RTB-based permanent magnet, magnet and motor

Abstract

RTB-based permanent magnet comprising: a demagnetization curve with a slope ΔJ / Δ(H / HcJ) of less than 40.0 T in a region where the value of the magnetic field is Hk or less in the demagnetization curve, where: the composition of R by R1 1-x R2 x and T represents one or more transition metal elements containing Fe or contain a combination of Fe and Co, where: in R1 1-x R2 x R1 represents the rare earth element(s) composed of one or more elements selected from the group consisting of Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, R2 contains Y and 0.2 ≤ x ≤ 0.7, B represents boron, where boron is replaceable by carbon (C), Hk is the value of the magnetic field when the magnetic flux density becomes 90% of the remaining magnetic flux density (Br), where the remaining magnetic flux density Br is 1.2 T or more and the coercive force HcJ is less than 636.62 kA / m, and where the perpendicularity ratio Hk / HcJ is 80% or more.

Description

[0001] The present invention relates to an RTB-based permanent magnet. BACKGROUND

[0002] The RTB-based permanent magnet (R stands for a rare earth element, T stands for Fe or Fe with part of it replaced by Co, and B stands for Boron), which uses the tetragonal compound R 2 T 14 B as the main phase, is known to have excellent magnetic properties and has been a representative high-performance permanent magnet since its invention in 1982 (Patent Document 1: JP S59 - 46 008 A).

[0003] The RTB-based magnet in which the rare earth element R is formed of Nd, Pr, Dy, Ho, and / or Tb is preferably a permanent magnet material having a large anisotropy magnetic field Ha. Among them, the Nd-Fe-B-based magnet with Nd as the rare earth element R is widely used because it has a good balance between the saturation magnetization Is, the Curie temperature Tc, and the anisotropy magnetic field Ha, and is better in terms of resources and corrosion resistance than RTB-based magnets with other rare earth elements.

[0004] As a power unit used in human life, industries, and conveying equipment, the permanent magnet synchronous motor has been widely used. However, the permanent magnet synchronous motor, in which the magnetic field generated by the permanent magnet is constant, is difficult to drive because the induced voltage increases in proportion to the rotational speed. Therefore, when the permanent magnet synchronous motor is operated in a medium / high speed range or under a light load, a field-weakening controller is required to use the magnetic flux generated by the armature current to counteract the magnetic flux of the permanent magnet, thereby reducing the induced voltage below the supply voltage. This results in the problem of deteriorating motor efficiency.

[0005] To solve the above-mentioned technical problem, a variable flux motor is developed using a magnet in which the magnetic force changes reversibly by means of an external magnetic field (a variable flux magnet). When the variable flux motor is operated in the medium / high speed range or under a low load, the decrease in motor efficiency due to the field weakening effect in the prior art can be prevented by reducing the magnetic force of the variable flux magnet. PATENT DOCUMENTS Patent document 1: JP S59 - 46 008 A Patent document 2: JP 2010 - 34 522 A Patent document 3: JP 2009 - 302 262 A

[0006] In the variable flux motor, a constant magnet with a fixed magnetic force and a variable magnet with a variable magnetic force are used in combination. To ensure the high power and high efficiency of the variable flux motor, the variable magnet must provide a magnetic flux equivalent to that of the constant magnet. However, when the variable magnet is arranged inside a motor, the magnetization state of the variable magnet must be regulated by applying a small external magnetic field. In other words, the variable magnet requires magnetic properties such as high residual magnetic flux density and low coercive force.

[0007] Patent Document 2 discloses a variable magnetic flux motor using an Sm-Co-based permanent magnet as the variable magnet, and the efficiency of the motor can be improved by using an Nd-Fe-B-based permanent magnet as the constant magnet. However, the Sm-Co-based permanent magnet used as the variable magnet has a residual magnetic flux density Br of about 10 kG (1.0 T), which is lower than the residual magnetic flux density of about 13 kG (1.3 T) in the Nd-Fe-B-based permanent magnet used as the constant magnet. This then becomes the reason why the performance and efficiency of the motor deteriorate.

[0008] Patent Document 3 discloses a variable magnetic flux motor using an RTB-based permanent magnet as the variable magnet, wherein the RTB-based permanent magnet necessarily contains Ce as the rare earth element R. When the RTB-based permanent magnet with an equivalent structure to the Nd-Fe-B-based permanent magnet, which is the constant magnet, is used as the variable magnet, a residual magnetic flux density Br equivalent to that of the constant magnet is expected in the variable magnet. Nevertheless, in Patent Document 3, when Ce is included as the rare earth element R as a necessary component to regulate the coercive force to a low level, which is preferable for the variable magnet, the residual magnetic flux density Br is approximately 8 kG (0.8 T) to 12.5 kG (1.2 T).In this way, the remaining magnetic flux density Br of the Nd-Fe-B based permanent magnet, which is the constant magnet, reaches about 13 kG (1.3 T).

[0009] Furthermore, the RTB-based magnet is difficult to control when used as the variable magnet. If the magnetic force is to be regulated by applying an external electric magnetic field, it is not easy to regulate the magnetic force when the magnetic force changes greatly with respect to the magnetic field. In addition, if the magnetic force of the variable magnet cannot be regulated at will, the efficiency of the variable flux motor will deteriorate. Furthermore, the article "Influence of Ce Content on the Rectangularity of Demagnetization Curves and Magnetic Properties of Re-Fe-B Magnets Sintered by Double Main Phase Alloy Method" (ZHU M. et al.; IEEE Transactions on Magnetics, Vol. 50, No. 1, 2014; ISSN: 0018-9464) refers to Re-Fe-B magnets with Ce as a substitution element for Nd. High-density microcrystalline magnets are known from US 2009 / 0 032 147 A1.The article "Achievement of high coercivity in sintered R-Fe-B magnets based on misch-metal by dual alloy method" (NIU, E. [et al]; Journal of Applied Physics, Vol. 115, No. 11, 2014, ISSN: 0021-8979) also mentions R-Fe-B magnets. JP 2010-45068 A shows an RTB magnet containing lanthanum. SUMMARY

[0010] In view of the above-mentioned problems, an RTB-based permanent magnet is provided according to independent claim 1. Dependent claims provide advantageous embodiments. The present invention aims to provide a variable magnet with a high residual magnetic flux density, a low coercive force, and excellent controllable magnetic force, which can be suitably used in a variable magnetic flux motor while maintaining its efficiency at a high level over a wide rotational speed range.

[0011] The RTB-based permanent magnet of the present invention is characterized in that a demagnetization curve has a slope ΔJ / Δ(H / HcJ) of less than 400 kG (40 T) in a region where the value of the magnetic field is Hk or smaller, wherein it is preferable that R in the composition of RTB is represented by (R1 1-x R2 x ) and T represents one or more transition metal elements containing Fe or a combination of Fe and Co if necessary, wherein: R1 represents the rare earth element(s) composed of one or more elements selected from the group consisting of Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and R2 contains Y, and 0.2 ≤ x ≤ 0.7.

[0012] The present inventors found that in the demagnetization curve of the RTB-based permanent magnet, the smaller the gradient of ΔJ / Δ(H / HcJ) on the coercive force side, where the value is smaller than Hk, the easier the magnetic flux is to regulate, and the more conveniently the variable magnet can be used in the variable magnetic flux motor. In particular, when a specified amount of the rare earth element R is any of Y, Ce, and La, or a combination thereof, a permanent magnet can be obtained with the properties suitable for use as a variable magnet for the variable magnetic flux motor, having a high residual magnetic flux density and a low coercive force, and whose magnetization state can be regulated by a small external magnetic field.

[0013] If the magnetic force of a magnetized magnet is to be eliminated, a magnetic field opposite to the direction of magnetization must be applied. The required magnetic field varies depending on the coercive force-inducing mechanism or the absolute value of the magnet's coercive force, but a magnetic field equal to or greater than the coercive force is required. The reversed magnetic field is usually provided by a current flowing through the coil winding near the magnet. The flowing current varies depending on the condition or temperature of the winding wire or the condition of the current-regulating system, so the value of the flowing current need not necessarily be constant. The current value is directly related to the strength of the reversed magnetic field.If the magnetic flux changes based on the strength of the reversed magnetic field, it is difficult to maintain the magnetic flux of the variable magnet at a certain value after the reversed magnetic field is applied. In this case, a variable magnet whose magnetic flux responds slowly to the reversed magnetic field is required.

[0014] In other words, it is desired that the magnetization be reduced slowly in the region where the magnetization decreases sharply in the demagnetization curve. As the magnetization decreases slowly, the range of the reversed magnetic field for the desired allowable magnetization degree is expanded. As the absolute value of the required magnetic field increases, controllability deteriorates even if the absolute value for the range of the reversed magnetic field remains the same. Thus, ΔJ / Δ(H / HcJ), which is obtained by dividing H by the coercivity HcJ, but not ΔJ / ΔH, is expected to be small.

[0015] In the variable flux motor, the variable magnet can be magnetized to a value other than 0 by applying the reverse magnetic field. However, if the magnetization is changed to a value other than 0, if ΔJ / Δ(H / HcJ) is small, it cannot be expected that the controllability will improve.

[0016] If the squareness ratio (Hk / HcJ) is small, demagnetization is likely to occur even if ΔJ / Δ(H / HcJ) is small. In this regard, if the squareness ratio is maintained at a certain level or above, ΔJ / Δ(H / HcJ) is desirably small. Here, Hk refers to the value of the magnetic field when the magnetic flux density becomes 90% of the remaining magnetic flux density (Br). Here, the slope from Hk to HcJ is referred to as ΔJ / Δ(H / HcJ) in the present invention.

[0017] The inventors of the present application made great efforts to fabricate a magnet with a small ΔJ / Δ(H / HcJ). As a result, they found that a magnet with a small ΔJ / Δ(H / HcJ) can be provided by adjusting the composition of the RTB-based magnet. To enable ΔJ / Δ(H / HcJ) to be small, a wide distribution of coercivity for respective particles within the magnet is required. The coercivity-inducing mechanism of the RTB-based magnet is the nucleation type, that is, the state of magnetic separation among particles provided by the grain boundary phases affects the coercivity of each particle. If the magnetic separation is not uniform, the coercivity is distributed over a wider range, which further decreases ΔJ / Δ(H / HcJ).

[0018] As a method to make magnetic separation uneven, it is effective to make the grain boundary phases uneven. The grain boundary phase of the Nd-Fe-B-based magnet is mainly composed of a phase with Nd as the main component, which is called the Nd-rich phase. The Nd-rich phase has good magnetic separation and exhibits high coercivity. In contrast, if the Y-rich phase, the Ce-rich phase, or the La-rich phase have different magnetic separation properties compared to the Nd-rich phase, then a coercivity distribution exists by compounding these phases with the Nd-rich phase.

[0019] In contrast, when only Y, Ce, or La are added as grain boundary phases, uniform solid solution phases are formed, making it difficult to achieve a non-uniform coercivity distribution. Here, the Y-rich phase, the Ce-rich phase, or the La-rich phase is formed in the grain boundary regions by performing a long-term heat treatment of 6 hours or more. These phases form a multiple phase with the Nd-rich phase, thus successfully obtaining the coercivity distribution.

[0020] According to the present invention, when a demagnetization curve has a slope ΔJ / Δ(H / HcJ) of less than 400 kG (40 T) in a region where the value of the magnetic field is Hk or smaller, a permanent magnet having the properties suitably used as a variable magnet for the variable magnetic flux motor can be obtained, and can have a high residual magnetic flux density and a low coercivity, and its magnetization state can be regulated by a small external magnetic field, and thus has good controllability. BRIEF DESCRIPTION OF THE DRAWINGS The Fig. Figure 1 is a magnetization-magnetic field curve used to calculate ΔJ / Δ(H / HcJ) in the present invention. DETAILED DESCRIPTION OF EMBODIMENTS

[0021] The preferred embodiments of the present invention are described in detail below. These embodiments are exemplary and do not limit the present invention. Furthermore, not all features described in the embodiments or combinations thereof are necessarily limited to the essential content of the invention.

[0022] The RTB-based permanent magnet of the present invention is characterized in that a demagnetization curve has a slope ΔJ / Δ(H / HcJ) of less than 400 kG (40 T) in a region where the value of the magnetic field is Hk or smaller, wherein it is preferable that R in the composition of RTB is represented by (R1 1-x R2 x) and T represents one or more transition metal elements containing Fe or a combination of Fe and Co if necessary, wherein: R1 represents the rare earth element(s) composed of one or more elements selected from the group consisting of Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and R2 contains at least one element selected from the group consisting of Y, Ce and La, and 0.2 ≤ x ≤ 0.7.

[0023] In the present embodiment, a part of B may be replaced by C. The amount of C to replace B is preferably 10 atomic % or less with respect to B.

[0024] In the present embodiment, as the remainder of the composition, T represents one or more transition metal elements containing Fe or a combination of Fe and Co as needed. The amount of Co is preferably 0 atomic % or more and 10 atomic % or less with respect to the amount of T. With the increase in the amount of Co, the Curie temperature can be raised, and the decrease in coercivity with respect to the increase in temperature can be suppressed to a small extent. Furthermore, the corrosion resistance of the rare earth-based permanent magnet can be improved by increasing the amount of Co.

[0025] The preferred example of the manufacturing method in the present invention will be described below.

[0026] In the production of the RTB-based permanent magnet in the present embodiment, the starting alloy(s) is / are first prepared, whereby an RTB-based magnet with the desired composition can be obtained. The starting alloy(s) can be produced by the strip casting method or other well-known melting methods under vacuum or in an inert atmosphere, preferably in an Ar atmosphere. In the strip casting method, the molten metal obtained by melting the starting metal in a non-oxidative atmosphere such as an Ar atmosphere is sprayed onto the surface of a rotating roll. The molten metal, which is quenched or cooled on the roll, is solidified into a thin plate or sheet (a flake). The quenched and solidified alloy is provided with a homogeneous structure with a crystal particle size of 1 to 50 μm.The method for producing the base alloy is not limited to the strip casting method, and the base alloy can also be obtained by melting methods such as the high-frequency induction melting method. Furthermore, to prevent the occurrence of segregation, for example, the molten metal can be poured onto a water-cooled copper plate to solidify it. The alloy obtained by the reduction-diffusion method can also be used as the base alloy.

[0027] In the present invention, in the production of the RTB-based permanent magnet, the starting alloy is basically prepared by using a single alloying method in which one type of alloy is used to produce the magnet. The mixed method can also be used in which the main phase alloy (the alloy with a small amount of R) containing the R 2 T 14B crystals (which are the main phase grains) as the main part, as well as the alloy (the alloy with a high amount of R) which effectively contributes to forming the grain boundaries and contains more R than the alloy with a low amount of R.

[0028] The starting alloy is subjected to a pulverization process. When the mixing method is used, the alloy with a low R content and the alloy with a high R content are pulverized separately or pulverized together. There are a coarse pulverization process and a fine pulverization process in the pulverization process. First, the starting alloy is coarsely pulverized to have a particle size of about several hundred micrometers. The coarse pulverization process is preferably carried out in an inert atmosphere using a stamp mill, a jaw crusher, a Braun mill, or the like. The pulverization process is effectively carried out when hydrogen is adsorbed onto the starting alloy and then discharged before the coarse pulverization process.The hydrogen removal treatment is performed to reduce the hydrogen constituting impurities in the rare earth-based sintered magnet. The heating and maintaining temperature for hydrogen adsorption is 200°C or higher, preferably 350°C or higher. The maintaining time varies depending on its relationship to the maintaining temperature and the thickness of the base alloy or the like, but is at least 30 minutes or longer, preferably 1 hour or longer. The hydrogen removal treatment is performed under vacuum or under an Ar stream. Furthermore, the hydrogen absorption treatment and the hydrogen removal treatment are not required. Also, hydrogen pulverization can be used as a coarse pulverization process, thus omitting the mechanical coarse pulverization.

[0029] After the coarse pulverization process, the resulting particles are transferred to the fine pulverization process. In the fine pulverization process, the jet mill is mainly used to convert the coarsely pulverized powder with a particle size of about several hundred micrometers into a powder with an average particle size of 2.5 to 6 µm, preferably 3 to 5 µm. The jet mill jets inert gas at high pressure through a narrow nozzle to generate a high-speed gas stream, which accelerates the coarsely pulverized powder. Then, the coarsely pulverized powder collides with or impacts the target or the wall of the container to complete pulverization.

[0030] Wet pulverization can also be applied in the fine pulverization process. In wet pulverization, a ball mill or wet attritor is used to convert the coarsely pulverized powder with a particle size of approximately several hundred micrometers into a powder with an average particle size of 1.5 to 5 µm, preferably 2 to 4.5 µm. The magnetic powder is pulverized without any contact with oxygen by selecting a suitable dispersing medium, so that a fine powder with a low oxygen concentration is obtained.

[0031] During fine pulverization, about 0.01 to 0.3 wt% of fatty acid or a derivative of fatty acid or hydrocarbon may be added to improve lubrication and orientation in the molding process, such as zinc stearate, calcium stearate, aluminum stearate, octadecanamide, oleamide, ethylenebis(isostearamide) (all of which are stearic acid-based or oleic acid-based compounds); paraffin and naphthalene (both of which are hydrocarbons) or the like.

[0032] The finely pulverized powder is subjected to a forming process in a magnetic field. In the forming process under a magnetic field, the forming pressure is increased to 0.3 to 3 tons / cm 2(30 to 300 MPa). The forming pressure can be constant from the beginning to the end of forming, or increased or decreased at the end, and can also be changed arbitrarily. The lower the forming pressure, the better the orientation. If the forming pressure is too low, the strength of the formed article will be insufficient, leading to handling problems. Therefore, the forming pressure should be set within the above range. The formed article obtained in the forming process under a magnetic field typically has a final relative density of 40 to 60%.

[0033] The applied magnetic field has an intensity of approximately 400 to 1600 kA / m (5 to 20 kOe). The applied magnetic field is not limited to the static magnetic field. A pulsed magnetic field can also be used. Furthermore, the static magnetic field and the pulsed magnetic field can be used in combination.

[0034] The molded article undergoes a sintering process. The sintering process is carried out under vacuum or in an inert atmosphere. The temperature varies depending on the composition. Nevertheless, the process is preferably carried out at 1000 to 1100°C.

[0035] After sintering, the resulting sintered article is subjected to aging treatment. This process is important for regulating coercivity. If the aging treatment is divided into two stages, it is effective to conduct the process at approximately 800°C and then at approximately 500°C for a specified time. If a heat treatment at approximately 800°C is performed after the sintering process, the coercivity increases. Furthermore, a heat treatment at approximately 500°C obviously increases the coercivity. Therefore, if there is only one stage in the aging treatment, the aging treatment can be performed at approximately 500°C. Examples

[0036] Hereinafter, the present invention will be described in further detail based on examples and comparative examples. However, the present invention is not limited to the examples described below.

[0037] Specified amounts of the rare earth metal(s), electrolytic iron, and iron-boron were weighed in such a way that the composition of the main phase grains became the desired one, and a sheet such as RTB alloy was obtained by the strip casting method. The alloy was subjected to heat treatment with stirring under a hydrogen stream to provide a coarse powder. Thereafter, oleamide was added as a lubricating agent, and then a fine powder (average particle size of 4.3 µm) was provided using a jet mill in a non-oxidative atmosphere. The resulting fine powder was filled into a mold (cupboard size: 20 mm × 18 mm), and a magnetic field (2T) was applied in a direction perpendicular to the direction in which the pressure was applied while forming by uniaxial compression at a pressure of 2.0 tons / cm 2The resulting molded article was heated to 1050°C and held at that temperature for a specified time. It was then cooled to room temperature. Following this, an aging treatment was performed at 850°C for 1 hour and then at 530°C for 1 hour to obtain a sintered article.

[0038] The magnetic properties of the sintered article were measured using a BH tracer. The ΔJ / Δ (H / HcJ) value was calculated based on the obtained demagnetization curve.

[0039] The resulting sintered article was embedded in the epoxy resin, and then its section was polished. Commercially available sandpapers were used in the polishing process. Specifically, the polishing process was performed using sandpapers with increasing abrasive sizes in sequence. Finally, a polishing wheel and diamond abrasive grains were used in the polishing process. Here, the polishing process was performed without the provision of any water or the like. If water was used, the grain boundary phases might be eroded.

[0040] The polished specimen was observed under an electron microscope to determine the state of the phases in the grain boundary regions. The different compositions of the grain boundary phases could be identified by the reflected electron image based on their color tone. This allowed us to identify whether the R-rich phase in the grain boundaries was a multiple phase, in which multiple phases were intermixed, or a solid solution phase, in which multiple R components were dissolved as solids. Furthermore, a single phase was observed when only Nd was used as the R. [Examples 1 to 8 and Comparative Examples 1 to 2]

[0041] To 14.2 mol% R and 5.8 mol% B, the remaining Fe, which were the basic components, 0.5 mass% Co, 0.18 mass% Al, and 0.1 mass% Cu were added. A sintered article with such a composition was then prepared. The composition of R (atomic %) and the sintering time were listed in Table 1. The magnetic properties, residual magnetism deviation, and demagnetization in the resulting sintered articles were measured, and the results are listed in Table 1.

[0042] Compared with the sintered article containing 100% Nd, the addition of Y, Ce, and / or La resulted in a decrease in the absolute value of the coercivity HcJ. Furthermore, the ΔJ / Δ(H / HcJ) was also low. As a result, the residual magnetism deviation was small, and the magnetization could be well controlled. Since the perpendicularity ratio (HK / HcJ) was high, no demagnetization was observed. In Comparative Examples 1 and 2, the coercivity HcJ was high, and the residual magnetism deviation became larger. Example 6 showed a lower ΔJ / Δ(H / HcJ) and a reduced residual magnetism deviation. Conversely, if the coercivity HcJ decreased sharply to 1.2 kOe (95.49 kA / m), demagnetization could occur. [Comparison examples 3 to 5]

[0043] The sintered articles in Comparative Examples 3 and 4 were manufactured as in Examples 2 and 4, except that the sintering time was set to 2 hours. The sintered article in Comparative Example 6 was manufactured as in Comparative Example 1, except that the sintering time was set to 12 hours. Compared with those in Examples 2 and 4, the coercivity HcJ of the sintered articles in Comparative Examples 3 and 4 did not change significantly, but the ΔJ / Δ(H / HcJ) was greatly increased. As a result, the residual magnetism deviation became larger. This was because the segregation in the grain boundary phases was small and the coercivity distribution became narrower.

[0044] In Comparative Example 5, the sintering time was the same as in Examples 1 to 8. Compared with Comparative Example 1, the coercivity HcJ decreased slightly, but the ΔJ / Δ(H / HcJ) did not increase. This was because no segregation of Y, Ce, and La was induced, and no dispersion occurred during magnetic separation or deposition in the grain boundary phases. [Table 1] composition Condition Sintering R-rich phase HcJ (kA / m) Br (T) Hk / HcJ (%) ΔJ / Δ(H / HcJ) (T) Residual magnetism deviation (T Example 1 80%Nd-20%Y Sintering for a long time 12 hours Multiple Phase 596,83 1,31 97,1 35,2 0,078 Example 2 50%Nd-50%Y Sintering for a long time 12 hours Multiple Phase 127,32 1,25 92,6 4,2 0,009 Example 3 80%Nd-20%Ce Sintering for a long time 12 hours Multiple Phase 628,66 1,32 96,6 38,0 0,081 Example 4 50%Nd-50%Ce Sintering for a long time 12 hours Multiple Phase 198,94 1,25 89,8 4,8 0,015 Example 5 35%Nd-65%Ce Sintering for a long time 12 hours Multiple Phase 159,15 1,22 85,2 4,0 0,015 Example 6 25%Nd-75%Y Sintering for a long time 12 hours Multiple Phase 95,49 1,2 92,1 3,7 0,011 Example 7 50%Nd-50%La Sintering for a long time 12 hours Multiple Phase 167,11 1,24 84,1 10,3 0,031 Example 8 50%Nd-25%Y-25%Ce Sintering for a long time 12 hours Multiple Phase 190,99 1,25 95,3 3,8 0,012 Comparison 100%Nd Sintering for a 2 hours Single phase 1098,17 1,35 98,1 75,6 0,209 example 1 short time Comparison example 2 90%Nd-10%Y Sintering for a long time 12 hours Multiple Phase 835,56 1,35 97,4 63,4 0,154 Comparison example 3 50%Nd-50%Y Sintering for a short time 2 hours Solid-solution phase 111,41 1,31 96,5 45,0 0,221 Comparison example 4 50%Nd-50%Ce Sintering for a short time 2 hours Solid-solution phase 183,03 1,25 87,5 42,3 0,202 Comparison example 5 100%Nd Sintering for a long time 12 hours Single phase 1058,38 1,34 97,9 70,5 0,231

[0045] As described above, the RTB-based permanent magnet of the present invention has a high residual magnetic flux density, and its magnetization can be well controlled by an external magnetic field. Thus, such a permanent magnet can be suitably used as a variable magnetic force magnet for a variable magnetic flux motor, which can provide high efficiency in operations requiring variable speed in human life, industries, and conveying equipment.

Claims

[1] RTB-based permanent magnet comprising: a demagnetization curve with a slope ΔJ / Δ(H / HcJ) of less than 40.0 T in a region where the value of the magnetic field is Hk or less in the demagnetization curve, where: the composition of R by R1 1-x R2 x and T represents one or more transition metal elements containing Fe or contain a combination of Fe and Co, where: in R1 1-x R2 x R1 represents the rare earth element(s) composed of one or more elements selected from the group consisting of Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, R2 contains Y and 0.2 ≤ x ≤ 0.7, B represents boron, where boron is replaceable by carbon (C), Hk is the value of the magnetic field when the magnetic flux density becomes 90% of the remaining magnetic flux density (Br), where the remaining magnetic flux density Br is 1.2 T or more and the coercive force HcJ is less than 636.62 kA / m, and where the perpendicularity ratio Hk / HcJ is 80% or more. [2] The RTB-based permanent magnet according to claim 1, wherein the grain boundary phase contains an R-rich phase, and the R-rich phase is composed of a multiple phase of an R1-rich phase and an R2-rich phase. [3] A variable magnetic flux magnet using the RTB-based permanent magnet according to claim 1 or 2. [4] A variable magnetic flux motor using the RTB-based permanent magnet according to claim 1 or 2.

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