JP2019207954A - Rare earth permanent magnet - Google Patents

Abstract

To obtain a rare earth permanent magnet having a high residual magnetic flux density and a high magnetic coercive force.SOLUTION: A rare earth permanent magnet contains R and T. The R is a rare earth element essentially comprising Sm, and the T is a single Fe or Fe and Co. The rare earth permanent magnet contains a crystal particle having NdFe-type crystal structure as a main phase. At least one part of the crystal particle is a flat particle having a flat shape. In the case of measuring a frequency distribution of a long diameter in the crystal particle, a means long diameter in the crystal particle of which a cumulative frequency is 10% or more and 90% or less exceeds 300 nm.SELECTED DRAWING: None

Description

  The present invention relates to a rare earth permanent magnet.

  Rare earth magnets are increasing in production year by year due to their high magnetic properties, and are used in various applications such as for various motors, various actuators, and MRI apparatuses.

For example, a magnet material having a main phase of Sm ₅ Fe ₁₇ intermetallic compound described in Patent Document 1 has a very high coercive force at room temperature. Non-Patent Document 1 describes a magnet having a main phase of Sm ₅ Fe ₁₇ intermetallic compound having a density of more than 90% obtained by a discharge plasma sintering method (SPS method). I have a magnetic force.

However, the permanent magnet having the main phase of Sm ₅ Fe ₁₇ intermetallic compound has a drawback that the magnetization is smaller than that of the permanent magnet having the main phase of Nd ₂ Fe ₁₄ B intermetallic compound.

The crystal grains of the permanent magnet material described in Patent Document 2 have a Sm ₅ Fe ₁₇ system as a main component, and the crystal grains are anisotropic flaky crystal grains. However, at present, there is a demand for permanent magnets having even higher magnetic properties.

JP 2008-13396 A Chinese Patent Application No. 1056757979

Materials Science and Engineering 1 (2009) 012032

  The present invention has been made in view of such a situation, and an object thereof is to obtain a rare earth permanent magnet having a high residual magnetic flux density and a high coercive force.

The present invention is a rare earth permanent magnet containing R and T,
R is a rare earth element essential for Sm, T is Fe alone or Fe and Co,
The rare earth permanent magnet is a flat particle that includes crystal particles having an Nd ₅ Fe ₁₇ type crystal structure as a main phase, and at least a part of the crystal particles has a flat shape,
When measuring the frequency distribution of the major axis of the crystal grains, the average major axis of the crystal grains having a cumulative frequency of 10% to 90% is more than 300 nm.

  The rare earth permanent magnet according to the present invention is a rare earth permanent magnet having excellent magnetic characteristics, that is, residual magnetic flux density Br and coercive force HcJ due to the above characteristics.

  In the rare earth permanent magnet according to the present invention, an average aspect ratio of all the crystal grains may be 1.6 or more.

  The rare earth permanent magnet according to the present invention may further contain Pr and / or Nd as R, and the content ratio of Sm with respect to the entire R may be 50 at% or more and 99 at% or less, and the total content of Pr and Nd The ratio may be 1 at% or more and 50 at% or less.

  In the rare earth permanent magnet according to the present invention, an R enriched portion may exist at a grain boundary between the crystal grains, and an area ratio of the R enriched portion in an arbitrary cross section may be 3% or more and 20% or less. .

  The rare earth permanent magnet according to the present invention may further contain C, and the C content may be greater than 0 at% and not greater than 15 at%.

  Embodiments for carrying out the present invention will be described in detail. The present invention is not limited by the contents described in the following embodiments. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

The rare earth permanent magnet according to the present embodiment has crystal grains having an Nd ₅ Fe ₁₇ type crystal structure (space group P6 ₃ / mcm) as a main phase. In the present embodiment, the main phase refers to a portion occupying 70 vol% or more with respect to the entire rare earth permanent magnet.

The rare earth permanent magnet according to the present embodiment is a crystal particle other than the crystal particles having the R ₅ T ₁₇ type crystal structure (hereinafter also referred to as R ₅ T ₁₇ type crystal particles) including the Nd ₅ Fe ₁₇ type crystal structure. May be included as a subphase. For example, crystals such as RT ₂ type crystal structure, RT ₃ type crystal structure, R ₂ T ₇ type crystal structure, RT ₅ type crystal structure, RT ₇ type crystal structure, R ₂ T ₁₇ type crystal structure, RT ₁₂ type crystal structure, etc. Examples thereof include crystal particles having a structure. The crystal structure of the rare earth permanent magnet according to the present embodiment can be confirmed using, for example, an X-ray diffraction method (XRD).

In the rare earth permanent magnet according to the present embodiment, at least a part of the R ₅ T ₁₇ type crystal particles are flat particles having a flat shape. In the crystal particles having an R ₅ T ₁₇ type crystal structure and having a flat shape, the major axis direction substantially coincides with the direction of the easy axis of magnetization.

Furthermore, the R ₅ T ₁₇ type crystal particles in the rare earth permanent magnet according to the present embodiment are coarser than the conventional R ₅ T ₁₇ type crystal particles. Specifically, when the frequency distribution of the major axis of the R ₅ T ₁₇ type crystal particles is measured, the average major axis of the R ₅ T ₁₇ type crystal particles having a cumulative frequency of 10% or more and 90% or less is more than 300 nm.

A small number of very small R ₅ T ₁₇ type crystal particles and very large R ₅ T ₁₇ type crystal particles have a relatively small influence on the magnetic properties of the rare earth permanent magnet of this embodiment. However, the effect of a small number of very small _R 5 _{T 17} type crystal particles and very large _R 5 _{T 17} type crystal grains gives the average major axis of the _R 5 _{T 17} type crystal grains relatively large. That is, calculating the average major axis only with R ₅ T ₁₇ type crystal particles having a cumulative frequency of 10% or more and 90% or less in the frequency distribution of the major axis does not consider a small number of very small crystal particles and very large crystal particles. This is because the relationship between the average major axis and the magnetic characteristics becomes clearer.

Preferably has an average major axis in the R ₅ T ₁₇ type when measuring the frequency distribution of the major axis of the crystal grains cumulative frequency of 10% or more to 90% or less _R 5 _{T 17} type crystal grains is not less than 305 nm, is 500nm exceeds More preferably, it is more preferably 502 nm or more. The average major axis has no upper limit, but may be, for example, 2000 nm or less, preferably 1500 nm or less, and more preferably 1053 nm or less. Since the average major axis is large, the coercive force of the obtained rare earth permanent magnet is improved. When the R ₅ T ₁₇ type crystal particles are not flat particles, the major axis and the minor axis are assumed to be equal.

When the frequency distribution of the minor axis of the R ₅ T ₁₇ type crystal particles is measured, the average minor axis in the R ₅ T ₁₇ type crystal particles having a cumulative frequency of 10% or more and 90% or less is arbitrary. Good.

_Further, it is preferred that the number ratio of _R 5 _{T 17} type crystal grains major axis to the entire R _{5 T 17} type crystal particles is 300nm greater is 60% or more. When the number ratio of crystal grains having a long major axis is large, the magnetic characteristics are further improved.

  Furthermore, in the rare earth permanent magnet according to the present embodiment, the major axis directions of the flat particles are substantially uniform. As a result, the rare earth permanent magnet according to the present embodiment is an anisotropic rare earth permanent magnet, and is a magnet having excellent residual magnetic flux density Br and coercive force HcJ in the easy axis direction.

  The rare earth permanent magnet according to the present embodiment includes R and T. R is a rare earth element in which Sm is essential. The content ratio of R in the rare earth permanent magnet according to the present embodiment is arbitrary, but may be 20.0 at% or more and 37.1 at%. About the rare earth permanent magnet which concerns on this embodiment, the one where the ratio of Sm which occupies for R is large is preferable, and the content rate of Sm with respect to the whole R in the whole rare earth permanent magnet becomes like this.

R may include Pr and / or Nd. Since the effective magnetic moment of Pr ³⁺ and Nd ³⁺ is larger than the effective magnetic moment of Sm ³⁺ , the residual magnetic flux density tends to be improved when Pr or Nd is contained. Furthermore, Pr or Nd has an effect of suppressing the generation of a subphase which is a low coercive force component. However, if the total content ratio of Pr and Nd in R is too large, the magnetocrystalline anisotropy is reduced, and a secondary phase that is a low coercive force component is likely to be generated, and the coercive force HcJ is likely to be lowered.

  Therefore, the content ratio of Sm with respect to the entire R is preferably 50 at% or more and 99 at% or less, and more preferably 50 at% or more and 97 at% or less. The total content ratio of Pr and Nd is preferably 1 at% or more and 50 at% or less, and more preferably 3 at% or more and 50 at% or less. In addition, a rare earth element other than Sm, Pr, and Nd may be included as R within a range that does not significantly affect the magnetic characteristics of the rare earth permanent magnet according to the present embodiment. The content of rare earth elements other than Sm, Pr and Nd is, for example, 5 at% or less.

  The content ratio of T in the rare earth permanent magnet according to the present embodiment is arbitrary, but may be 47.9 at% or less and 80.0 at% or less. T is Fe alone or Fe and Co. Further, the content ratio of Co with respect to the entire T is arbitrary, but may be 0 at% or more and 20 at% or less. The smaller the Co content, the higher the coercive force. Further, the larger the Co content ratio, the higher the magnetization and the higher the residual magnetic flux density.

The rare earth permanent magnet according to the present embodiment may contain C, and the coercive force HcJ tends to be improved by containing C. The reason why the coercive force HcJ is improved is unknown, but the rare earth permanent magnet contains C, so that the concentration of R is higher in the grain boundary between the crystal grains than in the crystal grains having the R ₅ T ₁₇ type crystal structure. The present inventors consider that this is because the portion is easily formed. The present inventors consider that the coercive force HcJ of the rare earth permanent magnet is improved because the R enriched portion is a nonmagnetic phase and has a high magnetic separation effect. When the rare earth permanent magnet according to the present embodiment contains C, it is preferably more than 0 at% and at most 15 at%.

  It is preferable that the rare earth permanent magnet according to the present embodiment does not substantially contain elements other than the above R, T, and C. The phrase “substantially free of elements other than R, T, and C” refers to the case where the content ratio of elements other than R, T, and C with respect to the entire rare earth permanent magnet is 3 at% or less. Examples of other element types include Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, Ge, Cu, and Zn. Intrusive elements may also be included as other elements, and are elements composed of one or more of N, H, Be, and P.

  In addition, ICP mass spectrometry is used for the analysis of the composition ratio of the whole rare earth permanent magnet according to the present embodiment. Moreover, you may use together the combustion in oxygen stream-infrared absorption method as needed.

    Hereinafter, a preferred example of the method for producing a rare earth permanent magnet according to the present embodiment will be described.

    Among the rare earth permanent magnets according to the present embodiment, an anisotropic rare earth permanent magnet can be obtained, for example, by hot working an isotropic rare earth permanent magnet.

  The manufacturing method of the isotropic rare earth permanent magnet is arbitrary, and can be manufactured by appropriately combining a book mold method, a strip cast method, a rapid quench solidification method, a vapor deposition method, an HDDR method, and the like. Hereinafter, an example of the manufacturing method by the rapid quench solidification method will be described.

    Specific examples of the ultra rapid solidification method include a single roll method, a twin roll method, a centrifugal quench method, and a gas atomization method, and it is preferable to use a single roll method. In the single roll method, the molten alloy is discharged from a nozzle and collided with the peripheral surface of the cooling roll, whereby the molten alloy is rapidly cooled to obtain a ribbon-like or flaky quenched alloy. The single roll method has higher mass productivity and better reproducibility of the rapid cooling conditions than other ultra rapid solidification methods.

    First, an alloy ingot having a desired composition ratio is prepared as a raw material. The raw material alloy can be produced by dissolving a raw material metal containing R and T in an inert gas, preferably an Ar atmosphere, by a melting method such as arc melting.

    A quenched ribbon is produced from the alloy ingot produced by the above method by an ultra-quick solidification method. As the ultra-rapid solidification method, for example, the above-mentioned alloy ingot is cut into small pieces by a stamp mill or the like to obtain small pieces, and the obtained small pieces are melted at a high frequency in an Ar atmosphere to obtain a molten metal. It is possible to use a melt spin method that discharges onto a rotating cooling roll and rapidly solidifies. The melt rapidly cooled by the cooling roll becomes a rapidly cooled ribbon that is rapidly solidified into a thin strip.

  In addition, the method of fragmenting is not limited to a stamp mill. The atmosphere during high frequency melting is not limited to the Ar atmosphere. The rotation speed of the cooling roll is arbitrary. For example, it is good also as 10 m / s or more and 100 m / s or less. The material of the cooling roll is arbitrary. For example, a copper roll may be used as the cooling roll.

Next, the obtained quenched ribbon is heat-treated to generate crystal particles having an R ₅ T ₁₇ type crystal structure. The heating rate and cooling rate during the heat treatment are arbitrary. For example, it may be 0.01 ° C./s or more and 30 ° C./s or less. The heat treatment may be performed in one stage or in multiple stages. The holding temperature at the time of heat treatment is arbitrary, but as the crystal particles having the R ₅ T ₁₇ type crystal structure are higher in the range not thermally decomposed, the grain size of the crystal particles becomes larger, and the anisotropic rare earth permanent magnet finally obtained The above-mentioned average major axis becomes larger. The holding temperature during the heat treatment may be, for example, 575 ° C. or higher and 800 ° C. or lower. Although the holding time is arbitrary, since it is necessary to sufficiently increase the particle size of the crystal particles having the R ₅ T ₁₇ type crystal structure, the holding time may be, for example, 48 hours to 120 hours.

Next, the quenched ribbon after the heat treatment is coarsely pulverized to obtain a coarse powder having a particle size of about several tens to several hundreds of μm. The method of coarse pulverization is arbitrary. For example, a mortar may be used. In addition, each particle contained in the coarse powder has a structure in which a large number of crystal particles each having an R ₅ T ₁₇ type crystal structure are aggregated.

  And the bulk body densified can be obtained by passing through the process of low-temperature sintering, filling coarse metal powder in a metal mold | die and pressurizing. This bulk body is an isotropic rare earth permanent magnet. Although the pressure at the time of pressurization is arbitrary, it is good also as 1 MPa or more and 1 GPa or less, for example. Moreover, the method of low temperature sintering is arbitrary. Examples thereof include electric current sintering, discharge plasma sintering, high-frequency heating sintering, HIP (hot isostatic pressing). The temperature and time of the low-temperature sintering are arbitrary. For example, it can be 0.01 hour or more and 1 hour or less at 500 degreeC or more and 700 degrees C or less.

  Two types of rapid cooling ribbons may be obtained by preparing two types of alloy ingots, an alloy ingot that mainly forms crystal grains as a main phase and an alloy ingot that mainly forms grain boundaries. In the case of a two-alloy method using two types of quenched ribbons, it is preferable to mix during coarse pulverization or after coarse pulverization and before pressurization. By using the 2-alloy method, the grain boundaries can be increased, and the R enrichment part can be increased. Furthermore, when using the two-alloy method, each coarse powder may be coated before being pressed.

  Alternatively, the amorphous quenching ribbon may be coarsely pulverized without performing the above heat treatment step. Thereafter, crystallization and densification may be simultaneously performed by performing heat treatment and pressurization on the amorphous coarse powder.

  Hereinafter, hot working will be described.

  The anisotropic rare earth permanent magnet according to the present embodiment plastically deforms the isotropic rare earth permanent magnet by pressurization and heating by performing hot working on the above isotropic rare earth permanent magnet. Can be obtained.

  The method of hot working is arbitrary. For example, hot compression (die up set), hot extrusion, hot forging, hot rolling and the like can be mentioned.

The hot working temperature at the time of hot working is arbitrary. For example, it can be set to 600 ° C. or higher and 800 ° C. or lower. However, if the hot working temperature is too high, the R ₅ T ₁₇ type crystal particles are thermally decomposed, and the residual magnetic flux density Br and the coercive force HcJ are significantly reduced.

When a part of Sm is substituted with Nd and / or Pr, the R ₅ T ₁₇ type crystal particles are not easily thermally decomposed even if the hot working temperature is relatively high. As a result, it becomes easy to increase the average aspect ratio, and a suitable residual magnetic flux density Br and coercive force HcJ can be obtained.

  By hot working, every single crystal particle is crushed in the pressing direction. Some crystal grains grow perpendicularly to the pressing direction. As a result, each crystal particle has a flat shape. When a cross section parallel to the pressing direction is observed with a TEM or the like, crystal grains whose major axis direction is substantially aligned in a direction perpendicular to the pressing direction are observed. The major axis and minor axis of the crystal particle are the length of the long side and the length of the short side of the smallest rectangle (circumscribed rectangle) when the crystal particle in the magnet cross section is surrounded by a rectangle. The major axis direction of the crystal grain is the direction of the long side of the circumscribed rectangle of the crystal grain. Note that the size of the observation region in the cross section parallel to the pressing direction is arbitrary, but it is set to a size at which at least 200 crystal particles can be observed.

  In the observation region, the area ratio of the R concentrating portion is preferably 3% or more and 20% or less. When the area of the R concentrating portion is within the above range, the magnetic properties can be further enhanced. The area ratio of the R concentrating part tends to increase as the hot working temperature is increased.

Further, the aspect ratio (major axis length / minor axis length) of the R ₅ T ₁₇ type crystal particles in the present embodiment is arbitrary. The average aspect ratio obtained by averaging the aspect ratios of the R ₅ T ₁₇ type crystal grains in the cross section parallel to the pressing direction is preferably 1.6 or more, and more preferably 1.9 or more. The average aspect ratio is calculated, in all R ₅ for T ₁₇ type crystal grains were measured frequency distribution of major diameter, the cumulative frequency of 10% or more and 90% or less R ₅ T ₁₇ type crystal particles in the observation region Calculate and average the aspect ratio.

  As mentioned above, although the example of the manufacturing method of the rare earth permanent magnet which concerns on this embodiment was demonstrated, the manufacturing method of a rare earth permanent magnet is arbitrary. The use of the rare earth permanent magnet according to the present embodiment is also arbitrary.

    Hereinafter, although the content of the present invention is explained in detail using an example and a comparative example, the present invention is not limited to the following examples.

(Experimental example 1)
First, a raw material made of a simple substance or an alloy of Sm, Pr, Nd, Fe and / or C was prepared. Each raw material was blended so that the composition of the obtained rare earth permanent magnet (quenched ribbon) had the composition shown in Table 1 below, and an alloy ingot was produced by arc melting in an Ar atmosphere. Next, the alloy ingot was cut into small pieces using a stamp mill to obtain small pieces. Next, the small piece was melted at high frequency in an Ar atmosphere of 50 kPa to obtain a molten metal.

  Next, a quenched ribbon was obtained from the molten metal by a single roll method. Specifically, the molten metal was discharged onto a cooling roll (copper roll) rotated at a peripheral speed of 40 m / s to obtain a quenched ribbon.

  Next, the obtained quenched ribbon was heat-treated. Specifically, it was heated to the holding temperature shown in the following table, heated for the holding time shown in the following table, and then cooled. In the experimental example in which the heat treatment was performed in two stages, after the heat treatment in the first stage in a short time was completed, the heat treatment was performed for a long time in the second stage after cooling to the holding temperature in the second stage. All heating rates were 10 ° C./s, and all cooling rates were 10 ° C./s.

  Next, the quenched ribbon obtained using a mortar was coarsely pulverized to obtain a coarse powder having a particle size of about several tens to 100 μm. Note that this particle size is the particle size of the coarse powder, not the crystal particle size contained in the coarse powder.

  Next, the bulk powder (isotropic rare earth permanent magnet) was obtained by filling the coarse powder into a mold and conducting current sintering while applying pressure. The pressure during pressurization was 50 MPa, and the electric current sintering was performed at 600 ° C. for 0.1 hour.

  Next, except for Comparative Example 1 and Comparative Example 3, hot processing was performed on the isotropic bulk body to obtain an anisotropic rare earth permanent magnet. Hot working was performed by plastically deforming an isotropic bulk body by hot compression (die up set). The temperature during hot working and the hot working rate are shown in the table below. The hot working rate is the ratio of the height that is deformed and reduced during hot working when the height of the isotropic bulk body before hot working is 100%.

  Thereafter, various parameters were measured for the rare earth permanent magnets of each experimental example in which the obtained rare earth permanent magnets were processed to 3.0 mm × 3.0 mm × 1.5 mm. In addition to Comparative Example 1 and Comparative Example 3, the side parallel to the compression direction during hot working was set to be a side having a length of 1.5 mm.

<Magnet composition>
The content ratio of rare earth elements and transition metal elements in the magnet composition was measured by ICP mass spectrometry. In addition, the composition of each magnet in Experimental Example 1 produced by the one alloy method was substantially the same as the composition of the alloy ingot.

<Identification of crystal grains and grain boundaries>
The rare earth permanent magnet was cut by an arbitrary cross section perpendicular to the compression direction at the time of hot working (an arbitrary cross section in Comparative Example 1 and Comparative Example 3) and specified by performing composition mapping with TEM-EDS. Locations where R and Fe are observed at an atomic ratio of about 5:17 are Nd ₅ Fe ₁₇ type crystal particles, and locations where two or more Nd ₅ Fe ₁₇ type crystal particles are present are grain boundaries. . Note that the size of the observation region was such that at least 200 crystal grains were observed.

  The composition mapping of the cross section was performed using TEM-EDS, and crystal grains and grain boundaries in the TEM image were distinguished.

<R enrichment area ratio>
In the composition mapping, the portion of the grain boundary where the concentration of R is higher than that of the crystal grains was defined as the R concentration portion, and the cross-sectional area was measured. The results are shown in the table below.

<Average major axis and average minor axis>
The major axis and minor axis length of all Nd ₅ Fe ₁₇ type crystal particles in the above observation region were measured. Specifically, the length of the longer side in the minimum rectangle (circumscribed rectangle) when each crystal particle is surrounded by a rectangle is defined as the major axis, and the length of the shorter side is defined as the minor axis. Then, the frequency distribution of the major axis was confirmed, and the average major axis of the crystal particles having a cumulative frequency of 10% or more and 90% or less was calculated. Furthermore, the frequency distribution of the minor axis was confirmed, and the average minor axis of the crystal particles having a cumulative frequency of 10% or more and 90% or less was calculated. Further, in all _embodiments, it was confirmed that the number ratio of _R 5 _{T 17} type crystal grains major axis to the entire R _{5 T 17} type crystal particles is 300nm greater is 60% or more.

<Average aspect ratio of crystal grains>
The major axis and minor axis length of all Nd ₅ Fe ₁₇ type crystal particles in the above observation region were measured. Then, the aspect ratio of each crystal particle, that is, (length of major axis / length of minor axis) was measured. The average aspect ratio was calculated by averaging the aspect ratio of each crystal grain. The results are shown in the table below.

<Magnetic properties, anisotropy>
Magnetic properties (residual magnetic flux density Br and coercive force HcJ) were measured by performing sample vibration type magnetometer measurement (VSM measurement) using a physical property measuring device (PPMS). For anisotropic rare earth permanent magnets other than Comparative Example 1 and Comparative Example 3, Br and HcJ were measured in a direction perpendicular to the compression direction during hot working. The results are shown in the table below. In addition, Br made 4.5 kG or more favorable, and made 5.0 kG or more still more favorable. HcJ was 20 kOe or more, and 25 kOe or more was even better.

  Moreover, the presence or absence of anisotropy was confirmed and it confirmed that all Examples and Comparative Examples other than the comparative example 1 and the comparative example 3 which did not perform hot processing have anisotropy. The presence or absence of anisotropy was judged by comparing the magnetic properties in the direction perpendicular to the compression direction during hot working and the magnetic properties in the direction parallel to the compression direction during hot working.

  The shape of the crystal particles other than Comparative Example 1 and Comparative Example 3 is a flat shape, which means that an anisotropic rare earth permanent magnet can be cut even in any cross section parallel to the compression direction during hot working, Each of an arbitrary cross section perpendicular to the compression direction and an arbitrary cross section parallel to the compression direction during hot working was confirmed from the result of observation by TEM.

Each example in which the average major axis of the Nd ₅ Fe ₁₇ type crystal particles is more than 300 nm has excellent magnetic characteristics. In particular, the residual magnetic flux density Br was particularly excellent in each example in which the average major axis of the Nd ₅ Fe ₁₇ type crystal particles exceeded 500 nm. In addition, the coercive force HcJ was particularly excellent when the average major axis of the Nd ₅ Fe ₁₇ type crystal particles was 1500 nm or less.

On the other hand, in Comparative Example 1 and Comparative Example 2 in which the heat treatment time is as short as 1 hour in total, the crystal grains themselves are small because the grain growth of the crystal grains themselves is insufficient. The average major axis of the _Nd 5 _{Fe 17} type crystal grains or without hot working is 300nm or less. As a result, in Comparative Example 1 and Comparative Example 2, the residual magnetic flux density Br was not sufficient.

  Comparative Example 3 and Example 1 are carried out under the same conditions except for the presence or absence of hot working. As a result of hot working, Example 1 in which the average major axis increased and exceeded 300 nm resulted in excellent magnetic properties. In contrast, in Comparative Example 3 in which the hot working was not performed and the average major axis was 300 nm or less, the residual magnetic flux density Br was not sufficient.

Comparative Example 4 is performed under the same conditions as in Example 1 except that the hot working temperature is increased. In Comparative Example 4, since the hot working temperature was too high, most of the crystal particles having the Nd ₅ Fe ₁₇ type crystal structure were decomposed during hot working to produce 2-17 phase and 1-3 phase. As a result, the crystal grains having the Nd ₅ Fe ₁₇ type crystal structure were not the main phase, and the residual magnetic flux density Br and the coercive force HcJ were significantly reduced. The crystal grains in Comparative Example 5, similarly as in Comparative Example 4, the degradation of crystal grains having a Nd ₅ Fe ₁₇ type crystal structure for hot working temperature is too high advances have Nd ₅ Fe ₁₇ type crystal structure Is no longer the main phase, and the residual magnetic flux density Br and the coercive force HcJ are significantly reduced.

(Experimental example 2)
In Experimental Example 2, the quenching ribbon used in Example 2 was prepared as the quenching ribbon for the main phase, and (Sm _0.8 Pr _0.2 ) _70.0 Cu ₃₀ was used as the quenching ribbon for the grain boundary phase. _A quenched ribbon made of _0.0 alloy (atomic ratio) was prepared. Then, the coarse powder for main phase obtained by roughly pulverizing the quenched ribbon for main phase and the coarse powder for grain boundary obtained by roughly pulverizing the quenched ribbon for grain boundary were mixed. The main phase coarse powder and the grain boundary phase coarse powder were appropriately mixed so that the finally obtained magnet composition had the composition shown in Table 2 below. The heat treatment conditions shown in Table 2 are the heat treatment conditions for the quenching ribbon for the main phase. The quenching ribbon for the grain boundary phase was coarsely pulverized without heat treatment and mixed with the coarse powder for the main phase. Table 2 below shows the results of manufacturing an anisotropic rare earth permanent magnet under the same conditions as in Example 2 of Experimental Example 1 except that the above two alloy method is used.

From Table 2, Examples 21 to 23 performed by the two-alloy method using (Sm _0.8 Pr _0.2 ) _70.0 Cu _30.0 alloy as the grain boundary phase alloy were performed by the one-alloy method. Compared to Example 2, the area ratio of the grain boundary phase was increased, and the area ratio of the R concentrated portion was increased. Further, the residual magnetic flux density Br and the coercive force HcJ were superior to those of Example 2.

Claims (5)

A rare earth permanent magnet comprising R and T,
R is a rare earth element essential for Sm, T is Fe alone or Fe and Co,
The rare earth permanent magnet is a flat particle that includes crystal particles having an Nd ₅ Fe ₁₇ type crystal structure as a main phase, and at least a part of the crystal particles has a flat shape,
A rare earth permanent magnet having an average major axis of more than 300 nm in crystal grains having a cumulative frequency of not less than 10% and not more than 90% when the major axis frequency distribution of the crystal grains is measured.   The rare earth permanent magnet according to claim 1, wherein an average aspect ratio of the crystal grains is 1.6 or more. R further contains Pr and / or Nd,
3. The rare earth permanent magnet according to claim 1, wherein a content ratio of Sm with respect to the entire R is 50 at% or more and 99 at% or less, and a total content ratio of Pr and Nd is 1 at% or more and 50 at% or less. There is an R enriched part at the grain boundary between the crystal grains,
The rare earth permanent magnet according to any one of claims 1 to 3, wherein an area ratio of the R enriched portion in an arbitrary cross section is 3% or more and 20% or less.   The rare earth permanent magnet according to any one of claims 1 to 4, further comprising C, wherein the content ratio of C is more than 0 at% and not more than 15 at%.