JP2012246174A - Method for manufacturing iron nitride material, and iron nitride material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an iron nitride material, by which an iron nitride material having a high content of an α"FeNphase can be obtained, and to provide such an iron nitride material.SOLUTION: The manufacturing method includes a step of generating an α"FeNphase by heating an Fe-containing base material such as pure iron, an iron alloy or an iron compound in a nitrogen element-containing gas atmosphere such as a nitrogen atmosphere, while applying a magnetic field to the base material. The applied magnetic field H is a strong magnetic field with H≥(7/3)+2×Nf, wherein Nf (Nf=0-1) is a demagnetization coefficient prescribed from the shape of the base material. Since the strong magnetic field with H≥(7/3)+2×Nf is applied to the base material, the primitive lattice of Fe elongates in the applied magnetic field direction (one direction) and the intrusion position of N is easily restricted to this one direction. Therefore, excess nitrogen is controlled, the α"FeNphase excellent in magnetic properties is easily generated, and the objective iron nitride material having a high content of the α"FeNphase can be manufactured.

Description

  The present invention relates to an iron nitride material suitable for a material of a magnetic member such as a permanent magnet, and a manufacturing method thereof. In particular, the present invention relates to a method for producing an iron nitride material from which an iron nitride material having a high content of ferromagnetic iron nitride is obtained.

  As permanent magnets used in motors and generators, metal magnets (typically alnico magnets) made of metal materials such as Fe-Al-Ni-Co alloys and Fe-Cr-Co alloys, oxidation Ferrite magnets made of ferrite composed mainly of iron are used. In addition, rare earth magnets (typically, Nd—Fe—B magnets and Sm—Fe—N magnets) are known as magnets having superior magnetic properties.

Furthermore, as a magnetic material with very high saturation magnetization and excellent magnetic properties, α ”Fe ₁₆ N ₂ (saturation magnetization: about 2.8 T in tetragonal calculations, tetragonal crystal, a = 5.72Å, c = 6.29 鉄, crystal symbol: I4 / mmm) (see Patent Document 1). Magnets containing α ″ Fe ₁₆ N ₂ are expected to yield magnets with better magnetic properties than the rare earth magnets. .

JP 2003-160314 A

An iron nitride material containing α ”Fe ₁₆ N ₂ is obtained by heat-treating an Fe base material made of a thin film or nanoparticles in a nitrogen atmosphere or an ammonia atmosphere to produce α” Fe ₁₆ N ₂ in the base material. Manufacturing is under consideration. However, in this method, the amount of α ″ Fe ₁₆ N _{2 produced} is small, and the obtained iron nitride material has little effect of improving the magnetic properties due to the content of α ″ Fe ₁₆ N ₂ . Patent Document 1 proposes plasma irradiation, but the content of α ″ Fe ₁₆ N _{2 in} the obtained iron nitride material is only about 30%. Therefore, the content of α ″ Fe ₁₆ N ₂ is included. It is desired to develop a production method capable of obtaining a larger amount of iron nitride material.

Accordingly, one of the objects of the present invention is to provide a method for producing an iron nitride material from which an iron nitride material having a high content of α ″ Fe ₁₆ N ₂ is obtained. Another object of the present invention is to provide an α “To provide an iron nitride material having a high content of Fe ₁₆ N ₂ .

The crystal structure of Fe ₁₆ N ₂ is Fe atoms aligned in one direction along any axis among the lattice axes (a-axis, b-axis, c-axis) of the basic lattice of iron (BCC). It is an arrangement in which every other N atom invades between Fe atoms. That is, they are aligned with Fe atom-N atom-Fe atom-Fe atom-N atom-Fe atom. Accordingly, it can be said that α ″ Fe ₁₆ N ₂ can be efficiently generated if N atoms can be positively arranged between the Fe atoms arranged in one direction.

When simply nitriding iron, iron alloy, or iron compound, not only between Fe atoms-Fe atoms arranged in any one direction (e.g. c-axis direction) of the body-centered cubic lattice, but also in another two directions (e.g. a-axis N atoms also invade between the Fe atoms and the Fe atoms aligned in the direction and the b-axis direction). That is, N atoms randomly invade in three directions along the lattice axis of the body-centered cubic lattice, and N atoms are arranged between Fe atoms-Fe atoms arranged in a plurality of axial directions. As a result, nitrogen is excessively taken in and compounds such as Fe ₄ N and Fe ₃ N having poor magnetic properties are generated.

  Therefore, in order to selectively arrange N atoms between Fe atoms arranged in one arbitrary direction, it is effective to distort the basic lattice in one direction. As a method of distorting in any one direction, it is conceivable to apply pressure / compression or to apply a tensile stress. However, when pressurizing / compressing or applying a tensile stress, the shape of the base material is limited.

  On the other hand, when a magnetic field is applied to iron, the basic lattice of iron extends in the direction of the applied magnetic field due to magnetostriction. Therefore, if a magnetic field is used, an iron basic lattice can be distorted in an arbitrary direction with respect to a base material having an arbitrary shape. Therefore, the present invention proposes to apply a magnetic field in the step of nitriding iron.

  In addition, when the base material is heated during nitriding, electrons that cause ferromagnetism in the base material are subjected to thermal fluctuation, and the amount of expansion and contraction due to magnetostriction is reduced, so it is necessary to compensate for the reduction in magnetostriction effect due to heating. is there. Furthermore, since the magnitude of the demagnetizing field varies depending on the shape of the base material, it is necessary to consider the influence of the demagnetizing field. Therefore, in the present invention, it is proposed to set the magnitude of the magnetic field to be applied in consideration of the thermal influence during nitriding and the influence of the demagnetizing field.

The method for producing an iron nitride material according to the present invention relates to a method for producing an iron nitride material containing an α ″ Fe ₁₆ N ₂ phase by nitriding a base material containing Fe, and the composition and structure of the base material. The following three methods are proposed.

(Form made of single-phase material (hereinafter sometimes referred to as single-phase form))
This embodiment includes a step (nitriding treatment step) of generating an α ″ Fe ₁₆ N ₂ phase by heating in a nitrogen element-containing gas atmosphere with a magnetic field applied to a base material containing Fe.
The applied magnetic field H is H = (7/3) + 2 × Nf or higher when the demagnetizing factor defined by the shape of the base material is Nf (Nf = 0 to 1). .

(Form comprising a magnetic phase and a non-magnetic phase (hereinafter sometimes referred to as a two-phase form))
This form is in a state where a magnetic field is applied to a base material made of a mixture of a first phase containing Fe and the second phase made of a material having a saturation magnetization of 0.2 T or less, in contact with the first phase. And heating in a nitrogen element-containing gas atmosphere to form an α ″ Fe ₁₆ N ₂ phase in the first phase (nitriding treatment step).
And, the magnetic field Hm to be applied is Nf (Nf = 0 to 1) as a demagnetizing factor defined by the shape of the base material, and V1 (V1 = 0 to 1) as a volume ratio of the first phase to the base material. In this case, the magnetic field is Hm = (7/3) + 2 × (Nf / V1) or more.

(Form having a plurality of magnetic phases (hereinafter, sometimes referred to as a plurality of magnetic phase forms))
In this form, a magnetic field is applied to a base material made of a mixture of a first magnetic phase containing Fe and a second magnetic phase that is in contact with the first magnetic phase and has a saturation magnetization of 0.4 T or more. A step (nitriding treatment step) of generating an α ″ Fe ₁₆ N ₂ phase in the first magnetic phase by heating in a nitrogen element-containing gas atmosphere in an applied state is provided.
The applied magnetic field H is H = (7/3) + 2 × Nf or higher when the demagnetizing factor defined by the shape of the base material is Nf (Nf = 0 to 1). .

In any of the above-described forms of the manufacturing method of the present invention, by applying a strong magnetic field having a specific magnitude to the base material, the iron basic lattice can be stretched in the applied magnetic field direction. N atoms can easily enter between Fe atoms arranged in one direction along the same direction, and N atoms can be prevented from entering in the other two directions. That is, the production method of the present invention can regulate the penetration direction of N atoms. Therefore, the present invention production process, alpha "Fe ₁₆ N ₂ phase is efficiently be generated, alpha" Fe ₁₆ N content of _2-phase can be produced more iron nitride. Therefore, it is expected that the production method of the present invention can provide an iron nitride material having a sufficient content effect of the α ″ Fe ₁₆ N ₂ phase and having excellent magnetic properties, and a permanent magnet made of this iron nitride material. In addition, since the manufacturing method of the present invention uses application of a magnetic field, it can be applied to a base material having an arbitrary shape such as a powder, a powder compact, or a thin film, and can provide an iron nitride material that is large and has excellent magnetic properties. It is expected.

As one form of the production method of the present invention, the atmosphere is selected from a nitrogen (N ₂ ) atmosphere, an ammonia (NH ₃ ) atmosphere, and a mixed gas atmosphere of a gas containing a nitrogen element and a rare gas or hydrogen (H ₂ ) gas. The form which is a kind to be mentioned is mentioned.

  In any of the above forms, N atoms can be sufficiently supplied, and Fe in the base material can be sufficiently nitrided. In particular, since the atmosphere containing hydrogen gas is a reducing atmosphere, it is possible to prevent the oxidation of Fe and the oxidation of the generated iron nitride, and also prevent the nitridation from proceeding due to the oxidation of Fe. Can be generated.

  As an embodiment of the production method of the present invention, an embodiment in which the heating temperature is 150 ° C. or more and 400 ° C. or less can be mentioned.

In the above-described form, the reactivity between the base material Fe and the nitrogen element can be sufficiently increased, the α ″ Fe ₁₆ N ₂ phase can be sufficiently generated, and the applied magnetic field is not significantly reduced by the high temperature, and the α ″ Fe ₁₆ N ₂ phase can be generated efficiently.

  As one form of the production method of the present invention, the atmosphere includes a form in which the oxygen content is 100 ppm or less by volume.

  Since the above-mentioned form has a low oxygen concentration, it is possible to effectively prevent the iron component from being oxidized.

  Examples of the single phase form include a form in which the base material is a powder having an average particle size of 10 nm or more and 500 nm or less. Moreover, it is preferable to apply a magnetic field in a state where the powder is aggregated.

  In the above form, so-called nano-powder is used as a raw material, and thus the obtained iron nitride material becomes a nano-order ultra-fine powder and is excellent in magnetic properties such as saturation magnetization and coercive force. Moreover, an iron nitride material can be efficiently manufactured by collecting the nano-powder materials and applying a magnetic field.

  Examples of the single phase form include a form in which the base material is a thin film having an average thickness of 10 nm to 500 nm. Further, it is preferable to apply a magnetic field in a direction perpendicular to the surface of the thin film.

  As in the case of using the above-mentioned nano powder, the above-mentioned form also provides a nano-order iron nitride material and is excellent in magnetic properties. Moreover, the said form can form a large sized iron nitride material compared with the case where the above-mentioned nano powder is used, and is excellent in the productivity of an iron nitride material.

  A magnetic field can be applied in a state where the thin film and an intermediate film made of an inorganic material different from the constituent material of the thin film are alternately stacked in multiple layers.

  The said form can obtain the iron nitride material excellent also in characteristics other than a magnetic characteristic, for example, intensity | strength, electrical conductivity, etc. by providing the thin film containing Fe in multiple layers. Moreover, the said form can manufacture a larger iron nitride material, can manufacture the iron nitride material which has flexibility, or can manufacture the iron nitride material which can suppress an eddy current when a high frequency electric power is supplied. . Examples of the constituent material of the intermediate film include nonmagnetic materials.

  Examples of the two-phase form include a form in which the first phase is a rod-like body and the average value of the minimum width of each rod-like body is 10 nm or more and 100 nm or less.

The average value of the minimum width of each rod-shaped body is taken by taking a cross-section of the base material and observing it with a transmission electron microscope: TEM, etc., and extracting 100 or more rod-shaped (columnar) first phases existing in this cross-section. The minimum width of each rod-shaped body is measured, and the average of the minimum widths of 100 or more measured rod-shaped bodies is taken. The above form is a form in which the second phase is a matrix and the first phase is present in a rod shape, and the width of the rod-like body is as small as nano-order. Accordingly, the α ″ Fe ₁₆ N ₂ phase formed from the Fe component of the first phase also becomes a nano-order ultrafine phase, and an iron nitride material having excellent magnetic properties can be obtained from its size.

  Examples of the two-phase form include a form in which the base material is a powder having an average particle size of 10 μm or more and 1000 μm or less. Moreover, it is preferable to apply a magnetic field in a state where the powder is aggregated.

  The said form can form easily the state which aggregated powder, such as a powder molded object, because a base material is a powder of a specific magnitude | size. Moreover, an iron nitride material can be efficiently manufactured by applying a magnetic field in a state where powder such as a powder compact is gathered. Furthermore, when a powder molded body is used, a large-sized iron nitride material having a desired shape can be produced.

  Examples of the two-phase form include a form in which the second phase contains a total of 70 atomic% or more of two or more elements selected from Al, Ni, Co, Cr, and Si.

In the above embodiment, a base material can be manufactured by subjecting a known alloy such as an Fe-Al-Ni-Co alloy or an Fe-Cr-Co alloy to a phase separation process using spinodal decomposition. Easy to prepare. In addition, since the magnetic body phase of the obtained iron nitride material has an α ″ Fe ₁₆ N ₂ phase with high saturation magnetization, it is not necessary to generate a Fe—Co phase like a conventional alnico magnet. An alloy that does not contain it or an alloy that contains less Co can be used as the base material.

  Examples of the plurality of magnetic phase forms include a form in which the average of the minimum distances of the first magnetic phase sandwiched between the adjacent second magnetic phases is 10 nm or more and 50 nm or less.

  The average of the minimum distances of the first magnetic phase is obtained as follows. Take a cross-section of the base material, select one first magnetic phase, contact P1 with the second magnetic phase adjacent to the first magnetic phase, and another second magnetic phase adjacent to the first magnetic phase And the minimum distance among the distances between the two contacts P1 and P2 is examined. The minimum distance of each first magnetic phase existing in the cross section is examined, and the average is defined as the average of the minimum distances of the first magnetic phase.

In the above embodiment, there is an interval of 10 nm to 50 nm corresponding to the average of the minimum distances between the second magnetic phases existing with one first magnetic phase interposed therebetween. By using such a base material, in the above embodiment, the first magnetic phase mainly composed of the α ″ Fe ₁₆ N ₂ phase and a stronger magnetocrystalline anisotropy than the first magnetic phase are obtained. And an iron nitride material having a second magnetic phase having a magnetocrystalline anisotropy that has a longer magnetic interaction generation distance than the first magnetic phase, and both magnetic phases have a magnetic interaction This iron nitride material has very good magnetic properties.

  As the plurality of magnetic phase forms, the second magnetic phase of the base material is at least one selected from RE = Y, La, Ce, Pr, Nd, Dy, Tb and Sm, X = B, C and N A form containing at least 80% by volume of RE-Fe-X compound or RE-Fe-ME-X compound when at least one selected from ME = Co, Cu, Mn and Ni is selected Is mentioned.

  In the above embodiment, since the base material contains a rare earth compound containing the rare earth element represented by RE, the obtained iron nitride material also includes a magnetic phase (second magnetic phase) made of this rare earth compound. . Since the rare earth compound is excellent in magnetic properties, the above form provides an iron nitride material that is extremely excellent in magnetic properties.

  As the multiple magnetic phase form, when the second magnetic phase of the base material is at least one selected from MA = Ca, Sr and Ba, a MA-Fe-O compound, or La-MA-Fe-Co The form which contains 80 volume% or more of -O compounds is mentioned.

  In the above embodiment, since the base material contains an iron oxide called a ferrite-based magnet, the obtained iron nitride material also includes a magnetic phase (second magnetic phase) made of this iron oxide. Since the raw material of the iron oxide is inexpensive, the above embodiment can produce an iron nitride material having excellent magnetic properties at a low cost.

  As the plurality of magnetic phase forms, the second magnetic phase of the base material is 80% by volume or more in total of at least one selected from a Pt—Fe alloy, a Pt—Co alloy, and a Pt— (Fe, Co) compound. The form to contain is mentioned.

  Since alloys and compounds such as the Pt—Fe alloy are excellent in corrosion resistance, the above embodiment can produce an iron nitride material excellent in corrosion resistance.

By the production method of the present invention, an iron nitride material having a large content of α ″ Fe ₁₆ N ₂ phase can be obtained. For example, the iron nitride material of the present invention is obtained by the production method of the iron nitride material of the present invention, and is mainly composed of iron nitride. There is a form in which 80% by volume or more of α ″ Fe ₁₆ N ₂ phase is contained in the magnetic phase.

The iron nitride material of the present invention sufficiently contains α ″ Fe ₁₆ N ₂ phase having excellent magnetic properties and is very excellent in magnetic properties. Therefore, the iron nitride material of the present invention can be suitably used as a material for permanent magnets. .

The method for producing an iron nitride material of the present invention can produce an iron nitride material having a high content of α ″ Fe ₁₆ N ₂ phase with high productivity. The iron nitride material of the present invention has a high content of α ″ Fe ₁₆ N ₂ phase and has a magnetic property. Excellent properties.

FIG. 1 is a graph showing the relationship between the demagnetizing factor Nf of a base material used as a raw material in the manufacture of an iron nitride material and the applied magnetic field H during nitriding in Test Example 1. FIG. 2 shows the ratio of the demagnetizing factor Nf to the volume ratio V1 of the first phase: Nf / V1 and the applied magnetic field Hm during nitriding in the base material used as a raw material in the manufacture of the iron nitride material in Test Example 2. It is a graph which shows the relationship. FIG. 3 is a graph showing the relationship between the demagnetizing factor Nf of the base material used as a raw material in the manufacture of the iron nitride material and the applied magnetic field H during nitriding in Test Example 3. FIG. 4 is an explanatory diagram for explaining a method for correcting the demagnetizing field coefficient.

Hereinafter, the present invention will be described in more detail.
〔Production method〕
[Base material]
The base material used as the raw material in the production method of the present invention contains at least Fe. Examples of the material of the single-phase base material include pure iron (Fe: 98 mass% or more, balance: inevitable impurities), iron alloy, and iron compound. Examples of iron alloys include Fe-Si alloys, Fe-Ni alloys, Fe-Al alloys, Fe-Co alloys, Fe-Cr alloys, and Fe-Si-Al alloys (Sendust). . Examples of the iron compound include Fe-O compounds (for example, iron oxide) and Fe-C compounds (for example, organic acid salt compounds and organic acid complexes). When the iron compound is used as a raw material, an appropriate treatment such as a reduction treatment is performed in advance to remove oxygen, organic components, and the like to obtain pure iron or an iron alloy, and then a nitriding treatment described later is performed.

Various shapes can be used as the shape of the base material made of pure iron or iron alloy. Typical examples include particles and film materials. In the single-phase form, the shape and size of the generated α ”Fe ₁₆ N ₂ phase is substantially equal to the shape and size of the base material. The α” Fe ₁₆ N ₂ phase is excellent when it is in the nano order. It is preferable that the base material is also nano-order because of its magnetic properties. For example, the base material may be nanopowder having a particle size in the nano order. In particular, when a nano-powder having an average particle size of 10 nm or more is used as a base material, it is difficult for thermal fluctuation to occur, and magnetic characteristics are not easily lowered due to thermal fluctuation. Further, when a nanopowder of 500 nm or less is used as a base material, an iron nitride material (powder) having excellent magnetic properties can be obtained. Therefore, the average particle size of the base material is preferably 10 nm or more and 500 nm or less. In addition, since the particles made of iron-based material have a maximum coercive force when the particle size is around 10 nm and an iron nitride material that is superior in magnetic properties is obtained, the average particle size of the base material is 10 nm to 100 nm. More preferably, it is 10 nm or more and 50 nm or less. Such an ultrafine powder can be produced by using, for example, a reverse micelle method or a sol-gel method.

  The nano-powder is inferior in productivity when nitriding each of the particles constituting the powder, so that the nitriding treatment is preferably performed in an assembled state. Examples of the state in which the powder is aggregated include attaching the powder to an adhesive film or mixing the powder in a sol-like substance or a gel-like substance.

  Alternatively, examples of the base material include a thin film having an average thickness of nano-order. In particular, when the average thickness is 10 nm or more and 500 nm or less, preferably 10 nm to 100 nm, an iron nitride material having high coercive force and excellent magnetic properties can be obtained. Such a thin film can be formed by a vapor deposition method such as a physical vapor deposition method (PVD method) such as a sputtering method or a chemical vapor deposition method (CVD method). When forming a thin film of an iron alloy, prepare an Fe evaporation source and an evaporation source of an element that forms the alloy, or use an alloy evaporation source of the desired composition so that an alloy of the desired composition can be obtained. You may do it. A thin film base material having a desired composition, thickness, and size can be easily formed by appropriately selecting film formation conditions (evaporation source, film formation time, film formation area, etc.).

The thin film may be a single layer, but if it is a multilayer, a large iron nitride material can be obtained. In the case of a multi-layer structure, for example, an intermediate film made of an inorganic material different from the constituent material of the film can be formed between the films made of the pure iron or the iron alloy. More specifically, a form in which films made of pure iron and a film made of iron alloy are alternately laminated, or a film made of iron alloys having different compositions can be alternately laminated. In this case, one of them functions as an intermediate film, and an α ″ Fe ₁₆ N ₂ phase can be generated in all films. Therefore, when a thin film having a multilayer structure is used as a base material, it is large and has a magnetic property. In addition, the material of the intermediate film is composed of a second phase constituent material (typically a nonmagnetic material), which will be described later, and a second magnetic phase in the form of multiple magnetic phases. The thickness of the intermediate film may be set to a thickness that does not cause magnetic interaction between adjacent films, for example, about 20 nm to 50 nm.

When the base material is a thin film, for example, after forming the base material film containing Fe such as pure iron, the base material film is formed and the nitriding processing is repeated, such as performing nitriding treatment described later. By doing so, it is possible to manufacture an iron nitride material having a multi-layered iron nitride layer in which α ″ Fe ₁₆ N ₂ phase is uniformly formed. Alternatively, a base material film containing Fe such as pure iron When the nitriding process described later is performed after the lamination, the nitriding process is completed once and the number of processes can be reduced, however, in this case, there is a possibility that insufficient penetration of nitrogen may occur depending on the area of each base material film. In the case of producing an iron nitride material having a multi-layered iron nitride layer, it is preferable to perform nitriding every time a base material film containing Fe is formed. , Formation of base material film → nitriding treatment described later → intermediate film forming (hereinafter referred to as the above process) Ri returns) through the process such as can be produced nitriding iron comprising an iron nitride layer of a multilayer structure.

  When the base material is a single-layer or multilayer thin film as described above, for example, when a magnetic field is applied in a direction perpendicular to the film surface (a direction parallel to the film thickness direction), a so-called perpendicular magnetic recording medium or magnetic An iron nitride material suitable for a so-called semi-hard magnetic material such as a head can be obtained. On the other hand, when a magnetic field is applied in parallel to the film surface, both the effect of the demagnetizing field and the effect of crystal magnetic anisotropy of iron nitride can be obtained, and an iron nitride material having excellent properties as a magnet material can be obtained.

As described above, the base material of the two-phase form uses a material having a phase separation structure in which a first phase containing Fe and a second phase made of a material having a saturation magnetization of 0.2 T or less are adjacent to each other. To do. In the first phase of the base metal, Fe, which is the main component, is used to generate the α ”Fe ₁₆ N ₂ phase and functions as a precursor for forming the magnetic phase in the iron nitride material. The second phase is typically composed of a non-magnetic material, and generally exists as it is after nitriding, and as an intervening phase that exists so that magnetic interaction between the magnetic phases in the iron nitride material does not occur. Function.

  The base material having the above specific structure contains, for example, two or more elements selected from Al, Ni, Co, Cr and Si, and spinodal decomposition is used for an iron alloy composed of Fe and inevitable impurities as the balance. It can be produced by subjecting the obtained phase separation treatment to the precipitation of the first phase. Examples of the iron alloy include Fe-Al-Ni-Co alloys, Fe-Cr-Co alloys, Fe-Si-Ni alloys, and the like, and known alloys can be used. Other Fe-Al-Ni alloys that do not substantially contain Co (Co content: less than 5 atomic%), Fe-Cr-Co based on low Co with Co content of 5 atomic% to 10 atomic% Alloys can also be used, and the use of Co can reduce the amount of Co used. As the conditions for the phase separation treatment, the conditions for the phase separation treatment used for the production of metal magnets such as alnico magnets can be applied. For example, when using a Fe-Al-Ni alloy as a raw material, the heating temperature of the solution treatment: 850 ° C to 1300 ° C (preferably 1000 ° C or more), the holding time: 10 minutes to 10 hours, 900 ° C to 700 ° C The temperature decreasing rate in the phase separation temperature region of the material in the temperature range: 0.05 ° C / sec or more and 5 ° C / sec or less. For example, when using a Fe-Cr-Co alloy as a raw material, the heating temperature of the solution treatment: 700 ° C to 1200 ° C (preferably 1000 ° C or higher), the holding time: 10 minutes to 10 hours, heated to 1000 ° C or higher After that, the cooling rate in the cooling process to 550 ° C .: 5.0 ° C./sec or more, in the temperature range of 550 ° C. to 450 ° C., the cooling rate in the phase separation temperature range of the material: 0.05 ° C./sec or more and 5 ° C./sec or less It is done.

  When the magnetic field is applied during the temperature drop in the above phase separation temperature range (0.4 MA / m (5 kOe) or more, or 0.5 T or more), the width of the first phase containing Fe is nano-order, and the length is micro-order. It can be made into a nano-sized rod having a very large ratio, and can be made granular when no magnetic field is applied. When the first phase is rod-shaped, the second phase becomes a cylindrical matrix that wraps around the first phase, and when the cross-sectional structure is observed, it becomes a structure in which both phases are alternately arranged like a pattern. A second phase exists around the periphery of the one-phase particles. When performing the nitriding reaction, if the diffusion of nitrogen into the second phase is small compared to the first phase, a structure in which the first phase is rod-like is preferable, and the nitrogen of the second phase compared to the first phase If the diffusion is large, the first phase may be granular.

  By the above phase separation treatment, the first phase is substantially composed of Fe phase, Fe-Co phase, etc., and the second phase is composed of two or more elements selected from Al, Ni, Co, Cr and Si. The contained phase, typically an alloy such as Al—Ni or Cr—Co. An alloy such as Al—Ni or Cr—Co is usually a nonmagnetic material and has a saturation magnetization of 0.2 T or less. The higher the proportion of the alloy component in the second phase is, the more preferable, 70 atomic% or more, 80 atomic% or more, particularly 90 atomic% or more is preferable. Since the ratio of the nonmagnetic component of the base material is high, it is possible to effectively prevent magnetic interaction between the magnetic phases due to the nonmagnetic component in the obtained iron nitride material.

The shape and size of the magnetic phase in the iron nitride material are substantially equal to the shape and size of the first phase of the base material. As described above, the α ″ Fe ₁₆ N ₂ phase has excellent magnetic properties when in the nano order, and therefore the first phase is also preferably in the nano order. For example, the first phase is a rod-shaped body as described above. Yes, if the average value of the minimum width of each rod-shaped body is 10 nm or more, the α ”Fe ₁₆ N ₂ phase generated in the iron nitride material also becomes a rod-shaped body of 10 nm or more, and the saturation magnetization becomes high. Is 100 nm or less, the α ”Fe ₁₆ N ₂ phase also becomes an ultrafine phase with a width of 100 nm or less, and an iron nitride material with excellent magnetic properties is obtained. The average value of the minimum width of the first phase is 20 nm or more and 50 nm The following is more preferable.

The base material in the two-phase form is preferably a powder so that it can sufficiently come into contact with nitrogen. In particular, when the powder has an average particle size of 10 μm or more and 1000 μm or less, and preferably 20 μm or more and 200 μm or less, a powder molded body having a desired shape and size can be easily produced. In the powder compact, gaps between particles constituting the raw material powder remain, and nitrogen can enter through the gaps between the particles. Therefore, the powder molded body can be suitably used as a base material because a large amount of powder can be nitrided at a time and a large nitriding material can be formed and the productivity of the iron nitride material is excellent. When a powder compact is used as a base material, the higher the relative density, the higher the ratio of magnetic component, and the more the iron nitride material can be obtained. However, if it is too dense, a sufficient nitrogen penetration path cannot be secured, and α ”Fe ₁₆ N ₂ For this reason, it is difficult to produce a phase efficiently, and therefore, a powder molded body having a relative density of 90% or more and 94% or less is preferable, although the molding pressure depends on the temperature of the molding die, for example, 0.5 GPa to 2.0 GPa. If the atmosphere during molding is an atmosphere with a low oxygen content (oxygen: 100 ppm by volume or less) or an atmosphere that does not substantially contain oxygen (for example, an inert atmosphere such as a rare gas such as Ar), The oxidation of the material can be prevented.

In the iron nitride material obtained from this two-phase form, the α ″ Fe ₁₆ N ₂ phase, which is the main component in the magnetic phase, functions as a hard magnetic material.

The base material in the form of multiple magnetic phases has a multiphase structure in which a first magnetic phase containing Fe and a second magnetic phase made of a magnetic material having a saturation magnetization of 0.4 T or more are adjacent to each other. Use. In the first magnetic phase in the base material, Fe, which is the main component, is used to generate the α ″ Fe ₁₆ N ₂ phase, and functions as a precursor for forming the first magnetic phase in the iron nitride material. The second magnetic phase in the base material exists almost as it is after the nitriding treatment, and functions as a second magnetic phase different from the first magnetic phase. The α ”Fe ₁₆ N ₂ phase generated from the first magnetic phase functions as a soft magnetic material for the so-called nanocomposite magnet (exchange spring magnet), and the second magnetic phase (substantially the second magnetic phase of the base material). Equal) can function as a hard magnetic material and can be a very strong magnet.

  The base material having the above specific structure is made of, for example, a rare earth compound containing Fe, an oxide containing Fe, an alloy containing Fe, an intermetallic compound, or the like as a raw material, and excessively containing Fe in the raw material. Then, the obtained molten metal is rapidly cooled to obtain an amorphous material, and then the amorphous material is crystallized so that a first magnetic phase containing Fe is generated (precipitated). It can be manufactured. The method using the crystallization treatment can manufacture the base material relatively easily and is excellent in the productivity of the base material.

  The rare earth compound is, for example, at least one selected from RE = Y, La, Ce, Pr, Nd, Dy, Tb and Sm, one selected from X = B, C and N, ME = Co, When at least one selected from Cu, Mn, and Ni, a RE-Fe-X compound or a RE-Fe-ME-X compound may be mentioned. Specific examples include Nd—Fe—B, Nd—Fe—C, Sm—Fe—N, Nd—Fe—Co—B, and the like. A known material used for a rare earth magnet can be used as a raw material. The conditions for the crystallization treatment include heating temperature: 450 ° C. to 600 ° C., holding time: 0.01 hour to 0.1 hour. The atmosphere during crystallization treatment is a non-oxidizing atmosphere, for example, an inert gas atmosphere such as a rare gas such as Ar or a vacuum atmosphere (vacuum degree: about 0.01 Pa to 10 Pa) in order to prevent oxidation of rare earth elements. preferable.

  When the rare earth compound is used as a raw material, the first magnetic phase in the base material is substantially composed of an Fe phase, and the second magnetic phase in the base material is the RE-Fe-X compound or RE- Consists of Fe-ME-X compounds. RE-Fe-X compounds and RE-Fe-ME-X compounds have high saturation magnetization, 0.4 T or more, and depending on the composition, 0.7 T or more, and further 1.0 T or more, and have excellent magnetic properties. The higher the ratio of the rare earth compound component having a high coercive force in the base material, the more excellent the iron nitride material having excellent magnetic properties can be obtained. Therefore, the higher the proportion of the rare earth compound component in the second magnetic phase is, the more preferable, 80% by volume or more, particularly 90% by volume or more is preferable.

  For example, when the oxide is at least one selected from MA = Ca, Sr and Ba, a MA-Fe-O compound or a La-MA-Fe-Co-O compound may be mentioned. Specific examples include Sr—Fe—O, Ba—Fe—O, and La—Sr—Fe—Co—O. A known material used for a ferrite magnet can be used as a raw material, and a base material can be prepared relatively inexpensively. The oxide can be produced, for example, as follows. To obtain an iron oxide (ferrite) having a desired composition, Fe is excessively blended and dissolved in a metal element other than iron, and the resulting molten metal is rapidly cooled to obtain an amorphous material. This amorphous material is subjected to a crystallization treatment so that Fe precipitates in an isolated spherical shape, and then the oxide is obtained by oxidizing only the alloy phase containing the ferrite constituent metal element as a matrix. .

  When the oxide is used, the first magnetic phase in the base material is substantially composed of an Fe phase, and the second magnetic phase in the base material is the MA-Fe- It is composed of an O compound or a La-MA-Fe-Co-O compound. The higher the proportion of the oxide component in the second magnetic phase, the better the iron nitride material having better magnetic properties, so 80 volume% or more, particularly 90 volume% or more is preferred.

  Examples of the alloy and intermetallic compound include one selected from a Pt—Fe alloy, a Pt—Co alloy, and a Pt— (Fe, Co) compound (both have a saturation magnetization of 0.4 T or more), and are publicly known Can be used. Since these alloys and the like are extremely excellent in corrosion resistance, an iron nitride material having excellent corrosion resistance can be obtained by including these alloys and the like. The higher the proportion of the component such as the alloy in the second magnetic phase, the higher the corrosion resistance, and 80 vol% or more, particularly 90 vol% or more is preferable.

The shape and size of the first magnetic phase in the iron nitride material are substantially equal to the shape and size of the first magnetic phase of the base material. In the iron nitride material, the shape of the first magnetic phase is selected so that the first magnetic phase mainly composed of the α ″ Fe ₁₆ N ₂ phase has a desired shape and size. As described above, the α ″ Fe ₁₆ N ₂ If the phase is nano-order, the magnetic properties are excellent, and therefore the first magnetic phase is preferably nano-order. For example, when the average of the minimum distances of the first magnetic phase sandwiched between the adjacent second magnetic phases is 10 nm or more and 50 nm or less in the first magnetic phase sandwiched between the adjacent second magnetic phase in the iron nitride material The minimum distance is 10 nm to 50 nm, and the iron nitride material is excellent in magnetic properties. The average value of the minimum distance of the first magnetic phase is more preferably 10 nm or more and 30 nm or less. Examples of the shape of the first magnetic phase include a rod shape, a spherical shape, and a film shape.

When using an iron nitride material as a magnet material, in the direction in which the demagnetizing field due to the shape is minimized in the magnetic phase and the first magnetic phase mainly composed of the α ”Fe ₁₆ N ₂ phase in the iron nitride material, It is preferable that the c-axes of α ″ Fe ₁₆ N ₂ crystal are aligned. For example, when the magnetic material phase is rod-shaped, it is preferable that the c-axis is aligned in the major axis direction of the rod-shaped material. When the magnetic material phase is film-shaped, the c-axis is parallel to the film surface. It is preferable that they are aligned. In order to align the c-axis in this way, when the first phase in the two-phase form or the first magnetic phase in the plurality of magnetic phases is in a rod shape, the film direction is the long axis direction of the rod-shaped body. In this case, the magnetic field is applied so that the magnetic field direction is parallel to the film surface. In the perpendicular magnetic recording application, the magnetic field direction is preferably perpendicular to the film surface as described above.

[Applied magnetic field]
In the production method of the present invention, in the single phase form and the multiple magnetic phase form, the applied magnetic field is H = (7/3) + 2 × Nf or more, and in the two-phase form comprising the second phase made of a material of 0.2 T or less, , Hm = (7/3) + 2 × (Nf / V1) or more. As shown in the test example to be described later, the demagnetizing factor Nf is a variable, and the value of the magnetic field is set in consideration of the compensation value: (7/3). It is easy to regulate the penetration direction of N atoms in one direction. The upper limit of the magnetic field to be applied is within a range where there are no harmful effects due to environmental magnetic field problems or power cost problems industrially.

  A high-temperature superconducting magnet can be used for applying the magnetic field. The high-temperature superconducting magnet can change the magnetic field at high speed. When a low-temperature superconducting magnet is used, the magnetic field fluctuation speed is generally about 5 to 10 minutes per 1T, whereas with a high-temperature superconducting magnet, it can be performed in a very short time, for example, within 10 seconds per 1T. That is, since a desired strong magnetic field can be easily obtained, the processing time can be shortened by using a high-temperature superconducting magnet. By shortening the treatment time, the growth of crystal grains can be suppressed and the coarsening can be reduced, so that an iron nitride material having a large coercive force can be easily obtained. Furthermore, since the magnetic field fluctuation speed is fast, the application of the magnetic field, such as stopping the application of the magnetic field at the time of loading or unloading the material (OFF), or starting the application of the magnetic field during the heating (ON) is quickly performed. Yes. Therefore, when a high-temperature superconducting magnet is used, processing can be performed continuously and the productivity of the iron nitride material is excellent. A high-temperature superconducting magnet is typically used by cooling a superconducting coil composed of an oxide superconductor by conduction cooling using, for example, a refrigerator (operating temperature is about −260 ° C. or more).

  The demagnetizing factor Nf is usually 1/3 (0.33) perpendicular to the film surface with respect to the thin film when a spherical body such as a particle is a relatively low-density assembly and a magnetic field is applied to this assembly. Set to 1 when applying a magnetic field (when applying a magnetic field in the film thickness direction). In addition, the magnetization curve (IH curve) of the base material may be obtained, and the demagnetizing factor may be corrected as appropriate. Specifically, a magnetic field is applied to the base material so that it is in the same direction as the direction of magnetic field application in the nitriding treatment, and an IH curve (I = f (H)) is obtained with a vibrating sample magnetometer (VSM). Ask for. Then, as shown in FIG. 4, the horizontal axis (x axis) is the magnetic field H, the vertical axis (y axis) is the magnetization I, and the angle θ formed by the x axis and the magnetization curve is obtained so that the angle θ becomes 90 °. Then, a correction curve (I ′ = f (H− [Nf] × I)) is obtained, a demagnetizing factor [Nf] is determined, and the demagnetizing factor [Nf] after this correction is used.

[atmosphere]
The atmosphere of nitriding treatment is an atmosphere containing nitrogen element. For example, nitrogen atmosphere (N ₂ content: 99.999 vol% or more), ammonia atmosphere, nitrogen (N ₂ ), mixed atmosphere of ammonia and rare gases such as Ar, nitrogen (N ₂ ), ammonia and hydrogen gas A mixed atmosphere is mentioned. Nitrogen atmosphere can supply enough nitrogen, ammonia atmosphere and mixed atmosphere containing hydrogen can prevent excessive nitriding and also prevent oxidation of iron components and rare earth elements, etc. Mixture atmosphere containing rare gas also oxidizes Can be prevented.

[Heating temperature]
The higher the heating temperature during nitriding, the higher the reactivity between Fe and N, and the more sufficient N atoms can penetrate between the Fe and Fe atoms. However, if it is too high, the magnetostriction effect on the base material will be small. As a result, the production efficiency of the α ″ Fe ₁₆ N ₂ phase is lowered. Therefore, the heating temperature is preferably 150 ° C. or higher and 400 ° C. or lower, and more preferably 200 ° C. to 300 ° C.

Hereinafter, more specific embodiments of the present invention will be described with reference to test examples.
[Test Example 1: Single-phase form]
Pure iron was used as a base material, and nitriding treatment was performed while applying a magnetic field as appropriate, thereby producing an iron nitride material. In this test, pure iron powder and a thin film made of pure iron were prepared as base materials.

<Powder>
(Preparation of base material)
Two types of pure iron powders with different particle sizes were prepared. First, pure iron powder was synthesized from iron carbonyl (Fe (CO) ₅ ) by the reverse micelle method and the synthesis conditions were changed to prepare those having an average particle size of 5 nm to 50 nm. A known method can be used for the reverse micelle method. The other one was prepared by freezing and pulverizing commercially available carbonyl iron powder (particle size: 5 μm) and changing the degree of pulverization to prepare pure iron powder having an average particle size of 100 nm to 1000 nm. In addition, pure iron powder formed by a gas atomizing method can be used. All of the average particle diameters were measured by a wet method using a commercially available laser diffraction particle size distribution analyzer.

(Nitriding treatment)
Each obtained pure iron powder was affixed on a heat-resistant adhesive film (polyimide film provided with a silicone adhesive), and the film was rolled up to perform nitriding treatment in a state where the powder was assembled. The nitriding treatment was performed in a nitrogen atmosphere (oxygen concentration: 100 volume ppm or less) with a nitrogen stream of purity: 99.999 vol%, and a magnetic field selected from a range of 0T to 5T was applied, and a range of 100 ° C to 400 ° C was selected. The heating temperature was maintained for 3 hours. The film may be folded in addition to being wound in a cylindrical shape.

  After the nitriding treatment, the powder was taken out from the adhesive film, and the mass of the nitriding powder was measured. Further, the saturation magnetization of the extracted powder was measured using a vibrating sample magnetometer (VSM) with a maximum magnetic field of 2 T (≈1590 kA / m). Average particle diameter of pure iron powder (nm), heating temperature during nitriding (° C), applied magnetic field (magnetic field) (T), saturation magnetization of powder after nitriding (emu / g = J / (T · kg) )) Is shown in Table 1. In this test, each particle constituting the pure iron powder was treated as a sphere, and the demagnetizing factor Nf was 1/3 (0.33).

<Thin film>
(Preparation of base material)
The thin film was formed on a base material (silicon substrate) by a sputtering method, and a thin film (single layer) having an average thickness of 5 nm to 1000 nm was formed by changing the film formation time and the like. As the film forming conditions, known conditions were used. As for the average thickness, a commercially available contact film thickness meter was used.

(Nitriding treatment)
The thin film was subjected to nitriding treatment. The nitriding treatment is performed in a nitrogen atmosphere (oxygen concentration: 100 volume ppm or less) with a nitrogen stream of purity: 99.999% by volume, and a magnetic field selected from the range of 0T to 5T is applied perpendicularly to the film surface and 100 ° C. to 500 ° C. The heating temperature selected from the range of ° C. was held for 3 hours. A high temperature superconducting magnet was used to apply the magnetic field.

  The mass of the sample after the nitriding treatment was measured, and the mass of the thin film after the nitriding treatment was determined from the difference between the measurement result and the mass of the base material before film formation. The thin film was measured for saturation magnetization (emu / g) using a vibrating sample magnetometer (VSM) with a maximum magnetic field of 2T (≈1590 kA / m). Average thickness of thin film before nitriding treatment (nm), heating temperature during nitriding treatment (℃), applied magnetic field (magnetic field) (T), saturation magnetization of thin film after nitriding treatment (emu / g = J / (T・ Kg)) is shown in Table 2. In this test, the demagnetizing factor Nf of the thin film was set to 1.

  FIG. 1 shows the relationship between the demagnetizing factor Nf and the applied magnetic field when the powder is used as the base material and when a thin film is used. In FIG. 1, sample Nos. 1-1 to 1-3 and 2-1 to 2-2 are shown as examples, and sample Nos. 101 to 103 and 201 to 205 are shown as comparative examples.

  As shown in Tables 1 and 2, it can be seen that the saturation magnetization tends to increase when a magnetic field is applied, and the saturation magnetization of the iron nitride material differs depending on the magnitude of the applied magnetic field. Further, as shown in FIG. 1, it is understood that when the demagnetizing factor Nf is increased, the saturation magnetization of the iron nitride material can be increased by increasing the applied magnetic field. Therefore, it can be said that the demagnetizing factor Nf and the applied magnetic field H are in a linear relationship, and the sample with a large saturation magnetization and the sample with a small saturation magnetization are expressed by a linear expression: y = ax + b It can be said that they can be distinguished. When the sample shown in FIG. 1 is used, H = (7/3) + 2 × Nf can be derived as the linear expression. From this equation, it can be said that when Nf = 0.33, the applied magnetic field is preferably H≈2.99 or more, and when Nf = 1, the applied magnetic field is preferably H≈4.33 or more, and H = (7/3) + 2 × Nf The sample to which the above magnetic field is applied has high saturation magnetization.

The reason why the saturation magnetization of the sample to which a magnetic field of H = (7/3) + 2 × Nf or higher was applied was high was that the nitriding process formed iron nitride with a high content of α ”Fe ₁₆ N ₂ phase. Actually, for example, the iron nitride material of Sample Nos. 1-1 and 2-1 were cross-sectioned and subjected to TEM analysis and X-ray diffraction. As a result, α ″ Fe ₁₆ N ₂ phase was present. The ratio of α ”Fe ₁₆ N ₂ phase is 100% by volume of the entire iron nitride material. Sample No.1-1: 82% by volume, Sample No.2-1: 84% by volume (both 80% In addition, when the iron nitride materials of sample Nos. 101 and 201 to which no magnetic field was applied were examined in the same manner, α ″ Fe ₁₆ N ₂ phase was small (25% by volume or less), and Fe ₄ N or Fe compounds such as ₃ N there were many. The other samples were the same.

From the above test, a base material containing Fe is prepared, and a value obtained from the demagnetizing factor Nf defined by the shape of the base material: a state in which a strong magnetic field of H = (7/3) + 2 × Nf or more is applied It can be seen that an iron nitride material having excellent magnetic properties can be obtained by performing nitriding treatment with. It can also be seen that this iron nitride material has a high content of α ″ Fe ₁₆ N ₂ phase.

  Furthermore, from the above test, in order to obtain an iron nitride material with superior magnetic properties, the heating temperature during nitriding treatment is preferably 150 ° C. or more and 400 ° C. or less, the average particle diameter of the powder or the average thickness of the thin film: 10 nm or more and 500 nm or less is preferable. It can be said.

[Test Example 2: Two-phase form]
A mixture of a first phase containing Fe and a second phase made of a material of 0.2 T or less was used as a base material, and nitriding treatment was performed while applying a magnetic field as appropriate, thereby producing an iron nitride material. In this test, an Fe—Al—Ni alloy was prepared as a base material, and an alloy having a constant composition and an alloy having different contents of Al and Ni were prepared.

<< constant composition >>
(Preparation of base material)
A powder having an average particle diameter of 50 μm made of an Fe-17 atomic% Al-5.5 atomic% Ni alloy was prepared by gas atomization. The average particle diameter was measured by a wet method using a commercially available laser diffraction particle size distribution measuring apparatus. The obtained powder was subjected to a phase separation treatment. Here, after holding at 900 ° C. for 1 hour in an Ar atmosphere (in an Ar air stream), the temperature was lowered by controlling the cooling state in the temperature range of 850 ° C. to 750 ° C. while applying a 1 T magnetic field from the outside. The cooling state was adjusted by controlling the temperature in the heating furnace used for heating, and the cooling rate was 0.2 ° C./sec. After this controlled cooling, the powder was put into cooling oil and quenched. By this step, a base material (alloy powder) phase-separated into a first phase mainly composed of Fe and a second phase containing an AlNi component is obtained.

  In the obtained base material, after taking a cross section in the direction perpendicular to the application direction of the magnetic field at the time of the above-mentioned temperature drop, and thinning by ion milling, when observed with a transmission electron microscope: TEM (about 50000 times), the powder was It was confirmed that the first phase was present in the form of a rod in each of the constituting particles, and the cylindrical second phase was in contact with the first phase so as to wrap around the rod-shaped body. Using the observed image, the minimum width of each rod-like body (first phase) existing in the field of view was obtained, and the average was obtained. The results are shown in Table 3. Also, taking the cross-section of the obtained base material, and identifying the composition of each phase from the X-ray diffraction results of this cross-section and the spot analysis of electron diffraction during TEM observation, the rod-shaped first phase is It was substantially composed of Fe, and the second phase was confirmed to contain AlNi. Using the X-ray diffraction results, the volume ratio of the first phase to each particle constituting the powder is examined, and using the results of the X-ray diffraction results and spot analysis, the content of the AlNi component with respect to the second phase ( Atomic%). The results are shown in Table 3.

《Al, Ni adjustment composition》
(Preparation of base material)
By a gas atomization method, a powder made of an Fe-x atomic% Al-y atomic% Ni alloy and having an average particle diameter of 50 μm was produced. Table 4 shows the amounts of Al and Ni. The average particle size was measured with a commercially available particle size distribution measuring apparatus. The obtained powder was subjected to a phase separation treatment under the same conditions as in the case of the above constant composition, and a base material (alloy that was phase-separated into a first phase mainly composed of Fe and a second phase containing an AlNi component). Powder). The obtained base material had a second phase so as to be in contact with the rod-like first phase, as in the case of the above-mentioned constant composition.

  In the obtained base material, the average of the minimum width of the first phase (nm), the volume ratio of the first phase, and the content of AlNi component (atomic%) with respect to the second phase are examined as in the case of the above-mentioned constant composition. It was. The results are shown in Table 4. Note that when an Al—Ni—Fe alloy having the same composition ratio as that of the second phase was made and saturation magnetization was measured, the saturation magnetization of AlNi was 0.13 T to 0.16 T (0.2 T or less).

(Production of molded body)
Each obtained alloy powder was compression-molded by a hydraulic press (molding pressure: 1 GPa) to obtain a powder compact (diameter φ10 mm × height 10 mm, relative density 90%). The relative density was determined from the actual density with respect to the true density of the powder compact. The actual density was measured using a commercially available density measuring device, and the true density was measured using a pycnometer.

(Nitriding treatment)
The produced powder compact was subjected to nitriding treatment. The nitriding treatment was performed in a nitrogen atmosphere (oxygen concentration: 100 volume ppm or less) with a nitrogen stream of purity: 99.999 vol%, and a magnetic field selected from the range of 0T to 5T was applied and selected from the range of 100 ° C to 500 ° C. The heating temperature was maintained for 3 hours. A high temperature superconducting magnet was used to apply the magnetic field.

After the nitriding treatment, the residual magnetization (T) and coercive force (kOe) of the obtained iron nitride material were measured using a vibrating sample magnetometer (VSM) with a maximum magnetic field of 2T (≈1590 kA / m). Tables 3 and 4 show the heating temperature (° C.), applied magnetic field (magnetic field) (T), remanent magnetization (T), and coercive force (kOe = (10 ³ / 4π) kA / m) during nitriding. In this test, each particle constituting the alloy powder was treated as a sphere, and the demagnetizing factor Nf was 1/3 (0.33).

  FIG. 2 shows the relationship between the ratio of the demagnetizing factor Nf to the volume ratio V1 of the first phase of the base material: Nf / V1 and the applied magnetic field. In FIG. 2, sample Nos. 3-1 to 3-3 and 4-1 to 4-6 are shown as examples, and sample Nos. 301 to 304 and 401 to 404 are shown as comparative examples.

  As shown in Tables 3 and 4, even when using a phase-separated base material made of Fe-Al-Ni alloy, the coercive force tends to increase by applying a magnetic field during nitriding. It can be seen that the magnitude of the coercive force differs depending on the magnitude of the applied magnetic field. Further, as shown in FIG. 2, when the demagnetizing factor Nf is increased, it is understood that the coercive force of the iron nitride material can be increased by increasing the applied magnetic field. However, in this embodiment, the demagnetizing field is affected by the content (volume ratio) of the first phase. Therefore, if the ratio of the demagnetizing factor Nf to the volume ratio V1 of the first phase: Nf / V1 is a variable, it can be said that Nf / V1 and the applied magnetic field Hm are in a linear relationship, as in Test Example 1. Using the sample shown in FIG. 2, a linear equation for distinguishing a sample with a large coercive mark and a sample with a small coercive force is obtained as follows: Hm = (7/3) + 2 × (Nf / V1) can be derived. From this equation, when (Nf / V1) = 0.33 / 0.5≈0.66, the applied magnetic field is H≈3.65 or more, and when (Nf / V1) = 0.33 / 0.72≈0.46, the applied magnetic field is H≈3.25 or more. It can be said that a sample to which a magnetic field of Hm = (7/3) + 2 × (Nf / V1) or more is applied has a high coercive force.

The reason why the coercive force of the sample to which a magnetic field of Hm = (7/3) + 2 × (Nf / V1) or higher was applied was increased from the first phase Fe in the base material to α ”Fe ₁₆ N by nitriding treatment. _This is probably because _two phases were formed and an iron nitride material having a magnetic phase with a high content of α ″ Fe ₁₆ N ₂ phase was formed. Actually, for example, the iron nitride material of sample Nos. 3-2 and 4-3 is cross-sectioned and subjected to TEM analysis and X-ray diffraction. As a result, α ″ Fe ₁₆ N ₂ phase is present, and the magnetic phase The ratio of α ”Fe ₁₆ N ₂ phase in the sample is as follows: Sample No. 3-2: 84% by volume, Sample No. 4-3: 82% by volume (all 80% when the magnetic phase is 100% by volume) % Or more). On the other hand, when the iron nitride material of sample Nos. 301 and 401 to which no magnetic field was applied was examined in the same manner, the α′Fe ₁₆ N ₂ phase was small in the magnetic phase (31 vol% or less), and Fe ₄ N or Fe ₃ N There were many compounds such as etc. The other samples were also the same.

From the above test, prepare a base material composed of a mixture of the first phase containing Fe (volume ratio V1) and the second phase composed of a material of 0.2 T or less, and the demagnetizing field defined by the shape of the base material Value obtained by coefficient Nf and volume ratio V1: By applying nitriding with a strong magnetic field of Hm = (7/3) + 2 x (Nf / V1) or higher, an iron nitride material with excellent magnetic properties can be obtained. I understand that. Moreover, iron this nitride has a magnetic phase, it can be seen high content of the magnetic phase of the α "Fe ₁₆ N ₂ phase.

Furthermore, from the above test, it can be said that in order to obtain an iron nitride material with superior magnetic properties, it is preferable that the heating temperature during nitriding: 150 ° C. or more and 400 ° C. or less and the average of the first phase minimum width: 10 nm or more and 100 nm or less. In this test, an alloy that does not substantially contain Co was used as the base material. However, by producing an α ”Fe ₁₆ N ₂ phase, an iron nitride material having excellent magnetic properties was obtained, and the use of Co was used. It can be said that the amount can be reduced.

[Test Example 3: Multiple magnetic phase morphology]
A mixture of a first magnetic phase containing Fe and a second magnetic phase composed of a magnetic material of 0.4 T or more was used as a base material, and nitriding was performed while applying a magnetic field as appropriate, thereby producing an iron nitride material. In this test, Fe-x atomic% Nd-y atomic% B alloys having various compositions with different Nd and B contents were prepared as base materials.

(Preparation of base material)
A material alloy made of an Fe-x atomic% Nd-y atomic% B alloy was prepared by a melt span method by selecting x and y so that Nd and B had a desired content. This material alloy was crystallized by holding it at 470 ° C. for 0.1 hour in a state where a 2 T magnetic field was applied from the outside in an Ar atmosphere (in an Ar stream). The material subjected to this treatment was pulverized by a ball mill to obtain spherical powders having various average particle diameters. The average particle size was measured with a commercially available particle size distribution measuring apparatus. Through this step, a base material (alloy powder) phase-separated into a first magnetic phase mainly composed of Fe and a second magnetic phase containing an Fe—Nd—B component is obtained.

  In the obtained base material, the cross section in the direction perpendicular to the application direction of the magnetic field at the time of the decomposition treatment was taken, and after thinning by ion milling, observed with a transmission electron microscope: TEM (about 50000 times), the powder was It was confirmed that the second magnetic phase was present in contact with the first magnetic phase in each constituting particle. Using the observed image, the minimum distance of the first magnetic phase existing in the visual field and sandwiched between the second magnetic phases was obtained, and the average was obtained. The results are shown in Table 5. Moreover, when the cross section of the obtained base material was taken and the composition of each said phase was identified from the X-ray diffraction result of this cross section and the spot analysis of the electron beam diffraction at the time of TEM observation, it was comprised substantially from Fe Phase (first magnetic phase) and a magnetic material different from the first magnetic phase, and a phase adjacent to the first magnetic phase (second magnetic phase) can be confirmed, the second magnetic phase is Fe It was confirmed to contain -Nd-B. Using the X-ray diffraction results, the volume ratio of the first magnetic phase to each particle constituting the powder was examined, and using the results of the X-ray diffraction results and spot analysis, Fe-Nd- The content of B component (atomic%) was examined. The results are shown in Table 5. Note that the saturation magnetization of the Fe—Nd—B component is 1.4T to 1.5T (0.4T or more).

(Production of molded body)
Each obtained alloy powder was compression-molded by a hydraulic press (molding pressure: 1 GPa) to obtain a powder compact (diameter φ10 mm × height 10 mm, relative density 83%). The relative density (actual density of the powder compact / true density of the powder compact) was measured using a commercially available density measuring device, and the true density was measured using a pycnometer.

(Nitriding treatment)
The produced powder compact was subjected to nitriding treatment. The nitriding treatment was performed in a nitrogen atmosphere (oxygen concentration: 100 volume ppm or less) with a nitrogen stream of purity: 99.999 vol%, and a magnetic field selected from the range of 0T to 5T was applied and selected from the range of 100 ° C to 500 ° C. The heating temperature was maintained for 3 hours. A high temperature superconducting magnet was used to apply the magnetic field.

After the nitriding treatment, the residual magnetization (T) and coercive force (kOe) of the obtained iron nitride material were measured using a vibrating sample magnetometer (VSM) with a maximum magnetic field of 2T (≈1590 kA / m). Table 5 shows the heating temperature (° C.), the applied magnetic field (magnetic field) (T), the remanent magnetization (T), and the coercive force (kOe = (10 ³ / 4π) kA / m) during nitriding. In this test, each particle constituting the alloy powder was treated as a sphere, and the demagnetizing factor Nf was corrected to 0.28.

  FIG. 3 shows the relationship between the demagnetizing factor Nf of the base material and the applied magnetic field. In FIG. 3, sample Nos. 5-1 to 5-3 are shown as examples, and sample Nos. 501 to 503 are shown as comparative examples.

  As shown in Table 5, even when using a phase-separated base material made of an Fe-Nd-B alloy, the coercive force tends to be increased by applying a magnetic field during nitriding, and applied. It can be seen that the magnitude of the coercive force differs depending on the magnitude of the magnetic field. Further, as shown in FIG. 3, when the demagnetizing factor Nf is increased, the coercive force of the iron nitride material can be increased by increasing the applied magnetic field. That is, in this embodiment, it can be said that the demagnetizing factor Nf and the applied magnetic field H have a linear relationship. Here, when H = (7/3) + 2 × Nf obtained in Test Example 1 was applied, a sample with a large coercive force and a sample with a small coercive force are indicated by H = (7/3 ) + 2 × Nf. From this equation, when Nf = 0.28, it can be said that the applied magnetic field is preferably H≈2.89 or more, and the sample to which the specific magnetic field is applied has a high coercive force.

The reason why the coercive force of the sample applied with a magnetic field of H = (7/3) + 2 x Nf or higher was increased by the nitriding process from the first magnetic phase Fe in the base material to the α ”Fe ₁₆ N ₂ phase. This is probably because an iron nitride material was formed that had a magnetic phase (first magnetic phase) with a high content of α ″ Fe ₁₆ N ₂ phase. Actually, for example, as a result of taking a cross section of the iron nitride material of sample No. 5-1 and performing TEM analysis and X-ray diffraction, the first magnetic body phase containing α ″ Fe ₁₆ N ₂ phase and Fe—Nd -B is a second magnetic phase mainly composed of B, and the ratio of the α ”Fe ₁₆ N ₂ phase in the first magnetic phase is 100% by volume of the first magnetic phase. Sample No. 5-1: 83% by volume (80% by volume or more). Therefore, it can be said that the iron nitride material of sample No. 5-1 has an effect of improving the magnetic properties due to the presence of the α ”Fe ₁₆ N ₂ phase. On the other hand, the iron nitride material of sample No. 501 to which no magnetic field was applied was obtained. A similar investigation revealed that the α ″ Fe ₁₆ N ₂ phase was small (28% by volume in the first magnetic phase) and there were many compounds such as Fe ₄ N and Fe ₃ N. Therefore, it is considered that the iron nitride material of sample No. 501 was difficult to obtain the effect of improving the magnetic properties due to the presence of the α ″ Fe ₁₆ N ₂ phase. The same applies to the other samples.

From the above test, a base material containing a first magnetic phase containing Fe and a second magnetic phase composed of a magnetic material of 0.4 T or more is prepared, and the demagnetizing factor Nf defined by the shape of the base material is used. Required value: It can be seen that an iron nitride material having excellent magnetic properties can be obtained by performing nitriding in a state where a strong magnetic field of H = (7/3) + 2 × Nf or more is applied. In addition, this iron nitride material includes both a first magnetic phase containing a large amount of α ″ Fe ₁₆ N ₂ phase and a second magnetic phase made of a magnetic material having excellent magnetic properties such as Fe—Nd—B. Thus, it can be seen that the magnetic properties are very excellent.

  Furthermore, from the above test, in order to obtain an iron nitride material with better magnetic properties, it can be said that the heating temperature during nitriding treatment is preferably 150 ° C. or more and 400 ° C. or less, and the average of the minimum distances of the first magnetic phase is preferably 10 nm or more and 50 nm or less. .

  In addition, this invention is not limited to the form of embodiment mentioned above, It is possible to change suitably, without deviating from the summary of this invention. For example, the composition of the base material, the second phase, and the second magnetic phase, the atmosphere during nitriding, the holding time, and the like can be changed as appropriate.

The iron nitride material of the present invention can be suitably used as a permanent magnet, for example, a material of a permanent magnet used in various motors, in particular, a high-speed motor provided in a hybrid vehicle (HEV) or a hard disk drive (HDD). . In addition, the iron nitride material of the present invention is expected to be usable for electromagnetic wave interference / absorption materials up to a frequency region (terahertz region) in which the skin depth of the magnetic phase is close to the width of the magnetic phase. The method for producing an iron nitride material of the present invention can be suitably used for producing the iron nitride material of the present invention having a large content of α ″ Fe ₁₆ N ₂ phase.

Claims (19)

In a state in which a magnetic field is applied to a base material containing Fe and heated in a nitrogen element-containing gas atmosphere, a process of generating an α ″ Fe ₁₆ N ₂ phase is provided,
The magnetic field H to be applied is a strong magnetic field of H = (7/3) + 2 × Nf or more when the demagnetizing factor defined by the shape of the base material is Nf (Nf = 0 to 1). A method for producing a featured iron nitride material. A nitrogen element in a state in which a magnetic field is applied to a base material composed of a mixture of a first phase containing Fe and the second phase that is in contact with the first phase and has a saturation magnetization of 0.2 T or less. Heating in an atmosphere containing gas to produce an α ″ Fe ₁₆ N ₂ phase in the first phase,
The applied magnetic field Hm has a demagnetizing factor defined by the shape of the base material as Nf (Nf = 0 to 1), and a volume ratio of the first phase to the base material as V1 (V1 = 0 to 1). A method for producing an iron nitride material, characterized in that a strong magnetic field of Hm = (7/3) + 2 × (Nf / V1) or more is obtained. In a state where a magnetic field is applied to a base material made of a mixture of a first magnetic phase containing Fe and the second magnetic phase that exists in contact with the first magnetic phase and has a saturation magnetization of 0.4 T or more. And heating in a nitrogen element-containing gas atmosphere to produce an α ″ Fe ₁₆ N ₂ phase in the first magnetic phase,
The magnetic field H to be applied is a strong magnetic field of H = (7/3) + 2 × Nf or more when the demagnetizing factor defined by the shape of the base material is Nf (Nf = 0 to 1). A method for producing a featured iron nitride material. The atmosphere is a kind selected from a nitrogen (N ₂ ) atmosphere, an ammonia (NH ₃ ) atmosphere, and a mixed gas atmosphere of a gas containing a nitrogen element and a rare gas or hydrogen (H ₂ ) gas. The method for producing an iron nitride material according to any one of claims 1 to 3.   The method for producing an iron nitride material according to any one of claims 1 to 4, wherein the heating temperature is 150 ° C or higher and 400 ° C or lower.   6. The method for producing an iron nitride material according to claim 1, wherein the atmosphere has an oxygen content of 100 ppm or less by volume.   2. The method for producing an iron nitride material according to claim 1, wherein the base material is a powder having an average particle size of 10 nm to 500 nm.   8. The method for producing an iron nitride material according to claim 7, wherein a magnetic field is applied in a state where the powder is aggregated. The base material is a thin film having an average thickness of 10 nm to 500 nm,
2. The method for producing an iron nitride material according to claim 1, wherein a magnetic field is applied in a direction perpendicular to the surface of the thin film.   10. The method of manufacturing an iron nitride material according to claim 9, wherein a magnetic field is applied in a state where the thin films and intermediate films made of an inorganic material different from the constituent materials of the thin films are alternately laminated in multiple layers.   3. The method for producing an iron nitride material according to claim 2, wherein the first phase is a rod-shaped body, and an average value of minimum widths of the respective rod-shaped bodies is 10 nm or more and 100 nm or less.   12. The method for producing an iron nitride material according to claim 2, wherein the base material is a powder having an average particle size of 10 μm or more and 1000 μm or less.   The second phase contains two or more elements selected from Al, Ni, Co, Cr, and Si in total of 70 atomic% or more. The manufacturing method of the iron nitride material as described in 2.   13. The method for producing an iron nitride material according to claim 12, wherein a magnetic field is applied in a state where the powder is aggregated.   4. The method for producing an iron nitride material according to claim 3, wherein the average of the minimum distances of the first magnetic phases sandwiched between the adjacent second magnetic phases is 10 nm or more and 50 nm or less.   The second magnetic phase is at least one selected from RE = Y, La, Ce, Pr, Nd, Dy, Tb and Sm, one selected from X = B, C and N, ME = Co, 16. When containing at least one selected from Cu, Mn, and Ni, the RE-Fe-X compound or the RE-Fe-ME-X compound is contained in an amount of 80% by volume or more. The manufacturing method of the iron nitride material of description.   When the second magnetic phase is at least one selected from MA = Ca, Sr and Ba, it contains at least 80% by volume of a MA-Fe-O compound or a La-MA-Fe-Co-O compound. 16. The method for producing an iron nitride material according to claim 3 or 15, wherein:   The second magnetic phase contains at least 80% by volume in total of one selected from a Pt—Fe alloy, a Pt—Co alloy, and a Pt— (Fe, Co) compound. 15. The method for producing an iron nitride material according to 15. It is obtained by the method for producing an iron nitride material according to any one of claims 1 to 18, and has a magnetic phase mainly composed of iron nitride,
An iron nitride material characterized in that the magnetic phase contains 80% by volume or more of α ″ Fe ₁₆ N ₂ phase.

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