JP2012124189A - Sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve characteristics of a magnetic material without using heavy rare earth elements of scarce resources.SOLUTION: A fluorine-containing grain boundary phase is formed between a rare earth-iron crystal grain and an iron-cobalt alloy crystal grain, and magnetic coupling is developed in the iron-cobalt alloy crystal grain and the rare earth-iron crystal grain with an eccentrically-located rare earth element, so that a high energy product is achieved. A sintered magnet having a high saturation magnetic flux density, a coercive force of 10 kOe or more, and a Curie point of 600 K or more can be obtained when a weight of the iron-cobalt alloy crystal grain is in a range from 0.1 to 90% by weight relative to a weight of the entire sintered magnet.

Description

  The present invention relates to a sintered magnet containing a high saturation magnetic flux density crystal and in which rare earth elements are unevenly distributed.

Patent Documents 1 to 4 describe a permanent magnet using NdFeB-based powder, and Patent Document 1 discloses an example of a nanocomposite magnet composed of soft magnetism and hard magnetism. Patent Document 2 describes a magnet obtained by mixing and sintering Fe or FeCo crystal powder and R ₂ Fe ₁₄ B powder. Patent Document 3 discloses that in a rare earth iron boron based sintered magnet, a phase composed of rare earth oxygen fluorine is formed at the grain boundary. Patent Document 4 describes a composite material in which a fluorine compound is present between NdFeB magnetic powder and Fe powder.

JP 2003-158005 A JP 2003-217918 A JP 2007-157903 A JP 2008-60183 A

  The above-mentioned conventional invention has a description relating to the composite of an iron-based material exhibiting a soft magnetic and high saturation magnetic flux density with an NdFeB-based crystal in an NdFeB-based magnet material. A composite material called a nanocomposite magnet can be applied to a material such as a bond magnet having a small magnetic powder volume ratio because the magnetic properties deteriorate when heated to a sintering temperature range, but the magnetic powder occupation ratio is 95% or more. In addition, it is difficult to apply to a sintered magnet having anisotropy. Since the sintering temperature of NdFeB magnets is as high as 1000 to 1100 ° C, the materials used in the above-mentioned nanocomposite magnets tend to cause crystal grain growth and diffusion between crystal grains to ensure magnetic properties. It is difficult to do. Although it is disclosed that a fluorine-containing layer can be formed in a sintered magnet, in a sintered magnet in which a fluorine-containing layer is formed as a grain boundary phase between an FeCo-based crystal and an NdFeB-based crystal, the composition and crystal There is no description regarding the composition of the magnetic material such as the size of the grains and the magnetic properties such as the Curie temperature. In order to form an FeCo-based crystal and an NdFeB-based crystal in contact with a grain boundary in a sintered magnet, a grain boundary where both crystal grains can grow stably is formed between the crystal structures of the FeCo-based crystal and the NdFeB-based crystal. Only after formation can it be possible to provide a magnet in which all of the residual flux density, coercivity and energy product are increased. There is no description regarding the grain boundary and grain boundary formation method for realizing such a magnet, and the structure of FeCo-based crystals and NdFeB-based crystals in the vicinity of the grain boundaries.

It was difficult to increase all the characteristics of residual magnetic flux density, coercive force and energy product with the conventional method, as disclosed in the conventional method, Fe, FeCo and NdFeB-based sintered powders. It is necessary to add a heavy rare earth element that decreases the residual magnetic flux density to the NdFeB-based crystal in order to easily diffuse during sintering and increase the coercive force, and to add the amount of heavy rare earth element to increase the residual magnetic flux density. If it is decreased, it is related to a decrease in coercive force due to a decrease in magnetocrystalline anisotropy energy, and all of the residual magnetic flux density, coercive force and energy product of Nd ₂ Fe ₁₄ B sintered magnet are increased. No means have been found.

The residual magnetic flux density of the Nd ₂ Fe ₁₄ B sintered magnet is the upper limit value of the saturation magnetic flux density (1.61 T) of tetragonal Nd ₂ Fe ₁₄ B as the main phase. In order to increase the residual magnetic flux density, it is necessary to increase this upper limit value, but it has been found that it is difficult to increase it greatly by examining the material composition with various additives. So that composite magnetic material having a saturation magnetic flux density than a saturation magnetic flux density of the Nd ₂ Fe ₁₄ B (1.61T) is considered, the exchange coupling between Fe and FeCo-based crystal and Nd ₂ Fe ₁₄ B It was revealed by quenching magnetic powder that the saturation magnetic flux density is increased. However, such rapidly-cooled magnetic powder is easily applied to the sintering process due to crystal growth and diffusion reaction caused by heating. Similar to this, a magnet in which Fe and Nd ₂ Fe ₁₄ B crystal grains are combined is produced by a hot forming method or a sintering method, and an increase in residual magnetic flux density has been confirmed. The coercive force decreases abruptly when compounded with the system crystal grains. As a method for increasing the coercive force, there is a grain boundary diffusion method or the like, but the residual magnetic flux density decreases because of the method of diffusing heavy rare earth elements. As described above, no means for increasing all of the residual magnetic flux density, coercive force, and energy product of the Nd ₂ Fe ₁₄ B sintered magnet can be found in the conventional method.

  A fluorine-containing grain boundary phase is formed between the rare earth iron-based crystal grains and the iron cobalt alloy crystal grains, and magnetic coupling is expressed in the rare earth iron-based crystal grains and the iron cobalt alloy crystal grains in which the rare earth elements are unevenly distributed. The high energy product was realized.

  The sintered magnet of the present invention can reduce the amount of rare earth elements used, realize an increase in the energy product of the magnet and increase the Curie point, and can be reduced in size and weight when applied to a rotating machine, etc. It can be applied to a magnetic circuit that requires a high energy product including a voice coil motor.

Volume ratio and the coercive force of Fe ₇₀ Co ₃₀ crystal grains according to the present invention, is a diagram showing the relationship between the residual magnetic flux density. Volume ratio and the coercive force of Fe ₇₀ Co ₃₀ crystal grains according to the present invention, is a diagram showing the relationship between the residual magnetic flux density. It is a figure which shows the relationship of the fluoride volume ratio / FeCo type | system | group volume ratio based on this invention, a coercive force, and a residual magnetic flux density. It is a figure which shows the relationship between Co density | concentration which concerns on this invention, coercive force, and residual magnetic flux density. It is a figure which shows the relationship between Co density | concentration which concerns on this invention, coercive force, and residual magnetic flux density. It is a figure which shows the structure | tissue of the magnet cross section based on this invention.

Means for increasing all of the residual magnetic flux density, coercive force, and energy product of the Nd ₂ Fe ₁₄ B sintered magnet will be described below. The residual magnetic flux density of the Nd ₂ Fe ₁₄ B sintered magnet is the upper limit value of the saturation magnetic flux density (1.61 T) of tetragonal Nd ₂ Fe ₁₄ B as the main phase. In order to increase the residual magnetic flux density, it is necessary to increase the upper limit value, and a magnetic material having a higher saturation magnetic flux density than Nd ₂ Fe ₁₄ B is used. Since a material having a high saturation magnetic flux density is often soft magnetism having a small magnetic anisotropy energy, it is necessary to fix the magnetization of the soft magnetic material so that the magnetization is not easily reversed. Examples of magnetization fixing means include exchange coupling, super-exchange interaction, and magnetostatic coupling. These magnetic couplings greatly depend on the material system of the partner phase that contacts the soft magnetic phase at the interface, the composition near the interface, and the structure near the interface. At least three phases of the soft magnetic phase, the grain boundary phase, and the Nd ₂ Fe ₁₄ B phase need to be formed almost uniformly in the magnet through a sintering process subsequent to temporary forming in a magnetic field.

The conditions include the following. 1) Soft magnetic phase particles do not easily react with Nd ₂ Fe ₁₄ B phase particles or powder during sintering. 2) The soft magnetic phase and Nd ₂ Fe ₁₄ B phase particles can be mixed almost uniformly. 3) The Nd ₂ Fe ₁₄ B phase around the crystal grains of the soft magnetic phase has a high crystal magnetic anisotropy energy. 4) Even if soft magnetic phase particles are mixed, the Nd ₂ Fe ₁₄ B phase particles can be oriented by applying a magnetic field before sintering. 5) The soft magnetic phase after sintering has a saturation magnetic flux density equal to or higher than that before sintering. 6) The oxygen concentration in the Nd ₂ Fe ₁₄ B phase does not increase significantly by introducing particles of the soft magnetic phase. 7) Sinterable at a temperature of 1200 ° C or lower. 8) During sintering, the crystal grains of the soft magnetic phase hardly react with the liquid phase and change into a phase with a small saturation magnetic flux density. In order to satisfy these conditions and further improve the magnetic properties, the following conditions must be satisfied. 9) The Curie temperature of the soft magnetic phase is higher than the Curie temperature of the Nd ₂ Fe ₁₄ B phase, and the soft magnetic phase crystals formed in the sintered body are stable below the Curie point. 10) The Nd ₂ Fe ₁₄ B phase and the soft magnetic phase are magnetically coupled. 11) The coercive force of the Nd ₂ Fe ₁₄ B phase around the soft magnetic phase is sufficiently large. 12) The soft magnetic phase is dispersed inside the sintered body.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

An Fe-30 wt% Co alloy is prepared by weighing iron and cobalt and then melting them in vacuo. This alloy is heated and reduced to 1000 ° C. in an Ar + 5% H ₂ gas atmosphere to obtain an oxygen concentration of 200 ppm or less. This alloy is melted at high frequency in an Ar + 5% H ₂ gas atmosphere, and the molten metal is sprayed on a rotating roll to form a foil body. This foil is mixed in mineral oil without exposure to the atmosphere. Mineral oil is premixed with (Nd _0.7 Dy _0.3 ) ₂ Fe ₁₄ B powder having an average particle size of 3 μm and a Tb-F solution, and the mixture of mineral oil and foil is heated to 170 ° C. to advance the bead mill. ZrO ₂ (outer diameter 0.1 mm) is used for the beads, and at the same time the foil is pulverized by the beads, TbF _x (X = 1 to 3) becomes foil or (Nd _0.7 Dy _0.3 ) ₂ Fe ₁₄ B powder. Adhere to the surface. This powder is molded in a magnetic field (magnetic field: 10 kOe, 1 t / cm ² ) and sintered at a heat treatment temperature of 700 ° C. to 1200 ° C. The optimum sintering temperature range is 1000 to 1100 ° C., and the density after sintering becomes 7.0 to 7.8 g / cm ³ at a temperature of 700 to 900 ° C. (Nd _0.7 Dy _0.3 ) ₂ Fe ₁₄ B powder is sintered by heat treatment after forming in a magnetic field, and oxides and fluorine-containing phases such as rare earth rich phase, TbOF, NdOF, NdF ₂ are present in the vicinity of the grain boundary. It is formed. Tb is unevenly distributed near the grain boundary of (Nd _0.7 Dy _0.3 ) ₂ Fe ₁₄ B, and the coercive force is increased by the formation of this high crystal magnetic anisotropy energy phase. Magnetization reversal is suppressed by the coupling, and the magnetic properties of Fe ₇₀ Co _{30 having} a volume fraction of 20%, a residual magnetic flux density of 1.7 T, a coercive force of 20 kOe, and a Curie temperature of 680 ° C. have been confirmed. The vicinity of the grain boundary is a portion along the grain boundary at a distance of 100 nm or less from the interface with the grain boundary, and the average Tb concentration at a portion separated by 500 nm or more from the interface of the grain boundary and the maximum within 100 nm from the grain boundary interface. The Tb concentration ratio (Tb concentration in the vicinity of the grain boundary / Tb concentration in the grain) has a concentration difference more than twice.

The feature of the sintered magnet having a residual magnetic flux density exceeding 1.61 T of the saturation magnetic flux density of Nd ₂ Fe ₁₄ B and having a coercive force of 15 kOe or higher is as follows: 1) Saturation magnetic flux higher than Nd ₂ Fe ₁₄ B 2) Grain boundaries containing fluorine and heavy rare earth elements are formed between the Fe-based ferromagnetic crystal grains and the Nd ₂ Fe ₁₄ B-based crystal grains of the main phase. 3) the presence of heavy rare earth elements in the vicinity of the grain boundary of the main phase Nd ₂ Fe ₁₄ B-based grains; 4) the average grain size of the Fe-based ferromagnetic grains Is smaller than the average crystal grain size of Nd ₂ Fe ₁₄ B-based grains, 5) the volume fraction of heavy rare earth fluoride or oxyfluoride is smaller than the volume fraction of Fe-based ferromagnetic crystals, 6) The concentration of heavy rare earth elements is Nd ₂ Fe ₁₄ B based grains rather than Fe based ferromagnetic grains. The inside is higher. All the above conditions 1) to 6) are satisfied, and the residual magnetic flux density exceeds 1.61 T of the saturation magnetic flux density of Nd ₂ Fe ₁₄ B.

These features will be described below. Only when a ferromagnetic material having a saturation magnetic flux density exceeding 1.61 T of Nd ₂ Fe ₁₄ B is contained, a high magnetic flux density is obtained, and Fe, FeCo-based crystals, and alloys obtained by adding transition elements to these can be used. These alloy powders have a saturation magnetic flux density of 170 emu / g or more, and oxygen and carbon concentrations are in the range of 10 to 300 ppm. Among them, by using an FeCo binary alloy, high saturation magnetization is obtained, and a magnet having a high residual magnetic flux density is obtained. When oxygen or carbon alone exceeds 300 ppm, the saturation magnetization decreases, and the heavy rare earth element constituting the fluoride does not diffuse to form an oxyfluoride, and the heavy rare earth into the Nd ₂ Fe ₁₄ B crystal grains The uneven distribution of elements is suppressed, the coercive force is reduced, and as a result, the residual magnetic flux density is also reduced. If oxygen or carbon alone is less than 10 ppm, oxyfluoride or carbon-containing oxyfluoride on the surface of FeCo-based crystal powder will not grow, and the adhesion of fluoride will be reduced, making it easier for the fluoride to peel off. The magnetic properties decrease. Therefore, the average oxygen or carbon concentration of the FeCo-based crystal grains is preferably 3 to 300 ppm. In the sintering process, a rare earth-rich phase, which is a low melting point phase, forms a main liquid phase. FeCo-based crystal grains and Nd ₂ Fe ₁₄ B-based crystal grains remain surrounded by the liquid phase, and the outer periphery of these crystal grains part is formed with a high melting point phase such as acid fluorides, in during the sintering or aging treatment, Tb diffuses into Nd ₂ Fe ₁₄ B-based grain Nd ₂ Fe ₁₄ B-based grain outer peripheral portion It is unevenly distributed. Since Tb moves by diffusion between rare earth atoms, it is hardly unevenly distributed in the FeCo-based crystal, and the oxygen contained in the FeCo-based crystal and the Nd ₂ Fe ₁₄ B-based crystal is reduced by the fluoride and enters the grain boundary. Forms an oxygen-containing fluoride or an acid fluoride such as (Nd, Tb) OF.

The oxygen concentration in the FeCo-based crystal after sintering is 1 to 100 ppm. Many of the oxyfluoride crystals have a cubic crystal structure. If this fluorine-containing material becomes thicker and its volume fraction increases, the liquid phase sintering process during sintering is hindered, so the volume of FeCo-based crystal grains or Fe-based crystal grains (powder) to be added is reduced. There is a need. Further, when the average crystal grain size of the Fe-based ferromagnetic crystal grains is increased to about 10 times the average crystal grain size of the Nd ₂ Fe ₁₄ B-based crystal grains, the Fe-based ferromagnetic crystal grains are deformed during temporary forming in a magnetic field. The disorder of the orientation direction of the Nd ₂ Fe ₁₄ B-based crystal increases. Since Fe-based ferromagnetic crystal grains it is easily aligned to the orientation direction of the applied magnetic field in that in Nd ₂ Fe ₁₄ B-based crystal powder biting deformed in Nd ₂ Fe ₁₄ B based crystal powder, is caught hardly causes grain 10 times the average particle diameter of which is the magnitude Nd ₂ Fe ₁₄ B-based crystal powder below, under the average particle size or less of the Nd ₂ Fe ₁₄ B-based crystalline powder if desirable. The average crystal grain size before and after sintering does not vary greatly and is 50% to 200% (0.5 to 2 times) after sintering with respect to the average grain size before sintering. It can be controlled to 70% to 130% by optimizing the thickness.

  In this embodiment, a fluoride containing Tb is formed. However, a similar magnetic property can be obtained by forming a fluoride containing at least one Dy or other rare earth element or a Mn (manganese) containing fluoride in addition to Tb. The characteristics can be confirmed. Further, the fluoride may contain a transition element other than the rare earth element.

  The Curie point of the sintered magnet in which the increase in energy product has been confirmed is 590 to 1250K. Such an increase in the Curie point is a result of reflecting the magnetic properties of the FeCo-based crystal, and the effect of improving the heat resistance of the sintered magnet can be confirmed. That is, it has been confirmed that the absolute value of the temperature coefficient of the coercive force and the residual magnetic flux density is decreased and the thermal demagnetization is decreased.

In addition, by applying a magnetic field of 10 to 50 kOe substantially parallel to the c-axis direction of the Nd ₂ Fe ₁₄ B-based crystal in the sintering step or the aging heat treatment step after sintering, the anisotropic direction of the FeCo-based crystal and the Nd ₂ The c-axis direction of the Fe ₁₄ B-based crystal can be made substantially parallel, and this square heat treatment improves the squareness of the demagnetization curve and increases the energy product by 1 to 10%.

A Fe-50% Co alloy is melted in a vacuum to form a master alloy lump having a uniform composition. The alloy lump is melted at a high frequency in an Ar gas atmosphere, and the molten metal is sprayed onto a roll rotating at a rotational speed of 3000 rpm to prepare a coarse powder. This coarse powder is allowed to settle in a mineral oil and DyF ₃ mixture without exposure to the atmosphere. The mixed liquid of mineral oil and fluoride is a substantially transparent liquid in which 10% of DyF ₃ is dissolved in squalane. Using the bead mill apparatus without exposing the mixed solution of this Fe-50% Co alloy, mineral oil and DyF ₃ to the atmosphere, the diffusion reaction proceeds simultaneously with the pulverization. For the grinding of the bead mill apparatus, ZrO ₂ balls having a diameter of 0.5 mm were used and pulverized by heating at 200 ° C. If the temperature is 180 ° C. to 300 ° C., DyF ₃ is formed on the surface of the FeCo-based crystal powder, and oxyfluoride grows at the interface between the FeCo-based crystal powder and DyF ₃ . The DyF ₃ -coated FeCo crystal powder and Nd ₂ Fe ₁₄ B powder having an average particle diameter of 3 μm are mixed at a weight ratio of 1:10, and then temporarily molded and sintered in a magnetic field. After sintering, an aging treatment was performed, and a temperature in the vicinity of 500 ° C. was quenched at a cooling rate of 20 ° C./second, and then magnetized in the magnetic field application direction during molding in a magnetic field to obtain a sintered magnet.

FeCo-based crystals discontinuously disperse in the sintered magnet, and fluorides and oxyfluorides grow at grain boundaries near the FeCo-based crystal grains. Nd ₂ Fe ₁₄ in contact with these fluorides and oxyfluorides It is confirmed by EDX analysis of a transmission electron microscope that Dy is unevenly distributed on the outer peripheral side in the B-based crystal grains. The fluoride contains more Nd than heavy rare earth elements, and the concentration of Dy in the Nd ₂ Fe ₁₄ B crystal grains is higher than in the FeCo crystal grains. When the average grain size of FeCo-based crystal grains is 0.1 μm and the average Nd ₂ Fe ₁₄ B is 3 μm, a residual magnetic flux density of 1.7 T and a coercive force of 20 kOe can be realized. In the magnetization-temperature curve, a decrease in magnetization is observed at a temperature close to the magnetic transformation point of Nd ₂ Fe ₁₄ B, and a decrease in magnetization corresponding to the magnetic transformation point of the FeCo-based crystal can be confirmed on the high temperature side. Multiple sudden magnetization drops are observed, and the curve is not monotonous like the Langevin function.

  In the magnet of this example, the Curie point was 1050K. The increase in the Curie point reflects the magnetic properties of the FeCo-based crystal, and the temperature dependence of magnetization is not monotonous. That is, in the temperature dependence of magnetization, the change in magnetization corresponding to the Curie point of the main phase and the Curie point of the nanoparticles can be confirmed, and the Curie point of the nanoparticles is higher than the Curie point of the main phase. Even in the case where FeCo-based crystals in which the nanoparticles are partially agglomerated and have a large particle size are observed, the Curie point of the FeCo-based crystal is higher than the Curie point of the main phase, and the Curie point (magnetic disappearance temperature) of the magnet is FeCo-based. It becomes the Curie point of the crystal.

In order to realize such a rare earth sintered magnet, the following conditions are necessary. 1) At least one kind of heavy rare earth element is unevenly distributed inside the crystal grain in the vicinity of the grain boundary of the Nd ₂ Fe ₁₄ B-based compound, and the magnetocrystalline anisotropy of Nd ₂ Fe ₁₄ B containing the unevenly distributed heavy rare earth element is That it is increasing. 2) FeCo-based crystals are formed discontinuously dispersed via Nd ₂ Fe ₁₄ B-based compounds and fluorine-containing crystal grains, and FeCo-based crystal grains are observed in part of the grain boundaries. 3) The average crystal grain size of the FeCo-based crystal is preferably equal to or less than the average crystal grain size of the Nd ₂ Fe ₁₄ B-based compound. If possible, the average crystal grain size of the FeCo-based crystal is equal to the average crystal grain size of the Nd ₂ Fe ₁₄ B-based compound. 1/10 to 1/1000 is a range in which the coercive force increase and the residual magnetic flux density are remarkably increased. 4) The concentration of the heavy rare earth element in the FeCo-based crystal grains is lower than that of the heavy rare earth element unevenly distributed in the Nd ₂ Fe ₁₄ B-based compound grains. 5) The lattice constant of a part of the FeCo-based crystal is 2.851 to 3.120 nm, and the lattice is larger than that of the bulk FeCo-based crystal having the same composition. 6) Nd ₂ Fe ₁₄ B-based crystals have an orientation direction in the magnet. 7) Fluoride or oxyfluoride has an average higher continuity at the outer periphery of the FeCo-based crystal grains than at the outer periphery of the Nd ₂ Fe ₁₄ B-based crystal grains, and the outer periphery of the FeCo-based crystal grains is fluoride or High coverage with oxyfluoride.

The reason why FeCo-based crystal particles as in this example can remain in the sintered body after sintering is that a fluorine-containing film is formed on the surface of the FeCo-based crystal. The fluorine-containing film absorbs oxygen and carbon even after heat treatment at 1200 ° C. and stably grows on the surface of the FeCo-based crystal grains, and is protected by the fluorine-containing film while in contact with the liquid phase even during sintering. Can exist without reacting with the phase. For this reason, the state of the crystal grains or powder before temporary forming is maintained and sintered, and the size of the FeCo-based crystal grains before and after sintering does not vary greatly. When the FeCo-based crystals are nanoparticles, some of the FeCo-based crystals are agglomerated and the FeCo crystals are joined, or a fluorine-containing phase is formed between the particles. Adjacent to the crystal grains of Nd ₂ Fe ₁₄ B. When the FeCo-based crystal is a nanoparticle, one particle is a single crystal of the FeCo-based crystal, and anisotropy can be added as long as it is below the Curie point of the FeCo-based crystal by applying an external magnetic field. Even if the Curie temperature of the FeCo-based crystal is higher even near the sintering temperature, it is possible by selecting the composition, and the magnetic state and lattice distortion of the FeCo-based crystal and magnetic coupling with the surrounding crystal grains by an external magnetic field It is possible to change the state, and a new process which is not necessary for the conventional Nd ₂ Fe ₁₄ B sintered magnet greatly affects the magnetic properties. This is because the Curie temperature of the FeCo crystal is high and its magnetic properties change depending on the applied magnetic field and the heat treatment process, and the coercivity is determined because the FeCo crystal grows near the grain boundary of the Nd ₂ Fe ₁₄ B crystal grain. It is an important finding to influence the structure, magnetic coupling, anisotropy, and the like in the vicinity of the grain boundary of the Nd ₂ Fe ₁₄ B-based crystal grains.

The magnetic field in the heat treatment step is in the range of 1 to 200 kOe, and by adding a magnetic field at various directions and frequencies in a temperature range from the Curie temperature of Nd ₂ Fe ₁₄ B to the Curie point of the FeCo-based crystal, the FeCo-based crystal It is possible to change the magnetization state, lattice distortion, ordered irregular arrangement, and crystal structure of. Heat treatment in a magnetic field strengthens the magnetic coupling with the Nd ₂ Fe ₁₄ B-based crystal and contributes to the improvement of magnetic properties such as an increase in magnetic anisotropy energy of FeCo-based crystal, an increase in saturation magnetic flux density, and an increase in Curie point.

Fe having a purity of 99.9% is evaporated in an inert gas atmosphere to form nanoparticles having a particle size of 30 nm and precipitated in a TbF-based solution. Nd ₂ Fe ₁₄ B powder having a particle diameter of 3 μm is mixed with this solution. The mixing ratio of Fe nanoparticles and Nd ₂ Fe ₁₄ B powder is 1:10. Such a mixture of slurry-like solution and powder is inserted into a mold, molded in a magnetic field, and then sintered at 1100 ° C. Furthermore, it was rapidly cooled after aging treatment at 600 ° C. to obtain a sintered magnet. Oxidation is suppressed by making an inert gas atmosphere or a vacuum atmosphere from powder preparation to sintering.

The sintered magnet is composed of tetragonal Nd ₂ Fe ₁₄ B-based crystal grains, cubic or tetragonal Fe, and grain boundary phase fluoride, oxyfluoride, rare earth oxide, etc., and Nd ₂ Fe _A fluorine-containing phase can be confirmed between the ₁₄ B system crystal grains and the Fe crystal grains, and uneven distribution of Tb is observed in the Nd ₂ Fe ₁₄ B system crystal grains. The concentration of oxygen and carbon contained in the Fe crystal is 20 ppm or less. When the total concentration of oxygen and carbon exceeds 20 ppm, the value of the residual magnetic flux density decreases. Therefore, it is desirable to add Co and use an FeCo-based crystal instead of Fe. When the concentration of oxygen and carbon is 10 ppm in total, the magnetic characteristics of the sintered magnet are a residual magnetic flux density of 1.65 T, a coercive force of 15 kOe, and an energy product of 67 MGOe. This characteristic exceeds the theoretical value of the Nd ₂ Fe ₁₄ B magnet and can be used in various magnetic circuits.

In order to obtain magnetic characteristics exceeding the theoretical value of such an Nd ₂ Fe ₁₄ B magnet, the following conditions are required. 1) Tetragonal or cubic Fe or FeCo particles are present in a dispersed state. 2) Heavy rare earth elements are unevenly distributed in the Nd ₂ Fe ₁₄ B-based crystal grains. 3) The heavy rare earth element concentration in the Nd ₂ Fe ₁₄ B crystal grains is higher than the heavy rare earth element in the Fe or FeCo crystal grains. 4) A fluorine-containing phase has grown between the Fe or FeCo crystal grains and the Nd ₂ Fe ₁₄ B crystal grains. 5) The Fe or FeCo crystal grain size should be smaller than the Nd ₂ Fe ₁₄ B crystal grain size on average. 6) The volume fraction of the fluorine-containing phase is smaller than the volume fraction of Fe or FeCo-based crystal grains. 7) The fluorine-containing phase has higher continuity on the outer periphery side of Fe or FeCo-based crystal grains than on the outer periphery of Nd ₂ Fe ₁₄ B-based crystal grains.

By satisfying these conditions, it is possible to exceed the theoretical value of the Nd ₂ Fe ₁₄ B magnet, the composition of the sintered magnet is Nd _{2 to} 11 atomic%, heavy rare earth element 0.01 to 1 atomic%, fluorine 0 0.001 to 0.1 atomic%, Fe 5 to 92%, and Co 0.1 to 90%. Heavy rare earth elements are the highest on the outer peripheral side seen from the center of Nd ₂ Fe ₁₄ B type crystal grains, and are 2 to 100 times the center part, and fluorine is unevenly distributed at grain boundary parts such as double grain boundaries or triple grain boundary points. And partly forms oxyfluoride. This oxyfluoride has a cubic structure by rapid cooling, and some of the cubic oxyfluoride forms a coherent interface with Fe, FeCo or Nd ₂ Fe ₁₄ B-based crystal grains.

Table 1-1 and Table 1-2 show examples in which various nanoparticles and main-phase rare earth-containing compounds were used for magnets containing Fe-containing nanoparticles and a fluorine-containing phase as in this example. Show. In an example in which the average nanoparticle diameter exceeds 1000 nm, the particles are aggregated and partially combined. An oxyfluoride is observed in the fluorine-containing phase, and the volume fraction of the fluorine-containing phase is in the range of 0.5 to 30%. In addition, rare earth elements are unevenly distributed in the vicinity of the grain boundaries, the average oxygen concentration in the nanoparticles is lower than the average oxygen concentration of the rare earth-containing compound (matrix), and the fluorine concentration in the vicinity of the nanoparticle interface is the rare earth-containing compound. It is smaller than the fluorine concentration in the vicinity of the intergranular grain boundary. The Curie temperature is 755 to 1210 K, which is higher than the value of Nd ₂ Fe ₁₄ B (588 K).

  A typical structure of this example is shown in FIG. FIG. 6 shows the cross-sectional structure of the magnet, with 1 nanoparticle, 2 rare earth-containing compound as the main phase, and 3 fluorine-containing phase. A part of the fluorine-containing phase that is a grain boundary phase may be a rare earth-rich phase that does not contain fluorine. As shown in FIG. 6, some of the nanoparticles are in contact with the rare earth-containing compound that is the main phase, and the nanoparticles and the rare earth-containing compound are magnetically coupled. Some of the nanoparticles in contact with the fluorine compound are in contact with the rare earth-containing compound, and there is a tendency that the contact area between the nanoparticle and the rare earth-containing compound is increased and the magnetic properties are improved. When the nanoparticle volume fraction is 50% or less, the magnetic properties tend to increase with the nanoparticle volume fraction. However, when the nanoparticle volume fraction exceeds 50%, the nanoparticle becomes a structure completely covering the periphery of the rare earth-containing compound particles, and the coercive force tends to decrease. Show. Therefore, the volume fraction of nanoparticles is desirably less than 50%.

A 99.9% pure Fe-30% Co alloy is evaporated in an inert gas atmosphere to produce nanoparticles with a particle size of 30 nm and precipitated into mineral oil containing a TbF-based gel. To this solution, Nd ₂ Fe ₁₄ B powder having a particle size of 3 μm is added with a dispersing agent capable of dispersing nanoparticles and mixed to prevent aggregation. The mixing ratio of Fe-30% Co nanoparticles and Nd ₂ Fe ₁₄ B powder is 1:10. Such a mixture of a slurry-like solution and powder is inserted into a mold, molded in a magnetic field, and then sintered at 1000 ° C. Furthermore, it was rapidly cooled after aging treatment at 600 ° C. to obtain a sintered magnet. Oxidation is suppressed by making an inert gas atmosphere or a vacuum atmosphere from powder preparation to sintering.

The sintered magnet is composed of Nd ₂ Fe ₁₄ B crystal grains having a tetragonal structure, cubic or tetragonal FeCo crystals, and fluoride, oxyfluoride, rare earth oxide, etc. A fluorine-containing phase can be confirmed between the Nd ₂ Fe ₁₄ B crystal grains and the FeCo crystal grains, and Tb is unevenly distributed in the Nd ₂ Fe ₁₄ B crystal grains. The magnetic characteristics of the sintered magnet are a residual magnetic flux density of 1.7 T (17 kg), a coercive force of 19 kOe, and an energy product of 70 MGOe. This characteristic exceeds 64 MGOe, which is the theoretical value of the Nd ₂ Fe ₁₄ B magnet, and can be used for various magnetic circuits. The Curie point is 590 to 1100 K, which is higher than the value of Nd ₂ Fe ₁₄ B, and the heat resistance of the magnet is high.

FIG. 1 shows the relationship between the volume ratio of the Fe-30% Co alloy crystal, the residual magnetic flux density Br, and the coercive force Hc with respect to the Nd ₂ Fe ₁₄ B-based crystal. When the volume fraction of the Fe-30% Co alloy crystal is 1% or more and 90% or less, the coercive force and the residual magnetic flux density are increased. FIG. 2 shows the relationship between the volume fraction of Fe-30% Co alloy crystal, the residual magnetic flux density Br, and the coercive force Hc with respect to the (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B crystal. When the volume fraction of the Fe-30% Co alloy crystal is 1% or more and 90% or less, the coercive force and the residual magnetic flux density are increased. This is because if it exceeds 90%, the magnetic coupling between the FeCo-based crystal and the NdFeB-based compound does not work, and the magnetization of the FeCo-based crystal is easily reversed.

When Fe-30% Co alloy crystal is added to Nd ₂ Fe ₁₄ B, the volume fraction of the fluoride to be coated is also an important factor. As shown in FIG. 3, the residual magnetic flux density Br and the coercive force Hc are the fluoride volume. Depends on. The fluoride volume has an effect of increasing the coercive force and residual magnetic flux density in the range of 0.01 to 1 with respect to the volume of the FeCo-based crystal. Accordingly, the fluoride volume is desirably 1% to 100% with respect to the FeCo-based crystal.

The reason why the residual magnetic flux density is increased is that the Nd ₂ Fe ₁₄ B grains and the Fe—Co grains have a magnetic coupling. For improving the magnetic characteristics, the crystal grain size, the composition of the FeCo-based crystal, the heavy rare earth element are used. The composition distribution, grain boundary phase structure and composition, volume fraction, orientation, crystal grain shape, etc. are affected. The crystal grain size of the Fe—Co grains is preferably smaller than the crystal grain size of the Nd ₂ Fe ₁₄ B grains. Crystal grain size of the Fe-Co particles is facilitated diffusion between Nd ₂ Fe ₁₄ becomes larger than the B particles when Fe-Co particles and Nd ₂ Fe ₁₄ B grains, the coercive force of the Nd ₂ Fe ₁₄ B is decreased.

As in this example, a Tb-F film was formed on the nanoparticle surface when precipitated in mineral oil containing a TbF-based gel on the surface of the nanoparticle having a particle size of 30 nm, and the fluoride coverage on the nanoparticle surface. Is higher than the fluoride surface coverage of Nd ₂ Fe ₁₄ B grains added and mixed later. Therefore, Tb and fluorine tend to be detected at a high concentration in the vicinity of the FeCo-based nanoparticles even after sintering, and the Nd ₂ Fe ₁₄ B grains in the vicinity of Fe—Co have a pronounced Tb uneven distribution. Increases sex. Fe-Co grains alone show soft magnetic properties, but magnetic coupling such as magnetostatic coupling is caused by the fact that Nd ₂ Fe ₁₄ B grains in which Tb is unevenly distributed are adjacent via grain boundaries and strain is introduced by a fluorine-containing phase. As a result, the magnetization of the Fe—Co grains is fixed by the magnetization, magnetic field, or magnetic coupling of the Nd ₂ Fe ₁₄ B grains, the magnetization reversal is suppressed, and the soft magnetic properties change. The grain boundary may contain rare earth elements and fluorine-containing fluorides or oxyfluorides, or magnetic powder constituent elements such as hydrogen, carbon, nitrogen, iron, cobalt, or other transition metals in these phases. The width is 0.1 to 100 nm. The structure of the oxyfluoride grain boundary phase is mainly cubic, and a part of the structure is lattice-matched with FeCo crystal or Nd ₂ Fe ₁₄ B crystal.

  4 and 5 show the relationship between the magnetic characteristics and the Co concentration of the FeCo-based crystal. When the Co concentration is 0.1 atomic% or more, the coercive force and the residual magnetic flux density increase. Further, from FIG. 5, this increase effect is recognized when the Co concentration is 90 atomic% or less. The Co concentration of the FeCo-based crystal is preferably 0.1 to 90 atomic%.

When Co is less than 0.1 atomic%, the FeCo crystal surface easily reacts with carbon contained in mineral oil or the like, and magnetization is reduced. When the Co concentration is 0.001, the magnetization of the FeCo-based crystal nanoparticles is reduced by 10 to 30% from the bulk value, so the effect of increasing the residual magnetization of the Nd ₂ Fe ₁₄ B sintered body is small. The effect of increasing the remanent magnetization becomes remarkable when the Co concentration of the FeCo-based crystal is 0.1 to 90%. If the Co concentration is within this range, the saturation magnetization of the FeCo-based crystal nanoparticles is 90% or more of the bulk value. The residual magnetic flux density of the Nd ₂ Fe ₁₄ B-based sintered magnet can be increased, and the FeCo-based crystal grains and Nd ₂ Fe ₁₄ B due to the uneven distribution of heavy rare-earth Nd ₂ Fe ₁₄ B-based grains and fluorine-containing phases The increase in the residual magnetic flux density and the increase in the coercive force as described above can be achieved by the magnetic segmentation between the system crystal grains.

A Fe-40 wt% Co alloy is melted in vacuum and exposed to high frequency plasma to form a cluster. The cooled cluster is recovered from the wall surface or the like and has an average particle size of 30 nm. The particle shape is spherical, elliptical or flat. The Fe-40% Co particles are submerged in an alcohol in which TbF ₃ is dissolved without being exposed to the atmosphere, and 0.1% ammonium fluoride is mixed and heated to 170 ° C. by a circulating bead mill apparatus. By applying a uniaxial magnetic field in the bead mill apparatus and diffusing the particles while adding anisotropy, a powder with added magnetic anisotropy is produced. By inserting this powder into the mold without exposure to the atmosphere together with Nd ₂ Fe ₁₄ B-based crystal grains and molding in a magnetic field, a compact with a density of 60% can be produced. An anisotropic sintered magnet with enhanced magnetic coupling of the ferromagnetic phase can be produced by sintering this molded body at 1070 ° C. in a magnetic field and then aging and quenching in the magnetic field. When the ratio of Fe-40 wt% Co alloy powder to Nd ₂ Fe ₁₄ B crystal grains is 1: 3 and the TbF fluoride weight is 0.1 wt%, the residual magnetic flux density is 1.9 T, the coercive force is 25 kOe, A sintered magnet having a Curie temperature of 850 to 1210 K can be produced.

In order to produce such a magnet having an energy product exceeding 60 MGOe and a coercive force of 15 kOe or more, the following conditions must be satisfied. 1) The main phase is tetragonal structure Re ₂ Fe ₁₄ B (Re is at least one element selected from rare earth elements including Y), and the inside of the sintered magnet as a ferromagnetic phase having a composition different from that of the main phase. Cubic FeCo crystal grains having the maximum saturation magnetization are formed. The fact that the saturation magnetic flux density is high in the sintered magnet can confirm the magnetic moment and magnetic structure of the sintered magnet using neutron rays and synchrotron radiation, and the magnetization of this FeCo-based crystal exists as a single crystal grain. It has been found that the residual magnetic flux density of the sintered magnet is increased by being more magnetically restrained.

2) The composition of the FeCo-based crystal is desirably 0.1 to 90 atomic% of Co, and the FeCo-based crystal grains are coated with a fluorine-containing phase such as ReOF or ReF-based fluoride which is a fluorine-containing phase. The coverage is 10 to 100%. The fluorine-containing phase prevents interdiffusion of Fe and Co atoms between the FeCo-based crystal and Re ₂ Fe ₁₄ B at the sintering temperature of 1070 ° C., and the heavy rare earth is unevenly distributed in the vicinity of the Re ₂ Fe ₁₄ B grain boundary It plays a role to make it. When the Co concentration of the FeCo-based crystal is less than 0.1 atomic% or less than the measurement sensitivity of mass spectrometry, the effect of increasing the residual magnetic flux density of the sintered magnet is not remarkable. When the Fe nanoparticles not containing Co and (Nd, Dy) ₂ Fe ₁₄ B are mixed and sintered with 0.1 wt% of TbF fluoride, the residual magnetic flux density decreases. Since the surface of the nanoparticle is active, it is necessary to suppress reactions such as oxidation and carbonization that reduce magnetization as much as possible. Such oxidation and carbonization are also important during the sintering and pre-sintering processes. These reactions are suppressed by the addition of Co, the magnetization increases due to the progress of the reduction reaction with fluoride, and the NdFeB system after sintering. The value exceeds the saturation magnetization of the crystal. Sintering in a magnetic field (10 to 100 kOe) and aging cooling in a magnetic field (1 to 100 kOe) so that such highly saturated magnetization FeCo-based crystals and NdFeB-based crystals reduce magnetostatic energy through the fluorine-containing grain boundary phase. By adopting the process, it is possible to achieve a high coercive force and a high residual magnetic flux density by magnetically coupling and the heavy rare earth element being unevenly distributed in the vicinity of the grain boundary of the NdFeB-based crystal. The lattice is distorted by magnetostriction due to sintering in magnetic field or aging treatment, and magnetic anisotropy is strengthened. Therefore, it is important to use an FeCo-based crystal whose magnetostriction constant is not zero. In the magnetic field, a magnetic field of 1 kOe or higher is applied in a temperature range higher than the Curie temperature of the NdFeB-based crystal and lower than the Curie temperature of the FeCo-based crystal. Increase in magnetic anisotropy due to heat treatment increases energy product by 1-20%. Since the magnetic property is a Curie point higher than the sintering temperature or the aging heat treatment temperature, induced magnetic anisotropy occurs in the FeCo-based crystal by the applied magnetic field, and magnetic coupling with the NdFeB-based crystal is caused by the effect of the anisotropy. Is strengthened. The nanoparticles easily penetrate into the gaps of the NdFeB-based crystal powder having a large particle size during temporary molding before sintering, and do not hinder the magnetic field orientation of the NdFeB-based crystal powder. When the average particle size of the FeCo-based crystal is larger than the average particle size of the NdFeB-based crystal powder, there are few FeCo-based crystals entering the gaps of the NdFeB-based crystal powder, and the magnetic field orientation of the NdFeB-based crystal powder is disturbed. When it is large as described above, the magnetic properties after sintering are difficult to improve particularly when the volume ratio of the FeCo-based crystal is 30% or more. A transition element containing a bcc stabilizing element may be added to the FeCo-based crystal. Further, even if the FeCo-based crystal contains hydrogen, fluorine and nitrogen, the same result as the above can be obtained as long as the cubic structure is maintained. In addition to nitrogen, carbon, oxygen, and hydrogen, the fluorine-containing phase may contain magnet constituents and transition metals such as Cu, Zr, Al, Mn, Ti, Ag, Sn, Ga, Ge, and Bi. There is no. When Co exceeded 90%, hcp structure and fcc structure were recognized in a part of FeCo-based crystal grains, and it was difficult to significantly increase the energy product. The energy product is highest in the case where a part of the fluorine-containing phase is a cubic system, the FeCo phase is a bcc structure, and the NdFeB system crystal grains are unevenly distributed with heavy rare earth elements.

  3) The FeCo-based crystal structure is a cubic system with fourfold symmetry. The crystal structure depends on the composition and crystal structure of the adjacent fluorine-containing phase and becomes an irregular or regular phase of bcc or bct. The reason why the cubic FeCo crystal can remain in the magnetic characteristics of high saturation magnetization after sintering is that the diffusion reaction of Fe and Co during sintering is suppressed by being covered with the fluorine-containing phase. The heavy rare earth element remaining in the fluorine-containing phase is unevenly diffused and unevenly distributed in the vicinity of the grain boundary of the NdFeB-based crystal, and hardly diffuses in the FeCo-based crystal. Therefore, the fluorine-containing crystal grain boundary is formed of FeCo-based crystal grains and NdFeB. When it is between the crystal grains of the system crystal, the concentration distribution of the heavy rare earth element shows an asymmetric concentration distribution in the direction perpendicular to the grain boundary centering on the crystal grain boundary, and is high on the crystal grain side of the NdFeB system crystal, The concentration of heavy rare earth elements in the grains is lower than the center of the grains. The fluorine concentration is low between the crystal grains of the NdFeB-based crystal and is high at the crystal grain boundary near the FeCo-based crystal grain.

4) Since the sintered magnet of this example contains FeCo-based crystal grains, the Curie temperature of the sintered magnet is 850 to 1230 K, which is higher than the Curie temperature (588 K) in Nd ₂ Fe ₁₄ B, and Nd ₂ The magnetization at a temperature 50K higher than the Curie point of Fe ₁₄ B is 0.1 emu / g to 150 emu / g. Magnetization and magnetostatic or exchange coupling of a Re ₂ Fe ₁₄ B-based crystal in which FeCo-based crystal grains exhibiting such a high Curie temperature are separated by a fluorine-containing grain boundary, and super-exchange interaction via fluorine ions and oxygen ions Thus, a high residual magnetic flux density is obtained by suppressing the coupling or the domain wall movement that makes it difficult to reverse the magnetization. By applying a magnetic field in the magnetization direction during rapid cooling after aging heat treatment, uniaxial anisotropy is induced in the FeCo-based crystal grains, the squareness of the demagnetization curve is improved, and the Curie point is raised.

5) FeCo-based crystal grains are recognized in a crystal grain shape different from Nd ₂ Fe ₁₄ B-based crystal grains on either the surface of the sintered magnet or the grain boundary triple point or two-particle grain boundary inside the sintered magnet. A plurality of particles are in contact with each other via a fluorine-containing grain boundary phase. In order to achieve both the residual magnetic flux density and the high coercive force, FeCo-based crystal particles are formed more at the grain boundary triple points than at the two-grain grain boundaries to suppress the decrease in magnetostatic coupling. When the FeCo crystal grains is larger than the particle size of the aggregate into Re ₂ Fe ₁₄ B-based crystal weakens the magnetic coupling between the FeCo crystal grains and Re ₂ Fe ₁₄ B-based crystals, decrease of squareness, This leads to a decrease in coercive force and energy product. Therefore, even when the FeCo-based crystal particles are aggregated, the size of the aggregate needs to be smaller than the average particle size of the Re ₂ Fe ₁₄ B-based crystal. In order to suppress such agglomeration, a dispersing agent is added to the pre-molding solution to disperse the FeCo-based crystal particles, or an alternating magnetic field is applied to obtain a substantially uniform mixed state with the Re ₂ Fe ₁₄ B-based crystal particles. It is desirable.

6) The grain boundary width of the fluorine-containing grain boundary phase needs to be smaller than the average particle diameter of the FeCo-based crystal particles. When the grain boundary width of the fluorine-containing grain boundary phase is larger than the average particle diameter of the FeCo-based crystal particles, the magnetic coupling between the FeCo-based crystal particles and the Re ₂ Fe ₁₄ B-based crystal is weakened, and the fluorine-containing grain boundary phase Since the magnetization of is small, the residual magnetic flux density decreases as its volume increases.

7) Cubic crystals are observed in the crystal structure of the fluorine-containing grain boundary phase, and some of the cubic crystals have a matching relationship with the FeCo-based crystal grains. This is because the fluorine-containing grain boundary phase and the FeCo crystal system are the same, and the lattice constant difference including an integer multiple of the lattice constant is small. It can be presumed that the magnetic saturation is affected by the fact that the highly saturated magnetization phase and the grain boundary phase have the same crystal structure of cubic crystals and that some crystals are in a matching relationship. The fluorine-containing grain boundary phase is formed at the FeCo-based crystal grain interface, and the fluorine concentration at the FeCo-based crystal grain interface is higher than the fluorine concentration between the Re ₂ Fe ₁₄ B-based crystal grains. This is because the fluorine-containing phase is formed so as to surround the FeCo-based crystal grains, and the FeCo-based crystal grains coated with the fluorine-containing phase are larger than the Re ₂ Fe ₁₄ B-based crystal grains, and the Re ₂ Fe ₁₄ B-based crystal Fluorine is not detected at part of the two-particle interface.

A sintered magnet having a saturation magnetic flux density higher than the saturation magnetic flux density of the Re ₂ Fe ₁₄ B crystal as in this embodiment, a coercive force of 10 kOe or more and a Curie point of 600 K or more is a Re ₂ Fe ₁₄ B system. This can be achieved when FeCo-based crystal grains having a diameter smaller than that of the crystal grains are adjusted to a weight in the range of 0.1 wt% to 90 wt% with respect to the entire sintered magnet. If it is less than 0.1%, the effect of the FeCo-based crystal does not appear remarkably, and the saturation magnetic flux density is almost equal to the value of the Re ₂ Fe ₁₄ B-based crystal. Note that oxygen, nitrogen, carbon, hydrogen, phosphorus, sulfur, and copper that are inevitably mixed will not be a major factor for deteriorating magnetic properties unless the conditions and configuration are changed.

Since the high-performance sintered magnet contains FeCo-based crystals, the amount of rare earth elements used is less than that of conventional Re ₂ Fe ₁₄ B-based sintered magnets. Hot extrusion molding, warm molding, molding using shock waves, heat treatment in magnetic field, spinodal decomposition heat treatment, warm plastic working, strong magnetic field molding, hydrostatic pressing, reduction low temperature sintering, swaging, cutting, Compound production for bonded magnets using magnetic powder, various bonded magnet molding processes, etc. can also be used. Further, by adding a rare earth element grain boundary diffusion process using slurry, solution or steam to the sintered magnet of this embodiment, it is possible to increase the coercive force or improve the squareness of the demagnetization curve.

In addition, the combination of the FeCo-based crystal and the fluorine-containing phase of this example can be applied to other magnetic materials having high crystal magnetic anisotropy energy, and the energy product increases, the Curie point increases, decreases. The effects of improving the squareness of the magnetic curve, increasing the coercive force, improving the magnetization, and improving the grain orientation can be confirmed. Furthermore, the magnetic anisotropy can be increased by making the magnetostriction constant of the FeCo-based crystal larger than 1 × 10 ⁻⁷ in absolute value, and the physical properties of the magnet can be controlled by controlling the crystal orientation relationship with various additive elements and grain boundaries. Can be improved. An alloy system includes an FeCoGa alloy, and an effect of increasing magnetic anisotropy by heat treatment in a magnetic field can be obtained even in an FeGa alloy system. The improvement of the physical property value of the magnet using the induced magnetic anisotropy by the heat treatment in the magnetic field such as sintering or aging is achieved by all the magnetic materials having an absolute value of the magnetostriction constant larger than 1 × 10 ⁻⁷ and the fluorine-containing grain boundary. This can be applied to the case where the phase and hard magnetic material are sintered.

  Other characteristics can be added to the magnet material by sintering using another magnetic material instead of the FeCo-based crystal of this embodiment. A magnet material having a magnetic refrigeration effect can be obtained by using Gd, LaFeSi-based, or GdSiGe-based alloy and setting the entropy change of the magnet material to −1 to −50 J / kgK. A magnet material having a thermoelectric effect in a magnetic field can be obtained by using a Bi-based alloy instead of an FeCo-based crystal. A magnetic material having a Peltier cooling effect can be obtained by using a magnetic material having a Co / Cr interface instead of an FeCo-based crystal. Further, it is possible to increase anisotropy by using an actinoid alloy instead of the FeCo crystal.

After melting 99.99% pure iron and cobalt in a vacuum, it is dissolved in a reducing atmosphere of Ar + 10% H ₂ and evaporated in a nitrogen atmosphere to obtain Fe-30 wt% Co particles having an average particle diameter of 50 nm from the wall surface. Collect and settle into a clear mineral oil containing TbF fluoride. After heating the slurry-like Fe-30% Co particles at 700 ° C., a TbF-based film is formed on the surface, mixed with Re ₂ Fe ₁₄ B-based crystal (Re is a plurality of rare earth elements) powder, and then temporarily formed in a magnetic field. A temporary molded body was obtained. The temporary molded body was sintered by heating to 1050 ° C. in a vacuum, and a sintered magnet was produced by aging heat treatment at 500 ° C. and magnetizing after quenching. When the oxygen concentration is 100 ppm or less without exposure to the atmosphere from raw material preparation to aging heat treatment, and when Fe-30% Co particles are mixed with (Nd, Pr) ₂ Fe ₁₄ B at a volume ratio of 30%, residual magnetic flux density The characteristics of 1.7 T and coercive force of 20 kOe were obtained. It was confirmed that this characteristic showed higher residual magnetic flux density and higher coercive force than when Fe-30% Co particles were not used.

Conventionally, the relationship between the residual magnetic flux density of Re ₂ Fe ₁₄ B and the coercive force has shown a tendency that the coercive force decreases when the residual magnetic flux density is increased. However, in this embodiment, the residual magnetic flux density and the coercive force increase. The amount of increase is the composition of FeCo grains, crystal structure, shape, composition of fluorine-containing grain boundary phase, structure, continuity, and composition, orientation, grain size distribution, grain boundary of the main phase, Re ₂ Fe ₁₄ B-based crystals. Although it depends on uneven distribution width, uneven distribution element, impurity concentration, consistency with grain boundary phase, etc., the use of FeCo-based crystal grains shows a maximum residual magnetic flux density of 2.0 T and an energy product of 98 MGOe. This energy product value is a value that greatly exceeds 64 MGOe, which is the theoretical energy product of Nd ₂ Fe ₁₄ B, and is extremely useful in practice.

Thus, it is important to satisfy all of the following conditions in order to obtain magnetic characteristics equivalent to or higher than the theoretical energy product of Nd ₂ Fe ₁₄ B. 1) The average grain size of the FeCo-based crystal should be equal to or smaller than the average grain size of the main phase, Re ₂ Fe ₁₄ B. 2) Cubic or tetragonal FeCo crystal grains are formed. 3) The composition of the FeCo-based crystal is desirably 0.1 to 90 atomic% of Co, and considering the cost and magnet performance, the optimal Co concentration is 0.1 to 50%. 4) FeCo-based crystal grains or agglomerated crystal grains are almost covered with a fluorine-containing phase such as ReOF or ReF-based fluoride which is a fluorine-containing phase. Here, Re is at least one kind of rare earth element. 5) Heavy rare earth elements are unevenly distributed near the grain boundaries of the NdFeB-based crystal. Here, the vicinity of the grain boundary means a distance within 500 nm from the grain boundary phase where fluorine is detected into the NdFeB-based crystal grain. 6) After sintering, the cubic FeCo crystal remains in the magnet in a state of higher saturation magnetization and Curie temperature than the NdFeB crystal. This means that when the magnet is heated, the temperature dependence of magnetization consists of two or three stages and a plurality of magnetic transition points, and the aging temperature is higher than the Curie point. There is an increase in sex. In the temperature dependence of magnetization, a rapid decrease in magnetization is confirmed at 250 to 320 ° C., and a rapid decrease in magnetization can be confirmed on the high temperature side from 400 ° C. to 900 ° C. 7) The Curie temperature of the sintered magnet is 327 to 957 ° C. (600 to 1230 K), which is higher than 588 K of Nd ₂ Fe ₁₄ B. 8) FeCo-based crystal grains are observed either at grain boundary triple points, two grain boundaries, in crystal grains, or on the magnet surface. 9) The average grain boundary width of the fluorine-containing grain boundary phase is narrower than the average particle diameter of the FeCo-based crystal particles. 10) Cubic, hexagonal, orthorhombic and rhombohedral crystals are observed in the crystal structure of the fluorine-containing grain boundary phase. 11) The FeCo-based crystal particles can be sintered at 0.1 to 90% of the whole, and the improvement in magnetic properties by the FeCo-based crystal can be confirmed at 0.1 to 80%. 12) The average crystal grain size of the FeCo-based crystal grains before and after sintering does not vary greatly and is 50% to 200% (0.5 to 2 times) after sintering with respect to the average grain size before sintering. It can be seen that some FeCo crystal grains are aggregated and coarsened.

  By satisfying all of the above conditions, a sintered magnet exceeding 60 MGOe can be produced, and the coercive force can be further increased by diffusing and unevenly distributing heavy rare earth elements at grain boundaries using various methods. It is. The sintered magnet created in this example is composed of at least two ferromagnetic phases of an iron-cobalt alloy system having a saturation magnetic flux density higher than that of a rare earth iron boron system and a rare earth iron boron system compound, and a fluorine-containing grain boundary phase. The iron-cobalt alloy crystal has a cubic crystal structure containing 0.1 to 90% cobalt, and the average crystal grain size of the iron-cobalt alloy system is a rare-earth iron boron-based average crystal. The grain size of the iron-cobalt alloy alloy is smaller than the grain size, and the crystal grain of the iron-cobalt alloy alloy is found at either the grain boundary triple point or the two-grain grain boundary, and is almost covered with a fluorine-containing phase such as ReOF or ReF fluoride. The fluorine concentration is the highest at the iron cobalt alloy crystal grain interface, and the fluorine concentration at the grain boundary between the rare earth iron boron crystal grains is lower than the fluorine concentration at the iron cobalt alloy crystal grain interface. . The ratio of the fluorine concentration at the grain boundary between the two grains of the rare earth iron boron-based crystal grain and the fluorine concentration at the iron-cobalt alloy-based crystal grain interface is smaller than 1/2 on average. When it becomes 1/2 or more, a large amount of fluoride or oxyfluoride grows, which tends to cause sintering failure. Heavy rare earth elements are unevenly distributed in the vicinity of the grain boundaries where the fluorine concentration is high, and heavy rare earth elements are unevenly distributed in the vicinity of the grain boundaries of the rare earth iron boron-based crystal grains. The sintered magnet of this example is characterized by a Curie temperature of 600 to 1230K.

  Of particular importance in such characteristics is that the above properties cannot be achieved without the addition of cobalt (Co). In the case of iron alone, the surface of the iron particles is easily combined with a light element such as carbon during heating by a carbon-containing solvent such as mineral oil or alcohol as described above, so that the magnetization is lowered, so that high performance is difficult. On the other hand, in the alloy with 0.1% Co added, carbides are less likely to grow, and oxygen on the particle surface is reduced by heat treatment at 700 ° C., as in this example, to form oxyfluoride on the surface. It became clear that the particles could be chemically stable, and it became clear that the increase in the magnetization of the particles and the effect of increasing the Curie point led to the improvement of the characteristics, and it was possible to improve the performance of the sintered magnet. Further, in the sintered magnet of this example, the FeCo-based crystal grains have a lattice constant of 0.05 to 1.5%, which is larger than the lattice constant of the same composition in the bulk. Analysis of electron diffraction and X-ray diffraction From the above, in the case of Fe-30% Co alloy particles, the lattice constant is larger than that of Fe. This indicates that the FeCo-based crystal grains have lattice strain accompanying lattice matching from the surrounding oxyfluoride and fluoride, and such lattice strain increases saturation magnetization and Curie temperature. It is a cause.

  Enumerating the process of creating a high-performance sintered magnet that can be used in methods other than this example, impregnation process using a fluorine-containing solution after temporary molding, crushing process using a bead mill, using a dispersing agent Crushing process, cooling process in one direction magnetic field, cooling process in AC magnetic field, sintering process in magnetic field, anisotropy adding process by applying magnetic field, diffusion treatment process after sintering using steam or slurry, bonding magnet forming process , Hot forming, hot extrusion forming, sintering process using selective heating using electromagnetic waves, low temperature pressure sintering process using hot forming, hot forming in pressurized magnetic field, current forming, radial anisotropy These are an addition process, a polar anisotropy addition process, and various plating processes for improving corrosion resistance. In addition, even if impurity elements such as nitrogen, oxygen, hydrogen, carbon, copper, and manganese that are inevitably mixed are unevenly distributed in the magnet, there is no problem as long as the above conditions are satisfied, and the FeCo-based crystal has a regular phase or an irregular phase. Even if it is a ternary or quaternary alloy containing a transition element, there is no problem as long as 0.1 to 90% Co is contained, which is higher than that of an NdFeB crystal grain containing 0.1% Co. You may use the particle | grains of the several composition which has a saturation magnetic flux density. If the volume of the FeCo-based crystal in the entire magnet is less than 0.1%, it is difficult to increase all of the coercive force, energy product, and Curie temperature in the mass production process. It is possible to increase all of the coercive force, energy product, and Curie temperature when the FeCo-based crystal is 0.1 to 80%, even using a mass production process. If the FeCo-based crystal exceeds 80%, the amount of fluoride increases and it becomes difficult to sinter at a temperature at which magnet characteristics can be obtained.

  Fe-5 wt% Ce (cerium) is evaporated in plasma to prepare a powder having a powder diameter of 100 nm. By flowing HF gas into the plasma, the powder being evaporated is fluorinated, and an Fe-5 wt% Ce-2 wt% F alloy is produced. In the cooling process from powder to powder, a unidirectional magnetic field of 10 kOe is applied to add induced anisotropy. After the powder prepared by such a method is inserted into a mold together with Fe-30% Co particles without being exposed to the atmosphere, a temporary molded body is prepared by temporary molding in a magnetic field, and further heat molded at 700 ° C.

A ternary fluoride such as FeF ₂ containing 0.1 to 10 atomic% of Ce or Fe—Co—F—Ce—O _{4 quaternary} fluoride grows in the grain boundary after forming, and forms iron particles. Also, it was confirmed that Ce contained and CenFem or CeaFebFc was growing. In the above, Ce is cerium, Fe is iron, F is fluorine, and n, m, a, b, and c are positive numbers. In particular, in this example, the growth of CeFe ₁₉ , CeFe ₁₉ Fc, CeFe ₂₁ , CeFe ₂₁ F _c (c is 0.1 to 3) can be confirmed in addition to the FeCo-based crystal, and the saturation magnetic flux density is 1.5 T and the coercive force is 17 kOe. The magnet shown was made.

Such a magnet having a rare earth element concentration of 1 to 5 atomic% has the following characteristics. 1) A fluorine-containing phase grows at a part of the grain boundary. 2) A compound having a high iron content in which the concentration ratio of light rare earth elements to iron is 1:19 or more in atomic concentration ratio is growing. 3) A compound containing an interstitial element such as fluorine is growing. 4) FeCo-based crystal grains having a Co concentration of 0.01% or more are formed through the fluorine-containing phase. 5) Does not contain heavy rare earth elements. Among the above, compounds having a high iron content in which the concentration ratio of light rare earth element to iron is 1:19 or more in atomic concentration ratio usually do not grow in an iron-light rare earth element binary system that does not contain fluorine. It is a fluorine-containing phase that enables growth, which is considered to have grown as a crystal phase that can maintain an alignment relationship with oxyfluoride or fluoride, and has lattice distortion. As a high-concentration iron-containing compound that can be grown by introducing such lattice strain, there are Re _n Fe _{m and} Re _a Fe _b F _c . Here, Re is a rare earth element, Fe is iron, F is fluorine, n, m, a, b, and c are positive numbers, and n / m ≦ 19 and a / b ≦ 19. Thus, a compound that can grow in alignment with the grain boundary phase of oxyfluoride or fluoride can increase the coercive force because it has lattice distortion near the interface and increases the magnetocrystalline anisotropy. Instead of fluorine contained in the ferromagnetic compound, hydrogen, nitrogen, carbon or halogen elements other than fluorine and a plurality of these elements can be used.

The Fe-30 wt% Co alloy is evaporated in an ultra-high vacuum to form a powder with an average particle size of 5 to 100 nm, and precipitated in mineral oil in an Ar gas atmosphere to prevent oxidation. In this mineral oil, a Tb-F-based gel is dissolved at a weight concentration of 0.1 to 5%, and NH ₄ F is added by 1%. A Tb-F-based film is formed on the surface of some FeCo-based powders. Is formed with a film thickness smaller than the particle diameter. NH ₄ F is chemically bonded to the surface of the FeCo-based powder and advances the layering of the TbF-based film. When the fluoride film is thicker than the particle size, the residual magnetic flux density is significantly reduced. It has been confirmed that the FeCo-based crystal powder in which the fluoride is formed increases the saturation magnetization by 1 to 10% by heat treatment at 200 ° C. to 1000 ° C. This increase in saturation magnetization is due to the fact that elements such as oxygen and carbon, which are impurities in the particles, are absorbed by the fluoride, and the composition and crystal structure of the fluoride are changed by the heat treatment. Even when the particles are oxidized or various protective layers are formed on the surface, the saturation magnetization is increased by the heat treatment after forming the fluoride, and reaches 90 to 99% of the bulk saturation magnetization.

  An anisotropic sintered magnet can be formed by mixing the FeCo-based powder on which the fluoride film is formed with the NdFeB-based magnetic powder, which is a magnetic powder having a large crystal magnetic anisotropy, and then magnetic field orientation and sintering. A magnet composed mainly of a FeCo-based crystal, a fluorine-containing grain boundary phase, and a ferromagnetic phase having a large crystal magnetic anisotropy can be prepared, and the residual magnetic flux density and Coercivity increases. The formation of a fluorine-containing grain boundary phase is indispensable for achieving both an increase in residual magnetic flux density and an increase in coercive force, increasing the saturation magnetization of FeCo-based phases with low magnetocrystalline anisotropy and removing impurities near the interface. This is very important.

Fluoride has a function of absorbing impurities such as oxygen and carbon in Fe and FeCo-based crystals, and the average magnetic moment in the vicinity of the Fe and FeCo-based crystal interface (within 2 nm from the interface) is 1.8 to 2. to become a 3.mu. _B (Bohr magneton) are confirmed by magnetic measurement using a spin SEM and synchrotron radiation or neutrons. When the oxygen concentration is 100 ppm or more, the average magnetic moment is reduced and the exchange coupling force is also weakened, so that the residual magnetic flux density is reduced. Therefore, it is important to absorb and remove oxygen in Fe and FeCo-based crystals with fluoride.

  In addition, it can be confirmed that Tb, which is a fluoride constituent element, easily diffuses into a phase having a larger magnetocrystalline anisotropy than that of the Fe or FeCo-based crystal. It is important to select a combination that can increase the physical property value. Further, since a part of the Fe or FeCo phase grows in a specific crystal orientation relationship with the fluorine-containing phase, the lattice of the Fe or FeCo phase is locally distorted. It is clear from the measurement analysis of interatomic distance using electron diffraction and synchrotron radiation that bct is present, and a bct phase with a lattice constant axial ratio of 1.001 to 1.300 grows near the interface. To do. Such growth of the bct phase contributes to an increase in magnetic anisotropy and an increase in magnetic flux density. In the case of a bcc (body-centered cubic) structure having a lattice constant of only one value in the FeCo-based crystal lattice, the consistency with the fluorine-containing phase is low. Since the exchange coupling is weak and the magnetic anisotropy of the FeCo-based crystal is small, the coercive force of the entire magnet is small. On the other hand, when the FeCo-based crystal lattice is a tetragonal crystal having two types of lattice constants, it has high lattice matching near the interface with the fluorine-containing phase and has an anisotropic energy higher than bcc. The exchange coupling with the highly crystalline magnetic anisotropic phase, which is a phase, is strong, and the coercive force of the entire magnet is increased. It was confirmed that the magnetic anisotropy was larger than that of the bcc structure in the bct phase having an axial ratio of 1.001 or more. Also, the structure of the bct phase becomes unstable to release the lattice strain with respect to the temperature when the axial ratio becomes large, and when it exceeds 1.550, the bct phase transitions from bct to bcc at 500 ° C. or more, so that the bct exceeds 1.550. Although it is possible to produce a bonded magnet for the phase, it is usually difficult to obtain a magnet having a magnetic density of 98% or more because a sintering process cannot be used. When the phase having a large magnetocrystalline anisotropy was an FeCo-based crystal having a bct structure, a residual magnetic flux density of 2.1 T and a coercive force of 18 kOe could be confirmed.

In order to realize a high residual magnetic flux density and a high coercive force as in this embodiment, it is necessary to satisfy all the following requirements. 1) A fluorine-containing phase grows in a part of the grain boundary, and the oxygen and carbon concentrations in the grain boundary are higher than in the grain. 2) The oxygen concentration in the vicinity of the interface of the Fe or FeCo phase with a saturation magnetic flux density in the range of 1.6 to 2.7 T is greater than the average oxygen concentration in the crystal having a magnetocrystalline anisotropy energy of 0.5 MJ / m ³ or more. Also small. That is, in the magnet, the phase having the minimum oxygen concentration is a highly saturated magnetization phase such as Fe or FeCo phase. 3) A fluorine-containing phase is formed at a part of the interface of the Fe or FeCo phase, and a part of the constituent elements of the fluorine-containing phase is unevenly distributed in the vicinity of the crystal grain boundary of the high crystal magnetic anisotropy. 4) Magnetic coupling such as magnetostatic coupling and exchange coupling is recognized between the two types of ferromagnetic phases via the fluorine-containing phase. 5) Bct (tetragonal) is growing on some Fe or FeCo crystal grains, or lattice distortion is observed. 6) Fe or FeCo-based crystal particles are discontinuously formed at the grain boundary, and a portion where a plurality of Fe or FeCo-based crystal particles are in contact via a fluorine-containing phase is observed in the sintered body. 7) The magnetization of the fluorine-containing phase formed at the grain boundary is in the range of 0.001 to 100 emu / g.

FIG. 6 shows a typical structure of a cross section of a magnet obtained by forming a TbF-based film on an Fe-50% Co alloy and then sintering it after mixing with Nd ₂ Fe ₁₄ B-based powder. In the figure, the part that can be distinguished from Fe of the bcc structure is a gray (hatched) part, and the black line is a grain boundary mainly composed of Nd ₂ Fe ₁₄ B crystal grains. The bcc structure is detected mainly along the grain boundary, and there are more bcc phases growing along the grain boundary than in the grain. In the Bcc phase, Fe and Co were detected from the EDX analysis results, and the rare earth elements were in the range of about 0.01 to 5 atomic%. Therefore, it was found that bcc is an FeCo-based crystal, and the FeCo-based crystal is grown adjacent to the Nd ₂ Fe ₁₄ B-based crystal grain. The grain boundaries of the sintered magnet are FeCo / rare earth oxyfluoride, FeCo / rare earth oxide, Nd ₂ , in addition to FeCo crystal and Nd ₂ Fe ₁₄ B intergrain boundary (FeCo / Nd ₂ Fe ₁₄ B). There are grain boundaries composed of different types of interfaces such as Fe ₁₄ B / rare earth acid fluoride, Nd ₂ Fe ₁₄ B / rare earth fluoride.

Among the grain boundaries, magnetic coupling such as exchange coupling and magnetostatic coupling acts on the grain boundary between FeCo-based crystal and Nd ₂ Fe ₁₄ B-based intergrain (FeCo / Nd ₂ Fe ₁₄ B). The uneven distribution of heavy rare earth elements such as Tb is confirmed in the vicinity of the boundary, and the magnetization reversal of the FeCo-based crystal is suppressed by increasing the magnetic anisotropy energy of the Nd ₂ Fe ₁₄ B-based crystal due to Tb. The formation of such FeCo / Nd ₂ Fe ₁₄ B grain boundaries in which heavy rare earth elements are unevenly distributed is a condition for achieving both an increase in the energy product of the sintered magnet and a reduction in the amount of rare earth used.

In a magnetic circuit such as a motor, it is effective to create a stacked structure of FeCo and Nd ₂ Fe ₁₄ B-based crystal, and the c-axis direction of the Nd ₂ Fe ₁₄ B-based crystal is almost perpendicular to the stacked interface, and the magnetization direction It is desirable to form FeCo-based crystal grains or FeCo-based crystals extending perpendicularly. Such laminates by laminating a sintered plate of the FeCo crystal plate or the foil and the Nd ₂ Fe ₁₄ B-based crystal, by unevenly distributed the heavy rare-earth element in the vicinity of the surface of Nd ₂ Fe ₁₄ B-based crystal realizable.

Cobalt acetate tetrahydrate (Co (OCOCH ₃ )) ₂ · 4H ₂ O, iron chloride tetrahydrate (FeCl ₂ · 4H ₂ O), sodium hydroxide (NaOH) and polyvinylpyrrolidone are dissolved in ethylene glycol, The mixture was heated to 120 ° C., added with a gel having a TbF ₃ composition, and then heated to 140 ° C. to prepare a ferromagnetic powder in which FeCo-based crystal particles were coated with a Tb—F film. The particle diameter and particle composition depend on the concentration of Fe and Co in the solution, the heating rate, the heating temperature, etc., and the surface of the Fe-30% Co alloy particle having an average particle diameter of 50 nm is coated with a Tb-F film. Powder is obtained.

By subjecting the obtained FeCo-based crystal particles to a vacuum heat treatment at 900 ° C., it can be confirmed that the saturation magnetization increases with the heat treatment temperature, and an Fe-30% Co alloy powder with an average particle diameter of 50 nm has an average film thickness of 2 nm and TbOF or When TbF ₂ and TbF ₃ were coated, the saturation magnetization of the ferromagnetic portion was 230 emu / g. Saturation magnetization is increased by heat treatment in which impurities such as oxygen and carbon in the particles are diffused and absorbed by fluoride. Furthermore, by rapidly cooling the temperature range of 300 ° C. or higher at a rate of 10 ° C./second or more after this heat treatment, a part of the oxyfluoride is stabilized to cubic to room temperature, leaving lattice strain in the particles, Some Fe-30% Co alloys grow a phase having two values of lattice constants. By introducing the lattice strain, the magnetocrystalline anisotropy energy of the Fe-30% Co alloy increases and the coercive force increases.

  After mixing the above magnetic powder with NdFeB magnetic powder, compression molding in a magnetic field, or densification by heat molding after temporary molding in a magnetic field, hot molding, sintering after temporary molding in a magnetic field, impact compression molding, isostatic pressing, etc. When NdFeB magnetic powder: Fe-30% Co alloy powder is 2: 8, a magnet having a residual magnetic flux density of 2.1 T, a coercive force of 25 kOe, and a Curie temperature of 710 ° C. can be produced.

  Such a magnet having a residual magnetic flux density exceeding 2.0 T can be realized with the following composition and structure. That is, 1) the main phase is an FeCo-based crystal, 2) a part of the main phase has lattice distortion, and the lattice constant has two values. Thus, having two lattice constants increases the magnetocrystalline anisotropy and increases the coercive force. 3) A metastable fluorine-containing phase is formed in contact with the main phase, and the crystal orientation relationship can be confirmed at some main phase / fluorine-containing phase interfaces, and there is lattice distortion in the vicinity of the interface. 4) The arrangement direction of the main phase particles constituting the compact has anisotropy. 5) The average particle diameter of the NdFeB-based particles is 10,000 nm or less and 5 nm or more. By satisfying all the above conditions, a high-performance magnet can be obtained.

  Next, the above 1) to 5) will be further described. 1) is a limitation relating to the composition of the main phase, but in order to make the residual magnetic flux density 2.0 T or higher, it is necessary to use an FeCo system in which the saturation magnetic flux density is 2.0 T or higher. Such an alloy system is desirable because there is no material with a saturation magnetic flux density higher than 2.0T and containing no Fe or Co. Fe-N, Fe-C, Fe-B, Fe-F, and other Fe and FeCo-based alloys added with light elements, compound-based and composition-modulated alloys, etc. have a saturation magnetic flux density of 2.degree. A material system of 0T or more can also be applied. The maximum value of the saturation magnetic flux density is 2.7T. The main phase particles may include ferromagnetic materials containing rare earth elements such as Fe-rare earth elements and Fe-rare earth elements-light elements, and a plurality of types of particles mixed in combination of these materials.

  2) By having lattice distortion in the vicinity of the grain boundary, the symmetry of the crystal becomes low and the magnetic anisotropy energy increases. Lattice strain can be introduced by applying a magnetic field in the temperature range below the Curie point of FeCo-based crystals by sintering in a magnetic field or aging heat treatment in a magnetic field after sintering, and is 0.1% to 25% near the grain boundary. It depends on the structure and orientation of the oxyfluoride or fluoride phase, the magnetic field strength, the magnetic field application direction, and the like. The lattice distortion can be confirmed by analyzing a diffraction image of a transmission electron microscope and analyzing an atomic position and an interatomic distance using synchrotron radiation. Various defects such as transition and stacking faults can be observed in the lattice strain introduction portion.

  3) By forming a fluorine-containing phase at the grain boundary, the fluoride diffuses and absorbs impurities in the main phase, and forms a grain boundary interface having a crystal orientation relationship with the main phase. Introduce lattice distortion. The fluoride is preferably a transition metal fluoride other than the Tb-F system or a transition element-containing oxyfluoride, and its average thickness is 0.1 to 10 nm. If the thickness is less than 0.1 nm, the fluoride is not layered, and it is difficult to introduce lattice distortion to the entire main phase interface, and the coercive force is reduced. Further, when the average thickness exceeds 10 nm, the coercive force can be secured, but the energy volume decreases because the fluoride volume ratio increases and the residual magnetic flux density decreases. The fluoride contains oxygen and the oxygen concentration is higher in the fluoride than in the main phase. Various elements may be added to adjust the lattice constant. Fluoride or oxyfluoride in contact with the main phase has different crystal structures at room temperature and high temperature, and has a plurality of crystal structures depending on temperature or oxygen concentration. It is desirable that the lattice of the main phase and fluoride or oxyfluoride (phase stable at room temperature or high temperature) is partially consistent in the vicinity of the interface.

  4) The residual magnetic flux density is increased by adding anisotropy in the orientation direction in the step before forming the molded body. If the average crystal orientation of the compact is not anisotropic, a residual magnetic flux density of 2.0 T or more cannot be achieved. Since the FeCo-based crystal grains have a higher magnetic permeability than the NdFeB-based particles, the magnetic field at the time of temporary forming is concentrated, contributing to the parallelization of the magnetic field distribution and the increase of the magnetic field strength, and the degree of orientation of the NdFeB-based magnetic powder can be increased. Also, the magnetization after sintering is improved. Furthermore, by applying a magnetic field during sintering, the orientation is increased and the magnet characteristics are improved.

5) When the average grain size of the FeCo-based crystal is 10 μm or more, the ratio of lattice strain added is small, so the coercive force and the residual magnetic flux density are small. The average particle diameter at which the coercive force is manifested at less than 10 μm and the residual magnetic flux density is 2.0 or more is 100 to 200 nm. If it is less than 5 nm, the residual magnetic flux density becomes 0.5-1.5T due to the increase in the volume fraction of the fluoride volume at the grain boundary, the difficulty in producing particles, and the difficulty in controlling the anisotropy. I can't get it. Furthermore, the shape of the main phase particles constituting the molded body is not an isotropic spherical shape, but a cubic shape, a flat shape or an elliptic shape with shape anisotropy, and a part of the main phase or fluorine-containing phase is regular. Introduction of matching strain due to the structure is an indispensable element for increasing the coercive force. Such magnets must be in a range that does not significantly affect the structure and lattice distortion of the fluorine-containing phase and the main phase even if the impurities of various light elements and transition elements inevitably contained are present in the grains or at the grain boundaries. Magnetic properties can be maintained. Part of this material process is (Nd, Dy) ₂ Fe ₁₄ B system, (Nd, Pr, Dy) ₂ Fe ₁₄ B magnet or Sm ₂ Co ₁₇ system magnet, alnico system magnet, MnAl system magnet, MnBi system magnet, Composite magnets and laminated magnets can be created by using them in combination with FeCr-based magnets or ferrite-based magnets, and can be applied to various magnetic circuits.

(Nd, Dy) ₂ Fe ₁₄ B magnetic particles having an average particle diameter of 0.1 to 5 μm and Fe-30% Co particles having an average particle diameter of 0.05 to 1 μm are composed of (Nd, Dy) ₂ Fe _14. About 20% is mixed with B powder. This mixed powder is subjected to bead milling at 130 ° C. for 10 hours in mineral oil containing 20% ammonium fluoride, and fluorination and pulverization proceed simultaneously. As the beads, TbF ₃ particles having a particle diameter of 100 nm were used. After the bead mill, an anisotropic sintered magnet is obtained by drying, temporary forming in a magnetic field, sintering, and aging heat treatment in a magnetic field after sintering. By adopting a bead mill with fluoride formation, fluoride is formed on the surface of the powder, and fluoride, oxyfluoride, or carbon-containing oxyfluoride grows on the grain boundary after sintering.

In the sintered body, crystal grains containing fluorides such as (Nd, Dy) ₂ Fe ₁₄ B, Fe-30% Co, (Nd, Tb) OF, NdF ₂ , NdF ₃ , TbF ₂ , TbF ₃ are formed. A sintered magnet having a residual magnetic flux density of 1.65 T, a coercive force of 25 kOe, and an energy product of 67 MGOe is obtained. In this sintered magnet, a cubic crystal having a lattice strain, that is, a tetragonal crystal has grown, and the fact that a lattice strain exists in the ferromagnetic phase in the range of 0.1 to 1% is also confirmed by electron beam diffraction of an electron microscope. Confirmed from image analysis.

Further, Tb diffuses more in the (Nd, Dy) ₂ Fe ₁₄ B grain than in the Fe-30% Co grain, and (Nd, Dy) in the vicinity of the Fe-30% Co grain through the fluorine-containing grain boundary. _{2 It} is unevenly distributed in the Fe ₁₄ B crystal grains and increases the magnetocrystalline anisotropy energy of the (Nd, Dy) ₂ Fe ₁₄ B crystal, and between (Nd, Dy, Tb) ₂ Fe ₁₄ B and Fe-30% Co particles Increase the magnetic coupling. Magnetic coupling such as magnetostatic coupling or exchange coupling works between (Nd, Dy, Tb) ₂ Fe ₁₄ B in which Tb is unevenly distributed and Fe-30% Co particles, and the saturation magnetic flux density of the FeCo-based crystal is (Nd , Dy) ₂ Fe ₁₄ B, the residual magnetic flux density becomes higher, and an energy product exceeding (Nd, Dy) ₂ Fe ₁₄ B can be realized.

Fe-30% Co particles have an irregular or regular bcc or bct structure, and the coercive force tends to increase as the proportion of the bct structure increases. Similar to the present invention, the combination of ferromagnetic tetragonal crystal having lattice strain and high crystal magnetic anisotropy is not limited to the RE ₂ Fe ₁₄ B / Fe—Co system (RE is a rare earth element), and RE ₂ Fe _14. B / Fe-based or _{RE 2 Fe 17 N x / Fe} , RE 2 Fe 17 F x / Fe-Co _{-based, REFe 11 M y F x /} Fe _{system, RE 2 Co 17 / Fe-} Co -based, such as (X 0 0.01 to 4) high crystalline magnetic anisotropy energy compound containing rare earth element and high saturation magnetic flux density material, and in combination of these, a fluorine-containing phase is formed at the grain boundary, and the high saturation magnetic flux in the vicinity of the grain boundary is formed. When the lattice strain of the density material is 0.1% or more and 20% or less, the energy product is 40 to 100 MGOe, and the Curie point can be 600 to 1050K.

  When the lattice strain is 20% or more, the structure of the high saturation magnetic flux density material becomes unstable, the lattice strain is easily relaxed at 400 to 600 ° C., and it is difficult to use at high temperature. Further, when the lattice strain is 0.1% or less, the crystallinity of the high saturation magnetic flux density material is poor and the dispersion of magnetization is large, so that the bond with the high crystal magnetic anisotropy is weak and the squareness is lowered. An energy product of 70 MGOe is observed.

  When the volume ratio of the high saturation magnetic flux density material is 2 to 90%, an increase in the energy product is recognized as compared with the case where the high saturation magnetic flux density material is not used. When the volume fraction of the high saturation magnetic flux density material is less than 2%, the effect of increasing the energy product and the effect of decreasing the magnetization due to the growth of the fluorine-containing grain boundary phase are offset. When the volume fraction of the high saturation magnetic flux density material exceeds 90%, the high saturation magnetic flux density material has high continuity and high crystal magnetic anisotropy crystal grains come into contact and overlap, resulting in high crystal magnetic anisotropy. Since the ratio of magnetostatic coupling and exchange coupling with the magnetic field decreases, the lattice strain is released and the energy product decreases. When the volume ratio of the high saturation magnetic flux density material exceeds 10%, the corrosion resistance is improved in addition to the increase in the energy product. Furthermore, when the volume ratio of the high saturation magnetic flux density material is 30 to 90%, the loss reduction effect due to the increase in the electric resistance can be confirmed in addition to the improvement in the corrosion resistance. In addition, improvement in magnetism and increase in Curie point can be confirmed for all magnets with increased energy product.

A magnet capable of reducing the amount of rare earth element used as in this embodiment needs to satisfy the following conditions. 1) The grain boundary contains fluorine. 2) An FeCo-based crystal having a saturation magnetic flux density higher than that of Nd ₂ Fe ₁₄ B (1.61T) is formed. 3) The phase containing the rare earth element is Re _a Fe _b X _c (Re is at least one rare earth element, Fe is iron or an iron-transition metal multi-element alloy, X is B, C, N, F, Cl, H, And at least one of S, P, Al, and Si, a, b, and c are positive numbers and b> a + c), and the FeCo-based crystal is grown through the fluorine-containing phase. 4) A rare earth element is contained in a part of the fluorine-containing phase. 5) A part of the sintered body can confirm that the easy magnetization direction of the Re _a Fe _{b Xc} crystal is parallel to the easy magnetization direction of the FeCo-based crystal. For example, it can be confirmed by diffraction experiments that Nd ₂ Fe ₁₄ B {00n} and {00n} of the FeCo-based crystal are parallel on average.

The fluorine-containing grain boundary phase is a phase containing fluorine such as an acid fluoride, a carbon-containing fluoride, a fluoride containing a transition element or an acid fluoride, and may be a metastable phase such as amorphous. In the case of an oxyfluoride, the main structure has cubic crystals and contains rare earth elements. In addition to cubic crystals, the fluorine-containing phase grows with orthorhombic, hexagonal, rhombohedral and monoclinic crystal structures. The fluorine concentration of the fluorine-containing grain boundary is highest near the FeCo-based crystal grain interface, and the grain boundary phase between the Re _a Fe _{b Xc} crystals has a low fluorine concentration. The FeCo crystal may be an alloy having a Co concentration of 0.1 to 90 atomic% or a third element added in this composition range, and the crystal structure is bcc or bct. If the Co concentration is less than 0.1%, oxidation, carbonization or oxidation is likely to occur, and the saturation magnetic flux density decreases. If the Co concentration is in the range of 0.1 to 90%, such oxidation and carbonization can be prevented, the coverage of the fluorine compound can be increased, and a saturation magnetic flux density higher than that of Nd ₂ Fe ₁₄ B (1.61T) can be obtained. . If the Co concentration exceeds 90%, an hcp or fcc phase is likely to be formed, and the stability of the interface between the fluorine compound and the FeCo-based crystal grains is lowered. There is a decline. The Co concentration may fluctuate or vary in the FeCo-based crystal, and various additive elements may be unevenly distributed or inevitable impurities may be mixed. Instead of Nd ₂ Fe ₁₄ B, Nd ₂ Fe ₁₄ B compounds containing a plurality of rare earth elements, rare earth iron fluorine compounds, rare earth iron nitrogen compounds, LaSrCo ferrites, rare earth iron halides, FeCrCo alloys, AiNiCo alloys Etc. can be used.

In this example, Fe-30% Co particles are sintered with (Nd, Dy) ₂ Fe ₁₄ B powder mixed with about 20%, but all the magnetic properties of residual magnetic flux density, coercive force and energy product are sintered. The volume fraction of Fe-30% Co particles that can improve the characteristics is 0.1 to 80%. In particular, when the volume fraction of Fe-30% Co particles is 1 to 20%, it is possible to improve the magnetic properties by improving the mass production process of the conventional Nd ₂ Fe ₁₄ B-based sintered magnet.

Cobalt acetate tetrahydrate (Co (OCOCH ₃ )) ₂ · 4H ₂ O, iron chloride tetrahydrate (FeCl ₂ · 4H ₂ O), sodium hydroxide (NaOH) and polyvinylpyrrolidone are dissolved in ethylene glycol, Fe-Co-F-H-based particles are obtained by adding 5% ammonium fluoride, cooling to 170 ° C. and then cooling. The average grain size is 100 nm, and Fe—Co—F—H type grains having crystal magnetic anisotropy and shape magnetic anisotropy or stress-induced magnetic anisotropy by applying a magnetic field of 10 kOe during grain growth. An anisotropic magnet can be prepared by mixing with Nd ₂ Fe ₁₄ B powder having an average particle diameter of 2 μm, followed by temporary molding in a magnetic field, compression molding and sintering.

By applying a magnetic field during sintering and cooling, fluoride and oxyfluoride grow on the grain boundary, and lattice distortion due to cooling in the magnetic field is introduced into the FeCo-based crystal, and c / a (the lengths of c and a axes) ) Grows tetragonal crystals having a ratio of 1.001 to 1.20. When a phase having a lattice constant ratio or an axial ratio of tetragonal crystal of 1.1 to 1.2 grows, the coercive force is increased by increasing the magnetocrystalline anisotropy energy. Tetragonal crystals with an axial ratio exceeding 1.30 can also be formed, but structural instability increases, so it is necessary to contain a large amount of nonmagnetic elements, so the axial ratio should be 1.30 or less. 1.20 or less is desirable. FeCo crystal, Nd ₂ Fe ₁₄ B tetragonal crystal, FeCo crystal and fluoride cubic crystal part of the crystal grains are magnetically coupled to achieve both high saturation magnetic flux density and high residual magnetic flux density. And a residual magnetic flux density of 1.6 to 2.3 T and a coercive force of 10 to 40 kOe can be realized. In order to stabilize the tetragonal structure of the FeCo-based crystal, a transition element can be added to the FeCo-based crystal, and a magnet in which the tetragonal crystal is stable even at 400 ° C. can be provided. Applicable to all magnet application products including circuits.

The features of the magnet of this embodiment are as follows. 1) A crystal phase having an axial ratio larger than 1 such as a tetragonal crystal accompanied by lattice distortion grows. 2) A fluorine-containing compound or an oxyfluorine compound is formed at the grain boundary. 3) A ferromagnetic phase having a rare earth element concentration lower than the EDX detection concentration is formed. 4) A phase with an axial ratio greater than 1 and at least three types of crystal phases, an Fe-based cubic crystal and a fluorine-containing grain boundary phase, grow between the phase with an axial ratio greater than 1 and an Fe-based cubic crystal. Binding is allowed. 5) The formed magnet has crystal orientation and magnetic anisotropy, and the magnetic powder constituting it has magnetic anisotropy. 6) The average particle diameter of the FeCo-based crystal is 1000 nm or less and 5 nm or more. If these are satisfied, even if carbon, oxygen, hydrogen, and transition metal elements contained inevitably are detected, there is no significant effect. 7) An FeCo-based crystal grows through the Nd ₂ Fe ₁₄ B-based crystal and the fluorine-containing phase, and a rare earth element is detected in the fluorine-containing phase. In addition to the fluorine-containing phase, an oxide, nitride, carbide, or amorphous phase may grow on the grain boundary, and uneven distribution of transition elements may be observed near the grain boundary. 8) The grain boundary width of the fluorine-containing grain boundary is smaller than the average grain diameter of the FeCo-based crystal, and a plurality of FeCo-based crystals may be locally aggregated or bonded without a fluorine-containing grain boundary.

In addition, Fe-Co-Ni system, Fe-Co-Al system, Fe-Co-Mn system, Fe-Co-N system, Fe-Co-F system, Co-Cr system can be used as an alternative to FeCo system of similar materials. , Fe—Pt system, Co—Pt system and the like can be confirmed. Compounds containing rare earth elements such as Sm ₂ Fe ₁₇ N ₃ and Sm ₂ Co ₁₇ instead of Nd ₂ Fe ₁₄ B, AlNiCo alloys, MnAl alloys, MnBi alloys, MnAs alloys, FeCrCo alloys, ferrites, etc. Can be used. The reason why fluorine has higher magnetic properties than other material systems is derived from the high electronegativity (electron affinity) of fluorine atoms. When fluorine atoms are arranged in the vicinity of the interface between the grain boundary phase and the ferromagnetic phase, the distribution of the electronic state density of the surrounding iron atoms is changed, and anisotropy occurs in the state density of iron, which increases the magnetic anisotropy energy. .

  A magnet material having lattice strain as in this embodiment can control reversible changes in lattice strain by a magnetic field, heat, electromagnetic field, and the like. For example, by applying an electromagnetic field having a frequency that generates heat only in the fluorine-containing phase, heat is generated only in the vicinity of the grain boundary, lattice distortion is relaxed, and coercive force is reduced. When the application of the electromagnetic field is stopped, the lattice strain or the axial ratio of the crystal lattice is reversibly restored. When a magnet incorporated in a product is demagnetized and then re-magnetized, it can be easily subjected to magnetic flux or coercive force by applying stress and heat (including light irradiation) by magnetostrictive materials such as electromagnetic fields, pulsed magnetic fields, and FeGa alloys. Control is possible. Assuming that the change in magnetic flux is 1 after magnetization, it can be reversibly demagnetized to 0.1 to 0.5 and 50 to 90% when the strain is released. When the magnetized magnet is operated with a rotating machine that rotates at high speed, the loss due to the magnetic flux of the magnet cannot be ignored. In such a case, it is possible to weaken the magnetic flux of the magnet only during high-speed rotation and increase the residual magnetic flux density and energy product only when low-speed magnet torque is required.

The sintered magnet of this embodiment can be applied to various magnetic circuits. In a motor, a sintered magnet is inserted into a surface magnet motor, an embedded magnet motor, a flat motor, a spherical motor, etc. it can. It can also be applied to medical equipment and generators such as MRI, and can also be used as a VCM magnet for HDD. In these magnetic circuits, other magnetic materials such as Nd ₂ Fe ₁₄ B system, Sm ₂ Co ₁₇ system, AlNiCo system, Sm ₂ Fe ₁₇ N _x system, Sm ₂ Fe ₁₇ F _x system, MnAlC system, and MnBi system are available. It can be applied to the above-mentioned various magnetic circuits by designing a plurality of magnet arrangements and laminated magnets in combination with all conventional magnet materials that do not use a system crystal.

Fe-50% Co alloy nanoparticles are produced in an inert gas using high-frequency plasma, and a CeF-based film is deposited on the nanoparticle surface in the same apparatus. The average particle diameter of the nanoparticles is 10 nm and is spherical, ellipsoidal or flat. The CeF-based film has an average thickness of 0.5 nm. These particles are mixed with Ce ₂ Fe ₁₄ B, sintered in a magnetic field, and then sintered. The mixing ratio of Fe-50% Co alloy and Ce ₂ Fe ₁₄ B powder is 20: 1. After sintering at 1050 ° C., lattice strain is introduced into the Fe-50% Co crystal grains by the fluorine-containing phase at the grain boundaries by aging and quenching. Part of the Fe-50% Co crystal is tetragonal, and the axial ratio is 1.01 to 1.2. Some Fe-50% Co crystals in the vicinity of the grain boundaries are ordered phases, and the magnetocrystalline anisotropy energy increases.

  The magnetic characteristics of such a sintered magnet are that a part of the main phase is a tetragonal FeCo-based crystal, so that the residual magnetic flux density is larger than that of a conventional rare earth sintered magnet, and the tetragonal crystal is about 5 in the FeCo-based crystal. When the volume%, it becomes 1.5 to 2.1 T at 20 ° C. A fluorine-containing phase and a rare earth oxide phase are formed at the grain boundary, and a metastable grain boundary phase is grown by rapid cooling during heat treatment, and strain is introduced between the metastable grain boundary phase and the Fe-50% Co crystal. Such distortion deforms the lattice and improves the magnet characteristics. In order to realize an axial ratio of 1.01 to 1.2, when the grain boundary phase is a fluorine-containing phase, the average grain size of Fe-50% Co crystal grains needs to be 30 nm or less. The change of the Fe-50% Co crystal to a crystal having a lattice distortion such as a tetragonal crystal requires deformation of a cubic lattice, and the tetragonal crystal grows near a crystal grain or the surface of the particle. Since tetragonal crystals are grown by generating stress or strain on the surface of such crystal grains and grains, the structure of the cubic crystals on the outer peripheral side of the cubic crystals at the center is deformed. Therefore, it is difficult to increase the phase volume having a structure having a deformed lattice unless the particle size has a large surface area such as nanoparticles, and the average particle size needs to be 100 nm or less, preferably 30 nm or less. . Since the cubic crystal at the center of the grain is stable, the lattice strain determines whether or not the deformed lattice on the outer peripheral side can grow in a metastable state by the energy balance between the cubic crystal at the center of the particle and the deformed lattice on the outer peripheral side. If the volume of the cubic crystal, that is, the particle diameter is large, the deformation on the outer peripheral side is difficult to grow because the effect of the stable cubic crystal is strong even when trying to deform.

A sintered magnet having a high residual magnetic flux density is composed of cubic FeCo-based crystal grains having a tetragonal structure or lattice distortion, a fluorine-containing grain boundary phase, and a rare earth-containing phase capable of forming a fluorine-containing grain boundary phase in a sintering process. Mainly configured, the fluorine-containing grain boundary phase is a metastable phase, and there is distortion between the FeCo-based crystal grains and the fluorine-containing crystals, and the fluorine-containing grain boundary phase is more than the rare earth oxide grain boundary phase. Large volume ratio. The crystal grains surrounded by the fluorine-containing grain boundary phase are FeCo-based crystals, and the coverage is 50% or more. The fluorine concentration of the fluorine-containing grain boundary phase between Ce ₂ Fe ₁₄ B crystal grains is lower than the fluorine concentration of the fluorine-containing phase formed at the grain interface of the FeCo-based crystal. The fluorine-containing phase in contact with the FeCo crystal grains may be antiferromagnetic, ferrimagnetic, ferromagnetic, or paramagnetic. An antiferromagnetic material such as Mn, FeO, CoO, NiO, FeF ₂ , MnF ₂ , Cr, or Fe ₂ O ₃ , a perovskite compound, or a NiAs type compound may be mixed in the fluorine-containing compound. If the FeCo-based crystal is a regular phase, the coercive force can be further increased, and a tetragonal regular phase can be formed by setting the aging temperature to a temperature just below the regular-disorder transformation point. is there.

  The sintered magnet of this example is composed of at least three types of phases represented by the following equations.

_{Fe x Co y M z + T} a F b O c + RE u Fe v B w (1)
Here, Fe is iron, Co is cobalt, M is a transition element other than iron and cobalt, T is a transition element, F is a halogen element such as fluorine, O is oxygen, RE is a rare earth element, B is a metalloid or halogen element, x, y, z, a, b, c, u, v, and w are positive numbers, satisfy x + y> z ≧ 0, u + v> w ≧ 0, and the volume fraction of the first phase is the volume of the second phase. Greater than rate. The first phase of Fe _x Co _y M _z is the most high saturation magnetic flux density phase the value is not less than 1.7 T, or is covered by a T _a F _b O _c of the second phase, the first phase A second phase is formed between the third phase, a cubic crystal is formed in a part of each of the first phase and the second phase, and a part of the cubic crystal is a regular phase. A specific orientation relationship is recognized in the crystal orientation between the two phases or between the first phase and the third phase, and the first phase crystal has a lattice strain. The lattice distortion can be confirmed by electron diffraction, and a strain of 0.01 to 10% is recognized on the outer periphery of the crystal grain. There is a magnetic coupling between the first phase and the third phase. That is, the demagnetization curve can be measured as a curve of one magnet, and no demagnetization part corresponding to the low coercivity part of the soft magnetic component is recognized. In particular, cubic crystals and tetragonal crystals are distorted, M elements are unevenly distributed in the distorted crystals, and the volume of the distorted phase is larger than the volume of the second phase, which leads to improved magnetic properties. Such a strain appears near the interface between the first phase and the second phase or near the interface between the first phase and the third phase. Here, the vicinity of the interface refers to a distance within 20 nm from the interface. When the Fe _x Co _y M _z lattice strain is less than 0.01%, the magnetocrystalline anisotropy energy does not become maximum. Some elements of the first-phase M or third-phase RE elements are unevenly distributed in the vicinity of the grain boundaries, contributing to improved lattice strain stability, increased magnetocrystalline anisotropy energy, and improved interface stability. Therefore, the lattice strain of the first phase in the vicinity of the grain boundary where the uneven distribution of the RE element is recognized is larger than the lattice strain in the vicinity of the grain boundary where the uneven distribution is small.

  The concentration of the rare earth element in the entire sintered magnet is 0.1 to 5 atomic%, which is not only lower than the conventional rare earth sintered magnet but also lower in raw material cost, and can secure resource security because the rare earth element concentration is low. If the volume fraction is smaller than the volume fraction of the second phase, even if oxide, fluoride, carbide, nitride, boride, etc. are contained in addition to the above three phases, equivalent magnetic properties can be obtained. . Inevitable mixing of oxygen, hydrogen, nitrogen, carbon, phosphorus, copper, etc. is not a problem as long as the concentration is less than the concentration of halogen elements such as fluorine in the second phase. The sintered magnet composed of at least three phases can confirm an energy product of 100 MGOe at the maximum.

  A sintered magnet of 60 to 100 MGOe at 20 ° C. with an energy product lower than this maximum value is mainly composed of three phases, and a Fe-based high saturation magnetic flux density material having a saturation magnetic flux density of 1.6 T or more in the first phase. The second phase is a fluorine-containing phase, the third phase is a rare earth-containing iron compound, and the first phase or a part of the second phase is a cubic regular lattice and is between the first phase and the second phase or between the first phase and the third phase. There is a crystal orientation relationship at a part of the interface between the phases, lattice distortion occurs near the interface, and the fluorine concentration near the grain interface of the first phase is the grain boundary near the two-grain boundary between the third phase. This is achieved by the fact that a part of the rare earth element is unevenly distributed near the grain boundary of the third phase and the first phase and the third phase are magnetically coupled.

Cobalt acetate tetrahydrate (Co (OCOCH ₃ )) ₂ · 4H ₂ O, iron chloride tetrahydrate (FeCl ₂ · 4H ₂ O), sodium hydroxide (NaOH) and polyvinylpyrrolidone are dissolved in ethylene glycol, The TbF-based gel is reacted with a 1% ammonium fluoride additive solution dissolved in an alcohol solution in a magnetic field of 10 kOe to prepare a solution in which cubic FeCo-based nanoparticles covered with a TbF-based film are dispersed in alcohol. The average size of the FeCo-based nanoparticles is 15 × 14.8 × 15.1 nm ³ , and the average thickness of the TbF-based film is 0.2 to 1 nm. This solution was applied to the surface of the Nd ₂ Fe ₁₄ B magnetic powder at 15 wt%, then subjected to temporary forming in a magnetic field, sintered in a magnetic field at 1010 ° C., and then subjected to aging treatment in a magnetic field to obtain a Nd ₂ Fe ₁₄ B sintered body.

In the Nd ₂ Fe ₁₄ B sintered body, an FeCo-based crystal covered with a fluorine-containing phase is formed, and the uneven distribution of Tb can be confirmed in the vicinity of the Nd ₂ Fe ₁₄ B-based grain boundary, and Nd ₂ Fe ₁₄ B A fluorine-containing grain boundary phase is observed between the system crystal grains and the FeCo crystal. The fluorine-containing grain boundary NdOF, (Nd, Tb) OF , (Nd, Tb, Fe) OF, (Nd, Tb, Fe) (O, C) F, such as _{NdF 2, NdF 3, TbF 2} , TbF 3 And Tb and Nd in the Nd ₂ Fe ₁₄ B-based crystal undergo a composition change due to mutual diffusion.

As a result, it was confirmed that Tb was unevenly distributed along the grain boundary in the vicinity of the grain boundary where the Nd ₂ Fe ₁₄ B-based crystal was adjacent to the fluorine-containing phase. A part of the oxyfluoride has a cubic structure due to the aging and quenching treatment in the magnetic field after sintering, and has a specific crystal orientation relationship with the adjacent FeCo-based crystal grains, and lattice strain is recognized at the interface. The FeCo-based crystal in the sintered body has a plane (00n) perpendicular to the magnetic field direction, and the bct crystal has its c-axis direction being the magnetic field application direction and substantially parallel to the c-axis of the Nd ₂ Fe ₁₄ B-based crystal. Become. When the easy magnetization direction of the FeCo-based crystal and the easy magnetization axis direction of the Nd ₂ Fe ₁₄ B-based crystal are substantially parallel, the FeCo-based crystal magnetic anisotropy increases, and the Nd ₂ Fe ₁₄ B-based crystal and the FeCo-based crystal Since the magnetic coupling with the crystal becomes stronger, any of the effects of improving the squareness of the demagnetization curve, increasing the saturation magnetization, increasing the energy product, increasing the Curie temperature, improving the magnetization, and reducing the thermal demagnetization can be confirmed.

  The sintered magnet of this example has an energy product of 70 MGOe, which exceeds the theoretical value of the NdFeB-based sintered magnet. The composition of the entire sintered magnet was Nd 10 at%, Co 7.6 at%, Tb 0.2 at%, B 4.7 at%, Fe 77.0 at%, and F 0.5 at%. Increasing the volume fraction of the FeCo-based crystal results in a larger energy product, and the composition ranges exceeding the theoretical values of the NdFeB-based sintered magnet are Nd 1-11 at%, Co 0.01-15 at%, Tb 0.01-2 at%, B2 to 5.2 at%, Fe60 to 79.0 at%, and F 0.001 to 5 at%. Here, some or all of Nd and Tb may be replaced with other rare earth elements.

  Impurities that are inevitably mixed and trace unevenly distributed elements may be contained separately from the above composition. By introducing lattice strain into the FeCo-based crystal and increasing the magnetocrystalline anisotropy, the amount of rare earth element used can be further reduced from the above composition range. In a process of heat treatment in a temperature range (588 K to 1350 K) higher than the Curie point of the FeCo-based crystal at a temperature higher than the Curie point of the NdFeB-based compound, such as sintering or aging heat treatment, by applying a magnetic field of 1-100 kOe, Lattice distortion can be introduced into the FeCo-based crystal by adding isotropic properties to the FeCo-based crystal particles. The amount of lattice distortion is 0.1 to 25%. FeCo-based magnetocrystalline anisotropy energy increases due to such lattice deformation and lattice strain introduction, and rare earth elements are used as the liquid phase in the liquid phase sintering method, and the amount of rare earth elements used can be reduced to 1 at% or less. It becomes possible.

A discontinuous film of Fe ₆₀ Co ₄₀ was formed on a MgO (001) single crystal substrate by a sputtering method. Crystal grains having an average grain size of 10 nm grow on the discontinuous film. During sputtering, a magnetic field of 10 kOe is applied to the substrate surface to add induced magnetic anisotropy. After removing the crystal grains by the lift-off method, an NdF-based thin film is formed on the crystal grain surface by NdF solution treatment. The average film thickness of the NdF-based thin film is 0.1 nm. A uniaxially anisotropic shaped magnet is obtained by pre-molding this in a magnetic field and then heat-molding in a magnetic field. Fe ₆₀ Co ₄₀ crystal lattice grain boundaries NdOF and NdF _3, NdF ₂ grows, the crystal in order to grow the Fe ₆₀ Co ₄₀ part of fluoride in a specific orientation relationship to the crystal of Fe ₆₀ Co ₄₀ The lattice is deformed, and tetragonal and orthorhombic crystals grow. Regarding the orientation relationship, the plane index (abc) of Fe ₆₀ Co ₄₀ // the plane index (hkl) of NdOF, and a, b, c, h, k, and l are shown as positive numbers. The ratio of tetragonal a-axis to c-axis was 1.01 to 1.25. The c-axis direction was almost parallel to the magnetic field direction during heat forming. Such a magnetic material has increased magnetocrystalline anisotropy due to lattice distortion, and a magnet having an energy product of 110 MGOe was obtained. Although the lattice strain is easily released near the Curie temperature, it can be added again by quenching in the magnetic field from near the Curie temperature. Such a magnet having an energy product of 100 MGOe needs to satisfy the following conditions. 1) The rare earth element concentration is 0.1 to 5 at%. 2) A fluorine-containing phase is formed at the grain boundary, and there is a specific orientation relationship with the FeCo-based crystal, and the FeCo-based crystal has an axial ratio of 1.01 to 1.25. The axial ratio should be large near the grain boundary and small within the grain. In addition, FeCo-based crystal lattices with different axial ratios in a single particle must be consistent, and matching strain should be observed in the crystal lattice. 3) The volume of the FeCo-based crystal is 90 to 99%, and the size of the crystal grains is an average of 100 nm or less and 5 nm or more. It can be confirmed by structural analysis such as electron diffraction and neutron diffraction that the lattice of the FeCo-based crystal is distorted. 4) Uniaxial magnetic anisotropy is added by the magnetic field application step after molding. 5) The width of the fluorine-containing phase grown on the grain boundary is 0.1 to 5 nm on average. FeCo-based crystals can contain various transition elements, part of which also diffuses into the fluorine-containing phase and is unevenly distributed in the vicinity of some grain boundaries. Even if the inevitable impurities such as hydrogen, oxygen, carbon, nitrogen, phosphorus, sulfur, chlorine, boron, copper, gallium, nickel, and aluminum are contained, if the above conditions do not change greatly, the sintering with equivalent magnetic properties A magnetized magnet is obtained.

A magnetic powder for sintering of (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B is inserted into a nonmagnetic mold to prepare a temporary molded body having a density after magnetic field orientation of 40 to 70%. The average particle size of the magnetic powder is 2 to 7 μm. The orientation condition in the magnetic field is a load of 1 t / cm ² with a magnetic field of 10 kOe. This process proceeded in an inert gas atmosphere to prevent oxidation. Without removing the temporary molded body from the mold, a mixed solution of fluoride solution containing dispersed FeCo-based crystal nanoparticles is poured into the gaps of the temporary molded body. The composition of the FeCo-based crystal is Fe 60% -Co 40%, and the average particle size of the nanoparticles is 5 nm. After injecting the mixed solution into a gap inside the temporary molded body or a crack portion of the magnetic powder, a magnetic field of 20 kOe is applied to the temporary molded body to orient the nanoparticles and (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B powder. The temporary molded body is inserted into a sintering furnace without being exposed to the atmosphere, and sintered in a magnetic field. The sintering temperature is 1050 ° C. Next, the structure and composition in the vicinity of the FeCo crystal were controlled by aging treatment in a magnetic field to obtain a sintered body.

When the amount of FeCo-based crystal nanoparticles added is 10% by volume with respect to the entire sintered magnet, the easy magnetization direction of the FeCo-based crystal and the easy magnetization direction of (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B are perpendicular or parallel, or As a result of making three types when there is no directional relationship and evaluating the characteristics, the easy magnetization direction of FeCo-based crystal and the easy magnetization direction of (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B are parallel on average The result with the highest energy product was obtained, and in each case, 50 MGOe, which was a higher energy product than the (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B sintered magnet, could be realized. The effect of the high energy product by adding FeCo-based nanoparticles is that the Fe concentration is 0.1 to 90% in the FeCo-based crystal, the average particle size of the FeCo-based crystal is 1 to 200 nm, and the added amount to the sintered magnet is 0.1. It was confirmed at ˜50%.

  If the Co concentration is less than 0.1%, the magnetization of the FeCo-based nanoparticles decreases due to carbon, oxygen, etc. in the solution, so that the energy product is difficult to increase. When the Co concentration is 90% or more, a crystal with a small saturation magnetization having a crystal structure other than the bcc or bct structure is likely to grow and the magnetization is difficult to increase. When the average particle diameter is less than 1 nm, the saturation magnetization of the FeCo crystal coated with fluoride is small, and the energy product is difficult to increase. When the average particle diameter exceeds 200 nm, it becomes difficult to inject into the gaps and cracks in the temporary molded body as in this example, and the particle size needs to be small. Even under conditions where the density of the temporary molded body is reduced, the amount of nanoparticles added is 50% at the maximum, and if it exceeds 50%, it is difficult to inject the nanoparticles to the center of the temporary molded body. If the addition amount is less than 0.1%, the effect of increasing the coercive force due to the effect of adding nanoparticles can be confirmed, but the effect of increasing the energy product has not been confirmed. The injection process of the nanoparticle-containing solution into the temporary molded body is a sintered magnet with an increased energy product even if the temporary molded body is a mixture of FeCo-based crystal nanoparticles and NdFeB-based powder previously coated with fluoride. Can be obtained.

The energy product was 120 MGOe when 50% Fe65% Co35% nanoparticles with an average particle size of 10 nm were added to Nd ₂ Fe ₁₄ B powder and a TbF-based solution was used. Such a high energy product sintered magnet has the following characteristics. 1) Tb is unevenly distributed in the vicinity of the grain boundary of the Nd ₂ Fe ₁₄ B-based crystal, and a part of the grain boundary is a cubic oxyfluoride. 2) FeCo-based crystals are formed so as to be covered with oxyfluoride grain boundaries, and oxyfluoride grows between the FeCo-based crystals and the Nd ₂ Fe ₁₄ B-based crystals, and the average oxygen concentration in the FeCo-based crystals Is 100 ppm or less. 3) A part of the FeCo-based crystal has (001) or (110) parallel to the c-axis direction of the Nd ₂ Fe ₁₄ B-based crystal. 4) Lattice distortion is observed in the vicinity of some grain boundaries of the FeCo-based crystal grains. 5) The average crystal grain size of the FeCo-based crystal is 200 nm or less and 1 nm or more. 6) In addition to heavy rare earth elements, uneven distribution of transition elements such as Cu and Zr is recognized at the grain boundaries.

Fe ₇₀ Co ₃₀ alloy nanoparticles are prepared by a high-frequency plasma method. By controlling the plasma conditions, nanoparticles of Fe ₇₀ Co ₃₀ alloy having an average of 35 nm are prepared. An average of 1 nm of TbF film is applied to the surface of the nanoparticles by solution treatment. After the solution treatment, the solution is heated to 1100 ° C. to diffuse and absorb impurities in the FeCo crystal. By this heat treatment, a part of the fluoride becomes an oxyfluoride or a carbon-containing fluoride, and the melting point of the fluoride rises. The fluoride-treated FeCo-based crystal nanoparticles are crushed, mixed with (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B powder, and inserted into a mold. The mixing ratio is 10% for FeCo-based nanoparticles and ₉₀ % for (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B powder. After applying a magnetic field of 10 kOe with a mold and preparing a temporary molded body with a load of 1 t / cm ² , sintering is performed at 1050 ° C. After sintering, an aging treatment was performed at 500 ° C. in a magnetic field of 10 kOe, followed by rapid cooling to obtain a sintered body. As a result of evaluating the magnetic properties after magnetizing the sintered body, the energy product increased by about 20% compared to the case of (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B powder alone.

The conditions necessary to increase the energy product are as follows. 1) Tb is unevenly distributed near the grain boundary of the (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B crystal grains. 2) A fluorine-containing phase is formed at the grain boundary of the FeCo-based nanoparticle, and Tb diffuses from the fluorine-containing phase into the (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B crystal. 3) Interdiffusion in which Tb of fluoride and Nd of (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B crystal are exchanged proceeds. 4) FeCo-based crystal grains are smaller than (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B crystal grains. 5) FeCo-based nanoparticles are partially agglomerated, but the average particle size is less variable before and after sintering. In this embodiment, the average particle size after sintering is 0.5 to 2 times that before sintering. 6) The concentration of Tb and fluorine tends to be high near the FeCo grain boundary and low at the (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B two-particle interface. 7) The crystal structure of the oxyfluoride is mainly cubic, and part of it is compatible with (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B crystal and FeCo crystal. 8) The Co concentration of the FeCo-based crystal is in the range of 0.1 to 90%. 9) Magnetic coupling is acting between the FeCo-based crystal and (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B. For this reason, the demagnetization curve after magnetization shows a curve like one magnet. 10) The Curie temperature that is the magnetization disappearance temperature of the sintered body is higher than the Curie temperature of (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B. 11) The saturation magnetization of the fluoride-coated FeCo powder mixed with the (Nd ₉₀ Dy ₁₀ ) ₂ Fe ₁₄ B powder is 200 to 250 emu / g.

  In the present invention, fluoride plays an important role, and prevents FeCo-based nanoparticles from being lost by diffusion or reaction during sintering, protects FeCo-based nanoparticles from oxidation, etc., FeCo-based The removal of impurities in the nanoparticles increases the magnetization, the heavy rare earth elements in the fluoride coated on the surface of the FeCo nanoparticles are diffusely distributed in the NdFeB crystals, and in the vicinity of the FeCo nanoparticles. Increasing the coercive force by increasing the anisotropy energy of NdFeB-based crystal grains, making the magnetization of FeCo-based nanoparticles difficult to reverse due to this increase in coercive force, and some oxyfluorides and fluorides Increases the FeCo-based magnetocrystalline anisotropy energy by forming a coherent interface with the FeCo-based nanoparticles and distorting the lattice, and NdFeB-based crystal grains and Fe That it is appropriately separated magnetic domains of the magnetic domain and the FeCo crystal NdFeB-based crystal by fluoride between the o based crystal grains grow. These have led to an increase in the energy product of the sintered magnet.

  By using the effects of the above-described fluoride-coated FeCo-based crystal nanoparticles, a sintered magnet satisfying all of an increase in energy product, an increase in coercive force, an increase in Curie point, and a decrease in the amount of rare earth elements used can be obtained. The present invention can be applied to all magnets composed of at least one material system among SmCo, MnAl, and MnBi. In addition, the coating solution in which FeCo-based nanoparticles are slurried can be applied and diffused in the bond magnet powder to increase the energy product or improve the heat resistance.

  FeCo-based crystal nanoparticles can confirm the above-mentioned effect of improving magnetic properties in both the regular phase and the disordered phase, but the FeCo-based crystal magnetic anisotropy is in the regular phase and the lattice strain is in the range of 0.1 to 25%. Since energy increases, NdFeB-based crystals are not always necessary. That is, a magnet material can be created only with FeCo-based crystals by using a fluoride heat treatment.

The FeCo-based crystal used in this example has an oxygen or carbon concentration of 50 ppm or less by heat treatment after fluoride application, and lattice strain is introduced near the interface with the fluoride layer. Magnetostrictive material in which fluoride is multilayered, Fe, Co or additive element concentration gradient is formed in FeCo crystal grains, and the additive and magnetostriction constant absolute value for increasing lattice strain is larger than 2 × 10 ⁻⁶ It is possible to obtain a magnet having an energy product of 50 to 150 MGOe of FeCo-based crystal as a main phase by introducing a lattice strain of 10 to 25% by the formation of.

1 Nanoparticle 2 Rare earth-containing compound 3 Fluorine-containing phase

Claims (9)

In a sintered magnet in which a fluorine-containing phase is formed as a grain boundary phase between an FeCo-based crystal and an NdFeB-based crystal,
The Co concentration of the FeCo-based crystal is 0.1 to 90 atomic%;
The FeCo-based crystal has a cubic structure or a tetragonal structure, and is a sintered magnet. The sintered magnet according to claim 1, wherein
The sintered magnet, wherein the fluorine-containing phase has a cubic structure. The sintered magnet according to claim 1 or 2,
A sintered magnet characterized in that heavy rare earth elements are unevenly distributed in the vicinity of a grain boundary of the NdFeB-based crystal. In the sintered magnet according to any one of claims 1 to 3,
The sintered magnet according to claim 1, wherein an average crystal grain size of the FeCo-based crystal is smaller than an average crystal grain size of the NdFeB-based crystal. In the sintered magnet according to any one of claims 1 to 4,
A sintered magnet, wherein a fluorine concentration at a grain boundary near the FeCo-based crystal is higher than a fluorine concentration at a grain boundary formed between the NdFeB-based crystals. In the sintered magnet according to any one of claims 1 to 5,
A sintered magnet having a Curie point of 850 to 1230K. The sintered magnet according to any one of claims 1 to 6,
A sintered magnet characterized in that the magnetization at a temperature 50K higher than the Curie point of the NdFeB-based crystal is 0.1 emu / g to 150 emu / g. In the sintered magnet according to any one of claims 1 to 7,
The ratio of the FeCo-based crystal to the entire sintered magnet is in the range of 0.1% to 90% by weight. The sintered magnet according to any one of claims 1 to 8,
A sintered magnet, wherein the saturation magnetization of the FeCo-based crystal is higher than the saturation magnetization of the NdFeB-based crystal.

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