment 3 has a main phase 10 and a subphase 20. The subphase 20 is present between the main phases 10 and includes a first subphase 21 and a second subphase 22 as described in embodiments 1 and 2.

[0036] In the third embodiment, a rare earth sintered magnet 1 is shown in which La and Sm are selected as the rare earth element R. When La and Sm are selected as the rare earth element R, the magnetic properties are improved while the use of Nd and the heavy rare earth element RH is reduced, and the effect of having superior magnetization compared to conventional magnets is further enhanced. In this example, the main phase 10 is (Nd, La, Sm)Fe. 14 It has the formula RFeB. 14 The reason why the rare earth element R in the rare earth sintered magnet 1 having the B crystal structure is a rare earth element containing La and Sm is that calculations of the magnetic interaction energy using molecular orbital methods have shown that adding La and Sm to the composition can significantly suppress the deterioration of magnetic properties that occurs with increasing temperature, resulting in a practical rare earth sintered magnet 1. Furthermore, by intentionally segregating La and Sm to the grain boundaries, which are an example of subphases 20, Nd can be relatively diffused into the main phase 10, thereby increasing the magnetocrystalline anisotropy of the main phase 10.

[0037] However, if the amounts of La and Sm added are too large, the amount of Nd, which is an element with a high magnetic anisotropy constant and saturation magnetic polarization, decreases, resulting in a deterioration of magnetic properties. Therefore, when the composition ratios of Nd, La, and Sm are A, B, and C, respectively, it is preferable that A > (B + C).

[0038] The rare earth sintered magnet 1 according to the third embodiment assumes that R = La and Sm. Similar to the first and second embodiments, the magnet has a main phase 10 and a subphase 20. The subphase 20 includes a crystalline first subphase 21 based on an oxide phase containing the element M as a trace component and having a main component represented by the formula (Nd, La, Sm, RH)-O, and a crystalline second subphase 22 containing the element M as a trace component and having a main component represented by the formula (Nd, La, RH)-O. La is present in both the first subphase 21 and the second subphase 22. The first subphase 21 has a higher Sm concentration than the second subphase 22. In other words, the first subphase 21 forms an Sm-enriched portion 41 with a higher Sm concentration than the second subphase 22. This not only improves the magnetic properties at room temperature, but also suppresses the degradation of the magnetic properties as the temperature increases.

[0039] Here, "the concentration of Sm is higher in the first subphase 21 than in the second subphase 22" means that, by mapping analysis using EPMA, the detection intensity of Sm in the first subphase 21 is higher on average than that in the second subphase 22.

[0040] The crystalline subphase 20 is a collective term for the crystalline first subphase 21 and the crystalline second subphase 22, which exist between the main phase 10. The crystalline first subphase 21 is represented by (Nd, La, Sm, RH)—O, and the crystalline second subphase 22 is represented by (Nd, La, RH)—O. Here, (Nd, La, Sm, RH) means that part of the Nd is replaced by La, Sm, and the heavy rare earth element RH. Note that, because the main component elements are listed in parentheses, the first subphase 21 and the second subphase 22 may contain trace amounts of other components in addition to the elements listed in parentheses. In one example, the second subphase 22 represented by (Nd, La, RH)—O contains a trace amount of Sm.

[0041] In the rare earth sintered magnet 1 according to the third embodiment, there is a difference in the concentrations of La and Sm between the main phase 10 and the subphase 20, and La and Sm are more segregated in the subphase 20 than in the main phase 10. The concentrations of La and Sm in the subphase 20 are equal to or greater than the concentrations of La and Sm in the main phase 10. In other words, the sum of the La concentrations in the first subphase 21 and the second subphase 22 is equal to or greater than the La concentration in the main phase 10, and the sum of the Sm concentrations in the first subphase 21 and the second subphase 22 is equal to or greater than the Sm concentration in the main phase 10.

[0042] Here, when the concentration of La contained in the main phase 10 is X, the concentration of La contained in the first subphase 21 is X1, the concentration of La contained in the second subphase 22 is X2, the concentration of Sm contained in the main phase 10 is Y, the concentration of Sm contained in the first subphase 21 is Y1, and the concentration of Sm contained in the second subphase 22 is Y2, the relationship of the following formula (1) is satisfied.

[0043] 1<(Y1+Y2) / Y<(X1+X2) / X (1)

[0044] Furthermore, from the viewpoint of improving magnetic properties, the concentration of Nd contained in the main phase 10 satisfies the relationship of the following formula (2), where the concentration of Nd contained in the main phase 10 is CmNd.

[0045] CmNd>(X+Y)...(2)

[0046] When viewed locally, the respective concentrations of La and Sm in the main phase 10 and the sum of the respective concentrations of La and Sm in the first subphase 21 and the second subphase 22 may not satisfy the above-mentioned relationship. Therefore, more specifically, the La concentration in the main phase 10 indicates the average La concentration in the main phase 10, and the Sm concentration in the main phase 10 indicates the average Sm concentration in the main phase 10. In this case, the La concentration in the subphase 20, i.e., the sum of the La concentrations in the first subphase 21 and the second subphase 22, means the average La concentration in the first subphase 21 and the second subphase 22. Furthermore, the Sm concentration in the subphase 20, i.e., the sum of the Sm concentrations in the first subphase 21 and the second subphase 22, means the average Sm concentration in the first subphase 21 and the second subphase 22.

[0047] La is present in high concentrations at grain boundaries during the manufacturing process, particularly during heat treatment, and thus relatively diffuses Nd into the main phase 10. As a result, in the rare earth sintered magnet 1 according to embodiment 3, Nd in the main phase 10 is not consumed at the grain boundaries, improving the magnetocrystalline anisotropy. Sm is also present in higher concentrations in the subphase 20, particularly the first subphase 21, compared to the main phase 10, and thus, like La, relatively diffuses Nd into the main phase 10, improving the magnetocrystalline anisotropy.

[0048] As described in the second embodiment, the subphase 20 contains the heavy rare-earth element RH, and therefore the first subphase 21 and the second subphase 22 also contain the heavy rare-earth element RH, but the distribution of the heavy rare-earth element RH differs between the first subphase 21 and the second subphase 22. In the second subphase 22, which has a lower Sm concentration than the first subphase 21, the heavy rare-earth element RH is uniformly distributed within the second subphase 22. On the other hand, in the first subphase 21 forming the Sm-enriched portion 41, the heavy rare-earth element RH is not uniformly distributed within the first subphase 21, but is selectively distributed between the outer periphery of the first subphase 21 and the Sm-enriched portion 41, i.e., in the outer periphery including the surface of the first subphase 21. Specifically, the heavy rare-earth element RH is present so as to selectively surround the outer periphery of the Sm-enriched portion 41 of the first subphase 21, where the Sm concentration is high. From this, it can be said that the first subphase 21 has an Sm-enriched portion 41 and a heavy rare-earth element-containing portion 42 in which the heavy rare-earth element RH is present and which selectively surrounds the outer periphery of the Sm-enriched portion 41. The outer periphery of the first subphase 21 is the boundary between the first subphase 21 and the main phase 10 or the second subphase 22.

[0049] Note that there is a difference in the concentration of the heavy rare-earth element RH between the Sm-enriched portion 41 and the heavy rare-earth element-containing portion 42 in the first subphase 21. For this reason, it can be said that the Sm-enriched portion 41 corresponds to the first region or core portion 211, which has a first concentration of the heavy rare-earth element RH. It can also be said that the heavy rare-earth element-containing portion 42 corresponds to the second region or shell portion 212, which has a second concentration of the heavy rare-earth element RH that is higher than the first concentration.

[0050] As in embodiment 2, first subphases 21 and second subphases 22 containing the heavy rare earth element RH are present between the main phases 10. For this reason, it can be considered that the heavy rare earth element RH has penetrated into a portion of the surface of the main phase 10 that is in contact with the first subphase 21 or second subphase 22 containing the heavy rare earth element RH. In other words, it can be considered that the heavy rare earth element RH of the subphases 20 has penetrated into a portion of the main phase 10. For this reason, as in embodiments 1 and 2, the rare earth sintered magnet 1 according to embodiment 3 can also suppress a decrease in remanence while improving the coercivity of the rare earth sintered magnet 1.

[0051] FE-EPMA analysis of a cross section of the rare earth sintered magnet 1 according to embodiment 3 confirms the presence of a main phase 10 and a subphase 20 present between the main phases 10, as shown in FIG. 2 . It also confirms the presence of a first subphase 21 having an Sm-enriched portion 41 and a second subphase 22 having a lower Sm concentration than the first subphase 21. That is, the second subphase 22 exhibits no variation in the concentration of the heavy rare earth element RH, and is uniformly distributed as described above. Meanwhile, the first subphase 21 exhibits variation in the concentration of the heavy rare earth element RH, i.e., exhibits a bias in the distribution of the heavy rare earth element RH. It also confirms the presence of a heavy rare earth element-containing portion 42 that selectively surrounds the Sm-enriched portion 41 in the first subphase 21, where the Sm concentration is high. Furthermore, it is confirmed that the heavy rare-earth element RH is hardly present in the Sm-enriched portion 41. It is also confirmed that the concentration of the heavy rare-earth element RH selectively distributed around the Sm-enriched portion 41 is higher than the concentration of the heavy rare-earth element RH distributed throughout the second subphase 22.

[0052] Next, La and Sm form tetragonal RFe 14 The following explains which atomic sites in the tetragonal NdFeB crystal structure are substituted. 14 3 is a diagram showing atomic sites in the B crystal structure. The crystal structure shown in FIG. 3 is, for example, shown in FIG. 1 of Reference Technical Document 1 below. The stabilization energy due to substitution is calculated by band calculation and molecular field approximation of the Heisenberg model, and the substituted site is determined by the value of that energy. (Reference Technical Document 1) JFHerbst et al. "Relationships between crystal structure and magnetic properties in Nd2Fe 14 PHYSICAL REVIEW B. 1984, Vol.29, No.7, p. 4176-4178.

[0053] First, we will explain how to calculate the stabilization energy in La. The stabilization energy in La is calculated using the formula: 56Using a B4 crystal cell, (Nd7La1)Fe 56 B4 + Nd and Nd8 (Fe 55 The energy difference between La and B+Fe can be calculated. The smaller the energy value, the more stable the site is when an atom is substituted at that site. In other words, La is likely to be substituted at the atomic site with the smallest energy. In this calculation, when La is substituted for the original atom, the tetragonal RFe 14 The lattice constant in the B crystal structure does not change with the difference in atomic radius. Table 1 shows the stabilization energy of La at each substitution site when the environmental temperature is changed.

[0054]

[0055] According to Table 1, the stable substitution site for La is the Nd(f) site at temperatures above 1000 K, and the Fe(c) site at temperatures of 293 K and 500 K. As described below, the rare earth sintered magnet 1 according to embodiment 3 is produced by heating the raw materials of the rare earth sintered magnet 1 to a temperature of 1000 K or above, melting them, and then rapidly cooling them. Therefore, the raw materials of the rare earth sintered magnet 1 are believed to be maintained at a temperature above 1000 K, i.e., 727°C or above, and preferably at approximately 1300 K, i.e., 1027°C. At this time, La is believed to be substituted at the Nd(f) site or the Nd(g) site. While La is believed to preferentially substitute for the energetically stable Nd(f) site, it is also possible for La to substitute for the Nd(g) site, which has a smaller energy difference among the La substitution sites. For this reason, the Nd(g) site is also considered a candidate for La substitution.

[0056] Furthermore, when rare earth sintered magnet 1 is produced using the manufacturing method described below, the temperature during sintering is above 1000 K. However, by undergoing the first, second, third, and fourth aging steps, as well as the cooling step described below, the Fe(c) sites listed in Table 1 are repeatedly maintained in an energetically stable temperature range. In other words, the substitution of La at the Nd sites of main phase 10 is maintained in an unstable energy state. In other words, while La was primarily substituted at the Nd sites of main phase 10 in the raw material stage of rare earth sintered magnet 1, the manufacturing method described below repeatedly holds rare earth sintered magnet 1 in a temperature range that is intentionally unstable in energy relative to the Nd sites of main phase 10. As a result, a certain amount of La is selectively released from the Nd sites of main phase 10, resulting in La segregation in subphase 20.

[0057] Next, we will explain how to calculate the stabilization energy of Sm. The stabilization energy of Sm is calculated by (Nd7Sm1)Fe 56 B4 + Nd and Nd8 (Fe 55 Sm1)B4 + Fe. By substituting atoms, tetragonal R2Fe 14 The lattice constant in the B crystal structure does not change, as in the case of La. Table 2 shows the stabilization energy of Sm at each substitution site when the ambient temperature is changed.

[0058]

[0059] According to Table 2, the stable substitution site of Sm is the Nd(g) site at any temperature, unlike La. It is thought that Sm is preferentially substituted at the energetically stable Nd(g) site, but substitution at the Nd(f) site, which has a small energy difference among the substitution sites of Sm, is also possible.

[0060] When rare earth sintered magnet 1 is produced by the production method described below, substitution at the Nd(g) site of main phase 10 is most stable in terms of energy. However, as described above, by maintaining the temperature range in which substitution of La at the Nd site of main phase 10 becomes unstable, some Sm is released from the Nd site of main phase 10 along with La and segregates into subphase 20. As a result, there is a difference in the concentrations of La and Sm between main phase 10 and subphase 20. The sum of the La concentrations in first subphase 21 and second subphase 22 is equal to or greater than the La concentration in main phase 10, and the sum of the Sm concentrations in first subphase 21 and second subphase 22 is equal to or greater than the Sm concentration in main phase 10. In other words, La and Sm segregate into subphase 20.

[0061] Comparing La and Sm, it can be seen that, from an energetic perspective, La, which is maintained in a temperature range where the energy state is unstable, is overwhelmingly more likely to segregate into subphase 20. As a result, in the case of a rare earth sintered magnet 1 prepared with La and Sm at approximately the same concentrations, La will segregate to a greater extent into subphase 20 than Sm present in rare earth sintered magnet 1. By repeatedly maintaining this temperature range, a difference in concentration of Sm, which has a lower segregation rate, is created in subphase 20, and a first subphase 21 and a second subphase 22 are formed.

[0062] Furthermore, element M, i.e., elements such as Ga, Al, Cu, and Co, which form nonmagnetic phases at grain boundaries and contribute to high coercivity, are also originally present in subphases 20. However, as described above, the aging and cooling processes result in La and Sm segregating to similar subphases 20, resulting in element M being present primarily in subphases 20 different from La and Sm. In other words, rather than each element being present uniformly, the concentration of element M, which includes Ga, Al, Cu, and Co, is higher in the second subphase 22 than in the first subphase 21. As a result, the first subphase 21 has a higher Sm concentration than the second subphase 22, and the second subphase 22 has a higher M concentration than the first subphase 21. In this way, a rare earth sintered magnet 1 is obtained that has the characteristic that Sm and element M have higher concentrations in different types of subphases 20.

[0063] As described above, the rare earth sintered magnet 1 according to the third embodiment is a rare earth sintered magnet 1 in which the element M is one or more elements selected from the group consisting of Ga, Al, Cu, and Co, and which satisfies the general formula (Nd, La, Sm, RH)-Fe-B-M, and RFe 14 The rare earth sintered magnet 1 according to the third embodiment has a main phase 10 containing crystal grains based on a B crystal structure, a crystalline first subphase 21 whose main component is an oxide phase represented by (Nd, La, Sm, RH)-O, and a crystalline second subphase 22 whose main component is an oxide phase represented by (Nd, La, RH)-O. Furthermore, in the rare earth sintered magnet 1 according to the third embodiment, the first subphase 21 has a higher Sm concentration than the second subphase 22, and the second subphase 22 has a higher M concentration than the first subphase 21. In other words, the subphase 20 has a different concentration of Sm and the element M. As a result, Sm is present in high concentration in the first subphase 21, which relatively diffuses Nd into the main phase 10 and improves the magnetocrystalline anisotropy of the main phase 10. Furthermore, since Sm is also present within the crystal grains of the main phase 10, it bonds with the ferromagnetic Fe in the same magnetization direction, thereby contributing to improving the remanence. The element M is present in high concentrations in the second subphase 22, forming a nonmagnetic phase that magnetically separates the main phases 10, thereby contributing to improving the magnetic properties. The presence of high concentrations of Sm and element M in different subphases 20 makes it possible to simultaneously improve the remanence and coercivity. Furthermore, the effect of improving the magnetic properties can be further enhanced while reducing the use of Nd and the heavy rare earth element RH compared to conventional methods.

[0064] Furthermore, in the third embodiment, as in the first embodiment, it is possible to obtain a rare earth sintered magnet 1 that has improved coercivity compared to conventional magnets and suppresses a significant decrease in remanence while minimizing the use of the heavy rare earth element RH. Furthermore, because the coercivity is significantly improved compared to conventional rare earth sintered magnets, the magnetic properties of the rare earth sintered magnet 1 when subjected to a thermal load are also better than conventional magnets. In other words, it is possible to obtain a rare earth sintered magnet 1 with improved magnetic properties compared to conventional magnets, i.e., high coercivity and high remanence, capable of driving a motor even in high-temperature environments exceeding 100°C, such as those used in industrial motors. Furthermore, it is possible to provide a high-performance rare earth sintered magnet 1 that uses less Nd and heavy rare earth elements, which are raw materials with unstable procurement and high procurement costs.

[0065] Furthermore, the main phase 10 is a tetragonal RFe alloy in which the rare earth elements R are Nd, La, and Sm. 14 The Nd—Fe—B crystal structure allows for suppression of deterioration in magnetic properties with increasing temperature, resulting in rare earth sintered magnet 1. As a result, compared to rare earth sintered magnets that satisfy the Nd—Fe—B formula, it is possible to obtain rare earth sintered magnet 1 that achieves improved magnetic properties at room temperature and suppresses deterioration in magnetic properties with increasing temperature, while using less Nd and heavy rare earth element RH.

[0066] In the first to third embodiments, the main phase 10 satisfies (Nd, R)-Fe-B-M, and NdFe 14 It is sufficient that the crystal grains have a B crystal structure as a base. Furthermore, the main phase 10 may be crystal grains with a structure without any gradient in the Nd concentration, or may be crystal grains with a gradient. As an example of a structure with gradient, the main phase 10 may have a structure in which the rare earth element R is Pr (praseodymium), and the main phase 10 includes a first main phase in which the Nd concentration is lower in the periphery, including the surface, of the crystal grains than in the center, and a second main phase in which the Nd concentration is higher in the periphery, including the surface, of the crystal grains than in the center. Furthermore, the main phase 10 may include a heavy rare earth element RH.

[0067] Embodiment 4. In embodiment 4, a method for manufacturing the rare earth sintered magnet 1 described in embodiments 1, 2, and 3 will be described. Fig. 4 is a flowchart showing an example of the steps of the method for manufacturing the rare earth sintered magnet according to embodiment 4. As shown in Fig. 4, the method for manufacturing the rare earth sintered magnet 1 includes a rare earth sintered magnet alloy manufacturing step (step S10) for manufacturing a rare earth sintered magnet alloy that serves as a raw material for a diffusion precursor, which is a sintered body before diffusing the heavy rare earth element RH into the rare earth sintered magnet 1, a diffusion precursor manufacturing step (step S20) for forming the diffusion precursor, and a diffusion treatment step (step S30) for diffusing the heavy rare earth element RH into the diffusion precursor.

[0068] First, the rare earth sintered magnet alloy manufacturing process of step S10 will be described in detail. FIG. 5 is a flowchart showing an example of the procedure of the rare earth sintered magnet alloy manufacturing process shown in FIG. 4. As shown in FIG. 5, the manufacturing process of the rare earth sintered magnet alloy serving as the raw material for the diffusion precursor includes a melting step (step S11) in which the raw material for the rare earth sintered magnet alloy containing the elements constituting the diffusion precursor is heated to a temperature of 1000 K or higher to melt it, a first cooling step (step S12) in which the molten raw material is cooled on a rotating body to obtain a solidified alloy, and a second cooling step (step S13) in which the solidified alloy is further cooled in a container. This allows the rare earth sintered magnet alloy to be manufactured. Each step will be described below. The first cooling step of step S12 and the second cooling step of step S13 correspond to the alloy cooling step in which the raw material in the molten state in the melting step is cooled to obtain a solidified alloy.

[0069] In the melting step of step S11, the raw material of the diffusion precursor is heated to a temperature of 1000 K or higher in a crucible in an atmosphere containing an inert gas such as Ar (argon) or in a vacuum to melt it. This produces a molten alloy of a molten rare earth sintered magnet alloy. When producing the rare earth sintered magnet 1 of Embodiments 1 and 2, Nd, R, Fe, B, and M can be used as the raw materials. When producing the rare earth sintered magnet 1 of Embodiment 3, Nd, La, Sm, Fe, B, and M can be used as the raw materials. The case of Embodiment 3 corresponds to the case where the rare earth element R in Embodiments 1 and 2 is La and Sm. R can be a rare earth element other than Nd. R can also be one or more heavy rare earth elements selected from the group consisting of Dy, Tb, and Ho. M can be one or more elements selected from the group consisting of Ga, Al, Cu, and Co. Furthermore, FeB can be used instead of B as a raw material.

[0070] Next, in the primary cooling step of step S12, the molten alloy prepared in the melting step is poured into a tundish and then onto a single roll, which is a rotating body. As a result, the molten alloy is rapidly cooled on the single roll rotating in a predetermined direction, and a solidified alloy thinner than the ingot alloy is prepared from the molten alloy on the single roll. Here, a single roll is used as the rotating body, but this is not limiting, and the molten alloy may also be rapidly cooled by contacting it with a twin roll, a rotating disk, a rotating cylindrical mold, or the like. From the viewpoint of efficiently obtaining a thin solidified alloy, the cooling rate in the primary cooling step is set to 10°C / sec or more and 10°C / sec or more. 7 ° C. / sec or less, and 3 °C / sec or more 10 4 The melting rate is preferably set to 0.03°C / sec or less. The thickness of the solidified alloy is in the range of 0.03 mm to 10 mm. The molten alloy starts to solidify from the portion in contact with the single roll, and crystals grow in a columnar or needle shape in the thickness direction from the contact surface with the single roll.

[0071] Thereafter, in the second cooling step of step S13, the thin solidified alloy prepared in the first cooling step is placed in a tray container and cooled. The thin solidified alloy is broken into flakes of rare earth sintered magnet alloy when it enters the tray container and is cooled. Depending on the cooling rate, a ribbon-shaped rare earth sintered magnet alloy may be obtained, and the shape is not limited to flakes. From the viewpoint of obtaining a rare earth sintered magnet alloy having a structure with good temperature characteristics of magnetic properties, the cooling rate in the second cooling step is set to 10 -2 °C / sec or more 10 5 ° C. / sec or less, and -1 °C / sec or more 10 2 It is more preferable to set it to ° C. / sec or less.

[0072] The rare earth sintered magnet alloy obtained through these processes has a minor axis size of 3 μm to 10 μm and a major axis size of 10 μm to 300 μm. In the third embodiment, the magnet alloy has a fine crystalline structure containing a (Nd, La, Sm)-Fe-B-M crystalline phase and a crystalline subphase 20 of an oxide represented by (Nd, La, Sm)-O. Hereinafter, the crystalline subphase 20 of an oxide represented by (Nd, La, Sm)-O will be referred to as the (Nd, La, Sm)-O phase. The (Nd, La, Sm)-O phase is a nonmagnetic phase consisting of an oxide with a relatively high concentration of rare earth element R. The (Nd, La, Sm)-O phase also contains element M as a trace component. The thickness of the (Nd, La, Sm)-O phase corresponds to the width of the grain boundary and is 10 μm or less. The rare earth sintered magnet alloy produced by the above manufacturing process has undergone a rapid cooling process, and therefore has a finer structure than the rare earth sintered magnet alloy obtained by mold casting.

[0073] Next, the diffusion precursor production process of step S20 in FIG. 4 will be described. FIG. 6 is a flowchart showing an example of the procedure of the diffusion precursor production process in FIG. 4. As shown in FIG. 6, the diffusion precursor production process includes a crushing step (step S21) of crushing a rare earth sintered magnet alloy containing a crystal layer satisfying the (Nd, R)-Fe-B-M relationship; a compacting step (step S22) of compacting the powder of the rare earth sintered magnet alloy crushed in the crushing step to prepare a compact; a sintering step (step S23) of sintering the compact at a predetermined sintering temperature to obtain a sintered body; an aging step (step S24) of holding the sintered body at a first aging temperature below the sintering temperature to improve the magnetic properties, such as the coercivity, of the rare earth sintered magnet 1; and a sintered body cooling step (step S25) of cooling the sintered body at a temperature below the first aging temperature to obtain a diffusion precursor. The aging step of step S24 corresponds to the first aging step. Although each step will be described below using the example of producing the rare earth sintered magnet 1 of embodiment 3, the rare earth sintered magnet 1 of embodiments 1 and 2 can be produced by changing the raw material of the rare earth sintered magnet alloy used. In other words, the La and Sm of embodiment 3 can be replaced with a rare earth element R other than Nd.

[0074] In the pulverization step S21, the rare earth sintered magnet alloy having a (Nd, La, Sm)-Fe-B-M crystalline phase and a (Nd, La, Sm)-O phase, produced according to the rare earth sintered magnet alloy production process of FIG. 5, is pulverized to obtain a rare earth sintered magnet alloy powder having a particle size of 200 μm or less, preferably 0.5 μm to 100 μm, and further, when considering magnetization performance, approximately 1 μm to 10 μm. The rare earth sintered magnet alloy is pulverized, for example, using an agate mortar, stamp mill, jaw crusher, or jet mill. In particular, to reduce the particle size of the powder, it is preferable to pulverize the rare earth sintered magnet alloy in an atmosphere containing an inert gas. Pulverizing the rare earth sintered magnet alloy in an atmosphere containing an inert gas can suppress the incorporation of oxygen into the powder. However, if the atmosphere during pulverization does not affect the magnetic properties of the magnet, the rare earth sintered magnet alloy may be pulverized in air. When manufacturing the rare earth sintered magnet 1 of the first and second embodiments, the La and Sm in the rare earth sintered magnet alloy used to manufacture the rare earth sintered magnet 1 of the third embodiment can be replaced with a rare earth element R other than Nd. In other words, it is sufficient to pulverize a rare earth sintered magnet alloy having a (Nd, R)-Fe-B-M crystalline phase and a (Nd, R)-O phase.

[0075] In the molding step of step S22, the rare earth sintered magnet alloy powder is compression molded in a mold to which a magnetic field is applied to prepare a molded body. Here, the magnetic field applied can be, for example, 2 T. Note that molding may be performed without applying a magnetic field, rather than in a magnetic field.

[0076] In the sintering step of step S23, the compression-molded compact is held at a sintering temperature in the range of 950°C to 1300°C, preferably 1000°C to less than 1150°C, for a time in the range of 0.1 to 10 hours, preferably 1.0 to 6.0 hours, to obtain a sintered body. Sintering is preferably carried out in an atmosphere containing an inert gas or in a vacuum to suppress oxidation. Sintering may also be carried out while applying a magnetic field.

[0077] The aging step of step S24 is a process of aging the sintered body to improve the magnetic properties, such as the coercivity, of the rare earth sintered magnet 1. In the case of Figure 6, the aging step of step S24 includes a first aging step of step S24-1, a second aging step of step S24-2, a third aging step of step S24-3, and a fourth aging step of step S24-4. To suppress oxidation, the aging is preferably carried out in an atmosphere containing an inert gas or in a vacuum.

[0078] In the first aging step of step S24-1, the obtained sintered body is maintained at a first aging temperature, which is lower than the sintering temperature, for a time period ranging from 0.1 to 10 hours, preferably from 0.5 to 5 hours. The first aging temperature is specifically a temperature ranging from 700°C to lower than 950°C, which is lower than the sintering temperature.

[0079] In the second aging step of step S24-2, after the first aging step, the sintered body held in the first aging step is held at a second aging temperature, which is lower than the first aging temperature, for a time period ranging from 0.1 to 10 hours, preferably from 1.0 to 7 hours. The second aging temperature is specifically a temperature ranging from 450°C to lower than 700°C, which is lower than the first aging temperature.

[0080] In the third aging step of step S24-3, after the second aging step, the sintered body held in the second aging step is again heated to the first aging temperature, specifically, a temperature in the range of 700°C or higher and lower than 950°C, and held at the first aging temperature for a time in the range of 0.1 hour or higher and 10 hours or lower, preferably 0.5 hour or higher and 5 hours or lower.

[0081] In the fourth aging step of step S24-4, after the third aging step, the sintered body held in the third aging step is again held at the second aging temperature, specifically, at a temperature in the range of 450°C or higher and lower than 700°C, for a time in the range of 0.1 hour or higher and 10 hours or lower, preferably 1.0 hour or higher and 7 hours or lower.

[0082] Finally, in step S25, the sintered body cooling step, the sintered body held in the fourth aging step is held at a cooling temperature in the range of 200°C or higher but lower than 450°C for a time in the range of 0.1 hour to 5 hours. The sintered body is then cooled to room temperature to produce a diffusion precursor of the rare earth sintered magnet 1. Cooling is also preferably carried out in an atmosphere containing an inert gas or in a vacuum to suppress oxidation.

[0083] In this manner, a diffusion precursor is formed, which is a sintered body having the final shape of the rare earth sintered magnet 1 .

[0084] Next, the diffusion treatment step of step S30 in FIG. 4 will be described. FIG. 7 is a flowchart showing an example of the procedure for the diffusion treatment step in FIG. 4. As shown in FIG. 7, the diffusion treatment step includes a grain boundary diffusion step (step S31) in which heat treatment is performed at a diffusion temperature below the sintering temperature in the presence of a diffusion precursor and a heavy rare earth element to cause grain boundary diffusion of the heavy rare earth element RH into the diffusion precursor; an aging step (step S32) in which the diffusion precursor with the heavy rare earth element RH diffused therein obtained in the grain boundary diffusion step is held at a second aging temperature below the diffusion temperature; and a cooling step (step S33) in which the diffusion precursor with the heavy rare earth element RH diffused therein is cooled to obtain the rare earth sintered magnet 1. The aging step of step S32 corresponds to the second aging step. Each step will be described below.

[0085] In the grain boundary diffusion step of step S31, a heat treatment is performed under conditions in which the diffusion precursor produced according to the diffusion precursor production step of FIG. 6 and the heavy rare-earth element RH are present, thereby diffusing the heavy rare-earth element RH through grain boundaries into the diffusion precursor. In one example, a heat treatment is performed in which the diffusion precursor is maintained at a diffusion temperature lower than the sintering temperature in the sintering step of step S23. The grain boundary diffusion step may be performed simultaneously with the aging step of step S32. In the grain boundary diffusion step, the heavy rare-earth element RH is selectively diffused into at least a portion of the outer periphery of the Sm-enriched portion 41 of the first subphase 21 and uniformly diffused into the second subphase 22. This results in a diffusion precursor in which the heavy rare-earth element RH is diffused into the first subphase 21 and the second subphase 22, satisfying the relationship CRH<SRH and RH2<SRH. The diffusion precursor in which the heavy rare-earth element RH is diffused also satisfies the relationship CRH<RH2.

[0086] The grain boundary diffusion process can be carried out by a known grain boundary diffusion method. Various grain boundary diffusion methods have been proposed depending on the supply form of the heavy rare earth element RH, and typical methods include coating diffusion, sputter diffusion, and vapor diffusion. These typical grain boundary diffusion methods will be described below.

[0087] <Coating Diffusion Method> In the coating diffusion method, the grain boundary diffusion step includes a diffusing element attachment step of attaching a heavy rare earth element supplying portion, which is a material containing a heavy rare earth element (RH) and serves as a supply source of the heavy rare earth element (RH), to the diffusion precursor, and a diffusion heat treatment step of performing heat treatment to diffuse the heavy rare earth element (RH) from the heavy rare earth element supplying portion into the diffusion precursor. In the diffusing element attachment step, a slurry prepared by mixing a powdered heavy rare earth element compound with water or an organic solvent is attached to the surface of the diffusion precursor. The slurry attached to the surface of the diffusion precursor serves as the heavy rare earth element supplying portion. The slurry attachment can be performed by spraying, dip coating, spin coating, screen printing, electrodeposition, or the like. In the diffusion heat treatment step, the diffusion precursor to which the heavy rare earth element supplying portion is attached is heat-treated at a diffusion temperature lower than the sintering temperature in the sintering step of step S23, thereby diffusing the heavy rare earth element (RH) into the diffusion precursor. The heat treatment conditions are a diffusion temperature lower than the sintering temperature and a time period ranging from 0.1 to 100 hours. The diffusion temperature is, for example, in the range of 300° C. or higher and lower than 950° C., which is lower than the sintering temperature. The heat treatment is preferably carried out in an atmosphere containing an inert gas or in a vacuum in order to suppress oxidation.

[0088] <Sputter Diffusion Method> In the sputter diffusion method, as in the coating diffusion method, the grain boundary diffusion step includes a diffusing element deposition step and a diffusion heat treatment step. In the diffusing element deposition step, a thin film of a heavy rare earth element RH elemental metal or alloy composition is formed on the surface of the diffusion precursor in a dry environment. The thin film formed on the surface of the diffusion precursor serves as a heavy rare earth element supply portion. The thin film is formed, for example, by a sputtering method. In the diffusion heat treatment step, the diffusion precursor with the heavy rare earth element supply portion formed thereon is heat-treated at a diffusion temperature lower than the sintering temperature in the sintering step of step S23, thereby diffusing the heavy rare earth element RH into the interior of the diffusion precursor. The heat treatment conditions are a diffusion temperature lower than the sintering temperature and a time period ranging from 0.1 to 100 hours. In one example, the diffusion temperature is a temperature ranging from 300°C to 950°C, lower than the sintering temperature. The heat treatment is preferably performed in an atmosphere containing an inert gas or in a vacuum to suppress oxidation.

[0089] <Vapor Diffusion Method> In the vapor diffusion method, a diffusion precursor and a heavy rare earth element supply unit are placed in a vacuum furnace, and then the diffusion precursor is heat-treated in the vacuum furnace at a temperature lower than the sintering temperature in the sintering step of step S23, thereby diffusing the heavy rare earth element RH into the diffusion precursor. In the heat treatment, the heavy rare earth element supply unit is converted into a gas phase by vacuum heating, and the heavy rare earth element RH is supplied to the diffusion precursor through the gas phase. The heat treatment conditions are a diffusion temperature lower than the sintering temperature and a time period ranging from 0.1 to 100 hours. The diffusion temperature is, for example, from 600 to 900°C, lower than the sintering temperature. Furthermore, unlike the coating diffusion method and the sputter diffusion method, the vapor diffusion method does not require the heavy rare earth element supply unit to be attached to the diffusion precursor, and therefore the diffusion element attachment step can be omitted, thereby shortening the time required for the grain boundary diffusion step.

[0090] In the aging step of step S32, the diffusion precursor with the heavy rare earth element RH diffused therein is aged to improve the magnetic properties, such as the coercivity, of the rare earth sintered magnet 1. In the aging step of step S32, the diffusion precursor with the heavy rare earth element RH diffused therein is held at a second aging temperature lower than the sintering temperature of step S23 for a time period ranging from 0.1 to 100 hours. The second aging temperature is, for example, a temperature ranging from 600°C to 950°C, which is lower than the sintering temperature. Alternatively, an aging treatment including multiple steps may be performed, such as holding the diffusion precursor with the heavy rare earth element RH diffused at a temperature ranging from 600°C to 950°C, followed by holding it at a temperature ranging from 300°C to 600°C. As described above, the aging step of step S32 may be performed simultaneously with the grain boundary diffusion step of step S31.

[0091] In the cooling step of step S33, the diffusion precursor into which the heavy rare-earth element RH has been diffused is maintained at a temperature below 300°C for a time period ranging from 0.1 to 5 hours. The resulting mixture is then cooled to room temperature, thereby forming the rare earth sintered magnet 1 shown in any of the first to third embodiments. In the first embodiment, the resulting rare earth sintered magnet 1 has a core portion 211 and a shell portion 212 covering the core portion 211, and includes a first subphase 21 in which the concentration of the heavy rare-earth element RH satisfies the relationship CRH<SRH. In the second embodiment, the resulting rare earth sintered magnet 1 has a subphase 20 including the first subphase 21 in which the concentration of the heavy rare-earth element RH is lower than that of the shell portion 212 of the first subphase 21, and the second subphase 22 has a higher concentration of the element M than that of the first subphase 21. In the case of the third embodiment, when the R contained in the subphase 20 is La and Sm, La is present in the first subphase 21 and the second subphase 22, and a rare earth sintered magnet 1 is formed in which the concentration of Sm is higher in the first subphase 21 than in the second subphase 22. Cooling is preferably performed in an atmosphere containing an inert gas or in a vacuum to suppress oxidation.

[0092] As described above, by diffusing the heavy rare earth element RH through grain boundaries into the diffusion precursor having the shape of the final rare earth sintered magnet 1, a rare earth sintered magnet 1 having a desired shape can be obtained.

[0093] If raw materials not containing the heavy rare earth element RH are used in the rare earth sintered magnet alloy manufacturing process, the heavy rare earth element RH will diffuse into the diffusion precursor at grain boundaries in the diffusion treatment process, and some of the heavy rare earth element RH diffused through grain boundaries may diffuse into the main phase 10. In other words, there is a possibility that the heavy rare earth element RH will be included in the main phase 10 due to grain boundary diffusion.

[0094] As described above, in the fourth embodiment, a rare earth sintered magnet alloy having a (Nd, La, Sm)-Fe-B-M crystalline phase and a (Nd, La, Sm)-O phase is pulverized to form a rare earth sintered magnet alloy powder, and the resulting compact is sintered to form a sintered body, which is then aged to obtain a diffusion precursor. The heavy rare earth element RH is then diffused into the diffusion precursor at grain boundaries, followed by aging and cooling, to produce the rare earth sintered magnet 1. This allows the production of the rare earth sintered magnet 1 having the structure described in the third embodiment.

[0095] In addition, in embodiment 4, the temperature and time in the grain boundary diffusion step and the aging step are controlled. As a result, in the case of embodiment 1, a rare earth sintered magnet 1 is formed that has a core portion 211 and a shell portion 212 covering the core portion 211, and includes a first subphase 21 in which the concentrations of the heavy rare earth element RH in the core portion 211 and the shell portion 212 satisfy the relationship CRH<SRH. In the case of embodiment 2, a rare earth sintered magnet 1 is formed that has a subphase 20 that includes the first subphase 21 that satisfies the relationship CRH<SRH and a second subphase 22 in which the concentration of the heavy rare earth element RH is lower than that of the shell portion 212 of the first subphase 21, and in which the concentration of element M is higher in the second subphase 22 than in the first subphase 21. In the case of embodiment 3, when the R contained in the subphase 20 is La and Sm, La is present in the first subphase 21 and the second subphase 22, and a rare earth sintered magnet 1 is formed in which the concentration of Sm is higher in the first subphase 21 than in the second subphase 22.

[0096] In addition, in a method for manufacturing a rare earth sintered magnet 1 according to a fourth embodiment, an R-Fe-B-M rare earth sintered magnet alloy containing Nd, La, and Sm as rare earth elements R is pulverized, and a powder compact of the R-Fe-B-M rare earth sintered magnet alloy is sintered and aging-treated. This produces a diffusion precursor having a first subphase 21 with an Sm-enriched portion 41 where Sm is enriched, and a second subphase 22 with a lower Sm concentration than the first subphase 21. The diffusion precursor is then subjected to heat treatment to diffuse the heavy rare earth element RH through grain boundaries. This makes it possible to produce a rare earth sintered magnet 1 in which the heavy rare earth element RH selectively surrounds the outer periphery of the Sm-enriched portion 41 in the first subphase 21 and in which the heavy rare earth element RH is uniformly distributed in the second subphase 22.

[0097] The anisotropic rare earth sintered magnet of Patent Document 1 has a structure in which the main phase and subphase contain a large amount of Ce, making it impossible to form a texture with a sufficiently enhanced anisotropy magnetic field. However, in Embodiment 1, the amount of Ce used is smaller than in Patent Document 1, or no Ce is used at all, making it possible to form a rare earth sintered magnet 1 with a texture that is sufficiently enhanced in anisotropy magnetic field compared to the anisotropic rare earth sintered magnet described in Patent Document 1. In other words, the rare earth sintered magnet 1 produced by the method for producing a rare earth sintered magnet 1 according to Embodiment 4 can achieve better magnetic properties than Patent Document 1.

[0098] Furthermore, in the rare earth sintered magnet of Patent Document 2, the grain boundary triple junction is a transition metal-rich phase, and an R-rich phase and an HR-rich phase simply coexist. In particular, the HR-rich phase is present throughout the grain boundary triple junction, making it difficult to achieve both a significant reduction in the heavy rare earth element RH and high magnetic properties. In contrast, in Embodiment 4, a rare earth sintered magnet 1 is produced that includes a first subphase 21 in which the concentration of the heavy rare earth element RH is higher in the outer periphery, including the surface, than in the center surrounded by the outer periphery. In other words, the subphase 20 includes a first subphase 21 in which the heavy rare earth element RH is unevenly distributed in the outer periphery. As a result, compared to the case in Patent Document 2 in which the heavy rare earth element RH is present throughout the grain boundary triple junction, the rare earth sintered magnet 1 produced by the production method of Embodiment 4 can reduce the amount of heavy rare earth element RH used and achieve even higher magnetic properties.

[0099] Furthermore, in the subphase 20, the element M is present in high concentration in the second subphase 22, and therefore forms a non-magnetic phase that magnetically separates the main phases 10, thereby contributing to improving the magnetic properties. In other words, by making the concentration of element M higher in the second subphase 22 than in the first subphase 21, high magnetic properties, particularly coercivity, can be obtained and deterioration of the magnetic properties due to temperature increase can be suppressed.

[0100] This makes it possible to obtain a rare earth sintered magnet 1 that has improved magnetic properties compared to conventional magnets while using less of the heavy rare earth element RH than conventional magnets.

[0101] Embodiment 5 In embodiment 5, a rotor using the rare earth sintered magnet 1 of embodiments 1, 2, and 3 manufactured by the manufacturing method of embodiment 4 will be described. Figure 8 is a cross-sectional view schematically showing an example of the configuration of a rotor equipped with a rare earth sintered magnet according to embodiment 5. Figure 8 shows a cross section perpendicular to the rotation axis RA of the rotor 100.

[0102] The rotor 100 is rotatable about a rotation axis RA. The rotor 100 includes a rotor core 101 and rare earth sintered magnets 1 that are inserted into magnet insertion holes 102 provided in the rotor core 101 along the circumferential direction of the rotor 100. While Fig. 8 shows an example in which four magnet insertion holes 102 are provided in the rotor core 101 and four rare earth sintered magnets 1 are inserted into the magnet insertion holes 102, the number of magnet insertion holes 102 and the number of rare earth sintered magnets 1 may be changed depending on the design of the rotor 100. The rotor core 101 is formed by stacking a plurality of disk-shaped electromagnetic steel plates in the axial direction of the rotation axis RA.

[0103] The rare earth sintered magnets 1 are manufactured according to the manufacturing method described in embodiment 4. The four rare earth sintered magnets 1 are inserted into the corresponding magnet insertion holes 102. The four rare earth sintered magnets 1 are each magnetized so that the magnetic poles of the rare earth sintered magnets 1 on the radially outer side of the rotor 100 are different from adjacent rare earth sintered magnets 1.

[0104] As described above, rotor 100 according to embodiment 5 includes rare earth sintered magnet 1 according to embodiment 1, 2, or 3, which is capable of improving magnetic properties at room temperature and suppressing degradation of magnetic properties with increasing temperature. Because rotor 100 includes rare earth sintered magnet 1 that uses less heavy rare earth element RH than conventional magnets and can suppress degradation of magnetic properties with increasing temperature while maintaining high remanence and coercivity, degradation of magnetic properties is suppressed even in high-temperature environments exceeding 100°C. This allows for improved magnetic properties and magnetization, while substituting inexpensive rare earth element R for Nd and heavy rare earth element RH, which are expensive, unevenly distributed across regions, and present a procurement risk. This allows rotor 100 to operate stably even in high-temperature environments exceeding 100°C.

[0105] Sixth Embodiment In the sixth embodiment, a rotating machine equipped with the rotor 100 according to the fifth embodiment will be described. Fig. 9 is a cross-sectional view schematically showing an example of the configuration of a rotating machine according to the sixth embodiment. Fig. 9 shows a cross section in a direction perpendicular to the rotation axis RA of the rotor 100.

[0106] The rotating machine 120 includes the rotor 100 described in the fifth embodiment, which is rotatable about the rotation axis RA, and an annular stator 130 that is coaxial with the rotor 100 and disposed opposite the rotor 100. The stator 130 is formed by laminating a plurality of electromagnetic steel sheets in the axial direction of the rotation axis RA. The configuration of the stator 130 is not limited to this, and an existing configuration can also be adopted. The stator 130 has teeth 131 that protrude toward the rotor 100 and are disposed along the inner surface of the stator 130. Windings 132 are attached to the teeth 131. The windings 132 may be wound in a concentrated winding or a distributed winding manner, for example. In other words, the stator 130 has windings 132 attached to the teeth 131 that protrude toward the rotor 100 on the inner surface on the side where the rotor 100 is disposed, and has an annular structure that is disposed opposite the rotor 100. The rotor 100 in the rotating machine 120 needs to have two or more magnetic poles, i.e., two or more rare earth sintered magnets 1. Also, while Fig. 9 shows an example of an embedded magnet rotor 100, it may also be a surface magnet rotor 100 in which the rare earth sintered magnets 1 are fixed to the outer periphery with an adhesive.

[0107] Thus, the rotating machine 120 of embodiment 6 includes the rare earth sintered magnet 1 of embodiment 1, embodiment 2, or embodiment 3, which can achieve improved magnetic properties at room temperature and suppressed degradation of magnetic properties with increasing temperature. In other words, the rare earth sintered magnet 1 uses less heavy rare earth element RH than conventional magnets, maintaining high remanence and coercivity while suppressing degradation of magnetic properties with increasing temperature. Therefore, degradation of magnetic properties is suppressed even in high-temperature environments exceeding 100°C. As a result, while replacing expensive Nd and heavy rare earth element RH, which are unevenly distributed across regions and present procurement risks, with the inexpensive rare earth element R, magnetic properties and magnetization are improved, and the rotor 100 can be stably driven, even in high-temperature environments exceeding 100°C, resulting in stable operation of the rotating machine 120. In other words, the motor can be driven even in high-temperature environments exceeding 100°C.

[0108] The rare earth sintered magnet 1 of the present disclosure will be described in detail below with reference to examples and comparative examples.

[0109] In Examples 1 to 9, rare earth sintered magnet 1 was manufactured by the method shown in Embodiment 4 using samples of rare earth sintered magnet alloys with different compositions represented by (Nd, La, Sm)-Fe-B-Co. In Examples 1 to 9, rare earth sintered magnet alloys with varying contents of Nd, La, and Sm were used to form a diffusion precursor, and Tb, which is a heavy rare earth element RH, was diffused into the diffusion precursor at grain boundaries so that the Tb concentration was 0.08 at. %, thereby manufacturing rare earth sintered magnet 1. In other words, in Examples 1 to 9, rare earth sintered magnet 1 was manufactured by using the manufacturing method shown in Embodiment 4 from a rare earth sintered magnet alloy represented by (Nd, La, Sm)-Fe-B-Co, into which Tb, which is a heavy rare earth element RH, was diffused at a concentration of 0.08 at. %.

[0110] In Comparative Examples 1 to 10, samples of multiple rare earth sintered magnet alloys with different compositions, designated R-Fe-B or R-Fe-B-Co, were used to experimentally produce rare earth sintered magnets in which Tb, the heavy rare earth element RH, was diffused through grain boundaries using a general method for producing a rare earth sintered magnet, such as that shown in Patent Document 1 or Patent Document 2. In the rare earth sintered magnet samples of Comparative Examples 1 to 10, the R portion was changed.

[0111] In Comparative Example 1, a diffusion precursor is formed from a rare earth sintered magnet alloy in which R is Nd using the manufacturing method disclosed in Patent Document 1, and then 0.16 at. % of Tb, which is the heavy rare earth element RH, is diffused into this diffusion precursor using a known grain boundary diffusion method to produce a rare earth sintered magnet.

[0112] In Comparative Example 2, a diffusion precursor is formed from a rare earth sintered magnet alloy in which R is Nd and Ce using the manufacturing method disclosed in Patent Document 1, and then 0.16 at. % of Tb, which is a heavy rare earth element RH, is diffused into this diffusion precursor using a known grain boundary diffusion method to produce a rare earth sintered magnet.

[0113] In Comparative Example 3, a diffusion precursor is formed from a rare earth sintered magnet alloy in which R is Nd and Ce and M is Co using the manufacturing method disclosed in Patent Document 1, and 0.16 at. % of Tb, which is a heavy rare earth element RH, is diffused into this diffusion precursor using a known grain boundary diffusion method to produce a rare earth sintered magnet.

[0114] In Comparative Example 4, a diffusion precursor is formed from a rare earth sintered magnet alloy in which R is Nd and Dy and M is Co using the manufacturing method disclosed in Patent Document 2, and 0.16 at. % of Tb, which is a heavy rare earth element RH, is diffused into this diffusion precursor using a known grain boundary diffusion method to produce a rare earth sintered magnet.

[0115] In Comparative Example 5, a diffusion precursor is formed from a rare earth sintered magnet alloy in which R is Nd, La, and Sm using the manufacturing method disclosed in Patent Document 2, and then 0.16 at. % of Tb, which is a heavy rare earth element RH, is diffused into this diffusion precursor using a known grain boundary diffusion method to produce a rare earth sintered magnet.

[0116] In Comparative Examples 6 and 7, a diffusion precursor was formed from a rare earth sintered magnet alloy in which R was Nd, La, and Sm and M was Co using the manufacturing method disclosed in Patent Document 2, and then 0.16 at. % and 0.08 at. % of Tb, which is a heavy rare earth element RH, was diffused into this diffusion precursor using a known grain boundary diffusion method to produce rare earth sintered magnets.

[0117] In Comparative Example 8, a rare earth sintered magnet is produced from a rare earth sintered magnet alloy in which R is Nd, La, and Sm and M is Co, using the production method disclosed in Patent Document 2. The rare earth sintered magnet of Comparative Example 8 does not have Tb, which is the heavy rare earth element RH, diffused therein.

[0118] In Comparative Examples 9 and 10, a diffusion precursor was formed from a rare earth sintered magnet alloy in which R was Nd, La, Sm, and Dy and M was Co using the manufacturing method disclosed in Patent Document 2, and then 0.16 at. % and 0.08 at. % of Tb, which is a heavy rare earth element RH, was diffused into this diffusion precursor using a known grain boundary diffusion method to produce rare earth sintered magnets.

[0119] Table 3 shows the general formula of the rare earth sintered magnets of Examples 1 to 9 and Comparative Examples 1 to 10, the contents of the elements constituting R, the amount of diffused heavy rare earth element RH, the analysis results of the structural morphology of the subphases, and the evaluation results of the magnetic properties. The general formula in Table 3 shows the general formula of the main phase 10 of each sample, which is the rare earth sintered magnet 1 of Examples 1 to 9 and Comparative Examples 1 to 10.

[0120]

[0121] Next, a method for analyzing the structure of the rare earth sintered magnet 1 of Examples 1 to 9 and Comparative Examples 1 to 10 will be described. The structure of the rare earth sintered magnet 1 is determined by elemental analysis using a scanning electron microscope (SEM) and an electron probe microanalyzer (EPMA). Here, an FE-EPMA (manufactured by JEOL Ltd., product name: JXA-8530F) is used as the SEM and EPMA. The elemental analysis conditions are an acceleration voltage of 15.0 kV, a probe current of 2.271 e -008A, the irradiation time is 130 ms, the number of pixels is 512 pixels x 512 pixels, the magnification is 5000 times, and the number of integrations is 1.

[0122] Next, we will explain how to evaluate the magnetic properties of the rare earth sintered magnets 1 of Examples 1 to 9 and Comparative Examples 1 to 10. The magnetic properties were evaluated by measuring the coercivity of multiple samples using a pulse-excitation BH tracer. The maximum magnetic field applied by the BH tracer was 6 T or more, at which point the rare earth sintered magnet 1 was fully magnetized. In addition to pulse-excitation BH tracers, DC magnetic flux meters (also known as DC BH tracers), vibrating sample magnetometers (VSMs), magnetic property measurement systems (MPMSs), physical property measurement systems (PPMSs), and other instruments may also be used, as long as they can generate a maximum magnetic field of 6 T or more. Measurements were performed in an atmosphere containing an inert gas such as nitrogen. The magnetic properties of each sample were measured by detecting the magnetization of the rare earth sintered magnet 1 magnetized by the applied magnetic field, picked up by a search coil or magnetic sensor. The magnetic properties are measured from the JH curve or BH curve, which is the measured magnetic hysteresis.

[0123] First, we will explain the analysis results of each sample from Examples 1 to 9 and Comparative Examples 1 to 10. FIG. 10 is a trace of a composition image obtained by analyzing the cross section of the rare earth sintered magnets from Examples 1 to 9 with FE-EPMA. FIGS. 11 to 16 are elemental maps obtained by analyzing the cross section of the rare earth sintered magnets from Examples 1 to 9 with FE-EPMA. FIG. 11 is an elemental map of Nd, FIG. 12 is an elemental map of O, FIG. 13 is an elemental map of Tb, FIG. 14 is an elemental map of Co, FIG. 15 is an elemental map of La, and FIG. 16 is an elemental map of Sm. Note that FIGS. 11 to 16 are elemental maps of the region shown in FIG. 10. Furthermore, since the rare earth sintered magnets 1 from Examples 1 to 9 all showed similar results, FIGS. 10 to 16 show representative examples from Examples 1 to 9. Furthermore, the same components as those in FIGS. 1 and 2 are designated by the same reference numerals.

[0124] As shown in FIGS. 11 to 16, in each sample of Examples 1 to 9, R is La and Sm, the general formula (Nd, La, Sm)-Fe-B-M is satisfied, and NdFe 14 A main phase 10 containing crystal grains based on the B crystal structure and a subphase 20 existing between the main phases 10 can be confirmed.

[0125] The subphase 20 can be confirmed to include a crystalline first subphase 21 based on an oxide phase whose main component is expressed as (Nd, La, Sm)—O, and a crystalline second subphase 22 whose main component is expressed as (Nd, La)—O. It can also be confirmed that the concentrations of La and Sm are higher in the first subphase 21 than in the second subphase 22. It can also be confirmed that in the first subphase 21, the concentration of Tb, which is a heavy rare-earth element RH, is higher in the shell portion 212 than in the core portion 211, i.e., the relationship CRH<SRH is satisfied. It can also be confirmed that the Tb concentration is uniform and lower than the concentration in the shell portion 212 of the first subphase 21, i.e., the relationship RH2<SRH is satisfied. It can also be confirmed that the concentration of Tb in the second subphase 22 is higher than that in the core portion 211 of the first subphase 21, i.e., the relational expression CRH<RH2 is satisfied. It can also be confirmed that the concentration of Co, which is the additive element M, is higher in the second subphase 22 than in the first subphase 21. It can also be confirmed that the subphase 20 forms an R-rich phase having a higher concentration of rare earth elements R such as Nd, and an RH-rich phase having a higher concentration of heavy rare earth elements RH such as Tb, compared to the main phase 10. The formation of the R-rich phase and the RH-rich phase in the grain boundary phase, which is the subphase 20, results in high magnetic properties.

[0126] In Table 3, for samples in which the state of the first subphase 21 where CRH < SRH and the state of the second subphase 22 where RH2 < SRH were confirmed, a white circle is entered in the column for the first subphase 21 and the second subphase 22, respectively. For samples in which this was not confirmed, a cross is entered in the column for the first subphase 21 and the second subphase 22, respectively. The concentration difference indicated by the inequality sign indicates that, by mapping analysis using EPMA, a clear difference in the detected intensity of Tb was found between the core portion 211 and the shell portion 212 of the first subphase 21, and also indicates that a clear difference in the detected intensity of Tb was found between the shell portion 212 and the second subphase 22 of the first subphase 21. To give a specific example, in the case of the first subphase 21, the detected intensity by EPMA for the Tb concentration in the shell portion 212 is higher than average, and the detected intensity by EPMA for the Tb concentration in the core portion 211 is lower than average. In the case of the second subphase 22, the Tb concentration calculated from the EPMA detection intensity of the second subphase 22 is lower than the Tb concentration calculated from the EPMA detection intensity of the shell portion 212 of the first subphase 21.

[0127] Next, the results of measuring the magnetic properties of each sample in Examples 1 to 9 and Comparative Examples 1 to 10 will be described. Each sample used to measure the magnetic properties was a block with dimensions of 7 mm in length, width, and height. The measurement temperature was room temperature, 23°C.

[0128] First, the remanence and coercivity of each sample in Examples 1 to 9 and Comparative Examples 2 to 10 are judged by comparison with Comparative Example 1. If the remanence and coercivity values ​​of each sample at 23°C are within 1%, which is considered to be a measurement error, compared to the values ​​in Comparative Example 1, they are judged as "equivalent." If they are 1% or more higher, they are judged as "good." If they are 1% or less lower, they are judged as "poor." The above judgment results for remanence and coercivity are shown in Table 3.

[0129] Comparative Example 1 is a rare earth sintered magnet sample prepared according to the manufacturing method described in Patent Document 1 using Nd, Fe, and FeB as raw materials to form an Nd—Fe—B magnet, to which 0.16 at. % Tb was diffused. When the structural morphology of this sample was observed according to the method described above, the presence of a first subphase 21, which has a core portion 211 and a shell portion 212 covering the core portion 211, and in which the concentration of the heavy rare earth element RH satisfies the relationship CRH < SRH, was not confirmed. Furthermore, the presence of a second subphase 22, in which the concentration of the heavy rare earth element RH satisfies the relationship RH2 < SRH, was not confirmed. When the magnetic properties of this sample were evaluated according to the method described above, the remanence was 1.3 T and the coercivity was 1450 kA / m. These values ​​of Comparative Example 1 are used as references.

[0130] Comparative Example 2 is a rare earth sintered magnet sample prepared according to the manufacturing method described in Patent Document 1 using Nd, Ce, Fe, and FeB as raw materials, to form a (Nd, Ce)—Fe—B structure, with 0.16 at. % Tb diffused therein. Observation of the morphology of this sample using the method described above revealed no presence of a first subphase 21 having a core portion 211 and a shell portion 212 covering the core portion 211, in which the concentration of the heavy rare earth element RH satisfies the relationship C<SR. Furthermore, no presence of a second subphase 22 having the concentration of the heavy rare earth element RH satisfying the relationship RH2<SR. The magnetic properties of this sample were evaluated using the method described above, and compared with the reference, both the remanence and coercivity were "poor." This result reflects the degradation of magnetic properties due to the substitution of Ce, which does not have magnetocrystalline anisotropy, for part of the Nd.

[0131] Comparative Example 3 is a rare earth sintered magnet sample prepared according to the manufacturing method described in Patent Document 1 using Nd, Ce, Fe, FeB, and Co as raw materials to form a (Nd, Ce)—Fe—B—Co structure, with 0.16 at. % Tb diffused into the magnet. Observation of the structural morphology of this sample using the method described above revealed no presence of a first subphase 21 having a core portion 211 and a shell portion 212 covering the core portion 211, in which the concentration of the heavy rare earth element RH satisfies the relationship C<SR. Furthermore, no presence of a second subphase 22 having the concentration of the heavy rare earth element RH satisfying the relationship RH2<SRH was confirmed. The magnetic properties of this sample were evaluated using the method described above, and compared with those of the reference, revealing that the remanence was "similar" and the coercivity was "poor." This is a result that reflects the fact that Ce, which does not have magnetocrystalline anisotropy, has substituted for part of Nd, but the addition of Co, which is a ferromagnetic material, improves the residual magnetic flux density.

[0132] Comparative Example 4 is a rare earth sintered magnet sample prepared according to the manufacturing method described in Patent Document 2 using Nd, Dy, Fe, FeB, and Co as raw materials to form a (Nd, Dy)-Fe-B-Co structure, to which 0.16 at. % Tb was diffused. Observation of the structural morphology of this sample using the method described above revealed no presence of a first subphase 21 having a core portion 211 and a shell portion 212 covering the core portion 211, in which the concentration of the heavy rare earth element RH satisfies the relationship CRH < SRH. Furthermore, no presence of a second subphase 22 in which the concentration of the heavy rare earth element RH satisfies the relationship RH2 < SRH was confirmed. The magnetic properties of this sample were evaluated using the method described above and compared with those of the reference, revealing a "poor" remanence and a "good" coercivity. This is a result that reflects the fact that the coercivity is improved by substituting part of the Nd with Dy, which has high crystalline magnetic anisotropy, but the residual magnetic flux density is reduced due to a decrease in the maximum energy product, which is the maximum value of the product B×H of the magnetic flux density B and the magnetic field H on the BH demagnetization curve.

[0133] Comparative Example 5 is a rare earth sintered magnet sample prepared according to the manufacturing method described in Patent Document 2 using Nd, La, Sm, Fe, and FeB as raw materials to form a (Nd, La, Sm)—Fe—B structure, to which 0.16 at. % Tb was diffused. Observation of the morphology of this sample using the method described above revealed the absence of a first subphase 21 having a core portion 211 and a shell portion 212 covering the core portion 211, in which the concentration of the heavy rare earth element RH satisfies the relationship C<SR. Furthermore, the presence of a second subphase 22 having the concentration of the heavy rare earth element RH satisfying the relationship RH<SR. The magnetic properties of this sample were evaluated using the method described above, and compared with the reference, the remanence and coercivity were found to be "similar." This result reflects the fact that only a small amount of La and Sm was substituted for the Nd present in the main phase, the subphase structure was not optimized, and the magnetic properties were not significantly changed.

[0134] Comparative Example 6 is a rare earth sintered magnet sample prepared according to the manufacturing method described in Patent Document 2 using Nd, La, Sm, Fe, FeB, and Co as raw materials to form a (Nd, La, Sm)-Fe-B-Co structure, with 0.16 at. % Tb diffused therein. Observation of the morphology of this sample using the method described above revealed no presence of a first subphase 21 having a core portion 211 and a shell portion 212 covering the core portion 211, in which the concentration of the heavy rare earth element RH satisfies the relationship C<SR. Furthermore, no presence of a second subphase 22 having the concentration of the heavy rare earth element RH satisfying the relationship RH2<SR. The magnetic properties of this sample were evaluated using the method described above, and compared with the reference, the remanence was found to be "good" and the coercivity to be "same." This result reflects the improved remanence due to the addition of Co, a ferromagnetic material, to the composition of Comparative Example 5.

[0135] Comparative Example 7 is a rare earth sintered magnet sample prepared according to the manufacturing method described in Patent Document 2 using Nd, La, Sm, Fe, FeB, and Co as raw materials to form a (Nd, La, Sm)-Fe-B-Co structure, with 0.08 at. % Tb diffused therein. The composition ratio of Nd, La, and Sm differs from that of Comparative Example 6, and the amount of Tb diffused is half that of Comparative Example 6. Observation of the structural morphology of this sample using the method described above revealed no presence of a first subphase 21 having a core portion 211 and a shell portion 212 covering the core portion 211, in which the concentration of the heavy rare earth element RH satisfies the relationship CRH < SRH. Furthermore, no presence of a second subphase 22 in which the concentration of the heavy rare earth element RH satisfies the relationship RH2 < SRH was confirmed. The magnetic properties of this sample were evaluated using the method described above, and compared with those of the reference, revealing a "good" remanence and a "poor" coercivity. This result reflects the fact that the coercivity is reduced by half of the amount of the heavy rare-earth element RH diffused into the grain boundaries compared to the composition of Comparative Example 6. Furthermore, as described in the first to third embodiments, when the structural state of the subphase 20 is not optimal, the result reflects the fact that the magnetic properties are reduced by the amount of diffusion of the heavy rare-earth element RH.

[0136] Comparative Example 8 is a rare earth sintered magnet sample produced according to the manufacturing method described in Patent Document 2 using Nd, La, Sm, Fe, FeB, and Co as raw materials to form a (Nd, La, Sm)-Fe-B-Co structure. The composition ratio of Nd, La, and Sm is the same as that of Comparative Example 7, but Tb is not diffused. Observation of the structural morphology of this sample using the method described above reveals that the first subphase 21, which has a core portion 211 and a shell portion 212 covering the core portion 211 and in which the concentration of the heavy rare earth element RH satisfies the relationship CRH < SRH, is not confirmed. Furthermore, the presence of the second subphase 22, in which the concentration of the heavy rare earth element RH satisfies the relationship RH2 < SRH, is not confirmed. The magnetic properties of this sample were evaluated using the method described above and compared with the reference, revealing a "good" remanence and a "poor" coercivity. This result reflects the significant decrease in coercivity due to the reduction in the amount of grain boundary diffusion element to zero compared to the composition of Comparative Example 7. Furthermore, as described in the first to third embodiments, when the structural state of the subphase 20 is not optimal, the result reflects the decrease in magnetic properties due to the reduction in the amount of diffusion of the heavy rare-earth element RH.

[0137] Comparative Example 9 is a rare earth sintered magnet sample prepared according to the manufacturing method described in Patent Document 2 using Nd, La, Sm, Dy, Fe, FeB, and Co as raw materials to form a (Nd, La, Sm, Dy)-Fe-B-Co structure, with 0.16 at. % Tb diffused therein. Observation of the structural morphology of this sample using the method described above revealed no presence of a first subphase 21 having a core portion 211 and a shell portion 212 covering the core portion 211, in which the concentration of the heavy rare earth element RH satisfies the relationship C<SR. Furthermore, no presence of a second subphase 22 having the concentration of the heavy rare earth element RH satisfying the relationship RH2<SR. The magnetic properties of this sample were evaluated using the method described above, and compared with those of the reference, revealing a "poor" remanence and a "good" coercivity. It is thought that by substituting a portion of Nd with La or Sm, it is possible to suppress the substitution of Dy for Nd and thereby suppress the decrease in remanence due to the substitution of Dy for Nd. However, as a result, a portion of Nd is substituted with Dy, resulting in a decrease in remanence, and the result reflects the significant improvement in coercivity due to the inclusion of an excessive amount of the heavy rare earth element RH in the main phase 10 and the subphase 20. As described in the first to third embodiments, unless the structural state of the subphase 20 is optimized, it is difficult to improve the magnetic properties while reducing the amount of the heavy rare earth element RH.

[0138] Comparative Example 10 is a rare earth sintered magnet sample prepared according to the manufacturing method described in Patent Document 2 using Nd, La, Sm, Dy, Fe, FeB, and Co as raw materials to form a (Nd, La, Sm, Dy)-Fe-B-Co structure, to which 0.08 at. % Tb was diffused. The composition ratio of Nd:Dy differs from that of Comparative Example 9, and the amount of Tb diffused is half that of Comparative Example 9. Observing the structural morphology of this sample using the method described above revealed the absence of a first subphase 21 having a core portion 211 and a shell portion 212 covering the core portion 211, in which the concentration of the heavy rare earth element RH satisfies the relationship C<SR. Furthermore, the presence of a second subphase 22 in which the concentration of the heavy rare earth element RH satisfies the relationship RH2<SRH was also not confirmed. The magnetic properties of this sample were evaluated according to the above-described method and compared with the reference. The remanence was found to be "poor" and the coercivity was found to be "good." Because the amount of the heavy rare-earth element RH in Comparative Example 9 was excessive, the amount of the heavy rare-earth element RH was reduced in Comparative Example 10. By substituting La and Sm for a portion of Nd, the decrease in remanence due to the substitution of Dy for Nd could be significantly suppressed. Furthermore, since Dy improves the coercivity, it was possible to reduce the amount of Tb, which is the heavy rare-earth element RH, that diffused. However, the result reflects the decrease in remanence due to the substitution of Dy for a portion of Nd. As with Comparative Example 9, the results show that it is difficult to improve the magnetic properties while reducing the amount of the heavy rare-earth element RH unless the structural state of the subphase 20 is optimized as described in the first to third embodiments.

[0139] The samples of Examples 1 to 9 satisfy the general formula (Nd, R)-Fe-B-M when R is one or more rare earth elements selected from the group consisting of Nd, Al, Cu, and Co, and are NdFe. 14It was confirmed that the samples contained subphases 20 formed between a plurality of main phases 10 containing crystal grains based on the Nd-B crystal structure. The subphases 20 were also confirmed to be crystalline subphases 20 primarily composed of an oxide phase represented by the formula (Nd, R, RH)-O, where RH is one or more heavy rare earth elements selected from the group consisting of Dy, Tb, and Ho. It was also confirmed that, in the samples of Examples 1 to 9, the subphases 20 had an inverted core-shell structure having a core portion 211 and a shell portion 212 covering the core portion 211, and contained a first subphase 21 in which the concentration of the heavy rare earth element RH satisfied the relational expression CRH<SRH, and a second subphase 22 in which the concentration of the heavy rare earth element RH satisfied the relational expression RH2<SRH. The magnetic properties of these samples were evaluated according to the above-described method, and compared with the reference, the remanence was found to be "good" and the coercivity was found to be "good." Furthermore, the amount of heavy rare earth element R used in grain boundary diffusion is half that of the reference. As a result, the rare earth sintered magnets 1 of Examples 1 to 9 have the advantage of being able to significantly improve coercivity without reducing remanence, while reducing the use of heavy rare earth element R, which is expensive and subject to regional uneven distribution and procurement risks. In other words, the rare earth sintered magnets 1 of Examples 1 to 9 have the advantage of having magnetic properties that are superior to those of conventional magnets.

[0140] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0141] Various aspects of the present disclosure are summarized below as appendices.

[0142] [Note 1] When R is one or more rare earth elements selected from the group consisting of Nd and M is one or more elements selected from the group consisting of Ga, Al, Cu, and Co, the general formula (Nd, R)-Fe-B-M is satisfied, and NdFe 14A rare earth sintered magnet comprising: a main phase including crystal grains having a Nd-B crystal structure; and a subphase present between the main phase and the main phase, wherein the subphase has a crystalline first subphase whose main component is an oxide phase represented by the formula (Nd, R, RH)-O, where RH is one or more heavy rare earth elements selected from the group consisting of Dy, Tb, and Ho, and the first subphase has a first region having a first concentration of the heavy rare earth element and a second region surrounding the first region having a second concentration of the heavy rare earth element higher than the first concentration. [Appendix 2] The rare earth sintered magnet according to Appendices 1, wherein the subphase further comprises a second subphase having a third concentration of the heavy rare earth element lower than the second concentration, and wherein the second subphase has a higher concentration of the element M than the first subphase. [Appendix 3] The rare earth sintered magnet according to Appendix 2, characterized in that, when R is La and Sm, La is present in the first subphase and the second subphase, and the concentration of Sm is higher in the first subphase than in the second subphase. [Appendix 4] The rare earth sintered magnet according to Appendix 2 or 3, characterized in that the third concentration of the heavy rare earth element in the second subphase is higher than the first concentration and lower than the second concentration.[Appendix 5] A method for producing a rare earth sintered magnet according to any one of Appendices 1 to 4, comprising: a rare earth sintered magnet alloy production step of producing a rare earth sintered magnet alloy that serves as a raw material for a diffusion precursor before diffusing the heavy rare earth element into the rare earth sintered magnet; a diffusion precursor production step of producing the diffusion precursor; and a diffusion treatment step of diffusing the heavy rare earth element into the diffusion precursor, wherein the rare earth sintered magnet alloy production step comprises: a melting step of melting raw materials for the rare earth sintered magnet alloy that contain elements that constitute the diffusion precursor; and an alloy cooling step of cooling the raw materials in a molten state obtained in the melting step to obtain a solidified alloy, wherein the diffusion precursor production step comprises: a crushing step of crushing the rare earth sintered magnet alloy that contains a crystal layer that satisfies (Nd, R)-Fe-B-M; a compacting step of compacting powder of the rare earth sintered magnet alloy crushed in the crushing step to prepare a green body; and a sintering step of sintering the green body at a predetermined sintering temperature to obtain a sintered body. a first aging step of holding the sintered body at a first aging temperature that is lower than the sintering temperature, and a sintered body cooling step of cooling the sintered body at a temperature lower than the first aging temperature to obtain the diffusion precursor, wherein the diffusion treatment step includes a grain boundary diffusion step of performing a heat treatment at a diffusion temperature that is lower than the sintering temperature in the presence of the diffusion precursor and the heavy rare earth element to cause grain boundary diffusion of the heavy rare earth element into the diffusion precursor, a second aging step of holding the diffusion precursor with the heavy rare earth element diffused therein, obtained in the grain boundary diffusion step, at a second aging temperature that is lower than the diffusion temperature, and a cooling step of cooling the diffusion precursor with the heavy rare earth element diffused therein. [Appendix 6] A rotor comprising: a rotor core; and the rare earth sintered magnet according to any one of Appendices 1 to 4, provided in the rotor core. [Supplementary Note 7] A rotating machine comprising: the rotor according to Supplementary Note 6; and an annular stator disposed opposite the rotor, the stator having windings attached to teeth protruding toward the rotor on an inner surface on the side where the rotor is disposed.

[0143] 1 Rare earth sintered magnet, 10 Main phase, 20 Subphase, 21 First subphase, 22 Second subphase, 41 Sm-enriched portion, 42 Heavy rare earth element-containing portion, 100 Rotor, 101 Rotor core, 102 Magnet insertion hole, 120 Rotating machine, 130 Stator, 131 Teeth, 132 Winding, 211 Core portion, 212 Shell portion.

Claims

1. When R is one or more rare earth elements selected from the group consisting of Nd and M is one or more elements selected from the group consisting of Ga, Al, Cu, and Co, the general formula (Nd, R)-Fe-B-M is satisfied, and NdFe 14 1. A rare earth sintered magnet comprising: a main phase including crystal grains having a Nd-B crystal structure; and a subphase present between the main phase and the subphase; wherein the subphase has a crystalline first subphase whose main component is an oxide phase represented by the formula (Nd, R, RH)-O, where RH is one or more heavy rare earth elements selected from the group consisting of Dy, Tb, and Ho; and wherein the first subphase has a first region in which the heavy rare earth element has a first concentration, and a second region in which the heavy rare earth element has a second concentration higher than the first concentration, surrounding the first region.

2. The rare earth sintered magnet according to claim 1, characterized in that the subphases further include a second subphase in which the concentration of the heavy rare earth element is a third concentration lower than the second concentration, and the concentration of element M is higher in the second subphase than in the first subphase.

3. The rare earth sintered magnet according to claim 2, wherein, when R is La and Sm, La is present in the first subphase and the second subphase, and the concentration of Sm is higher in the first subphase than in the second subphase.

4. A rare earth sintered magnet according to claim 2 or 3, wherein the third concentration of the heavy rare earth element in the second subphase is higher than the first concentration and lower than the second concentration.

5. A method for producing a rare earth sintered magnet according to any one of claims 1 to 4, comprising: a rare earth sintered magnet alloy production process for producing a rare earth sintered magnet alloy that serves as a raw material for a diffusion precursor before diffusing the heavy rare earth element into the rare earth sintered magnet; a diffusion precursor production process for producing the diffusion precursor; and a diffusion treatment process for diffusing the heavy rare earth element into the diffusion precursor, wherein the rare earth sintered magnet alloy production process comprises: a melting process for melting raw materials for the rare earth sintered magnet alloy that contain elements that constitute the diffusion precursor; and an alloy cooling process for cooling the raw materials in a molten state obtained in the melting process to obtain a solidified alloy, wherein the diffusion precursor production process comprises: a crushing process for crushing the rare earth sintered magnet alloy that contains a crystal layer that satisfies the (Nd, R)-Fe-B-M relationship; a compacting process for preparing a compact by compacting powder of the rare earth sintered magnet alloy crushed in the crushing process; and a sintering process for sintering the compact at a predetermined sintering temperature to obtain a sintered body. a first aging step of holding the sintered body at a first aging temperature that is lower than the sintering temperature; and a sintered body cooling step of cooling the sintered body at a temperature lower than the first aging temperature to obtain the diffusion precursor, wherein the diffusion treatment step includes: a grain boundary diffusion step of performing heat treatment at a diffusion temperature that is lower than the sintering temperature in the presence of the diffusion precursor and the heavy rare earth element, thereby causing the heavy rare earth element to diffuse through grain boundaries into the diffusion precursor; a second aging step of holding the diffusion precursor in which the heavy rare earth element has been diffused, obtained in the grain boundary diffusion step, at a second aging temperature that is lower than the diffusion temperature; and a cooling step of cooling the diffusion precursor in which the heavy rare earth element has been diffused.

6. A rotor comprising: a rotor core; and the rare earth sintered magnet according to any one of claims 1 to 4 provided in the rotor core.

7. A rotating machine comprising: a rotor according to claim 6; and an annular stator disposed opposite the rotor, the stator having windings attached to teeth protruding toward the rotor on the inner surface on the side where the rotor is disposed.

Images