Method for producing Sm-Fe-N magnetic powder, Sm-Fe-N raw material powder for sintered magnets, and method for producing Sm-Fe-N sintered magnets

Abstract

This invention provides a technology to improve the coercivity and remanent magnetization of Sm-Fe-N based magnetic powders. [Solution] The Sm-Fe-N magnetic powder has a particle size distribution D50 of 2 μm or more and 3 μm or less, and the full width at half maximum of the diffraction intensity peak in the (220) plane obtained from X-ray diffraction of the Sm-Fe-N magnetic powder is 0.1 degrees or more and 0.2 degrees or less.

Description

[Technical Field]

[0001] This disclosure relates to Sm-Fe-N sintered magnets. [Background technology]

[0002] In recent years, Sm (samarium)-Fe (iron)-N (nitrogen) magnets have been developed as high-performance magnets. Sm-Fe-N compounds are known to exhibit high spontaneous magnetization and anisotropic magnetic field strength, as well as high heat resistance. Techniques for obtaining Sm-Fe-N magnets with high magnetic properties have been proposed (see, for example, Patent Documents 1-4).

[0003] For example, Patent Documents 1 and 2 disclose techniques for obtaining Sm-Fe-N magnetic powder by reduction-diffusion. Patent Document 3 discloses a technique for providing magnetic powder with high residual magnetization by reducing the grinding damage when grinding the coarse powder obtained by reduction-diffusion. Patent Document 4 discloses a technique for producing powder with excellent crystallinity by manufacturing Sm-Fe-N magnetic powder using a dry jet mill. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-189753 [Patent Document 2] Japanese Patent Publication No. 2022-189752 [Patent Document 3] Japanese Patent Publication No. 2016-15459 [Patent Document 4] Patent No. 7076740 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the Sm-Fe-N magnet powder produced by the technology described in Patent Document 1 is a chemically synthesized powder, and oxygen may be incorporated during the water washing process, which could significantly reduce the coercivity during sintering. Similarly, the technology described in Patent Document 2 also uses a chemically synthesized powder, and as mentioned above, the inclusion of oxygen could reduce the holding power of the sintered magnet.

[0006] In the technology described in Patent Document 3, surface oxidation during the grinding of coarse powder cannot be avoided, and even if the magnetic powder has high properties, there is a risk that a significant decrease in coercivity will occur during sintering due to surface oxidation.

[0007] Patent document 4 describes a technique for producing Sm-Fe-N-based magnetic powder with significantly superior crystallinity, achieving both saturation magnetization and coercivity, but it makes no mention of remanent magnetization. It seems that further investigation is needed to determine whether increasing the crystallinity of the Sm-Fe-N-based magnetic powder is sufficient to increase remanent magnetization.

[0008] This disclosure is made to solve the problems described above and aims to provide a technology to improve the coercivity and, in particular, the remanent magnetization of Sm-Fe-N magnetic powders. [Means for solving the problem]

[0009] This disclosure is made to solve at least one of the above-mentioned problems and can be implemented in the following forms.

[0010] <1> According to one embodiment of the present disclosure, an Sm-Fe-N magnetic powder containing Sm, Fe, and N is provided. This Sm-Fe-N magnetic powder has a particle size distribution D50 of 2 μm or more and 3 μm or less, and the full width at half maximum of the diffraction intensity peak in the (220) plane obtained from X-ray diffraction of the Sm-Fe-N magnetic powder is 0.1 degree or more and 0.2 degrees or less.

[0011] In this form of Sm-Fe-N magnetic powder, the particle size distribution D50 is between 2 μm and 3 μm, thus possessing sufficient coercivity as a magnetic powder and ensuring sinterability. The fact that the full width at half maximum of the diffraction intensity peak in the (220) plane obtained from X-ray diffraction of the Sm-Fe-N magnetic powder is between 0.1 degree and 0.2 degree indicates that the crystallinity of the magnetic powder is high. If the full width at half maximum of the diffraction intensity peak is between 0.1 degree and 0.2 degree, a magnetic powder with high remanent magnetization can be obtained. Hereinafter, the diffraction intensity peak will also be referred to as the "diffraction peak".

[0012] <2> In the above-described Sm-Fe-N magnetic powder, when the diffraction intensity at the (220) plane obtained from X-ray diffraction of the Sm-Fe-N magnetic powder is defined as I1, and the diffraction intensity of the valley portion formed between the diffraction intensity peak at the (220) plane and the diffraction intensity peak at the (303) plane is defined as I2, I1 / I2≧3 That's fine.

[0013] In this form of Sm-Fe-N magnetic powder, the particle size distribution D50 is between 2 μm and 3 μm, thus providing sufficient coercivity as a magnetic powder and ensuring sinterability. Satisfying I1 / I2≧3 indicates that the crystallinity of the magnetic powder is high, and if I1 / I2≧3, a magnetic powder with high remanent magnetization can be obtained.

[0014] <3> The above-described Sm-Fe-N magnetic powder may also have an oxygen content of 1.5% by mass or less. In this way, when manufacturing a sintered magnet using the Sm-Fe-N magnetic powder, the decrease in coercivity during sintering can be suppressed.

[0015] <4> The above-described Sm-Fe-N magnetic powder may have a nitrogen content of 3.4% by mass or more and 3.6% by mass or less. This allows for an increase in the ratio of remanent magnetization to saturation magnetization σr / σ9sT, thereby improving magnetic properties and stability.

[0016] <5>The Sm-Fe-N-based magnetic powder of the above form may have a particle size distribution D50 of 2.0 μm or more and 2.4 μm or less. By doing so, the coercive force can be further increased.

[0017] <6>The Sm-Fe-N-based magnetic powder of the above form may have a standard deviation SD in the particle size distribution of 2 μm or less. Here, the standard deviation SD = (D84 - D16) / 2, D84 represents the particle size (μm) at the point where the cumulative distribution is 84%, and D16 represents the particle size (μm) at the point where the cumulative distribution is 16%. By doing so, the decrease in residual magnetization can be suppressed by minimizing the increase in the fine particle ratio.

[0018] <7>According to another aspect of the present disclosure, there is provided a method for producing a raw material powder for a Sm-Fe-N-based sintered magnet including the Sm-Fe-N-based magnetic powder of the above form. The method for producing the raw material powder for the Sm-Fe-N-based sintered magnet includes a pulverization step of wet-pulverizing a coarse powder containing a Sm-Fe-N single crystal in an environment with an oxygen concentration of 0.5 ppm or less to obtain the Sm-Fe-N-based magnetic powder.

[0019] According to the method for producing the raw material powder for the Sm-Fe-N-based sintered magnet of this form, since the coarse powder is pulverized in an environment with an oxygen concentration of 0.5 ppm or less, oxidation of the Sm-Fe-N-based magnetic powder can be suppressed. Further, by wet-pulverizing the coarse powder, the strain accumulated in the Sm-Fe-N crystal in the pulverization step can be suppressed as compared with dry pulverization, and the crystallinity can be improved. Therefore, the magnetic properties of the sintered body using the raw material powder for the Sm-Fe-N-based sintered magnet produced by this method can be improved.

[0020] <8>According to another aspect of the present disclosure, there is provided a method for producing a Sm-Fe-N-based sintered magnet. The method for producing the Sm-Fe-N-based sintered magnet has a sintering step of pressure-sintering a raw material powder for a Sm-Fe-N-based sintered magnet including the Sm-Fe-N-based magnetic powder at a sintering temperature of 600 °C or less in a low oxygen concentration atmosphere.

[0021] According to this method for manufacturing Sm-Fe-N sintered magnets, the thermal decomposition of the Sm-Fe-N magnetic powder can be suppressed by keeping the sintering temperature below 600°C, and oxidation of the Sm-Fe-N magnetic powder can be suppressed by performing this process in a low-oxygen atmosphere. As a result, the density of the sintered magnet can be improved, and a sintered magnet with high residual magnetization can be manufactured.

[0022] <9> The method for manufacturing an Sm-Fe-N sintered magnet according to the above-described form may be a mixed powder further comprising an alloy powder containing at least one of the Group 2 elements and rare earth elements, and having a melting point of 180°C or higher and 620°C or lower.

[0023] Since the raw material powder for Sm-Fe-N sintered magnets contains the above-mentioned alloy powder, a second phase of the alloy is formed in the Sm-Fe-N sintered magnet. The melting point of the alloy forming the second phase 20 is 620°C or lower, which is a temperature at which the main phase Sm-Fe-N magnetic powder does not decompose. Therefore, when manufacturing the sintered magnet, the main phase does not decompose even when heated at the temperature at which the alloy melts. For this reason, by using an alloy of the above composition for the second phase 20, liquid-phase sintering can be performed, and the second phase 20 made of the alloy of the above composition can be formed as a grain boundary phase at the interface of the Sm-Fe-N crystal grains. Furthermore, since the alloy of the above composition has excellent wettability with respect to the main phase, a dense sintered body can be obtained, and the magnetic properties of the Sm-Fe-N sintered magnet can be improved.

[0024] Furthermore, this disclosure can be implemented in various forms, for example, in the form of Sm-Fe-N sintered magnets, permanent magnets for motors, and so on. [Brief explanation of the drawing]

[0025] [Figure 1] This is a process diagram showing an example of a method for producing Sm-Fe-N magnetic powder. [Figure 2] This is an explanatory diagram conceptually showing the cross-sectional structure of a sintered magnet. [Figure 3]This is a process diagram showing an example of a manufacturing method for sintered magnets. [Figure 4] This figure shows the evaluation results of the samples. [Modes for carrying out the invention]

[0026] <Embodiment> The Sm-Fe-N magnetic powder of this embodiment is for use in Sm-Fe-N sintered magnets. Hereinafter, the Sm-Fe-N magnetic powder will also be simply referred to as "magnetic powder". The Sm-Fe-N magnetic powder contains samarium (Sm), iron (Fe), and nitrogen (N), and has a particle size distribution D50 of 2 μm or more and 3 μm or less. The particle size distribution D50 can be evaluated by adopting the volume-based results obtained using a dry-type particle size distribution analyzer, HELOS&RODOS (manufactured by Sympatec). If the particle size distribution D50 is greater than 3 μm, sufficient coercivity cannot be obtained, and if the particle size distribution D50 is less than 2 μm, the coercivity increases but the remanent magnetization decreases. By setting the particle size distribution D50 of the Sm-Fe-N magnetic powder to 2 μm or more and 3 μm or less, the magnetic powder can possess sufficient coercivity and remanent magnetization, ensuring sinterability.

[0027] It is preferable that the full width at half maximum (FMAX) of the diffraction peak in the (220) plane obtained from X-ray diffraction of Sm-Fe-N magnetic powder is between 0.1 degrees and 0.2 degrees. A FMAX of 0.1 degrees or more and 0.2 degrees or less indicates that the crystallinity of the magnetic powder is high. In this embodiment, if the FMAX of the diffraction peak in the (220) plane obtained from X-ray diffraction is between 0.1 degrees and 0.2 degrees, it can be said that the Sm-Fe-N magnetic powder has high remanent magnetization.

[0028] When the diffraction intensity peak at the (220) plane obtained from X-ray diffraction of Sm-Fe-N magnetic powder is denoted as I1, and the diffraction intensity of the valley region formed between the diffraction intensity peak at the (220) plane and the diffraction intensity peak at the (303) plane is denoted as I2, it is preferable that I1 / I2 ≥ 3. The diffraction intensity I2 in the valley region is the lowest value between the (220) plane and the (303) plane. In Sm-Fe-N magnetic powder, the (220) plane and the (303) plane are the planes where the maximum peak intensity is obtained. I1 / I2 is an indicator of crystallinity, and satisfying I1 / I2 ≥ 3 indicates that the crystallinity of the magnetic powder is high. In this embodiment, if I1 / I2 ≥ 3, the Sm-Fe-N magnetic powder can be said to have high remanent magnetization.

[0029] In the Sm-Fe-N magnetic powder of this embodiment, the oxygen content is not particularly limited, but is preferably 1.5% by mass or less. A lower oxygen content is preferable, with 0% by mass being most preferable. If an oxide film layer is formed on the surface of the Sm-Fe-N magnetic powder, it will cause a significant decrease in coercivity during sintering when manufacturing a sintered magnet using the Sm-Fe-N magnetic powder. When the oxygen content of the Sm-Fe-N magnetic powder is 1.5% by mass or less, the formation of an oxide film layer on the surface of the magnetic powder is suppressed, and the decrease in coercivity of a sintered magnet using the Sm-Fe-N magnetic powder can be suppressed.

[0030] In the Sm-Fe-N magnetic powder of this embodiment, the nitrogen content is not particularly limited, but it is preferably 3.4% by mass or more and 3.6% by mass or less. This increases the ratio of remanent magnetization to saturation magnetization σr / σ9sT, thereby improving magnetic properties and stability.

[0031] In the Sm-Fe-N magnetic powder of this embodiment, the particle size distribution D50 is not particularly limited, but it is preferable that the particle size distribution D50 is 2.0 μm or more and 2.4 μm or less. This allows for a higher coercivity.

[0032] In the Sm-Fe-N magnetic powder of this embodiment, the standard deviation SD in the particle size distribution is not particularly limited, but a standard deviation SD of 2 μm or less is preferred. Here, the standard deviation SD = (D84 - D16) / 2, where D84 represents the particle size (μm) at the point where the cumulative distribution is 84%, and D16 represents the particle size (μm) at the point where the cumulative distribution is 16%. The standard deviation SD referred to here is a guideline for the distribution width of the particle size distribution and does not mean the statistical standard deviation (statistical error). By setting the standard deviation SD within the above range, the decrease in remanent magnetization can be suppressed by minimizing the increase in the proportion of fine particles.

[0033] As described above, the Sm-Fe-N magnetic powder of this embodiment can achieve both high coercivity and high remanent magnetization, thus providing an Sm-Fe-N sintered magnet with high coercivity and high remanent magnetization.

[0034] Figure 1 is a process diagram showing an example of a method for producing Sm-Fe-N magnetic powder according to this embodiment. The method for producing Sm-Fe-N magnetic powder according to this embodiment is not particularly limited, but for example, it can be produced by the following method. In the method for producing Sm-Fe-N magnetic powder, the steps are carried out in the following order: grinding step P11, drying step P12, and classification step P13 (Figure 1).

[0035] In the grinding process P11, the coarse powder containing Sm-Fe-N single crystals is wet-ground in an environment with an oxygen concentration of 0.5 ppm or less. By wet-grounding the coarse powder, crystal strain can be suppressed compared to dry grinding. As the coarse powder, for example, a powder with the composition Sm2Fe 17The material used is N3, and has an average particle size of 10 μm to 200 μm. The average particle size of the Sm-Fe-N magnetic powder after grinding is not particularly limited, but it is preferable that the particle size distribution D50 is 0.1 μm to 20 μm, more preferably 0.4 μm to 10 μm, even more preferably 1 μm to 5 μm, and still more preferably 2.0 μm to 2.4 μm. Grinding is carried out using, for example, a grinder or a planetary ball mill. As a solvent, for example, ethanol or isopropanol, or heptane as an oxygen-free solvent can be used. The oxygen concentration is adjusted by controlling the atmosphere during the grinding process. For example, an oxygen concentration of 0.5 ppm or less can be achieved by injecting an inert gas into a vacuum chamber. By grinding the coarse powder in an environment with an oxygen concentration of 0.5 ppm or less, oxidation of the Sm-Fe-N magnetic powder can be suppressed.

[0036] In drying step P12, the slurry obtained in grinding step P11 is sieved and dried in a vibrating dryer. In the classification step P13, the Sm-Fe-N magnetic powder dried in the drying step P12 is classified by sieving to obtain Sm-Fe-N magnetic powder 12 with a particle size distribution D50 of 2 μm or more and 3 μm or less.

[0037] The Sm-Fe-N magnetic powder 12 produced by this method has a particle size distribution D50 of 2 μm to 3 μm, thus possessing sufficient coercivity as a magnetic powder and ensuring sinterability. Furthermore, since wet grinding is performed in the grinding step P11, crystal strain can be suppressed, resulting in a magnetic powder with high crystallinity. In addition, since the grinding step P11 is carried out in an environment with an oxygen concentration of 0.5 ppm or less, oxidation of the magnetic powder can be suppressed, and when manufacturing sintered magnets using the magnetic powder produced by this method, the decrease in coercivity caused by the surface oxide film of the magnetic powder during sintering can be suppressed.

[0038] The Sm-Fe-N sintered magnet manufactured using the Sm-Fe-N magnetic powder of this embodiment will be described below. Figure 2 is a conceptual diagram illustrating the cross-sectional structure of a sintered magnet 100 manufactured using the Sm-Fe-N magnetic powder of the embodiment. The sintered magnet 100 is made of Th2Zn 17 The material comprises a first phase 10 mainly consisting of Sm-Fe-N (samarium-iron-nitrogen) crystalline grains having a specific structure, and a second phase 20 consisting of an alloy containing at least one element from group 2 and / or rare earth elements, with a melting point of 180°C or higher and 620°C or lower.

[0039] In Figure 2, the first phase 10 is marked with upward-sloping diagonal hatching, and the second phase 20 is marked with downward-sloping diagonal hatching. As shown in the figure, the first phase 10 has multiple Sm-Fe-N crystal grains 10G. The second phase 20 is located at the grain boundaries between the Sm-Fe-N crystal grains 10G and the Sm-Fe-N crystal grains 10G. The sintered magnet 100 may have voids V at the grain boundaries between the Sm-Fe-N crystal grains 10G and the Sm-Fe-N crystal grains 10G.

[0040] The main phase, Sm-Fe-N crystal grain 10G, is Th2Zn 17 Sm2Fe with a type structure 17 It is N3. The sintered magnet 100 exhibits magnetism due to the Sm-Fe-N crystal grain 10G (main phase). The crystal structure of the main phase can be identified by, for example, X-ray diffraction analysis of the sintered magnet 100. The main phase refers to the compound that determines the properties of the sintered magnet.

[0041] Sm2Fe 17 N3 has excellent saturation magnetization and a huge anisotropic magnetic field, so it can withstand heat and reverse magnetic fields and generate high magnetic fields. The first phase 10 is made of Th2Ni as Sm-Fe-N crystal grain 10G. 17 The structure may include structures different from the main phase, such as a type structure or a TbCu7 type structure. Here, Tb is terbium and Cu is copper.

[0042] The average grain size of the Sm-Fe-N crystal grains 10G in the first phase 10 is between 2 μm and 3 μm. 17The critical diameter of single-domain particles in N3 is 0.356 μm. Particles with a diameter greater than this critical diameter can exist energetically as magnetic powder, and can also be used to create more densely packed sintered magnets. As a result, magnetization can be improved.

[0043] The average grain size of the Sm-Fe-N crystal grains 10G is approximately the same before and after sintering. The sintered magnet 100 uses the Sm-Fe-N magnetic powder 12 of this embodiment, and since the grain size distribution D50 is 2 μm or more and 3 μm or less, the average grain size of the Sm-Fe-N crystal grains 10G of the first phase 10 is 2 μm or more and 3 μm or less. The average grain size of the Sm-Fe-N crystal grains 10G of the first phase 10 in the sintered magnet 100 can be calculated using SEM (Scanning Electron Microscope) images.

[0044] Phase 20 consists of an alloy containing at least one element from either Group 2 or rare earth elements, with a melting point between 180°C and 620°C. Group 2 elements are elements belonging to Group 2 of the periodic table and include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Rare earth elements include scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), eurobium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0045] Phase 20 may contain elements other than Group 2 elements and rare earth elements. For example, it may contain silver (Ag), aluminum (Al), copper (Cu), zinc (Zn), etc.

[0046] As described above, the Sm-Fe-N-based magnetic powder 12 of the present embodiment has sufficient coercive force and high residual magnetization. Since the sintered magnet 100 uses the Sm-Fe-N-based magnetic powder 12 of the present embodiment, it achieves both high coercive force and high residual magnetization.

[0047] Sm-Fe-N-based magnets are subject to sintering temperature constraints because they undergo thermal decomposition at 620°C or higher. Conventionally, it has been impossible to obtain a high-density sintered body. In contrast, in the sintered magnet 100 of the present embodiment, the melting point of the alloy that forms the second phase 20 is 620°C or lower, which is a temperature at which the main phase does not decompose. Therefore, when manufacturing the sintered magnet 100, even if it is heated to the temperature at which the alloy melts, the main phase does not decompose. Therefore, by using the alloy with the above composition for the second phase 20, liquid-phase sintering can occur, and Sm2Fe 17 N3 / Sm2Fe 17 A second phase 20 composed of the alloy with the above composition can be formed as a grain boundary phase at the interface of N3. Also, the alloy with the above composition has excellent wettability with respect to the main phase (Sm2Fe 17 N3). Therefore, a dense sintered body can be obtained. Also, since the melting point of the alloy that forms the second phase 20 is 180°C or higher, for example, the sintered magnet 100 can also be used in devices such as motors for EVs that generate heat and reach high temperatures.

[0048] The melting point of the second phase can be measured using a DSC (differential scanning calorimeter). Weigh 10 - 20 mg of the liquid-quenched foil obtained by melt spinning, which will be described later, and use this as the measurement sample. For the measurement, use a pan made of BN (boron nitride) material, set the measurement temperature range from room temperature to 700°C, and set the heating rate to 10°C / min. The melting point is determined using the melting peak temperature that appears within the measurement temperature range.

[0049] The sintered magnet 100 may contain unavoidable impurity elements, etc., to the extent that it does not impair the magnetic properties of the main phase. Unavoidable impurity elements are impurity elements that cannot be avoided when manufacturing the sintered magnet 100 of the embodiment, or whose inclusion would lead to a significant increase in manufacturing costs if avoided. Examples of such unavoidable impurity elements include impurity elements in the raw materials, elements contained in lubricants used during molding, etc. In other examples, the sintered magnet may have a second phase different from that described above.

[0050] Figure 3 is a process diagram showing an example of a method for manufacturing the sintered magnet 100. The method for manufacturing the sintered magnet 100 in this embodiment is not particularly limited, but for example, it can be manufactured by the following method. As shown in Figure 3, in the manufacturing method of the sintered magnet 100, the steps are carried out in the order of preparation of raw material powder for sintered magnets P0, followed by a sintering step P4. In the preparation of raw material powder for sintered magnets P0, the steps are carried out in the order of magnetic powder manufacturing step P1, alloy powder manufacturing step P2, and mixing step P3.

[0051] In the magnetic powder manufacturing process P1, as described above (Figure 1), Sm-Fe-N based magnetic powder with a particle size distribution D50 of 2 μm or more and 3 μm or less is manufactured.

[0052] In the alloy powder preparation step P2, a powder of a predetermined size of the alloy that will become the second phase is prepared to obtain alloy powder.

[0053] In mixing step P3, the Sm-Fe-N magnetic powder and the alloy powder are dispersed to obtain a mixed powder, which is the raw material powder for sintered magnets. Mixing step P3 may be a wet process in which the Sm-Fe-N magnetic powder and the alloy powder are dispersed in a solvent (e.g., ethanol), or a dry process in which the Sm-Fe-N magnetic powder and the alloy powder are dispersed in an inert gas (e.g., argon gas, helium gas, nitrogen gas, etc.).

[0054] The magnetic powder manufacturing process P1, the alloy powder manufacturing process P2, and the mixing process P3 described above are all carried out under a low-oxygen atmosphere. The oxygen concentration is adjusted by controlling the atmosphere in each process. A low oxygen concentration is a concentration lower than the oxygen concentration in the atmosphere (approximately 21 vol%). The oxygen concentration is preferably 100 ppm or less, more preferably 10 ppm or less, and even more preferably 0.5 ppm or less. For example, a low-oxygen atmosphere can be achieved by injecting an inert gas into a vacuum chamber. By carrying out the above processes under a low-oxygen atmosphere, oxidation of the Sm-Fe-N magnetic powder and alloy powder can be prevented, and the wettability of the Sm-Fe-N magnetic powder and alloy powder can be ensured. In other examples, in the preparation process P0 for sintered magnet powder, pre-manufactured Sm-Fe-N magnetic powder and auxiliary alloy powder may be prepared and mixed, or sintered magnet powder may be prepared in which the Sm-Fe-N magnetic powder and auxiliary alloy powder are pre-mixed.

[0055] In the sintering process P4, the raw material powder for sintered magnets produced in the manufacturing process P0 is molded and pressure-sintered at a sintering temperature of 600°C or lower in a low-oxygen atmosphere. In the sintering process P4, firing is carried out in an oxygen concentration atmosphere similar to that of the Sm-Fe-N magnetic powder manufacturing process P1 to the mixing process P3. By setting the sintering temperature to 600°C or lower, thermal decomposition of the Sm-Fe-N magnetic powder can be suppressed. Furthermore, by performing the sintering process P4 in a low-oxygen atmosphere, oxidation of the Sm-Fe-N magnetic powder and alloy powder can be suppressed. As a result, density can be improved, and the residual magnetization of the sintered magnet 100 can be improved.

[0056] The magnetic powder of this embodiment can be used as a raw material for permanent magnet sintering materials for various motors, such as motors for electric vehicles (EVs), motors built into robots, motors built into drones, and motors for elevators. [Examples]

[0057] The present disclosure will be further described by examples. Figure 4 shows the evaluation results for samples 1 to 11.

[0058] 1. Preparation of the sample (Sm-Fe-N magnetic powder) The Sm-Fe-N magnetic powders of Samples 1-7 were manufactured using the manufacturing method exemplified in the above embodiment (Figure 1). Specifically, they were manufactured as follows.

[0059] As a coarse powder containing Sm-Fe-N single crystals, Sm2Fe has a particle size distribution D50 of 30 μm. 17 N3 powder was used. In a glove box where the oxygen concentration was controlled to 0.5 ppm or less, stainless steel pebbles, the above-mentioned coarse powder, and ethanol as a solvent were placed in a stainless steel pot, and the pot was ball-milled under conditions of rotation time: 1 hour to 24 hours and rotation speed: 120 rpm to 300 rpm. The obtained slurry was sieved through a 25 μm mesh sieve in the same glove box and dried in a vibrating dryer. The obtained powder was sieved through a 250 μm mesh sieve to obtain Sm-Fe-N magnetic powder.

[0060] Sample 8 was prepared using a dry jet mill instead of wet milling on the above-mentioned coarse powder. Samples 9 and 10 were wet-milled under milling conditions (milling time, rotation speed) that deviated from the preparation conditions of the example. Sample 11 was prepared as a chemically synthesized powder using the reduction-diffusion method.

[0061] 2. Evaluation Method (1) Particle size distribution measurement The particle size distribution of each sample was measured using a dry particle size distribution analyzer (HELOS & RODOS: Sympatec), and the particle size distribution D50 and standard deviation SD were obtained. Here, the standard deviation SD is the value obtained by subtracting the cumulative distribution D16 (particle size at the point where the cumulative distribution reaches 16% (μm)) from the cumulative distribution D84 (particle size at the point where the cumulative distribution reaches 84% ​​(μm)) and dividing the result by 2, and is expressed by the following formula: (D84-D16) / 2. This is an indication of the distribution range of the particle size distribution and does not represent the statistical standard deviation (statistical error). (2) Oxygen and nitrogen content analysis The oxygen and nitrogen content in each sample of Sm-Fe-N magnetic powder was analyzed using an oxygen / nitrogen analyzer (EMGA-920: Horiba, Ltd.). (3) Evaluation of the crystallinity of magnetic powder by X-ray diffraction The crystallinity of each sample of Sm-Fe-N magnetic powder was evaluated using an X-ray diffractometer. Sm2Fe 17 Because N3 powder contains a large amount of Fe as a constituent element, when measured with a Cu tube commonly used in XRD, the background increases due to the generation of fluorescent X-rays, and the diffraction peak intensity and signal-to-noise ratio decrease. Therefore, measurements were performed using a Co tube. Measurements were performed at diffraction angles of 20 to 80 degrees, and X-ray diffraction profiles were obtained. The obtained X-ray profiles were processed to remove Ka2 lines and background, and peak processing was performed. After peak processing, smoothing was performed, and the full width at half maximum (FWHM) of the diffraction peak at the (220) plane was calculated. Furthermore, the profile after smoothing was analyzed for Sm2Fe 17 The peak intensity I1 of the (220) plane of N3, the peak intensity I3 of the (303) plane, and Sm2Fe 17 The diffraction intensities I2 in the valleys formed between the (220) and (303) planes, which are diffraction planes of N3, were read. Then, their ratio I1 / I2 was calculated. (4) Evaluation of magnetic properties of magnetic powders The saturation and remanent magnetization of each sample of Sm-Fe-N magnetic powder was measured using a vibrating sample magnetometer (VSM). Sm2Fe 17 N3 has a very large anisotropic magnetic field of 260 kOe, making it difficult to completely saturate it. Therefore, a VSM was used to apply a magnetic field up to 9 T (90 kOe), and the saturation magnetization σ at that point was measured. s9T The saturation magnetization value was used. In addition, the remanent magnetization σ r The coercivity Hcj was also measured.

[0062] 3. Evaluation Results 3-1. Particle Size Distribution Evaluation Samples 1-7 described in the examples were confirmed to have a particle size distribution D50 of 2 μm to 3 μm. All of them had a coercivity of 6 kOe or more, which is a sufficient value for magnetic powder. Furthermore, samples 1-7 were able to suppress the decrease in remanent magnetization compared to samples 8-10. Among these, samples 6 and 7 had a particle size distribution D50 of 2.0 μm to 2.4 μm, and coercivity of 10.0 kOe and 9.7 kOe, respectively, which were confirmed to be higher than samples 1-6.

[0063] Of samples 1-7, samples 6 and 7 were confirmed to have a standard deviation (SD) of 2 μm or less in their particle size distribution. Compared to samples 1-5, samples 6 and 7 were able to suppress the decrease in remanent magnetization by minimizing the increase in the proportion of fine particles.

[0064] 3-2. Evaluation by X-ray diffraction For samples 1-7, the full width at half maximum (FWHM) of the diffraction peaks in the (220) plane, as determined by X-ray diffraction, is between 0.1 degrees and 0.2 degrees. FWHM is an indicator of the shape of the intensity peak in the X-ray diffraction pattern; a larger FWHM indicates a wider peak and lower crystallinity. In other words, samples 1-7, with FWHMs between 0.1 degrees and 0.2 degrees, were confirmed to have high crystallinity. In particular, samples 3-7 have smaller FWHMs compared to samples 1 and 2, indicating even higher crystallinity.

[0065] Furthermore, samples 1-6 have a diffraction intensity ratio I1 / I2 of 3 or higher as determined by X-ray diffraction. Similarly, I1 / I2 is an indicator of the shape of the intensity peak in the X-ray diffraction pattern; a smaller I1 / I2 indicates a broader peak and lower crystallinity. In other words, samples 1-6 and 11 have an I1 / I2 of 3 or higher, confirming their high crystallinity. In particular, samples 3-5 have a diffraction intensity ratio I1 / I2 of 4 or higher, indicating even higher crystallinity.

[0066] In comparison, samples 8-10 had a full width at half maximum (FWHM) greater than 0.2 degrees, indicating reduced crystallinity. Sample 11 had a FWHM less than 0.1 degrees, demonstrating even higher crystallinity than samples 1-7. This is likely because it is a chemically synthesized powder, produced without the strain accumulated during the grinding process forming within the particles, resulting in a highly crystalline powder. However, despite its extremely high crystallinity, sample 11 did not show improvement in remanent magnetization. This is thought to be because remanent magnetization is not solely governed by crystallinity, but is also influenced by other factors such as particle orientation and dispersibility. In fact, when attempting to produce extremely high crystallinity without grinding strain through methods such as reduction-diffusion synthesis, as in sample 11, secondary necking and bonding between particles are unavoidable. This can lead to excessive crystallinity and, as a result, a decrease in remanent magnetization.

[0067] Samples 1-7 satisfy the following requirements [1]-[3] (Figure 4). [1] The particle size distribution D50 of the Sm-Fe-N magnetic powder is 2 μm or more and 3 μm or less. [2] The full width at half maximum of the diffraction peak in the (220) plane obtained by X-ray diffraction of the Sm-Fe-N magnetic powder is 0.1 degrees or more and 0.2 degrees or less. [3] When the diffraction intensity peak at the (220) plane obtained from X-ray diffraction of Sm-Fe-N magnetic powder is denoted as I1, and the diffraction intensity of the valley formed between the diffraction intensity peak at the (220) plane and the diffraction intensity peak at the (303) plane is denoted as I2, then I1 / I2 ≥ 3.

[0068] Samples 1-7 satisfy the requirements of [1] above, possessing sufficient coercivity as magnetic powders and ensuring sinterability. Furthermore, samples 1-7 satisfy the requirements of [2] and [3] above and possess high crystallinity. Since samples 1-7 could be placed within the predetermined crystallinity range as evaluated by the full width at half maximum of XRD, the remanent magnetization could be increased.

[0069] Samples 6 and 7 also satisfy the following requirements [4] and [5] (Figure 4). [4] The particle size distribution D50 is between 2.0 μm and 2.4 μm. [5] The standard deviation (SD) in the degree distribution is 2 μm or less.

[0070] Samples 6 and 7 were able to further improve their coercivity compared to samples 1-5 in order to meet the requirements of [4] above. Furthermore, samples 6 and 7 were able to suppress the decrease in remanent magnetization while suppressing the increase in the proportion of fine particles compared to samples 1-5 in order to meet the requirements of [5] above.

[0071] 3-3. Evaluation of oxygen and nitrogen content in magnetic powder In all of the samples 1 to 7 described in the examples, the oxygen content was 1.5% by mass or less. Furthermore, the nitrogen content of samples 1 to 7 was confirmed to be between 3.4% by mass and 3.6% by mass. In other words, samples 1 to 7 also satisfy the requirements of [4] and [5] below (Figure 4). [6] The oxygen content is 1.5% by mass or less. [7] The nitrogen content is 3.4% by mass or more and 3.6% by mass or less.

[0072] Samples 1-7, due to their low oxygen content, were able to reduce the oxide film formed on the surface of the magnetic powder, suppressing the decrease in coercivity and resulting in sufficient coercivity (Figure 4).

[0073] Furthermore, since samples 1 to 7 had a nitrogen content of 3.4% to 3.6% by mass, it was confirmed that the saturation and remanent magnetization of the magnetic powder could be improved, and that Sm-Fe-N-based magnetic powders with high magnetization could be produced.

[0074] As explained above, Samples 1 to 7 satisfy all of the requirements of [1] to [3] above and are examples of the Sm-Fe-N magnetic powder of the above embodiment. The Sm-Fe-N magnetic powders of these samples have high crystallinity and were able to achieve both high coercivity and high remanent magnetization. That is, using the Sm-Fe-N magnetic powders of Samples 1 to 7, Sm2Fe 17 By manufacturing N3 sintered bodies, it is possible to obtain sintered magnets with high magnetic performance.

[0075] The present disclosure has been described above based on embodiments and examples, but the embodiments described above are for the purpose of facilitating understanding of the present disclosure and do not limit it. The present disclosure may be modified and improved without departing from its spirit and the claims, and equivalents thereof are included in the present disclosure. Furthermore, any technical features that are not described as essential in this specification may be deleted as appropriate.

[0076] This disclosure can also be realized in the following application examples. [Application Example 1] A magnetic powder containing Sm, Fe, and N, The particle size distribution D50 is between 2 μm and 3 μm. The Sm-Fe-N magnetic powder is characterized in that the full width at half maximum of the diffraction intensity peak in the (220) plane obtained from X-ray diffraction is 0.1 degrees or more and 0.2 degrees or less. Sm-Fe-N magnetic powder. [Application Example 2] The Sm-Fe-N magnetic powder described in Application Example 1, When the diffraction intensity peak at the (220) plane obtained from X-ray diffraction of Sm-Fe-N magnetic powder is denoted as I1, and the diffraction intensity of the valley region formed between the diffraction intensity peak at the (220) plane and the diffraction intensity peak at the (303) plane is denoted as I2, I1 / I2≧3 Characterized by, Sm-Fe-N magnetic powder. [Application Example 3] The Sm-Fe-N magnetic powder described in Application Example 1 or Application Example 2, It is characterized by having an oxygen content of 1.5% by mass or less. Sm-Fe-N magnetic powder. [Application Example 4] A Sm-Fe-N magnetic powder according to any one of Application Examples 1 to 3, It is characterized by having a nitrogen content of 3.4% by mass or more and 3.6% by mass or less. Sm-Fe-N magnetic powder. [Application Example 5] A Sm-Fe-N magnetic powder according to any one of Application Examples 1 to 4, It is characterized by having a particle size distribution D50 of 2.0 μm or more and 2.4 μm or less. Sm-Fe-N magnetic powder. [Application Example 6] A Sm-Fe-N magnetic powder according to any one of Application Examples 1 to 5, A characteristic feature is that the standard deviation (SD) of the particle size distribution is 2 μm or less. Sm-Fe-N magnetic powder. Here, the standard deviation SD = (D84 - D16) / 2, where D84 represents the particle size (μm) at the point where the cumulative volume particle size distribution curve reaches 84%, and D16 represents the particle size (μm) at the point where the cumulative volume particle size distribution curve reaches 16%. [Application Example 7] A method for producing raw material powder for Sm-Fe-N sintered magnets, comprising the Sm-Fe-N magnetic powder described in any one of Application Examples 1 to 6, The method is characterized by including a grinding step of wet grinding a coarse powder containing Sm-Fe-N single crystals in an environment with an oxygen concentration of 0.5 ppm or less to obtain the Sm-Fe-N-based magnetic powder. A method for producing raw material powder for Sm-Fe-N sintered magnets. [Application Example 8] A method for manufacturing an Sm-Fe-N sintered magnet, The invention is characterized by having a sintering step in which a raw material powder for an Sm-Fe-N sintered magnet, containing the Sm-Fe-N magnetic powder described in any one of Application Examples 1 to 6, is pressurized and sintered at a sintering temperature of 600°C or lower under a low oxygen concentration atmosphere. A method for manufacturing Sm-Fe-N sintered magnets. [Application Example 9] A method for manufacturing an Sm-Fe-N sintered magnet as described in Application Example 8, The raw material powder for Sm-Fe-N sintered magnets is characterized by being a mixed powder further containing an alloy powder that contains at least one of the Group 2 elements and rare earth elements, and has a melting point of 180°C or higher and 620°C or lower. A method for manufacturing Sm-Fe-N sintered magnets. [Explanation of Symbols]

[0077] 10…First phase 10G…Sm-Fe-N crystal grain 12...Sm-Fe-N magnetic powder 20…Second phase 100... Sintered magnets V...Void

Claims

1. A magnetic powder containing Sm, Fe, and N, The particle size distribution D50 is between 2 μm and 3 μm. The Sm-Fe-N magnetic powder is characterized in that the full width at half maximum of the diffraction intensity peak in the (220) plane obtained from X-ray diffraction is 0.1 degrees or more and 0.2 degrees or less. Sm-Fe-N magnetic powder.

2. The Sm-Fe-N magnetic powder according to claim 1, When the diffraction intensity peak in the (220) plane obtained from the X-ray diffraction of the Sm-Fe-N magnetic powder is defined as I1, and the diffraction intensity of the valley formed between the diffraction intensity peak in the (220) plane and the diffraction intensity peak in the (303) plane is defined as I2, I1 / I2 ≥ 3 Characterized by, Sm-Fe-N magnetic powder.

3. The Sm-Fe-N magnetic powder according to claim 1, Characterized by having an oxygen content of 1.5% by mass or less, Sm-Fe-N magnetic powder.

4. The Sm-Fe-N magnetic powder according to claim 1, It is characterized by having a nitrogen content of 3.4% by mass or more and 3.6% by mass or less. Sm-Fe-N magnetic powder.

5. The Sm-Fe-N magnetic powder according to claim 1, It is characterized by having a particle size distribution D50 of 2.0 μm or more and 2.4 μm or less. Sm-Fe-N magnetic powder.

6. Sm-Fe-N based magnetic powder according to any one of claims 1 to 5, Characterized by having a standard deviation (SD) of 2 μm or less in the particle size distribution. Sm-Fe-N magnetic powder. Here, the standard deviation SD = (D84 - D16) / 2, where D84 represents the particle size (μm) at the point where the cumulative distribution is 84%, and D16 represents the particle size (μm) at the point where the cumulative distribution is 16%.

7. A method for producing raw material powder for Sm-Fe-N sintered magnets, comprising the Sm-Fe-N magnetic powder described in claim 6, The method is characterized by including a grinding step of wet grinding a coarse powder containing an Sm-Fe-N single crystal in an environment with an oxygen concentration of 0.5 ppm or less to obtain the Sm-Fe-N-based magnetic powder. A method for producing raw material powder for Sm-Fe-N sintered magnets.

8. A method for manufacturing an Sm-Fe-N sintered magnet, The present invention is characterized by comprising a sintering step in which a raw material powder for an Sm-Fe-N sintered magnet, containing the Sm-Fe-N magnetic powder described in claim 6, is pressurized and sintered at a sintering temperature of 600°C or lower in a low-oxygen atmosphere. A method for manufacturing Sm-Fe-N sintered magnets.

9. A method for manufacturing an Sm-Fe-N sintered magnet according to claim 8, The raw material powder for Sm-Fe-N sintered magnets is characterized by being a mixed powder further containing an alloy powder that contains at least one of the Group 2 elements and rare earth elements, and has a melting point of 180°C or higher and 620°C or lower. A method for manufacturing Sm-Fe-N sintered magnets.

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