FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] RARE EARTH SINTERED MAGNET, METHOD FOR PRODUCING RARE EARTH SINTERED MAGNET, ROTOR, AND ROTARY MACHINE; MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. 2 DESCRIPTION TITLE OF THE INVENTION: RARE EARTH SINTERED MAGNET, METHOD FOR PRODUCING RARE EARTH SINTERED MAGNET, ROTOR, AND ROTARY MACHINE5 Field [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, a10 method for producing a rare earth sintered magnet, a rotor, and a rotary machine. Background [0002] R-T-B-based permanent magnets having a tetragonal15 R2T14B intermetallic compound as a main phase are known. Here, the element R is a rare earth element, the element T is a transition metal element including Fe (iron) or Fe partially replaced by cobalt (Co), and B is boron. R-T-B- based permanent magnets are used for various high value-20 added components including industrial motors. In particular, Nd-Fe-B-based sintered magnets in which the element R is neodymium (Nd) are used for various components due to excellent magnetic properties. In addition, because industrial motors are often used in a high temperature25 environment exceeding 100°C, attempts have been made to improve coercive force by adding heavy rare earth elements such as dysprosium (Dy) to Nd-T-B-based permanent magnets. [0003] In recent years, the production of Nd-Fe-B-based sintered magnets has been expanded, and the consumption of30 Nd and heavy rare earth elements such as Dy and terbium (Tb) has been increased. However, Nd and heavy rare earth elements are expensive and also have a procurement risk due 3 to high distribution unevenness. In view of this, a possible measure for reducing the consumption of Nd and heavy rare earth elements is to use other rare earth elements as the element R, such as cerium (Ce), lanthanum (La), samarium (Sm), scandium (Sc), gadolinium (Gd),5 yttrium (Y), and lutetium (Lu). However, magnetic properties are known to be significantly degraded by substituting these elements for all or a part of Nd. Therefore, attempts have been conventionally made to develop technology that allows for prevention of10 degradation of magnetic properties associated with temperature rise in the case of using these elements for producing Nd-Fe-B-based sintered magnets. [0004] For example, Patent Literature 1 discloses a rare earth magnet alloy including a main phase having a15 tetragonal R2Fe14B crystal structure and mainly composed of Fe, B, and one or more elements selected from the group consisting of Nd, La, and Sm, and a crystalline subphase mainly composed of oxygen (O) and one or more elements selected from the group consisting of Nd, La, and Sm. In20 the rare earth magnet alloy described in Patent Literature 1, La is segregated in the crystalline subphase, and Sm is dispersed without segregation in the main phase and the crystalline subphase. In the rare earth magnet alloy described in Patent Literature 1, the above-described25 structure form prevents degradation of magnetic properties associated with temperature rise. [0005] Patent Literature 2 discloses a rare earth magnet including a first phase containing a compound represented by RaTbX, a grain boundary phase which is present at the30 crystal grain boundary of the first phase and has a higher concentration of the element R than RaTbX, and a second phase consisting of a single crystal of a compound 4 represented by ScMd. Here, the element R is one or more rare earth elements including Nd, the element T is one or more transition metal elements including Fe, and the element X is one or more elements selected from B and carbon (C). The element S is one or more rare earth5 elements including Sm, and the element M is one or more transition metal elements including Co. According to the technique described in Patent Literature 2, a rare earth magnet having sufficient magnetic properties even at a high temperature is obtained.10 [0006] Patent Literature 3 discloses an R-T-B-based sintered magnet including a first main phase composed of crystal grains of an R-T-B-based alloy containing a light rare earth element as the element R, a second main phase composed of crystal grains of an R-T-B-based alloy15 containing a heavy rare earth element as the element R, a surface phase surrounding the surfaces of the crystal grains constituting the first main phase and the second main phase, and a grain boundary alloy phase present at the grain boundary triple point. Here, the element T is Fe or20 Fe partially replaced by Co. In the R-T-B-based sintered magnet described in Patent Literature 3, the concentration of the heavy rare earth element is lower in the first main phase and the grain boundary alloy phase than that in the second main phase and the surface phase. According to the25 technique described in Patent Literature 3, the coercive force can be effectively improved using rare earth elements that give a high coercive force. Citation List30 Patent Literature [0007] Patent Literature 1: PCT Patent Application Laid- open No. 2021/048916 5 Patent Literature 2: Japanese Patent Application Laid-open No. 2021-9862 Patent Literature 3: Japanese Patent Application Laid-open No. 2018-174205 5 Summary of Invention Problem to be solved by the Invention [0008] However, the rare earth magnet alloy described in Patent Literature 1, in which Sm is uniformly dispersed in the main phase and the subphase in the rare earth magnet10 alloy, can prevent degradation of magnetic properties associated with temperature rise, but may not contribute to improvement of magnetic properties at room temperature. In addition, in the rare earth magnet described in Patent Literature 2, the second phase is composed of a single15 crystal, and the elements present in the second phase do not differ in concentration. That is, the second phases distributed in the rare earth magnet have the same composition at any positions, and are formed of one kind of compound having a uniform concentration distribution. For20 this reason, the rare earth magnet described in Patent Literature 2 does not have an optimal structure for improvement of magnetic properties at room temperature. In short, the problem is that there is room for further improvement in magnetic properties. In addition, the R-T-25 B-based sintered magnet described in Patent Literature 3 is configured to always contain a heavy rare earth element, which results in a high coercive force. However, there is a problem in that the residual magnetic flux density required for industrial motors or the like cannot be30 obtained, which leads to degradation of magnetic properties. Thus, there has been a demand for a rare earth sintered magnet that achieves both improvement of magnetic 6 properties at room temperature and prevention of degradation of magnetic properties associated with temperature rise. [0009] The present disclosure has been made in view of the above, and an object thereof is to obtain a rare earth5 sintered magnet capable of improving magnetic properties at room temperature and preventing degradation of magnetic properties associated with temperature rise with reduced use of Nd and heavy rare earth elements. 10 Means to Solve the Problem [0010] To solve the problems above and achieve an object, the present disclosure is directed to a rare earth sintered magnet satisfying a general formula (Nd, La, Sm)- Fe-B-M, where element M is one or more elements selected15 from a group consisting of Cu, Al, and Ga, the rare earth sintered magnet including: a main phase including crystal grains based on an R2Fe14B crystal structure; a first subphase that is crystalline and mainly composed of an oxide phase represented by (Nd, La, Sm)-O; and a second20 subphase that is crystalline and mainly composed of an oxide phase represented by (Nd, La)-O. A concentration of Sm is higher in the first subphase than in the second subphase, and a concentration of the element M is higher in the second subphase than in the first subphase.25 Effects of the Invention [0011] The present disclosure can achieve the effect of improving magnetic properties at room temperature and preventing degradation of magnetic properties associated30 with temperature rise with reduced use of Nd and heavy rare earth elements. 7 Brief Description of Drawings [0012] FIG. 1 is a diagram schematically illustrating an exemplary sintered structure of a rare earth sintered magnet according to a first embodiment. FIG. 2 is a diagram illustrating atomic sites in a5 tetragonal Nd2Fe14B crystal structure. FIG. 3 is a flowchart illustrating an exemplary procedure of a method for producing a rare earth magnet alloy according to a second embodiment. FIG. 4 is a diagram schematically illustrating the10 method for producing a rare earth magnet alloy according to the second embodiment. FIG. 5 is a flowchart illustrating an exemplary procedure of a method for producing a rare earth sintered magnet according to the second embodiment.15 FIG. 6 is a cross-sectional view schematically illustrating an exemplary configuration of a rotor equipped with a rare earth sintered magnet according to a third embodiment. FIG. 7 is a cross-sectional view schematically20 illustrating an exemplary configuration of a rotary machine according to a fourth embodiment. FIG. 8 is a composition image obtained by analyzing a cross section of a rare earth sintered magnet according to Examples 1 to 8 with FE-EPMA.25 FIG. 9 is an element map of Nd obtained by analyzing a cross section of a rare earth sintered magnet according to Examples 1 to 8 with FE-EPMA. FIG. 10 is an element map of O obtained by analyzing a cross section of a rare earth sintered magnet according to30 Examples 1 to 8 with FE-EPMA. FIG. 11 is an element map of La obtained by analyzing a cross section of a rare earth sintered magnet according 8 to Examples 1 to 8 with FE-EPMA. FIG. 12 is an element map of Sm obtained by analyzing a cross section of a rare earth sintered magnet according to Examples 1 to 8 with FE-EPMA. FIG. 13 is an element map of Cu obtained by analyzing5 a cross section of a rare earth sintered magnet according to Examples 1 to 8 with FE-EPMA. FIG. 14 is an element map of Al obtained by analyzing a cross section of a rare earth sintered magnet according to Examples 1 to 8 with FE-EPMA.10 FIG. 15 is an element map of Ga obtained by analyzing a cross section of a rare earth sintered magnet according to Examples 1 to 8 with FE-EPMA. Description of Embodiments15 [0013] Hereinafter, a rare earth sintered magnet, a method for producing a rare earth sintered magnet, a rotor, and a rotary machine according to embodiments of the present disclosure will be described in detail with reference to the drawings.20 [0014] First Embodiment. FIG. 1 is a diagram schematically illustrating an exemplary sintered structure of a rare earth sintered magnet according to the first embodiment. The permanent magnet according to the first embodiment is a rare earth25 sintered magnet 1 satisfying the general formula (Nd, La, Sm)-Fe-B-M, and including a main phase 10 including crystal grains based on an R2Fe14B crystal structure and a subphase 20. The subphase 20 includes a first subphase 21 that is crystalline and mainly composed of an oxide phase30 represented by (Nd, La, Sm)-O, and a second subphase 22 that is crystalline and mainly composed of an oxide phase represented by (Nd, La)-O. The element M indicates one or 9 more elements selected from the group consisting of copper (Cu), aluminum (Al), and gallium (Ga). [0015] The main phase 10 has a tetragonal R2Fe14B crystal structure in which the element R is Nd, La, and Sm. That is, the main phase 10 has the composition formula (Nd, La,5 Sm)2Fe14B. The reason why the element R of the rare earth sintered magnet 1 having a tetragonal R2Fe14B crystal structure is rare earth elements consisting of Nd, La, and Sm is from the calculation of magnetic interaction energy with the use of a molecular orbital method. The10 calculation shows that a composition in which La and Sm are added to Nd can produce the rare earth sintered magnet 1 which is practical in that degradation of magnetic properties associated with temperature rise can be prevented. In addition, by intentionally segregating La15 and Sm also in the grain boundary that is an example of the subphase 20, it is possible to make Nd relatively diffused throughout the main phase 10 so that magnetocrystalline anisotropy of the main phase 10 is enhanced. Consequently, a pseudo core-shell structure is formed in which a portion20 having high magnetic anisotropy and a portion having low magnetic anisotropy exist in the main phase 10. As a result, the effect of preventing degradation of magnetic properties associated with temperature rise is further enhanced.25 [0016] Note that when too much La and Sm are added, it causes a decrease in the amount of Nd, which is an element having a high magnetic anisotropy constant and a high saturation magnetic polarization, which results in degradation of magnetic properties. Therefore, it is30 preferable to satisfy a>(b+c), where a, b, and c represent the composition ratios of Nd, La, and Sm, respectively. [0017] The average grain size of the crystal grains of 10 the main phase 10 is preferably 100 μm or less, and more preferably 0.1 μm to 50 μm for improving magnetic properties. [0018] The crystalline subphase 20 is a generic term for the first subphase 21 and the second subphase 22 that are5 crystalline, and is present between the main phases 10. The crystalline first subphase 21 is represented by (Nd, La, Sm)-O as described above, and the crystalline second subphase 22 is represented by (Nd, La)-O as described above. Here, (Nd, La, Sm)-O means that a part of Nd is10 replaced by La and Sm. Note that the elements of the main components are described in parentheses; therefore, the first subphase 21 and the second subphase 22 may contain a small amount of another component. In one example, the second subphase 22 represented by (Nd, La)-O contains an15 extremely small amount of Sm. [0019] In the rare earth sintered magnet 1 according to the first embodiment, the concentration of Sm is higher in the first subphase 21 than in the second subphase 22, and the concentration of the element M is higher in the second20 subphase 22 than in the first subphase 21. In other words, it means that Sm and the element M are segregated in different subphases 20. Sm is present at a higher concentration in the first subphase 21. Thus, Nd in the Nd-rich phase is relatively diffused throughout the main25 phase 10, which results in improved magnetocrystalline anisotropy of the main phase 10. Furthermore, Sm also exists in the crystal grains of the main phase 10, and thus contributes to improvement of the residual magnetic flux density by being coupled in the same magnetization30 direction with Fe, a ferromagnetic substance. The element M is present at a high concentration in the second subphase 22. Thus, the element M forms a nonmagnetic phase that 11 magnetically separates the main phases 10 from each other, and contributes to improvement of magnetic properties. Because Sm and the element M are present at a high concentration in the different subphases 20, it is possible to improve both the residual magnetic flux density and the5 coercive force. [0020] In the rare earth sintered magnet 1 according to the first embodiment, the concentrations of La and Sm differ between the main phase 10 and the subphase 20: the sum of the concentrations of La in the first subphase 2110 and the second subphase 22 is equal to or greater than the concentration of La in the main phase 10, and the sum of the concentrations of Sm in the first subphase 21 and the second subphase 22 is equal to or greater than the concentration of Sm in the main phase 10. Specifically,15 the concentrations of La and Sm in the subphase 20 are equal to or higher than the concentrations of La and Sm in the main phase 10. Furthermore, the concentration of La also differs between the first subphase 21 and the second subphase 22: the concentration of La in the first subphase20 21 is equal to or higher than the concentration of La in the second subphase 22. [0021] Here, given that X represents the concentration of La contained in the main phase 10, X1 represents the concentration of La contained in the first subphase 21, X225 represents the concentration of La contained in the second subphase 22, Y represents the concentration of Sm contained in the main phase 10, Y1 represents the concentration of Sm contained in the first subphase 21, and Y2 represents the concentration of Sm contained in the second subphase 22,30 the relationship of Formula (1) below is satisfied. [0022] 1<(Y1+Y2)/Y<(X1+X2)/X ··· (1) [0023] La is present at a high concentration in the 12 grain boundary in the process of production, particularly in the heat treatment, whereby Nd is relatively diffused throughout the main phase 10. As a result, in the rare earth sintered magnet 1 according to the first embodiment, Nd in the main phase 10 is not consumed at the grain5 boundary, which leads to improve magnetocrystalline anisotropy. Sm is also present at a higher concentration in the subphase 20, particularly in the first subphase 21, than in the main phase 10. Thus, Nd is relatively diffused throughout the main phase 10 as in the case of La,10 resulting in improved magnetocrystalline anisotropy. [0024] The rare earth sintered magnet 1 according to the first embodiment may contain an additive element N that improves magnetic properties. The additive element N is one or more elements selected from the group consisting of15 Co, zirconium (Zr), titanium (Ti), praseodymium (Pr), niobium (Nb), Dy, Tb, manganese (Mn), Gd, and holmium (Ho). [0025] Therefore, the rare earth sintered magnet 1 according to the first embodiment is expressed by the general formula (NdaLabSmc)FedBeMfNg, where the additive20 element N is one or more elements selected from the group consisting of Co, Zr, Ti, Pr, Nb, Dy, Tb, Mn, Gd, and Ho. It is desirable that a, b, c, d, e, f, and g satisfy the following relational expressions. 5≤a≤2025 0 second subphase” in structure form, and the state in which the concentration of the element M is25 higher in the second subphase 22 than in the first subphase 21 is indicated in the item “concentration of element M: first subphase < second subphase” in structure form. Among Examples 1 to 8 and Comparative Examples 1 to 6, samples in which these states were confirmed are indicated by “○”, and30 samples in which these states were not be confirmed are indicated by “×”. [0075] In addition, it is confirmed from the intensity 35 ratio of the element maps obtained with the FE-EPMA analysis that the sum of the concentrations of La in the first subphase 21 and the second subphase 22 is equal to or greater than the concentration of La in the main phase 10, and the sum of the concentrations of Sm in the first5 subphase 21 and the second subphase 22 is equal to or greater than the concentration of Sm in the main phase 10. Furthermore, it is confirmed that the concentration of La in the first subphase 21 is equal to or higher than the concentration of La in the second subphase 22.10 [0076] Here, from the intensity ratio of the element maps obtained through FE-EPMA analysis of the concentration of La contained in the main phase 10, the first subphase 21, and the second subphase 22 and the concentration of Sm contained in the main phase 10, the first subphase 21, and15 the second subphase 22, it is confirmed that the relationship between the concentration of La contained in the main phase 10, the first subphase 21, and the second subphase 22 and the concentration of Sm contained in the main phase 10, the first subphase 21, and the second20 subphase 22 satisfies Formula (1) above. [0077] Next, the results of measurement of the magnetic properties in each sample according to Examples 1 to 8 and Comparative Examples 1 to 6 will be described. The shape of each sample that is the subject of magnetic measurement25 is a block shape having a length, a width, and a height of 7 mm. The first measurement temperature T1 is 23°C, and the second measurement temperature T2 is 200°C. 23°C is room temperature. 200°C is a temperature that can occur as an environment in which automobile motors and industrial30 motors operate. [0078] First, the residual magnetic flux density and the coercive force in each sample according to Examples 1 to 8 36 and Comparative Examples 2 to 6 are determined in comparison with Comparative Example 1. When the values of the residual magnetic flux density and the coercive force of each sample at 23°C are within an allowable measurement error of 1% compared with the values of Comparative Example5 1, the values are rated as “equivalent”. Values of 1% or more higher are rated as “good”, and values of 1% or more lower are rated as “poor”. [0079] Next, the temperature coefficient α of residual magnetic flux density is calculated using the residual10 magnetic flux density at the first measurement temperature T1 of 23°C and the residual magnetic flux density at the second measurement temperature T2 of 200°C. The temperature coefficient β of coercive force is calculated using the coercive force at the first measurement15 temperature T1 of 23°C and the coercive force at the second measurement temperature T2 of 200°C. The temperature coefficient of residual magnetic flux density and the temperature coefficient of coercive force in each sample according to Examples 1 to 8 and Comparative Examples 2 to20 6 are determined in comparison with Comparative Example 1. When the values of each sample are within an allowable measurement error of ±1% compared with the absolute value |α| of the temperature coefficient of residual magnetic flux density and the absolute value |β| of the temperature25 coefficient of coercive force in the sample of Comparative Example 1, the values are rated as “equivalent”. Values of −1% or more lower are rated as “good”, and values of +1% or more higher are rated as “poor”. Because the samples determined to be “good” have a smaller temperature30 coefficient, it is possible to provide the rare earth sintered magnet 1 having stable magnetic properties even in a high temperature environment while reducing or preventing 37 degradation of magnetic properties associated with temperature rise. [0080] The results of determination of the residual magnetic flux density, the coercive force, the temperature coefficient of residual magnetic flux density, and the5 temperature coefficient of coercive force are shown in Table 3. [0081] Comparative Example 1 is a sample of the rare earth sintered magnet 1 prepared in the form of Nd-Fe-B with the production method according to the second10 embodiment using Nd, Fe, and FeB as raw materials. From the observation of the structure form of this sample according to the above-described method, due to the absence of Sm, it is not confirmed that the concentration of Sm is higher in the first subphase 21 than in the second subphase15 22. Furthermore, due to the absence of the element M, it is not confirmed that the concentration of the element M is higher in the second subphase 22 than in the first subphase 21. The evaluation of the magnetic properties of this sample with the method described above shows that the20 residual magnetic flux density is 1.3 T and the coercive force is 1000 kA/m. The temperature coefficients of residual magnetic flux density and coercive force are |α|=0.191 %/°C and |β|=0.460 %/°C, respectively. These values of Comparative Example 1 are used as a reference.25 [0082] Comparative Example 2 is a sample of the rare earth sintered magnet 1 prepared in the form of (Nd, Dy)- Fe-B with the production method according to the second embodiment using Nd, Dy, Fe, and FeB as raw materials. From the observation of the structure form of this sample30 according to the above-described method, due to the absence of Sm, it is not confirmed that the concentration of Sm is higher in the first subphase 21 than in the second subphase 38 22. Furthermore, due to the absence of the element M, it is not confirmed that the concentration of the element M is higher in the second subphase 22 than in the first subphase 21. The evaluation of the magnetic properties of this sample with the method described above shows that the5 residual magnetic flux density is “poor”, the coercive force is “good”, the temperature coefficient of residual magnetic flux density is “equivalent”, and the temperature coefficient of coercive force is “equivalent”. This result indicates that the coercive force is improved by10 substituting Dy having high magnetocrystalline anisotropy for a part of Nd. [0083] Comparative Example 3 is a sample of the rare earth sintered magnet 1 prepared in the form of Nd-Fe-B-M with the production method according to the second15 embodiment using Nd, Fe, FeB, and further the element M as raw materials. From the observation of the structure form of this sample according to the above-described method, due to the absence of Sm, it is not confirmed that the concentration of Sm is higher in the first subphase 21 than20 in the second subphase 22. In addition, despite the addition of the element M, the first subphase 21 and the second subphase 22 are not formed due to the absence of Sm, and it is not confirmed that the concentration of the element M is higher in the second subphase 22 than in the25 first subphase 21. The evaluation of the magnetic properties of this sample with the method described above shows that the residual magnetic flux density is “equivalent”, the coercive force is “good”, the temperature coefficient of residual magnetic flux density is30 “equivalent”, and the temperature coefficient of coercive force is “equivalent”. This result reflects the fact that the crystal grain boundary is made non-magnetic by the 39 element M, and the coercive force is improved, but the concentration of Sm and the concentration of the element M in the subphase 20 do not accord with an appropriate structure form due to the absence of La and Sm. [0084] Comparative Example 4 is a sample of the rare5 earth sintered magnet 1 prepared in the form of (Nd,Dy)-Fe- B-M with the production method according to the second embodiment using Nd, Dy, Fe, FeB, and further the element M as raw materials. From the observation of the structure form of this sample according to the above-described10 method, due to the absence of Sm, it is not confirmed that the concentration of Sm is higher in the first subphase 21 than in the second subphase 22. In addition, despite the addition of the element M, the first subphase 21 and the second subphase 22 are not formed due to the absence of Sm,15 and it is not confirmed that the concentration of the element M is higher in the second subphase 22 than in the first subphase 21. The evaluation of the magnetic properties of this sample with the method described above shows that the residual magnetic flux density is “poor”,20 the coercive force is “good”, the temperature coefficient of residual magnetic flux density is “equivalent”, and the temperature coefficient of coercive force is “equivalent”. This result reflects the fact that a part of Nd is replaced by Dy having high magnetocrystalline anisotropy, and the25 crystal grain boundary is made non-magnetic by M, whereby the coercive force is improved, but the concentration of Sm and the concentration of the element M in the subphase 20 do not accord with an appropriate structure form due to the absence of La and Sm.30 [0085] Comparative Example 5 is a sample of the rare earth sintered magnet 1 prepared in the form of (Nd, La, Sm)-Fe-B with the production method according to the second 40 embodiment using Nd, La, Sm, Fe, and FeB as raw materials. From the observation of the structure form of this sample according to the above-described method, the two types of subphases 20, namely the first subphase 21 and the second subphase 22, are not confirmed due to the absence of M5 despite the addition of Sm, and the concentration of Sm is uniformly dispersed in the main phase 10 and the subphase 20. Furthermore, because the two types of subphases 20 are not present, it is not confirmed that the first subphase 21 is higher than the second subphase 22. Furthermore, due to10 the absence of the element M, it is not confirmed that the concentration of the element M is higher in the second subphase 22 than in the first subphase 21. The evaluation of the magnetic properties of this sample with the method described above shows that the residual magnetic flux15 density is “poor”, the coercive force is “poor”, the temperature coefficient of residual magnetic flux density is “good”, and the temperature coefficient of coercive force is “good”. This result reflects the fact that the presence of La and Sm in the main phase 10 or the subphase20 20 gives a good result in the temperature coefficient of the magnetic properties, but the two types of subphases 20 are not present, and the concentration of Sm and the concentration of the element M in these subphases 20 do not accord with an appropriate structure form.25 [0086] Comparative Example 6 is a sample of the rare earth sintered magnet 1 prepared in the form of (Nd, La, Sm)-Fe-B-N with the production method according to the second embodiment using Nd, La, Sm, Fe, and FeB, and further one or more additive elements N selected from the30 group consisting of Co, Zr, Ti, Pr, Nb, Dy, Tb, Mn, Gd, and Ho as raw materials. From the observation of the structure form of this sample according to the above-described 41 method, the two types of subphases 20, namely the first subphase 21 and the second subphase 22, are not confirmed due to the absence of the element M despite the addition of Sm, and the concentration of Sm is uniformly dispersed in the main phase 10 and the subphase 20. Furthermore,5 because the two types of subphases 20 are not present, it is not confirmed that the first subphase 21 is higher than the second subphase 22. Furthermore, due to the absence of the element M, it is not confirmed that the concentration of the element M is higher in the second subphase 22 than10 in the first subphase 21. The evaluation of the magnetic properties of this sample with the method described above shows that the residual magnetic flux density is “good”, the coercive force is “poor”, the temperature coefficient of residual magnetic flux density is “good”, and the15 temperature coefficient of coercive force is “good”. The presence of La and Sm in the main phase 10 or the subphase 20 gives a good result in the temperature coefficient of the magnetic properties. In addition, the magnetic flux density is improved by the effect of the additive element N20 such as Co, which is a magnetic material. However, the result reflects the fact that the two types of subphases 20 are not present, and the concentration of Sm and the concentration of the element M in these subphases 20 do not accord with an appropriate structure form.25 [0087] Examples 1 to 7 are samples of the rare earth sintered magnet 1 prepared in the form of (Nd, La, Sm)-Fe- B-M with the production method according to the second embodiment using Nd, La, Sm, Fe, FeB, and further the element M as raw materials. From the observation of the30 structure form of these samples according to the above- described method, it is confirmed that the concentration of Sm is higher in the first subphase 21 than in the second 42 subphase 22. Furthermore, it is confirmed that the concentration of the element M is higher in the second subphase 22 than in the first subphase 21. The evaluation of the magnetic properties of these samples with the method described above shows that the residual magnetic flux5 density is “good”, the coercive force is “good”, the temperature coefficient of residual magnetic flux density is “good”, and the temperature coefficient of coercive force is “good”. [0088] Example 8 is a sample of the rare earth sintered10 magnet 1 prepared in the form of (Nd, La, Sm)-Fe-B-M with the production method according to the second embodiment using Nd, La, Sm, Fe, FeB, the element M, and further the additive element N as raw materials. From the observation of the structure form of this sample according to the15 above-described method, it is confirmed that the concentration of Sm is higher in the first subphase 21 than in the second subphase 22. Furthermore, it is confirmed that the concentration of the element M is higher in the second subphase 22 than in the first subphase 21. The20 evaluation of the magnetic properties of these samples with the method described above shows that the residual magnetic flux density is “good”, the coercive force is “good”, the temperature coefficient of residual magnetic flux density is “good”, and the temperature property evaluation of25 coercive force is “good”. This indicates that the obtained effect is not influenced by the addition of the additive element N as long as a proper structure form is formed. [0089] The samples of Examples 1 to 8 are the rare earth sintered magnets 1 satisfying the general formula (Nd, La,30 Sm)-Fe-B-M and including: the main phase 10 including crystal grains based on an R2Fe14B crystal structure; the first subphase 21 that is crystalline and mainly composed 43 of an oxide phase represented by (Nd, La, Sm)-O; and the second subphase 22 that is crystalline and mainly composed of an oxide phase represented by (Nd, La)-O. As described above, in the rare earth sintered magnets 1 according to Examples 1 to 8, the concentration of Sm is higher in the5 first subphase 21 than in the second subphase 22, and the concentration of the element M is higher in the second subphase 22 than in the first subphase 21. As a result, these rare earth sintered magnets 1 are capable of improving magnetic properties at room temperature and10 reducing or preventing degradation of magnetic properties associated with temperature rise with reduced use of Nd and heavy rare earth elements, which are expensive and have a procurement risk due to high distribution unevenness, compared with the rare earth sintered magnet satisfying Nd-15 Fe-B. [0090] The configurations described in the above- mentioned embodiments indicate examples. The embodiments can be combined with another well-known technique and with each other, and some of the configurations can be omitted20 or changed in a range not departing from the gist. Reference Signs List [0091] 1 rare earth sintered magnet; 10 main phase; 20 subphase; 21 first subphase; 22 second subphase; 3125 crucible; 32 molten alloy; 33 tundish; 34 single roll; 35 solidified alloy; 36 tray container; 37 rare earth magnet alloy; 100 rotor; 101 rotor core; 102 magnet insertion hole; 120 rotary machine; 130 stator; 131 teeth; 132 winding.30 44 We Claim : [Claim 1] A rare earth sintered magnet satisfying a general formula (Nd, La, Sm)-Fe-B-M, where element M is one or more elements selected from a group consisting of Cu, Al, and Ga, the rare earth sintered magnet comprising:5 a main phase including crystal grains based on an R2Fe14B crystal structure; a first subphase that is crystalline and mainly composed of an oxide phase represented by (Nd, La, Sm)-O; and10 a second subphase that is crystalline and mainly composed of an oxide phase represented by (Nd, La)-O, wherein a concentration of Sm is higher in the first subphase than in the second subphase, and15 a concentration of the element M is higher in the second subphase than in the first subphase. [Claim 2] The rare earth sintered magnet according to claim 1, wherein20 a sum of concentrations of La in the first subphase and the second subphase is equal to or greater than a concentration of La in the main phase, and a sum of concentrations of Sm in the first subphase and the second subphase is equal to or greater than a25 concentration of Sm in the main phase. [Claim 3] The rare earth sintered magnet according to claim 1 or 2, wherein a concentration of La in the first subphase is equal to or higher than a concentration of La in the30 second subphase. [Claim 4] The rare earth sintered magnet according to any 45 one of claims 1 to 3, wherein a>(b+c) is satisfied, where a, b, and c represent composition ratios of Nd, La, and Sm, respectively. [Claim 5] The rare earth sintered magnet according to any5 one of claims 1 to 4, wherein 1<(Y1+Y2)/Y<(X1+X2)/X is satisfied, where X represents the concentration of La contained in the main phase, X1 represents the concentration of La contained in the first subphase, X2 represents the concentration of La contained in the second10 subphase, Y represents the concentration of Sm contained in the main phase, Y1 represents the concentration of Sm contained in the first subphase, and Y2 represents the concentration of Sm contained in the second subphase. 15 [Claim 6] The rare earth sintered magnet according to any one of claims 1 to 5, further comprising: one or more additive elements N selected from a group consisting of Co, Zr, Ti, Pr, Nb, Dy, Tb, Mn, Gd, and Ho. 20 [Claim 7] A method for producing the rare earth sintered magnet according to any one of claims 1 to 6, the method comprising: a melting step of melting a raw material of a rare earth magnet alloy containing an element constituting the25 rare earth sintered magnet; a pulverizing step of pulverizing the rare earth magnet alloy satisfying (Nd, La, Sm)-Fe-B-M; a molding step of preparing a molded body by molding powder of the rare earth magnet alloy;30 a sintering step of preparing a sintered body by holding the molded body at a sintering temperature in a range of 900°C to 1300°C for a period of time in a range of 46 0.1 hours to 10 hours; a primary aging step of holding the sintered body at a primary aging temperature that is a temperature lower than the sintering temperature; a secondary aging step of holding the sintered body at5 a secondary aging temperature that is a temperature lower than the primary aging temperature; and a cooling step of cooling at a temperature lower than the secondary aging temperature. 10 [Claim 8] The method for producing a rare earth sintered magnet according to claim 7, wherein, in the first aging step, the sintered body is held at a temperature of 700°C or higher but lower than 900°C for 0.1 hours to 10 hours. 15 [Claim 9] The method for producing a rare earth sintered magnet according to claim 7 or 8, wherein, in the second aging step, the sintered body is held at a temperature of 450°C or higher but lower than 700°C for 0.1 hours to 10 hours.20 [Claim 10] The method for producing a rare earth sintered magnet according to any one of claims 7 to 9, wherein, in the cooling step, the sintered body is held at a temperature of 200°C or higher but lower than 450°C for25 0.1 hours to 5 hours. [Claim 11] A rotor comprising: a rotor core; and the rare earth sintered magnet according to any one of30 claims 1 to 6 provided in the rotor core. [Claim 12] A rotary machine comprising: 47 the rotor according to claim 11; and an annular stator facing the rotor and including, on an inner surface on a side where the rotor is placed, teeth protruding toward the rotor and windings provided on the teeth.5