JP2022177699A - Rare earth-iron-nitrogen magnetic powder, compound for bond magnets, bond magnet and method for producing rare earth-iron-nitrogen magnetic powder - Google Patents

Abstract

To provide a rare earth-iron-nitrogen magnetic powder having excellent heat resistance and magnetization characteristics and a method for producing the same, a compound for bond magnets and a bond magnet.SOLUTION: A rare earth-iron-nitrogen magnetic powder has an average particle size of 1.0 μm or more and 10.0 μm or less and contains a rare earth element (R) of 22.0 mass% or more and 30.0 mass% or less and nitrogen (N) of 2.5 mass% or more and 4.0 mass% or less. The magnetic powder has a core having a crystal structure selected from Th2Zn17, Th2Ni17 and TbCu7 and a shell layer provided on the surface of the core with the thickness of the shell layer being 1 nm or more and 30 nm or less. The shell layer contains the rare earth element (R) and iron (Fe) with the R/Fe atomic ratio being 0.3 or more and 5.0 or less, and further contains nitrogen (N) of more than 0 atom% and 10 atom% or less. The magnetic powder contains compound particles composed of the rare earth element (R) and phosphorus (P), with the residual magnetization σr being 90 Am2/kg or more.SELECTED DRAWING: Figure 3

Description

TECHNICAL FIELD The present invention relates to rare earth iron nitrogen-based magnetic powders, compounds for bonded magnets, bonded magnets, and methods for producing rare earth iron nitrogen-based magnetic powders.

Many of the R ₂ Fe ₁₇ N _x (R is a rare earth element) nitride compounds having Th ₂ Zn _17- type, Th ₂ Ni ₁₇ -type, and TbCu ₇ -type crystal structures of the rare earth iron nitrogen system generate nucleation-type coercive force. It is known as a magnetic material that has a mechanism and excellent magnetic properties. Among them, the magnetic powder whose main phase compound is Sm ₂ Fe ₁₇ N ₃ with x=3, in which the rare earth element (R) is samarium (Sm), is a high-performance magnetic powder for permanent magnets. Bonded magnets containing this magnetic powder and containing thermoplastic resins such as polyamide 12 and ethylene ethyl acrylate, or thermosetting resins such as epoxy resins and unsaturated polyester resins as binders are used in many fields.

Dissolution and reduction-diffusion methods are conventionally known as methods for producing rare earth iron nitrogen-based magnetic powders represented by Sm ₂ Fe ₁₇ N ₃ . In the melting method, a rare earth metal is used as a raw material, which is melted and reacted with a metal such as iron to produce a magnetic powder. On the other hand, in the reduction-diffusion method, rare earth oxides are used as raw materials, which are simultaneously reduced and reacted with metals such as iron to form magnetic powder. The reduction-diffusion method is considered a desirable technique because it allows the use of inexpensive rare earth oxides.

By the way, the rare earth iron nitrogen-based magnetic powder has a drawback of poor heat resistance (oxidation resistance). If the heat resistance of the powder is poor, the magnetic properties are degraded due to heating in the kneading/forming process during production of the bonded magnet. Bonded magnets may also be exposed to high temperatures of 100° C. or higher during use, and their magnetic properties deteriorate during such use. Therefore, in order to solve these problems, in the rare earth iron nitrogen-based magnetic powder, part of the iron (Fe) is replaced with another element, the fine powder ratio is reduced, or an oxidation-resistant coating is formed on the powder surface. , It has been proposed to improve the heat resistance of the powder.

For example, in Patent Document 1, Non-Patent Document 1 and Non-Patent Document 2, in rare earth iron nitrogen-based magnetic powders produced by a dissolution method or a reduction diffusion method, part of iron (Fe) is replaced with manganese (Mn). have been proposed to improve heat resistance and oxidation resistance. That is, in Patent Document 1, the general formula R _{α-Fe(100-α-β-γ)} Mn _β N _γ (where 3 ≤ α ≤ 20, 0.5 ≤ β ≤ 25, 17 ≤ γ ≤ 25) and having an average particle size of 10 μm or more, Sm, Fe, and Mn are melted and mixed in a high-frequency melting furnace to prepare an alloy, and the alloy is heat-treated in an ammonia mixed gas flow. It is stated that Sm-Fe-Mn-N powder is prepared, and that it has excellent oxidation resistance and temperature characteristics (Claim 1 of Patent Document 1, [0048] to [0050] and [0070]). In addition, Non-Patent Document 1 and Non-Patent Document 2 disclose Sm ₂ (Fe, Mn) ₁₇ N _x (x>4) magnet powder in which part of Fe is replaced with Mn, regarding the magnet powder produced by the reduction diffusion method. exhibits superior heat resistance compared to Sm ₂ Fe ₁₇ N ₃ magnet powder (p. 881 of Non-Patent Document 1).

Further, Patent Document 2 describes a step (a) of pulverizing a master alloy containing a rare earth metal (R) and a transition metal (TM), mixing the pulverized master alloy powder with a rare earth oxide powder and a reducing agent, and adding an inert Step (b) of heat-treating in a gas, Step (c) of embrittlement and pulverization of the obtained reaction product, Step (d) of nitriding the obtained reaction product powder to obtain magnet alloy powder, and Disclosed is a method for producing a rare earth-transition metal-nitrogen based magnet alloy powder, which includes a step (e) of washing the magnet alloy powder with water, and the magnet alloy powder contains very few fine particles of less than 1 μm, so that it is difficult to handle in the atmosphere. It is described that the magnet material becomes easy and has excellent heat resistance and weather resistance (Claim 1 and [0025] of Patent Document 2).

Further, Patent Document 3 relates to a method for producing rare earth-iron-nitrogen magnet powder for bonded magnets, which includes a step of pulverizing rare earth-iron-nitrogen magnet coarse powder in an organic solvent containing phosphoric acid. In order to increase the strength, it is described that a phosphate film is formed on the surface by placing magnet powder in phosphoric acid and treating it (Patent Document 3, claim 1 and [0002]). Further, Patent Document 4 describes a rare earth bonded magnet composed of an anisotropic rare earth alloy magnetic powder having a surface-coated metal layer and a resin, in which Sm--Fe--N alloy magnetic powder produced by the reduction diffusion method is treated in Zn vapor. It is stated that a magnetic powder having a 0.05 micron Zn coating layer on the surface was obtained, and that demagnetization at high temperatures of about 180°C or higher for a long period of time can be suppressed, resulting in a bonded magnet with unprecedented high performance and heat resistance. (Claim 1, [0068] and [0071] of Patent Document 4).

Patent Document 5 relates to the production of rare earth-transition metal alloy powder by the reduction diffusion reaction method, in which the reduction product after heat treatment is subjected to hydrogen treatment, and the hydrogen-treated reduction product is naturally exposed to the atmosphere. Since the disintegration progresses, it is described that it is possible to shorten the time in the water washing and separation process and to omit further pulverization (claim 1 and [0011] of Patent Document 5). Patent Document 6 relates to the production of rare earth-transition metal alloy powder by the reduction diffusion method. It is described that the pressure is increased by 0.11 MPa to cause the alloy to self-heat, and then the pressurization is continued so that the pressure becomes higher than the atmospheric pressure until the alloy does not generate heat substantially (claims 1 and 3 of Patent Document 6). ).

JP-A-08-055712 JP 2005-272986 A Japanese Patent No. 5071160 Japanese Patent Application Laid-Open No. 2003-168602 JP-A-11-124605 JP 2005-008950 A

Transactions of the Institute of Electrical Engineers of Japan A, 124 (2004) 881 Proc. 12th Int. Workshop on RE Magnets and their Applications, Canberra, (1992) 218.

Demand for iron-based bonded magnets containing rare earth elements, which are formed by mixing magnet powder with a resin binder, is increasing in a wide range of fields, including general home appliances, communication/audio equipment, medical equipment, and general industrial equipment. In addition, the storage and transportation of materials for bonded magnets and the usage conditions of products are becoming stricter. Therefore, there is a need for magnetic powders for bonded magnets that have even better heat resistance and high properties such as coercive force.

However, conventionally proposed techniques are not sufficient. For example, the methods of Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2 in which a portion of iron (Fe) is replaced with manganese (Mn) improve the heat resistance of the magnetic powder, but the magnetization decreases. There's a problem. In fact, in Patent Document 1, the magnetic material having a Mn content of 3.5 atomic % (Example 1) has a saturation magnetization of 84 emu / g, whereas the magnetic material with an increased Mn content of 10.3 atomic % (Example 4) shows that the saturation magnetization is reduced to 72 emu/g ([0069] Table 1 of Patent Document 1). In addition, Non-Patent Document 1 describes that in a Sm ₂ (Fe, Mn) ₁₇ N compound, as the amount of Mn increases, the Curie temperature T _c and the maximum magnetization σ _m monotonously decrease ( Non-Patent Document 1, page 885). Furthermore, the technique of reducing the fine powder ratio and the technique of forming an oxidation-resistant film on the powder surface disclosed in Patent Documents 2 to 4 have a certain effect, but there is room for improvement in terms of heat resistance.

The present inventors have extensively studied to solve the above-mentioned problems in rare earth iron nitrogen (R ₂ Fe ₁₇ N ₃ ) magnetic powder having a nucleation type coercive force generation mechanism. As a result, the R ₂ Fe ₁₇ N ₃ compound phase is provided as the main internal volume portion (core portion), and the rare earth (R) richer phase than R ₂ Fe ₁₇ N ₃ is provided as the particle surface layer (shell layer). It was found that a magnetic powder having both high heat resistance and magnetic properties can be obtained by forming a core-shell structure.

The present invention was completed based on such findings, and aims to provide a rare earth iron nitrogen-based magnetic powder having excellent heat resistance and magnetic properties, and a method for producing the same. Another object of the present invention is to provide a compound for a bonded magnet containing rare earth iron nitrogen-based magnetic powder and a bonded magnet.

The present invention includes the following aspects (1) to (14). In the present specification, the expression "~" includes both numerical values. For example, "a to b" is synonymous with "a or more and b or less".

(1) A rare earth iron nitrogen-based magnetic powder containing a rare earth element (R), iron (Fe) and nitrogen (N) as main constituents,
The magnetic powder has an average particle diameter of 1.0 μm or more and 10.0 μm or less, and contains 22.0% by mass or more and 30.0% by mass or less of a rare earth element (R) and 2.5% by mass of nitrogen (N). % or more and 4.0% by mass or less,
The magnetic powder comprises a core portion having a crystal structure of one of Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, and TbCu ₇ type, and a shell layer having a thickness of 1 nm or more and 30 nm or less provided on the surface of the core portion. , and
The shell layer contains a rare earth element (R) and iron (Fe) such that the R/Fe atomic ratio is 0.3 or more and 5.0 or less, and nitrogen (N) is more than 0 atomic % and 10 atomic % or less. containing an amount of
The magnetic powder contains compound particles composed of a rare earth element (R) and phosphorus (P), and has a residual magnetization σr of 90 Am ² /kg or more.

(2) the shell layer has a two-layer structure consisting of an outer layer and an inner layer;
The outer layer contains oxygen (O) and calcium (Ca) in addition to rare earth elements (R), iron (Fe) and nitrogen (N),
The magnetic powder according to (1) above, wherein the inner layer contains oxygen (O) but does not contain calcium (Ca) in addition to a rare earth element (R), iron (Fe) and nitrogen (N).

(3) the shell layer has a two-layer structure consisting of an outer layer and an inner layer;
The magnetic powder according to (2) above, wherein the R/Fe atomic ratio (A) of the outer layer and the R/Fe atomic ratio (B) of the inner layer satisfy B<A.

(4) The magnetic powder according to any one of (1) to (3) above, containing samarium (Sm) as the rare earth element (R).

(5) The magnetic powder according to any one of (1) to (4), further comprising a phosphoric acid compound coating on the outermost surface of the magnetic powder.

(6) When heated at 300 ° C. for 1 hour in an argon (Ar) atmosphere, the retention rate (H _c , 300) is the ratio of the coercive force (H _{c, 300 )} after heating to the coercive force (H c ) before heating. /H _c ) is 70% or more, the magnetic powder according to any one of the above (1) to (5).

(7) A compound for a bonded magnet, containing the magnetic powder according to any one of (1) to (6) above and a resin binder.

(8) A bonded magnet comprising the magnetic powder according to any one of (1) to (6) above and a resin binder.

(9) A method for producing a rare earth iron nitrogen-based magnetic powder according to any one of (1) to (6) above, comprising the following steps;
a preparation step of preparing a rare earth iron alloy powder and a rare earth oxide powder having a crystal structure of one of Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, and TbCu ₇ type;
100 parts by mass of the rare earth iron alloy powder is mixed with 1 to 20 parts by mass of the rare earth oxide powder to contain a rare earth iron alloy powder having a particle size of 15.0 μm or less and a rare earth oxide powder having a particle size of 2.0 μm or less. A mixing step of forming a raw material mixture;
The raw material obtained by adding and mixing a reducing agent in an amount 1.1 to 10.0 times the equivalent required to reduce the oxygen component contained in the raw material mixture to the raw material mixture, and further adding the reducing agent. a reduction diffusion treatment step of heat-treating the mixture at a temperature within the range of 730 to 1050° C. in a non-oxidizing atmosphere to form a reduction diffusion reaction product;
The reduction-diffusion reaction product is exposed to a hydrogen gas atmosphere so that the temperature of the reduction-diffusion reaction product does not exceed 300° C., thereby causing the reduction-diffusion reaction product to absorb hydrogen, thereby disintegrating the reduction-diffusion reaction product. A crushing treatment step of applying
a nitriding heat treatment step of nitriding the crushed reduction-diffusion reaction product at a temperature within the range of 300 to 500° C. in a gas stream containing nitrogen and/or ammonia to form a nitriding reaction product. ,
A method, wherein a phosphoric acid-based compound coating is formed on the rare earth iron alloy powder in either one or both of the preparation step and the mixing step.

(10) In the mixing step, the rare earth iron alloy powder and the rare earth oxide powder are mixed and pulverized in a grinding solvent containing a phosphoric acid surface treatment agent to form a phosphoric acid compound coating on the rare earth iron alloy powder. The method of (9) above.

(11) A wet treatment is performed in which the reduction-diffusion reaction product and/or nitridation reaction product is put into a washing liquid containing water and/or glycol to disintegrate, thereby reducing the reducing agent-derived components in the product. The method of (9) or (10) above, further comprising a step.

(12) The method according to any one of (9) to (11) above, further comprising the step of forming a phosphoric acid-based compound coating on the surface of the product after the nitriding heat treatment.

(13) The method according to any one of (9) to (12) above, wherein the weight loss on heating of the raw material mixture is less than 1% by mass.

(14) The method according to any one of (9) to (13) above, wherein the heat treatment for forming the diffusion reaction product is performed for 0 to 10 hours.

INDUSTRIAL APPLICABILITY According to the present invention, a rare earth iron nitrogen-based magnetic powder having excellent heat resistance and magnetic properties and a method for producing the same are provided. Further, according to the present invention, a bonded magnet compound and a bonded magnet containing rare earth iron nitrogen-based magnetic powder are provided.

An example of the cross-sectional schematic diagram of magnetic powder is shown. SEM secondary electron images of magnetic powder are shown. 1 shows an HAADF-TEM image of magnetic powder. FIG. 4 shows a line extraction diagram of the EDS surface analysis result of the magnetic powder. Fig. 2 shows XRD patterns of magnetic powders; SEM backscattered electron images of magnetic powder are shown.

A specific embodiment of the present invention (hereinafter referred to as "this embodiment") will be described. The present invention is not limited to the following embodiments, and various modifications are possible within the scope of the present invention.

≪Rare earth iron nitrogen-based magnetic powder≫
The rare-earth iron-nitrogen-based magnetic powder (hereinafter sometimes collectively referred to as "magnetic powder") of the present embodiment contains a rare-earth element (R), iron (Fe), and nitrogen (N) as main constituents. This magnetic powder has an average particle size of 1.0 μm or more and 10.0 μm or less, and contains 22.0% by mass or more and 30.0% by mass or less of a rare earth element (R) and 2.5% by mass of nitrogen (N). % or more and 4.0 mass % or less. This magnetic powder has a core portion having a crystal structure of one of Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, and TbCu ₇ type, and a shell layer having a thickness of 1 nm or more and 30 nm or less provided on the surface of the core portion. , provided. This shell layer contains a rare earth element (R) and iron (Fe) such that the R/Fe atomic ratio is 0.3 or more and 5.0 or less, and nitrogen (N) is more than 0 atomic % and 10 atomic % or less. in the amount of Furthermore, this magnetic powder contains compound particles composed of a rare earth element (R) and phosphorus (P). This magnetic powder has a residual magnetization σr of 90 Am ² /kg or more.

Rare earth elements (R) are not particularly limited, but are lanthanum (La), cerium (Ce), samarium (Sm), praseodymium (Pr), neodymium (Nd), gadolinium (Gd), and terbium (Tb). It is preferable that at least one element selected from the group consisting of is included. Alternatively, it preferably further contains at least one element selected from the group consisting of dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm) and ytterbium (Yb). Among them, those containing samarium (Sm) and/or neodymium (Nd) are particularly preferable because the effects of the present embodiment are exhibited remarkably. When applied to bonded magnets, it is desirable that 50 atomic % or more of it is samarium (Sm), and when it is applied to high-frequency magnetic materials, 50 atomic % or more of it is neodymium (Nd). is desirable.

The magnetic powder may contain components other than rare earth elements (R), iron (Fe) and nitrogen (N). For example, cobalt (Co), nickel (Ni), manganese (Mn), chromium (Cr) may be included. However, since nickel (Ni), manganese (Mn) and chromium (Cr) may lower the magnetization, the content thereof should preferably be as small as possible. When other components other than rare earth elements (R), iron (Fe) and nitrogen (N) are included, the content is preferably 10 atomic % or less, more preferably 5 atomic % or less, and 1 atomic % or less. More preferred. However, cobalt (Co) should be 20 atomic % or less. The magnetic powder may contain rare earth elements (R), iron (Fe) and nitrogen (N), and the balance may be unavoidable impurities.

The magnetic powder of this embodiment has an average particle size of 1.0 μm or more and 10.0 μm or less. If the average particle size is less than 1.0 μm, it becomes difficult to handle the magnetic powder. Moreover, the volume ratio of the core portion to the whole particle becomes small. Since the core portion has high magnetic properties, if the volume ratio of the core portion becomes small, it becomes difficult to increase the magnetic properties of the magnetic powder. The average particle size may be 2.0 μm or more, and may be 3.0 μm or more. On the other hand, when the average particle size is larger than 10 μm, it is difficult to obtain a sufficiently high coercive force (H _c ) as a magnetic material. The average particle size may be 9.0 μm or less, and may be 8.0 μm or less.

The magnetic powder of the present embodiment contains a rare earth element (R) in an amount of 22.0% by mass or more and 30.0% by mass or less. If the amount of rare earth element (R) is less than 22% by mass in the composition of the entire magnetic powder, the coercive force is lowered. On the other hand, if it exceeds 30% by mass, the shell layer with low magnetization becomes thick, and compound particles (RP compound particles) composed of rare earth elements (R) and phosphorus (P) and RFe ₃ nitride phase increase. Therefore, the residual magnetization (σ _r ) is reduced. The rare earth (R) content is preferably 24.0% by mass or more and 29.0% by mass or less, more preferably 25.0% by mass or more and 28.0% by mass or less.

Further, the magnetic powder of the present embodiment contains nitrogen (N) in an amount of 2.5% by mass or more and 4.0% by mass or less. If the nitrogen (N) content is less than 2.5% by mass, insufficiently nitrided particles are formed. Such particles have low saturation magnetization and magnetic anisotropy. As a result, the residual magnetization and coercive force of the magnetic powder are reduced. On the other hand, when the amount of nitrogen (N) exceeds 4.0% by mass, the number of excessively nitrided particles increases and the residual magnetization and coercive force decrease. The nitrogen (N) content is preferably 2.8% by mass or more and 3.6% by mass or less, more preferably 2.9% by mass or more and 3.4% by mass or less.

Furthermore, the magnetic powder of the present embodiment has a core portion having a crystal structure of one of Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type and TbCu ₇ type. A magnetic powder having excellent magnetic properties can be obtained by providing a core portion having such a crystal structure. The crystal structure of the core portion can be determined from the peak positions obtained by ordinary powder X-ray diffraction. In this case, the thickness of the shell layer is measured including the shell layer, and the thickness of the shell layer is sufficiently thinner than that of the core portion. Therefore, the influence of the shell layer is hardly seen in the X-ray diffraction pattern.

The magnetic powder of this embodiment has a shell layer provided on the surface of the core portion. The shell layer has a thickness of 1 nm or more and 30 nm or less, contains a rare earth element (R) and iron (Fe) in an R/Fe atomic ratio of 0.3 or more and 5.0 or less, and further contains nitrogen (N). in an amount of more than 0 atomic % and 10 atomic % or less. By providing such a shell layer on the surface of the particles (core portion) having an average particle diameter of 1 to 10 μm, both heat resistance and magnetic properties can be achieved. The shell layer formed here is presumed to be R phase, RFe ₂ phase, RFe ₃ phase, or nitrides of these, which are richer in rare earth elements than R ₂ Fe ₁₇ N ₃ phase. If R/Fe is less than 0.3, the composition of the shell layer becomes close to that of the core, and improvement in heat resistance cannot be expected. On the other hand, when R/Fe exceeds 5.0, residual magnetization may decrease. R/Fe is preferably 0.5 or more and 3.0 or less. If the thickness of the shell layer is less than 1 nm, the effect of improving the heat resistance is small, and if it exceeds 30 nm, the residual magnetization decreases. The thickness is preferably 3 nm or more and 20 nm or less. Also, if the shell layer does not contain nitrogen, the residual magnetization, coercive force and heat resistance of the magnetic powder may be lowered. On the other hand, even if the nitrogen content of the shell layer exceeds 10 atomic %, the residual magnetization, coercive force and heat resistance of the magnetic powder are lowered.

The magnetic powder of this embodiment contains compound particles (RP compound particles) composed of a rare earth element (R) and phosphorus (P). The RP compound particles herein include rare earth phosphide phases such as samarium phosphide (SmP) phases. The RP compound has the function of suppressing the formation of RFe ₂ phase and RFe ₃ phase, which cause deterioration of coercive force and heat resistance. Therefore, by including the RP compound particles in the magnetic powder, it is possible to suppress the deterioration of coercive force and heat resistance. The amount of RP compound particles is not particularly limited. However, from the viewpoint of suppressing deterioration, the amount of RP compound particles in the magnetic powder may be 0.01% by mass or more, 0.1% by mass or more, or 1.0% by mass or more. On the other hand, if there are too many RP compound particles, the residual magnetization may decrease. The amount of RP compound particles may be 15.0 wt% or less, may be 10.0 wt% or less, or may be 5.0 wt% or less. The size of the RP compound particles is not limited, but is, for example, about 100 nm to 5 μm.

The magnetic powder of this embodiment has a residual magnetization σr of 90 Am ² /kg or more. In other words, this magnetic powder has a small amount of α-Fe, which is a different phase. If the magnetic powder contains a large amount of α-Fe, the magnetic properties of the magnetic powder deteriorate. That is, since α-Fe is soft magnetic, if it is contained in a large amount, the squareness of the magnetization curve of the magnetic powder deteriorates. If the squareness deteriorates, not only the residual magnetization but also the coercive force retention rate, that is, the heat resistance, is lowered. In addition, α-Fe acts as a nucleus for generation of reversed magnetic domains, thereby reducing the coercive force of the particles. The magnetic powder of the present embodiment has a small amount of α-Fe and is therefore excellent in magnetic properties including residual magnetization σr. σr may be 95 Am ² /kg or more, 100 Am ² /kg or more, 105 Am ² /kg or more, or 110 Am ² /kg or more. Note that the residual magnetization σr is measured with the magnetic powder oriented. Specifically, it is measured by a method performed in Examples described later.

The magnetic powder preferably has a two-layer structure in which the shell layer consists of an outer layer and an inner layer. Further, the outer layer contains oxygen (O) and calcium (Ca) in addition to the rare earth element (R), iron (Fe) and nitrogen (N), and the inner layer contains the rare earth element (R), Fe (Fe) and In addition to nitrogen (N), it more preferably contains oxygen (O) but does not contain calcium (Ca). The structure of such magnetic powder will be described with reference to FIG. FIG. 1 shows an example of a schematic cross-sectional view of magnetic powder as a model. The magnetic powder (1) comprises a core portion (2), an inner shell layer (3) provided on the surface of the core portion (2), and an outer shell layer (4) provided on the surface of the inner shell layer (3). It consists of The core portion (2) has _a crystal _structure of any one of _Th2Zn17 type, _Th2Ni17 type and _TbCu7 type. The outer shell layer (4) contains calcium (Ca), whereas the inner shell layer (3) does not contain calcium (Ca). Such a two-layer structure of a Ca-containing outer layer and a Ca-free inner layer is expected to have the effect of suppressing the diffusion of oxygen. In the present specification, the term "does not contain calcium (Ca)" means that the amount of Ca is less than 1.0 atomic percent.

In the magnetic powder, the R/Fe atomic ratio (A) of the outer layer and the R/Fe atomic ratio (B) of the inner layer preferably satisfy B<A. By making the composition of the outer layer richer in rare earth elements (R) than the inner layer in this way, the effect of suppressing the diffusion of oxygen is expected as with Ca.

The magnetic powder preferably contains samarium (Sm) as rare earth element (R). This makes it possible to suitably use the magnetic powder as a bonded magnet.

The magnetic powder preferably further has a phosphoric acid compound coating on its outermost surface. If a known phosphoric acid-based compound coating is provided on the outside of the magnetic powder shell layer, the stability in a humid environment can be enhanced. The thickness of the phosphoric acid-based compound coating is desirably thinner than the thickness of the shell layer. The thickness is, for example, 30 nm or less, preferably 5 nm or more and 20 nm or less. If the thickness of the phosphoric acid compound coating exceeds 30 nm, the magnetic properties may deteriorate.

The magnetic powder may have a coercive force (H _c ) of 600 kA/m or more, 800 kA/m or more, 1000 kA/m or more, 1200 kA/m or more, 1400 kA/m or more. or more. Furthermore, this magnetic powder may have a coercivity retention rate (Hc _,300 / _Hc ) of 70% or more, 75% or more, 80% or more, or 85% or more. It may be 90% or more. Here, the coercive force retention ratio (H _c,300 /H _c ) is defined as the coercive force (H is the ratio of coercivity after heating (H _c,300 ) to _c ).

The magnetic powder of the present embodiment is characterized by excellent magnetic properties, particularly magnetization and coercive force, as well as heat resistance and weather resistance. That is, this magnetic powder has higher heat resistance than conventional magnetic powder represented by Sm ₂ Fe ₁₇ N ₃ . In addition, the magnetic properties are equal to or higher than those of highly heat-resistant R ₂ (Fe, M) ₁₇ N _x magnetic powder (M=Cr, Mn) in which part of iron (Fe) is replaced with other elements (Mn, Cr). have

The magnetic powder of this embodiment, which is excellent in heat resistance and magnetic properties, is suitable for producing a bonded magnet by mixing it with a resin binder. That is, the magnetic powder may be exposed to high temperatures when producing a bonded magnet using the magnetic powder. For example, when a bonded magnet is manufactured using a highly heat-resistant thermoplastic resin such as polyphenylene sulfide resin or aromatic polyamide resin as a binder, the material is exposed during the mixing and kneading process of the magnetic powder and the resin binder and the injection molding process. Temperatures can exceed 300°C. The magnetic powder of the present embodiment is prevented from deteriorating in magnetic properties even after being exposed to such a high temperature.

<<Method for producing rare earth iron nitrogen-based magnetic powder>>
The method for producing the rare earth iron nitrogen-based magnetic powder is not limited as long as the resulting magnetic powder satisfies the above requirements. However, it is preferably produced by the reduction diffusion method, and particularly preferably by the technique described below.

The method for producing the rare earth iron nitrogen-based magnetic powder of the present embodiment includes the following steps: a rare earth iron alloy powder having a crystal structure of one of Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, and TbCu ₇ type, and a rare earth oxide. 100 parts by mass of the rare earth iron alloy powder is mixed with 1 to 20 parts by mass of the rare earth oxide powder to obtain a rare earth iron alloy powder having a particle size of 15.0 μm or less and a particle size of 2.0 μm or less. A mixing step of obtaining a raw material mixture containing the rare earth oxide powder and the reducing agent in an amount 1.1 to 10.0 times the equivalent amount required to reduce the oxygen component contained in the raw material mixture. A reduction diffusion treatment step of adding and mixing to the mixture, and further heat-treating the raw material mixture to which a reducing agent is added at a temperature within the range of 730 to 1050 ° C. in a non-oxidizing atmosphere to make a reduction diffusion reaction product, and this reduction The diffusion reaction product is exposed to a hydrogen gas atmosphere so that the temperature does not exceed 300° C., thereby causing the reduction diffusion reaction product to absorb hydrogen, thereby subjecting the reduction diffusion reaction product to a crushing treatment. a treatment step, and a nitriding heat treatment step of nitriding the reduced-diffusion reaction product subjected to the crushing treatment at a temperature within the range of 300 to 500° C. in a gas stream containing nitrogen and/or ammonia to form a nitriding reaction product. ,including. In one or both of the preparation step and the mixing step, a phosphoric acid compound coating is formed on the rare earth iron alloy powder. Details of each step are described below.

<Preparation process>
In the preparation step, rare earth iron alloy powder and rare earth oxide powder are prepared. Here, the rare earth iron alloy powder is mainly a raw material for forming the core portion, and is a powder having a crystal structure of one of Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, and TbCu ₇ type, such as R ₂ Fe ₁₇ The composition is a powder. Rare-earth-iron-alloy powder may be selected that will have a particle size of 15.0 μm or less in the subsequent mixing step. That is, powder with a particle size of 15.0 μm or less may be used, or powder with a particle size of more than 15.0 μm may be used. When using a powder with a particle size of more than 15 μm, it may be pulverized to a particle size of 15.0 μm or less in the mixing step. In the present specification, an alloy is a concept that includes not only solid solutions of multiple kinds of metals, but also intermetallic compounds and mixed crystals. It may be crystalline or amorphous.

Rare earth iron alloy powder (R ₂ Fe ₁₇ powder, etc.) can be produced by a known method such as reduction diffusion method, melting casting method, or liquid quenching method. Among these methods, the reduction diffusion method can directly produce an alloy powder having a desired particle size by adjusting conditions such as the size of the iron particles as the raw material and the temperature during the reduction diffusion reaction. Alternatively, it can be produced by pulverizing a starting material consisting of an alloy powder or an alloy lump having a larger particle size to a desired particle size.

In the rare earth iron alloy powder produced by the reduction diffusion method, hydrogen is contained in the intermetallic compound depending on the production conditions, resulting in hydrogen-containing substances (hydrogen-containing rare earth iron alloy powder such as R ₂ Fe ₁₇ H _x powder). There may be Although this hydrogen-containing material has the same crystal structure as the rare earth iron alloy (R ₂ Fe ₁₇ ), it may have a larger lattice constant. Moreover, even in the case of manufacturing by the melting casting method or the liquid quenching method, the alloy powder pulverized by occluding hydrogen may similarly become a hydrogen-containing material having a large lattice constant. There is no problem even if the alloy powder contains such hydrogen. However, the rare earth iron alloy powder preferably has a water content (weight loss on heating) of less than 1% by mass.

Rare earth oxide powder is mainly a raw material for forming the shell layer. The rare earth element (R) constituting the rare earth oxide powder may be the same as or different from the rare earth element constituting the rare earth iron alloy powder. However, it is preferred that both are identical. Also, the rare earth oxide powder may be selected so that the particle size becomes 2.0 μm or less in the subsequent mixing step. That is, powder with a particle size of 2.0 μm or less may be used, or powder with a particle size of more than 2.0 μm may be used. When using a powder with a particle size of more than 2.0 μm, it may be pulverized to a particle size of 2.0 μm or less in the mixing step.

<Mixing process>
In the mixing step, 100 parts by mass of the prepared rare earth iron alloy powder is mixed with 1 to 20 parts by mass of the rare earth oxide powder to obtain a raw material mixture. When the amount of the rare earth oxide powder is less than 1 part by mass, α-Fe is generated on the surface of the rare earth iron alloy powder (R ₂ Fe ₁₇ powder, etc.) after the reduction diffusion treatment described later, and the magnetic powder finally obtained is deteriorated. Coercive force decreases. On the other hand, when the amount of the rare earth oxide powder exceeds 20 parts by mass, more rare earth (R)-rich _RFe3 and/or _RFe2 compounds are produced than the rare earth iron alloy, and the yield of the finally obtained magnetic powder is reduced. descend.

In the production method of the present embodiment, a phosphoric acid-based compound coating is formed on the rare earth iron alloy powder in one or both of the preparation step and the mixing step. Therefore, the rare earth iron alloy powder in the mixture obtained in the mixing step is provided with a phosphoric acid compound coating. For example, when the prepared rare earth iron alloy powder has a particle size of 15.0 μm or less, the alloy powder may be previously coated with a phosphoric acid compound coating. Alternatively, a phosphoric acid-based compound coating may be formed on the rare earth iron alloy powder in the main mixing step. In any case, it is sufficient that the rare earth iron alloy powder in the mixture obtained in the mixing step is provided with a phosphoric acid compound coating. By providing the phosphoric acid-based compound film in this way, it is possible to improve the coercive force and heat resistance of the manufactured magnetic powder. That is, in the subsequent reduction diffusion reaction step, phosphorus (P) contained in the phosphoric acid-based compound coating reacts with the excess rare earth element (R) to form compound particles (RP) composed of rare earth element (R) and phosphorus (P). compound particles) are precipitated. The RP compound particles suppress the formation of coarse RFe ₂ phases and RFe ₃ phases, which deteriorate the coercive force and heat resistance of the magnetic powder. On the other hand, when a rare earth iron alloy powder not provided with a phosphoric acid compound coating is used, a coarse RFe _2- phase or RFe _3- phase is generated separately from the shell layer, deteriorating the coercive force and heat resistance of the magnetic powder. Sometimes.

In order to form the phosphoric acid-based compound coating, the rare earth iron alloy powder may be subjected to surface treatment using a phosphoric acid-based surface treatment agent. As the phosphoric acid-based surface treatment agent, a known compound as disclosed in Patent Document 3 can be used. Specifically, phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, linear polyphosphoric acid, cyclic metaphosphoric acid, ammonium phosphate, magnesium ammonium phosphate, zinc phosphate, zinc calcium phosphate, manganese phosphate, and iron phosphate. etc. Phosphoric acid may be mixed with a chelating agent and a neutralizing agent to form a treating agent.

Surface treatment may be performed by a known method. For example, when forming a film in the preparation step, the rare earth iron alloy powder is immersed in a solution containing a phosphoric acid-based surface treatment agent to form a film, and then solid-liquid separation is performed to form a film of the rare earth iron alloy powder. You can collect it. In the case of forming the coating in the mixing step, the coating may be formed by immersing a preliminary mixture of the rare earth iron alloy powder and the rare earth oxide powder in a solvent containing the phosphoric acid surface treatment agent. When forming the film, the rare earth iron alloy powder and/or the rare earth oxide powder may be pulverized in a solvent using a pulverizer such as a medium stirring mill. The type of solvent is not particularly limited. For example, alcohols such as isopropyl alcohol, ethanol and methanol, lower hydrocarbons such as pentane and hexane, aromatics such as benzene, toluene and xylene, and organic solvents such as ketones and mixtures thereof can be used.

Formation of the phosphoric acid-based compound film may be performed in either one or both of the preparation process and the mixing process. However, it is preferred to do so in a mixing step. In this case, it is preferable to mix and pulverize the rare earth iron alloy powder and the rare earth oxide powder in a pulverizing solvent containing a phosphoric acid surface treatment agent to form a phosphoric acid compound coating on the rare earth iron alloy powder. That is, when the rare earth iron alloy powder is pulverized, a new surface appears. If the coating is formed in the mixing process, it is possible to form the coating on the new surfaces that appear in this process. In addition, the raw material powder (rare earth iron alloy powder, rare earth oxide powder) can be mixed, pulverized and coated at once, which contributes to a reduction in manufacturing costs.

The optimum coating amount of the phosphoric acid-based compound coating depends on the particle size and surface area of the rare earth iron alloy powder, so it cannot be determined unconditionally. However, when the film is formed using a solvent containing a phosphoric acid-based surface treatment agent, the amount of phosphoric acid can be 0.1 to 0.5 mol/kg with respect to the entire rare earth iron alloy powder.

The raw material mixture obtained in the mixing step contains a rare earth iron alloy powder having a particle size of 15.0 μm or less and a rare earth oxide powder having a particle size of 2.0 μm or less, which is coated with a phosphoric acid compound. That is, the maximum particle size of the rare earth iron alloy powder and the rare earth oxide powder contained in the raw material mixture is set to 15.0 μm or less and 2.0 μm or less, respectively. The rare earth iron alloy powder is a raw material that becomes the core of the magnetic powder. Considering the grain growth, agglomeration and sintering due to the subsequent reduction and diffusion heat treatment, and the formation of the shell layer, the maximum grain size of the alloy powder is the grain size of the magnetic powder (1.0 μm or more and 10.0 μm or less). ). Therefore, the grain size of the alloy powder in the raw material mixed powder is set to 15.0 μm or less. Also, the rare earth oxide powder is desirably a fine powder in order to uniformly form a shell layer with a desired thickness. Therefore, the particle size of the oxide powder in the raw material mixed powder is set to 2.0 μm or less. The particle size of the oxide powder is preferably 1.5 μm or less, more preferably 1.0 μm or less. The grain size can be easily confirmed with a scanning electron microscope (SEM).

In the mixing step, the operation of mixing the rare earth iron alloy powder and the rare earth oxide powder is important. In order to provide a uniform shell layer, it is desirable to make the particle size of the rare earth oxide powder as fine as possible and to disperse it uniformly. Mixing may be done by either a dry method or a wet method. Dry mixing may be performed in an inert gas atmosphere using a dry mixer such as Henschel Mixer, Compix, Mechanohybrid, Mechanofusion, Nobilta, Hybridization System, Miraro, Tumbler Mixer, Theta Composer or Spartan Mixer. . Wet mixing may be performed using a wet mixer such as a bead mill, a ball mill, a nanomizer, a wet cyclone, a homogenizer, a dissolver, and a filmix.

When the rare earth iron alloy powder and the rare earth oxide powder are mixed, they may be pulverized at the same time to obtain a desired particle size. In this case, a phosphoric acid compound coating may be formed during pulverization. A homogeneous mixture can be obtained by adding the rare earth oxide powder and pulverizing at the same time. For fine pulverization, a dry pulverizer such as a jet mill, or a wet pulverizer such as a vibrating mill, a rotating ball mill, or a medium stirring mill can be used. In wet pulverization, organic solvents such as ketones, lower hydrocarbons such as hexane, aromatics such as toluene, alcohols such as ethanol or isopropyl alcohol, fluorine-based inert liquids, or mixtures thereof are pulverized. It can be used as a medium. Alternatively, if an organic solvent to which a phosphoric acid-based surface treatment agent such as orthophosphoric acid is added is used as a grinding medium, a phosphoric acid-based compound film can be formed during pulverization. Such a technique is preferable because the phosphoric acid-based compound coating is formed on the pulverized rare earth iron alloy powder, and at the same time, the rare earth oxide powder is finely pulverized and uniformly dispersed. In the wet method, the raw material mixture can be obtained by drying and removing the organic solvent from the slurry after pulverization.

It is desirable that the weight loss on heating of the raw material mixture is less than 1% by mass. The weight loss on heating is the amount of impurities contained in the mixed powder after drying, and is mainly composed of water. Carbon may also be included depending on the type of organic solvent used during mixing, dispersing aids, or handling processes. If the weight loss on heating exceeds 1% by mass, a large amount of water vapor or carbon dioxide may be generated during the subsequent reduction diffusion treatment. When a large amount of water vapor or carbon dioxide gas is generated, these oxidize the reducing agent (such as Ca grains) and suppress the reduction diffusion reaction. As a result, α-Fe, which is not desirable for obtaining excellent magnetic properties, is produced in the finally obtained magnetic powder. Therefore, it is desirable to sufficiently dry the raw material mixture under reduced pressure. This sufficiently removes not only the contained moisture but also the carbon. The weight loss on heating is obtained by measuring the weight loss α when 50 g of a sample is heated at 400° C. for 5 hours in vacuum.

<Reduction diffusion treatment step>
In the reduction-diffusion treatment step, a reducing agent is added to and mixed with the obtained raw material mixture, and the raw material mixture to which the reducing agent is added is heat-treated to obtain a reduction-diffusion reaction product. Here, the amount of the reducing agent to be added is 1.1 to 10.0 times the equivalent amount required to reduce the oxygen component contained in the raw material mixture. Further, the heat treatment is performed at a temperature within the range of 730 to 1050° C. in a non-oxidizing atmosphere.

At least one selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and hydrides thereof can be used as the reducing agent. Among these, calcium (Ca) is particularly useful. The reducing agent is often supplied in granular form. It is desirable to use a reducing agent with a particle size of 0.5-3.0 mm.

The amount of the reducing agent (such as Ca grains) added is 1.1 to 10.0 times the equivalent. Here, the equivalent is the amount necessary to reduce the oxygen component in the raw material mixture, that is, the oxygen contained in the rare earth iron alloy powder and the rare earth oxide powder. If the added amount is less than 1.1 times, the reduction of the oxide is insufficient, so that the diffusion of the rare earth element (R) generated by the reduction is difficult to proceed. On the other hand, if the amount added exceeds 10 times, the reducing agent will remain in an excessively large amount, which is not preferable. A large amount of residual reducing agent may hinder diffusion of the rare earth element (R). In addition, the amount of residue caused by the reducing agent increases, and it takes time and effort to remove it.

In the mixing step, it is desirable to uniformly mix the raw material mixture and the reducing agent (such as Ca grains). As a mixer, V blender, S blender, ribbon mixer, ball mill, Henschel mixer, Mechanofusion, Nobilta, Hybridization system, Miraro, etc. can be used. It is desirable to mix uniformly, and in particular, to avoid segregation of the rare earth oxide powder in the raw material rare earth iron alloy powder. This is because the segregation of the rare earth oxide powder causes variations in the thickness of the shell layer.

Next, the raw material mixture to which the reducing agent is added is heat-treated to form a reduction diffusion reaction product. This heat treatment may be performed, for example, as follows. That is, the obtained mixture is charged into an iron crucible, and this crucible is placed in a reaction vessel and placed in an electric furnace. From mixing to installation in the electric furnace, it is preferable to avoid contact with the atmosphere and water vapor as much as possible. In order to remove air and water vapor remaining in the mixture, it is preferable to evacuate the inside of the reaction vessel and replace it with an inert gas such as helium (He) or argon (Ar).

Thereafter, the inside of the reaction vessel is evacuated again, or the mixture is subjected to reduction diffusion treatment in a non-oxidizing atmosphere while flowing an inert gas such as helium (He) or argon (Ar) into the vessel. It is important to perform this heat treatment at a temperature within the range of 730-1050°C. When the temperature is lower than 730°C, the vaporized reducing agent (such as Ca grains) promotes the reduction of the rare earth oxides, but formation of a shell layer due to the diffusion reaction on the surface of the rare earth iron alloy powder (such as the R ₂ Fe ₁₇ powder) does not occur. Difficult to proceed. Therefore, the heat resistance of the finally obtained magnetic powder cannot be expected to be improved. On the other hand, if the temperature exceeds 1050° C., grain growth, agglomeration and sintering of the magnetic powder proceed, and residual magnetization and coercive force decrease. The heat treatment temperature is preferably 750 to 1000°C.

The heating and holding time may be set together with the heating temperature so as to suppress grain growth, agglomeration and sintering of the finally obtained magnetic powder. For example, the set temperature is maintained for 0 to 10 hours. After 8 hours, grain growth, agglomeration, and sintering become significant, and it may become difficult to obtain the desired magnetic powder with an average particle size of 1 μm or more and 10 μm or less. The retention time may be 0-8 hours, 0-5 hours, or 0-3 hours. The holding time of "0 hours" means cooling immediately after reaching the set temperature.

By such heat treatment, a core portion containing a rare earth iron alloy having a crystal structure of one of Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type and TbCu ₇ type is formed, and a reduced rare earth element (R ) to form a shell layer. This shell layer contains a rare earth element (R) and iron (Fe) such that the R/Fe atomic ratio is 0.3 or more and 5.0 or less, and furthermore, nitrogen (N) is more than atomic % and 10 atomic % or less. Including quantity. In addition, since the rare earth iron alloy powder is provided with a phosphoric acid compound coating, phosphorus (P) contained in the coating reacts with excess rare earth element (R) during the diffusion reaction due to heating. As a result, compound particles (RP compound particles) composed of rare earth elements (R) and phosphorus (P) are precipitated in the magnetic powder.

Rare earth iron nitrogen-based magnetic powder has a nucleation type coercive force generation mechanism. If a soft magnetic phase such as α-Fe or a crystal defect that lowers the magnetocrystalline anisotropy is present on the grain surface, it becomes a nucleation of a reverse magnetic domain and reduces the coercive force of the grain. The reason why the heat resistance of conventional magnetic powders is poor is that the R ₂ Fe ₁₇ N ₃ compound phase is decomposed by heating to generate soft magnetic phases such as α-Fe and Fe nitrides, which become reverse magnetic domain generation nuclei. It's for. In contrast, in the present embodiment, the heat resistance (oxidation resistance) of the magnetic powder is improved by forming a shell layer having an R/Fe atomic ratio of 0.3 to 5.0 on the surface. The reason for this is presumed to be that the shell layer is less likely to be decomposed by heating than the R ₂ Fe ₁₇ N ₃ compound phase. Moreover, this effect can be advantageously obtained when the heat treatment conditions are set to two stages, for example.

That is, in the process of the reduction diffusion treatment, the heat treatment conditions are set in two stages, in the former stage, the temperature is maintained at a temperature within the range of 730 to 810 ° C. for 0.5 to 4 hours, and in the latter stage, the temperature is further increased to 800 to 800 ° C. A temperature within the range of 1000° C. may be maintained within 3 hours. Under these conditions, the rare earth oxide powder is sufficiently reduced to the rare earth metal, the R ₂ Fe ₁₇ rare earth iron alloy becomes the core, and the diffusion reaction of the rare earth element (R) is promoted on the surface to form the shell layer. It is formed.

The reaction product after the heat treatment is rare earth iron alloy particles having a shell layer on the surface (R ₂ Fe ₁₇ powder, etc.), R metal, RFe ₃ and / or RFe ₂ compounds, RP compound particles, components derived from reducing agents It is a sintered body. Here, the reducing agent-derived component consists of by-produced reducing agent oxide particles (CaO, etc.) and unreacted residual reducing agent (Ca, etc.).

<Crushing treatment process>
In the crushing treatment step, the product (reduction-diffusion reaction product) after the reduction-diffusion treatment is exposed to a hydrogen gas atmosphere so that the temperature does not exceed 300° C., thereby causing the reduction-diffusion reaction product to absorb hydrogen. , thereby subjecting the reduction-diffusion reaction product to a crushing treatment. By exposing the product to a hydrogen gas atmosphere under predetermined conditions in this manner, the R metal, _RFe3 and/or _RFe2 compounds contained in the product absorb hydrogen. Since volume expansion occurs at that time, the product is pulverized using this expansion. The pulverization treatment may be performed by mixing an inert gas such as argon, helium and nitrogen with the hydrogen gas. However, it is preferable to carry out in an atmosphere of hydrogen gas alone. At this time, in order to prevent oxygen from remaining, it is preferable to replace the atmosphere in the heating furnace with an inert gas such as argon before introducing hydrogen. In this case, it is preferable to once evacuate the interior of the furnace after replacing the inert gas, and then introduce hydrogen gas.

The hydrogen absorption treatment (crushing treatment) is started by heating the reduction-diffusion reaction product to a predetermined temperature, eg, 50 to 200° C. in a hydrogen atmosphere. When the reaction product absorbs hydrogen, it self-heats, and this heat builds up the absorption more rapidly. As a result of self-heating due to absorption, the temperature of the reaction product is higher than the heating temperature. However, at this time, it is important to maintain the temperature of the reaction product below 300°C. If the temperature of the reaction product exceeds 300° C., α-Fe, which is a different phase, may remain in the magnetic powder as the final product. Remaining α-Fe deteriorates the squareness of the magnetization curve and reduces the residual magnetization of the magnetic powder.

In order to maintain the temperature of the reaction product at a low temperature of 300° C. or less, the hydrogen partial pressure with respect to the reaction product should be lowered to gradually absorb hydrogen. Methods of reducing the hydrogen partial pressure include, for example, suppressing the amount of hydrogen to be supplied or using a mixed gas of hydrogen gas and inert gas. It is preferable to perform the hydrogen absorption treatment (crushing treatment) under a negative pressure lower than the atmospheric pressure by suppressing the amount of hydrogen to be supplied. This facilitates keeping the reaction product at a low temperature. In this regard, in the production methods disclosed in Patent Documents 5 and 6, the hydrogen absorption treatment is performed under atmospheric pressure or under pressure. However, if the hydrogen absorption treatment is carried out in an atmosphere of atmospheric pressure or higher, hydrogen absorption may proceed excessively rapidly. Therefore, the temperature of the reaction product rises to a high temperature exceeding 300° C. As a result, α-Fe may remain in the magnetic powder. In fact, when the inventors of the present invention investigated, when the temperature of the reaction product exceeded 300° C., the residual magnetization of the finally obtained magnetic powder was low. Since α-Fe was observed in the XRD profile of this magnetic powder, it is considered that the decrease in remanent magnetization is due to the generated α-Fe.

<Nitriding heat treatment process>
In the nitriding heat treatment step, the product (reduction-diffusion reaction product) after reduction-diffusion treatment or pulverization treatment is subjected to nitriding heat treatment in a stream of gas containing nitrogen and/or ammonia to form a nitriding reaction product. Nitriding heat treatment may be performed by a known method, for example, nitrogen (N ₂ ) gas atmosphere, mixed atmosphere _of nitrogen (N ₂ ) gas and hydrogen (H 2 ) gas, ammonia (NH ₃ ) gas atmosphere, ammonia (NH ₃ ) gas atmosphere. Mixed atmosphere of gas and hydrogen (H ₂ ) gas, mixed gas atmosphere of ammonia (NH ₃ ) gas and nitrogen (N ₂ ) gas, ammonia (NH ₃ ) gas, nitrogen (N ₂ ) gas and hydrogen (H ₂ ) gas can be carried out in a mixed gas atmosphere.

The nitriding heat treatment is performed at a temperature within the range of 300-500.degree. If the heating temperature is less than 300° C., the nitriding does not proceed, which is not preferable. If the temperature exceeds 500° C., the alloy decomposes into nitrides of rare earth elements and iron, which is not preferable. The heating temperature may be 350° C. or higher, or 400° C. or higher. Also, the heating temperature may be 480° C. or lower, or 450° C. or lower.

The treatment time of the nitriding heat treatment may be determined according to the gas species, gas flow rate and heating temperature. The smaller (lower) the gas flow rate and the heating temperature, the longer the treatment time. In the case of a mixed atmosphere of ammonia (NH ₃ ) gas and hydrogen (H ₂ ) gas, for example, 1 to 6 hours is preferable, and 2 to 4 hours is more preferable. Further, when a nitrogen (N ₂ ) gas atmosphere is used, it is preferably 10 to 40 hours, and when a mixed atmosphere with hydrogen (H ₂ ) gas is used, it is preferably 5 to 25 hours. After the nitriding heat treatment, the cooled nitriding reaction product is recovered. Further, if necessary, the magnet powder may be heated in a vacuum or in an atmosphere of an inert gas such as argon gas following the nitriding heat treatment. As a result, nitrogen and hydrogen excessively introduced into the magnetic powder are discharged, and the nitrogen distribution in the core of the magnetic powder becomes more uniform. As a result, the squareness of the magnetic powder is improved.

<Wet treatment process>
If necessary, a step (wet treatment step) of subjecting the product (reduction diffusion reaction product and/or nitridation reaction product) obtained in the reduction diffusion treatment step and/or the nitriding heat treatment step to a wet treatment may be provided. good. In the wet process, the reduction-diffusion reaction products and/or nitridation reaction products are disintegrated by immersing them in a cleaning solution containing water and/or glycol. As a result, reducing agent-derived components (by-produced reducing agent oxide particles and unreacted residual reducing agent) in the product are reduced. When the product is put into a washing liquid (water and/or glycol) and left for 0.1 to 24 hours, it breaks up finely and becomes a slurry. This slurry has a pH of about 10-12. The injection of the washing liquid, stirring and removal of the supernatant (decantation) are repeated until the pH becomes 10 or less. After that, a weak acid such as acetic acid is added as necessary so that the pH of the slurry becomes 6 to 7 to dissolve and remove hydroxylated reducing agent components (Ca(OH) ₂ etc.) in the slurry. If the slurry contains surplus nitrides derived from the R metal, _RFe3 and/or _RFe2 compounds, continue stirring and washing while adding an acid so as to maintain the pH at 6-7 to remove these surplus nitrides. Nitrides are also dissolved and removed. After that, the remaining acid component is washed off with water and/or glycol, substituted with alcohol such as methanol or ethanol, and then solid-liquid separated and dried. Drying may be carried out by heating to 100 to 300°C, preferably 150 to 250°C, in vacuum or in an inert gas atmosphere.

As the glycol, one or more alkylene glycols selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol and tripropylene glycol can be used. It is preferred to use these glycols and mixtures thereof as such. If the viscosity is high and it is difficult to separate and remove the reaction product and the reducing agent component after slurrying, glycol diluted with water can be used. However, it is preferable to set the water content in the cleaning liquid to 50% by mass or less. Here, the water content is the weight ratio of water/(glycol+water) expressed as a percentage. If the water content exceeds 50% by mass, the particles may be significantly oxidized. The water content is more preferably 30% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less. The amount of glycol to be used is not particularly limited, but glycol can be used in an amount of 2 to 10 times the equivalent of the reducing agent component in the reaction product reacting with glycol. Preference is given to using 3 to 8 times the amount of glycol relative to the mass of reaction product.

<Micronization treatment step>
If necessary, a step of crushing and pulverizing the product obtained in the nitriding heat treatment step and/or the wet treatment step (pulverization treatment step) may be provided. Depending on the conditions of the reduction diffusion treatment, the obtained powder may be sintered to cause necking. When the finally obtained magnetic powder is applied to an anisotropic magnet material, crushing it can prevent deterioration of the orientation of the magnetic powder in the magnetic field due to necking. For pulverization, a dry pulverizer such as a jet mill or a wet pulverizer such as a medium stirring mill can be used. In any crusher, it is desirable to avoid crushing by strong shearing or collision, and to operate under weak crushing conditions to loosen the necked portion so that the shell layer can be maintained.

<Coating process>
If necessary, a step of forming a phosphoric acid-based compound coating on the surface of the obtained product (powder) (coating step) may be provided. In particular, when the magnetic powder is used in a high-humidity environment, the stability of the powder properties can be enhanced by providing the phosphoric acid-based compound film. The type of phosphoric acid-based compound coating and the method of forming the coating are known as disclosed in Patent Document 3. In this embodiment, the phosphoric acid-based compound coating may be thinly provided in consideration of the shell layer. If the thickness is more than 20 nm, the magnetization may be lowered, so it is desirable to make the film thickness about 5 to 20 nm.

Thus, the magnetic powder of this embodiment can be produced. This magnetic powder contains a rare earth element (R), iron (Fe) and nitrogen (N) as main constituents, has an average particle size of 1.0 μm or more and 10.0 μm or less, and contains 22% of the rare earth element (R). 0% by mass or more and 30.0% by mass or less, and nitrogen (N) in an amount of 2.5% by mass or more and 4.0% by mass or less. Further, this magnetic powder has a core portion having a crystal structure of any one of Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, and TbCu ₇ type, and a shell layer having a thickness of 1 nm or more and 30 nm or less provided on the surface of the core portion. And prepare. This shell layer contains a rare earth element (R) and iron (Fe) such that the R/Fe atomic ratio is 0.3 or more and 5.0 or less, and nitrogen (N) is more than 0 atomic % and 10 atomic % or less. in the amount of Further, this magnetic powder contains compound particles (RP compound particles) composed of rare earth elements (R) and phosphorus (P). This magnetic powder has the effect of being excellent not only in heat resistance and weather resistance but also in magnetic properties.

As far as the inventors of the present invention know, the magnetic powder of this embodiment and the method for producing the same have not been known in the past. For example, Patent Document 2 describes a step (a) of pulverizing a master alloy containing a rare earth metal (R) and a transition metal (TM), and mixing the pulverized master alloy powder with a rare earth oxide powder and a reducing agent to obtain an inert A method for producing a rare earth-transition metal-nitrogen magnet alloy powder including a step (b) of heat-treating in gas is disclosed. However, unlike the manufacturing method of this embodiment, Patent Document 2 does not use fine rare earth oxide powder having a particle size of 2.0 μm or less. Also, only the master alloy is pulverized, and then mixed with the rare earth oxide powder. Therefore, the method of Patent Document 2 cannot form a core-shell structure.

Patent Document 3 discloses that coarse rare earth-iron-nitrogen magnet powder is pulverized in an organic solvent containing phosphoric acid to form a phosphate film. However, the object on which the phosphate coating is formed is the magnet powder after the nitriding treatment, not the rare earth iron alloy powder as the raw material. Therefore, it is clearly different from the manufacturing method of this embodiment. Further, in Patent Document 3, fine rare earth oxide powder having a particle size of 2.0 μm or less is not used. Therefore, the method of Patent Document 3 cannot form a core-shell structure.

Patent Document 4 discloses a single magnetic powder comprising an anisotropic rare earth alloy magnetic powder having a surface-coated metal layer and a resin, wherein the metal of the surface-coated metal layer is at least one of Zn, Sn, In, Al, Si, and rare earth elements. A rare earth bonded magnet of one metal or alloy is disclosed (claims 1 and 2 of Patent Document 4). However, Patent Document 4 discloses that the surface coating metal layer contains a rare earth element (R), iron (Fe) and nitrogen (N) so that the R/Fe atomic ratio is 0.3 or more and 5.0 or less. This surface coating metal layer is completely different from the shell layer of this embodiment.

<Compound for bond magnet>
The compound for bonded magnets of the present embodiment contains the above-described rare earth iron nitrogen-based magnetic powder and a resin binder. This compound is produced by mixing magnetic powder and a resin binder. For mixing, the magnetic powder and the resin binder may be melt-kneaded using a kneader such as a Banbury mixer, kneader, roll, kneader-ruder, single-screw extruder, or twin-screw extruder.

The resin binder may be either a thermoplastic resin or a thermosetting resin. The type of thermoplastic resin binder is not particularly limited. For example, 6 nylon, 6-6 nylon, 11 nylon, 12 nylon, 6-12 nylon, aromatic nylon, polyamide resin such as modified nylon obtained by partially modifying or copolymerizing these molecules, linear polyphenylene Sulfide resin, crosslinked polyphenylene sulfide resin, semi-crosslinked polyphenylene sulfide resin, low density polyethylene, linear low density polyethylene resin, high density polyethylene resin, ultra-high molecular weight polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer resin, ethylene - Ethyl acrylate copolymer resin, ionomer resin, polymethylpentene resin, polystyrene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylonitrile-styrene copolymer resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polyvinyl alcohol resin, polyvinyl butyral resin, polyvinyl formal resin, methacrylic resin, polyvinylidene fluoride resin, polytrifluoroethylene chloride resin, tetrafluoroethylene-propylene hexafluoride copolymer resin, ethylene-tetrafluoroethylene copolymer resin, Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, polytetrafluoroethylene resin, polycarbonate resin, polyacetal resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyphenylene oxide resin, polyallyl ether allyl sulfone resin, polyether sulfone resin, Polyether ether ketone resins, polyarylate resins, aromatic polyester resins, cellulose acetate resins, the aforementioned resin-based elastomers, and the like can be used. In addition, these homopolymers, random copolymers with other kinds of monomers, block copolymers, graft copolymers, and those whose terminal groups are modified with other substances are also included. Furthermore, examples of thermosetting resins include unsaturated polyester resins and epoxy resins.

Among these, 12-nylon and modified nylon thereof, nylon-based elastomers, and polyphenylene sulfide resins are preferred in terms of various properties of the resulting molded article and ease of production thereof. Blends of two or more of these thermoplastics can of course also be used.

In this embodiment, as the raw material powder, _{R 2} (Fe _{, M} ) ₁₇ N _x magnetic powder (M=Cr, A magnetic powder having magnetic properties equal to or higher than those of Mn) is used. Since the magnetic powder has high heat resistance, high-temperature molding is possible using thermoplastic resins such as polyphenylene sulfide resins and aromatic polyamide resins, which themselves have high heat resistance, as binders. Therefore, it is effective for preparing high-performance, high-heat-resistant bonded magnets.

The blending amount of the resin binder is not particularly limited, but is preferably 1 to 50 parts by mass with respect to 100 parts by mass of the compound. If the amount is less than 1 part by mass, not only will the kneading torque be significantly increased and the fluidity will be lowered, molding will be difficult, but also the magnetic properties will be insufficient. On the other hand, if it is more than 50 parts by mass, desired magnetic properties may not be obtained. The blending amount of the resin binder may be 3 to 50 parts by mass, 5 to 30 parts by mass, or 7 to 20 parts by mass.

Addition of reactive diluents, unreactive diluents, thickeners, lubricants, release agents, UV absorbers, flame retardants, various stabilizers, etc. Agents and fillers can be added. Further, other magnet powders than the magnetic powder of the present embodiment may be blended according to required magnetic properties. As other magnet powders, those used for ordinary bonded magnets can be employed, such as rare earth magnet powders, ferrite magnet powders and alnico magnet powders. Not only anisotropic magnet powder but also isotropic magnet powder can be mixed, but it is preferable to use magnet powder having an anisotropic magnetic field _HA of 4.0 MA/m (50 kOe) or more.

<Bond magnet>
The bonded magnet of this embodiment contains the above-described rare earth iron nitrogen-based magnetic powder and a resin binder. This bonded magnet is produced by injection molding, extrusion molding, or compression molding of the compound for bonded magnets described above. A particularly preferred molding method is injection molding. The components and their content in the bonded magnet are the same as those of the compound for bonded magnets.

When injection-molding the compound for a bonded magnet, it is preferable to perform the molding under conditions such that the maximum hysteresis temperature is 330° C. or less, preferably 310° C. or less, and more preferably 300° C. or less. If the maximum history temperature exceeds 330°C, the magnetic properties may deteriorate. However, the bonded magnet of the present embodiment has higher magnetic properties than those using conventional magnetic powders that do not have a shell layer.

When the compound for a bonded magnet contains anisotropic magnetic powder, an anisotropic magnetic powder can be obtained by incorporating a magnetic circuit into the mold of the molding machine and applying an oriented magnetic field to the molding space (mold cavity) of the compound. of bonded magnets can be manufactured. At this time, by setting the orientation magnetic field to 400 kA/m or more, preferably 800 kA/m or more, a bonded magnet with high magnetic properties can be obtained. When the bond magnet compound contains isotropic magnetic powder, the molding may be carried out without applying an oriented magnetic field to the molding space (mold cavity) of the compound.

The bonded magnet of this embodiment is extremely useful in a wide range of fields, including automobiles, general household appliances, communication/audio equipment, medical equipment, and general industrial equipment. Further, according to this embodiment, since the magnetic powder has high heat resistance and high magnetic properties, it is possible to produce a magnet by compacting and sintering the magnetic powder. Therefore, it is possible to obtain a binderless high-performance magnet in which coercive force deterioration is suppressed.

The invention is explained in more detail with the following examples. However, the invention is not limited to the following examples.

(1) Evaluation In preparing the rare earth iron nitrogen-based magnetic powder, various characteristics were evaluated as follows.

<Powder particle size>
The powder was observed under a scanning electron microscope (SEM) to assess its particle size. During the observation, each component particle was distinguished from the difference in contrast in the SEM backscattered electron image at a magnification of about 1000 times, and the long axis diameter was obtained and used as the particle size. Using a laser diffraction particle size distribution analyzer (Nippon Laser Co., Ltd., HELOS & RODOS), the 50% particle size (D ₅₀ ) in the volume distribution of the powder was determined and taken as the average particle size.

<Heat loss>
50 g of the powder was heated at 400° C. for 5 hours in vacuum, and the mass before and after heating was compared to determine the heat loss (α). Specifically, (mass before heating−mass after heating)/mass before heating was taken as the loss on heating (α).

<Magnetic properties>
The magnetic properties of the powder (residual magnetization σ _r and coercive force H _c ) were measured with a vibrating sample magnetometer. The measurement was performed in accordance with Bonded Magnet Test Method Guidebook BMG-2005 (Japan Bonded Magnetic Materials Association). First, about 20 mg of a powder sample was placed in a transparent acrylic case having an inner diameter of 2 mm and a length of 7 mm together with paraffin. The case was heated with a dryer while applying a magnetic field of 1.6 MA/m in the longitudinal direction to melt the paraffin. After orienting the powder, it was cooled to harden the paraffin to prepare a measurement sample. The magnetizing magnetic field of the sample was set to 3.2 MA/m.

<Heat resistance>
The heat resistance of the powder was evaluated by comparing the coercivity (H _c ) of the powder before and after heating. Heating was performed under conditions of 300° C.×90 minutes in an argon (Ar) atmosphere at atmospheric pressure. The coercive force (H _c ) before heating and the coercive force (H _c,300 ) after heating were measured, and the coercive force retention rate (H _c,300 /H _c ) was calculated.

<Powder crystal structure>
The crystal structure of the powder was evaluated by powder X-ray diffraction (XRD) method. The X-ray diffraction measurement was performed using a Cu target under the conditions of an acceleration voltage of 45 kV and a current of 40 mA, and 2θ was measured for 2 minutes. /deg. was scanned at a speed of After that, the obtained X-ray diffraction (XRD) pattern was analyzed to identify the crystal structure.

<Composition analysis and thickness of shell layer>
The composition analysis and average thickness of the shell layer were evaluated using a transmission electron microscope (TEM; JEOL Ltd., JEM-ARM200F; accelerating voltage 200 kV) and an EDS detector (Thermo Fisher Scientific, NSS). At that time, a cross-sectional slice with a thickness of 100 nm, which was prepared by embedding the powder in a thermosetting resin and processing it using a focused ion beam apparatus, was used as an observation sample.

<Composition of magnetic powder>
The rare earth (R) composition (amount) and the nitrogen (N) composition (amount) of the magnetic powder were each analyzed by ICP emission spectrometry and thermal conductivity.

(2) Preparation of Rare Earth Iron Nitrogen Based Magnetic Powder For Examples 1 to 9 and Comparative Examples 1 to 11, rare earth iron nitrogen based magnetic powder was prepared and its properties were evaluated. Tables 1 and 2 show the manufacturing conditions and characteristics of the magnetic powder.

[Example 1]
<Preparation process>
Sm ₂ Fe ₁₇ alloy powder was prepared as the rare earth iron alloy powder, and samarium oxide (Sm ₂ O ₃ ) powder was prepared as the rare earth oxide powder. Sm ₂ Fe ₁₇ alloy powder (rare earth iron alloy powder) was produced according to the following procedure.

Samarium oxide (Sm ₂ O ₃ ) powder with an average particle size (D ₅₀ ) of 2.3 μm, iron (Fe) powder with an average particle size (D ₅₀ ) of 40 μm, and granular metallic calcium (Ca) were prepared. Next, 0.44 kg of samarium oxide powder, 1.0 kg of iron powder and 0.23 kg of granular metallic calcium were mixed with a mixer. The resulting mixture was placed in an iron crucible and heat-treated at 1150° C. for 8 hours under an argon (Ar) gas atmosphere to obtain a reaction product.

The reaction product taken out after cooling was poured into 2 L of water and left in an argon (Ar) gas atmosphere for 12 hours to form a slurry. After discarding the supernatant of this slurry, 2 L of water was newly added and stirred, and when the SmFe alloy powder settled, the supernatant containing the suspended calcium hydroxide was discarded. The operations of adding water, stirring and removing the supernatant were repeated until the pH became 11 or less. Next, while the alloy powder and 2 L of water were being stirred, acetic acid was added until the pH reached 6. Stirring was continued in this state for 30 minutes, and then the supernatant was discarded. The operation of adding 2 L of water again, stirring, and discarding the supernatant was repeated five times. Finally, after replacing the water with alcohol, the alloy powder was recovered using a Nutsche. The collected alloy powder was put in a mixer and dried under the conditions of 100° C. for 10 hours while stirring under reduced pressure to obtain 1.3 kg of Sm ₂ Fe ₁₇ alloy powder (rare earth iron alloy powder). The average particle size of the obtained Sm ₂ Fe ₁₇ alloy powder was 30 μm.

The obtained rare earth iron alloy powder contained 24.5% by mass of samarium (Sm), 0.15% by mass of oxygen (O), 0.54% by mass of hydrogen (H), and 0.01% by mass of calcium (Ca). The main phase was Sm ₂ Fe ₁₇ having a Th ₂ Zn ₁₇ -type crystal structure with a composition of less than mass % and the balance being iron (Fe).

<Mixing process>
100 g of samarium oxide powder (rare earth oxide powder) was preliminarily mixed with 1 kg of Sm ₂ Fe ₁₇ alloy powder (rare earth iron alloy powder) obtained in the preparation step with a rocking mixer. The average particle size (D ₅₀ ) of the samarium oxide powder used was 2.3 μm. The amount of samarium oxide mixed was equivalent to 10 parts by mass with respect to 100 parts by mass of the Sm ₂ Fe ₁₇ alloy powder. Using a mixed solution of 2.2 kg of isopropyl alcohol and 23.1 g of 85% phosphoric acid as a solvent, the resulting premix was ground in a medium agitation mill to obtain a slurry.

The resulting slurry was placed in a mixer, heated under reduced pressure to evaporate the solvent, and cooled to room temperature. After that, nitrogen gas with an oxygen concentration of 4% by volume was flowed while stirring was continued with a mixer, and the oxygen concentration was gradually increased to 10% by volume while taking care that the oxidation heat of the mixed powder did not exceed 40°C. After confirming the end of heat generation, the pulverized mixture was recovered. When the recovered pulverized mixture was placed in an electric furnace and heated to 210° C. in a vacuum, deterioration of the degree of vacuum due to gas release was confirmed. When the gas generation ended and the degree of vacuum returned, the mixture was cooled and the pulverized mixture (raw material mixture) was taken out.

When the pulverized mixture was observed with an SEM backscattered electron image, the maximum particle size of the Sm ₂ Fe ₁₇ alloy particles (Sm ₂ Fe ₁₇ fine powder) was 10 µm, and the maximum particle size of the samarium oxide particles (Sm ₂ O ₃ fine powder) was 1 µm. 0 μm. The composition of the pulverized mixture is 28.8% by mass of samarium (Sm), 0.54% by mass of phosphorus (P), 3.7% by mass of oxygen (O), 0.41% by mass of hydrogen (H), The balance was iron (Fe). The average particle size (D ₅₀ ) of the entire mixture was 1.2 μm. TEM observation after processing the FIB cross section revealed that a phosphoric acid-based compound film containing Sm, Fe, P, and O was formed on the surface of the Sm ₂ Fe ₁₇ alloy particles. The thickness of this coating was 5-10 nm. Furthermore, the heat loss (α) of the pulverized mixture was 0.4% by mass.

<Reduction diffusion treatment step>
The resulting pulverized mixture was subjected to reduction diffusion treatment. First, 46.6 g of a reducing agent was added to 200 g of the pulverized mixture and mixed. Granular metallic calcium (Ca) above a 1.0 mm sieve and below a 2.0 mm sieve was used as a reducing agent. The amount of the reducing agent mixed was 2.5 times the amount (equivalent) required for reduction calculated from the amount of oxygen in the pulverized mixture. The mixture was then placed in an iron crucible, heated under an argon (Ar) gas atmosphere, held at 930° C. for 2 hours, and then cooled. Thus, a reaction product (reduction-diffusion reaction product) was obtained.

<Crushing treatment process>
The recovered reaction product was placed in a tubular furnace, and the interior of the furnace was replaced with argon (Ar) gas. After that, the pressure inside the furnace was once reduced to −100 kPa, hydrogen (H ₂ ) gas was introduced to atmospheric pressure, and the temperature was raised to 150° C. in a hydrogen (H ₂ ) gas stream at a flow rate of 1 L/min, and held for 30 minutes. and cooled. The reaction product absorbed hydrogen when the temperature exceeded 80° C., and the temperature began to rise as the internal pressure of the tubular furnace decreased to a maximum of -60 kPa. Since the inside of the furnace became negative pressure while heat was generated due to hydrogen absorption, the valve on the exhaust side of the tubular furnace was closed to continue supplying hydrogen gas at a maximum flow rate of 1 L/min. The maximum temperature of the exothermic reaction product was 170°C. After cooling, a pulverized reaction product was obtained.

<Nitriding heat treatment process>
The pulverized reaction product was heated in a nitrogen (N ₂ ) gas stream at a flow rate of 200 cc/min, held at 450° C. for 24 hours, and then cooled. A nitriding reaction product was thus obtained.

<Wet treatment process>
A wet treatment was applied to the recovered nitriding reaction product. First, 20 g of the nitriding reaction product was put into 200 cc of deionized water. After that, it was allowed to stand in an argon (Ar) gas atmosphere for 1 hour to form a slurry, and the supernatant of the slurry was discarded. 200 cc of ion-exchanged water was newly added, and the mixture was stirred for 1 minute. The operation of adding ion-exchanged water and removing the supernatant was repeated 15 times. Next, 100 cc of isopropyl alcohol was added, stirred, and filtered using a Nutsche. The resulting cake was placed in a stationary dryer and dried in vacuum at 150° C. for 1 hour. Thus, a rare earth iron nitrogen-based magnetic powder was obtained.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. Further, in the XRD profile, in addition to the Sm ₂ Fe ₁₇ N ₃ peak of the Th ₂ Zn ₁₇ -type crystal structure, the peak of the SmP phase was observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 3.6 μm. Observation with a SEM secondary electron image confirmed aggregation of spherical particles with sizes ranging from 100 nm to 5 μm, as shown in FIG.

The composition of the magnetic powder was, as shown in Table 2, 27.1% by mass of Sm, 3.0% by mass of N, and 0.26% by mass of P. As for the magnetic properties, the residual magnetization (σ _r ) was 101 Am ² /kg and the coercive force (H _c ) was 1006 kA/m. Furthermore, regarding the heat resistance, the coercive force (H _c,300 ) after heating was 922 kA/m, and the retention ratio (H _c,300 /H _c ) was 92%.

The particle surfaces of the obtained magnetic powder were observed by TEM. At that time, a cross-sectional thin piece sample prepared by embedding magnetic powder in a thermosetting resin and then processing it was used as an observation sample. FIG. 3 shows an HAADF (high angle annular dark field) image of the surface, and FIG. 4 shows a line extraction diagram of the EDS (energy dispersive X-ray spectroscopy) plane analysis result in the thickness direction. FIG. 4 shows line extraction of the EDS-analyzed composition from point X to point Y in FIG. Also, the total amount of Sm, Fe, N, Ca, O and P is normalized to 100 atomic %.

As shown in FIG. 3, a shell layer with a thickness of about 10 nm was formed on the surface of the magnetic powder particles. Focusing on the contrast of the HAADF image, it was found that a bright outer layer and a dark inner layer constitute the shell layer. The thickness of these layers was about 4 nm for the outer layer and about 6 nm for the inner layer. Also, as shown in FIG. 4, the maximum Sm/Fe ratio (A) of the outer layer was 2.5. Since the Sm/Fe ratio of the main phase Sm ₂ Fe ₁₇ N ₃ which is the core is about 0.12, it was confirmed that the outer layer is Sm-rich. In addition, the outer layer contained N up to 7 atomic %, and further contained O and Ca. On the other hand, the Sm/Fe ratio (B) of the inner layer close to the main phase side was about 0.2, which was found to be richer in Sm than the main phase. The inner layer contained about 5 atomic % of N at the maximum, and contained O but no Ca. The outer layer Sm/Fe ratio (A) and the inner layer Sm/Fe ratio (B) satisfied the relationship of A>B.

[Example 2]
Reduction diffusion treatment, pulverization treatment, nitriding heat treatment and wet treatment were performed as follows. A rare earth iron nitrogen-based magnetic powder was prepared in the same manner as in Example 1 except for the above.

<Reduction diffusion treatment step>
46.6 g of a reducing agent was added to 200 g of the pulverized mixture (raw material mixture) prepared in Example 1 and mixed. Granular metallic calcium (Ca) above a 1.0 mm sieve and below a 2.0 mm sieve was used as a reducing agent. The amount of the reducing agent mixed was 2.5 times the amount required for reduction calculated from the amount of oxygen in the pulverized mixture. The mixture was then placed in an iron crucible, heated under an argon (Ar) gas atmosphere, held at 900° C. for 2 hours, and then cooled. This gave a reduction diffusion reaction product.

<Crushing treatment process>
The recovered reaction product was placed in a tubular furnace, and the interior of the furnace was replaced with argon (Ar) gas. After that, the pressure in the furnace was once reduced to −100 kPa, hydrogen (H ₂ ) gas was introduced to atmospheric pressure, the temperature was raised to 300° C. in a hydrogen (H ₂ ) gas stream at a flow rate of 1 L/min, and the temperature was maintained for 30 minutes. and cooled. The reaction product absorbed hydrogen when the temperature exceeded 110° C., and the temperature began to rise as the internal pressure of the tubular furnace decreased to a maximum of -70 kPa. Since the inside of the furnace became negative pressure while heat was generated due to hydrogen absorption, the valve on the exhaust side of the tubular furnace was closed to continue supplying hydrogen gas at a maximum flow rate of 1 L/min. The maximum temperature of the reaction product was 300°C. After cooling, a pulverized reaction product was obtained.

<Nitriding heat treatment process>
The pulverized reaction product was heated in a nitrogen (N ₂ ) gas stream at a flow rate of 200 cc/min, held at 450° C. for 24 hours, and then cooled. A nitriding reaction product was thus obtained.

<Wet treatment process>
10 g of the recovered nitriding reaction product was put into 100 cc of deionized water. After that, it was allowed to stand in an argon (Ar) gas atmosphere for 2 hours to form a slurry, and the supernatant of the slurry was discarded. 100 cc of ion-exchanged water was newly added, and the mixture was stirred for 1 minute. The operation of adding ion-exchanged water and removing the supernatant was repeated 15 times. Next, 50 cc of isopropyl alcohol was added, stirred, and filtered using a Nutsche. The resulting cake was placed in a stationary dryer and dried under vacuum conditions of 150° C. for 1 hour. Thus, a rare earth iron nitrogen-based magnetic powder was obtained.

When the obtained rare earth iron nitrogen magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure as shown in FIG. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 3.3 μm. Observation with a backscattered electron image of a SEM confirmed aggregation of spherical particles with sizes ranging from 100 nm to 4 μm, as shown in FIG.

As shown in FIG. 5, the XRD profile showed SmP phase peaks in addition to the Sm ₂ Fe ₁₇ N ₃ peaks of the Th ₂ Zn ₁₇ -type crystal structure. According to Rietveld analysis, the SmP phase content was 3.3 mass %. Particles of several hundred nm to 2 μm shown in bright contrast in FIG. 6 were the SmP phase.

The composition of the magnetic powder, as shown in Table 2, was 27.5% by mass of Sm, 3.1% by mass of N, and 0.27% by mass of P. As for the magnetic properties, the residual magnetization was 102 Am ² /kg and the coercive force was 1123 kA/m. Furthermore, regarding the heat resistance, the coercive force (H _c,300 ) after heating was 851 kA/m, and the retention ratio (H _c,300 /H _c ) was 76%. When the particle surface was observed by TEM in the same manner as in Example 1, a shell layer with a thickness of 2 nm was formed. The maximum Sm/Fe ratio of the shell layer was 0.5, and the maximum amount of N was 3 atomic %. Furthermore, the shell layer is composed of an outer layer and an inner layer, the outer layer containing Sm, Fe, N, O and Ca, whereas the inner layer containing Sm, Fe, N and O but not Ca, the outer layer Sm/Fe The ratio (A) and the inner layer Sm/Fe ratio (B) satisfied the relationship of A>B.

[Example 3]
Wet processing was carried out as indicated below. A rare earth iron nitrogen-based magnetic powder was prepared in the same manner as in Example 1 except for the above.

<Wet treatment process>
20 g of the nitriding reaction product prepared in Example 1 was put into 1 L of ethylene glycol having a water content of 20% by mass defined by water/(ethylene glycol+water). Then, it was stirred in an argon (Ar) gas atmosphere for 3 hours to form a slurry, and the supernatant of the slurry was discarded. 1 L of ethylene glycol having a water content of 20% by mass was newly added, stirred for 5 minutes, left to stand until the nitrided alloy powder settled, and the supernatant in which the calcium component was suspended was discarded. The operation of adding ethylene glycol and removing the supernatant was repeated three times in an argon (Ar) gas atmosphere. Next, 500 cc of dehydrated ethanol was added and the mixture was stirred, allowed to stand until the nitrided alloy powder settled, and the supernatant was discarded. The operation of adding dehydrated ethanol and removing the supernatant was repeated three times in an argon (Ar) gas atmosphere. Finally, it was filtered using a Nutsche, and the resulting cake was placed in a mixer and stirred and dried under vacuum conditions of 150° C. for 1 hour. Thus, a rare earth iron nitrogen-based magnetic powder was obtained.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. Further, in the XRD profile, in addition to the Sm ₂ Fe ₁₇ N ₃ peak of the Th ₂ Zn ₁₇ -type crystal structure, the peak of the SmP phase was observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 4.4 μm. As a result of SEM observation, as in Example 1, aggregation of spherical particles with sizes ranging from 100 nm to 5 μm was confirmed. TEM observation of the particle surface revealed that a 10 nm-thick shell layer having a two-layer structure was formed. The maximum Sm/Fe ratio of the shell layer was 2.1, and the maximum amount of N was 5 atomic %. Furthermore, the shell layer is composed of an outer layer and an inner layer, the outer layer containing Sm, Fe, N, O and Ca, whereas the inner layer containing Sm, Fe, N and O but not Ca, the outer layer Sm/Fe The ratio (A) and the inner layer Sm/Fe ratio (B) satisfied the relationship of A>B.

[Example 4]
Wet processing was carried out as indicated below. A rare earth iron nitrogen-based magnetic powder was prepared in the same manner as in Example 1 except for the above.

<Wet treatment process>
The nitriding reaction product prepared in Example 1 was put into 1 L of ethylene glycol and stirred for 3 hours in an argon (Ar) gas atmosphere to form a slurry. The supernatant liquid of this slurry was discarded, 1 L of ethylene glycol was newly added, and the mixture was stirred for 10 minutes. The operation of adding ethylene glycol and removing the supernatant was repeated 10 times in an argon gas atmosphere. Next, 500 cc of dehydrated ethanol was added, and the mixture was stirred, left to stand until the nitrided alloy powder settled, and the supernatant was discarded. The operation of adding dehydrated ethanol and removing the supernatant was repeated five times in an argon gas atmosphere. Finally, the cake was filtered using a Nutsche in an argon (Ar) gas atmosphere, and the resulting cake was placed in a mixer and stirred and dried under vacuum conditions of 150° C. for 1 hour. Thus, a rare earth iron nitrogen-based magnetic powder was obtained.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. Further, in the XRD profile, in addition to the Sm ₂ Fe ₁₇ N ₃ peak of the Th ₂ Zn ₁₇ -type crystal structure, the peak of the SmP phase was observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 4.8 μm. As a result of SEM observation, as in Example 1, aggregation of spherical particles with sizes ranging from 100 nm to 5 μm was confirmed. TEM observation of the particle surface revealed that a shell layer having a two-layer structure and a thickness of 22 nm was formed. The shell layer had a maximum Sm/Fe ratio of 3.7 and a maximum N content of 9 atomic %. Furthermore, the shell layer is composed of an outer layer and an inner layer, the outer layer containing Sm, Fe, N, O and Ca, whereas the inner layer containing Sm, Fe, N and O but not Ca, the outer layer Sm/Fe The ratio (A) and the inner layer Sm/Fe ratio (B) satisfied the relationship of A>B.

[Example 5]
Mixing and reduction diffusion treatments were performed as described below. A rare earth iron nitrogen-based magnetic powder was prepared in the same manner as in Example 1 except for the above.

<Mixing process>
The milling time of the media agitation mill was adjusted when making the milling mixture. Mixing was carried out in the same manner as in Example 1 except for the above. The maximum particle size of the Sm ₂ Fe ₁₇ alloy particles in the pulverized mixture was 7 μm, and the maximum particle size of the samarium oxide particles was 0.6 μm. The composition of the pulverized mixture was 28.6 wt% Sm, 0.57 wt% P, 4.7 wt% O, 0.48 wt% H, and the balance Fe. The average particle size ( _D50 ) of the whole mixture was 1.1 μm. A phosphoric acid compound film having a thickness of 5 to 10 nm was formed on the surface of the Sm ₂ Fe ₁₇ alloy particles. Furthermore, the heat loss (α) of the pulverized mixture was 0.8% by mass.

<Reduction diffusion treatment step>
70.6 g of a reducing agent was added to 200 g of the resulting pulverized mixture and mixed. Granular metallic calcium (Ca) above a 1.0 mm sieve and below a 2.0 mm sieve was used as a reducing agent. The amount of the reducing agent mixed was 3.0 times the amount required for reduction calculated from the amount of oxygen in the pulverized mixture. The mixture was then placed in an iron crucible, heated under an argon (Ar) gas atmosphere, held at 730° C. for 10 hours, and then cooled. Thus, a reaction product (reduction-diffusion reaction product) was obtained.

The resulting reaction product was subjected to nitriding heat treatment and wet treatment in the same manner as in Example 1 to produce magnetic powder.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. Further, in the XRD profile, in addition to the Sm ₂ Fe ₁₇ N ₃ peak of the Th ₂ Zn ₁₇ -type crystal structure, the peak of the SmP phase was observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 2.8 μm. As a result of SEM observation, as in Example 1, aggregation of spherical particles with sizes ranging from 10 nm to 3 μm was confirmed. TEM observation of the particle surface revealed that a shell layer having a two-layer structure and a thickness of 6 nm was formed. The shell layer had a maximum Sm/Fe ratio of 1.8 and a maximum N content of 6 atomic %. Furthermore, the shell layer is composed of an outer layer and an inner layer, the outer layer containing Sm, Fe, N, O and Ca, whereas the inner layer containing Sm, Fe, N and O but not Ca, the outer layer Sm/Fe The ratio (A) and the inner layer Sm/Fe ratio (B) satisfied the relationship of A>B.

[Example 6]
Mixing, reduction diffusion treatment, crushing treatment and nitriding heat treatment were carried out as follows. A rare earth iron nitrogen-based magnetic powder was prepared in the same manner as in Example 1 except for the above.

<Mixing process>
The milling time of the media agitation mill was adjusted when making the milling mixture. Mixing was carried out in the same manner as in Example 1 except for the above. The maximum particle size of the Sm ₂ Fe ₁₇ alloy particles in the pulverized mixture was 15 μm, and the maximum particle size of the samarium oxide particles was 1.8 μm. The composition of the ground mixture was 29.1% by weight Sm, 0.52% by weight P, 2.5% by weight O, 0.28% by weight H, and the balance Fe. The average particle size ( _D50 ) of the whole mixture was 2.7 μm. A phosphoric acid compound film having a thickness of 5 to 10 nm was formed on the surface of the Sm ₂ Fe ₁₇ alloy particles. Furthermore, the heat loss (α) of the pulverized mixture was 0.2% by mass.

<Reduction diffusion treatment step>
122.7 g of a reducing agent was added to 200 g of the pulverized mixture obtained and mixed. Granular metallic calcium (Ca) above a 1.0 mm sieve and below a 2.0 mm sieve was used as a reducing agent. The amount of the reducing agent mixed was 9.8 times the amount required for reduction calculated from the amount of oxygen in the pulverized mixture. The mixture was then placed in an iron crucible, heated under an argon (Ar) gas atmosphere, held at 860° C. for 4 hours, and then cooled. Thus, a reaction product (reduction-diffusion reaction product) was obtained.

<Crushing treatment>
The recovered reaction product was placed in a tubular furnace, and the interior of the furnace was replaced with argon (Ar) gas. After that, the pressure inside the furnace was once reduced to −100 kPa, hydrogen (H ₂ ) gas was introduced to atmospheric pressure, and the temperature was raised to 150° C. in a hydrogen (H ₂ ) gas stream at a flow rate of 1 L/min, and held for 30 minutes. and cooled. The reaction product absorbed hydrogen when the temperature exceeded 90° C., and the temperature began to rise as the internal pressure of the tubular furnace decreased to a maximum of -60 kPa. Since the inside of the furnace became negative pressure while heat was generated due to hydrogen absorption, the valve on the exhaust side of the tubular furnace was closed to continue supplying hydrogen gas at a maximum flow rate of 1 L/min. The maximum temperature of the exothermic reaction product was 200°C. After cooling, a pulverized reaction product was obtained.

<Nitriding heat treatment process>
The pulverized reaction product was heated in a mixed gas stream of ammonia (NH ₃ ) gas at a flow rate of 50 cc/min and hydrogen (H ₂ ) gas at a flow rate of 100 cc/min, and held at 420° C. for 2 hours. cooled. A nitriding reaction product was thus obtained.

The obtained nitriding reaction product was subjected to a wet treatment in the same manner as in Example 1 to prepare a magnetic powder.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. Further, in the XRD profile, in addition to the Sm ₂ Fe ₁₇ N ₃ peak of the Th ₂ Zn ₁₇ -type crystal structure, the peak of the SmP phase was observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 9.1 μm. As a result of SEM observation, as in Example 1, aggregation of spherical particles with sizes ranging from 100 nm to 4 μm was confirmed. TEM observation of the particle surface revealed that a shell layer having a two-layer structure and a thickness of 8 nm was formed. The shell layer had a maximum Sm/Fe ratio of 2.9 and a maximum N content of 7 atomic %. Furthermore, the shell layer is composed of an outer layer and an inner layer, the outer layer containing Sm, Fe, N, O and Ca, whereas the inner layer containing Sm, Fe, N and O but not Ca, the outer layer Sm/Fe The ratio (A) and the inner layer Sm/Fe ratio (B) satisfied the relationship of A>B.

[Example 7]
Mixing, reduction diffusion treatment, diffusion treatment and nitriding heat treatment were performed as follows. A rare earth iron nitrogen-based magnetic powder was prepared in the same manner as in Example 1 except for the above.

<Mixing process>
The milling time of the media agitation mill was adjusted when making the milling mixture. Mixing was carried out in the same manner as in Example 1 except for the above. The maximum particle size of the Sm ₂ Fe ₁₇ alloy particles in the pulverized mixture was 3 μm, and the maximum particle size of the samarium oxide particles was 0.2 μm. The composition of the ground mixture was 27.5% by weight Sm, 0.61% by weight P, 6.2% by weight O, 0.51% by weight H, and the balance Fe. The average particle size ( _D50 ) of the whole mixture was 1.1 μm. A phosphoric acid compound film having a thickness of 5 to 10 nm was formed on the surface of the Sm ₂ Fe ₁₇ alloy particles. Furthermore, the heat loss (α) of the pulverized mixture was 0.9% by mass.

<Reduction diffusion treatment step>
217.4 g of a reducing agent was added to 200 g of the resulting pulverized mixture and mixed. Granular metallic calcium (Ca) above a 1.0 mm sieve and below a 2.0 mm sieve was used as a reducing agent. The amount of the reducing agent mixed was 7.0 times the amount required for reduction calculated from the amount of oxygen in the pulverized mixture. The mixture was then placed in an iron crucible, heated under an argon (Ar) gas atmosphere, held at 1050° C. for 0.5 hours, and then cooled. Thus, a reaction product (reduction-diffusion reaction product) was obtained.

<Crushing treatment process>
The recovered reaction product was placed in a tubular furnace, and the interior of the furnace was replaced with argon (Ar) gas. After that, the pressure inside the furnace was once reduced to −100 kPa, hydrogen (H ₂ ) gas was introduced to atmospheric pressure, and the temperature was raised to 150° C. in a hydrogen (H ₂ ) gas stream at a flow rate of 1 L/min, and held for 30 minutes. and cooled. The reaction product absorbed hydrogen when the temperature exceeded 100° C., and the temperature began to rise as the internal pressure of the tubular furnace decreased to a maximum of −55 kPa. Since the inside of the furnace became negative pressure while heat was generated due to hydrogen absorption, the valve on the exhaust side of the tubular furnace was closed to continue supplying hydrogen gas at a maximum flow rate of 1 L/min. The maximum temperature of the exothermic reaction product was 160°C. After cooling, a pulverized reaction product was obtained.

<Nitriding heat treatment process>
The pulverized reaction product was heated in a mixed gas stream of ammonia (NH ₃ ) gas at a flow rate of 50 cc/min and hydrogen (H ₂ ) gas at a flow rate of 100 cc/min, and held at 430° C. for 2 hours. cooled. A nitriding reaction product was thus obtained.

The obtained nitriding reaction product was subjected to a wet treatment in the same manner as in Example 1 to prepare a magnetic powder.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. Further, in the XRD profile, in addition to the Sm ₂ Fe ₁₇ N ₃ peak of the Th ₂ Zn ₁₇ -type crystal structure, the peak of the SmP phase was observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 4.2 μm. As a result of SEM observation, as in Example 1, aggregation of spherical particles with sizes ranging from 100 nm to 5 μm was confirmed. TEM observation of the particle surface revealed that a 14 nm-thick shell layer having a two-layer structure was formed. The shell layer had a maximum Sm/Fe ratio of 4.5 and a maximum N content of 8 atomic %. Furthermore, the shell layer is composed of an outer layer and an inner layer, the outer layer containing Sm, Fe, N, O and Ca, whereas the inner layer containing Sm, Fe, N and O but not Ca, the outer layer Sm/Fe The ratio (A) and the inner layer Sm/Fe ratio (B) satisfied the relationship of A>B.

[Example 8]
Mixing, reduction diffusion treatment, crushing treatment and nitriding heat treatment were carried out as follows. A rare earth iron nitrogen-based magnetic powder was prepared in the same manner as in Example 1 except for the above.

<Mixing process>
When preparing the pulverized mixture, the mixed amount of samarium oxide was set to 200 g, and the medium stirring mill pulverization time was adjusted. The amount of samarium oxide mixed was equivalent to 20 parts by mass with respect to 100 parts by mass of the Sm ₂ Fe ₁₇ alloy powder. Mixing was carried out in the same manner as in Example 1 except for the above. The maximum particle size of the Sm ₂ Fe ₁₇ alloy particles was 12 μm and the maximum of the samarium oxide particles was 1.1 μm in the milled mixture. The composition of the pulverized mixture was 33.8% by weight Sm, 0.52% by weight P, 3.5% by weight O, 0.38% by weight H, and the balance Fe. The average particle size (D ₅₀ ) of the whole mixture was 1.7 μm. A phosphoric acid compound film having a thickness of 5 to 10 nm was formed on the surface of the Sm ₂ Fe ₁₇ alloy particles. Furthermore, the heat loss (α) of the pulverized mixture was 0.5% by mass.

<Reduction diffusion treatment step>
31.6 g of a reducing agent was added to 200 g of the pulverized mixture obtained and mixed. Granular metallic calcium (Ca) above a 1.0 mm sieve and below a 2.0 mm sieve was used as a reducing agent. The amount of the reducing agent mixed was 1.8 times the amount required for reduction calculated from the amount of oxygen in the pulverized mixture. The mixture was then placed in an iron crucible, heated under an argon (Ar) gas atmosphere, held at 820° C. for 3 hours, and then cooled. Thus, a reaction product (reduction-diffusion reaction product) was obtained.

<Crushing treatment process>
The recovered reaction product was placed in a tubular furnace, and the interior of the furnace was replaced with argon (Ar) gas. After that, the pressure inside the furnace was once reduced to −100 kPa, hydrogen (H ₂ ) gas was introduced to atmospheric pressure, and the temperature was raised to 150° C. in a hydrogen (H ₂ ) gas stream at a flow rate of 1 L/min, and held for 30 minutes. and cooled. The reaction product absorbed hydrogen when the temperature exceeded 80° C., and the temperature began to rise as the internal pressure of the tubular furnace decreased to a maximum of −87 kPa. Since the inside of the furnace became negative pressure while heat was generated due to hydrogen absorption, the valve on the exhaust side of the tubular furnace was closed to continue supplying hydrogen gas at a maximum flow rate of 1 L/min. The maximum temperature of the exothermic reaction product was 250°C. After cooling, a pulverized reaction product was obtained.

<Nitriding heat treatment process>
The pulverized reaction product was heated in a nitrogen (N ₂ ) gas stream at a flow rate of 200 cc/min, held at 450° C. for 24 hours, and then cooled. A nitriding reaction product was thus obtained.

The obtained nitriding reaction product was subjected to a wet treatment in the same manner as in Example 1 to prepare a magnetic powder.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. Further, in the XRD profile, in addition to the Sm ₂ Fe ₁₇ N ₃ peak of the Th ₂ Zn ₁₇ -type crystal structure, the peak of the SmP phase was observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 5.2 μm. As a result of SEM observation, as in Example 1, aggregation of spherical particles with sizes ranging from 100 nm to 5 μm was confirmed. TEM observation of the particle surface revealed that a shell layer having a two-layer structure and a thickness of 17 nm was formed. The shell layer had a maximum Sm/Fe ratio of 4.9 and a maximum N content of 10 atomic %. Furthermore, the shell layer is composed of an outer layer and an inner layer, the outer layer containing Sm, Fe, N, O and Ca, whereas the inner layer containing Sm, Fe, N and O but not Ca, the outer layer Sm/Fe The ratio (A) and the inner layer Sm/Fe ratio (B) satisfied the relationship of A>B.

[Example 9]
Mixing, reduction diffusion treatment, crushing treatment and nitriding heat treatment were carried out as follows. A rare earth iron nitrogen-based magnetic powder was prepared in the same manner as in Example 1 except for the above.

<Mixing process>
When preparing the pulverized mixture, the mixed amount of samarium oxide was set to 10 g, and the medium stirring mill pulverization time was adjusted. The amount of samarium oxide mixed was equivalent to 1 part by mass with respect to 100 parts by mass of the Sm ₂ Fe ₁₇ alloy powder. Mixing was carried out in the same manner as in Example 1 except for the above. The maximum particle size of the Sm ₂ Fe ₁₇ alloy particles in the pulverized mixture was 4 μm, and the maximum particle size of the samarium oxide particles was 0.3 μm. The composition of the ground mixture was 23.8 wt% Sm, 0.43 wt% P, 5.8 wt% O, 0.29 wt% H, and the balance Fe. The average particle size (D ₅₀ ) of the whole mixture was 1.3 μm. A phosphoric acid compound film having a thickness of 5 to 10 nm was formed on the surface of the Sm ₂ Fe ₁₇ alloy particles. Furthermore, the heat loss (α) of the pulverized mixture was 0.3% by mass.

<Reduction diffusion treatment step>
34.9 g of a reducing agent was added to 200 g of the resulting pulverized mixture and mixed. Granular metallic calcium (Ca) above a 1.0 mm sieve and below a 2.0 mm sieve was used as a reducing agent. The amount of the reducing agent mixed was 1.2 times the amount required for reduction calculated from the amount of oxygen in the pulverized mixture. The mixture was then placed in an iron crucible, heated under an argon (Ar) gas atmosphere, held at 1000° C. for 1 hour, and then cooled. Thus, a reaction product (reduction-diffusion reaction product) was obtained.

<Crushing treatment process>
The recovered reaction product was placed in a tubular furnace, and the interior of the furnace was replaced with argon (Ar) gas. Thereafter, the temperature was raised to 150° C. in a hydrogen (H ₂ ) gas stream at a flow rate of 1 L/min, and the temperature was maintained for 30 minutes to cool. The reaction product absorbed hydrogen when the temperature exceeded 130° C., and the temperature began to rise as the internal pressure of the tubular furnace decreased to a maximum of -40 kPa. Since the inside of the furnace became negative pressure while heat was generated due to hydrogen absorption, the valve on the exhaust side of the tubular furnace was closed to continue supplying hydrogen gas at a maximum flow rate of 1 L/min. The maximum temperature of the reaction product was 150°C. After cooling, a pulverized reaction product was obtained.

<Nitriding heat treatment process>
The pulverized reaction product was heated in a nitrogen (N ₂ ) gas stream at a flow rate of 200 cc/min, held at 470° C. for 20 hours, and then cooled. A nitriding reaction product was thus obtained.

The obtained nitriding reaction product was subjected to a wet treatment in the same manner as in Example 1 to prepare a magnetic powder.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. Further, in the XRD profile, in addition to the Sm ₂ Fe ₁₇ N ₃ peak of the Th ₂ Zn ₁₇ -type crystal structure, the peak of the SmP phase was observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 3.7 μm. As a result of SEM observation, as in Example 1, aggregation of spherical particles with sizes ranging from 100 nm to 7 μm was confirmed. TEM observation of the particle surface revealed that a shell layer having a two-layer structure and a thickness of 5 nm was formed. The shell layer had a maximum Sm/Fe ratio of 1.3 and a maximum N content of 6 atomic %. Furthermore, the shell layer is composed of an outer layer and an inner layer, the outer layer containing Sm, Fe, N, O and Ca, whereas the inner layer containing Sm, Fe, N and O but not Ca, the outer layer Sm/Fe The ratio (A) and the inner layer Sm/Fe ratio (B) satisfied the relationship of A>B.

[Comparative Example 1]
Reduction diffusion treatment was performed under the conditions of 710° C.×2 hours. A magnetic powder was produced in the same manner as in Example 1 except for the above.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. However, diffraction lines of α-Fe were also observed. When the particle surface was observed by TEM, no shell layer was confirmed.

[Comparative Example 2]
Reduction diffusion treatment was performed under the conditions of 1100° C.×1 hour. In the nitriding heat treatment, a mixed gas of ammonia (NH ₃ ) gas at a flow rate of 50 cc/min and hydrogen (H ₂ ) gas at a flow rate of 100 cc/min was used, and the nitriding time was set to 3 hours. A magnetic powder was produced in the same manner as in Example 1 except for the above.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. Further, SEM/EDS analysis confirmed a coarse SmFe ₃ phase between particles. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 10.4 μm. When the particle surface was observed by TEM, no shell layer was confirmed.

[Comparative Example 3]
The amount of samarium oxide mixed was increased to 220 g (equivalent to 22 parts by mass with respect to 100 parts by mass of the Sm ₂ Fe ₁₇ alloy powder) when preparing the pulverized mixture. In addition, the mixed amount of granular metallic calcium (reducing agent) was set to 64.5 g (3.3 times the amount required for reduction calculated from the amount of oxygen in the pulverized mixture) during the reduction diffusion treatment. Furthermore, a mixed gas of ammonia (NH ₃ ) gas at a flow rate of 50 cc/min and hydrogen (H ₂ ) gas at a flow rate of 100 cc/min was used during the nitriding heat treatment, and the nitriding time was set to 3 hours. A magnetic powder was produced in the same manner as in Example 1 except for the above.

When the pulverized mixture was observed with an SEM backscattered electron image, the maximum particle size of the Sm ₂ Fe ₁₇ alloy particles was 12 μm, and the maximum particle size of the samarium oxide particles was 1.4 μm. The composition of the ground mixture was 32.2% by weight Sm, 0.52% by weight P, 3.9% by weight O, 0.02% by weight H, and the balance Fe. The average particle size (D ₅₀ ) of the whole mixture was 2.5 μm. Furthermore, the heat loss (α) of the pulverized mixture was 0.7% by mass.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 3.3 μm. As a result of SEM observation, aggregation of spherical particles with sizes ranging from 100 nm to 8 μm was confirmed. Also, in SEM observation, a large amount of SmFe ₃ nitride phase was observed in addition to SmP particles. When the particle surface was observed by TEM, a shell layer was recognized. The shell layer had a thickness of 32 nm, a maximum Sm/Fe ratio of 5.3, and a maximum N content of 16 atomic %.

[Comparative Example 4]
When preparing the pulverized mixture, the amount of samarium oxide mixed was reduced to 9 g (corresponding to 0.9 parts by mass with respect to 100 parts by mass of Sm ₂ Fe ₁₇ alloy powder). In addition, the amount of granular metallic calcium (reducing agent) mixed was 36.1 g (3.0 times the amount required for reduction calculated from the amount of oxygen in the pulverized mixture) during the reduction diffusion treatment. A magnetic powder was produced in the same manner as in Example 1 except for the above.

When the pulverized mixture was observed with an SEM backscattered electron image, the maximum particle size of the Sm ₂ Fe ₁₇ alloy particles was 9 μm, and the maximum particle size of the samarium oxide particles was 0.7 μm. The composition of the ground mixture was 24.4% by weight Sm, 0.51% by weight P, 2.4% by weight O, 0.01% by weight H, and the balance Fe. The average particle size ( _D50 ) of the whole mixture was 2.1 μm. Furthermore, the heat loss (α) of the pulverized mixture was 0.3% by mass.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. However, strong diffraction lines of α-Fe were also observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 4.6 μm. As a result of SEM observation, aggregation of spherical particles with sizes ranging from 100 nm to 7 μm was confirmed. When the particle surface was observed by TEM, no shell layer was confirmed.

[Comparative Example 5]
A nitriding heat treatment was performed under the conditions of 290° C.×24 hours. A magnetic powder was produced in the same manner as in Example 1 except for the above.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 4.8 μm. As a result of SEM observation, aggregation of spherical particles with sizes ranging from 100 nm to 7 μm was confirmed. When the particle surface was observed with a TEM, a shell layer with a two-layer structure was formed, but the amount of N was at the background level.

[Comparative Example 6]
A nitriding heat treatment was performed at 510° C. for 3 hours. A mixed gas of ammonia (NH ₃ ) gas at a flow rate of 50 cc/min and hydrogen (H ₂ ) gas at a flow rate of 100 cc/min was used during the nitriding heat treatment. A magnetic powder was produced in the same manner as in Example 1 except for the above.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. However, strong diffraction lines of α-Fe were also observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 3.1 μm. As a result of SEM observation, aggregation of spherical particles with sizes ranging from 100 nm to 6 μm was confirmed. When the surface of the particles in the powder was observed with a TEM, it was found that a shell layer with a two-layer structure was formed, but the maximum amount of N was 14 atomic %.

[Comparative Example 7]
The milling time of the media agitation mill was adjusted when making the milling mixture. Also, the amount of granular metallic calcium (reducing agent) mixed in the reduction diffusion treatment was set to 38.8 g (2.5 times the amount required for reduction calculated from the amount of oxygen in the pulverized mixture). A magnetic powder was produced in the same manner as in Example 1 except for the above.

The maximum particle size of the Sm ₂ Fe ₁₇ alloy particles in the pulverized mixture was 18 μm, and the maximum particle size of the samarium oxide particles was 2.8 μm. The composition of the pulverized mixture was 29.0 wt% Sm, 0.55 wt% P, 3.1 wt% O, 0.009 wt% H, and the balance Fe. The average particle size (D ₅₀ ) of the whole mixture was 3.7 μm. Furthermore, the heat loss (α) of the pulverized mixture was 0.05% by mass.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 8.1 μm. SEM observation confirmed aggregation of spherical particles with a size of 1 μm to 10 μm. When the particle surface was observed with a TEM, it was found that there were portions where the shell layer was formed and portions where the shell layer was not formed. Therefore, there were variations in the formation of the shell layer.

[Comparative Example 8]
The mixed amount of granular metallic calcium (reducing agent) was 18.5 g (1.0 times the amount required for reduction calculated from the amount of oxygen in the pulverized mixture) during the reduction diffusion treatment. A magnetic powder was produced in the same manner as in Example 1 except for the above.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. However, strong diffraction lines of α-Fe were also observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 7.3 μm. As a result of SEM observation, aggregation of spherical particles with sizes ranging from 100 nm to 8 μm was confirmed. Further, when the particle surface was observed by TEM, no shell layer could be confirmed.

[Comparative Example 9]
The amount of granular metallic calcium (reducing agent) mixed during the reduction diffusion treatment was 202.1 g (10.9 times the amount required for reduction calculated from the amount of oxygen in the pulverized mixture). A magnetic powder was produced in the same manner as in Example 1 except for the above.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. However, strong diffraction lines of α-Fe were also observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 9.2 μm. As a result of SEM observation, aggregation of spherical particles with sizes ranging from 100 nm to 10 μm was confirmed. When the particle surface was observed by TEM, no shell layer was confirmed.

[Comparative Example 10]
A commercially available Sm ₂ Fe ₁₇ N ₃ magnetic powder (SFN alloy fine powder B manufactured by Sumitomo Metal Mining Co., Ltd.) was prepared and its properties were evaluated. When the heat resistance was examined, the coercive force (H _c ) before heating was 844 kA/m, the coercive force (H _{c, 300} ) after heating was 407 kA/m, and the retention rate (H _{c, 300} /H _c ). was 48%.

[Comparative Example 11]
The hydrogen gas flow rate in the crushing process was set to 10 L/min. A magnetic powder was produced in the same manner as in Example 2 except for the above. In the crushing process, the reaction product absorbed hydrogen when the temperature exceeded 118° C., but since the amount of hydrogen gas supplied was large, the pressure inside the furnace did not become negative. The exotherm of the reaction product was vigorous and its maximum temperature was 370°C.

When the obtained rare earth iron nitrogen-based magnetic powder was analyzed by the XRD method, it was confirmed to have a Th ₂ Zn ₁₇ -type crystal structure. However, diffraction lines of α-Fe were also observed. The average particle size (D ₅₀ ) measured with a laser diffraction particle size distribution meter was 2.9 μm. As a result of SEM observation, aggregation of spherical particles with sizes ranging from 100 nm to 5 μm was confirmed. When the surface of the particles in the powder was observed with a TEM, it was found that a shell layer with a two-layer structure was formed, but fine precipitates thought to be α-Fe were also confirmed on the surface of the core portion.

(3) Evaluation Results The rare earth iron nitrogen-based magnetic powders of Examples 1 to 12 are mainly composed of samarium (Sm), iron (Fe) and nitrogen (N), and the amount of samarium (Sm) is 23.2 to 29. .9% by mass, and the amount of nitrogen (N) was 2.8 to 3.9% by mass. This magnetic powder had a Th ₂ Zn ₁₇ -type crystal structure and an average particle size of 2.8 to 9.1 μm. Further, this magnetic powder has a Sm/Fe atomic ratio of 0.5 to 4.9, contains 3 to 10 atomic percent of nitrogen (N), and has a shell layer with a thickness of 2 to 22 nm on the particle surface. rice field. This magnetic powder has a residual magnetization (σ _r ) of 90 Am ² /kg or more, a coercive force (H _c ) of 754 kA/m or more, and a coercive force retention rate (H _{c, 300} /H _c ) of 71% or more. Met. This magnetic powder exhibited high heat resistance.

In contrast, the magnetic powder of Comparative Example 1 had a reduction diffusion temperature (710° C.) lower than 730° C. at the time of production. retention rate (43%) was inferior to 70%. In addition, the magnetic powder of Comparative Example 2 has a reduction diffusion temperature (1100° C.) higher than 1050° C. at the time of production, so its average particle size (10.4 μm) exceeds 10 μm and coercive force (420 kA/m). was low, and the coercive force retention rate (55%) was inferior to 70%.

In the magnetic powder of Comparative Example 3, the mixed amount of samarium oxide (22 parts by mass with respect to 100 parts by mass of the Sm ₂ Fe ₁₇ alloy powder) at the time of production exceeded 20 parts by mass. Therefore, the amount of samarium (32.2% by mass) exceeded 30% by mass and the amount of nitrogen (5.2% by mass) exceeded 4.0% by mass. Also, many SmFe _three- phase nitrides were observed in the powder. As a result, the shell layer thickness (32 nm) exceeded 30 nm, the Sm/Fe atomic ratio (5.3) exceeded 5.0, and the residual magnetization (50 Am ² /kg) was low. In the magnetic powder of Comparative Example 4, the mixed amount of samarium oxide (0.9 parts by mass with respect to 100 parts by mass of the Sm ₂ Fe ₁₇ alloy powder) at the time of production was less than 1 part by mass. Therefore, the amount of samarium (21.9% by mass) was less than 22% by mass. As a result, no shell layer was observed, and the residual magnetization (43 Am ² /kg) and coercive force (283 kA/m) were low.

The magnetic powder of Comparative Example 5 was below the nitriding temperature (290°C) and 300°C during production. Therefore, the nitrogen content (1.7% by mass) was less than 2.5% by mass. Also, although a shell layer was observed, the nitrogen in the shell layer was at background levels for the TEM/EDS detector. As a result, the residual magnetization (39 Am ² /kg) and coercive force (109 kA/m) of the magnetic powder were low. In the magnetic powder of Comparative Example 6, the nitriding temperature (510°C) during production exceeded 500°C. The nitrogen content (5.3% by mass) of the magnetic powder exceeded 4.0% by mass, and the residual magnetization (48 Am ² /kg) and coercive force (227 kA/m) were low.

In the magnetic powder of Comparative Example 7, the maximum particle size (18 μm) of the Sm ₂ Fe ₁₇ alloy powder in the raw material exceeded 15 μm, and the maximum particle size (2.8 μm) of the samarium oxide powder exceeded 2 μm. . Therefore, some particles had a shell layer observed and some did not, and there was variation in the formation of the shell layer. It is considered that this is because the raw material powder has a coarse particle size, and unevenness occurs when the samarium reduced in the reduction diffusion step penetrates into the raw material. As a result, the residual magnetization (77 Am ² /kg) and coercive force (491 kA/m) were low. The coercive force retention rate (47%) was lower than 70%, indicating poor heat resistance.

In the magnetic powder of Comparative Example 8, the amount of metallic calcium compounded (1.0 times the equivalent) was less than 1.1 times. Therefore, the samarium content (21.7% by mass) of the magnetic powder was less than 22% by mass, and the nitrogen (N) content (2.3% by mass) was also less than 2.5% by mass. Remanent magnetization (53 Am ² /kg) and coercive force (173 kA/m) were low. No shell layer was observed. The coercive force retention rate (36%) was much lower than 70%, indicating poor heat resistance. The magnetic powder of Comparative Example 9 contained more than 10 times the amount of metallic calcium (10.9 times the equivalent). Therefore, the samarium content (21.5% by mass) of the magnetic powder was less than 22% by mass, and the nitrogen content (1.9% by mass) was also less than 2.5% by mass. It is thought that the amount of calcium was too large, and the diffusion of samarium was inhibited. Remanent magnetization (48 Am ² /kg) and coercive force (93 kA/m) were low. No shell layer was observed. The coercive force retention rate (43%) was lower than 70%, indicating poor heat resistance.

Comparative Example 10, which uses commercially available Sm ₂ Fe ₁₇ N ₃ magnetic powder as a conventional example, had a coercive force retention rate (48%) lower than 70%.

In the magnetic powder of Comparative Example 11, in the pulverization process, sufficient hydrogen was supplied so that the inside of the furnace did not become negative pressure, and the reaction product rapidly absorbed hydrogen and generated heat violently, and the temperature of the reaction product exceeded 300°C. , and reached 370°C. Although the samarium content, nitrogen (N) content, and phosphorus (P) content of the magnetic powder as a whole were the same as in Example 2, the average particle size was as small as 2.9 μm, and the squareness of the magnetization curve was reduced, resulting in remanent magnetization. (85 Am ² /kg) and coercive force (1007 kA/m), which were lower than those of Example 2. This is believed to be due to α-Fe whose precipitation was confirmed. Moreover, the coercive force retention rate (68%) was lower than 70%, indicating poor heat resistance.

Claims (14)

A rare earth iron nitrogen-based magnetic powder containing a rare earth element (R), iron (Fe) and nitrogen (N) as main constituents,
The magnetic powder has an average particle diameter of 1.0 μm or more and 10.0 μm or less, and contains 22.0% by mass or more and 30.0% by mass or less of a rare earth element (R) and 2.5% by mass of nitrogen (N). % or more and 4.0% by mass or less,
The magnetic powder comprises a core portion having a crystal structure of one of Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, and TbCu ₇ type, and a shell layer having a thickness of 1 nm or more and 30 nm or less provided on the surface of the core portion. , and
The shell layer contains a rare earth element (R) and iron (Fe) such that the R/Fe atomic ratio is 0.3 or more and 5.0 or less, and nitrogen (N) is more than 0 atomic % and 10 atomic % or less. contains an amount of
The magnetic powder contains compound particles composed of a rare earth element (R) and phosphorus (P), and has a residual magnetization σr of 90 Am ² /kg or more. The shell layer has a two-layer structure consisting of an outer layer and an inner layer,
The outer layer contains oxygen (O) and calcium (Ca) in addition to rare earth elements (R), iron (Fe) and nitrogen (N),
The magnetic powder according to claim 1, wherein the inner layer contains oxygen (O) but no calcium (Ca) in addition to rare earth elements (R), iron (Fe) and nitrogen (N). The shell layer has a two-layer structure consisting of an outer layer and an inner layer,
3. The magnetic powder according to claim 2, wherein the R/Fe atomic ratio (A) of the outer layer and the R/Fe atomic ratio (B) of the inner layer satisfy B<A. The magnetic powder according to any one of claims 1 to 3, containing samarium (Sm) as the rare earth element (R). The magnetic powder according to any one of claims 1 to 4, further comprising a phosphoric acid compound coating on the outermost surface of the magnetic powder. When heated at 300° C. for 1 hour in an argon (Ar) atmosphere, the retention ratio (H c,300 /H _c ) is the ratio of the coercive force after heating (H _{c ,300} ) to the coercive force (H c ) before heating _. ) is 70% or more, the magnetic powder according to any one of claims 1 to 5. A compound for a bonded magnet, comprising the magnetic powder according to any one of claims 1 to 6 and a resin binder. A bonded magnet comprising the magnetic powder according to any one of claims 1 to 6 and a resin binder. A method for producing a rare earth iron nitrogen-based magnetic powder according to any one of claims 1 to 6, comprising the following steps;
a preparation step of preparing a rare earth iron alloy powder and a rare earth oxide powder having a crystal structure of one of Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, and TbCu ₇ type;
100 parts by mass of the rare earth iron alloy powder is mixed with 1 to 20 parts by mass of the rare earth oxide powder to contain a rare earth iron alloy powder having a particle size of 15.0 μm or less and a rare earth oxide powder having a particle size of 2.0 μm or less. A mixing step of forming a raw material mixture;
The raw material obtained by adding and mixing a reducing agent in an amount 1.1 to 10.0 times the equivalent required to reduce the oxygen component contained in the raw material mixture to the raw material mixture, and further adding the reducing agent. a reduction diffusion treatment step of heat-treating the mixture at a temperature within the range of 730 to 1050° C. in a non-oxidizing atmosphere to form a reduction diffusion reaction product;
The reduction-diffusion reaction product is exposed to a hydrogen gas atmosphere so that the temperature of the reduction-diffusion reaction product does not exceed 300° C., thereby causing the reduction-diffusion reaction product to absorb hydrogen, thereby disintegrating the reduction-diffusion reaction product. A crushing treatment step of applying
a nitriding heat treatment step of nitriding the crushed reduction-diffusion reaction product at a temperature within the range of 300 to 500° C. in a gas stream containing nitrogen and/or ammonia to form a nitriding reaction product. ,
A method, wherein a phosphoric acid-based compound coating is formed on the rare earth iron alloy powder in either one or both of the preparation step and the mixing step. In the mixing step, the rare earth iron alloy powder and the rare earth oxide powder are mixed and pulverized in a pulverizing solvent containing a phosphoric acid surface treatment agent to form a phosphoric acid compound coating on the rare earth iron alloy powder. Item 9. The method of Item 9. The step of subjecting the reduction-diffusion reaction product and/or the nitridation reaction product to a washing liquid containing water and/or glycol to disintegrate the reaction product, thereby reducing reducing agent-derived components in the product. 11. A method according to claim 9 or 10, comprising The method according to any one of claims 9 to 11, further comprising the step of forming a phosphoric acid-based compound coating on the surface of the product after the nitriding heat treatment. The method according to any one of claims 9 to 12, wherein the weight loss on heating of the raw material mixture is less than 1% by mass. The method according to any one of claims 9 to 13, wherein the heat treatment for forming the diffusion reaction product is performed for 0 to 10 hours.

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