Permanent magnets and devices

Abstract

To provide a permanent magnet with an excellent magnetic characteristic and a device having the permanent magnet.SOLUTION: The permanent magnet is a sintered body including 23-27 wt.% of R (R is the total of rare earths including Sm), 22-27 wt.% of Fe, 0.3-2.5 wt.% of Mn, and 4.0-5.0 wt.% of Cu, and the balance Cu with inevitable impurities. The permanent magnet includes a plurality of crystal grains and a grain boundary phase and the concentration of Cu in the grain boundary phase is at least 45 at%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to permanent magnets and devices. [Background technology]

[0002] Rare earth cobalt permanent magnets, such as samarium cobalt magnets, are known as one type of permanent magnet. Rare earth cobalt permanent magnets with added elements such as Fe, Cu, and Zr are being investigated for various reasons, including the improvement of magnetic properties.

[0003] For example, Patent Document 1 discloses a method for producing a ZnO alloy containing specific amounts of rare earth elements, Fe, Cu, Co, Zr, Ti, and Hf. 17 The document discloses a permanent magnet having a structure including crystal grains made of a main phase including a crystalline phase and crystal boundaries of the crystal grains, the average grain size of the crystal grains being 50 to 100 μm.

[0004] Patent Document 2 describes a method for producing a ZnO alloy containing specific amounts of rare earth elements, Fe, Cu, Co, Zr, Ti, and Hf. 17 The present invention discloses a specific permanent magnet that includes a cell phase having a crystalline phase and a Cu-rich phase having a higher Cu concentration than the cell phase, and the average diameter of the cell phase is 220 nm or less.

[0005] Patent Document 3 also describes a method for producing a ZnO alloy containing specific amounts of rare earth elements R, Fe, Cu, Co, and Zr. 17 The present invention discloses a rare earth-cobalt permanent magnet comprising a cell phase having a RCo5-type crystalline phase and a cell wall surrounding the cell phase, the cell wall containing a crystalline phase having an RCo5-type structure, wherein the concentration of the rare earth element in the cell wall is at least 25 at% higher than the concentration of the rare earth element in the cell phase. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-168827 [Patent Document 2] International Publication No. 2015 / 140829 [Patent Document 3] Japanese Patent Publication No. 2020-188140 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a permanent magnet having excellent magnetic properties, particularly excellent coercive force and squareness, and a device including such a permanent magnet. [Means for solving the problem]

[0008] The permanent magnet according to the present invention is a sintered body having a composition containing 23 to 27 wt% R (where R is the total of rare earth elements including at least Sm), 22 to 27 wt% Fe, 0.3 to 2.5 wt% Mn, 4.0 to 5.0 wt% Cu, with the remainder being Co and unavoidable impurities, and having a plurality of crystal grains and a grain boundary phase, with the Cu concentration in at least a portion of the grain boundary phase being 45 at% or more.

[0009] The permanent magnet may contain 1.7 to 2.5 wt % of Zr.

[0010] In any of the above permanent magnets, the crystal grains are 17 It may have a phase of the RCo5 type structure and a phase of the RCo6 type structure.

[0011] In any of the permanent magnets described above, the average grain size (AG) of the crystal grains may be 100 μm or more.

[0012] In any of the permanent magnets described above, the coefficient of variation (CV) of the grain size of the crystal grains may be 0.60 or less.

[0013] In any of the permanent magnets described above, the thickness t of the grain boundary phase may be 5 to 200 nm.

[0014] In any of the permanent magnets described above, when a reverse magnetic field is applied, reverse magnetic domains may be generated within at least some of the crystal grains, and the reverse magnetic domains may propagate throughout the entire crystal grains.

[0015] A device according to the present invention includes any one of the permanent magnets described above. [Effects of the Invention]

[0016] The present invention provides a permanent magnet having excellent magnetic properties, particularly excellent coercive force and squareness, and a device including the permanent magnet. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a schematic diagram showing an example of a cross section of a permanent magnet according to the present embodiment. [Figure 2] FIG. 2 is an enlarged schematic view of part A (a part of a crystal grain) in FIG. [Figure 3] 1 is a schematic hysteresis curve of a permanent magnet for explaining physical quantities such as squareness ratio. [Figure 4] 1 is a schematic diagram for explaining the process of generation and propagation of reverse magnetic domains in a typical permanent magnet. FIG. [Figure 5] 3A and 3B are schematic diagrams for explaining the process of generation and propagation of reverse magnetic domains in the permanent magnet of the present embodiment. [Figure 6] 3A to 3C are schematic diagrams for explaining a method for manufacturing a permanent magnet according to the present embodiment. [Figure 7] 10 is a graph showing the composition of the grain boundary phase of the permanent magnet of Example 2. [Figure 8] 10 is a graph showing the composition of the grain boundary phase of the permanent magnet of Comparative Example 5. [Figure 9] FIG. 2 is a diagram showing the relationship between the attenuation curve and reverse magnetic domain propagation of the permanent magnet of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] The permanent magnet and device according to the present invention will be described below. For clarity of explanation, the following description and drawings have been simplified as appropriate, and the scale of each component in the drawings may differ significantly for ease of explanation. Furthermore, unless otherwise specified, the symbol "to" indicating a range of values ​​includes the lower and upper limits.

[0019] [Permanent magnet] The permanent magnet according to the present invention (hereinafter also referred to as the present permanent magnet) is a sintered body having a composition containing 23 to 27 wt% R (where R is the total of rare earth elements including at least Sm), 22 to 27 wt% Fe, 0.3 to 2.5 wt% Mn, 4.0 to 5.0 wt% Cu, with the remainder being Co and unavoidable impurities, and having a plurality of crystal grains and a grain boundary phase, with the Cu concentration in at least a portion of the grain boundary phase being 45 at% or more.

[0020] The metallographic structure of the permanent magnet according to this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a schematic diagram showing an example of a cross section of this permanent magnet, and Figure 2 is a schematic diagram showing an enlarged view of part A (a part of crystal grains 10) in Figure 1. As shown in the example of Figure 1, this permanent magnet 100 has a plurality of crystal grains 10 and a grain boundary phase 20 present between the crystal grains 10. Furthermore, as shown in the example of Figure 2, the crystal grains 10 are composed of Th2Zn 17 The crystal grains 10 have a phase 11 of a TbCu7-type structure (hereinafter, sometimes referred to as the 2-17 phase) and a phase 12 of an RCo5-type structure (hereinafter, sometimes referred to as the 1-5 phase), with the 2-17 phase being the main phase (with a volume ratio of 50% or more). Note that the crystal grains 10 may further have a crystalline phase of a TbCu7-type structure (hereinafter, sometimes referred to as the 1-7 phase) (not shown). Th2Zn 17 Phase 11 of the RCo5 structure has a crystal structure with an R-3m space group, and in this permanent magnet, the Th sites are typically occupied by rare earth elements and Zr, and the Zn sites are typically occupied by Co, Cu, Fe, and Zr. Phase 12 of the RCo5 structure typically has the R sites occupied by rare earth elements and Zr, and the Co sites are typically occupied by Co, Cu, and Fe. Crystal phases of the TbCu7 structure typically have the Tb sites occupied by rare earth elements and Zr, and the Cu sites are typically occupied by Co, Cu, and Fe. The crystal structure can be determined by X-ray diffraction.

[0021] This permanent magnet contains 0.3 to 2.5 wt% Mn, and by manufacturing it using the manufacturing method described below, it is possible to concentrate Cu to 45 at% or more in at least a portion of the grain boundary phase 20. As a result, it is possible to obtain a permanent magnet with excellent magnetic properties, especially a high squareness ratio.

[0022] The squareness ratio and other factors will be explained with reference to Figure 3. Figure 3 is a schematic hysteresis curve of a permanent magnet, showing the first and second quadrants (decay curve). The vertical axis represents magnetization (magnetic polarization), and the horizontal axis represents magnetic field strength. Positive values ​​on the horizontal axis represent the strength of the magnetic field applied in the direction that magnetizes the permanent magnet, and negative values ​​represent the strength of the magnetic field applied in the direction that demagnetizes the permanent magnet. When a positive magnetic field is applied to a permanent magnet, magnetic polarization occurs according to the initial magnetization curve, and saturation magnetization is reached. If a negative magnetic field is then applied to a permanent magnet in a saturated magnetization state, it will rapidly demagnetize after passing through a knickpoint. The strength of the magnetic field when magnetic polarization becomes 0 is the intrinsic coercivity (Hcj). In this embodiment, the magnetic field at 90% remanence is defined as Hk, and the ratio of this to the intrinsic coercivity Hcj (Hk / Hcj) is defined as the squareness ratio. This permanent magnet can achieve a squareness ratio of 65% or more, preferably 70% or more.

[0023] Next, the mechanism by which reverse magnetic domains are generated in the permanent magnet of this embodiment will be described with reference to Figures 4 and 5. Figure 4 is a schematic diagram for explaining the process by which reverse magnetic domains are generated and propagated in a typical permanent magnet, and Figure 5 is a schematic diagram for explaining the process by which reverse magnetic domains are generated and propagated in the permanent magnet of this embodiment.

[0024] As shown in Figure 4, in the initial state (when no reverse magnetic field is applied) of the decay curve of a permanent magnet, no reverse magnetic domains are generated. When a reverse magnetic field H1 is applied to a permanent magnet, reverse magnetic domains generally occur near the interface (grain boundary) of the grain boundary phase 20 of the crystal grain 10. Subsequently, as the reverse magnetic field is strengthened, reverse magnetic domains propagate from the grain boundary phase 20 into the crystal grain 10 (reverse magnetic field H2). As the reverse magnetic field is further strengthened, reverse magnetic domains 14 spread within the crystal grain 10, and reverse magnetic domains 15 also occur within the crystal grain 10 (reverse magnetic field H3). Then, as the reverse magnetic field is further strengthened (H4 to H5), reverse magnetic domains 14 within the crystal grain 10 further spread, and reverse magnetic domains 15 generated within the crystal grain 10 propagate within the crystal grain 10, spreading reverse magnetic domains 16 throughout the crystal grain 10, completing the magnetization reversal of the permanent magnet. Note that H1 to H5 in Figures 4 and 5 are negative values, with absolute values ​​increasing in the order of H1, H2, etc.

[0025] In the permanent magnet of this embodiment, the high Cu concentration in the grain boundary phase 20 results in significant demagnetization, which presumably makes it difficult for reverse magnetic domains to form at the grain boundaries. Therefore, it is presumed that the main mechanism for reverse magnetic domain generation and propagation is that reverse magnetic domains 15 first form inside the crystal grains 10 when a certain reverse magnetic field (e.g., H3) is applied, and these reverse magnetic domains 15 then propagate throughout the entire crystal grain. As a result, the slope of the attenuation curve (second quadrant) in Figure 3 becomes smaller in the region of the weak reverse magnetic field than the knickpoint, resulting in a significant improvement in squareness.

[0026] Next, the composition and metal structure of the permanent magnet of this embodiment will be described. In this embodiment, the rare earth element R is a collective term for Sc, Y, and lanthanoids (elements with atomic numbers 57 to 71), and includes at least Sm as the rare earth element R. The rare earth element R may be Sm alone, or may be a combination of Sm with one or more other rare earth elements. From the viewpoint of magnetic properties, the other rare earth elements are preferably Pr, Nd, Ce, and La. Furthermore, from the viewpoint of magnetic properties, the content of Sm relative to the total rare earth elements R is preferably 80 wt% or more, more preferably 90 wt% or more, and even more preferably 95 wt% or more. The present permanent magnet contains 23 to 27 wt % of rare earth element R. By including the rare earth element R in this proportion, a permanent magnet having high magnetic anisotropy and high coercive force can be obtained.

[0027] This permanent magnet contains 22 to 27 wt% Fe. By containing 22 wt% or more Fe, the saturation magnetization is improved. Furthermore, by keeping the Fe content at 27 wt% or less, the permanent magnet has high coercive force.

[0028] This permanent magnet contains 4.0 to 5.0 wt% Cu. By containing 4.0 wt% or more Cu, the Cu concentration in the grain boundary phase can be achieved to 45 at% or more, resulting in a permanent magnet with high coercivity. Furthermore, by keeping the Cu content at 5.0 wt% or less, a decrease in magnetization is suppressed.

[0029] This permanent magnet contains 0.3 to 2.5 wt% Mn. By including 0.3 wt% or more Mn, the Cu concentration in the grain boundary phase can be increased. Furthermore, including Mn within this range makes it easier to obtain a crystalline structure with relatively large, uniform grains, improving the squareness ratio. On the other hand, if the Mn content exceeds 2.5 wt%, the grain size tends to become smaller. It is believed that the inclusion of 0.3 wt% or more Mn lowers the melting point, and a large amount of liquid phase appears during sintering, causing a concentration distribution in Cu and other elements. Furthermore, the appearance of a large amount of liquid phase is believed to increase the grain size. Furthermore, Mn is believed to contribute to the demagnetization of the grain boundary phase, suppressing the occurrence of reverse magnetic domains in the grain boundary phase.

[0030] The permanent magnet preferably further contains 1.7 to 2.5 wt% Zr. By containing 1.7 to 2.5% Zr, a permanent magnet with a high maximum energy product (BH)m, which is the maximum magnetostatic energy that the magnet can hold, can be obtained.

[0031] The balance of the permanent magnet is Co and unavoidable impurities. The inclusion of Co improves the thermal stability of the permanent magnet. However, an excessive Co content relatively reduces the Fe content. Inevitable impurities are elements that are inevitably mixed in from raw materials or during the manufacturing process, and specific examples include, but are not limited to, C, N, P, S, Al, Ti, Cr, Ni, Hf, Sn, and W. The total content of inevitable impurities in the permanent magnet is preferably 5 wt% or less, more preferably 1 wt% or less, and even more preferably 0.1 wt% or less, based on the total weight of the permanent magnet. The local content of each element in a permanent magnet can be measured using, for example, energy dispersive X-ray spectrometry (EDX).

[0032] The permanent magnet of this embodiment preferably has a metal structure with an average grain size (AG) of 100 μm or more, and the coefficient of variation (CV) of the grain size of the crystal grains is preferably 0.6 or less. The method for measuring the average grain size (AG) and coefficient of variation (CV) of the crystal grains of this permanent magnet will be explained. First, the permanent magnet to be measured is polished with waterproof abrasive paper. Coarse waterproof abrasive paper is used first, and then gradually changed to finer ones. After polishing with the waterproof abrasive paper, it is polished to a mirror finish using a buffing machine or similar. After mirror polishing, the permanent magnet is immersed in an acid solvent and etched. During this process, the grain boundary phase 20 corrodes faster than the crystal grains 10, so the grain boundaries become clearly visible and each crystal grain can be clearly observed. It is then washed with pure water or similar and dried. The crystal grains can be confirmed by observing the treated surface of the resulting permanent magnet with an optical microscope. In this embodiment, the grain size of the crystal grains is determined by the maximum Feret diameter. The Feret diameter is defined as the distance between two parallel lines that sandwich the crystal grain, and in the present invention, the maximum value of the Feret diameter is determined as the grain size of the crystal grains. Note that the grain size of the crystal grains can be determined more accurately by using image processing software. The measurement area is set to 500 μm×500 μm, and the grain size of the crystal grains present in the plane is determined. From these values, the average grain size (AG) and coefficient of variation (CV) are calculated. The average crystal grain size (AG) is sufficient as long as it is 100 μm or more, and preferably 120 μm or more. On the other hand, although there is no particular upper limit, it is usually 1000 μm or less, and preferably 500 μm or less. The coefficient of variation (CV) may be 0.6 or less, and preferably 0.5 or less.

[0033] Furthermore, in the permanent magnet of this embodiment, the thickness t of the grain boundary phase is preferably 5 to 200 nm. The thickness of the grain boundary phase may be determined from the average distance between the crystal grains when measuring the grain size of the crystal grains, but in this embodiment, since a grain boundary phase with a thickness of 100 nm or less is formed, the thickness of the grain boundary phase is defined as the range in which the Cu concentration is 10 at% or more in the energy dispersive X-ray analysis.

[0034] <Manufacturing method of permanent magnets> The permanent magnet described above is not particularly limited, but the Cu concentration in the grain boundary phase can be increased, for example, by adjusting the heat treatment conditions. One example is a method in which the solution treatment process after sintering is divided into two stages (see Figure 6). In the example of Figure 6, the first solution treatment promotes solid-phase diffusion throughout most of the crystal grains, while leaving a liquid phase in the grain boundary phase. Next, the temperature drop rate is controlled to expel elements other than Cu from the liquid phase to the solid phase, and Cu is concentrated in the liquid phase. The temperature drop rate is preferably 0.1 to 5°C / min. Next, the liquid phase is completely eliminated in the second solution treatment, and solid-phase diffusion promotes composition homogenization. This manufacturing method can increase the Cu concentration in the grain boundary phase. Each step is described in more detail below.

[0035] First, an alloy is prepared having a composition containing 23 to 27 wt% R (where R is the total of rare earth elements including at least Sm), 22 to 27 wt% Fe, 0.3 to 2.5 wt% Mn, 4.0 to 5.0 wt% Cu, with the remainder being Co and unavoidable impurities. The alloy may be prepared by purchasing a commercially available alloy having the desired composition, or by mixing the elements to obtain the desired composition. A specific example of how each element is blended will be described below. As raw materials, a desired rare earth element, Fe, Mn, and Co metal elements, and a master alloy are prepared. Here, it is preferable to select a master alloy with a low eutectic temperature, as this facilitates homogenization of the composition of the resulting alloy. In the present invention, it is preferable to select and use FeZr or CuZr as the master alloy. For example, FeZr with approximately 20% Fe and 80% Zr is preferable. For example, CuZr with approximately 50% Cu and 50% Zr is preferable. These raw materials are mixed to obtain the desired composition, and placed in a crucible made of alumina or the like. -2 A homogenized alloy can be obtained by melting the alloy in a high-frequency melting furnace in a vacuum of less than torr or in an inert gas atmosphere. The present invention may further include a step of casting the molten alloy in a mold to produce an alloy ingot. Alternatively, the molten alloy may be dropped onto a copper roll to produce flakes of the alloy about 1 mm thick (strip casting method). When an alloy ingot is produced by the casting, the alloy ingot may be heat-treated for 1 to 20 hours at the solution temperature of the alloy ingot, which may be adjusted appropriately depending on the composition of the alloy, etc.

[0036] Next, the alloy is pulverized to form a powder. The pulverization method for the alloy is not particularly limited and may be appropriately selected from conventionally known methods. One suitable example is a method in which an alloy ingot or flake-like alloy is first coarsely pulverized to a size of approximately 100 to 500 μm using a known pulverizer, and then finely pulverized using a ball mill, jet mill, or the like. The average particle size of the powder is not particularly limited, but in order to shorten the sintering time in the sintering step described below and to produce a uniform permanent magnet, the powder should have an average particle size of 1 μm to 10 μm, preferably 6 μm or less, and more preferably 60 mass% or more of the powder should have an average particle size of 8 μm or less.

[0037] Next, the obtained powder is pressure-molded to form a compact of the desired shape. In this manufacturing method, pressure molding is preferably performed in a constant magnetic field in order to align the crystal orientation of the powder and improve magnetic properties. The relationship between the direction of the magnetic field and the pressing direction is not particularly limited and may be selected appropriately depending on the shape of the product, etc. For example, when manufacturing a ring magnet or a thin plate magnet, parallel magnetic field pressing can be used, in which a magnetic field is applied parallel to the pressing direction. On the other hand, perpendicular magnetic field pressing, in which a magnetic field is applied perpendicular to the pressing direction, is preferred in order to achieve excellent magnetic properties.

[0038] The strength of the magnetic field is not particularly limited, and may be, for example, 15 kOe or less or 15 kOe or more depending on the application of the product. In particular, from the viewpoint of excellent magnetic properties, it is preferable to perform pressure molding in a magnetic field of 15 kOe or more. The pressure during pressure molding may be adjusted appropriately depending on the size, shape, etc. of the product. For example, it may be 0.5 to 2.0 ton / cm. 2 That is, in the method for producing a permanent magnet of the present invention, from the viewpoint of magnetic properties, the powder is subjected to a magnetic field of 15 kOe or more and a pressure of 0.5 to 2.0 ton / cm perpendicular to the magnetic field. 2 It is particularly preferable to carry out the pressing at the following pressures:

[0039] Next, the molded body is heated to form a sintered body. In this manufacturing method, the sintering conditions may be any known conditions as long as the resulting sintered body is sufficiently densified. From the viewpoint of densifying the sintered body, the sintering temperature is preferably 1170 to 1215°C, more preferably 1180 to 1205°C. By setting the sintering temperature at 1215°C or less, evaporation of rare earth elements, particularly Sm, is suppressed, making it possible to manufacture a permanent magnet with excellent magnetic properties. Furthermore, in the present invention, since the presence of Mn tends to lower the melting point, sufficient sintering is possible at 1215°C or less. In order to remove adsorbed gases contained in the compact, the temperature rise conditions in the sintering step are preferably such that evacuation is first started at room temperature and the temperature is raised at a rate of 1 to 10°C / min. During the temperature rise process, a hydrogen atmosphere may be used instead of evacuation. In this case, too, it is preferable to switch to a vacuum atmosphere at a temperature of 1150°C or lower. The sintering time is preferably 20 to 210 minutes, more preferably 30 to 150 minutes, from the viewpoint of sufficiently densifying the material while suppressing evaporation of Sm. In addition, from the viewpoint of suppressing oxidation, the sintering step is preferably carried out in a vacuum of 1000 Pa or less or in an inert gas atmosphere, and more preferably in a vacuum of 100 Pa or less from the viewpoint of increasing the density of the sintered body.

[0040] After sintering, the temperature is lowered to the solution temperature for solution treatment. In order to make the grain size uniform (to suppress an increase in the coefficient of variation (CV)), the temperature is preferably lowered to the solution temperature at a rate of 0.01 to 3°C / min.

[0041] Solution treatment is a process for forming the 1-7 phase (TbCu7 structure), which is a precursor for separating into the 2-17 phase and the 1-5 phase. In this manufacturing method, solution treatment is performed in two stages. The first solution treatment temperature is preferably 1130°C to 1180°C, more preferably 1140°C to 1170°C, from the viewpoint of retaining a liquid phase in the grain boundary phase. The first solution treatment time is preferably 5 to 150 hours, more preferably 10 to 100 hours, from the viewpoint of homogenizing elements other than Cu. Next, the temperature drop rate is controlled to expel elements other than Cu from the liquid phase to the solid phase, and Cu is concentrated in the liquid phase. The temperature drop rate is preferably 0.1 to 5°C / min. In the second solution treatment, the liquid phase is completely eliminated, and the composition is homogenized by solid-phase diffusion. The second solution treatment temperature is preferably 1110°C to 1165°C, more preferably 1120°C to 1160°C. The second solution treatment time is preferably 5 to 150 hours, more preferably 10 to 100 hours, from the viewpoint of homogenization. The solution treatment is preferably carried out in a vacuum of 1000 Pa or less or in an inert atmosphere.

[0042] After the solution treatment, it is preferable to rapidly cool the material to at least 600°C or less. The rapid cooling rate is preferably 80°C / min or more. Rapid cooling maintains the 1-7 phase crystal structure. On the other hand, the upper limit of the cooling rate depends on the shape of the compact, but is preferably 250°C / min or less, for example.

[0043] Next, the compact after the quenching step is subjected to aging treatment to form the 2-17 and 1-5 phases. While the aging temperature is not particularly limited, in order to obtain a permanent magnet having the 2-17 phase as the main phase and a homogeneous mixture of the 2-17 and 1-5 phases, a preferred method is to hold the compact at a temperature of 700 to 900°C for 2 to 20 hours, and then cool it down to at least 400°C at a cooling rate of 2°C / min or less. Holding the compact at a temperature of 700 to 900°C for 2 to 20 hours allows the 2-17 and 1-5 phases to be homogeneously formed. Aging treatment at a temperature range of 800 to 850°C is particularly preferred. To obtain good magnetic properties, a cooling rate of 2°C / min or less is preferred, and 0.5°C / min or less is even more preferred.

[0044] The above manufacturing method makes it possible to obtain a permanent magnet having a plurality of crystal grains and a grain boundary phase, in which the Cu concentration in at least a portion of the grain boundary phase is 45 at% or more. Furthermore, the above manufacturing method also makes it easy to produce a permanent magnet having a metal structure in which the average grain size (AG) of the crystal grains is 100 μm or more and the coefficient of variation (CV) of the grain size is 0.60 or less.

[0045] [device] The present invention further provides a device comprising the present permanent magnet. Specific examples of such devices include watches, electric motors, various instruments, communication devices, computer terminals, speakers, video disks, sensors, etc. Furthermore, as described above, the present permanent magnet has a high residual magnetic flux density, low coercive force, and a high squareness ratio, making it particularly suitable for use in variable magnetic field motors, allowing for the production of variable magnetic field motors that achieve high efficiency from low to high speeds. [Example]

[0046] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these descriptions.

[0047] (Examples 1 to 3) A master alloy of 20% Fe and 80% Zr and each raw material were prepared so as to have the composition of Examples 1 to 3 in Table 1, melted in a high-frequency melting furnace, and cast to obtain alloy ingots. The obtained master alloy was coarsely pulverized in an inert gas to an average size of about 100 to 500 μm, and then finely pulverized in an inert gas using a ball mill to an average size of about 6 μm. These powders were each subjected to a magnetic field of 15 kOe at 1 ton / cm 2 A compact was obtained by pressing at a pressure of 1000 kJ / cm. This compact was sintered in a vacuum of less than 1000 Pa at 1200°C for 80 minutes, then subjected to a first solution treatment at 1150°C for 20 hours, slowly cooled at 1.0°C / min, and a second solution treatment at 1135°C for 50 hours. It was then rapidly cooled from 1000 to 600°C at a cooling rate of 80°C / min. After quenching, it was held at 850°C for 12 hours, and then slowly cooled to 350°C at a cooling rate of 0.5°C / min, resulting in an aging treatment to obtain a permanent magnet.

[0048] (Comparative Examples 1 and 2) A permanent magnet was obtained in the same manner as in Examples 1 to 3 except that the composition was changed as in Comparative Examples 1 and 2 in Table 1.

[0049] Examples 4 to 6 Permanent magnets were obtained in the same manner as in Examples 1 to 3, except that the composition was changed as in Examples 4 to 6 in Table 2 and the slow cooling rate from the first solution treatment to the second solution treatment was changed as in Table 2.

[0050] (Comparative Examples 3 to 4) Permanent magnets were obtained in the same manner as in Examples 1 to 3, except that the composition was changed as shown in Comparative Examples 3 and 4 in Table 2 and the slow cooling rate from the first solution treatment to the second solution treatment was changed as shown in Table 2.

[0051] (Comparative Example 5) A permanent magnet of Comparative Example 5 was obtained in the same manner as in Example 1, except that Mn was not added.

[0052] [evaluation] <Squareness ratio measurement> The magnetic properties of the obtained permanent magnets were measured using a BH tracer, and the squareness ratio, which is the ratio (Hk / Hcj) of the magnetic field (Hk) when the magnetization is 90% of the remanence, to the coercive force (Hcj), was calculated. The results are shown in Tables 1 and 2.

[0053] <Measurement of Cu concentration in grain boundary phase> The resulting permanent magnet was cut, and the cross section including the grain boundary phase was measured using an energy dispersive X-ray analyzer. The maximum Cu concentration is shown in Tables 1 and 2. The measurement results for Example 2 and Comparative Example 5 are shown in Figs. 7 and 8.

[0054] <Mechanism of reversed magnetic domain generation> The magnetic domains of the obtained permanent magnets were observed using a Kerr effect microscope while applying a magnetic field, and the mechanism of the main reverse magnetic domain generation was determined. The results are shown in Tables 1 and 2.

[0055] [Table 1]

[0056] 7 and 8, concentration of Cu in the grain boundary phase is observed in both Example 2 and Comparative Example 5, but the inclusion of 0.3 to 2.5 wt% of Mn as in Example 2 makes it much easier for Cu concentration to proceed. As a result, in Example 2, portions with a Cu concentration of 45 at% or more are observed in the grain boundary phase. Similarly, in Example 1 and Examples 3 to 6, portions with a Cu concentration of 45 at% or more are observed in the grain boundary phase. FIG. 9 shows the relationship between the decay curve and reverse magnetic domain propagation for the permanent magnet of Example 1. FIG. 9 focuses on one crystal grain 10. In this crystal grain 10, reverse magnetic domains 15 are not observed when the reverse magnetic field is between 0 and -8 kOe. Reverse magnetic domains 15 are first observed within the crystal grain at -8 kOe, and magnetization reversal is complete at -13 kOe. Thus, the permanent magnet of the present invention requires a strong reverse magnetic field from the generation of reverse magnetic domains to the completion of magnetization reversal. As a result, the slope of the decay curve in the region of small reverse magnetic fields relative to the knickpoint is smaller, resulting in a significant improvement in squareness. Similar results were obtained in other examples.

[0057] As shown in Tables 1 and 2, the permanent magnets of Examples 1 to 6 were confirmed to have a plurality of crystal grains and a grain boundary phase, with a Cu concentration of 45 at% or more in at least a portion of the grain boundary phase. It was confirmed that reverse magnetic domains were generated within the crystal grains of the permanent magnets of Examples 1 to 6, and that the squareness ratio (Hk / Hcj) was 65% or more.

[0058] The present invention has been described above in accordance with the above-mentioned embodiment, but the present invention is not limited to the configuration of the above-mentioned embodiment, and naturally includes various modifications, alterations, and combinations that a person skilled in the art can make within the scope of the invention as defined in the claims of this application. [Explanation of symbols]

[0059] 10 grains 11 Th2Zn 17 Type structure phase (2-17 phase) 12 RCo5 structure phase (phases 1-5) 14, 15, 16 Reverse magnetic domain 20 Grain boundary phase

Claims

1. A sintered body having a composition containing 23 to 27 wt% R (where R is the total of rare earth elements including at least Sm), 22 to 27 wt% Fe, 0.3 to 2.5 wt% Mn, 4.0 to 5.0 wt% Cu, 1.7 to 2.5 wt% Zr, and the balance being Co and inevitable impurities, Sm is 80 wt % or more relative to the total amount of rare earth elements R, The alloy has a plurality of crystal grains and a grain boundary phase, and the concentration of Cu in at least a part of the grain boundary phase is 45 at% or more; The crystal grains have a phase of a Th 2 Zn 17 type structure and a phase of a RCo 5 type structure, A permanent magnet, wherein the phase having the Th 2 Zn 17 type structure is a main phase with a volume ratio of 50% or more.

2. 2. The permanent magnet according to claim 1, wherein the average grain size (A.G.) of the crystal grains is 100 μm or more.

3. 3. The permanent magnet according to claim 2, wherein the coefficient of variation (C.V.) of the grain size of said crystal grains is 0.60 or less.

4. 2. The permanent magnet according to claim 1, wherein the thickness t of the grain boundary phase is 5 to 200 nm.

5. 2. The permanent magnet according to claim 1, wherein, when a reverse magnetic field is applied to the permanent magnet, reverse magnetic domains are generated within at least some of the crystal grains, and the reverse magnetic domains propagate throughout the entire crystal grains.

6. A device comprising a permanent magnet according to any one of claims 1 to 5.

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