JP7589402B2 - Manufacturing method for samarium-iron-nitrogen magnets - Google Patents

Description

The present invention relates to a method for producing samarium-iron-nitrogen magnets.

Samarium-iron-nitrogen magnets have a high theoretical coercive force and are considered promising as high-performance permanent magnets.

When manufacturing samarium-iron-nitrogen magnets, a process is required to solidify the samarium-iron-nitrogen magnet powder. However, because the thermal decomposition temperature of samarium-iron-nitrogen magnet powder is around 600°C, there is a problem in that the magnetic properties deteriorate when the powder is sintered at a temperature above 600°C.

In light of this background, Patent Document 1 describes a method for producing a magnet compact by compacting samarium-iron-nitrogen magnet powder instead of sintering it.

International Publication No. WO2015/199096

The magnetic compact obtained by the manufacturing method described in Patent Document 1 has a problem in that the particles are not sintered together, so the magnetic compact has low strength and is difficult to process. For example, if an attempt is made to cut or change the shape of the magnetic compact, the magnetic compact crumbles relatively easily.

To address this issue, it is possible to add a resin binder when molding the magnet powder to increase the bonding between the magnet particles. However, adding a resin binder to a magnet molding reduces the effective magnet volume, which can lead to problems with the magnetic properties of the magnet.

The present invention has been made in consideration of this background, and aims to provide a method for producing a samarium-iron-nitrogen magnet that has good processability and significantly suppresses the decrease in coercive force.

In the present invention,
A method for producing a samarium-iron-nitrogen (Sm—Fe—N) based magnet, comprising the steps of:
(1) A step of preparing Sm—Fe—N based magnet powder,
the magnet powder has a residual oxygen content of 1 mass % or less, a cumulative distribution of particles having an aspect ratio of 1 to 2 of 90% or more, and a _Th2Zn17 type crystal structure _;
(2) A step of pressure sintering the magnet powder,
the magnet powder is held at a maximum temperature _Tmax for a predetermined time and compressed at a maximum pressure in the range of 1.0 GPa to 1.8 GPa during at least a portion of the time that the magnet powder is at the maximum temperature _Tmax , the maximum temperature _Tmax being equal to or greater than 400°C and less than 600°C, and the predetermined time being in the range of 1 minute to 10 minutes;
having
A method is provided in which substantially no pressure is applied to the magnet powder when the magnet powder is below 100°C and above 600°C.

The present invention provides a method for producing samarium-iron-nitrogen magnets that have good processability and significantly suppress the decrease in coercivity.

FIG. 1 is a diagram showing a schematic diagram of an expected relationship between the temperature and coercivity of magnet powder when a Sm—Fe—N magnet is manufactured through a sintering process. 2 is a diagram showing an example of a flow of a method for manufacturing a magnet according to an embodiment of the present invention; FIG. FIG. 2 is a diagram showing a schematic diagram of an example of a flow of a method for producing magnet powder in a magnet production method according to an embodiment of the present invention. FIG. 3 is a diagram showing an example of a temperature and pressure profile that can be used in the pressure sintering step of the magnet powder in the magnet manufacturing method shown in FIG. 2 . 5A to 5C are diagrams illustrating an example of a flow of a method for manufacturing a magnet according to another embodiment of the present invention. FIG. 6 is a diagram showing an example of a temperature and pressure profile of magnet powder that can be applied to a magnetic field application compaction step in the magnet manufacturing method shown in FIG. 5 . 11 is a diagram showing an example of a flow of a magnet manufacturing method according to yet another embodiment of the present invention. FIG. FIG. 8 is a schematic diagram showing an example of a temperature and pressure profile that can be used in the manufacturing method of the magnet shown in FIG. FIG. 2 shows the temperature and pressure profiles used in the pressure sintering process in the examples.

One embodiment of the present invention is described below.

Samarium-iron-nitrogen (Sm-Fe-N) magnet powder has two types of crystal structure, TbCu ₇ type and Th ₂ Zn ₁₇ type. However, the present application targets Sm-Fe-N magnet powder having Th ₂ Zn ₁₇ type crystal structure as samarium-iron-nitrogen (Sm-Fe-N) magnet powder. This is because Th ₂ Zn ₁₇ type can exhibit higher coercive force than TbCu ₇ type.

As mentioned above, the magnet molding obtained by the manufacturing method described in Patent Document 1 has the problem that it has low strength and is difficult to process. In addition, if a resin binder is added when molding the magnet powder to address this problem, the magnetic properties of the magnet will be reduced.

In order to prevent the strength of the magnet compact from decreasing, it is possible to sinter the magnet powder. However, according to the present inventors, as shown in Figure 1 below, it has been recognized that in Sm-Fe-N magnets, when magnets are manufactured by sintering Sm-Fe-N magnet powder, the coercive force decreases.

Figure 1 shows a schematic diagram of the expected relationship between the temperature of magnetic powder and the coercive force when an Sm-Fe-N magnet is manufactured through a sintering process. Note that it is assumed here that the manufacturing method of the magnet includes a step (first step) of magnetically compacting the Sm-Fe-N magnetic powder, followed by a pressure sintering step (second step). The coercive force value on the vertical axis is the value at room temperature.

In the first step, a magnetic field and pressure are applied to the magnetic powder to form the magnetic powder. During this process, the coercive force of the powder decreases, as shown in region I in Figure 1.

This first step is usually carried out at a low temperature, such as room temperature. For this reason, it is believed that the application of pressure causes distortion inside each particle, which is the cause of the decrease in the coercive force of the powder.

In particular, when the particles are fine and have a shape close to spherical (defined in this application as particles with an aspect ratio of 1 to 2), the particles are less likely to be broken down into finer particles when pressure is applied, and distortion is more likely to accumulate inside the particles. Therefore, in this case, it is believed that a greater decrease in coercivity may occur in region I.

Next, in the second process where the magnet powder is pressure sintered, the coercivity of the powder is further reduced, as shown in region II in Figure 1.

The decrease in coercivity in region II is believed to be due to iron oxide present on the surface of each particle.

That is, under high temperature and pressure, oxygen contained in the iron oxide on the particle surface is separated as shown in the following reaction formula (1), and the oxygen is bonded to Sm inside the particle.

2Fe ₂ O ₃ +2Sm ₂ Fe ₁₇ N ₃ → 19Fe+2Sm ₂ O ₃ +3N ₂ ↑ (1)

When such a decomposition reaction occurs, the amount of Sm--Fe--N composition contained in the magnet powder decreases, resulting in a decrease in coercive force.

However, it is believed that once the iron oxide present on the surface of the particles is depleted, reaction (1) will no longer occur. Therefore, it is believed that the decrease in coercivity in region II will eventually saturate. It is believed that the plateau portion of coercivity occurs in region II in Figure 1 for the above reasons.

Also, in Figure 1, the subsequent decrease in coercivity in region III is due to thermal decomposition of the magnet powder.

As such, when Sm-Fe-N magnets are manufactured by sintering Sm-Fe-N magnet powder, there is a high possibility that the resulting magnet will not exhibit the desired coercive force.

In the above example, it is assumed that the magnetic field molding process (first step) is carried out before the pressure sintering process (second step). However, in normal manufacturing processes, the first step is often omitted. However, even in such manufacturing processes, it is believed that the same behavior of change in coercivity as that shown in Figure 1 can be obtained. This is because, even if the manufacturing process does not include the first step, in the second step, pressure is applied when the magnet powder is at room temperature or a relatively low temperature.

The inventors of the present application have conducted extensive research to address these issues. They have discovered that even when the manufacturing process for Sm-Fe-N magnets includes a sintering process, the decrease in the coercivity of the manufactured magnets can be significantly suppressed by optimizing the pressure and temperature profile applied to the magnet powder.

That is, in one embodiment of the present invention,
A method for producing a samarium-iron-nitrogen (Sm—Fe—N) based magnet, comprising the steps of:
(1) A step of preparing Sm—Fe—N based magnet powder,
the magnet powder has a residual oxygen content of 1 mass % or less, a cumulative distribution of particles having an aspect ratio of 1 to 2 of 90% or more, and a _Th2Zn17 type crystal structure _;
(2) A step of pressure sintering the magnet powder,
the magnet powder is held at a maximum temperature _Tmax for a predetermined time and compressed at a maximum pressure in the range of 1.0 GPa to 1.8 GPa during at least a portion of the time that the magnet powder is at the maximum temperature _Tmax , the maximum temperature _Tmax being equal to or greater than 400°C and less than 600°C, and the predetermined time being in the range of 1 minute to 10 minutes;
having
A method is provided in which substantially no pressure is applied to the magnet powder when the magnet powder is below 100°C and above 600°C.

In the manufacturing method according to one embodiment of the present invention, Sm-Fe-N based magnet powder having a Th ₂ Zn ₁₇ type crystal structure is used as the magnet powder. As described above, Sm-Fe-N based magnet powder having a Th ₂ Zn ₁₇ type crystal structure can exhibit high coercive force.

The magnet powder is also characterized by a residual oxygen content of 1 wt% or less and a cumulative distribution of particles with an aspect ratio of 1 to 2 of 90% or more.

When the manufacturing method of the present invention is used, residual oxygen in the magnet powder tends to be present in large amounts on the surface of each particle. Furthermore, as described above, the oxygen present on the surface oxidizes the Sm within the particles during the pressure sintering process (second process) of the powder according to reaction formula (1), which causes a decrease in the coercive force of the magnet.

However, in the manufacturing method according to one embodiment of the present invention, the amount of residual oxygen in the magnet powder is suppressed to 1 wt% or less, so the decrease in coercivity in region II can be significantly suppressed.

The manufacturing method according to one embodiment of the present invention is characterized in that the cumulative distribution of particles with an aspect ratio of 1 to 2 in the magnet powder used is 90% or more. This means that the majority of the magnet particles are roughly spherical.

It is generally known that magnetic powders made up of spherical particles can have a higher coercive force than magnetic powders made up of non-spherical particles. Therefore, by using magnetic powders in which the majority of particles are roughly spherical and have an aspect ratio of 1 or more and 2 or less, the coercive force can be further increased.

The manufacturing method according to one embodiment of the present invention is characterized in that substantially no pressure is applied to the magnetic powder when the magnetic powder is in a temperature range below 100°C.

In this case, the distortion occurring within the particles in the first step described above is significantly suppressed. Therefore, the decrease in coercivity of the magnet powder that may occur in region I can be significantly suppressed.

In the manufacturing method according to an embodiment of the present invention, in the pressure sintering step of the magnetic powder, the maximum pressure (maximum pressure _Pmax ) is applied so that at least a part of the application period overlaps with at least a part of the period during which the magnetic powder is at the maximum temperature _Tmax . The time during which the magnetic powder is held at the maximum temperature _Tmax ranges from 1 minute to 10 minutes.

In this way, by relatively shortening the time during which the magnetic powder is held at the maximum temperature _Tmax and the maximum pressure _Pmax , the reaction shown in reaction formula (1) can be significantly suppressed in region II shown in Fig. 1. As a result, the decrease in coercivity of the magnetic powder that may occur in region II can be significantly suppressed.

In addition, in the manufacturing method according to one embodiment of the present invention, the pressure sintering step is carried out in a temperature range in which the maximum temperature _Tmax is equal to or higher than 400° C. and lower than 600° C. Furthermore, the manufacturing method according to one embodiment of the present invention has a feature in that substantially no pressure is applied to the magnet powder when the magnet powder is in a temperature range of 600° C. or higher.

In this case, the thermal decomposition of the magnet powder can be significantly suppressed. Therefore, the decrease in the coercive force of the magnet powder, as shown in region III of Figure 1 above, can be significantly suppressed.

Due to these effects, the manufacturing method according to one embodiment of the present invention, although it includes a pressure sintering process of the magnet powder, can significantly suppress the decrease in coercivity throughout the entire process.

Furthermore, in the manufacturing method according to one embodiment of the present invention, the magnet powder is sintered. Therefore, unlike the magnet moldings described in the aforementioned Patent Document 1, the resulting magnet has good strength and good processability.

As a result of the above effects, one embodiment of the present invention can provide a method for producing a samarium-iron-nitrogen magnet that has good processability and significantly suppresses the decrease in coercivity.

(Method of manufacturing a magnet according to one embodiment of the present invention)
The method for manufacturing a magnet according to an embodiment of the present invention will now be described in more detail with reference to FIG.

Figure 2 shows an example of the flow of a magnet manufacturing method according to one embodiment of the present invention (hereinafter referred to as the "first method").

As shown in FIG. 2, the first method is as follows:
A step of preparing Sm—Fe—N based magnet powder (step S110);
A step of pressure sintering the magnet powder (step S120);
has.

Each step is explained below.

(Step S110)
First, Sm--Fe--N based magnet powder is prepared.

The magnet powder is a Th ₂ Zn ₁₇ type Sm-Fe-N magnet powder with a residual oxygen content of 1 wt % or less and mostly made up of roughly spherical particles.

The manufacturing method of the magnetic powder is not particularly limited as long as such magnetic powder can be obtained.

Below, an example of a method for manufacturing magnet powder is explained using Figure 3.

Figure 3 shows a schematic flow of the manufacturing method for Sm-Fe-N magnetic powder.

As shown in FIG. 3, the method for producing the magnetic powder includes the following steps:
A step (S10) of preparing a precursor powder of an Sm—Fe based alloy;
A step (S20) of reducing and diffusing the precursor powder in an inert gas atmosphere to prepare a Sm—Fe based alloy powder;
A step (S30) of nitriding the Sm—Fe-based alloy powder to prepare a Sm—Fe—N-based alloy powder;
A step (S40) of washing the Sm—Fe—N based alloy powder;
has.

Each process is briefly explained below.

(Step S10)
First, a precursor powder of an Sm--Fe alloy is prepared.

The precursor powder may be, for example, Sm-Fe oxide powder or Sm-Fe hydroxide powder. In the following, Sm-Fe oxide powder and Sm-Fe hydroxide powder are collectively referred to as Sm-Fe (hydr)oxide powder.

The precursor powder may be produced, for example, by a coprecipitation method. In this method, a precipitant such as an alkali is first added to a solution containing a samarium salt and an iron salt to cause precipitation, and the precipitate is then collected by filtration, centrifugation, or the like. The precipitate is then washed and dried, and then pulverized to obtain a Sm-Fe-based (hydr)oxide powder.

The magnetic properties of Sm-Fe-N magnet powder deteriorate when it contains metallic iron. For this reason, it is preferable to add samarium in excess of the stoichiometric ratio when producing the precursor powder.

The counter ions in the samarium salts and iron salts may be inorganic ions such as chloride ions, sulfate ions, and nitrate ions, or organic ions such as alkoxides.

Water can be used as the solvent in the solution containing samarium salts and iron salts, but organic solvents such as ethanol can also be used.

As the alkali, hydroxides of alkali metals and alkaline earth metals, and ammonia can be used. In addition, compounds such as urea that decompose under external influences such as heat and act as a precipitant can also be used.

The obtained precursor powder may then be handled in an atmosphere-tight environment, such as a glove box, until the Sm-Fe-N magnet powder is produced. When using an inert gas atmosphere, it is preferable that the oxygen concentration be 1 ppm or less.

The obtained precursor powder is preferably pre-reduced in a reducing atmosphere. This reduces the amount of calcium used in the subsequent reduction and diffusion step (step S20) and also suppresses the generation of coarse Sm-Fe alloy particles.

Pre-reduction of the precursor powder may be carried out, for example, by heating the precursor powder to 400°C or higher in a hydrogen atmosphere. The treatment temperature is preferably in the range of 500°C to 800°C. When pre-reduction is carried out in this temperature range, it is possible to obtain Sm-Fe alloy powder with a uniform particle size.

(Step S20)
Next, the precursor powder is subjected to a reduction diffusion treatment under an inert gas atmosphere.

Examples of methods for reducing and diffusing the precursor powder include a method in which the precursor powder is mixed with calcium (Ca) or calcium hydride (CaH ₂ ) and then heated to a temperature (about 850° C.) equal to or higher than the melting point of Ca.

During this process, Sm reduced by Ca diffuses through the Ca melt and reacts with Fe to form Sm-Fe alloy powder.

There is a correlation between the temperature of the reduction diffusion process and the grain size of the crystals in the Sm-Fe alloy powder; the higher the temperature of the reduction diffusion, the larger the grain size of the Sm-Fe alloy powder.

The average grain size of the crystal grains is preferably 2.0 μm or less.
When the average grain size of the crystal grains is 0.0 μm or less, the coercive force of the magnet is further increased. The average grain size of the crystal grains is further preferably in the range of 0.6 μm to 2.0 μm.

In order to obtain Sm-Fe alloy powder with uniform particle size, it is preferable to subject the precursor powder to reduction and diffusion treatment in an inert gas atmosphere at 850°C to 1050°C for about 1 minute to 2 hours.

As reduction and diffusion in the precursor progresses, crystallization progresses and Sm-Fe alloy powder is formed. In the resulting Sm-Fe alloy powder, an Sm-rich phase is also formed on at least a portion of the surface of each particle.

In Sm-Fe alloy powder, the percentage of particles with an aspect ratio of 2.0 or more is preferably 10% or less, and more preferably 8% or less. If the percentage of particles with an aspect ratio of 2.0 or more is 10% or less, the coercive force of the magnetic powder will be even higher.

The amount of residual oxygen in the Sm-Fe alloy powder obtained after step S20 is preferably less than 1.0% by mass. If the amount of residual oxygen in the Sm-Fe alloy powder is less than 1.0% by mass, the coercive force of the magnet will be even higher.

(Step S30)
Next, the obtained Sm--Fe alloy powder is subjected to a nitriding treatment.

Methods for nitriding Sm-Fe alloy powder include heat treating the Sm-Fe alloy powder at 300°C to 500°C in an atmosphere of ammonia, a mixed gas of ammonia and hydrogen, nitrogen, or a mixed gas of nitrogen and hydrogen.

When ammonia is used, it is possible to nitride Sm-Fe alloy powder in a short time. However, there is a possibility that the nitrogen content in the Sm-Fe-N magnet powder will be higher than the optimum value. In this case, it is preferable to anneal the Sm-Fe alloy powder in hydrogen after nitriding it. This allows the excess nitrogen to be expelled from the crystal lattice.

The nitriding process produces Sm-Fe-N alloy powder.

The composition of the particles contained in the Sm-Fe-N alloy powder is preferably Sm ₂ Fe ₁₇ N ₃ .

For example, Sm-Fe alloy powder is heat treated at 350°C to 450°C for 10 minutes to 2 hours in an ammonia-hydrogen mixed atmosphere, and then annealed at 350°C to 450°C for 30 minutes to 2 hours in a hydrogen atmosphere. This allows the nitrogen content in the Sm-Fe-N magnet powder to be optimized.

(Step S40)
Next, the Sm--Fe--N alloy powder formed in step S30 is washed.

The Sm-Fe-N alloy powder formed in step S30 contains calcium compounds. The cleaning process is carried out to remove such calcium compounds.

The cleaning process is carried out using a cleaning solution such as water and/or alcohol. Alternatively, the cleaning solution may be an acid such as amidosulfuric acid. Alternatively, the Sm-Fe-N alloy powder may be cleaned using water and/or alcohol, followed by further cleaning using amidosulfuric acid.

The cleaning process may be carried out before the nitriding process.

The washed Sm-Fe-N alloy powder is then preferably dried.

The drying temperature is not particularly limited, but is preferably between room temperature and 100°C. By keeping the drying temperature at 100°C or less, oxidation of the Sm-Fe-N alloy powder can be suppressed.

The Sm-Fe-N alloy powder may also be subjected to a dehydrogenation process. This process removes hydrogen that has entered between the crystal lattices during the cleaning process.

The method of dehydrogenation is not particularly limited. For example, the dehydrogenation may be performed by heating the Sm-Fe-N alloy powder in a vacuum or in an inert gas atmosphere. For example, the dehydrogenation may be performed by heat treating the Sm-Fe-N alloy powder at 150°C to 250°C for 1 hour in a vacuum atmosphere.

By using the above process, Sm-Fe-N alloy powder can be produced. The amount of residual oxygen in the alloy powder is 1 mass% or less.

The average particle size of the resulting Sm-Fe-N alloy powder is preferably in the range of 0.6 μm to 2.0 μm.

The magnet powder may also be crushed.

It is important to note that "disintegration" is a different term from "pulverization." That is, "disintegration" refers to the separation of one or more particles from an aggregate of multiple particles that are clumped together. On the other hand, "pulverization" refers to the division of a single particle into multiple smaller pieces.

The crushing process is explained below.

(Crushing process)
The crushing process may be carried out in a wet manner.

Wet milling is performed by milling the Sm-Fe-N alloy powder in an organic solvent. A ball mill, a vibration mill, a media stirring mill, a bead mill, etc. can be used for wet milling.

By carrying out the crushing process, it is possible to more reliably obtain particles that are roughly "spherical."

Through the above process, in step S110, Sm-Fe-N magnet powder with a residual oxygen content of less than 1.0 mass% is prepared.

The residual oxygen content is preferably 0.9% by mass or less, and more preferably 0.8% by mass or less.

(Step S120)
Next, the magnet powder is subjected to a pressure sintering process.

The pressure sintering process may be carried out, for example, by a discharge plasma method, a hot press method, or a current pressure sintering method. Among these, the current pressure sintering method is preferred, which can achieve low thermal load sintering by rapid heating and short sintering time.

In the electric current pressure sintering method, the magnet powder can be heated by passing an electric current through the magnet powder under pressure.

Below, with reference to Figure 4, an example of a temperature and pressure profile that can be used in the pressure sintering process of step S120 is described.

Figure 4 shows a schematic diagram of the temperature and pressure changes over time of the magnetic powder during the pressure sintering process. In Figure 4, the horizontal axis is time, the left vertical axis is the temperature of the magnetic powder, and the right vertical axis is the pressure applied to the magnetic powder.

4, in this example, the temperature of the magnet powder reaches 100° C. at time t _C , and then reaches the maximum temperature T _max at time t _S. Furthermore, the magnet powder is maintained at the maximum temperature T _max until time t _E , and then cooled down to room temperature. Therefore, the retention time at the maximum temperature T _max is (t _E - t _S ).

The maximum temperature _Tmax is in the range of 400° C. or more and less than 600° C. If the maximum temperature _Tmax is less than 400° C., the sintering reaction does not proceed. If the maximum temperature _Tmax is 600° C. or more, thermal decomposition occurs in the magnet powder. The maximum temperature _Tmax is preferably 550° C. or less.

The retention time (t _E -t _S ) at the maximum temperature T _max ranges, for example, from 1 minute to 10 minutes.

On the other hand, the pressure applied to the magnet powder is "substantially" 0 (zero) until time _t1 , where time _t1 > time _tC .

Generally, in the pressure sintering process using an electric current pressurizing device, a preliminarily pressure of up to 3.5×10 ⁻² GPa may be applied to the magnet powder. Such preliminarily pressurizing is performed to bring the particles of the powder to be processed into contact with each other and ensure current flow. The preliminarily pressurizing has a different purpose and magnitude from the pressure used to sinter the particles in the pressure sintering process. Therefore, in this application, the pressure used in the preliminarily pressurizing is distinguished from the processing pressure applied for the actual sintering in the pressure sintering process.

In other words, in this application, the magnet powder may be pre-pressurized at a temperature of less than 100°C. In other words, it should be noted that in this application, "the applied pressure is substantially zero" includes cases where the pressure applied to the magnet powder is completely zero, as well as cases where the powder is pre-pressurized. In other words, "the applied pressure is substantially zero" means that the applied pressure does not exceed the pre-pressurization.

Next, a maximum pressure P _max is applied to the magnet powder from time t ₁ to time t _2. The maximum pressure P _max is in the range of 1.0 GPa to 1.8 GPa.

If the maximum pressure _Pmax is less than 1.0 GPa, it becomes difficult to sinter the magnet powder, and if the maximum pressure _Pmax exceeds 1.8 GPa, the life of the mold becomes shorter.

After time _t2 , the pressure applied to the magnet powder is released.

In the example shown in Fig. 4, time _t1 is greater than time _tS , and time _t2 is less than time _tE .

However, the relationship between time _t1 and time _tS is not particularly limited, and may be time _t1 ≦ time _tS . However, it is preferable that time _t1 ≧ time _tS . Similarly, the relationship between time _t2 and time _tE is not particularly limited, and may be time _t2 ≧ time _tE . However, it is preferable that time _t2 ≦ time _tE .

When such a temperature and pressure profile is applied to the magnet powder in step S120, it is possible to suppress the decrease in coercivity in regions I and II as shown in FIG. 1 above.

Moreover, in the first method, the maximum temperature _Tmax is controlled to be in the range of 400° C. or more and less than 600° C. Moreover, in the temperature range of 600° C. or more, substantially no pressure is applied to the magnet powder. Therefore, in the first method, the decrease in coercivity due to thermal decomposition as shown in the above-mentioned region III is also significantly suppressed.

As a result, the first method makes it possible to sinter the magnet powder while suppressing the decrease in the magnet powder's coercivity to some extent, and to produce a Sm-Fe-N magnet with high coercivity.

In addition, the Sm-Fe-N magnets produced by the first method have high strength because they have undergone a sintering process, making them suitable for processing such as cutting.

In the temperature and pressure profile shown in Fig. 4, no processing pressure is applied to the magnet powder until time _t1 . However, this is merely an example, and pressure may be applied to the magnet powder after time _tC . For example, in a temperature range of 100°C or higher, a pressure in the range of 0.1 GPa to the maximum pressure _Pmax may be applied to the magnet powder until time ts.

(Method of manufacturing a magnet according to another embodiment of the present invention)
Next, a method for manufacturing a magnet according to another embodiment of the present invention will be described with reference to FIG.

Figure 5 shows an example of the flow of a magnet manufacturing method according to another embodiment of the present invention (hereinafter referred to as the "second method").

As shown in FIG. 5, the second method is as follows:
A step of preparing Sm—Fe—N based magnet powder (step S210);
A step of applying a magnetic field to the magnet powder to mold the magnet powder into a molded body (step S220);
A step of pressure sintering the obtained compact (step S230);
has.

The second method is different from the first method described above in that it includes a magnetic field application molding step (step S220). That is, in the second method, steps S210 and S230 are similar to steps S110 and S120, respectively, in the first method.

Therefore, step S220 will be explained in detail here.

(Step S220)
In the second method, a magnetic field application compaction step is performed on the magnet powder produced in step S210.

The magnetic field application molding process is carried out to form a compact in which the magnetic properties are oriented in a specific direction before sintering the magnet powder. When the magnetic field application molding process is carried out, an anisotropic magnet with high magnetic properties is obtained after step S230.

Figure 6 shows a schematic example of a temperature and pressure profile of magnet powder that can be applied to a magnetic field application molding process.

In Figure 6, the horizontal axis is time, the left vertical axis is the temperature of the magnet powder, and the right vertical axis is the pressure applied to the magnet powder.

6, in this example, the temperature of the magnet powder reaches 100°C at time _tC , and then reaches the molding temperature _T1 at time _tA . Furthermore, the magnet powder is maintained at the molding temperature _T1 until time _tB , and then cooled down to room temperature. Therefore, the retention time at the molding temperature _T1 is ( _tB - _tA ).

On the other hand, compacting pressure _P1 is applied to the magnet powder from time _t3 to time _t4 . That is, the application time of compacting pressure _P1 is ( _t4 - _t3 ).

Although not shown in FIG. 6, a magnetic field is applied to the magnet powder while the compacting pressure _P1 is being applied to the magnet powder.

The applied magnetic field may be, for example, 10 kOe or more.

This results in a molded body with magnetic properties oriented in a specific direction.

6, the molding temperature _T1 is, for example, in the range of 100° C. to 400° C. The molding temperature _T1 is preferably in the range of 100° C. to 200° C.

The molding pressure _P1 is, for example, in the range of 0.1 GPa to 1.8 GPa. It is preferable that the molding pressure _P1 is, for example, in the range of 0.1 GPa to 1.2 GPa.

Here, the time _t3 at which application of the compacting pressure _P1 starts satisfies _t3 ≥ _tC . Therefore, in the magnetic field application compaction process, the decrease in coercivity as shown in region I in Fig. 1 is significantly suppressed.

In the example shown in Fig. 6, _t3 > _tA and _t4 < _tB . However, this is merely an example. For example, _t3 < _tA and _t4 > _tB may be satisfied.

Then, in step S230, the magnetic powder is pressure sintered as described in step S120 of the first method above, to produce a Sm-Fe-N magnet.

This second method can achieve the same effect as the first method described above.

In other words, the second method makes it possible to sinter the magnet powder while suppressing a decrease in the coercive force of the magnet powder, and to produce a Sm-Fe-N magnet with high coercive force. In addition, the Sm-Fe-N magnet produced by the second method has high strength because it has been through a sintering process, and can be adequately processed, such as by cutting.

(Method of manufacturing a magnet according to yet another embodiment of the present invention)
Next, a method for manufacturing a magnet according to yet another embodiment of the present invention will be described with reference to FIG.

Figure 7 shows an example of the flow of a magnet manufacturing method according to yet another embodiment of the present invention (hereinafter referred to as the "third method").

As shown in FIG. 7, the third method is as follows:
A step of preparing Sm—Fe—N based magnet powder (step S310);
A step of forming a compact by molding the magnetic powder while applying a magnetic field to the magnetic powder (step S320), and subsequently pressure sintering the compact;
has.

The third method differs from the second method described above in that the magnetic field molding step (step S220) and the pressure sintering step (step S230) in the second method described above are carried out consecutively.

Therefore, step S320 will be explained in detail here.

(Step S320)
In the third method, the magnetic field compaction process and the pressure sintering process are successively performed on the magnet powder obtained in step S310. For example, the magnetic field compaction process and the pressure sintering process may be performed in the same device. In this case, the magnet can be rapidly manufactured.

Figure 8 shows a schematic example of a temperature and pressure profile of magnet powder that can be applied in step S320.

In Figure 8, the horizontal axis is time, the left vertical axis is the temperature of the magnetic powder, and the right vertical axis is the pressure applied to the magnetic powder.

8, in this example, the temperature of the magnet powder reaches 100° C. at time t _C , and then reaches the molding temperature T ₁ at time t _A. Furthermore, the magnet powder is maintained at the molding temperature T ₁ until time t _B. Therefore, the holding time at the molding temperature T ₁ is (t _B -t _A ).

Furthermore, the temperature of the magnet powder is increased from time t _B to time t _S , and reaches a maximum temperature T _max at time t _S. Furthermore, the magnet powder is maintained at the maximum temperature T _max until time t _E , and then cooled down to room temperature. Therefore, the retention time at the maximum temperature T _max is (t _E - t _S ).

On the other hand, the pressure applied to the magnet powder is substantially 0 until time _t3 , where time _t3 ≥ time _tC . Therefore, the magnet powder is not pressurized at a temperature below 100°C.

Thereafter, compacting pressure _P1 is applied to the magnet powder from time _t3 to time _t4 . Therefore, the pressurizing time by compacting pressure _P1 is ( _t4 - _t3 ).

Although not shown in FIG. 8, a magnetic field is applied to the magnet powder while the compacting pressure _P1 is being applied to the magnet powder.

This results in a compact that is magnetized in a specific direction.

Thereafter, the pressure on the magnet powder is released during the period from time t ₄ to time t ₁ .

Furthermore, a maximum pressure P _max is applied to the magnet powder between time t ₁ and time t _2. As described above, the maximum pressure P _max is in the range of 1.0 GPa to 1.8 GPa.

After time _t2 , the pressure applied to the magnet powder is released.

8, time _t3 = time _tA , time _t4 = time _tB , time _t1 = time _tS , and time _t2 = time _tE .

However, this is merely an example. As described above, the relationship between time _t1 and time _tE , and the relationship between time _t2 and time _tE are not particularly limited.

The relationship between time _t3 and time _tA is not particularly limited, and may be time _t3 > time _tA or time _t3 < time _tA . The same is true for time _t4 and time _tB . However, time _t3 ≧ time _tC . Also, time _t4 ≦ time _t1 .

8, the molding temperature _T1 is, for example, in the range of 100° C. to 400° C. The molding temperature _T1 is preferably in the range of 100° C. to 200° C.

The molding pressure _P1 is, for example, in the range of 0.1 GPa to 1.8 GPa. It is preferable that the molding pressure _P1 is, for example, in the range of 0.1 GPa to 1.2 GPa.

The maximum temperature T _max is in the range of 400° C. or higher and lower than 600° C. The holding time (t _E -t _S ) is in the range of 1 minute to 10 minutes. The holding time (t _E -t _S ) is preferably 5 minutes or shorter.

8, substantially no pressure is applied to the magnetic powder during the period from time _t4 to time _t1 . However, alternatively, pressure may be applied to the magnetic powder continuously during the period from time _t4 to time _t1 .

When such a temperature and pressure profile is applied to the magnetic powder, it is possible to suppress the decrease in coercivity in regions I and II, as shown in Figure 1 above.

In addition, in the third method, the decrease in coercivity due to thermal decomposition as shown in region III above is also significantly suppressed.

As a result, the third method makes it possible to sinter the magnet powder while suppressing a decrease in the magnet powder's coercivity, and to produce a Sm-Fe-N magnet with high coercivity.

In addition, the Sm-Fe-N magnets produced using the third method have high strength because they have undergone a sintering process, making them suitable for processing such as cutting.

Below, examples of the present invention will be described. In the following description, Examples 1 to 14 are examples, and Examples 21 to 25 are comparative examples.

(Example 1)
A sintered magnet was produced by the following method.

(Magnetic powder production)
First, Sm--Fe--N based magnet powder was prepared by the following method.

(Preparation of Sm-Fe-(hydr)oxide powder)
64.64 g of iron nitrate nonahydrate and 12.93 g of samarium nitrate hexahydrate were dissolved in 800 ml of water, and then 120 ml of 2 mol/L potassium hydroxide aqueous solution was dropped while stirring, and then stirred overnight at room temperature to prepare a suspension. Next, the suspension was filtered, and the filtered product was washed, and then dried overnight at 120°C in an air atmosphere using a hot air oven. Next, the filtered product was coarsely ground with a blade mill, and then finely ground in ethanol with a rotary mill using stainless steel balls. Next, the filtered product finely ground in ethanol was centrifuged and then vacuum dried to prepare Sm-Fe-(hydr)oxide powder.

(Pre-reduction)
The Sm-Fe-(hydr)oxide powder was pre-reduced by heat treatment at 600° C. for 6 hours in a hydrogen atmosphere to produce a powder (referred to as Powder A).

(Reduction and diffusion)
5 g of Powder A and 2.5 g of calcium powder were placed in an iron crucible, and then heated at 950° C. for 1 hour for reduction and diffusion to produce a powder (referred to as Powder B).

(nitridation)
Powder B was cooled to room temperature, and then heated to 380° C. in a hydrogen atmosphere. Next, the temperature was raised to 420° C. in an atmosphere of ammonia-hydrogen mixture with a volume ratio of 1:2, and maintained for 1 hour, thereby nitriding Powder B.

The powder was then annealed at 420°C for 1 hour in a hydrogen atmosphere, and then annealed at 420°C for 0.5 hour in an argon atmosphere to optimize the nitrogen content in the powder. This resulted in powder C.

(Washing)
Powder C was washed five times with pure water. The washed Powder C and an aqueous solution of amidosulfuric acid were added to adjust the pH to 5, and the mixture was maintained for 15 minutes to remove calcium compounds. Powder C was then washed with pure water to remove amidosulfuric acid. Powder D was thus obtained.

(Vacuum drying)
The water remaining in Powder D was replaced with 2-propanol, and then the powder was vacuum dried at room temperature.

The vacuum-dried powder D was dehydrogenated under vacuum at 200°C for 3 hours.

The steps after pre-reduction were carried out in a glove box under an argon atmosphere without exposure to the atmosphere.

Through the above process, Sm-Fe-N magnet powder was obtained. The magnet powder produced is referred to as "Magnet Powder 1."

(Magnetic production)
Next, the magnet powder 1 was pressure sintered to produce a sintered magnet by the following method.

For the pressure sintering process, an electric current sintering device equipped with a pressure mechanism using a servo-controlled press device was used. This device has a 5.5 mm square cylindrical mold made of cemented carbide that can be pulsed with electricity. Therefore, with magnet powder 1 (0.5 g) filled into the mold, electricity is passed through the mold and pressure is applied to the mold from above and below, allowing the magnet powder 1 to be pressure sintered.

Figure 9 shows the temperature and pressure profile used in the pressure sintering process. In Figure 9, the horizontal axis is time, the left vertical axis is temperature, and the right vertical axis is pressure.

First, the inside of the apparatus was evacuated to a vacuum atmosphere of 10 Pa or less, and then a preliminary pressure of 1.4×10 ⁻² GPa was applied to the mold. Note that the pressure value in FIG. 9 does not include the preliminary pressure.

In this state, magnet powder 1 was heated.

The temperature of the magnet powder 1 was increased in three stages. The first temperature increase stage was in the temperature range of room temperature to 250° C., and the temperature increase rate was 125° C./min. The second temperature increase stage was in the temperature range of 250° C. to (maximum temperature T _max -30° C.), and the temperature increase rate was 66.7° C./min. The third temperature increase stage was in the temperature range of (maximum temperature T _max -30° C.) to maximum temperature T _max , and the temperature increase rate was 10° C./min. In FIG. 9, the time t _Q =2 minutes.

After reaching the maximum temperature _Tmax , the magnet powder 1 was held at that temperature for a predetermined time and then rapidly cooled. As described above, if the time when the maximum temperature _Tmax was reached is _tS and the time when cooling started is _tE , the holding time at the maximum temperature _Tmax is ( _tE - _tS ).

In this Example 1, the maximum temperature T _max was set to 500° C., and the holding time (t _E −t _S ) at the maximum temperature T _max was set to 1 minute, where t _R =5.3 minutes and t _E =9.3 minutes.

On the other hand, pressure is applied as maximum pressure _Pmax from time _t1 to time _t2 . After time _t2 , the pressure applied to the magnet powder 1 is released. Time _t2 is set to time _tE .

In Example 1, the time t ₁ when the application of the maximum pressure started was set to the time when the temperature of the magnet powder 1 reached 100° C. (i.e., t _C ). Here, the time t ₁ = t _C = 0.8 minutes. The maximum pressure P _max was set to 1.2 GPa. Therefore, the application time of the maximum pressure (t ₂ - _{t 1} ) was 8.5 minutes.

As a result, a sintered magnet was obtained. The resulting sintered magnet is referred to as "Magnet 1."

(Example 2)
A sintered magnet was produced in the same manner as in Example 1. However, in Example 2, unlike Example 1, the temperature at which maximum pressure application began (the temperature at time _t1 ; the same applies below) was set to 400° C. Therefore, the time _t1 at which maximum pressure application began was 4.25 minutes, and the application time of maximum pressure ( _t2 − _t1 ) was approximately 5 minutes.

The resulting sintered magnet is referred to as "Magnet 2."

(Example 3)
A sintered magnet was produced in the same manner as in Example 1. However, in Example 3, unlike Example 1, the temperature at which the application of maximum pressure began was set to 500° C. Therefore, the time t ₁ at which the application of maximum pressure began was 8.3 minutes, and the application time of maximum pressure (t ₂ −t ₁ ) was 1 minute.

The resulting sintered magnet is referred to as "Magnet 3."

(Example 4)
A sintered magnet was produced in the same manner as in Example 1. However, in Example 4, unlike Example 1, the maximum temperature T _max was set to 550°C.

The application start temperature of the maximum pressure was set to 550° C. Therefore, the application start time of the maximum pressure, t ₁ =9 minutes, and the application time of the maximum pressure (t ₂ - _{t 1} ) was 1 minute.

The resulting sintered magnet is referred to as "Magnet 4."

(Example 5)
A sintered magnet was produced in the same manner as in Example 3. However, in Example 5, unlike Example 3, the maximum pressure P _max was set to 1.0 GPa.

The resulting sintered magnet is referred to as "Magnet 5."

(Example 6)
A sintered magnet was produced in the same manner as in Example 3. However, Example 6 differed from Example 3 in that the maximum pressure P _max was set to 1.8 GPa.

The resulting sintered magnet is referred to as "Magnet 6."

(Example 7)
A sintered magnet was produced in the same manner as in Example 3. However, in Example 7, a magnet powder different from that in Example 3 (referred to as "magnet powder 2") was used to produce the sintered magnet.

Magnetic powder 2 was prepared as follows:

In the process (Magnetic Powder Production) shown in Example 1 above, the temperature of the reduction and diffusion treatment of Powder A was set to 900°C to produce Powder B'. Thereafter, the same process as for Powder B was carried out to produce Sm-Fe-N based magnetic powder (Magnetic Powder 2).

The resulting sintered magnet is referred to as "Magnet 7."

(Example 8)
A sintered magnet was produced in the same manner as in Example 3. However, in Example 8, a magnet powder different from that in Example 3 (referred to as "magnet powder 3") was used to produce the sintered magnet.

In the process (production of magnet powder) shown in Example 1 above, the temperature of the reduction and diffusion treatment of powder A was set to 1050°C to produce powder B''. After that, the same process as for powder B was carried out to produce Sm-Fe-N magnet powder (magnet powder 3).

The resulting sintered magnet is referred to as "Magnet 8."

(Example 9)
A sintered magnet was produced in the same manner as in Example 1. However, in Example 9, unlike Example 1, the sintered magnet was produced by the above-mentioned third method.

That is, before pressure sintering the magnet powder 1, a magnetic field molding process was performed in an electric current sintering device, and then pressure sintering was performed in the same device.

The magnetic field compaction process used the temperature and pressure profile shown on the left side of Fig. 8. Specifically, magnet powder 1 was heated to compaction temperature _T1 at a temperature increase rate of 40°C/min and held for a predetermined time ( _tB - _tA ). The compaction temperature _T1 was 100°C, and the holding time ( _tB - _tA ) was 5 minutes. Thereafter, the next pressure sintering process was carried out without lowering the temperature.

On the other hand, the pressure profile was such that molding pressure _P1 was applied at time _t3 and maintained at molding pressure _P1 for time ( _t4 - _t3 ) in Fig. 8. Then, at time _t4 , the pressure was released once. The molding pressure _P1 was 0.1 GPa, and the time ( _t4 - _t3 ) was 5 minutes. Note that time _t3 = time _tA , and time _t4 = time _tB .

The conditions for the pressure sintering process are the same as in Example 1.

The resulting sintered magnet is referred to as "Magnet 9."

(Example 10)
A sintered magnet was produced in the same manner as in Example 9. However, in Example 10, the sintered magnet was produced using magnetic field compaction conditions different from those in Example 9. Specifically, in the magnetic field compaction process, the compaction temperature _T1 was set to 150°C.

Thus, in FIG. 8, time t _A =t ₃ =3.8 minutes, and time t _B =t ₄ =8.8 minutes.

The resulting sintered magnet is referred to as "Magnet 10."

(Example 11)
A sintered magnet was produced in the same manner as in Example 9. However, in Example 11, the sintered magnet was produced using magnetic field compaction conditions different from those in Example 9. Specifically, in the magnetic field compaction process, the compaction temperature _T1 was set to 200°C.

Therefore, in FIG. 8, time t _A =t ₃ =5 minutes, and time t _B =t ₄ =10 minutes. The obtained sintered magnet is referred to as "magnet 11."

(Example 12)
A sintered magnet was produced in the same manner as in Example 3. However, in Example 12, unlike Example 3, the holding time (t _S - _{t E} ) at the maximum temperature T _max was set to 2 minutes. The end time t ₂ of application of the maximum pressure P _max was set to the start time t _E of the temperature drop.

The resulting sintered magnet is referred to as "Magnet 12."

(Example 13)
A sintered magnet was produced in the same manner as in Example 3. However, in Example 13, unlike Example 3, the holding time (t _S - _{t E} ) at the maximum temperature T _max was set to 5 minutes. The end time t ₂ of application of the maximum pressure P _max was set to the start time t _E of the temperature drop.

The resulting sintered magnet is referred to as "Magnet 13."

(Example 14)
A sintered magnet was produced in the same manner as in Example 3. However, in Example 14, unlike Example 3, the holding time (t _S - t _E ) at the maximum temperature T _max was set to 10 minutes. The end time t ₂ of the application of the maximum pressure P _max was set to the start time t _E of the temperature drop.

The resulting sintered magnet is referred to as "Magnet 14."

(Example 21)
A sintered magnet was produced in the same manner as in Example 1. However, in Example 21, unlike Example 1, the temperature at which the application of maximum pressure began was 25° C. (room temperature). Therefore, the time at which the application of maximum pressure began was t ₁ =0 minutes, and the application time of maximum pressure (t ₂ - _{t 1} ) was 9.3 minutes.

The resulting sintered magnet is referred to as "Magnet 21."

(Example 22)
A sintered magnet was produced in the same manner as in Example 21. However, in Example 22, unlike Example 21, the maximum temperature T _max was set to 600°C.

The resulting sintered magnet is referred to as "magnet 22."

(Example 23)
An attempt was made to produce a sintered magnet in the same manner as in Example 1. However, in Example 23, unlike Example 1, the maximum temperature _Tmax was set to 300°C, and the temperature at which application of the maximum pressure began was also set to 300°C.

Therefore, the application start time of maximum pressure is t ₁ =5.3 minutes, and the application time of maximum pressure (t ₂ -t ₁ ) is 1 minute.

When the obtained magnet (hereinafter referred to as "Magnet 23") was removed from the mold, it disintegrated during demolding. Therefore, a sintered magnet was not obtained in Example 23.

(Example 24)
An attempt was made to produce a sintered magnet in the same manner as in Example 3. However, in Example 24, unlike Example 3, the maximum pressure P _max was set to 2.5 GPa.

After processing, the mold was inspected and found to be damaged. As a result, no sintered magnets were obtained.

The resulting treated body is hereinafter referred to as "magnet 24."

(Example 25)
A sintered magnet was produced in the same manner as in Example 4. However, in Example 25, unlike Example 4, the holding time (t _S - t _E ) at the maximum temperature T _max was set to 20 minutes. The end time t ₂ of application of the maximum pressure P _max was set to the start time t _E of the temperature drop.

The resulting sintered magnet is referred to as "Magnet 25."

The manufacturing conditions for each magnet are summarized in Table 1 below.

（評価）
磁石粉末１～磁石１４、および磁石２１、磁石２２および磁石２５を用いて、以下の評価を行った。

(evaluation)
The following evaluations were carried out using magnet powders 1 to 14, as well as magnets 21, 22 and 25.

(Evaluation of magnetic powder properties)
Using each of the magnet powders 1 to 3, the average particle size and aspect ratio, the amount of residual oxygen, and the coercive force were measured.

(Measurement of average particle size and aspect ratio)
The magnet powder and thermosetting epoxy resin were mixed and thermally cured, and then the mixture was irradiated with a focused ion beam (FIB) and etched to expose the cross section, thereby preparing the sample.

Using a scanning electron microscope (FE-SEM), the cross section of the sample was observed and outlines were drawn on more than 200 randomly selected particles.

The contour lines correspond to the surfaces of particles and/or surfaces of touching particles, although touching particles can be distinguished by FE-SEM backscattered electron imaging or energy dispersive X-ray spectroscopy (EDS) mapping.

Next, the diameter of a circle with the same area as the region enclosed by the outline is defined as the particle diameter of the particle. The average particle diameter was calculated by taking the arithmetic average of the particle diameters of these particles.

For each particle, a rectangle was determined that circumscribed the outline and had the smallest area. The aspect ratio of each particle was calculated by dividing the length of the long side of the resulting rectangle by the length of the short side. Furthermore, the proportion of particles with aspect ratios of 1 or more and 2 or less was evaluated.

(Measurement of Residual Oxygen Amount)
The amount of residual oxygen in each of the magnet powders 1 to 3 was evaluated by inert gas fusion-non-dispersive infrared absorption method.

(Measurement of coercive force)
After mixing the magnet powder with a thermoplastic resin, the mixture was oriented in a magnetic field of 20 kOe to prepare a sample for measuring the coercive force.

The coercivity P1 of each coercivity measurement sample was measured using a vibrating sample magnetometer (VSM).

The measurement temperature was 27°C and the maximum applied magnetic field was 90 kOe.

The characteristic evaluation results obtained for each of the magnet powders 1 to 3 are summarized in Table 2 below.

（磁石の特性評価）
磁石１～磁石１４、および磁石２１、磁石２２および磁石２５に対して、以下の評価を行った。

(Magnetic property evaluation)
Magnets 1 to 14, 21, 22 and 25 were evaluated as follows.

(Measurement of coercive force)
The coercive force P2 of each magnet was measured using a vibrating sample magnetometer (VSM).

The measurement temperature was 27°C and the maximum applied magnetic field was 90 kOe.

From the obtained results, the coercive force reduction rate P was calculated according to the following formula:

Coercive force reduction rate P (%) = (1 - (coercive force P2 of magnet / coercive force measurement sample P1)) x 100 (2)

Here, the magnetic powder contained in the magnet with "coercive force P2" in the numerator of the right-hand side of formula (2) corresponds to the magnetic powder contained in the measurement sample with "coercive force P1" in the denominator. In other words, when the coercive force measurement sample contains magnetic powder 1, formula (2) represents the reduction rate P of the coercive force of magnet 1 relative to magnetic powder 1. The same applies to other magnets.

The coercive force P2 and coercive force reduction rate P for each magnet are summarized in Table 3 below.

表３から、磁石２１、磁石２２および磁石２５では、保磁力低下率Ｐが最小でも５１％（磁石２１）であり、焼結処理により、保磁力が大きく低下することがわかる。これに対して、磁石１～磁石１４では、保磁力低下率Ｐは、いずれも４６％以下となっており、焼結処理による保磁力の低下が抑制されていることがわかる。

From Table 3, it can be seen that the coercivity reduction rate P for Magnets 21, 22, and 25 is at least 51% (Magnet 21), and that the sintering process reduces the coercivity significantly. In contrast, the coercivity reduction rate P for Magnets 1 to 14 is all 46% or less, and it can be seen that the reduction in coercivity due to the sintering process is suppressed.

In this way, it was found that the coercivity loss rate P can be significantly suppressed by optimizing the temperature and pressure profile of the magnet powder and performing pressure sintering or other processes.

Claims (7)

A method for producing a samarium-iron-nitrogen (Sm—Fe—N) based magnet, comprising the steps of:
(1) A step of preparing Sm—Fe—N based magnet powder,
the magnet powder has a residual oxygen content of 1 mass % or less, a cumulative distribution of particles having an aspect ratio of 1 to 2 of 90% or more, and a _Th2Zn17 type crystal structure _;
(2) A step of pressure sintering the magnet powder,
the magnet powder is held at a maximum temperature _Tmax for a predetermined time and compressed at a maximum pressure in the range of 1.0 GPa to 1.8 GPa during at least a portion of the time that the magnet powder is at the maximum temperature _Tmax , the maximum temperature _Tmax being equal to or greater than 400°C and less than 600°C, and the predetermined time being in the range of 1 minute to 10 minutes;
having
In the steps (1) and (2), substantially no pressure is applied to the magnetic powder when the magnetic powder is at a temperature below 100° C. and at a temperature above 600° C.;
Furthermore, after the step (1) and before the step (2),
(3) applying a molding pressure to the magnet powder while applying a magnetic field in a temperature range of 100°C to 400°C;
and when the temperature of the magnet powder is below 100° C., the molding pressure is not applied . The step (1) comprises:
The method according to claim 1 , further comprising the step of wet-grinding the magnet powder. The method of claim 1 , wherein the magnetic field is 10 kOe or greater. The method according to any one of claims 1 to 3 , wherein in the step (3), a molding pressure in the range of 0.1 GPa to 1.8 GPa is applied. The method according to claim 4 , wherein the step (2) is carried out continuously after the step (3) in the same apparatus as that used in the step (3). The method according to claim 1 , wherein the temperature of the magnetic powder when the application of the maximum pressure to the magnetic powder starts is the maximum temperature T _max . The method according to claim 1 , wherein the temperature of the magnetic powder when application of the maximum pressure to the magnetic powder starts is lower than the maximum temperature T _max .

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