Rare earth cobalt permanent magnet, preparation method and device thereof

Abstract

The rare earth cobalt permanent magnet according to the present disclosure contains: 24% to 26% by mass of a rare earth element R containing Sm; 25% to 27% by mass of Fe; 4.0% to 7.0% by mass of Cu; 2.0% to 3.5% by mass of Zr; and Co and inevitable impurities as the balance. The rare earth element R is any one of a combination of Sm and Nd, a combination of Sm and Pr, or a combination of Sm, Nd, and Pr. The rare earth cobalt permanent magnet contains a unit cell phase of a crystal phase having a Th2Zn 17 structure and a unit cell wall of a crystal phase having an RCo5 structure surrounding the unit cell phase, and the concentration of the rare earth element R in the unit cell wall is not less than 25 atomic% higher than the concentration of the rare earth element R in the unit cell phase.

Description

Technical Field

[0001] The present disclosure relates to rare earth cobalt permanent magnets, methods for preparing rare earth cobalt permanent magnets, and devices including the same. Background Art

[0002] From various viewpoints such as improving the magnetic properties of rare earth cobalt permanent magnets, some known rare earth cobalt permanent magnets contain, for example, Fe, Cu, Zr, etc.

[0003] Japanese Unexamined Patent Application Publication No. 2005-243884 discloses a technique related to a rare earth cobalt permanent magnet having a TbCu7 structure. Japanese Unexamined Patent Application Publication No. 2015-111675 discloses a technique related to an Sm-Co magnet having a high iron concentration composition. Summary of the Invention

[0004] The magnetic force of rare earth cobalt permanent magnets changes little with temperature, and they are rust-resistant. Therefore, rare earth cobalt permanent magnets are widely used in various devices. From the viewpoint of further improving the performance of such devices, rare earth cobalt permanent magnets having even more excellent magnetic properties (especially a high squareness ratio) are needed.

[0005] To solve the above problems, the present disclosure aims to provide rare earth cobalt permanent magnets having excellent magnetic properties, methods for preparing such rare earth cobalt permanent magnets, and devices including such rare earth cobalt permanent magnets.

[0006] A rare earth cobalt permanent magnet according to one aspect of the present disclosure contains: 24% to 26% by mass of a rare earth element R containing Sm; 25% to 27% by mass of Fe; 4.0% to 7.0% by mass of Cu; 2.0% to 3.5% by mass of Zr; and Co and inevitable impurities as the balance. R is any one of a combination of Sm and Nd (0 < Nd ≤ 25% by mass, the balance being Sm), a combination of Sm and Pr (0 < Pr ≤ 25% by mass, the balance being Sm), or a combination of Sm, Nd, and Pr (where 0 < Nd + Pr ≤ 25% by mass, the balance being Sm). The rare earth cobalt permanent magnet contains a cell phase of a crystal phase having a Th2Zn 17 structure and a cell wall of a crystal phase having an RCo5 structure surrounding the cell phase. The concentration of R in the cell wall is not less than 25 atomic% higher than the concentration of R in the cell phase.

[0007] According to one aspect of the present disclosure, a method for preparing a rare earth cobalt permanent magnet includes: step (I), preparing an alloy, the alloy comprising 24% to 26% by mass of a rare earth element R containing Sm; 25% to 27% by mass of Fe; 4.0% to 7.0% by mass of Cu; 2.0% to 3.5% by mass of Zr; and the balance being Co and unavoidable impurities (R is any one of a combination of Sm and Nd (where 0 < Nd ≤ 25% by mass and the balance is Sm), a combination of Sm and Pr (where 0 < Pr ≤ 25% by mass and the balance is Sm), or a combination of Sm, Nd and Pr (where 0 < Nd + Pr ≤ 25% by mass and the balance is Sm)); step (II), crushing the alloy into powder; step (III), molding the powder into a molded body; step (IV), sintering the molded body into a sintered body by heating the molded body at 1190 °C to 1225 °C for 0.5 hour to 3.0 hours; solution heat treatment step (V), heating the sintered body at 1120 °C to 1180 °C for 20 hours to 100 hours; rapid cooling step (VI), after the solution heat treatment step (V), cooling the temperature at a cooling rate of not less than 60 °C / minute to at least 600 °C from the solution heat treatment temperature; and aging treatment step (VII), forming a cell phase containing a crystal phase of a Th2Zn 17 structure and a cell wall of a crystal phase containing an RCo5 structure surrounding the cell phase. The concentration of R in the cell wall is not less than 25 atomic% higher than the concentration of R in the cell phase.

[0008] An apparatus according to one aspect of the present disclosure includes the above rare earth cobalt permanent magnet.

[0009] The present disclosure provides a rare earth cobalt permanent magnet having excellent magnetic properties, a method for preparing such a rare earth cobalt permanent magnet, and an apparatus including such a rare earth cobalt permanent magnet.

[0010] The above and other objects, features and advantages of the present disclosure will be more fully understood from the following detailed description and the accompanying drawings, which are only for illustration and are not considered to limit the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a graph showing the compositional change of the rare earth cobalt permanent magnet.

[0012] Figure 2 shows a TEM image of the rare earth cobalt permanent magnet.

[0013] Figure 3 is a schematic diagram for explaining the process of the expansion of reverse magnetic domains in the rare earth cobalt permanent magnet; and

[0014] Figure 4It is a flowchart of an example for describing the steps of preparing a rare earth cobalt permanent magnet. Detailed Description of the Invention

[0015] Hereinafter, a rare earth cobalt permanent magnet according to the present disclosure and a method for preparing the rare earth cobalt permanent magnet will be described in detail.

[0016] <Rare Earth Cobalt Permanent Magnet>

[0017] The rare earth cobalt permanent magnet according to the present disclosure contains 24% by mass to 26% by mass of a rare earth element R containing Sm; 25% by mass to 27% by mass of Fe; 4.0% by mass to 7.0% by mass of Cu; 2.0% by mass to 3.5% by mass of Zr; and Co and inevitable impurities as the balance. Herein, the rare earth element R is any one of (1) a combination of Sm and Nd (where 0 < Nd ≤ 25% by mass and the balance is Sm), (2) a combination of Sm and Pr (where 0 < Pr ≤ 25% by mass and the balance is Sm), or (3) a combination of Sm, Nd, and Pr (where 0 < Nd + Pr ≤ 25% by mass and the balance is Sm). Note that in this specification, the numerical range of "A% by mass to B% by mass" includes both values of A and B.

[0018] The rare earth cobalt permanent magnet according to the present disclosure contains a unit cell phase of a crystal phase having a Th2Zn 17 structure and a unit cell wall of a crystal phase having an RCo5 structure surrounding the unit cell phase. The concentration of the rare earth element R in the unit cell wall is not less than 25 at% (atomic percent) higher than the concentration of the rare earth element R in the unit cell phase.

[0019] The composition of the above Cu is preferably 4.2% by mass to 4.7% by mass. If the amount of Cu is too small, sufficient magnetic coercivity (Hcj) cannot be obtained. If the amount of Cu is too large, the saturation magnetization intensity decreases. The composition of the above Zr is preferably 2.1% by mass to 2.5% by mass. If the amount of Zr is too small, the crystal structure is unstable. Therefore, sufficient magnetic coercivity (Hcj) cannot be obtained in a region having a large amount of Fe. If the amount of Zr is too large, the saturation magnetization intensity decreases.

[0020] The density of the above rare earth cobalt permanent magnet is 8.20 g / cm 3 to 8.45 g / cm 3 or more preferably 8.25 g / cm 3 to 8.40 g / cm 3 .

[0021] In the rare earth cobalt permanent magnet according to the present invention, the remainder (i.e., 36.5% to 45% by mass) contains Co (cobalt) and inevitable impurities. The inevitable impurities are elements that are inevitably mixed from raw materials or mixed during the preparation process. Specific but non-limiting examples of the inevitable impurities include C (carbon), N (nitrogen), P (phosphorus), S (sulfur), Al (aluminum), Ti (titanium), Cr (chromium), Mn (manganese), Ni (nickel), Hf (hafnium), Sn (tin), and W (tungsten). In the present disclosure, the content ratio of the inevitable impurities relative to the total amount of the rare earth cobalt permanent magnet is preferably not more than 5% by mass in total, more preferably not more than 1% by mass in total, or even more preferably not more than 0.1% by mass in total.

[0022] The content ratio of each element in the rare earth cobalt permanent magnet can be measured, for example, by energy dispersive X-ray spectroscopy (EDX).

[0023] The rare earth cobalt permanent magnet according to the present disclosure contains a crystal phase of the Th2Zn 17 structure (hereinafter also referred to as the 2-17 phase) as the primary crystal phase. The Th2Zn 17 structure is a crystal structure having the R-3m space group. In the present disclosure, generally, rare earth elements and Zr occupy the Th site, and Co, Cu, Fe, and Zr occupy the Zn site. In addition, the rare earth cobalt permanent magnet according to the present invention contains a crystal phase of the RCo5 structure (hereinafter also referred to as the 1-5 phase). In the 1-5 phase, generally, rare earth elements and Zr occupy the R site, while Co, Cu, and Fe occupy the Co site.

[0024] The rare earth cobalt permanent magnet according to the present disclosure may contain a crystal phase of the TbCu7 structure (hereinafter also referred to as the 1-7 phase). In the 1-7 phase, generally, rare earth elements and Zr occupy the Tb position, while Co, Cu, and Fe occupy the Cu position. In the present disclosure, the 1-7 phase is the crystal phase that mainly exists before the aging treatment step (VII) described later, and the 2-17 phase and the 1-5 phase are the phases formed by the aging treatment step (VII) described later, respectively. The crystal structure can be identified by a known method such as X-ray diffraction.

[0025] Figure 1 is a graph showing the compositional change of the rare earth cobalt permanent magnet and shows the Figure 2 compositional change at the analysis site in the TEM image of the rare earth cobalt permanent magnet shown. In other words, Figure 1 shows the compositional change of the rare earth cobalt permanent magnet that sequentially passes through the "2-17 phase", the "1-5 phase", and the "2-17 phase". Here, the 2-17 phase corresponds to the crystal phase of the unit cell phase, and the 1-5 phase corresponds to the crystal phase of the unit cell wall surrounding the unit cell phase.

[0026] As Figure 1As shown, the ratios of Sm, Nd, and Cu in the 1-5 phase increase compared to those in the 2-17 phase. At the same time, the ratios of Fe and Co in the 1-5 phase decrease compared to those in the 2-17 phase. The ratio of Zr remains substantially constant in both the 1-5 phase and the 2-17 phase.

[0027] In this way, in the rare-earth cobalt permanent magnet according to the present embodiment, Sm and Nd show the same trend in terms of the compositional change from the cell phase (2-17 phase) to the cell wall (1-5 phase) in the rare-earth cobalt permanent magnet. This trend similarly applies to the combination of Sm and Pr and the combination of Sm, Nd, and Pr. In other words, in the present embodiment, Sm and at least one of Nd and Pr show the same trend in terms of the compositional change from the cell phase to the cell wall in the rare-earth cobalt permanent magnet.

[0028] In the present embodiment, the concentration of the rare-earth element R in the cell wall is not less than 25 at% (atomic percent) higher than the concentration of the rare-earth element R in the cell phase. Here, the rare-earth element R is any one of (1) a combination of Sm and Nd, (2) a combination of Sm and Pr, or (3) a combination of Sm, Nd, and Pr. Such a configuration can provide a rare-earth cobalt permanent magnet having excellent magnetic properties, namely, a high squareness ratio. Specifically, a rare-earth cobalt permanent magnet with a squareness ratio of not less than 63% can be obtained, where the squareness ratio is represented by the ratio (Hk / Hcj) of the magnetic field (Hk) to the coercivity (Hcj). The squareness ratio is a physical quantity represented by Hk / Hcj, where Hk is the reverse magnetic field at which the magnetic flux density is 90% of the residual magnetic flux density.

[0029] In the present embodiment, when the magnetic domain wall displacement is restricted between the 2-17 phase and the 1-5 phase, the coercivity (Hcj) is considered to occur. The coercivity (Hcj) is the magnitude of the magnetic field in the opposite direction required to demagnetize a magnetized magnetic body in a certain direction.

[0030] In the present embodiment, the concentration of the rare-earth element R in the cell wall (1-5 phase) is not less than 25 at% higher than the concentration of the rare-earth element R in the cell phase (2-17 phase). Therefore, the displacement of the magnetic domain wall can be effectively restricted by the cell wall (1-5 phase).

[0031] In the present embodiment, as Figure 1 shown, when the cell phase (2-17 phase) and the cell wall (1-5 phase) are separated from each other, Fe aggregates in the cell phase (2-17 phase) and Cu aggregates in the pore wall (1-5 phase). This increases the squareness ratio Hk / Hcj of the rare-earth cobalt permanent magnet, and the maximum energy product (BH)m increases. Here, the maximum energy product (BH)m is the maximum static magnetic energy that can be held by the magnetic body, and represents the maximum value of the integral of the magnetic flux density B and the magnetic field H on the BH decay curve in the second quadrant (decay curve) of the magnetization curve (BH curve).

[0032] Next, with reference to Figure 3 , the process of the expansion of reverse magnetic domains in the rare-earth cobalt permanent magnet according to the present embodiment will be described. As Figure 3 shown, the rare-earth cobalt permanent magnet includes crystal grains 11 and grain boundaries 12, and the grain boundaries 12 are the boundaries between the crystal grains 11. In the initial state, that is, in the state where no reverse magnetic field is applied, no reverse magnetic domains appear.

[0033] When a reverse magnetic field of H1 = -5 kOe is applied to the rare-earth cobalt permanent magnet, reverse magnetic domains appear in the grain boundaries 12. Thereafter, when the reverse magnetic field is enhanced and a reverse magnetic field of H2 = -6 kOe is applied, the reverse magnetic domains expand from the grain boundaries 12 into the crystal grains 11 (see the arrows in Figure 3 ). When the reverse magnetic field is further enhanced and a reverse magnetic field of H3 = -7 kOe is applied, the reverse magnetic domains 14 expand into the crystal grains 11, and reverse magnetic domains 15 appear in the crystal grains 11. When the reverse magnetic field is further enhanced and a reverse magnetic field of H4 = -9 kOe is applied, the reverse magnetic domains 14 in the crystal grains 11 further expand, and the reverse magnetic domains 15 that appear in the crystal grains 11 expand within the crystal grains 11. Thereafter, when the reverse magnetic field is enhanced and a reverse magnetic field of H5 = -16 kOe is applied, the reverse magnetic domains 16 expand throughout the crystal grains 11, and the magnetization reversal of the rare-earth cobalt permanent magnet is completed. Figure 3 The values of the reverse magnetic fields H1 to H5 shown in

[0034] are exemplary, and the values of the reverse magnetic fields H1 to H5 may be different from the above values in the present embodiment.

[0035] <Method for preparing a rare-earth cobalt permanent magnet>

[0036] Next, the method for preparing a rare-earth cobalt permanent magnet according to the present embodiment will be described.

[0037] The method for preparing a rare-earth cobalt permanent magnet according to the present embodiment includes:

[0038] Step (I): Prepare an alloy that contains 24% to 26% by mass of rare earth element R containing Sm, 25% to 27% by mass of Fe, 4.0% to 7.0% by mass of Cu, 2.0% to 3.5% by mass of Zr, and the balance Co and inevitable impurities (R is any one of a combination of Sm and Nd (where 0 < Nd ≤ 25% by mass and the balance is Sm), a combination of Sm and Pr (where 0 < Pr ≤ 25% by mass and the balance is Sm), or a combination of Sm, Nd, and Pr (where 0 < Nd + Pr ≤ 25% by mass and the balance is Sm));

[0039] Step (II): Crush the alloy into powder;

[0040] Step (III): Mold the powder into a shaped body;

[0041] Step (IV): Sinter the shaped body into a sintered body by heating the shaped body at 1190 °C to 1225 °C for 0.5 hour to 3.0 hours;

[0042] Solution heat treatment step (V): Heat the sintered body at 1120 °C to 1180 °C for 20 hours to 100 hours;

[0043] Rapid cooling step (VI): After the solution heat treatment step (V), cool the temperature at a cooling rate of at least 60 °C / minute from at least the solution heat treatment temperature to 600 °C; and

[0044] Aging treatment step (VII): Form a cell phase of a crystal phase containing a Th2Zn 17 structure and a cell wall of a crystal phase containing an RCo5 structure surrounding the cell phase.

[0045] The concentration of R in the cell wall is not less than 25 atomic% higher than the concentration of R in the cell phase.

[0046] According to the method for preparing a rare earth cobalt permanent magnet of the present embodiment described above, a rare earth cobalt permanent magnet having excellent magnetic properties (especially a high squareness ratio) can be prepared. Referring to Figure 4 the flowchart shown below, each step of the method for preparing a rare earth cobalt permanent magnet according to the present embodiment will be described.

[0047] First, an alloy is prepared, which contains: 24% to 26% by mass of rare earth element R containing Sm, 25% to 27% by mass of Fe, 4.0% to 7.0% by mass of Cu, 2.0% to 3.5% by mass of Zr, and the balance Co and inevitable impurities (Step S1: Step (I)). Herein, the rare earth element R is any one of a combination of Sm and Nd (where 0 < Nd ≤ 25% by mass and the balance is Sm), a combination of Sm and Pr (where 0 < Pr ≤ 25% by mass and the balance is Sm), or a combination of Sm, Nd, and Pr (where 0 < Nd + Pr ≤ 25% by mass and the balance is Sm). There is no particular limitation on the method for preparing the alloy. The alloy can be prepared by obtaining a commercially available alloy having a desired composition or by mixing each element to obtain a desired composition. Specific examples of mixing each element will be described below, but the present disclosure is not limited to this method.

[0048] First, intermediate alloys such as Fe, Cu, Zr, Co, and rare earth element R containing Sm are prepared as source materials. The rare earth element R is any one of a combination of Sm and Nd, a combination of Sm and Pr, or a combination of Sm, Nd, and Pr. Here, it is preferable to select an intermediate alloy having a composition with a eutectic temperature, because this helps to obtain an alloy having a uniform composition. Additionally, FeZr or CuZr can be selected as the intermediate alloy. In one example, FeZr of about Fe 80% / Zr 20% is suitable. Additionally, in one example, CuZr of about Cu 50% / Zr 50% is suitable.

[0049] These source materials are mixed to obtain a desired composition. Then the compound is placed in a crucible such as Al and melted by a high-frequency melting furnace in a vacuum of not more than 1×10 -2 Torr or in an inert gas atmosphere. Thus, a uniform alloy is obtained. The present disclosure may also include a step of casting the molten alloy with a mold to obtain an alloy ingot. In another method, the molten alloy can be dropped onto a copper roll to fabricate an alloy sheet having a thickness of about 1 mm (strip casting technique).

[0050] In the case of obtaining an alloy ingot by casting, it is preferable to perform Step (VIII) before Step (II) described later, and subject the alloy ingot to heat treatment at its solution heat treatment temperature for 1 hour to 20 hours. Step (VIII) can make the composition more uniform. The solution heat treatment temperature of the alloy ingot can be appropriately adjusted according to the composition of the alloy, etc.

[0051] Next, the alloy is crushed into powder (Step S2: Step (II)). The method of crushing the alloy is not particularly limited, and any method can be selected from known methods. In one example of a suitable method, first, the alloy ingot or alloy sheet is roughly crushed to a size of about 100 μm to 500 μm by a known crusher, and then the roughly crushed alloy is finely crushed using a ball mill, a jet mill, or the like. The average particle size of the powder is not particularly limited. However, in order to shorten the sintering duration of the sintering step described later and prepare a uniform permanent magnet, the average particle size of the powder is preferably 1 μm to 10 μm, or preferably about 6 μm.

[0052] Next, the obtained powder is compression-molded into a molded body having a desired shape (Step S3: Step (III)). In the present disclosure, in order to improve the magnetic properties by aligning the crystal orientations of the powder, it is preferable to compression-mold the powder in a constant magnetic field. The relationship between the magnetic field direction and the pressing direction is not particularly limited and can be appropriately selected according to the shape of the product and the like. For example, in the case of manufacturing an annular magnet or a thin plate-shaped magnet, a parallel magnetic field press can be used, in which a magnetic field is applied in a direction parallel to the pressing direction. At the same time, in order to obtain excellent magnetic properties, a vertical magnetic field press in which a magnetic field is applied perpendicular to the pressing direction is preferable.

[0053] There is no particular limitation on the magnitude of the magnetic field. For example, depending on the intended use of the product and the like, the magnetic field may be not greater than 15 kOe or may be not less than 15 kOe. In particular, in order to obtain excellent magnetic properties, it is preferable to compression-mold the powder in a magnetic field of not less than 15 kOe. The pressure applied in the compression molding can be appropriately adjusted according to the size, shape, etc. of the product. In one example, the pressure can be set to 0.5 ton / cm 2 to 2.0 ton / cm 2 . In other words, in the method for preparing a rare earth cobalt permanent magnet according to the present disclosure, from the viewpoint of magnetic properties, it is particularly preferable to compression-mold the powder in a magnetic field of not less than 15 kOe and at a pressure of 0.5 ton / cm 2 to 2.0 ton / cm 2 .

[0054] Next, the green compact is sintered into a sintered body by heating the green compact at 1190° C. to 1225° C. for 0.5 hour to 3.0 hours (step S4: step (IV)). Sintering the green compact at a temperature not lower than 1190° C. for not less than 0.5 hour results in a sufficiently dense sintered body. Additionally, heating the green compact at a temperature not higher than 1225° C. for not more than 3.0 hours prevents evaporation of rare earth elements, especially Sm, and a permanent magnet with excellent magnetic properties can be prepared. In the present disclosure, the sintering temperature is preferably 1195° C. to 1220° C., and the sintering duration is preferably 40 minutes to 2 hours. From the viewpoint of suppressing oxidation, the sintering step is preferably carried out in a vacuum of not more than 1×10 -2 Torr or in an inert gas atmosphere.

[0055] Next, a solution heat treatment of heating the sintered body at 1120° C. to 1180° C. for 20 hours to 100 hours is performed (step S5: step (V)). Heating the sintered body at a temperature not lower than 1120° C. can make the composition of the green compact uniform and can form the 1-7 phase, which is a precursor to the primary crystal phase in the aging treatment step (step S7: step (VII)) for the Th2Zn 17 structured crystal phase described later. At the same time, if the heating temperature exceeds 1180° C., it is difficult to form the 1-7 phase, and rare earth elements may further evaporate. The optimal solution heat treatment temperature of the sintered body varies according to the composition of the sintered body, so the solution heat treatment temperature is preferably adjusted appropriately within the above temperature range.

[0056] To sufficiently form the 1-7 phase and make each element uniform, the solution heat treatment time is not less than 20 hours. Additionally, to suppress evaporation of rare earth elements, especially Sm, the duration of the solution heat treatment is preferably not more than 100 hours. From the viewpoint of suppressing oxidation, the above solution heat treatment is preferably carried out in a vacuum of not more than 1×10 -2 Torr or in an inert gas atmosphere.

[0057] From the viewpoint of improving productivity, it is preferable to continuously carry out the sintering step (IV) and the solution heat treatment process (V). In other words, it is preferable to heat the green compact at 1190° C. to 1225° C. for 0.5 hour to 3.0 hours, and then perform the solution heat treatment for 20 hours to 100 hours by adjusting the temperature to 1120° C. to 1180° C. without reducing the temperature to room temperature.

[0058] Next, in the cooling process after the solution heat treatment step (V), the temperature is lowered from the solution heat treatment temperature to 600 °C at a cooling rate of at least 60 °C / minute (step S6). This rapid cooling is carried out to maintain the crystal structure of the 1-7 phase obtained in the solution heat treatment step (V). If the rapid cooling is insufficient, the 1-7 phase may change. In particular, reducing the time taken to lower the temperature from the solution heat treatment temperature to 600 °C makes it possible to maintain the crystal structure of the 1-7 phase. A cooling rate of at least 60 °C / minute is sufficient, and the cooling rate is preferably at least 70 °C / minute, more preferably at least 80 °C / minute. At the same time, in one example, the upper limit of the cooling rate is preferably not greater than 250 °C / minute, although it depends on the shape of the formed body.

[0059] Next, the formed body that has been rapidly cooled is subjected to aging treatment to form the 2-17 phase and the 1-5 phase (step S7: step (VII)). There is no particular limitation on the aging temperature. In order to obtain a rare earth cobalt permanent magnet having the 2-17 phase as the primary crystal phase and having a uniform 2-17 phase and 1-5 phase, it is preferable to hold the formed body at a temperature of 700 °C to 900 °C for 2 hours to 20 hours, and then set the cooling rate to not greater than 2 °C / minute during the period when the temperature is lowered to at least 400 °C. Holding the formed body at a temperature of 700 °C to 900 °C for 2 hours to 20 hours can make the 2-17 phase and the 1-5 phase uniform respectively. In particular, it is preferable to carry out the aging treatment in the temperature range of 800 °C to 850 °C. In order to obtain satisfactory magnetic properties, the cooling rate is preferably not greater than 2 °C / minute, or more preferably not greater than 0.5 °C / minute. If the cooling rate is too high, the elements cannot aggregate in the 2-17 phase and the 1-5 phase, and satisfactory magnetic properties cannot be obtained.

[0060] The preparation method as described above makes it possible to prepare a rare earth cobalt permanent magnet having excellent magnetic properties (especially a high squareness ratio).

[0061] <Observation of Structure and Observation of Magnetic Domains>

[0062] Next, a method for observing the microstructure of the rare earth cobalt permanent magnet according to the present disclosure using TEM will be described. The sample that has been subjected to aging treatment in step S7 is cut into an appropriate shape, and a thin slice is cut out from the sample along the easy magnetization axis. At this time, a surface perpendicular to the easy magnetization axis appears. This thinly cut surface includes a direction perpendicular to the easy magnetization axis. The surface is irradiated with an electron beam, and an image formed by the transmitted electron beam is observed.

[0063] Next, a method of observing magnetic domains in a rare earth cobalt permanent magnet according to the present disclosure using a Kerr effect microscope will be described. A Kerr effect microscope is a device that observes magnetic domains using a microscope through the magneto-optical Kerr effect. The magneto-optical Kerr effect is a phenomenon in which when linearly polarized light is incident on a magnetic material, the reflected light becomes elliptically polarized light, and the polarization direction rotates from the linear direction of the incident light. Three types of magneto-optical Kerr effects are known: the "polar Kerr effect" in which light is incident in a direction orthogonal to the magnetization direction of the magnetic material; the "longitudinal Kerr effect" in which light is incident in a direction parallel to the magnetization direction; and the "transverse Kerr effect" in which light is incident in a direction perpendicular to the magnetization direction within the incident plane. In the present disclosure, magnetic domains are observed by using the "longitudinal Kerr effect". The results of observing the magnetic domains are as Figure 2 shown.

[0064] <Device>

[0065] The present disclosure can further provide a device including the rare earth cobalt permanent magnet according to the above-described present disclosure. Specific examples of such a device include a clock, a motor, various measuring instruments, a communication device, a computer terminal, a speaker, a videodisc, and a sensor. Even in a high-temperature environment, the magnetic force of the rare earth cobalt permanent magnet according to the present invention does not deteriorate. Therefore, the rare earth cobalt permanent magnet according to the present disclosure can be applied to an angle sensor, an ignition coil, a drive motor of a hybrid electric vehicle (HEV), etc. to be provided in a vehicle engine compartment.

[0066] [Examples]

[0067] The present invention will be specifically described below by way of examples and comparative examples. The following description is not intended to limit the present disclosure.

[0068] <Examples 1 to 3>

[0069] The intermediate alloy of Fe8*% / Zr20% and each raw material were adjusted to achieve the compositions of Examples 1 to 3 in Table 1, and then the intermediate alloy and the raw materials were melted and cast by a high-frequency furnace to obtain alloy ingots. Then, the obtained intermediate alloy was coarsely pulverized in an inert gas to achieve an average particle size of 100 μm to 500 μm. Thereafter, the coarsely pulverized alloy was finely pulverized in an inert gas using a ball mill to achieve an average particle size of 6 μm, thereby obtaining powder. The powder was pressed under a pressure of 1 ton / cm 2 perpendicular to the applied magnetic field in a magnetic field of 15 kOe, thereby obtaining a compact.

[0070] The formed body was sintered at 1210 °C for 1.0 hour in a vacuum not greater than 10 Pa. Then, the formed body was solution heat-treated at 1150 °C for 30 hours and rapidly cooled from 1000 °C to 600 °C at a cooling rate of 80 °C / minute. After rapid cooling, the formed body was held at 850 °C for 12 hours, and then age-treated under the condition that the formed body was gradually cooled to 350 °C at a cooling rate of 0.5 °C / minute. Thus, the rare earth cobalt permanent magnets of each of Examples 1 to 3 were obtained.

[0071] <Comparative Example 1 and Comparative Example 2>

[0072] Except for adjusting each raw material to obtain the compositions in Table 1, the rare earth cobalt permanent magnets of each of Comparative Example 1 and Comparative Example 2 were prepared by a method similar to that of Example 1 above. Comparative Example 1 provided samples with a smaller Fe content than Examples 1 to 3. Comparative Example 2 provided samples with a larger Fe content than Examples 1 to 3.

[0073] <Examples 4 to 9>

[0074] Except for adjusting each raw material to obtain the compositions in Table 2 and except for the sintering conditions and solution heat-treatment conditions, the rare earth cobalt permanent magnets of each of Examples 4 to 9 were prepared by a method similar to that of Example 1 above.

[0075] In Examples 4 to 6, the formed body was sintered at 1190 °C for 3.0 hours in a vacuum not greater than 10 Pa. Then, the formed body was solution heat-treated at 1180 °C for 20 hours, 40 hours, and 60 hours, respectively, and rapidly cooled from 1000 °C to 600 °C at a cooling rate of 80 °C / minute. After rapid cooling, the formed body was held at 850 °C for 10 hours, and then age-treated under the condition that the formed body was gradually cooled to 350 °C at a cooling rate of 0.5 °C / minute. Thus, the rare earth cobalt permanent magnets of each of Examples 4 to 6 were obtained.

[0076] In Examples 7 to 9, the green compact was sintered at 1225 °C for 0.5 hour in a vacuum of not more than 10 Pa. Then, the green compact was solution heat-treated at 1120 °C for 20 hours, 50 hours, and 100 hours, respectively, and rapidly cooled from 1000 °C to 600 °C at a cooling rate of 80 °C / minute. After rapid cooling, the green compact was held at 850 °C for 10 hours, and then age-treated under the condition of gradually cooling the green compact to 350 °C at a cooling rate of 0.5 °C / minute. Thus, a rare earth-cobalt permanent magnet of each of Examples 7 to 9 was obtained. Here, in Examples 4 to 6, Sm and Pr were used as the rare earth element R, and in Examples 7 to 9, Sm and Nd were used as the rare earth element R. The solution heat-treatment temperature in Examples 7 to 9 was lower than that in Examples 4 to 6.

[0077] <Comparative Examples 3 to 6>

[0078] Except for adjusting each raw material to obtain the compositions in Table 2 and except for the sintering conditions and solution heat-treatment conditions, rare earth-cobalt permanent magnets of each of Comparative Examples 3 to 6 were prepared by a method similar to that of Example 1 above.

[0079] In Comparative Examples 3 and 4, the green compact was sintered at 1190 °C for 3.0 hours in a vacuum of not more than 10 Pa. Then, the green compact was solution heat-treated at 1180 °C for 5 hours and 10 hours, respectively, and rapidly cooled from 1000 °C to 600 °C at a cooling rate of 80 °C / minute. After rapid cooling, the green compact was held at 850 °C for 10 hours, and then age-treated under the condition of gradually cooling the green compact to 350 °C at a cooling rate of 0.5 °C / minute. Thus, a rare earth-cobalt permanent magnet of each of Comparative Examples 3 and 4 was obtained. Each of Comparative Examples 3 and 4 provided a sample obtained with a shorter solution heat-treatment duration than that of Examples 4 to 6.

[0080] In Comparative Examples 5 and 6, the green compact was sintered at 1225 °C for 0.5 hour in a vacuum of not more than 10 Pa. Then, the green compact was solution heat-treated at 1120 °C for 5 hours and 10 hours, respectively, and rapidly cooled from 1000 °C to 600 °C at a cooling rate of 80 °C / minute. After rapid cooling, the green compact was held at 850 °C for 10 hours, and then age-treated under the condition of gradually cooling the green compact to 350 °C at a cooling rate of 0.5 °C / minute. Thus, a rare earth-cobalt permanent magnet of each of Comparative Examples 5 and 6 was obtained. Each of Comparative Examples 5 and 6 provided a sample obtained with a shorter solution heat-treatment duration than that of Examples 7 to 9.

[0081] <Examples 10 to 15>

[0082] Except for adjusting each raw material to obtain the compositions in Table 3, rare earth cobalt permanent magnets of each of Examples 10 to 15 were prepared by a method similar to that of Example 1 above. In Examples 10 and 11, Sm and Nd were used as the rare earth element R. In Examples 12 to 13, Sm and Pr were used as the rare earth element R. In Examples 14 to 15, Sm, Nd, and Pr were used as the rare earth element R.

[0083] <Comparative Examples 7 and 8>

[0084] Except for adjusting each raw material to obtain the compositions in Table 3, rare earth cobalt permanent magnets of each of Comparative Examples 7 and 8 were prepared by a method similar to that of Example 1 above. Comparative Example 7 provided samples with a smaller content of the rare earth element R than Examples 10 to 15. Comparative Example 8 provided samples with a larger content of the rare earth element R than Examples 10 to 15.

[0085] <Examples 16 to 18>

[0086] Except for adjusting each raw material to obtain the compositions in Table 4, rare earth cobalt permanent magnets of each of Examples 16 to 18 were prepared by a method similar to that of Example 1 above. In Examples 16 to 18, the ratios of Nd, Pr, or (Nd + Pr) relative to the rare earth element R were varied. Specifically, in Example 16, the ratio of Nd relative to the rare earth element R was (6 / (18 + 6))×100 = 25.0 mass%. In Example 17, the ratio of Pr relative to the rare earth element R was (6 / (19 + 6))×100 = 24.0 mass%. In Example 18, the ratio of (Nd + Pr) relative to the rare earth element R was ((3.5 + 3) / (19.5 + 3.5 + 3))×100 = 25.0 mass%.

[0087] <Comparative Examples 9 and 10>

[0088] Except for adjusting each raw material to obtain the compositions in Table 4, rare earth cobalt permanent magnets of each of Comparative Example 9 and Comparative Example 10 were prepared by a method similar to that of Example 1 above. In Comparative Example 9, the ratio of Nd to rare earth element R was (7 / (17 + 7))×100 = 29.2 mass%. In Comparative Example 10, the ratio of (Nd + Pr) to rare earth element R was ((3.5 + 3.5) / (19.0 + 3.5 + 3.5))×100 = 26.9 mass%. In Comparative Example 9, the ratio of Nd to rare earth element R was 29.2 mass%, and compared with Example 16, Comparative Example 9 provided a sample with a higher ratio of Nd to rare earth element R. In Comparative Example 10, the ratio of (Nd + Pr) to rare earth element R was 26.9 mass%, and compared with Example 18, Comparative Example 10 provided a sample with a higher ratio of (Nd + Pr) to rare earth element R.

[0089] <Evaluation of Rare Earth Cobalt Permanent Magnets>

[0090] The magnetic properties of the rare earth cobalt permanent magnets obtained in the above Examples and Comparative Examples were measured using the shaped bodies. The magnetic properties were measured using a B-H tracer. The obtained magnetic properties, namely the maximum magnetic energy product (BH)m, the coercivity (Hcj), and the rectangular ratio represented by the ratio of the magnetic field (Hk) to the coercivity (Hk / Hcj) are shown in Tables 1 to 4.

[0091] In addition, magnetic domain observations were performed on samples that were manufactured simultaneously with the rare earth cobalt permanent magnets according to the above Examples and Comparative Examples and had the same composition as the rare earth cobalt permanent magnets. The magnetic domains of each treated sample were observed, and the composition of each treated sample was analyzed. The magnetic domains were observed using the Kerr effect microscope described above.

[0092] Using energy dispersive X-ray spectroscopy (EDX), the compositions of the cell phase (2-17 phase) and the cell wall (1-5 phase) of each rare earth cobalt permanent magnet of the above Examples and Comparative Examples were determined. Then, the increase rate of the concentration of Sm in the cell wall (1-5 phase) relative to the concentration of Sm in the cell phase (2-17 phase) was obtained. Specifically, the increase rate of the Sm concentration in the cell wall (1-5 phase) was obtained by the following expression, where D sm1 is the concentration of Sm in the cell phase (2-17 phase), and D sm2 is the concentration of Sm in the cell wall (1-5 phase):

[0093] ((D sm2 - D sm1 ) / D sm1 )×100 (at%).

[0094] In addition, obtain the increase rate of the concentration of Nd, Pr, or (Nd + Pr) in the cell wall (phases 1 - 5) relative to the concentration of Nd, Pr, or (Nd + Pr) in the cell phase (phases 2 - 17). Specifically, the increase rate of the concentration of Nd, Pr, or (Nd + Pr) in the cell wall (phases 1 - 5) is obtained through the following expression, where D NP1 is the concentration of Nd, Pr, or (Nd + Pr) in the cell phase (phases 2 - 17), and D NP2 is the concentration of Nd, Pr, or (Nd + Pr) in the cell wall (phases 1 - 5):

[0095] ((D NP2 - D NP1 ) / D NP1 ) × 100 (at%).

[0096] In the examples and comparative examples, there are three forms of the combination of rare earth elements R: (1) the combination of Sm and Nd, (2) the combination of Sm and Pr, and (3) the combination of Sm, Nd, and Pr.

[0097] [Table 1]

[0098]

[0099] [Table 2]

[0100]

[0101] [Table 3]

[0102]

[0103] [Table 4]

[0104]

[0105] <Summary of Results: Table 1>

[0106] The results summarized in Table 1 show the differences in the characteristics of the rare earth cobalt permanent magnets that occur when the composition of Fe is different. As shown in Table 1, in Examples 1 to 3, the content of Fe is 25.0 mass% to 27.0 mass%. Comparative Example 1 provides a sample having a lower Fe content than Examples 1 to 3, with an Fe content of 23.0 mass%. Comparative Example 2 provides a sample having a higher Fe content than Examples 1 to 3, and the Fe content is 28.0 mass%.

[0107] In the rare earth cobalt permanent magnets of Examples 1 to 3, the density is not less than 8.25 g / cm 3 ³, and the maximum energy product (BH)m is not less than 260 kJ / m 3, the coercivity Hcj is not less than 1675 A / m, and the squareness ratio Hk / Hcj is not less than 67%.

[0108] In the rare earth cobalt permanent magnets of Examples 1 to 3, the compositional changes of Sm and the compositional changes of Nd in the rare earth cobalt permanent magnets showed similar trends. The Sm concentration in the cell wall (1-5 phase) was not less than 31 at% higher than the Sm concentration in the cell phase (2-17 phase). Additionally, the Nd concentration in the cell wall (1-5 phase) was not less than 32 at% higher than the Nd concentration in the cell phase (2-17 phase).

[0109] The results of observing the magnetic domains using a Kerr effect microscope showed that in each of the rare earth cobalt permanent magnets of Examples 1 to 3, reverse magnetic domains appeared in the grain boundaries and then began to expand into the grains, as Figure 3 shown in the schematic diagram. Additionally, a process was observed in which different reverse magnetic domains emerged from the interior of the grains and ultimately expanded throughout the grains.

[0110] Meanwhile, in Comparative Example 1, the amount of Fe was less than that in Examples 1 to 3, and the squareness ratio Hk / Hcj was 52%, and the value of the squareness ratio Hk / Hcj was less than that in Examples 1 to 3. In Comparative Example 2, the amount of Fe was greater than that in Examples 1 to 3, and the squareness ratio Hk / Hcj was 61%, and the value of the squareness ratio Hk / Hcj was less than that in Examples 1 to 3.

[0111] In Comparative Example 1 and Comparative Example 2, the compositional changes of Sm and the compositional changes of Nd in the rare earth cobalt permanent magnets did not show similar trends. Additionally, in Comparative Example 1 and Comparative Example 2, the increase rate of the Sm concentration in the cell wall (1-5 phase) and the increase rate of the Nd concentration in the cell wall (1-5 phase) never reached 25 at% or exceeded 25 at% simultaneously.

[0112] The results of observing the magnetic domains using a Kerr effect microscope showed that in each of the rare earth cobalt permanent magnets of Comparative Example 1 and Comparative Example 2, reverse magnetic domains began to appear within the grains, then appeared in the grain boundaries, and finally expanded throughout the grains. The reverse magnetic domains exhibited behaviors different from those of Examples 1 to 3.

[0113] <Summary of Results: Table 2>

[0114] The results summarized in Table 2 show the differences in the properties of rare earth cobalt permanent magnets that occur when the types of rare earth elements and the solution heat treatment conditions are different. In Examples 4 to 6 shown in Table 2, the rare earth cobalt permanent magnet contains Sm and Pr as rare earth elements, the solution heat treatment temperature is 1180 °C, and the solution heat treatment durations are 20 hours, 40 hours, and 60 hours, respectively. Comparative Example 3 and Comparative Example 4 each provide samples obtained by solution heat treatment durations shorter than those of Examples 4 to 6, and the solution heat treatment times are 5 hours and 10 hours, respectively.

[0115] In Examples 7 to 9, the rare earth cobalt permanent magnet contains Sm and Nd as rare earth elements, the solution heat treatment temperature is 1120 °C, and the solution heat treatment durations are 20 hours, 50 hours, and 100 hours, respectively. Comparative Example 5 and Comparative Example 6 each provide samples obtained by solution heat treatment durations shorter than those of Examples 7 to 9, and the solution heat treatment times are 5 hours and 10 hours, respectively.

[0116] In the rare earth cobalt permanent magnets of Examples 4 to 9, the density is not less than 8.25 g / cm 3 、the maximum energy product (BH)m is not less than 255 kJ / m 3 、the magnetic coercivity Hcj is not less than 1613 A / m, and the squareness ratio Hk / Hcj is not less than 63%.

[0117] In the rare earth cobalt permanent magnets of Examples 4 to 9, the compositional changes of Sm and the compositional changes of Pr or Nd in the rare earth cobalt permanent magnet show similar trends. The Sm concentration in the cell wall (1-5 phase) is not less than 25 at% higher than the Sm concentration in the cell phase (2-17 phase). In addition, the Pr or Nd concentration in the cell wall (1-5 phase) is not less than 26 at% higher than the Pr or Nd concentration in the cell phase (2-17 phase).

[0118] The results of observing the magnetic domains using a Kerr effect microscope show that in each of the rare earth cobalt permanent magnets of Examples 4 to 9, reverse magnetic domains appear at the grain boundaries and then begin to expand into the grains, as shown in the schematic diagram of Figure 3 In addition, a process was observed in which different reverse magnetic domains emerged from within the grains and ultimately expanded throughout the grains.

[0119] Meanwhile, in Comparative Examples 3 and 4, where the solution heat treatment duration was less than that of Examples 4 to 6, the rectangular ratios Hk / Hcj were 45% and 62% respectively, and the values of the rectangular ratio Hk / Hcj were less than those in Examples 4 to 6. In Comparative Examples 5 and 6, where the solution heat treatment duration was less than that of Examples 7 to 9, the rectangular ratios Hk / Hcj were 50% and 60% respectively, and the values of the rectangular ratio Hk / Hcj were less than those in Examples 7 to 9.

[0120] In Comparative Examples 3 to 6, neither the compositional change of Sm nor the compositional change of Pr or Nd in the rare earth cobalt permanent magnet showed a similar trend. Additionally, in Comparative Examples 3 and 4, the increase rate of the concentration of Sm in the cell wall (1-5 phase) and the increase rate of the concentration of Pr in the cell wall (1-5 phase) never reached 25 at% or exceeded 25 at% simultaneously. Additionally, in Comparative Examples 5 and 6, the increase rate of the concentration of Sm in the cell wall (1-5 phase) and the increase rate of the concentration of Nd in the cell wall (1-5 phase) never reached 25 at% or exceeded 25 at% simultaneously.

[0121] The results of observing magnetic domains using a Kerr effect microscope showed that in each of the rare earth cobalt permanent magnets of Comparative Examples 3 to 6, reverse magnetic domains began to appear within the grains, then appeared at the grain boundaries, and finally spread throughout the grains. The reverse magnetic domains exhibited behaviors different from those of Examples 4 to 9.

[0122] <Summary of Results: Table 3>

[0123] The results summarized in Table 3 show the characteristic differences of rare earth cobalt permanent magnets that occur when the composition and type of rare earth element R are different. As shown in Table 3, in Examples 10 to 15, the content of rare earth element R was 24.0 mass% to 26.0 mass%. In Examples 10 and 11, the rare earth cobalt permanent magnet contained Sm and Nd as rare earth element R. In Examples 12 and 13, the rare earth cobalt permanent magnet contained Sm and Pr as rare earth element R. In Examples 14 and 15, the rare earth cobalt permanent magnet contained Sm, Nd, and Pr as rare earth element R. Comparative Example 7 provided a sample with a content of rare earth element R less than that of Examples 10 to 15, and the content of rare earth element R was 23.0 mass%. Comparative Example 8 provided a sample with a content of rare earth element R greater than that of Examples 10 to 15, and the content of rare earth element R was 27.0 mass%.

[0124] In the rare earth cobalt permanent magnets of Examples 10 to 15, the density was not less than 8.27 g / cm 3 、the maximum energy product (BH)m was not less than 260 kJ / m 3, the coercivity Hcj is not less than 1634 A / m, and the squareness ratio Hk / Hcj is not less than 67%.

[0125] In the rare earth cobalt permanent magnets of Examples 10 to 15, the compositional changes of Sm, Nd, and Pr in the rare earth cobalt permanent magnets showed similar trends. The Sm concentration in the cell wall (1-5 phase) was not less than 28 at% higher than the Sm concentration in the cell phase (2-17 phase). Additionally, the concentration of Nd, Pr, or (Nd+Pr) in the cell wall (1-5 phase) was not less than 25 at% higher than the concentration of Nd, Pr, or (Nd+Pr) in the cell phase (2-17 phase).

[0126] The results of observing the magnetic domains using a Kerr effect microscope showed that in each of the rare earth cobalt permanent magnets of Examples 10 to 15, reverse magnetic domains appeared at the grain boundaries and then began to expand into the grains, as Figure 3 shown in the schematic diagram. Additionally, a process was observed in which different reverse magnetic domains emerged from within the grains and eventually expanded throughout the grains.

[0127] Meanwhile, in Comparative Example 7, where the content of the rare earth element R was less than that of Examples 10 to 15, the squareness ratio Hk / Hcj was 61%, and the value of the squareness ratio Hk / Hcj was less than that of Examples 10 to 15. Meanwhile, in Comparative Example 8, where the content of the rare earth element R was greater than that of Examples 10 to 15, the squareness ratio Hk / Hcj was 48%, and the value of the squareness ratio Hk / Hcj was less than that of Examples 10 to 15.

[0128] In Comparative Example 7 and Comparative Example 8, the compositional changes of Sm, Nd, and Pr in the rare earth cobalt permanent magnets did not show similar trends. Additionally, in Comparative Example 7 and Comparative Example 8, the increase rate of the Sm concentration in the cell wall (1-5 phase) and the increase rate of the concentration of Nd, Pr, or (Nd+Pr) in the cell wall (1-5 phase) never reached 25 at% or exceeded 25 at% simultaneously.

[0129] The results of observing the magnetic domains using a Kerr effect microscope showed that in each of the rare earth cobalt permanent magnets of Comparative Example 7 and Comparative Example 8, reverse magnetic domains began to appear within the grains, then appeared at the grain boundaries, and finally expanded throughout the grains. The reverse magnetic domains exhibited behaviors different from those of Examples 10 to 15.

[0130] <Summary of Results: Table 4>

[0131] The results summarized in Table 4 show the characteristic differences of rare earth cobalt permanent magnets when the compositions of Nd, Pr, or (Nd + Pr) used as rare earth elements are different. As shown in Table 4, in Examples 16 to 18, the ratio of Nd, Pr, or (Nd + Pr) is 24.0 mass% to 25.0 mass%. In Comparative Example 9, the ratio of Nd to rare earth element R is 29.2 mass%. In Comparative Example 10, the ratio of (Nd + Pr) to rare earth element R is 26.9 mass%.

[0132] In the rare earth cobalt permanent magnets of Examples 16 to 18, the density is not less than 8.28 g / cm 3 、 the maximum energy product (BH)m is not less than 260 kJ / m 3 、 the coercivity Hcj is not less than 1606 A / m, and the squareness ratio Hk / Hcj is not less than 63%.

[0133] In the rare earth cobalt permanent magnets of Examples 16 to 18, the compositional changes of Sm, Nd, and Pr in the rare earth cobalt permanent magnets show similar trends. The Sm concentration in the cell wall (1-5 phase) is not less than 27 at% higher than the Sm concentration in the cell phase (2-17 phase). The concentration of Nd, Pr, or (Nd + Pr) in the cell wall (1-5 phase) is not less than 28 at% higher than the concentration of Nd, Pr, or (Nd + Pr) in the cell phase (2-17 phase).

[0134] The results of observing the magnetic domains using a Kerr effect microscope show that in each rare earth cobalt permanent magnet of Examples 16 to 18, reverse magnetic domains appear at the grain boundaries and then begin to expand into the grains, as shown in the schematic diagram of Figure 3 In addition, a process was observed in which different reverse magnetic domains emerged from the interior of the grains and eventually expanded throughout the grains.

[0135] At the same time, in Comparative Example 9, the squareness ratio Hk / Hcj is 60%, and the value of the squareness ratio Hk / Hcj is lower than that in Examples 16 to 18. In Comparative Example 10, the squareness ratio Hk / Hcj is 50%, and the value of the squareness ratio Hk / Hcj is lower than that in Examples 16 to 18.

[0136] In Comparative Example 9 and Comparative Example 10, the compositional changes of Sm, Nd, and Pr in the rare earth cobalt permanent magnets do not show similar trends. In addition, in Comparative Example 9 and Comparative Example 10, the increase rate of the Sm concentration in the cell wall (1-5 phase) and the increase rate of the concentration of Nd or (Nd + Pr) in the cell wall (1-5 phase) never reach 25 at% or exceed 25 at% simultaneously.

[0137] The results of observing magnetic domains using a Kerr effect microscope show that in each of the rare earth cobalt permanent magnets of Comparative Example 9 and Comparative Example 10, reverse magnetic domains began to appear within the grains, then appeared at the grain boundaries, and finally spread throughout the grains. The reverse magnetic domains exhibited different behaviors from those of Examples 10 to 15.

[0138] From the present disclosure thus described, it is apparent that the embodiments of the present disclosure can vary in many ways. Such variations will not be regarded as a departure from the spirit and scope of the present disclosure, and all such modifications that are obvious to those skilled in the art are intended to be included within the scope of the following claims.

Claims

1. A rare earth cobalt permanent magnet, comprising: 24% to 26% by mass of a rare earth element R containing Sm; 25% to 27% by mass of Fe; 4.0% to 7.0% by mass of Cu; 2.0% to 3.5% by mass of Zr; and Co and inevitable impurities as the balance, wherein R is any one of the following combinations: A combination of Sm and Nd, where 0 < Nd ≤ 25% by mass and the balance is Sm; A combination of Sm and Pr, where 0 < Pr ≤ 25% by mass and the balance is Sm; Or a combination of Sm, Nd, and Pr, where 0 < Nd + Pr ≤ 25% by mass and the balance is Sm, The rare earth cobalt permanent magnet includes a unit cell phase of a crystal phase containing a Th2Zn 17 structure and a unit cell wall of a crystal phase containing an RCo5 structure surrounding the unit cell phase, and The concentration of R in the cell wall is at least 25 atomic% higher than the concentration of R in the cell phase.

2. The rare earth cobalt permanent magnet according to claim 1, wherein Cu is 4.2% to 4.7% by mass, and Zr is 2.1% to 2.5% by mass.

3. The rare earth cobalt permanent magnet according to claim 1 or 2, wherein the density of the rare earth cobalt permanent magnet is 8.20 g / cm 3 to 8.45 g / cm 3 .

4. The rare earth cobalt permanent magnet according to claim 1 or 2, wherein the density of the rare earth cobalt permanent magnet is 8.25 g / cm 3 to 8.40 g / cm 3 .

5. The rare earth cobalt permanent magnet according to claim 1 or 2, wherein, In the rare earth cobalt permanent magnet, Sm and at least one of Nd and Pr show a similar trend in terms of the compositional change from the cell phase to the cell wall.

6. The rare earth cobalt permanent magnet according to claim 1 or 2, wherein when a reverse magnetic field is applied to the rare earth cobalt permanent magnet, the reverse magnetic domains that appear in the grain boundaries expand into the grains, and then another reverse magnetic domain appears in the grains and expands throughout the grains.

7. The rare earth cobalt permanent magnet according to claim 1 or 2, wherein the rectangular ratio of the rare earth cobalt permanent magnet is not less than 63%, and the rectangular ratio is represented by the ratio Hk / Hcj of the magnetic field Hk to the magnetic coercivity Hcj.

8. A method for preparing a rare earth cobalt permanent magnet, the method comprising: Step I, preparing an alloy comprising 24% to 26% by mass of a rare earth element R containing Sm; 25% to 27% by mass of Fe; 4.0% to 7.0% by mass of Cu; 2.0% to 3.5% by mass of Zr; and Co and inevitable impurities as the balance; wherein R is any one of the following combinations: A combination of Sm and Nd, where 0 < Nd ≤ 25% by mass and the balance is Sm; A combination of Sm and Pr, where 0 < Pr ≤ 25% by mass and the balance is Sm; Or a combination of Sm, Nd, and Pr, where 0 < Nd + Pr ≤ 25% by mass and the balance is Sm; Step II, crushing the alloy into powder; Step III, pressing the powder into a compact; Step IV, sintering the compact into a sintered body by heating the compact at 1190°C to 1225°C for 0.5 hour to 3.0 hours; Solution heat treatment step V, heating the sintered body at 1120°C to 1180°C for 30 hours to 100 hours; Rapid cooling step VI, after the solution heat treatment step V, cooling the temperature from at least the solution heat treatment temperature to 600°C at a cooling rate of not less than 60°C / minute; and Aging treatment step VII, forming a unit cell phase of a crystal phase containing a Th2Zn 17 structure and a unit cell wall of a crystal phase containing an RCo5 structure surrounding the unit cell phase, wherein the concentration of R in the unit cell wall is not less than 25 atomic% higher than the concentration of R in the unit cell phase.

9. An apparatus, comprising: The rare earth cobalt permanent magnet according to any one of claims 1 to 7.

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