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

Abstract

A rare earth sintered magnet (1) comprises: a main phase (10) containing crystal grains satisfying the general formula (Nd, Pr, RH, R)-Fe-B and based on an Nd2Fe14B crystal structure, where RH denotes a heavy rare earth element containing at least one of Dy and Tb, and R denotes one or more rare earth elements selected from other than Nd, Pr, Dy, and Tb; and a subphase (20) present among a plurality of the main phases. The main phase has core sections (11c, 12c) and shell sections (11s, 12s) covering the core sections. The main phase has a first main phase (11) in which CNd > CPr and a second main phase (12) in which CNd < CPr, where CNd denotes the concentration of Nd in the core section and CPr denotes the concentration of Pr in the core section. The concentration of the heavy rare earth element RH in the core section of the first main phase is higher than the concentration of the heavy rare earth element RH in the core section of the second main phase. The first and second main phases are mixed and heavy rare earth elements are present on at least a part of the surfaces in the first main phase and the second main phase.

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) to Nd-T-B system sintered magnets.

[0003] In recent years, the production volume of Nd—Fe—B sintered magnets has expanded, leading to an increase in the consumption of Nd and heavy rare earth elements such as Dy and Tb (terbium). However, Nd and heavy rare earth elements are expensive and unevenly distributed across regions, posing procurement risks. For this reason, research is being conducted into technologies to reduce the consumption of Nd and heavy rare earth elements.

[0004] In Patent Document 1, R2T 14 The present invention discloses an R-T-B based sintered magnet containing main phase particles made of B crystals, where R is one or more rare earth elements essentially containing a heavy rare earth element RH, T is one or more transition metal elements essentially containing Fe or Fe and Co, and B is boron, and some of the main phase particles contain multiple lower heavy rare earth element crystal phases and multiple nonmagnetic R-rich phases therein. Here, the lower heavy rare earth element crystal phase is R2T 14The nonmagnetic R-rich phase is a phase consisting of B crystals, in which the concentration of heavy rare earth elements is relatively low compared to the concentration of heavy rare earth elements in the main phase particles as a whole. The nonmagnetic R-rich phase is a phase in which the R content is 70 at. % or more and 100 at. % or less. Furthermore, some of the main phase particles have a single core-shell structure having a core portion and a shell portion surrounding the core portion and having a lower total heavy rare earth element concentration than the core portion. The technology described in Patent Document 1 makes it possible to obtain an R-T-B based sintered magnet with improved coercivity and at low cost.

[0005] In Patent Document 2, (R1 1-x R2 x ) a TM b B c M d The method for producing a rare earth magnet is disclosed, which comprises a first step of producing a sintered body having a structure represented by the composition formula below and consisting of a main phase and a grain boundary phase; a second step of producing a rare earth magnet precursor by hot plastic working the sintered body; and a third step of producing a rare earth magnet by diffusing and infiltrating a melt of an R3-M modified alloy into the grain boundary phase of the rare earth magnet precursor. Here, R1 is one or more rare earth elements including Y (yttrium), R2 is a rare earth element different from R1, TM is a transition metal including one or more of Fe, Ni (nickel), and Co, B is boron, and M is one or more of Ti (titanium), Ga (gallium), Zn (zinc), Si (silicon), Al (aluminum), Nb (niobium), Zr (zirconium), Ni, Co, Mn (manganese), V (vanadium), W (tungsten), Ta (tantalum), Ge (germanium), Cu (copper), Cr (chromium), Hf (hafnium), Mo (molybdenum), P (phosphorus), C (carbon), Mg (magnesium), Hg (mercury), Ag (silver), and Au (gold). Furthermore, x, a, b, c, and d are 0.01≦x≦1, 12≦a≦20, b=100-a-c-d, 5≦c≦20, and 0≦d≦3, all in atomic percent. Furthermore, R3 is a rare earth element containing R1 and R2. Hereinafter, the hot plastic processing applied to the sintered body will be referred to as hot processing. The technology described in Patent Document 2 reduces the heavy rare earth element content and enables the production of rare earth magnets that exhibit excellent magnetization and coercive force performance, even when the main phase ratio is high.

[0006] JP 2018-174313 A JP 2015-153813 A

[0007] However, while the R-T-B based sintered magnet described in Patent Document 1 can improve coercivity due to the presence of a phase containing a heavy rare earth element within the main phase, the structural structure of the R-T-B based sintered magnet described in Patent Document 1 does not provide the remanence required for industrial motors, etc., and there is a possibility that the magnetic properties will deteriorate due to thermal load. Also, while the rare earth magnet produced by the manufacturing method described in Patent Document 2 can reduce the heavy rare earth element content and improve coercivity, the manufacturing method includes hot working, which reduces the grain size of the main phase, resulting in the problem of poor magnetization performance.

[0008] The present disclosure has been made in light of the above, and aims to provide a rare earth sintered magnet that can improve coercivity without reducing remanence and magnetization performance 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, Pr, RH, R)-Fe-B, and has a structure of NdFe, when RH is a heavy rare earth element containing at least one of Dy and Tb, and R is one or more rare earth elements selected from the group consisting of Nd, Pr (praseodymium), Dy, and Tb. 14 The alloy comprises a main phase including crystal grains based on a B crystal structure, and subphases present between the multiple main phases. The main phase has a core portion and a shell portion covering the core portion. The main phase has a first main phase in which the Nd concentration in the core portion is CNd>CPr and a second main phase in which the Pr concentration in the core portion is CPr. The concentration of the heavy rare earth element RH in the core portion of the first main phase is higher than the concentration of the heavy rare earth element RH in the core portion of the second main phase. The first and second main phases are mixed, and the heavy rare earth element is present on at least a portion of the surfaces of the first and second main phases.

[0010] The rare earth sintered magnet according to the present disclosure has the effect of being able to improve the coercive force without reducing the remanence and magnetization performance compared to conventional magnets.

[0011] FIG. 1 is a diagram showing an example of the structure of a rare earth sintered magnet in a sintered state according to embodiment 1. FIG. 2 is a diagram showing an example of the structure of a rare earth sintered magnet in a sintered state according to embodiment 2. FIG. 3 is a diagram showing an example of the structure of a rare earth sintered magnet in a sintered state according to embodiment 3. Tetragonal NdFe 14 FIG. 1 is a diagram showing atomic sites in a B crystal structure. FIG. 2 is a flowchart showing an example of the procedure for a method for manufacturing a rare earth sintered magnet according to the fourth embodiment. FIG. 3 is a flowchart showing an example of the procedure for a rare earth sintered magnet alloy manufacturing process according to the fourth embodiment. FIG. 4 is a flowchart showing an example of the procedure for a diffusion precursor manufacturing process according to the fourth embodiment. FIG. 5 is a cross-sectional view schematically showing an example of the configuration of a rotor equipped with a rare earth sintered magnet according to the fifth embodiment. FIG. 6 is a cross-sectional view schematically showing an example of the configuration of a rotating machine according to the sixth embodiment.

[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, Pr, RH, R)—Fe—B, and is NdFe 14 The rare earth sintered magnet 1 has a main phase 10 containing crystal grains based on a B crystal structure, with the main phase 10 having a core portion and a shell portion covering the core portion. Here, RH is a heavy rare earth element, such as Dy, Tb, Gd (gadolinium), or Ho (holmium). Preferably, RH is a heavy rare earth element containing at least one of Dy and Tb. R is one or more rare earth elements selected from the group consisting of Nd, Pr, and RH. The shell portion has a different composition from the core portion and is provided to cover the core portion. The rare earth sintered magnet 1 further has subphases 20 present between the main phases 10, i.e., between multiple main phases 10. The subphases 20 are based on an oxide phase represented by the formula (Nd, Pr, R)—O as the main component. O is oxygen.

[0014] In rare earth sintered magnet 1 according to embodiment 1, when the concentration of Nd in core portions 11c and 12c is CNd and the concentration of Pr in core portions 11c and 12c is CPr, main phase 10 includes first main phase 11 in which CNd > CPr and second main phase 12 in which CNd < CPr, and first main phase 11 and second main phase 12 are mixed together. Furthermore, the concentration of the heavy rare earth element RH in core portion 11c of first main phase 11 is higher than the concentration of the heavy rare earth element RH in core portion 12c of second main phase 12. That is, when the concentration of the heavy rare earth element RH in core portion 11c of first main phase 11 is C1RH and the concentration of the heavy rare earth element RH in core portion 12c of second main phase 12 is C2RH, C1RH > C2RH. The first main phase 11 has a core portion 11c and a shell portion 11s that has a different composition from the core portion 11c and covers the core portion 11c. The second main phase 12 has a core portion 12c and a shell portion 12s that has a different composition from the core portion 12c and covers the core portion 12c.

[0015] Alternatively, in rare earth sintered magnet 1 according to embodiment 1, when the sum of the concentration of Nd and the concentration of the heavy rare earth element RH in core portions 11c, 12c is C(Nd, RH), main phase 10 has a first main phase 11 in which C(Nd, RH)>CPr and a second main phase 12 in which C(Nd, RH)<CPr, and it can be said that first main phase 11 and second main phase 12 are mixed together.

[0016] In other words, rare earth sintered magnet 1 contains two types of main phases 10: first main phase 11 and second main phase 12. Focusing on the cores 11c, 12c of the two types of main phases 10, the sum of the concentrations of Nd and the heavy rare earth element RH is higher than the concentration of Pr in first main phase 11. Conversely, in second main phase 12, the concentration of Pr is higher than the sum of the concentration of Nd and the concentration of the heavy rare earth element RH. By combining two types of main phases 10 with core-shell structures that have different anisotropy fields, i.e., magnetic anisotropies, and selectively including the heavy rare earth element RH within main phase 10, it is possible to reduce the amounts of Nd and the heavy rare earth element RH while maintaining good magnetization and improving remanence and coercivity. Furthermore, the addition of the heavy rare earth element RH significantly improves coercivity, thereby contributing to suppressing temperature-related degradation of magnetic properties.

[0017] The concentration difference indicated by "C1RH > C2RH" here 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 region 11c of the first main phase 11 and the core region 12c of the second main phase 12. Specifically, the EPMA detection intensity for the concentration of the heavy rare-earth element RH in the core region 11c of the first main phase 11 is higher than the average detection intensity for the heavy rare-earth element RH, while the EPMA detection intensity for the concentration of the heavy rare-earth element RH in the core region 12c of the second main phase 12 is near the lower limit of the detection intensity for the heavy rare-earth element RH. In one example, the heavy rare-earth element RH is contained in the core region 11c of the first main phase 11 but is hardly contained in the core region 12c of the second main phase 12.

[0018] Furthermore, the concentration difference shown between "the first main phase 11 where C(Nd, RH)>CPr and the second main phase 12 where C(Nd, RH)<CPr" means that a clear difference has been found between the detected intensities of Nd and the heavy rare-earth element RH and the detected intensities of Pr by mapping analysis using EPMA. Specifically, taking the first main phase 11 as an example, the detected intensities of Nd and the heavy rare-earth element RH in the core region 11c by EPMA are higher than the average of the detected intensities of Nd and the heavy rare-earth element RH, and the detected intensities of Pr by EPMA are near the lower limit of the detected intensities. It can be said that the second main phase 12 is the opposite of the first main phase 11.

[0019] Furthermore, in rare earth sintered magnet 1 according to embodiment 1, when the Nd concentration in core region 11c of first main phase 11 is C1Nd, the Nd concentration in core region 12c of second main phase 12 is C2Nd, the Pr concentration in core region 11c of first main phase 11 is C1Pr, and the Pr concentration in core region 12c of second main phase 12 is C2Pr, the following relationship is satisfied: C1Nd > C2Nd, C1Pr < C2Pr. In other words, the Nd concentration is higher in core region 11c of first main phase 11 than in core region 12c of second main phase 12, and conversely, the Pr concentration is higher in core region 12c of second main phase 12 than in core region 11c of first main phase 11. This difference in concentration also means that there is a difference in the detection intensities of Nd and Pr in the mapping analysis using EPMA described above. Specifically, in the case of the Nd concentration, this means that the EPMA detection intensity of Nd in the core region 11c of the first main phase 11 is higher than the average Nd detection intensity, and the EPMA detection intensity of Nd in the core region 12c of the second main phase 12 is lower than the average Nd detection intensity. In the case of the Pr concentration, this means that the EPMA detection intensity of Pr in the core region 12c of the second main phase 12 is higher than the average Pr detection intensity, and the EPMA detection intensity of Pr in the core region 11c of the first main phase 11 is lower than the average Pr detection intensity. In other words, the core region 12c of the second main phase 12, which has a low Nd concentration, contains a large amount of Pr, and conversely, the core region 11c of the first main phase 11, which has a low Pr concentration, contains a large amount of Nd. By controlling the microstructure in this way, it is possible to obtain a rare earth sintered magnet 1 with excellent magnetic properties.

[0020] Furthermore, in the rare earth sintered magnet 1 according to the first embodiment, there is more first main phase 11 in which C(Nd, RH)>CPr than there is second main phase 12 in which C(Nd, RH)<CPr. In other words, (Nd, RH)Fe 14 The number of the first main phases 11 having the composition formula of PrFe 14 This means that the number of the second main phases 12 having the composition formula of (Nd, RH)Fe is greater than the number of the second main phases 12 having the composition formula of (Nd, RH)Fe. 14 Increasing the first main phase 11 having the composition formula of PrFe 14This is because better magnetic properties and temperature characteristics can be obtained than by increasing the second main phase 12 having the composition formula of B. Furthermore, by controlling the structure in this way, the overall crystal grain size is also suppressed from becoming finer, so that it is possible to obtain better magnetic properties than before while maintaining magnetization.

[0021] Furthermore, in rare earth sintered magnet 1 according to embodiment 1, focusing on shell portions 11s, 12s of the core-shell structure, when the concentration of Nd in shell portions 11s, 12s is defined as SNd, the concentration of Pr in shell portions 11s, 12s is defined as SPr, and the concentration of heavy rare earth element RH in shell portions 11s, 12s is defined as SRH, first main phase 11 satisfies the relational expressions CNd>SNd, CPr<SPr, CRH>SRH, and second main phase 12 satisfies the relational expressions CNd<SNd, CPr>SPr, CRH<SRH. Specifically, the concentrations of Nd and heavy rare earth element RH in shell portion 11s of first main phase 11 are lower than in core portion 11c, but the concentration of Pr is higher than in core portion 11c. Furthermore, the shell portion 12s of the second main phase 12 has a lower concentration of Pr than the core portion 12c, but has higher concentrations of Nd and the heavy rare-earth element RH than the core portion 12c.

[0022] In other words, in rare earth sintered magnet 1 according to embodiment 1, focusing on shell portions 11s, 12s of the core-shell structure, when the sum of the concentrations of Nd and heavy rare earth element RH in shell portions 11s, 12s is S(Nd, RH) and the concentration of Pr in shell portions 11s, 12s is SPr, first main phase 11 satisfies the relational expression C(Nd, RH) > S(Nd, RH), CPr < SPr, and second main phase 12 satisfies the relational expression C(Nd, RH) < S(Nd, RH), CPr > SPr. Specifically, the sum of the concentration of Nd and the concentration of heavy rare earth element RH in shell portion 11s of first main phase 11 is smaller than that in core portion 11c, but the concentration of Pr is higher than that in core portion 11c. Furthermore, in the shell portion 12s of the second main phase 12, the concentration of Pr is lower than that in the core portion 12c, but the sum of the concentration of Nd and the concentration of the heavy rare-earth element RH is higher than that in the core portion 12c.

[0023] Coercivity can be improved by forming main phase 10 having shell portions 11s with a high concentration of Pr, as in first main phase 11. Furthermore, by forming main phase 10 having shell portions 12s with a high concentration of Nd and the sum of the heavy rare earth element RH, as in second main phase 12, coercivity can be maintained while suppressing a decrease in remanence. By selectively controlling the structure to achieve this, rare earth sintered magnet 1 can exhibit magnetic properties superior to conventional magnets.

[0024] Furthermore, the main phase 10 has a heavy rare-earth-element-containing layer 31 containing the heavy rare-earth element RH on at least a portion of its surface. That is, the heavy rare-earth element RH is present on at least a portion of the surface of the main phase 10, i.e., the first main phase 11 and the second main phase 12. More specifically, the heavy rare-earth element RH is present in the core portions 11c and 12c, and the heavy rare-earth element RH is also present on at least a portion of the outer circumferential surface of the shell portions 11s and 12s. In this way, the inclusion of the heavy rare-earth element RH in the R sites of the first main phase 11 and the second main phase 12 increases the coercive force. To achieve this effect, the proportion of the heavy rare-earth element RH in the main phase 10 is preferably greater than 0 at. % and not greater than 10 at. %.

[0025] Furthermore, 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.

[0026] The rare earth sintered magnet 1 according to the first embodiment may contain an additional element M that further improves the magnetic properties. The additional element M is one or more elements selected from the group consisting of Ga, Cu, Al, Co, Zr, Ti, Nb, and Mn. Therefore, the rare earth sintered magnet 1 according to the first embodiment has a general formula of (Nd a Prb R c RH d ) Fe e B f M g It is desirable that a, b, c, d, e, f, and g satisfy the following relational expression.

[0027] 5≦a+b≦20 0<c+d<(a+b) 0<d<10 70≦e≦90 0.5≦f≦10 0≦g≦5 a+b+c+d+e+f+g=100at. %

[0028] The rare earth sintered magnet 1 according to the first embodiment satisfies the general formula (Nd, Pr, RH, R)-Fe-B, where R is one or more rare earth elements selected from the group consisting of Nd, Pr, and a heavy rare earth element RH, and has a structure of NdFe. 14 The main phase 10 includes crystal grains based on the B crystal structure, and has core portions 11c, 12c and shell portions 11s, 12s that cover the core portions 11c, 12c. The main phase 10 has a first main phase 11 in which CNd > CPr and a second main phase 12 in which CNd < CPr. The concentration of the heavy rare earth element RH in the first main phase 11 is higher than the concentration of the heavy rare earth element RH in the second main phase 12, and the first main phase 11 and the second main phase 12 are mixed together. This configuration allows for the production of a rare earth sintered magnet 1 that has improved magnetic properties and magnetization compared to conventional magnets, while reducing the use of Nd and the heavy rare earth element RH.

[0029] The R-T-B based sintered magnet described in Patent Document 1 is compared with the rare earth sintered magnet 1 according to embodiment 1. The R-T-B based sintered magnet described in Patent Document 1 contains one or more rare earth elements, with the heavy rare earth element RH being an essential element, and has one type of main phase particles composed of a core and a shell. In other words, in Patent Document 1, all main phase particles in the R-T-B based sintered magnet contain the heavy rare earth element RH. On the other hand, in the rare earth sintered magnet 1 according to embodiment 1, the main phase 10 includes a first main phase 11 and a second main phase 12, and the concentration of the heavy rare earth element RH is lower in the second main phase 12 than in the first main phase 11. For example, the core 11c of the first main phase 11 contains the heavy rare earth element RH, but the core 12c of the second main phase 12 contains almost no heavy rare earth element RH. In other words, the heavy rare earth element RH is selectively located within the main phase 10. Thus, compared to the R-T-B based sintered magnet described in Patent Document 1, which requires that all of the only one type of main phase contain the heavy rare earth element RH, rare earth sintered magnet 1 according to embodiment 1, which includes main phase 10 having first main phase 11 and second main phase 12 that has a lower concentration of heavy rare earth element RH than first main phase 11, can reduce the amount of heavy rare earth element RH used. In particular, when second main phase 12 contains almost no heavy rare earth element RH, the heavy rare earth element RH is selectively located, and the amount of heavy rare earth element RH used can be reduced compared to the R-T-B based sintered magnet described in Patent Document 1.

[0030] A comparison is made between a rare earth magnet manufactured using the technique described in Patent Document 2 and the rare earth sintered magnet 1 according to embodiment 1. To obtain magnetic properties equivalent to those of the rare earth sintered magnet 1 according to embodiment 1 using a rare earth magnet manufactured using the technique described in Patent Document 2, a larger amount of the heavy rare earth element RH must be added compared to the rare earth sintered magnet 1 according to embodiment 1, as shown in the examples described below. In other words, to obtain the same magnetic properties, the rare earth sintered magnet 1 according to embodiment 1 can use less heavy rare earth element RH than the technique described in Patent Document 2. Alternatively, if the content of the heavy rare earth element RH in the rare earth magnet manufactured using the technique described in Patent Document 2 is made the same as the content of the heavy rare earth element RH in the rare earth sintered magnet 1 according to embodiments 1 and 2, the magnetic properties of the rare earth magnet manufactured using the technique described in Patent Document 2 will be lower than those of the rare earth sintered magnet 1 according to embodiments 1 and 2.

[0031] In the rare earth sintered magnet 1 according to the first embodiment, the first main phase 11 and the second main phase 12 are configured to satisfy the relational expressions C1Nd>C2Nd and C1Pr<C2Pr. Alternatively, the number of first main phases 11 is greater than the number of second main phases 12. Alternatively, the first main phases 11 are configured to satisfy the relational expressions CNd>SNd, CPr<SPr, CRH>SRH, and the second main phases 12 are configured to satisfy the relational expressions CNd<SNd, CPr>SPr, CRH<SRH. This also makes it possible to obtain a rare earth sintered magnet 1 with improved magnetic properties and magnetization while minimizing the use of neodymium and the heavy rare earth element RH.

[0032] Furthermore, the heavy rare earth element RH is present on at least a portion of the surface of the first main phase 11 and the second main phase 12. That is, the first main phase 11 and the second main phase 12 each have a heavy rare earth element-containing layer 31 on at least a portion of their surface. This also makes it 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 reducing the use of the heavy rare earth element RH. In other words, this has the effect of improving the magnetic properties of the rare earth sintered magnet 1 compared to conventional magnets.

[0033] Furthermore, because the main phase 10 contains the heavy rare earth element RH, the rare earth sintered magnet 1 has a significantly improved coercivity compared to conventional magnets. Furthermore, as will be shown in the examples described below, the rare earth sintered magnet 1 also has a better temperature coefficient of coercivity compared to conventional magnets. Therefore, even when a thermal load is applied to the rare earth sintered magnet 1, the coercivity is greater than conventional magnets, and the decrease in coercivity due to temperature rise is more gradual than conventional magnets. In other words, because the coercivity is significantly improved compared to conventional rare earth sintered magnets, the magnetic properties of the rare earth sintered magnet 1 when a thermal load is applied are also better than conventional magnets.

[0034] Embodiment 2. 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 2. Note that the same components as those in embodiment 1 are given the same reference numerals, and their description will be omitted. The rare earth sintered magnet 1 according to embodiment 2 has a main phase 10 and a subphase 20.

[0035] The main phase 10 has the same structure as in Embodiment 1. That is, the main phase 10 has a first main phase 11 and a second main phase 12 each having a core-shell structure, and the compositions of the core portions 11c and 12c and the shell portions 11s and 12s are the same as those described in Embodiment 1. However, in Embodiment 2, a heavy rare earth element-containing layer 31 may or may not be present on the surface of the main phase 10.

[0036] The subphase 20 is a phase based on an oxide phase represented by a main component of (Nd, Pr, RH, R)—O. That is, in the second embodiment, the subphase 20 contains a heavy rare-earth element RH. The heavy rare-earth element RH is distributed throughout the subphase 20. In one example, the heavy rare-earth element RH is uniformly distributed within the subphase 20.

[0037] Thus, in the second embodiment, subphases 20 containing the heavy rare earth element RH exist between the main phases 10. The heavy rare earth element RH is uniformly distributed within the subphases 20, and 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 contacts the subphases 20. In other words, it can be considered that the heavy rare earth element RH has penetrated into a portion of the shell portions 11s, 12s. Therefore, as in the first embodiment, it is possible to improve the coercivity of the rare earth sintered magnet 1 while suppressing a decrease in remanence.

[0038] As shown in FIG. 2 , in the rare earth sintered magnet 1, the main phase 10 contacts other main phases 10 without the subphase 20 therebetween, and also contacts other main phases 10 via the subphase 20. That is, at least a portion of the surface of the main phase 10 is in contact with the subphase 20. The subphase 20 also contains the heavy rare earth element RH. Therefore, at least a portion of the surface of the main phase 10 is covered with the subphase 20 containing the heavy rare earth element RH. From this, it can be said that the heavy rare earth element RH is present on at least a portion of the surface of the main phase 10, specifically on the surface of the main phase 10 in contact with the subphase 20. In other words, for the same rare earth sintered magnet 1, Embodiment 1 shows the distribution of the heavy rare earth element RH at the interface between the main phase 10 and the subphase 20, while Embodiment 2 shows the distribution of the heavy rare earth element RH at the subphase 20. In this way, it can be said that the first and second embodiments are the same rare earth sintered magnet 1 viewed from different angles.

[0039] As with embodiment 1, embodiment 2 also makes it possible to obtain a rare earth sintered magnet 1 that improves coercivity compared to conventional magnets and suppresses a significant decrease in remanence, while using less heavy rare earth element RH. Alternatively, it is possible to obtain a rare earth sintered magnet 1 that has magnetic properties equal to or better than conventional magnets, using 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, it has the effect of improving the magnetic properties of the rare earth sintered magnet 1 compared to conventional magnets.

[0040] Embodiment 3. Figure 3 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. As described in embodiment 1, the main phase 10 includes a first main phase 11 and a second main phase 12. The subphase 20 is present between the main phases 10.

[0041] In the rare earth sintered magnet 1 according to the third embodiment, La (lanthanum) and Sm (samarium) 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 suppressed, and the effect of having superior magnetization compared to conventional magnets is further enhanced. In this example, the main phase 10 is (Nd, Pr, RH, 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 significantly suppresses 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 and Pr can be relatively diffused into the main phase 10, thereby increasing the magnetocrystalline anisotropy of the main phase 10. This forms a core-shell structure in which there are areas of high and low magnetic anisotropy within the main phase 10, and a first main phase 11 in which CNd > CPr and a second main phase 12 in which CNd < CPr are mixed together, creating a condition that makes it easy to produce a rare earth sintered magnet 1 in which the concentration of the heavy rare earth element RH in the core portion 11c of the first main phase 11 is higher than the concentration of the heavy rare earth element RH in the core portion 12c of the second main phase 12.

[0042] However, if the amounts of La and Sm added are too large, the amounts of Nd and Pr, which are elements with high magnetic anisotropy constants and saturation magnetic polarization, will decrease, resulting in a deterioration of magnetic properties. Therefore, when the composition ratios of Nd, Pr, La, and Sm are A, B, C, and D, respectively, it is preferable that (A+B)>(C+D).

[0043] In the rare earth sintered magnet 1 according to the third embodiment, when R = La and Sm, the magnet has a subphase 20 in addition to the first and second main phases 11 and 12 of the first and second embodiments. The subphase 20 includes a crystalline first subphase 21 based on an oxide phase whose main component is expressed as (Nd, Pr, RH, La, Sm)-O, and a crystalline second subphase 22 whose main component is expressed as (Nd, Pr, RH, La)-O. The subphase 20 is characterized in that 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 whose Sm concentration is higher than that of 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.

[0044] 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 is higher on average in the first subphase 21 than in the second subphase 22.

[0045] 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, Pr, RH, La, Sm)-O, and the crystalline second subphase 22 is represented by (Nd, Pr, RH, La)-O. Here, (Nd, Pr, RH, La, Sm) means that some of the Nd and Pr are replaced by heavy rare-earth elements RH, La, and Sm. 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, Pr, RH, La)-O contains a trace amount of Sm.

[0046] 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. That is, 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. Specifically, the La and Sm concentrations in the subphase 20 are equal to or greater than the La and Sm concentrations in the main phase 10. Here, the La concentration in the main phase 10 is the sum of the La concentration in the first main phase 11 and the La concentration in the second main phase 12. That is, the sum of the La concentrations in the first subphase 21 and the second subphase 22 is higher than the sum of the La concentrations in the first main phase 11 and the second main phase 12. The Sm concentration in the main phase 10 is the sum of the Sm concentration in the first main phase 11 and the Sm concentration in the second main phase 12. In other words, the sum of the Sm concentrations in the first subphase 21 and the second subphase 22 is higher than the sum of the Sm concentrations in the first main phase 11 and the second main phase 12.

[0047] Here, when the La concentration contained in the main phase 10 is X, the La concentration contained in the first subphase 21 is X1, the La concentration contained in the second subphase 22 is X2, the Sm concentration contained in the main phase 10 is Y, the Sm concentration contained in the first subphase 21 is Y1, and the Sm concentration contained in the second subphase 22 is Y2, the relationship of the following formula (1) is satisfied.

[0048] 1<(Y1+Y2) / Y<(X1+X2) / X (1)

[0049] Furthermore, from the viewpoint of improving magnetic properties, the concentrations of Nd and Pr contained in the main phase 10 satisfy the relationships of the following formulas (2) and (3).

[0050] (CNd+SNd)>(X+Y)...(2) (CPr+SPr)>(X+Y)...(3)

[0051] In the above, the La concentration in the main phase 10 is the sum of the La concentrations in the first main phase 11 and the second main phase 12, and the Sm concentration in the main phase 10 is the sum of the Sm concentrations in the first main phase 11 and the second main phase 12. This indicates that both La and Sm are segregated in the subphase 20 rather than in the main phase 10. However, when viewed locally, the sum of the respective La and Sm concentrations in the first main phase 11 and the second main phase 12 and the sum of the respective La and Sm concentrations 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 of the La concentrations in the first main phase 11 and the second main phase 12, and the Sm concentration in the main phase 10 indicates the average of the Sm concentrations in the first main phase 11 and the second main phase 12. 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, and 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.

[0052] La is present in high concentrations at grain boundaries during the manufacturing process, particularly during heat treatment, and thus relatively diffuses Nd and Pr into main phase 10. As a result, rare earth sintered magnet 1 in embodiment 3 improves magnetocrystalline anisotropy without consuming Nd and Pr in main phase 10 at grain boundaries. Sm is also present in higher concentrations in subphase 20, particularly first subphase 21, than in main phase 10, and thus, like La, relatively diffuses Nd into main phase 10, improving magnetocrystalline anisotropy.

[0053] 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. However, in the third embodiment, 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 inner periphery of the outer periphery 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.

[0054] 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. Therefore, it can be considered that the heavy rare earth element RH has penetrated into parts of the surface of the main phase 10 that contact the first subphases 21 and second subphases 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 parts of the shell portions 11s, 12s. Therefore, as in embodiment 1, 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.

[0055] When a cross section of the rare earth sintered magnet according to the third embodiment is analyzed with a field emission electron probe microanalyzer (FE-EPMA), it is confirmed that a main phase 10 is present, including a first main phase 11 having a core region 11c in which the heavy rare earth element RH is distributed, and a second main phase 12 having a core region 12c in which the heavy rare earth element RH is hardly distributed, as shown in FIG. 3 , and that a subphase 20 is present between the main phases 10 and 10. It is also confirmed that the subphase 20 includes a first subphase 21 having an Sm-enriched region 41 and a second subphase 22 having a lower Sm concentration than the first subphase 21. As described above, Tb, which is the heavy rare earth element RH, is uniformly distributed in the second subphase 22, while it is confirmed that the distribution of Tb is uneven in the first subphase 21. It is also confirmed that a heavy rare-earth element-containing portion 42 is present so as to selectively surround the periphery of the Sm-enriched portion 41 where the Sm concentration is high in the first subphase 21. Furthermore, it is also confirmed that the heavy rare-earth element RH is almost absent in the Sm-enriched portion 41, and 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.

[0056] Next, La and Sm form tetragonal RFe 14 The following explains which atomic sites in the tetragonal NdFeB crystal structure are substituted. 14 4 is a diagram showing atomic sites in the B crystal structure. The crystal structure shown in FIG. 4 is, for example, shown in FIG. 1 of the following reference technical document 1. The substituted site is determined by the stabilization energy due to substitution calculated by band calculation and molecular field approximation of the Heisenberg model. (Reference technical document 1) JFHerbst et al. "Relationships between crystal structure and magnetic properties in NdFe 14 PHYSICAL REVIEW B. 1984, Vol.29, No.7, p. 4176-4178.

[0057] First, we will explain how to calculate the stabilization energy in La. The stabilization energy in La is calculated using the formula: 56 Using 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 is not changed by the difference in atomic radius. Table 1 shows the stabilization energy of La at each substitution site when the environmental temperature is changed.

[0058]

[0059] 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 for 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 for 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.

[0060] 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, fourth, and cooling steps 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 is 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. As a result, main phase 10 promotes the formation of a characteristic core-shell structure.

[0061] 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.

[0062]

[0063] 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.

[0064] 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. More specifically, the average La concentration in the first subphase 21 and the second subphase 22 is equal to or greater than the average La concentration in the first main phase 11 and the second main phase 12, and the average Sm concentration in the first subphase 21 and the second subphase 22 is equal to or greater than the average Sm concentration in the first main phase 11 and the second main phase 12. In other words, it can be said that La and Sm segregate in the subphase 20.

[0065] 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 the 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 the subphase 20 than Sm present in the rare earth sintered magnet 1. By repeatedly maintaining this temperature range, a difference in the concentration of Sm, which has a lower segregation rate, is created in the subphase 20, resulting in the formation of the first subphase 21 and the second subphase 22. This promotes the formation of a core-shell structure in the main phase 10.

[0066] Here, we will explain Nd as a representative element, as shown in Figure 4. However, since Nd and Pr are produced as a mixture, as exemplified by Di (didymium), it is thought that the energy levels of Nd and Pr are close. Therefore, the same can be said when Nd is replaced with Pr. By having both Nd and Pr present, it is possible to form a main phase 10 having two types of core-shell structures.

[0067] As described above, the rare earth sintered magnet 1 of the third embodiment satisfies the general formula (Nd, Pr, RH, R)-Fe-B when R is one or more rare earth elements selected from among those other than Nd, Pr, and RH, and is NdFe. 14 The alloy has a main phase 10 including crystal grains based on a B crystal structure. The main phase 10 has core portions 11c, 12c and shell portions 11s, 12s covering the core portions 11c, 12c. When R = La, Sm, the alloy also has a subphase 20 in addition to the first main phase 11 and second main phase 12 of the first embodiment. The subphase 20 has a crystalline first subphase 21 based on an oxide phase whose main component is represented by (Nd, Pr, RH, La, Sm)-O, and a crystalline second subphase 22 whose main component is represented by (Nd, Pr, RH, La)-O. The first subphase 21 has a higher Sm concentration than the second subphase 22, and the first subphase 21 has an Sm-enriched portion 41 in which Sm is selectively distributed. In other words, two types of main phases 10 and two types of subphases 20 are present. This makes it possible to provide a rare earth sintered magnet 1 with magnetic properties, such as temperature characteristics, that are superior to conventional magnets. Furthermore, by using La or Sm for R, the main phase 10 is a mixture of a first main phase 11 in which C(Nd, RH) > CPr and a second main phase 12 in which C(Nd, RH) < CPr. In other words, the rare earth sintered magnet 1 has two main phases 10, the first main phase 11 and the second main phase 12. Focusing on the cores 11c and 12c of the two main phases 10, the Nd concentration is higher than the Pr concentration in the first main phase 11, while the Pr concentration is higher than the Nd concentration in the second main phase 12. This facilitates the formation of two types of core-shell structured main phases 10. As a result, the magnetic properties can be improved while the amount of Nd and the heavy rare earth element RH used is reduced compared to the conventional case, and the effect of having superior magnetization compared to the conventional case can be further enhanced.

[0068] Furthermore, in the third embodiment, as in the first embodiment, it is possible to obtain a rare earth sintered magnet 1 that improves coercivity compared to conventional magnets and suppresses a significant decrease in remanence, while suppressing the use of heavy rare earth element RH. Furthermore, because the coercivity is significantly improved compared to conventional rare earth sintered magnets, the magnetic properties when a thermal load is applied to the rare earth sintered magnet 1 are also better than conventional magnets. In other words, it has the effect of improving the magnetic properties of the rare earth sintered magnet 1 compared to conventional magnets.

[0069] 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. 5 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. 5, 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 containing the heavy rare earth element RH; a diffusion precursor manufacturing step (step S20) for forming the diffusion precursor; a grain boundary diffusion step (step S30) for diffusing the heavy rare earth element RH into the diffusion precursor; and a cooling step (step S40) for cooling the diffusion precursor with the heavy rare earth element RH diffused therein to obtain the rare earth sintered magnet 1.

[0070] First, the rare earth sintered magnet alloy manufacturing process of step S10 will be described in detail. FIG. 6 is a flowchart showing an example of the procedure of the rare earth sintered magnet alloy manufacturing process according to the fourth embodiment. As shown in FIG. 6, the manufacturing process of the rare earth sintered magnet alloy, which serves 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.

[0071] 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, Pr, RH, R, Fe, and B can be used as the raw materials. When producing the rare earth sintered magnet 1 of Embodiment 3, Nd, Pr, RH, La, Sm, Fe, and B can be used as the raw materials. Embodiment 3 corresponds to the case where the rare earth element R in Embodiments 1 and 2 is La and Sm. Examples of RH include Dy and Tb. Furthermore, FeB may be used as the raw material instead of B. In this case, the raw material may contain one or more elements selected from the group consisting of Ga, Cu, Al, Co, Zr, Ti, Nb, and Mn as the additive element M.

[0072] 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 rapid cooling may also be achieved by contacting the molten alloy 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 It is more preferable to set the cooling rate at 100°C / second or less. The thickness of the solidified alloy is in the range of 0.03 mm to 10 mm. The molten alloy begins to solidify from the portion in contact with the single roll, and columnar or needle-like crystals grow from the contact surface with the single roll in the thickness direction. The primary cooling step in step S12 corresponds to the primary alloy cooling step.

[0073] 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 The second cooling step in step S13 corresponds to the second alloy cooling step.

[0074] 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, Pr, RH, La, Sm)-Fe-B crystalline phase and a crystalline subphase 20 of an oxide represented by (Nd, Pr, RH, La, Sm)-O. Hereinafter, the crystalline subphase 20 of an oxide represented by (Nd, Pr, RH, La, Sm)-O is referred to as the (Nd, Pr, RH, La, Sm)-O phase. The (Nd, Pr, RH, La, Sm)-O phase is a nonmagnetic phase composed of an oxide with a relatively high concentration of rare earth elements. The thickness of the (Nd, Pr, RH, 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.

[0075] Next, the diffusion precursor manufacturing process of step S20 in Fig. 5 will be described. Fig. 7 is a flowchart showing an example of the procedure of the diffusion precursor manufacturing process according to embodiment 4. The following describes the manufacturing of the rare earth sintered magnet 1 of embodiment 3 as an example, but the rare earth sintered magnet 1 of embodiments 1 and 2 can also be manufactured by changing the raw material of the rare earth sintered magnet alloy used. In other words, La and Sm in embodiment 3 can be replaced with a rare earth element R other than Nd, Pr, and a heavy rare earth element RH. 7 , the diffusion precursor production process includes a crushing step (step S21) of crushing a rare earth sintered magnet alloy having a (Nd, Pr, RH, La, Sm)—Fe—B crystalline phase and a (Nd, Pr, RH, La, Sm)—O phase, a compacting step (step S22) of compacting the crushed rare earth sintered magnet alloy powder 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 aging the sintered body to improve the magnetic properties such as the coercive force of the rare earth sintered magnet 1, and a sintered body cooling step (step S25) of cooling the aged sintered body. Each step will be described below.

[0076] In the pulverization step S21, the rare earth sintered magnet alloy having a (Nd, Pr, RH, La, Sm)-Fe-B crystalline phase and a (Nd, Pr, RH, La, Sm)-O phase manufactured according to the rare earth sintered magnet alloy manufacturing process of FIG. 6 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. For example, the rare earth sintered magnet alloy is pulverized 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 producing the rare earth sintered magnet 1 of Embodiments 1 and 2, the La and Sm in the rare earth sintered magnet alloy used to produce the rare earth sintered magnet 1 of Embodiment 3 can be replaced with a rare earth element R other than Nd, Pr, and the heavy rare earth element RH. In other words, a rare earth sintered magnet alloy having a (Nd, Pr, RH, R)-Fe-B crystalline phase and a (Nd, Pr, RH, R)-O phase can be pulverized.

[0077] 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.

[0078] 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.

[0079] 7, 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. The aging is preferably carried out in an atmosphere containing an inert gas or in a vacuum to suppress oxidation.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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 to 10 hours, preferably 1.0 hour to 7 hours.

[0084] 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.

[0085] In this manner, a diffusion precursor is formed, which is a sintered body having the final shape of the rare earth sintered magnet 1 .

[0086] Returning to FIG. 5 , in the grain boundary diffusion step of step S30, heat treatment is performed under conditions in which the diffusion precursor formed in step S25 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, heat treatment is performed by holding the diffusion precursor at a 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 S24. 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. A known grain boundary diffusion method can be used for the grain boundary diffusion step. Various techniques have been proposed for the grain boundary diffusion method, depending on the supply form of the heavy rare-earth element RH. Typical methods include coating diffusion, sputtering diffusion, and vapor diffusion. These typical grain boundary diffusion methods are 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. to 1000° 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 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 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 1000°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 source 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 attachment of a heavy rare earth element supply unit 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] Returning to FIG. 5 , in the final cooling step, step S40, the diffusion precursor into which the heavy rare-earth element RH has been diffused in the grain boundary diffusion step is maintained at a temperature below 200°C for a time period ranging from 0.1 to 5 hours. The resulting mixture is then cooled to room temperature, resulting in the formation of the rare-earth sintered magnet 1 shown in any of the first to third embodiments. In the first embodiment, the rare-earth sintered magnet 1 is formed in which the heavy rare-earth element RH is present on at least a portion of the surface of the main phase 10 containing the heavy rare-earth element RH. In the second embodiment, the rare-earth sintered magnet 1 is formed in which the heavy rare-earth element RH is diffused into the main phase 10 containing the heavy rare-earth element RH and the subphase 20 present between the main phase 10. In the third embodiment, the rare-earth sintered magnet 1 is formed, which includes the main phase 10 containing the heavy rare-earth element RH, a first subphase 21 in which the heavy rare-earth element RH has diffused so as to selectively surround the outer periphery of the Sm-enriched portion 41, and a second subphase 22 in which the heavy rare-earth element RH has been uniformly diffused. The cooling is preferably carried out in an atmosphere containing an inert gas or in a vacuum in order to prevent oxidation.

[0091] 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.

[0092] As described above, in the fourth embodiment, a rare earth sintered magnet 1 is manufactured by pulverizing a rare earth sintered magnet alloy having a (Nd, Pr, RH, La, Sm)—Fe—B crystalline phase and a (Nd, Pr, RH, La, Sm)—O phase to form a rare earth sintered magnet alloy powder, sintering the compact to form a sintered body, and then aging the sintered body. This makes it possible to manufacture the rare earth sintered magnet 1 having the structure described in the third embodiment. Furthermore, since the heavy rare earth element is adjusted to a desired concentration before manufacturing the rare earth sintered magnet alloy, and the rare earth sintered magnet 1 is manufactured using this rare earth sintered magnet alloy, the heavy rare earth element RH is more easily incorporated into the main phase 10.

[0093] In addition, in the fourth embodiment, the temperatures and times in the sintering step, aging step, and sintered body cooling step are controlled. In particular, in the first aging step, the obtained sintered body is maintained at a first aging temperature, which is lower than the sintering temperature, for 0.1 to 10 hours, preferably 0.5 to 5 hours. In the second aging step, the sintered body is maintained at a second aging temperature, which is lower than the first aging temperature, for 0.1 to 10 hours, preferably 1.0 to 7 hours. In the third aging step, the temperature is again raised to the first aging temperature, and the sintered body is maintained at the first aging temperature for 0.1 to 10 hours, preferably 0.5 to 5 hours. In the fourth aging step, the sintered body is again maintained at the second aging temperature for 0.1 to 10 hours, preferably 1.0 to 7 hours. In this way, the temperatures and times are controlled so that two sets of the first aging step and the second aging step are performed. This creates a state in which the sintered body is repeatedly maintained in a temperature range where the energy is unstable. As a result, a first main phase 11 consisting of CNd > CPr and a second main phase 12 consisting of CNd < CPr are mixed, making it possible to make the concentration of the heavy rare earth element RH in the first main phase 11 higher than the concentration of the heavy rare earth element RH in the second main phase 12. In other words, the rare earth sintered magnet 1 has two types of main phases 10, the first main phase 11 and the second main phase 12. Focusing on the cores 11c, 12c of the two types of main phases 10, it is possible to selectively produce a rare earth sintered magnet 1 in which the sum of the concentrations of Nd and the heavy rare earth element RH in the first main phase 11 is higher than the concentration of Pr, and conversely, the second main phase 12 has the concentration of Pr higher than the sum of the concentrations of Nd and the heavy rare earth element RH.

[0094] Furthermore, in addition to the first main phase 11 and second main phase 12 in embodiment 1, it is possible to selectively produce a rare earth sintered magnet 1 having a characteristic structural structure in which a crystalline first subphase 21 based on an oxide phase whose main component is expressed as (Nd, Pr, RH, La, Sm)-O and a crystalline second subphase 22 whose main component is expressed as (Nd, Pr, RH, La)-O are present, in which the Sm concentration is higher in the first subphase 21 than in the second subphase 22, and Sm-enriched portions 41 are formed in the first subphase 21.

[0095] Furthermore, in a method for producing a rare earth sintered magnet 1 according to the fourth embodiment, an R—Fe—B rare earth sintered magnet alloy containing rare earth elements R including Nd and Pr is pulverized, a powder compact of the R—Fe—B rare earth sintered magnet alloy is sintered, and the resulting compact is aged to form a diffusion precursor having a first main phase 11 and a second main phase 12, the first main phase 11 having a higher concentration of the heavy rare earth element RH than the second main phase 12. In the method for producing a rare earth sintered magnet 1 according to the fourth embodiment, a heat treatment is performed on the diffusion precursor to cause the heavy rare earth element RH to diffuse through grain boundaries, thereby producing a rare earth sintered magnet 1 in which the heavy rare earth element RH is present inside the first main phase 11 and the second main phase 12 and on parts of the surfaces of the first main phase 11 and the second main phase 12, or a rare earth sintered magnet 1 in which the heavy rare earth element RH is present in the subphase 20.

[0096] Furthermore, in the manufacturing method of the rare earth sintered magnet 1 according to the fourth embodiment, an R—Fe—B based rare earth sintered magnet alloy containing rare earth elements R including Nd, Pr, La, and Sm is pulverized, a powder compact of the R—Fe—B based rare earth sintered magnet alloy is sintered, and an aging treatment is performed to form a diffusion precursor having a first main phase 11 containing the heavy rare earth element RH and a second main phase 12 having a lower concentration of the heavy rare earth element RH than the first main phase 11, as well as a first subphase 21 having an Sm-enriched portion 41 where Sm is enriched, and a second subphase 22 having a lower Sm concentration than the first subphase 21. In the method for manufacturing the rare earth sintered magnet 1 according to the fourth embodiment, a heat treatment is performed in the diffusion precursor to cause the heavy rare earth element RH to diffuse at grain boundaries, thereby producing 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 the heavy rare earth element RH is uniformly distributed in the second subphase 22.

[0097] Compared to the R-T-B based sintered magnet described in Patent Document 1, the R-T-B based sintered magnet described in Patent Document 1 contains one or more rare earth elements, with the heavy rare earth element RH being an essential element, and has one type of main phase particle composed of a core portion and a shell portion. In other words, in Patent Document 1, all main phase particles contain the heavy rare earth element RH. On the other hand, the main phase 10 of the rare earth sintered magnet 1 according to Embodiment 1 is a mixture of a first main phase 11 in which the heavy rare earth element RH is contained in the core portion 11c and a second main phase 12 in which the heavy rare earth element RH is hardly contained in the core portion 12c. In other words, the heavy rare earth element RH is selectively disposed in the first main phase 11, which is one of the two types of main phases 10. Thus, compared to the R-T-B based sintered magnet described in Patent Document 1, which requires that all of the only one type of main phase contain the heavy rare earth element RH, the rare earth sintered magnet 1 according to embodiment 1 can reduce the amount of heavy rare earth element RH used, since it is sufficient that the heavy rare earth element RH is contained in first main phase 11, one of two types of main phases 10. Furthermore, because the volume of subphase 20 accounts for an extremely small proportion of the overall volume of rare earth sintered magnet 1, even if the heavy rare earth element RH is present in a diffused form in subphase 20, the amount of heavy rare earth element RH used can be reduced compared to the technology of Patent Document 1.

[0098] Furthermore, compared to the technique described in Patent Document 2, if a rare earth magnet produced by the method described in Patent Document 2 is to obtain magnetic properties equivalent to those of the rare earth sintered magnet 1 according to embodiment 1, a large amount of heavy rare earth element RH must be added, as described below. In other words, to obtain the same magnetic properties, the amount of heavy rare earth element RH used can be reduced with the rare earth sintered magnet 1 according to embodiment 1 compared to the technique described in Patent Document 2. Furthermore, while the method described in Patent Document 2 includes hot working, the method for producing the rare earth sintered magnet 1 according to embodiment 4 does not include hot working. This prevents the grain size of the main phase 10 from becoming smaller, and makes it possible to suppress decreases in remanence and magnetization compared to rare earth magnets produced by the technique described in Patent Document 2.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] Thus, rotor 100 according to embodiment 5 includes rare earth sintered magnet 1 according to embodiment 1, 2, or 3, which can achieve improved magnetic properties at room temperature and suppressed degradation of magnetic properties with increasing temperature. Because 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, degradation of magnetic properties is suppressed even in high-temperature environments exceeding 100°C. This allows for the substitution of inexpensive rare earth elements for Nd and heavy rare earth element RH, which are expensive, unevenly distributed across regions, and present a procurement risk, while improving magnetic properties and magnetization, thereby stabilizing operation of rotor 100 even in high-temperature environments exceeding 100°C. Furthermore, because rare earth sintered magnet 1 according to embodiment 1, 2, or 3 has superior magnetization performance compared to conventional magnets, it is possible to magnetize rotor 100 in an assembled state with rare earth sintered magnet 1 set therein, thereby facilitating handling in the manufacturing process. Furthermore, the magnetization process can be performed with reduced voltage, which contributes to energy savings.

[0104] 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.

[0105] 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.

[0106] Thus, the rotating machine 120 in embodiment 6 includes the 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 the rare earth sintered magnet 1 uses less heavy rare earth element RH than conventional magnets and is capable of suppressing 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. As a result, while replacing Nd and the heavy rare earth element RH, which are expensive, unevenly distributed across regions, and present a procurement risk, with inexpensive rare earth elements, the magnetic properties and magnetization are improved, and the rotor 100 can be stably driven, resulting in stable operation of the rotating machine 120, even in high-temperature environments exceeding 100°C.

[0107] The rare earth sintered magnet 1 of the present disclosure will be described in detail below with reference to examples and comparative examples.

[0108] In Examples 1 to 8, 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, Pr, Dy, La, Sm)-Fe-B. In Examples 1 to 8, rare earth sintered magnet alloys with varying contents of Nd, Pr, Dy, 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 content was 0.10 at. %, thereby manufacturing rare earth sintered magnet 1. In other words, in Examples 1 to 8, rare earth sintered magnet 1 with 0.10 at. % Tb, which is a heavy rare earth element RH, diffused was manufactured from a rare earth sintered magnet alloy represented by (Nd, Pr, Dy, La, Sm)-Fe-B using the manufacturing method shown in Embodiment 4.

[0109] In Comparative Examples 1 to 14, samples of a plurality of rare earth sintered magnet alloys R—Fe—B with different compositions were used to produce rare earth sintered magnet 1 in which Tb, the heavy rare earth element RH, was experimentally diffused through grain boundaries using a general rare earth magnet manufacturing method such as that shown in Patent Document 1 or Patent Document 2. In the samples of rare earth sintered magnet 1 according to Comparative Examples 1 to 14, the R portion was changed.

[0110] In Comparative Examples 1 to 7, rare earth sintered magnet 1 is produced from a rare earth sintered magnet alloy in which R is Nd, or from a rare earth sintered magnet alloy in which R includes Nd and one or more elements selected from the group consisting of Dy, Pr, La, and Sm, using the production method disclosed in Patent Document 1, with 0.15 at. % of Tb diffused therein as the heavy rare earth element RH.

[0111] In Comparative Examples 8 to 14, rare earth sintered magnet 1 was produced from a rare earth sintered magnet alloy in which R is Nd, or from a rare earth sintered magnet alloy in which R includes Nd and one or more elements selected from the group consisting of Dy, Pr, La, and Sm, using the production method disclosed in Patent Document 2, with 0.15 at. % of Tb diffused therein as the heavy rare earth element RH.

[0112] Table 3 shows the general formula of the rare earth sintered magnets of Examples 1 to 8 and Comparative Examples 1 to 14, the contents of the elements constituting R, the analysis results of the structural morphology, and the evaluation results of the magnetic properties and magnetization performance. Table 3 also shows the general formula of the main phase 10 of each sample, which is the rare earth sintered magnet 1 of Examples 1 to 8 and Comparative Examples 1 to 14.

[0113]

[0114] Next, a method for analyzing the structure of the rare earth sintered magnet 1 of Examples 1 to 8 and Comparative Examples 1 to 14 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 were an acceleration voltage of 15.0 kV, a probe current of 2.271 e -008 A, 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.

[0115] Next, we will explain how to evaluate the magnetic properties of the rare earth sintered magnets 1 of Examples 1 to 8 and Comparative Examples 1 to 14. 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, other instruments capable of generating a maximum magnetic field of 6 T or more, such as a DC magnetic fluxmeter (also known as a DC BH tracer), a vibrating sample magnetometer (VSM), a magnetic property measurement system (MPMS), or a physical property measurement system (PPMS), may also be used. Measurements are 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 an applied magnetic field using a search coil or magnetic sensor. The magnetic properties were measured from the measured magnetic hysteresis, which is the J-H curve or B-H curve. The magnetic properties of each sample were measured at a first measurement temperature T1 and a second measurement temperature T2, which were different from each other. The temperature coefficient α [% / °C] of the remanence is the ratio of the difference between the remanence at the first measurement temperature T1 and the remanence at the second measurement temperature T2 to the remanence at the first measurement temperature T1, divided by the temperature difference (T2 - T1). The temperature coefficient β [% / °C] of the coercivity is the ratio of the difference between the coercivity at the first measurement temperature T1 and the coercivity at the second measurement temperature T2 to the coercivity at the first measurement temperature T1, divided by the temperature difference (T2 - T1). Therefore, the smaller the absolute values ​​|α| and |β| of the temperature coefficients of the magnetic properties, the more suppressed is the deterioration of the magnetic properties of the magnet with increasing temperature.

[0116] Furthermore, the magnetization performance can be measured by calculating the magnetization rate from the ratio of the magnetic flux density measured from the magnetic hysteresis curve when an arbitrary magnetic field is applied at a constant permeance coefficient to the magnetic flux density measured from the magnetic hysteresis curve when a saturating magnetic field is applied. If a high magnetization rate can be obtained even in a weaker magnetic field, it can be said that the magnetization performance is high.

[0117] First, the analytical results of each sample according to Examples 1 to 8 and Comparative Examples 1 to 14 will be described. Although not shown in the figures, elemental mapping of each sample according to Examples 1 to 8 by FE-EPMA revealed that RH is Dy and Tb, R is one or more rare earth elements selected from among Nd, Pr, and RH, and the general formula (Nd, Pr, Dy, Tb, R)-Fe-B is satisfied, and NdFe 14 It can be seen that the main phase 10, which includes crystal grains based on the B crystal structure, has core portions 11c, 12c and shell portions 11s, 12s that cover the core portions 11c, 12c. It can also be seen that the main phase 10 contains a mixture of a first main phase 11 in which CNd > CPr and a second main phase 12 in which CNd < CPr. It can also be seen that when the Dy concentration in the first main phase 11 is C1Dy and the Dy concentration in the second main phase 12 is C2Dy, C1Dy > C2Dy.

[0118] Here, the concentration difference shown between "the first main phase 11 where CNd > CPr and the second main phase 12 where CNd < CPr" means that a clear difference has been found between the detected intensity of Nd and the detected intensity of Pr by mapping analysis using EPMA. Specifically, taking the first main phase 11 as an example, the detected intensity of Nd in the core region 11c by EPMA is higher than the average, and the detected intensity of Pr by EPMA is near the lower limit. It can be said that the second main phase 12 is the opposite of the first main phase 11.

[0119] Furthermore, the concentration difference indicated by "C1Dy>C2Dy" means that mapping analysis using EPMA reveals a clear difference between the detected intensity of Dy in the first main phase 11 and the detected intensity of Dy in the second main phase 12. Specifically, the detected intensity of Dy in the first main phase 11 by EPMA is higher than the average, and the detected intensity of Dy in the second main phase 12 by EPMA is near the lower limit.

[0120] Furthermore, when R = La, Sm, it can be confirmed that rare earth sintered magnet 1 has, in addition to first main phase 11 and second main phase 12 in embodiment 1, a crystalline first subphase 21 based on an oxide phase whose main component is expressed as (Nd, Pr, Dy, Tb, La, Sm)-O, and a crystalline second subphase 22 whose main component is expressed as (Nd, Pr, Dy, Tb, La)-O. Furthermore, it can be confirmed that the concentration of Sm is higher in first subphase 21 than in second subphase 22.

[0121] In Table 3, when the sum of the concentration of Nd and the concentration of Tb, which is a heavy rare-earth element RH, is expressed as C(Nd, Tb), samples in which the first main phase 11 satisfying C(Nd, RH) > CPr and the second main phase 12 satisfying C(Nd, RH) < CPr were confirmed are marked with "◯" in the columns for the first main phase 11 and the second main phase 12, respectively. Samples in which this was not confirmed are marked with "X" in the columns for the first main phase 11 and the second main phase 12, respectively. The concentration difference indicated by an inequality sign indicates a clear difference between the detected intensities of Nd and Dy and the detected intensities of Pr. To give a specific example, in the case of the first main phase 11, the detected intensities of Nd and Dy by EPMA are higher than average, while the detected intensities of Pr by EPMA are near the lower limit. In the case of the second main phase 12, the situation is the opposite to that of the first main phase 11. When only C(Nd, RH)<CPr, such as the second main phase 12, is confirmed, "◯" is entered only in the column for the second main phase 12, and "×" is entered in the column for the first main phase 11.

[0122] Furthermore, Table 3 shows samples having a crystalline first subphase 21 based on an oxide phase whose main component is expressed as (Nd, Pr, Dy, Tb, La, Sm)-O and a crystalline second subphase 22 whose main component is expressed as (Nd, Pr, Dy, Tb, La)-O. For samples in which it was confirmed that the first subphase 21 had a higher Sm concentration than the second subphase 22, a "◯" was entered in each of the columns for the first subphase 21 and the second subphase 22. For samples in which this was not confirmed, an "×" was entered in each of the columns for the first subphase 21 and the second subphase 22. For samples in which only one subphase 20 was present or there was no difference in Sm concentration between the subphases 20, it was determined that only the first subphase 21 was present, and a "◯" was entered only in the column for the first subphase 21 and an "×" was entered in the column for the second subphase 22. The concentration difference between the first subphase 21 and the second subphase 22 means that the detection intensity of Sm is higher on average in the first subphase 21 than in the second subphase 22, as determined by mapping analysis using EPMA.

[0123] Furthermore, it can be confirmed from the intensity ratio of element mapping obtained by FE-EPMA analysis that the number of first main phases 11 in which C(Nd, RH)>CPr is greater than the number of second main phases 12 in which C(Nd, RH)<CPr is present. When the Dy concentration in the core portions 11c and 12c is defined as CDy and the Dy concentration in the shell portions 11s and 12s is defined as SDy, and attention is focused on the shell portions 11s and 12s of the core-shell structure, it can also be confirmed that the first main phase 11 satisfies the relational expressions CNd>SNd, CPr<SPr, CDy>SDy, and the second main phase 12 satisfies the relational expressions CNd<SNd, CPr>SPr, CDy<SDy.

[0124] Next, the measurement results of the magnetic properties of each sample in Examples 1 to 8 and Comparative Examples 1 to 14 will be described. Each sample used for magnetic measurement was a block with length, width, and height all measuring 7 mm. The first measurement temperature T1 was 23°C, and the second measurement temperature T2 was 200°C. 23°C is room temperature. The second measurement temperature T2, 200°C, is a temperature that can occur in the operating environment of automotive motors and industrial motors.

[0125] First, the remanence and coercivity of each sample in Examples 1 to 8 and Comparative Examples 2 to 14 are judged by comparison with Comparative Example 1. If the remanence and coercivity values ​​at 23°C of each sample are within 1%, which is considered to be a measurement error, of the values ​​in Comparative Example 1, they are judged as "equivalent," if they are 1% or more higher, they are judged as "good," and if they are 1% or less lower, they are judged as "poor."

[0126] Next, the temperature coefficient α of the remanence is calculated using the remanence at the first measurement temperature T1 of 23°C and the remanence at the second measurement temperature T2 of 200°C. The temperature coefficient β of the coercivity is calculated using the coercivity at the first measurement temperature T1 of 23°C and the coercivity at the second measurement temperature T2 of 200°C. The temperature coefficients of the remanence and the coercivity for each sample in Examples 1 to 8 and Comparative Examples 2 to 14 are evaluated by comparing them with Comparative Example 1. For each sample, the absolute value |α| of the temperature coefficient of the remanence and the absolute value |β| of the temperature coefficient of the coercivity for the sample in Comparative Example 1 are compared. If the value is within ±1%, which is considered to be the measurement error, the sample is judged as "equivalent." If the value is lower than -1%, the sample is judged as "good." If the value is higher than +1%, the sample is judged as "poor." For samples judged to be "good," the temperature coefficient is smaller, which suppresses the deterioration of magnetic properties with increasing temperature, and it is possible to provide a rare earth sintered magnet 1 with stable magnetic properties even in high-temperature environments.

[0127] Next, the magnetization performance is calculated as the ratio of the magnetic flux density at the intersection of the magnetic hysteresis and permeance coefficient Pc at an applied magnetic field of 20 kOe to the magnetic flux density at the intersection of the magnetic hysteresis and permeance coefficient Pc at an applied magnetic field of 80 kOe, which represents a saturated magnetization state. The magnetization performance of each sample in Examples 1 to 8 and Comparative Examples 2 to 14 is evaluated by comparing it with Comparative Example 1. That is, for each sample, if the magnetization performance shows a value of -1% or more, which is considered to be a measurement error, compared to the magnetization performance of the sample in Comparative Example 1, it is evaluated as "equal to or better," and if the value is lower than -1%, it is evaluated as "poor." Samples evaluated as "equal to or better" can provide rare earth sintered magnets 1 with high magnetization performance.

[0128] The evaluation results of the residual magnetic flux density, coercive force, temperature coefficient of residual magnetic flux density, temperature coefficient of coercive force, and magnetization performance are shown in Table 3.

[0129] Comparative Example 1 is a sample of rare earth sintered magnet 1 prepared according to the manufacturing method described in Patent Document 1 using Nd, Dy, Fe, and FeB as raw materials, with 0.15 at. % Tb diffused therein to form a (Nd, Dy)—Fe—B structure. Observation of the morphology of this sample using the method described above reveals that, since Pr, La, and Sm are not added, a core-shell structure in the main phase 10 is not confirmed, nor is it confirmed that the Sm concentration in the subphase 20 is higher in the first subphase 21 than in the second subphase 22. Furthermore, evaluation of the magnetic properties of this sample using the method described above reveals a remanence of 1.25 T and a coercivity of 1900 kA / m. The temperature coefficients of the remanence and coercivity are |α| = 0.185% / °C and |β| = 0.455% / °C, respectively. The magnetization rate is 98.6%. These values ​​for Comparative Example 1 are used as references.

[0130] Comparative Example 2 is a sample of rare earth sintered magnet 1 prepared according to the manufacturing method described in Patent Document 1 using Nd, Fe, and FeB as raw materials, with 0.15 at. % Tb diffused therein to form an Nd—Fe—B magnet. Observation of the morphology of this sample using the method described above reveals that, because Pr, La, and Sm are not added, a core-shell structure in main phase 10 is not confirmed, nor is it confirmed that the Sm concentration in subphase 20 is higher in first subphase 21 than in second subphase 22. Furthermore, evaluation of the magnetic properties of this sample using the method described above reveals that, because the heavy rare earth elements Dy and Tb (RH) are not present in main phase 10, the remanence is "good" and the coercivity is "poor." Furthermore, the temperature coefficient of remanence is "same," the temperature coefficient of coercivity is "same," and the magnetization performance is "same or better."

[0131] Comparative Example 3 is a sample of rare earth sintered magnet 1 prepared according to the manufacturing method described in Patent Document 1 using Nd, Pr, Fe, and FeB as raw materials, with 0.15 at. % Tb diffused therein to form a (Nd,Pr)—Fe—B structure. Observation of the morphology of this sample using the method described above confirmed the presence of a main phase 10 in which Nd and Pr were mixed due to the addition of Pr, but no core-shell structure was formed. Furthermore, because La and Sm were not added, it was not possible to confirm that the Sm concentration in the subphase 20 was higher in the first subphase 21 than in the second subphase 22. Evaluation of the magnetic properties of this sample using the method described above revealed that the remanence was "good" and the coercivity was "poor" due to the absence of the heavy rare earth elements RH, Dy and Tb, in the matrix. Furthermore, the temperature coefficient of coercivity was "poor" due to the addition of Pr. Since the manufacturing method does not include hot working, the magnetization performance is "equal or better." The temperature coefficient of remanence is "equal." Furthermore, diffusing Tb, which is a heavy rare earth element (RH), into a diffusion precursor, which is a base material that does not contain the heavy rare earth element (RH), does not improve the magnetic properties.

[0132] Comparative Example 4 is a sample of rare earth sintered magnet 1 prepared according to the manufacturing method described in Patent Document 1 using Nd, Pr, Dy, Fe, and FeB as raw materials, with 0.15 at. % Tb diffused therein to form a (Nd, Pr, Dy)—Fe—B structure. Observation of the morphology of this sample using the method described above confirmed the presence of a main phase 10 containing a mixture of Nd and Pr, but no core-shell structure was formed. Furthermore, because no La or Sm was added, it was not possible to confirm that the Sm concentration in subphase 20 was higher in first subphase 21 than in second subphase 22. Furthermore, evaluation of the magnetic properties of this sample using the method described above revealed that the remanence was "similar" to that of Comparative Example 1, due to the addition of Pr and the addition of Dy, a heavy rare earth element RH, which was equivalent to that of Comparative Example 1. By adding Pr in addition to the heavy rare earth element RH, the coercivity becomes "good" and the temperature coefficient of coercivity becomes "poor." Because the manufacturing method does not include hot working, the magnetization performance becomes "equal or better." The temperature coefficient of remanence becomes "equal." This reflects the fact that the addition of Tb and Pr increases the magnetic anisotropy of the main phase 10 and improves the coercivity, but does not result in an optimal structure for the main phase 10 and subphase 20.

[0133] Comparative Example 5 is a sample of rare earth sintered magnet 1 prepared according to the manufacturing method described in Patent Document 1 using Nd, La, Sm, Fe, and FeB as raw materials, with 0.15 at. % Tb diffused therein to form a (Nd, La, Sm)-Fe-B structure. Observation of the morphology of this sample using the method described above reveals that, due to the absence of Pr, a core-shell structure of the main phase 10 is not observed. Furthermore, due to the addition of La and Sm, the Sm concentration is segregated to one subphase 20 in association with the segregation of La, but no second subphase 22 is present. Furthermore, it is not possible to confirm that the first subphase 21 has a higher Sm concentration than the second subphase 22. Furthermore, evaluation of the magnetic properties of this sample using the method described above reveals that, due to the absence of Dy, a heavy rare earth element RH, in the matrix, the remanence is "good" and the coercivity is "poor." Furthermore, the addition of La and Sm results in a "good" temperature coefficient of coercivity. Because the manufacturing method does not include hot working, the magnetization performance is "equal or better." The temperature coefficient of remanence is "equal." This is because, although the presence of La and Sm in the main phase 10 or subphase 20 results in a good temperature coefficient of the magnetic properties, the magnetic properties at room temperature do not improve, reflecting the fact that the main phase 10 and subphase 20 are not optimally structured. Furthermore, because the magnetic properties depend on the structure of the diffusion precursor, which is the base material, diffusing Tb, a heavy rare earth element RH, into such a diffusion precursor does not improve the magnetic properties.

[0134] Comparative Example 6 is a sample of rare earth sintered magnet 1 prepared according to the manufacturing method described in Patent Document 1 using Nd, La, Sm, Fe, and FeB as raw materials, with 0.15 at. % Tb diffused therein to form a (Nd, La, Sm)-Fe-B structure. The composition ratio of Nd, La, and Sm differs from that of Comparative Example 5. Observing the morphology of this sample using the method described above reveals that, due to the absence of Pr, a core-shell structure of the main phase 10 cannot be confirmed. Furthermore, due to the addition of La and Sm, the concentration of Sm segregates to one subphase 20 in association with the segregation of La, but the second subphase 22 does not exist. Furthermore, it cannot be confirmed that the concentration of Sm is higher in the first subphase 21 than in the second subphase 22. Furthermore, when the magnetic properties of this sample were evaluated according to the method described above, the remanence was "good" and the coercivity was "poor" because the base material did not contain Dy, a heavy rare-earth element RH. Furthermore, by optimizing the amounts of La and Sm added, the temperature coefficient of remanence was "good" and the temperature coefficient of coercivity was "good." Because the manufacturing method did not include hot working, the magnetization performance was "equal to or better." This indicates that although the temperature coefficient of the magnetic properties was good due to the presence of La and Sm in the main phase 10 or subphase 20, the magnetic properties at room temperature were not improved because Dy, a heavy rare-earth element RH, was not added to the base material, reflecting the suboptimal structural form of the main phase 10 and subphase 20. Even when the composition ratio of Nd, La, and Sm was changed, results similar to those of Comparative Example 5 were obtained. Furthermore, since the magnetic properties depend on the structure of the diffusion precursor, which is the base material, the magnetic properties do not improve even if Tb, which is a heavy rare earth element RH, is diffused into such a diffusion precursor.

[0135] Comparative Example 7 is a sample of rare earth sintered magnet 1 prepared according to the manufacturing method described in Patent Document 1 using Nd, Pr, La, Sm, Fe, and FeB as raw materials, with 0.15 at. % Tb diffused therein to form a (Nd, Pr, La, Sm)-Fe-B structure. Observation of the morphology of this sample using the method described above reveals that the addition of Pr results in the formation of a main phase 10 in which Nd and Pr are mixed, but no core-shell structure is formed. Furthermore, the addition of La and Sm results in the segregation of Sm into a single subphase 20, but no second subphase 22 is present. Furthermore, it is not possible to confirm that the concentration of Sm is higher in the first subphase 21 than in the second subphase 22. Furthermore, when the magnetic properties of this sample are evaluated according to the method described above, the remanence is "good" and the coercivity is "poor" because the base material does not contain Dy, a heavy rare earth element RH. Furthermore, by optimizing the amounts of La and Sm added, the temperature coefficient of the remanence and the temperature coefficient of the coercivity should be "good," but the addition of Pr reduces the temperature coefficient of the coercivity to "the same." Because the manufacturing method does not include hot working, the magnetization performance is "the same or better."

[0136] Comparative Example 8 is a sample of rare earth sintered magnet 1 prepared using Nd, Dy, Fe, and FeB as raw materials, according to the manufacturing method including hot working described in Patent Document 2, with 0.15 at. % Tb diffused therein to form a (Nd, Dy)—Fe—B structure. Observation of the morphology of this sample using the method described above reveals that, because Pr, La, and Sm are not added, a core-shell structure in the main phase 10 is not confirmed, nor is it confirmed that the Sm concentration in the subphase 20 is higher in the first subphase 21 than in the second subphase 22. However, the refinement of the structure, which is characteristic of magnets produced by hot working, is confirmed. Evaluation of the magnetic properties of this sample using the method described above reveals that, due to the refinement of the magnetic powder, the coercivity is "good" and the temperature coefficient of coercivity is "similar." Furthermore, due to the difficulty in aligning the magnetic moment, the remanence and magnetization performance are "poor." The temperature coefficient of remanence is "similar." This is because, although the absolute value of the coercive force and the temperature coefficient of the coercive force are improved as the magnetic powder is refined by hot working, it is difficult to align the magnetic moment, resulting in a decrease in the remanence and deterioration of the magnetization performance. Furthermore, because the magnetic properties depend on the structure of the diffusion precursor, which is the base material, diffusing Tb, which is a heavy rare earth element RH, into such a diffusion precursor does not improve the magnetic properties.

[0137] Comparative Example 9 is a sample of rare earth sintered magnet 1 produced using Nd, Fe, and FeB as raw materials according to the manufacturing method described in Patent Document 2, including hot working, to form Nd—Fe—B. 0.15 at. % Tb was diffused into the sample. Observation of the morphology of this sample using the method described above reveals that, because Pr, La, and Sm were not added, a core-shell structure in the main phase 10 was not observed, nor was it confirmed that the Sm concentration in the subphase 20 was higher in the first subphase 21 than in the second subphase 22. However, the refinement of the structure, a characteristic of magnets produced by hot working, was confirmed. Evaluation of the magnetic properties of this sample using the method described above revealed that, due to the refinement of the magnetic powder, the coercivity was "good" and the temperature coefficient of coercivity was "similar." Furthermore, due to the difficulty in aligning the magnetic moment, the remanence and magnetization performance were "poor." The temperature coefficient of remanence was "similar." This is because the coercive force is improved by the refinement of the structure by hot working, but the residual magnetic flux density is reduced. Furthermore, since the magnetic properties depend on the structure of the diffusion precursor, which is the base material, diffusing Tb, which is a heavy rare earth element RH, into such a diffusion precursor does not improve the magnetic properties.

[0138] Comparative Example 10 is a sample of rare earth sintered magnet 1 prepared using Nd, Pr, Fe, and FeB as raw materials, according to the manufacturing method including hot working described in Patent Document 2, with 0.15 at. % Tb diffused therein to form a (Nd,Pr)—Fe—B structure. Observation of the morphology of this sample using the method described above confirms that the addition of Pr and the hot working result in a core-shell structure. However, the core-shell structure is only observed in one type of main phase 10, where the Pr concentration is high in the core. Furthermore, because no La or Sm is added, it is not possible to confirm that the Sm concentration in the subphase 20 is higher in the first subphase 21 than in the second subphase 22. Evaluation of the magnetic properties of this sample using the method described above reveals that the coercivity is "good" due to the fine magnetic powder, and the temperature coefficient of coercivity is "similar." Furthermore, the remanence and magnetization performance are "poor" due to the difficulty in aligning the magnetic moment. The temperature coefficient of remanence is "similar." This is because, although the formation of a core-shell structure with a high Pr concentration in the core region significantly improves the coercivity to the level of rare earth sintered magnet 1 containing Dy, other properties reflect the refinement of the structure. Furthermore, because the magnetic properties depend on the structure of the diffusion precursor, which is the base material, diffusing Tb, which is a heavy rare earth element RH, into such a diffusion precursor does not improve the magnetic properties.

[0139] Comparative Example 11 is a sample of rare earth sintered magnet 1 prepared using Nd, Pr, Dy, Fe, and FeB as raw materials, according to the manufacturing method including hot working described in Patent Document 2, with 0.15 at. % Tb diffused therein, to form a (Nd, Pr, Dy)—Fe—B structure. When the morphology of this sample was observed using the method described above, a core-shell structure was confirmed due to the addition of Pr and the hot working. However, the core-shell structure was only observed in one type of main phase 10, with a high Pr concentration in the core. Furthermore, because no La or Sm was added, it was not confirmed that the Sm concentration in the subphase 20 was higher in the first subphase 21 than in the second subphase 22. Furthermore, when the magnetic properties of this sample were evaluated using the method described above, the coercivity was "good" due to the fine magnetic powder, and the temperature coefficient of coercivity was "similar." Furthermore, due to the difficulty in aligning the magnetic moment, the remanence and magnetization performance were "poor." The temperature coefficient of remanence is "equivalent." This is because, in addition to being produced by hot working, the coercivity is significantly improved by substituting part of the Nd with Dy, which has high magnetic crystalline anisotropy, but other properties reflect the refinement of the structure by hot working. Furthermore, since the magnetic properties depend on the structure of the diffusion precursor, which is the base material, diffusing Tb, which is a heavy rare earth element RH, into such a diffusion precursor does not improve the magnetic properties.

[0140] Comparative Example 12 is a sample of rare earth sintered magnet 1 prepared using Nd, La, Sm, Fe, and FeB as raw materials according to the manufacturing method including hot working described in Patent Document 2, with 0.15 at. % Tb diffused therein to form a (Nd, La, Sm)-Fe-B structure. Observation of the morphology of this sample using the method described above reveals that, due to the absence of Pr, a core-shell structure of the main phase 10 is not observed. Furthermore, due to the addition of La and Sm, the Sm concentration is segregated to one subphase 20 in association with the segregation of La, but no second subphase 22 is present. Furthermore, it is not possible to confirm that the first subphase 21 has a higher Sm concentration than the second subphase 22. Furthermore, evaluation of the magnetic properties of this sample using the method described above reveals that the coercivity and temperature coefficient of coercivity are "good" due to the fine magnetic powder. Furthermore, due to the difficulty in aligning the magnetic moment, the remanence and magnetization performance are "poor." The temperature coefficient of remanence is "good." This is because, although the presence of La and Sm in the main phase 10 or the subphase 20 indicates a good temperature coefficient of the magnetic properties, the magnetic moments are difficult to align, so the remanence and magnetization performance at room temperature are not improved, and this result reflects the fact that the main phase 10 and the subphase 20 are not in an optimal structural form. Furthermore, because the magnetic properties depend on the structural structure of the diffusion precursor, which is the base material, diffusing Tb, which is a heavy rare earth element RH, into such a diffusion precursor does not improve the magnetic properties.

[0141] Comparative Example 13 is a sample of rare earth sintered magnet 1 prepared using Nd, La, Sm, Fe, and FeB as raw materials according to the manufacturing method including hot working described in Patent Document 2, with 0.15 at. % Tb diffused therein to form a (Nd, La, Sm)-Fe-B structure. The composition ratio of Nd, La, and Sm differs from that of Comparative Example 12. Observation of the morphology of this sample using the method described above reveals that the absence of Pr results in no core-shell structure of the main phase 10. Furthermore, the addition of La and Sm results in the segregation of Sm into a single subphase 20, but no second subphase 22. Furthermore, it is not possible to confirm that the concentration of Sm is higher in the first subphase 21 than in the second subphase 22. Furthermore, evaluation of the magnetic properties of this sample using the method described above reveals that the coercivity and temperature coefficient of coercivity are "good" due to the refinement of the magnetic powder. Furthermore, because the magnetic moments are difficult to align, the remanence and magnetization performance are "poor." The temperature coefficient of the remanence is "good." This is because, although the temperature coefficient of the magnetic properties is good due to the presence of La and Sm in the main phase 10 or the subphase 20, the remanence and magnetization performance at room temperature are not improved because the magnetic moments are difficult to align, and this result reflects the fact that the main phase 10 and the subphase 20 are not in an optimal structural form. Even if the composition ratio of Nd, La, and Sm is changed, results similar to those of Comparative Example 12 are obtained. Furthermore, because the magnetic properties depend on the structural structure of the diffusion precursor, which is the base material, diffusing Tb, which is a heavy rare earth element RH, into such a diffusion precursor does not improve the magnetic properties.

[0142] Comparative Example 14 is a sample of rare earth sintered magnet 1 prepared using Nd, Pr, La, Sm, Fe, and FeB as raw materials, according to the manufacturing method including hot working described in Patent Document 2, with 0.15 at. % Tb diffused therein, to form (Nd, Pr, La, Sm)—Fe—B. When the morphology of this sample was observed according to the method described above, a core-shell structure was confirmed due to the addition of Pr and the hot working. However, the core-shell structure was confirmed only in one main phase 10, where the Pr concentration was high in the core. Furthermore, although the addition of La and Sm resulted in the Sm concentration being segregated to one subphase 20 due to the segregation of La, no second subphase 22 was present. Furthermore, it was not confirmed that the Sm concentration was higher in the first subphase 21 than in the second subphase 22. Furthermore, when the magnetic properties of this sample were evaluated according to the method described above, the coercivity and the temperature coefficient of coercivity were "good" due to the fine magnetic powder. Furthermore, because the magnetic moments are difficult to align, the remanence and magnetization performance are "poor." The temperature coefficient of remanence is "good." This is because the formation of a core-shell structure with a high Pr concentration in the core significantly improves the coercivity to the level of rare earth sintered magnet 1 containing Dy. The presence of La and Sm in the main phase 10 or subphase 20 results in good temperature coefficients of magnetic properties, particularly the temperature coefficient of coercivity. However, because the magnetic moments are difficult to align, the remanence at room temperature does not improve, reflecting the suboptimal structural form of the main phase 10 and subphase 20. Furthermore, because magnetic properties depend on the structural structure of the diffusion precursor, which is the base material, diffusing Tb, a heavy rare earth element RH, into such a diffusion precursor does not improve the magnetic properties.

[0143] In the samples of Examples 1 to 8, the heavy rare earth element RH is Dy or Tb, and R is one or more rare earth elements selected from the group consisting of Nd, Pr, Dy, and Tb, and satisfies the general formula (Nd, Pr, RH, R)-Fe-B, and NdFe 14The rare earth sintered magnet 1 has a main phase 10 containing crystal grains based on a B crystal structure, and the main phase 10 has core portions 11c, 12c and shell portions 11s, 12s covering the core portions 11c, 12c. The main phase 10 is a mixture of a first main phase 11 in which CNd > CPr and a second main phase 12 in which CNd < CPr. The concentration of Dy, which is a heavy rare earth element RH, in the core portion 11c of the first main phase 11 is higher than the concentration of Dy in the core portion 12c of the second main phase 12. Furthermore, the rare earth sintered magnet 1 of Examples 1 to 8 is a case where R = La, Sm, and has, in addition to a first main phase 11 and a second main phase 12, a crystalline first subphase 21 based on an oxide phase whose main component is expressed as (Nd, Pr, Dy, Tb, La, Sm)-O, and a crystalline second subphase 22 whose main component is expressed as (Nd, Pr, Dy, Tb, La)-O. The first subphase 21 has a higher Sm concentration than the second subphase 22, forming Sm-enriched portions 41 in the first subphase 21. When the magnetic properties of the samples of Examples 1 to 8 were evaluated according to the above-described method, the remanence was evaluated as "good," the coercivity was evaluated as "good," the temperature coefficient of the remanence was evaluated as "good," the temperature coefficient of the coercivity was evaluated as "good," and the magnetization performance was evaluated as "equal to or better." As a result, these rare earth sintered magnets 1 exhibit superior magnetic properties compared to conventional magnets while reducing the use of Nd and heavy rare earth elements Dy and Tb, which are expensive, unevenly distributed, and therefore pose a procurement risk. Furthermore, because magnetic properties depend on the microstructural structure of the diffusion precursor, which is the base material, diffusing Tb, a heavy rare earth element RH, into a diffusion precursor with good magnetic properties further improves the magnetic properties. Furthermore, in Examples 1 to 8, rare earth sintered magnets 1 with good magnetic properties can be obtained with a Tb diffusion amount of 0.10 at. %, which is lower than the 0.15 at. % diffusion amount used in Comparative Examples 1 to 14. In other words, compared to Comparative Examples 1 to 14, rare earth sintered magnets 1 can be obtained that significantly improve coercivity without reducing remanence while reducing the amount of heavy rare earth element RH used.

[0144] Furthermore, as can be seen from Table 3, the samples of Examples 1 to 8 contain less Dy, which is the heavy rare earth element RH in the general formula, and also have a smaller amount of diffused Tb, which is the heavy rare earth element RH, than the samples of Comparative Examples 1, 4, 8, and 11. However, their magnetic properties are superior to those of the samples of Comparative Examples 1, 4, 8, and 11. In particular, if the samples of Comparative Examples 8 and 11, manufactured by the manufacturing method of Patent Document 2, are to have magnetic properties equivalent to those of the samples of Examples 1 to 8, they must also contain Dy and Tb. Therefore, the rare earth sintered magnet 1 according to Embodiments 1, 2, and 3 has the advantage of being able to reduce the amount of heavy rare earth element RH used, compared to the technology of Patent Document 2. Alternatively, if the content of the heavy rare earth element RH in the rare earth magnet produced by the manufacturing method of Patent Document 2 were the same as the content of the heavy rare earth element RH in the rare earth sintered magnet 1 according to Embodiments 1, 2, and 3, the magnetic properties of the rare earth magnet produced by the manufacturing method of Patent Document 2 would be lower than the magnetic properties of the rare earth sintered magnet 1 according to Embodiments 1, 2, and 3. Table 3 also shows that, compared to the samples of Comparative Examples 1 and 4 produced by the manufacturing method of Patent Document 1, the samples of Examples 1 to 8 have improved magnetic properties while reducing the content of Dy, which is the heavy rare earth element RH in the general formula, and while also reducing the amount of Tb diffused, which is the heavy rare earth element RH.

[0145] 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.

[0146] REFERENCE SIGNS LIST 1 Rare earth sintered magnet, 10 Main phase, 11 First main phase, 11c, 12c Core portion, 11s, 12s Shell portion, 12 Second main phase, 20 Subphase, 21 First subphase, 22 Second subphase, 31 Heavy rare earth element-containing layer, 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.

Claims

1. When RH is a heavy rare earth element containing at least one of Dy and Tb, and R is one or more rare earth elements selected from the group consisting of Nd, Pr, Dy, and Tb, the general formula (Nd, Pr, RH, R)-Fe-B is satisfied, and Nd 2 Fe 14 a main phase including crystal grains based on a B crystal structure; a subphase present between a plurality of the main phases; Equipped with the main phase has a core portion and a shell portion that covers the core portion, the main phase has a first main phase satisfying CNd>CPr and a second main phase satisfying CNd<CPr, where CNd is a concentration of Nd in the core portion and CPr is a concentration of Pr in the core portion, the concentration of the heavy rare-earth element RH in the core portion of the first main phase is higher than the concentration of the heavy rare-earth element RH in the core portion of the second main phase; The first main phase and the second main phase are mixed, A rare earth sintered magnet, characterized in that a heavy rare earth element is present on at least a portion of the surface of the first main phase and the second main phase.

2. When RH is a heavy rare earth element containing at least one of Dy and Tb, and R is one or more rare earth elements selected from the group consisting of Nd, Pr, Dy, and Tb, the general formula (Nd, Pr, RH, R)-Fe-B is satisfied, and Nd 2 Fe 14 a main phase including crystal grains based on a B crystal structure; a subphase present between a plurality of the main phases; Equipped with the main phase has a core portion and a shell portion that covers the core portion, the main phase has a first main phase satisfying CNd>CPr and a second main phase satisfying CNd<CPr, where CNd is a concentration of Nd in the core portion and CPr is a concentration of Pr in the core portion, the concentration of the heavy rare-earth element RH in the core portion of the first main phase is higher than the concentration of the heavy rare-earth element RH in the core portion of the second main phase; The first main phase and the second main phase are mixed, A rare earth sintered magnet characterized in that a heavy rare earth element is present in the subphase.

3. 3. The rare earth sintered magnet according to claim 1, wherein the number of the first main phases is greater than the number of the second main phases.

4. When the concentration of Nd in the shell portion is defined as SNd, the concentration of Pr in the shell portion is defined as SPr, the concentration of the heavy rare earth element RH in the core portion of the main phase is defined as CRH, and the concentration of the heavy rare earth element RH in the shell portion is defined as SRH, 3. The rare earth sintered magnet according to claim 1, wherein the first main phase satisfies the relational expressions CNd>SNd, CPr<SPr, CRH>SRH, and the second main phase satisfies the relational expressions CNd<SNd, CPr>SPr, CRH<SRH.

5. The subphase has a crystalline first subphase based on an oxide phase whose main component is expressed as (Nd, Pr, RH, La, Sm)-O, where R is La and Sm, and a crystalline second subphase whose main component is expressed as (Nd, Pr, RH, La)-O, 3. The rare earth sintered magnet according to claim 1, wherein the first subphase has a higher Sm concentration than the second subphase.

6. 6. The rare earth sintered magnet according to claim 5, wherein the first subphase has an Sm-enriched portion having a higher Sm concentration than the second subphase.

7. 7. The rare earth sintered magnet according to claim 6, wherein in the first subphase, the heavy rare earth element is present so as to surround the outer periphery of the Sm-enriched portion.

8. 3. The method for producing a rare earth sintered magnet according to claim 1 or 2, a rare earth sintered magnet alloy manufacturing process for manufacturing 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 manufacturing step of manufacturing the diffusion precursor; a diffusion step of diffusing the heavy rare earth element into the diffusion precursor; a cooling step of cooling the diffusion precursor in which the heavy rare earth element has been diffused; Including, The rare earth sintered magnet alloy manufacturing process includes: a melting step of melting a raw material of the rare earth sintered magnet alloy containing the elements constituting the diffusion precursor; a primary alloy cooling step of cooling the raw material in a molten state in the melting step to obtain a solidified alloy; a second alloy cooling step of further cooling the solidified alloy to obtain a rare earth sintered magnet alloy; Including, The diffusion precursor manufacturing process includes: a pulverization step of pulverizing the rare earth sintered magnet alloy satisfying the (Nd, Pr, RH, R)—Fe—B composition; a compacting step of preparing a compact by compacting the powder of the rare earth sintered magnet alloy pulverized in the pulverizing step; a sintering step of 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; a second aging step of maintaining the sintered body maintained in the first aging step at a second aging temperature which is lower than the first aging temperature; a third aging step in which the sintered body held in the second aging step is held again at the first aging temperature; a fourth aging step of maintaining the sintered body maintained in the third aging step at the second aging temperature; a sintered body cooling step of cooling the sintered body held in the fourth aging step to obtain the diffusion precursor; Including, a diffusion step of heat-treating the diffusion precursor at a temperature lower than the sintering temperature in the presence of the diffusion precursor and the heavy rare earth element;

9. A rotor core; The rare earth sintered magnet according to claim 1 or 2, which is provided in the rotor core; A rotor comprising:

10. The rotor according to claim 9 ; 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; A rotating machine comprising: