RTB-type sintered magnet and method for manufacturing the same
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- MINEBEAMITSUMI INC
- Filing Date
- 2022-05-30
- Publication Date
- 2026-06-25
Smart Images
Figure 0007880234000006 
Figure 0007880234000007 
Figure 0007880234000008
Abstract
Description
Technical Field
[0001] The present invention relates to an R-T-B sintered magnet and a method for manufacturing the same.
Background Art
[0002] Conventionally, R (rare earth element R)-T (transition metal element T)-B permanent magnets have high magnetic properties. In particular, R (including Nd as a rare earth element)-T (such as Fe)-B sintered magnets have excellent magnetic properties, so they are widely used in motors, actuators, etc. mounted on various electronic devices, household appliances, and automobiles. R (including Nd as a rare earth element)-T (such as Fe)-B magnets used in motors, actuators, etc. are required to have a high coercive force even in a high-temperature environment because the coercive force of the permanent magnet decreases at high temperatures.
[0003] As a means for improving the coercive force of such R (including Nd as a rare earth element)-T (such as Fe)-B sintered magnets, it has conventionally been known to add dysprosium (Dy) or terbium (Tb), which are heavy rare earth elements. For example, Patent Document 1 describes that the coercive force is improved by substituting a part of Nd near the surface of the Nd2Fe 14 intermetallic compound of B with Dy and / or Tb.
[0004] Increasing the coercive force of the magnet leads to an increase in the magnetization field. That is, in order to fully exhibit the magnetization characteristics of an R (including Nd as a rare earth element)-T (such as Fe)-B sintered magnet added with dysprosium (Dy) or terbium (Tb), which are heavy rare earth elements, it is necessary to perform saturation magnetization. For example, Patent Document 2 states that when performing saturation magnetization, the magnetization field generally requires a magnetic field about 3 to 5 times the coercive force of the magnet to be magnetized. However, in the case of Nd-Fe-B sintered magnets, since the coercive force generation mechanism is of the nucleation type, it is also described that the initial magnetization field can be small and a magnetic field strength approximately equal to the coercive force is sufficient. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-096928 [Patent Document 2] Japanese Patent Application Publication No. 5-047558 [Overview of the Initiative] [Problems that the invention aims to solve]
[0006] However, as mentioned above, some Nd-Fe-B sintered magnets with added dysprosium (Dy) or terbium (Tb) have coercivity of 2785 kA / m or more (for example, N32EZ (product name of Shin-Etsu Chemical Co., Ltd., which is sample C described later)). When pulse magnetizing such Nd-Fe-B sintered magnets with high coercivity, a device capable of generating a large magnetizing magnetic field of at least approximately 2800 kA / m is required to achieve saturation magnetization. Furthermore, when the pole pitch is small and multi-pole magnetization is required, the wire diameter of the coil wound around the magnetizing yoke becomes thin, making it impossible to pass the high current necessary to generate the required magnetizing magnetic field, and thus a sufficient magnetizing magnetic field cannot be applied.
[0007] The present invention has been made in view of the above, and aims to provide an RTB-type sintered magnet that can be magnetized with multiple poles and can generate a large magnetic field after magnetization even when the pole pitch is reduced, and a method for manufacturing the same. [Means for solving the problem]
[0008] To solve the above-mentioned problems and achieve the objective, an RTB-type sintered magnet according to one aspect of the present invention is an RTB-type sintered magnet (where R represents a rare earth element including Nd, and T represents a transition metal element including Fe), wherein the RTB-type sintered magnet contains at least dysprosium (Dy) as a rare earth element, and when the value of the saturation remanent magnetization of the RTB-type sintered magnet is B, and the value of the magnetization when an external magnetic field of 500 kA / m is applied to the initial magnetization curve of the RTB-type sintered magnet is A, the magnetic ratio expressed as A / B is less than 1.0 (but greater than 0), and the pole pitch of the RTB-type sintered magnet is less than 4 mm (but greater than 0 mm). [Effects of the Invention]
[0009] According to an aspect of the present invention, it is possible to provide an RTB-type sintered magnet that can be magnetized with multiple poles and can generate a large magnetic field after magnetization even when the pole pitch is reduced. [Brief explanation of the drawing]
[0010] [Figure 1] Figure 1 shows a schematic example of a magnetization device used in the embodiment. [Figure 2] Figure 2 is a schematic perspective view showing the field magnets used in the field section. [Figure 3] Figure 3 is a schematic plan view illustrating the pole pitch in the magnetized object. [Figure 4] Figure 4 shows the relationship between each pole pitch and the magnetization index for each sample after magnetization using the magnetization device shown in Figure 1. [Figure 5] Figure 5 shows the relationship between each pole pitch and the magnetization index for each sample after pulse magnetization, with each sample serving as a comparative example. [Figure 6] Figure 6 shows the relationship between pole pitch and magnetization index in sample C (Example 3). [Figure 7] Figure 7 shows the first quadrant of the magnetic hysteresis curve for each sample. [Modes for carrying out the invention]
[0011] The RTB-type sintered magnet according to an embodiment of the present invention and its manufacturing method will be described in detail below with reference to the drawings. However, the present invention is not limited to this embodiment.
[0012] <RTB-type sintered magnet according to an embodiment> The RTB (boron)-based magnet constituting the RTB-based sintered magnet according to the embodiment will be described. The RTB-based magnet constituting the RTB-based magnet powder is a ternary tetragonal compound, R2T 14 Phase B (e.g., Nd2Fe) 14 It contains a type B compound phase as the main phase. RTB magnets also typically contain an R-rich phase, etc. R represents rare earth elements including Nd and / or Pr. In other words, R contains Nd and / or Pr as essential components.
[0013] Examples of rare earth elements include neodymium (Nd) and praseodymium (Pr), as well as scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Rare earth elements other than Nd and Pr may be used individually or in combination of two or more.
[0014] Specifically, R may consist of Nd alone, Pr alone, or Nd and Pr alone. Alternatively, Nd may be used with other rare earth elements, Pr with other rare earth elements, or Nd and Pr with other rare earth elements. It is preferable to use at least Nd as R.
[0015] T represents Fe, or Fe and Co. Thus, T may be only Fe, or a part thereof may be substituted with Co. When the total amount of T is 100 atomic %, it is preferable to contain Fe in an amount of 50 atomic % or more.
[0016] The R-T-B-based magnet may contain other elements. Examples of the other elements include titanium, zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W). The other elements may be used alone or in combination of two or more.
[0017] In the R-T-B-based magnet, R is preferably contained in an amount of 10 atomic % or more and 20 atomic % or less. B is preferably contained in an amount of 6 atomic % or more and 8 atomic % or less. When the above-described other elements are contained, the other elements are preferably contained in a total amount exceeding 0 atomic % and 3 atomic % or less. Here, the balance is the total amount of T and the unavoidably contained elements.
[0018] In the R-T-B-based magnet, it is preferable to contain at least dysprosium (Dy) as a heavy rare earth element. For a Nd-Fe-B-based sintered magnet in which the intrinsic coercive force is increased by adding a large amount of dysprosium (Dy), even when magnetized with a small pole pitch, the generated magnetic field after magnetization can be increased, which is preferable. Therefore, the pole pitch in the R-T-B-based sintered magnet can be made less than 4 mm (however, larger than 0 mm).
[0019] Furthermore, when measuring the magnetic hysteresis curve of the R-T-B-based sintered magnet, in the initial magnetization curve in the first quadrant, when the ratio of the residual magnetization to the saturation magnetization is defined as the magnetization ratio, it is preferable that the magnetization ratio is less than 0.5. When the magnetization ratio is less than 0.5, it is difficult to magnetize, but an R-T-B-based sintered magnet having a large holding force can be obtained. However, an R-T-B-based sintered magnet having a large coercive force can be easily obtained by the manufacturing method described below.
[0020] <Method for manufacturing an RTB-type sintered magnet according to an embodiment> The method for manufacturing an RTB-type sintered magnet according to the embodiment includes a step of preparing the RTB-type sintered magnet described above. Next, the method includes a magnetization step in which the prepared RTB-type sintered magnet is used as the object to be magnetized, and the magnetization device has a field section in which a plurality of permanent magnets for magnetization that generate a magnetic field with respect to the object to be magnetized are arranged at equal intervals, and a heating section having a heating surface that faces the object to be magnetized in the axial direction of the object to be magnetized and heats the object to be magnetized.
[0021] In the magnetization process described above, the object to be magnetized is placed on the field section, and the object to be magnetized is heated by the heating section to a temperature above the Curie point of the object to be magnetized but below the Curie point of the permanent magnet for magnetization, and then cooled down to a temperature below the Curie point of the object to be magnetized, while a magnetizing magnetic field is applied to the object to be magnetized by the permanent magnet for magnetization. The temperature below the Curie point of the permanent magnet for magnetization may be 800°C or higher, but considering the operating temperature of the magnetization device, a temperature of 350°C or lower is desirable. In the field section described above, the permanent magnets for magnetization are arranged such that the pole pitch of the object to be magnetized after the magnetization process is less than 4 mm (but greater than 0 mm).
[0022] In the magnetization process, the object to be magnetized is magnetized using a magnetization device. Figure 1 shows a schematic example of a magnetization device that performs UHM (Ultra High Magnetizing) magnetization, used in the embodiment.
[0023] As shown in Figure 1, the magnetization device 1 comprises a base unit 2, a moving unit 3, a heating unit 4, a preheating unit 5, a field unit 6, a holding member 7, a cooling unit 8, and a control unit 10. The object to be magnetized 100 is placed on the preheating unit 5, magnetization is performed, and the magnetized object after magnetization (post-magnetized object) is produced.
[0024] The frame section 2 is the base of the magnetization device 1 and is equipped with at least the moving section 3, heating section 4, preheating section 5, field section 6, holding member 7, cooling section 8, and control section 10.
[0025] The moving unit 3 moves the object to be magnetized 100 and the heating unit 4 relative to each other between a non-heated position and a heated position in the axial direction, which is the vertical direction in Figure 1. In this embodiment, the moving unit 3 includes a ceiling plate 31, an actuator 32, and a heating unit mounting base 33. The ceiling plate 31 is positioned spaced apart from the frame 2 in the axial direction, and the actuator 32 and the heating unit mounting base 33 are fixed to it. The actuator 32 moves the ceiling plate 31 relative to the frame 2 in the axial direction. The actuator 32 is a linear motion mechanism, such as a hydraulic cylinder, and is powered by an external power source (not shown), and is driven by the control unit 10. Multiple actuators 32 are arranged between the frame 2 and the ceiling plate 31, for example, two or four. The heating unit mounting base 33 has the heating unit 4 fixed to it and is fixed to the lower side surface of the ceiling plate 31.
[0026] The heating unit 4 provides heating to the object to be magnetized 100 for magnetization. The heating unit 4 is made of a non-magnetic metal material, such as non-magnetic stainless steel, and heats the object to be magnetized 100 to a temperature above the Curie point of the magnets that make up the object to be magnetized 100. In this embodiment, the heating unit 4 is formed in a disc shape, and of its two surfaces in the vertical direction, the upper surface is fixed to the heating unit mounting base 33 of the movable unit 3, and the lower surface is the heating surface (not shown). The heating surface has an outer diameter larger than the outer diameter of the object to be magnetized 100 and faces the mounting surface 6a of the field unit 6, which will be described later, in the axial direction. In other words, the heating surface 4a faces the object to be magnetized 100 placed on the mounting surface (not shown) of the preheating unit 5 in the axial direction. The heating surface also contacts the object to be magnetized 100 at the heating position. The heating unit 4 has one or more heaters, is powered by an external power source (not shown), and its temperature is controlled by the control unit 10.
[0027] The preheating unit 5 performs preliminary heating on the object to be magnetized 100. The preheating unit 5 is made of a non-magnetic metal material and heats the object to be magnetized 100 to a temperature below the Curie point (higher than room temperature) of the magnets that make up the object to be magnetized 100 before it reaches the heating position. Here, the preheating unit 5 heats the object to be magnetized 100 placed on the field unit 6 via the field unit 6 and the holding member 7. The preheating unit 5 is powered by an external power source (not shown) and has one or more heaters, and its temperature is controlled by the control unit 10.
[0028] The field section 6 generates a magnetic field with respect to the object to be magnetized 100. In this embodiment, the field section 6 magnetizes the object to be magnetized 100 in the axial direction. After placing the object to be magnetized 100 on the preheating section 5, the field section 6 is placed on top of the object to be magnetized 100, and then the holding member 7 holds and fixes the object to be magnetized 100 and the field section 6 on the preheating section 5 from above.
[0029] The field magnet used in the field section 6 is, for example, a rectangular samarium-cobalt magnet (Sm-Co magnet, Curie temperature is usually between 750°C and 900°C). As shown in Figure 2, the permanent magnet 61 has multiple strip-shaped N poles 62 and S poles 63 arranged alternately next to each other. In the field section 6, the N poles 62 and S poles 63 of the permanent magnet 61 are arranged such that the pole pitch in the magnetized object 100 after the magnetization process is less than 4 mm (but greater than 0 mm), preferably between 0.3 mm and 2.6 mm, and more preferably between 0.5 mm and 2.6 mm. Figure 3 is a schematic plan view illustrating the pole pitch in the magnetized object 100, showing the state in which six poles of N and S are alternately magnetized in the magnetized object 100.
[0030] The cooling unit 8 cools the object to be magnetized 100 that has been heated by the heating unit 4. In this embodiment, the cooling unit 8 is fixed to the frame unit 2 by a fixing member (not shown) and outputs air towards the object to be magnetized 100 placed on the field unit 6. The cooling unit 8 is, for example, an air-cooling fan or a compressor that supplies compressed air, and cools the object to be magnetized 100 after heating by forced air cooling, which has a high cooling efficiency, rather than natural air cooling. The cooling unit 8 is powered by an external power source (not shown), and the airflow is controlled by the control unit 10.
[0031] The control unit 10 controls the magnetization device 1 in order to magnetize the object to be magnetized 100. The control unit 10 controls the moving unit 3, the heating unit 4, the preheating unit 5, and the cooling unit 8. By driving the moving unit 3, the control unit 10 moves the heating unit 4 relative to the object to be magnetized 100 placed on the field unit 6 between a non-heating position and a heating position. Here, the non-heating position is a position in which the heating unit 4 is separated from the object to be magnetized 100 in the axial direction and does not contact the object to be magnetized 100, and the object to be magnetized 100 is not heated by the heating unit 4. On the other hand, the heating position is a position in which the heating unit 4 is close to the object to be magnetized 100 in the axial direction and contacts the object to be magnetized 100, and the object to be magnetized 100 is heated by the heating unit 4.
[0032] The control unit 10 controls the temperature of the heating unit 4 so that the heating temperature of the magnetized object 100 is above the Curie point of the magnets constituting the magnetized object 100. Specifically, in this embodiment, the heating unit 4 is heated to a temperature above the Curie point and below 350°C before reaching the heating position. The heating temperature is such that deterioration of the magnetic properties of the magnets constituting the magnetized object 100 is suppressed. After heating the magnetized object 100 in contact with the field unit 6, the cooling unit 8 cools the magnetized object 100 heated by the heating unit 4 to approximately room temperature, thereby producing a magnetized object 100. [Examples]
[0033] The above embodiments will be described in more detail below based on the examples. However, the above embodiments are not limited in any way by the following examples and comparative examples.
[0034] [Examples 1-3] Samples A to C, corresponding to Examples 1 to 3, were prepared as RTB-type sintered magnets. Samples A to C are all Nd-Fe-B-type sintered magnets manufactured by Shin-Etsu Chemical Co., Ltd., and as shown in Table 1, sample A is product name and model number: N37, sample B is product name and model number: N39UH, and sample C is product name and model number: N32EZ.
[0035] [Table 1]
[0036] Chemical analysis using an electron probe analyzer (EPMA) revealed that each of the samples A, B, and C contains the heavy rare earth element dysprosium (Dy), with the content in the order of sample A < sample B < sample C. Specifically, the analytical values are shown in Table 1. Furthermore, the intrinsic coercivity of each of the samples A, B, and C follows the order of sample A < sample B < sample C. Therefore, sample C, which contains a large amount of the heavy rare earth element dysprosium (Dy), is a highly heat-resistant sintered magnet.
[0037] Next, samples A, B, and C were magnetized using the magnetization device 1 shown in Figure 1. Each sample A, B, and C was prepared as the object to be magnetized 100, with a thickness of 7 mm × 7 mm × 1 mm. The field section 6, which is the field source for applying the magnetization magnetic field, consists of multiple roughly rectangular permanent magnets (Sm2Co 17 As shown in Figure 2, the magnets are arranged in a configuration of six magnets with alternating north poles (62) and south poles (63) adjacent to each other at a predetermined pole pitch. Permanent magnets with pole pitches (magnetization pitches) of 0.32 mm, 0.67 mm, and 0.96 mm were prepared.
[0038] Each sample A, B, and C was set on the preheating section 5 of the magnetization device 1 and held in place by a graphite retaining plate (7 mm x 7 mm x 1 mm thick) as a holding member 7. With the field section 6, which is a permanent magnet of the field source, in contact with the surface of each sample A, B, and C, the samples were heated by the heating section 4, which is a heating device, to a temperature above the Curie temperature of each sample A, B, and C, up to 350°C, and then cooled to approximately room temperature. This magnetized the samples in the thickness direction (axial direction) at predetermined pole pitches (0.32 mm, 0.67 mm, 0.96 mm), obtaining the magnetized object 100 shown in Figure 3.
[0039] After cooling each sample A, B, and C to approximately room temperature, a 50 μm square Hall element probe was used to hold each sample surface at a distance of 0.14 mm from the probe, and the magnetic field generated from each magnetized sample surface was measured. As a comparative example, the magnetic field strength at a distance of 0.14 mm from each sample surface was calculated when each sample A, B, and C were pulse-magnetized. Pulse magnetization is a mechanism where a magnetizing device typically consists of a magnet wire and electromagnetic soft iron, and a pulsed current is applied to the wire to generate a magnetizing magnetic field. The wire diameter and the current value that can be passed are limited due to the risk of heat generation and wire breakage, and the current density is 16 [kA / mm²]. 2 The calculation was performed using ] as the upper limit.
[0040] [evaluation] (Relationship between magnetic index and pole pitch) The magnetization index was determined from the relationship between the magnetic field generated from the surfaces of each magnetized sample A, B, and C and the saturation remanent magnetization, using the following equation (1). Magnetization index = Maximum magnetic field generated from the sample surface after magnetization (mT) / Saturation remanent magnetization Jr (T) (1)
[0041] Figure 4 shows the relationship between the magnetization index and each pole pitch (0.32 mm, 0.67 mm, 0.96 mm) for each sample A, B, and C after magnetization using the magnetization device 1 shown in Figure 1. Figure 5 shows the relationship between the magnetization index and each pole pitch (0.32 mm, 0.67 mm, 0.96 mm) for each sample A, B, and C after pulse magnetization as a comparative example. Furthermore, Tables 2 to 4 show the saturation remanent magnetization, generated magnetic field, and magnetization index for each sample A, B, and C, including the cases of Examples 1 to 3 magnetized using the magnetization device 1 in Figure 1, and the case of pulse magnetization as a comparative example.
[0042] [Table 2] [Table 3] [Table 4] As is clear from Figure 5, when the pole pitch is reduced in pulse magnetization using the comparative example, the magnetization index decreases as the pole pitch decreases for all samples A to C. In other words, the magnetic field generated from the sample surface decreases as the pole pitch decreases. Furthermore, sample C (Example 3), which has the largest intrinsic coercivity among the samples, has a smaller magnetization index compared to the other samples.
[0043] On the other hand, as shown in Figure 4, when magnetization is performed using the magnetization process in the magnetization device 1 shown in Figure 1, sample C (Example 3), which has the largest intrinsic coercivity among the samples, shows a larger magnetization index compared to the other samples. This is because, in conventional pulse magnetization, when the pole pitch is reduced, the intrinsic coercivity of the object to be magnetized 100 increases, making magnetization more difficult, and consequently, the generated magnetic field after magnetization also decreases. In contrast, when magnetization is performed using the magnetization device 1 shown in Figure 1, even when magnetizing an Nd-Fe-B sintered magnet with a large amount of dysprosium (Dy), a heavy rare earth element, by reducing the pole pitch, the generated magnetic field after magnetization can be increased.
[0044] Figure 6 shows the relationship between pole pitch and magnetization index for sample C (Example 3), which has the highest intrinsic coercivity among the samples. The values for pulse magnetization in the comparative example are calculated values, while the values for magnetization using magnetization device 1 shown in Figure 1 are calculated values for pole pitches of 1 mm or more. As can be seen from Figure 6, in the region of pole pitch less than 4 mm, the magnetization index can be improved by magnetizing with magnetization device 1 shown in Figure 1 compared to pulse magnetization in the comparative example.
[0045] (Magnetic ratio in each sample) For each of the samples A, B, and C, the relationship between the magnetic field and magnetization was determined, and the magnetic hysteresis curves were measured. Figure 7 shows the first quadrant of the magnetic hysteresis curves for each of the samples A, B, and C. As is clear from Figure 7, the initial magnetization curves of samples A and B rise steeply, while the initial magnetization curve of sample C rises more gently compared to samples A and B. It can also be seen that for all samples, the curve becomes gentler when the magnetic field exceeds 200 kA / m.
[0046] Next, for each sample A, B, and C, the magnetization ratio was calculated using the following equation (2) as the value of magnetization (A) in the initial magnetization curve when an external magnetic field of 500 kA / m was applied, relative to the value of saturation remanent magnetization (B). Magnetization ratio (A / B) = Magnetization in the initial magnetization curve (T) / Saturation remanent magnetization (T) (2)
[0047] Furthermore, the magnetic susceptibility ratio (A / B) values for each sample A, B, and C are summarized in Table 5. In Table 5, the magnetization (T) values are recorded based on measured values under a 3T magnetic field (values from Figure 7). For samples A and B, the saturated remanent magnetization (T) values are recorded from Figure 7, while the saturated remanent magnetization (T) value for sample C is the value recorded in the performance report from the manufacturer, Shin-Etsu Chemical Co., Ltd.
[0048] [Table 5] The magnetic susceptibility ratio was determined for the initial magnetization curve when an external magnetic field of 500 kA / m was applied. However, for each sample, when the magnetic field exceeds 200 kA / m, the initial magnetization curve becomes a gentler curve. Therefore, 500 kA / m was used as a representative magnetic susceptibility ratio near the saturation magnetization, where the curve becomes nearly horizontal. Consequently, the magnetic susceptibility ratio can also be determined for magnetic fields of approximately 400 to 700 kA / m.
[0049] The magnetic susceptibility ratio is preferably less than 1.0. Furthermore, it is even more preferable that the magnetic susceptibility ratio is less than 0.95, and even more preferable that it is less than 0.46. However, the magnetic susceptibility ratio is greater than 0. When the magnetic susceptibility ratio is less than 1.0, it is possible to obtain a magnet with high magnetization characteristics for high-coercivity RTB-type sintered magnets that are difficult to magnetize. Conversely, when the magnetic susceptibility ratio exceeds 1.0, it is undesirable because it results in a magnet with low magnetization characteristics for high-coercivity RTB-type sintered magnets that are difficult to magnetize. [Explanation of Symbols]
[0050] 1 Magnetizing device, 2 Stand, 3 Moving part, 4 Heating part, 5 Preheating part, 6 Field part, 61 Permanent magnet, 62 North pole, 63 South pole, 7 Holding member, 8 Cooling part, 10 Control unit, 32 Actuator, 33 Heating part mounting base, 100 Object to be magnetized
Claims
1. R-T-B sintered magnet (where R represents a rare earth element including Nd, and T represents a transition metal element including Fe), The R-T-B sintered magnet contains at least dysprosium (Dy) as a rare earth element. When the value of the saturation remanent magnetization of the R-T-B sintered magnet is B, and the value of the magnetization when an external magnetic field of 500 kA / m is applied to the initial magnetization curve of the R-T-B sintered magnet is A, then when the magnetic ratio is expressed as A / B, the magnetic ratio is 0.46 or less (but greater than 0). An R-T-B sintered magnet having a pole pitch of less than 4 mm (but greater than 0 mm).
2. A method for manufacturing an R-T-B sintered magnet (where R represents a rare earth element including Nd, and T represents a transition metal element including Fe), The R-T-B sintered magnet is characterized by containing at least dysprosium (Dy) as a rare earth element, and when the saturation remanent magnetization of the R-T-B sintered magnet is B, and the magnetization value when an external magnetic field of 500 kA / m is applied to the initial magnetization curve of the R-T-B sintered magnet is A, the magnetic ratio is expressed as A / B, and the magnetic ratio is 0.46 or less (but greater than 0). The process involves heating the R-T-B sintered magnet to a temperature above the Curie temperature of the R-T-B sintered magnet but below the Curie temperature of the permanent magnet that serves as the field source, then cooling it to approximately room temperature, during which time a magnetizing magnetic field is applied to the R-T-B sintered magnet using the permanent magnet to magnetize it at a predetermined pole pitch. A method for manufacturing R-T-B type sintered magnets, including the method described above.
3. The method for manufacturing an R-T-B sintered magnet according to claim 2, wherein the pole pitch in the R-T-B sintered magnet is less than 4 mm (but greater than 0 mm).
4. The method for manufacturing an R-T-B sintered magnet according to claim 3, wherein the heating of the permanent magnet to a temperature below the Curie temperature is to a temperature of 350°C.