JP2014194958A - Sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintered magnet that satisfies reduction of rare earth elements that are rare resources and increase of coercive force and a maximum energy product.SOLUTION: An Fe-based powder of high saturation magnetic flux density is mixed with a NdFeB-based magnetic powder. The Fe-based powder has shape anisotropy and a surface of which is coated with a fluoride containing heavy rare earth element by a solution treatment. An average particle diameter of the Fe-based powder is larger than an average particle diameter of the NdFeB-based magnetic powder.

Description

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

Patent Documents 1 to 4 describe a permanent magnet using an Fe-based high saturation magnetic flux density material and an NdFeB-based powder, and Patent Document 1 describes that the crystal grain size of the αFe phase and the Nd ₂ Fe ₁₄ B phase is 5 to 5. There is a description of a high performance rare earth permanent magnet alloy of 100 nm. Patent Document 2 discloses a technique in which R-Fe-B anisotropic alloy powder and soft magnetic metal powder are mixed and then densified. Patent Document 3 discloses that iron is contained in a fluorine compound. Further, Patent Document 4 describes a permanent magnet having a coercive force of 0.5 to 5 kOe in which a concentration distribution is recognized in a rare earth element at a grain boundary portion surrounding the main phase crystal grains. Patent Document 5 describes a cubic structure oxyfluoride and tetragonal Nd ₂ Fe ₁₄ B, and Patent Document 6 describes a structure composed of an R ₂ Fe ₁₄ B phase, an M-rich phase, and an R oxide phase. An anisotropic rare earth sintered magnet is disclosed, and Patent Document 7 discloses a sintered sample composed of Nd ₂ Fe ₁₄ B tetragonal crystal and Nd ₂ O ₃ cubic crystal, and Patent Document 8 describes an FeCo alloy. There is a description of a rare earth sintered magnet excellent in magnetism obtained by mixing and sintering coarse powder and alloy fine powder for rare earth sintering.

  Furthermore, in the NdFeB-based magnet, the method of unevenly distributing heavy rare earth elements does not reduce the amount of rare earth elements used. Further, when mixed and sintered with soft magnetic powder, the coercive force is reduced, and the heat resistance or demagnetization resistance of the magnet is significantly reduced.

JP 2001-323343 A JP 2009-260290 A JP 2008-60183 A JP 2010-74084 A JP 2010-267637 A JP 2002-25810 A Japanese Patent Laid-Open No. 2001-319806 JP 2003-217918 A

Permanent magnets using rare earth elements such as rare earth iron boron, represented by Nd ₂ Fe ₁₄ B based sintered magnets, are used in various magnetic circuits. Addition of heavy rare earth elements is essential for permanent magnets used in high temperature or large demagnetizing field environments. Reducing the amount of rare earth elements including heavy rare earth elements is an extremely important issue from the viewpoint of protecting earth resources. In the prior art, when the amount of rare earth elements used is reduced, either the maximum energy product or the coercive force is lowered, and it has been difficult to apply. The challenge is to satisfy the reduction in the amount of rare earth elements used, the increase in coercive force, and the increase in maximum energy product.

  In order to solve the above problems, an Fe-based powder having a high saturation magnetic flux density is mixed with an NdFeB-based magnetic powder. This Fe-based powder has shape anisotropy, and its surface is coated with a solution containing a heavy rare earth element by solution treatment. At this time, it is important that the average particle diameter of the Fe-based powder is larger than the average particle diameter of the NdFeB-based magnetic powder.

  According to the present invention, it is possible to satisfy rare earth element usage reduction, coercive force increase and maximum energy product increase of rare earth permanent magnets, reducing magnet usage and contributing to reduction in size and weight of various magnet application products. To do.

Relationship between residual magnetic flux density (Br) and coercive force (Hc) and average grain size ratio (FeCo alloy system / NdFeB system). Relationship between Hk / Hc and average crystal grain size ratio (FeCo alloy system / NdFeB system). Relationship between oxyfluoride volume and average crystal grain size ratio (FeCo alloy system / NdFeB system). The organization chart of a sintered magnet.

  In manufacturing the sintered magnet according to the present invention, Fe-based powder having a high saturation magnetic flux density is mixed with NdFeB-based magnetic powder. This Fe-based powder has shape anisotropy, and its surface is coated with a solution containing a heavy rare earth element by solution treatment. At this time, it is important that the average particle diameter of the Fe-based powder is larger than the average particle diameter of the NdFeB-based magnetic powder.

  Fe-based powders generally have a smaller coercive force than NdFeB-based magnetic powders, so magnetization reversal is easy. When Fe-based magnetic powders and NdFeB-based magnetic powders are mixed and sintered, the composition and structure near the grain boundaries of NdFeB-based crystals are adjacent at the interface between them. Due to the influence of the Fe-based crystals, the rare earth-rich phase is hardly formed due to diffusion during the sintering process. Since the composition and structure of the rare earth-rich phase affects the coercive force, heavy rare earth elements are unevenly distributed at the grain boundaries near the Fe-based particles, thereby increasing the coercive force.

By making the average grain size of the Fe-based crystal having high saturation magnetization larger than the average grain size of Nd ₂ Fe ₁₄ B, aggregation of crystal grains of the Fe-based alloy is prevented, and the additive volume of the sintering aid is set to 10 %. When the average particle diameter of the Fe-based alloy is larger than the average particle size of the Nd ₂ Fe ₁₄ B, Fe-based intermetallic alloy field between Nd ₂ Fe ₁₄ B than the area and Fe-based alloy and Nd between ₂ Fe ₁₄ B The sum of the interfacial areas is larger and the magnetization reversal is less likely.

In the present invention, an Fe-based alloy having a saturation magnetization higher than that of Nd ₂ Fe ₁₄ B is an alloy having a saturation magnetization of 170 emu / g, such as an FeCo-based alloy. In addition, rare earth elements, metalloid elements, and various metal elements may be contained. Since the saturation magnetization is higher than Nd ₂ Fe ₁₄ B, it is possible to increase the residual magnetic flux density by crystal grains and magnetically coupling Nd ₂ Fe ₁₄ B. The crystal grains of the Fe-based alloy and the crystal grains of Nd ₂ Fe ₁₄ B are adjacent to the heavy rare earth element uneven distribution phase through the grain boundary. This heavy rare earth unevenly distributed phase contains fluorine and oxygen.

The sintering aid also increases the amount of liquid phase at the sintering temperature, improves the wettability between the liquid phase and Fe-based alloy crystal grains and Nd ₂ Fe ₁₄ B crystal grains, and the density after sintering. Used to raise the Since the fluorine-containing phase easily reacts with a phase having a high rare earth element concentration, the amount of the liquid phase is reduced. For this reason, the density after sintering falls and the coercive force also falls. In order to suppress such a decrease in density and coercive force, Fe-70% Nd alloy powder or the like is added as a sintering aid.

Further, by applying a magnetic field perpendicular to the forming magnetic field during sintering, a magnetic field application effect can be realized in a temperature range in which only the Fe-based alloy has magnetization, and magnetic anisotropy is added to the Fe-based crystal. In addition, by applying a magnetic field in a direction parallel to the forming magnetic field during the aging and quenching treatment, it is possible to increase exchange coupling between the Fe-based alloy crystal grains and the Nd ₂ Fe ₁₄ B crystal grains. Contributes to increase and squareness improvement.

  As a manufacturing method, fluoride solution treatment is used to make the heavy rare earth elements unevenly distributed. Since the solution used for the fluoride solution treatment contains an anion component of the order of 100 ppm or less, a part of the surface of the material to be treated is corroded or oxidized in the treatment to a material containing a large amount of rare earth elements. In the present invention, the sintered magnet uses at least two kinds of ferromagnetic alloys of NdFeB alloy and Fe alloy, and the material subjected to the fluoride solution treatment is an alloy having a low rare earth element content. Prevent oxidation. Alloys with a low rare earth element content generally have a low coercive force, so uneven distribution of rare earth elements, especially heavy rare earth elements, in the vicinity of alloys with a low rare earth element content contributes to an increase in coercive force and a reduction in the amount of rare earth elements used. To do.

After 70% Fe30% Co alloy is melted in vacuum, molten metal reduced and melted in an Ar + 10% H ₂ gas atmosphere and melted on the surface of the copper rotating roll is injected, and the cooling rate is about 100 ° C./second to 500 ° C./second. After cooling, it was pulverized in an inert gas to obtain a flat 70% Fe30% Co alloy powder. The shape of the 70% Fe30% Co alloy powder is a flat powder and is a shape extending in a ribbon shape. The particle size of the 70% Fe30% Co alloy powder can be controlled depending on the jet mill pulverization time, and the average particle size in the long axis direction extending flatly in the range of 0.1 to 1000 μm can be controlled. In order to coat fluoride on the surface of 70% Fe 30% Co alloy powder, a TbF-based alcohol solution and 70% Fe 30% Co alloy powder are mixed, and the alcohol is evaporated to thereby convert the TbF-based film into 70% Fe 30% Co alloy powder. Create on the surface. 70% Fe 30% Co alloy powder and Nd ₂ Fe ₁₄ B powder coated with a TbF-based film having an average film thickness of 2 nm are mixed at a mixing ratio of 70% Fe 30% Co alloy powder 2: Nd ₂ Fe ₁₄ B powder 8. The average particle size of the Nd ₂ Fe ₁₄ B powder is 4 μm. About 1% of Fe-70% Nd alloy powder having an average particle size smaller than the average particle size of Nd ₂ Fe ₁₄ B powder was added to the mixed powder as a sintering aid to improve the sinterability. The flat 70% Fe30% Co alloy powder formed by forming in a magnetic field (10 kOe) is almost aligned with the magnetic field application direction in the major axis direction and sintered at 1100 ° C., and the magnetic field (10 kOe) is perpendicular to the forming magnetic field during liquid phase formation. Applied in the direction. The aging heat treatment after sintering was set to a temperature higher than the Curie point of Nd ₂ Fe ₁₄ B at 400 to 700 ° C., and a magnetic field (20 kOe) was applied in the same direction as the magnetic field direction of molding in the magnetic field. The rapid cooling rate in the aging heat treatment is 10 to 100 ° C./second.

When the average particle size of 70% Fe30% Co alloy powder is 10 μm, the compact after sintering in the magnetic field and after aging treatment in the magnetic field has a residual magnetic flux density (Br) of 1.66 T (16.6 kG). The magnetic force was 17.5 kOe. The value of Br exceeds 1.61 T which is the theoretical value of Nd ₂ Fe ₁₄ B, and the 70% Fe 30% Co alloy powder does not contain rare earth elements, so the amount of rare earth elements used can be reduced. In order to obtain a value of Br exceeding the theoretical value of Nd ₂ Fe ₁₄ B, the following conditions are required as in this embodiment.

[1] Use an Fe-based alloy having a saturation magnetization higher than that of Nd ₂ Fe ₁₄ B.
[2] An alloy that does not contain a rare earth element, such as an Fe-based alloy, does not form a liquid phase below the sintering temperature, so a sintering aid should be added.
[3] Applying a magnetic field perpendicular to the forming magnetic field during sintering.
[4] Applying a magnetic field in a direction parallel to the forming magnetic field during the aging and quenching treatment.
[5] The average particle size of the Fe-based alloy having high saturation magnetization is larger than the average particle size of Nd ₂ Fe ₁₄ B.

The conditions [1] to [5] will be described in detail below.
Condition [1]: An Fe-based alloy having a saturation magnetization higher than that of Nd ₂ Fe ₁₄ B is an alloy having a saturation magnetization of 170 emu / g, such as an FeCo-based alloy. And may contain rare earth elements, metalloid elements, and various metal elements. Since the saturation magnetization is higher than Nd ₂ Fe ₁₄ B, it is possible to increase the residual flux density by crystal grains and magnetically coupling Nd ₂ Fe ₁₄ B. The crystal grains of the Fe-based alloy and the crystal grains of Nd ₂ Fe ₁₄ B are in direct contact with each other or are adjacent to each other through a fluorine or oxygen-containing phase. The TbF-based film as in this example suppresses the reaction between the Fe-based alloy crystal grains and the Nd ₂ Fe ₁₄ B crystal grains during sintering, thereby preventing a decrease in coercive force. An Fe-based alloy having an unstable structure during sintering is difficult to use even if the saturation magnetization is 170 emu / g or more. Pure stable phases such as Fe ₁₆ N ₂ and Fe ₈ N are easily decomposed at a sintering temperature of 900 ° C. and cannot be used. The ordered or disordered FeCo alloy has a saturation magnetization of 220 to 240 emu / g, which is higher than 167 emu / g of the Nd ₂ Fe ₁₄ B system, so that the magnetic characteristics can be improved by magnetic coupling. An Fe-based alloy having a saturation magnetization of less than 170 emu / g cannot be expected to improve the residual magnetic flux density of the magnet performance because it is equal to or less than the saturation magnetization of the Nd ₂ Fe ₁₄ B system.

Condition [2]: The sintering aid increases the wettability between the liquid phase and the Fe-based alloy crystal grains and Nd ₂ Fe ₁₄ B crystal grains by sintering the liquid phase at the sintering temperature. Used to increase density later. Since the fluorine-containing phase easily reacts with a phase having a high rare earth element concentration, the amount of the liquid phase is reduced. For this reason, the density after sintering falls and the coercive force also falls. In order to suppress such a decrease in density and coercive force, Fe-70% Nd alloy powder is added as a sintering aid. When the addition amount is less than 0.1 wt%, the density is less than 7 g / cm ^{3 in} this embodiment, and the coercive force is less than 10 kOe. If the amount of the sintering aid added is 0.1% or more and less than 10%, a high-density sintered body having a density of 7 g / cm ³ or more can be obtained. Since the sintering aid has a small saturation magnetization, the saturation magnetic flux density decreases with the addition amount. Therefore, the optimum addition amount of the sintering aid is 0.2 to 5%. In order to secure Br of 1.6 T or more, it is necessary that the addition amount of the Fe-based alloy having a saturation magnetization higher than that of Nd ₂ Fe ₁₄ B is larger than the addition amount of the sintering aid.

As the sintering aid, a rare earth-containing alloy that becomes a liquid phase in a temperature range below the sintering temperature, or an alloy such as Al, Cu, Ga, Zr, Ti, Mn, and Cr can be used. The main crystal structure of the sintering aid, the oxyfluoride reacted with the sintering aid, and the rare earth oxide is cubic. Part of the added sintering aid reacts with the crystal grains or fluoride of Nd ₂ Fe ₁₄ B in the sintering heat treatment. Some of the reacted fluoride forms a cubic structure oxyfluoride. The lattice constant of the oxyfluoride is within ± 10% of the lattice constant of the NdO-based compound having the fcc structure and the lattice constant of the Fe-based alloy, and the lattice mismatch is small and a matching relationship with distortion occurs. Cheap. For this reason, magnetization reversal is suppressed.

  Further, rare earth elements constituting the sintering aid and some metal elements such as Al, Cu, Ga, Zr, Ti, Mn, and Cr are unevenly distributed at the grain boundaries. In particular, the effect of increasing the coercive force is present when rare earth elements and metallic elements such as Al, Cu, Ga, Zr, Ti, Mn, and Cr are unevenly distributed in the vicinity of grain boundaries of Fe-based alloy grains and within Fe-based alloy crystal grains. It is remarkable. This uneven distribution is in a band-like range along the grain boundary of 0.5 to 100 nm from the grain boundary center, and is concentrated in a concentration range 1.1 to 100 times higher than the average concentration of Fe-based alloy crystal grains. As a result, part of the crystal structure changes with oxygen, carbon, or fluorine. When the concentration is less than 1.1 times, almost no increase in coercive force due to uneven distribution is observed. On the other hand, when it exceeds 100 times, the magnetization of the unevenly distributed portion is greatly reduced, so that the residual magnetic flux density is reduced. Therefore, the uneven concentration of the metal element in the Fe alloy crystal grains is preferably 1.1 to 100 times the average concentration. When Ga, Cu, and Ta are unevenly distributed within a range of 5 nm from the grain boundary center, when the average concentration is 0.1, 0.3, and 0.2 wt%, respectively, the unevenly distributed portions are 2, 5, and 3 wt%, respectively. . At this time, the coercive force increases by 10 kOe without a decrease in the residual magnetic flux density as compared with the case where there is no uneven distribution.

Condition [3]: When a magnetic field is applied in the direction perpendicular to the forming magnetic field during sintering, the magnetic field application effect can be realized in a temperature range in which only the Fe-based alloy has magnetization, and the Fe-based alloy crystal grains are indefinite. It becomes easy to connect parallel to the magnetic field direction. The direction of the forming magnetic field applied in the temporary forming process is the anisotropic direction of the magnet. In parallel to the anisotropic direction, the amorphous Fe-based alloy crystal grains are divided, and in the direction perpendicular to the anisotropic direction, the temperature is high. Since the magnetic field is applied in a direction perpendicular to the forming magnetic field, the Fe-based alloy crystal grains are easily connected in the case of an indefinite shape. The Fe-based alloy crystal grains are sintered and have a shape, an interface structure, or anisotropic magnetic coupling with Nd ₂ Fe ₁₄ B crystal grains, so that the coercive force can be increased and the squareness of the demagnetization curve can be improved. . Such a magnetic field application effect can be confirmed by heating the sintered body to a temperature equal to or higher than the Curie temperature of Nd ₂ Fe ₁₄ B and measuring the magnetization curve. At such a high temperature, the magnetization curve of the Fe-based alloy shows Nd ₂ Fe _14. There is a difference in the magnetization curve between the magnetization direction of B and the perpendicular direction.

In this example, the anisotropy direction of the Fe-based alloy and the anisotropy direction of the Nd ₂ Fe ₁₄ B crystal grains are changed by changing the direction of the applied magnetic field during sintering and the applied magnetic field during temporary forming from 5 degrees to 90 degrees. Thus, the magnet characteristics after sintering can be improved. If it is less than 5 degrees, the effect due to the difference in magnetic field application direction is not remarkable. This is because the easy axis direction of the Fe-based alloy is substantially parallel to the easy axis direction of the Nd ₂ Fe ₁₄ B crystal grains. The range where the angle difference is 90 to 175 degrees is almost equivalent to the range of 5 to 90 degrees.

Condition [4]: By applying a magnetic field in a direction parallel to the forming magnetic field during the aging and quenching treatment, it is possible to increase exchange coupling between the Fe-based alloy crystal grains and the Nd ₂ Fe ₁₄ B crystal grains. Contributes to increased coercivity and improved squareness. In a sintered magnet having a residual magnetic flux density exceeding 1.5 T, the c-axis direction of the Nd ₂ Fe ₁₄ B crystal is almost the same as the magnetization direction, and the orientation of the Nd ₂ Fe ₁₄ B crystal is more than the orientation of the Fe-based alloy. The nature is high. It can be confirmed that (110), (100), or (210) of the Fe crystal grows in parallel to the c-axis direction of the Nd ₂ Fe ₁₄ B crystal. This is because the anisotropy energy of the Fe-based alloy is smaller than the anisotropy energy of Nd ₂ Fe ₁₄ B, so that the Nd ₂ Fe ₁₄ B crystal is more easily magnetically oriented.

  Oxides, carbides, fluorides, and oxyfluoride nitrides with high anisotropy energy are formed in the vicinity of the grain boundaries of the Fe-based alloy, and Fe of a bcc or bct structure adjacent to these compounds contains metal elements other than Fe. One or more species are unevenly distributed, and their magnetocrystalline anisotropy energy is higher than that of non-localized bcc-Fe. In particular, when the bct structure Fe or FeCo alloy contains at least one of Cu, Ga, Mn, Ta, W, Ag, Al, and Ge, the magnetocrystalline anisotropy energy increases by 10 to 50%. Furthermore, when oxides, carbides, fluorides, oxyfluorides, or nitrides grow on these bct structure Fe or FeCo alloys via grain boundaries, the magnetocrystalline anisotropy energy increases by 20 to 100%. , The coercive force is increased by 10 kOe.

Condition [5]: By making the average particle size of the Fe-based alloy having high saturation magnetization larger than the average particle size of Nd ₂ Fe ₁₄ B, the aggregation of crystal grains of the Fe-based alloy is prevented, and the sintering aid The added volume of can be less than 10%. When the average grain size of the Fe-based alloy is less than or equal to the average grain size of Nd ₂ Fe ₁₄ B, the surface area of the crystal grains of the Fe-based alloy is larger than the surface area of the crystal grains of Nd ₂ Fe ₁₄ B, and the Fe-based alloy crystal grains The volume of the fluoride or fluorine-containing film coated on the surface of the film increases. For this reason, it is possible to increase the addition amount of the sintering aid to 1% or more to obtain a high density and a high coercive force, but the residual magnetic flux density is lowered. For this reason, it is desirable that the average particle size of the Fe-based alloy be larger than the average particle size of Nd ₂ Fe ₁₄ B. When the average particle diameter of the Fe-based alloy is larger than the average particle size of the Nd ₂ Fe ₁₄ B, Fe-based intermetallic alloy field between Nd ₂ Fe ₁₄ B than the area and Fe-based alloy and Nd between ₂ Fe ₁₄ B The sum of the interfacial areas is larger. If towards the sum of the interfacial area between between Nd ₂ Fe ₁₄ B than the interfacial area and Fe-based alloy and Nd ₂ Fe ₁₄ B between the Fe-based alloy is small, weak magnetic coupling Fe alloy, Fe-based alloys The magnetization reversal is likely to occur.

  The average particle size was evaluated by the following method. After the cross section of the sintered body or the molded body is cut in parallel and perpendicular to the magnetic field application direction of the temporary molded body and mirror-finished, a field of view in which the grain boundary can be determined with an optical microscope or a scanning electron microscope is obtained. In order to make the grain boundary clear, it is desirable to perform etching using an acidic solution. The particle diameter is calculated from the distance between the line and the point where a plurality of straight lines intersect with the grain boundary for one field of view, and the average value is obtained from the particle diameters determined from the plurality of straight lines. The distance between the straight lines is preferably a length at which five or more grain boundaries intersect. The compositional analysis in the scanning electron microscope observation makes it possible to distinguish between the Fe-based alloy and the NdFeB-based, and the average particle diameter of each is determined. It should be noted that this average particle diameter evaluation method can be used in other examples.

FIG. 1 shows the relationship between Br (residual magnetic flux density) and Hc (coercive force) and the average particle diameter of FeCo alloy / average particle diameter ratio of NdFeB alloy (hereinafter abbreviated as particle diameter ratio). When the particle size ratio exceeds 1, Br exceeds 1.6T. The particle size ratio with Br exceeding 1.6T is in the range of 1-100. When the particle size ratio exceeds 100, the orientation of the Nd ₂ Fe ₁₄ B crystal grains is disturbed, and the uniaxial anisotropy is lowered. On the other hand, when the particle size ratio exceeds 100, it is difficult to suppress the magnetization reversal of the FeCo alloy by magnetic coupling, and the coercive force tends to decrease. Since a high coercive force is required for use at a temperature of 100 ° C. or higher, the particle size ratio is preferably 100 or less.

  FIG. 2 shows the relationship between the oxyfluoride volume fraction and the particle size ratio. In the range where the particle size ratio is smaller than 1, the volume fraction of oxyfluoride exceeds 0.5%, and it is presumed that Br decreases because the two-grain boundary phase or the grain boundary triple point phase with small magnetization increases. Is done.

FIG. 3 shows the relationship between the value of Hk / Hc (Hk is a magnetic field having a magnetic flux density of 90% of Br and Hc is a coercive force) and the particle size ratio. When the particle size ratio is 100 or less, Hk / Hc exceeds 0.7, and it has high orientation and uniaxial anisotropy. The reason why Hk / Hc decreases when the average particle size exceeds 100 is that the orientation of Nd ₂ Fe ₁₄ B crystal grains is disturbed.

FIG. 4 shows a schematic diagram relating to a typical sintered magnet structure of this example. Nd ₂ Fe ₁₄ B crystal grains 1, FeCo alloy crystal grains 5 and oxyfluoride 3 are formed, and a heavy rare earth element-containing FeCo alloy 6 is observed in the vicinity of the FeCo alloy crystal grains 5. The heavy rare earth element-containing oxide 2 grows at a part of the triple point of the grain boundary. A rare earth-rich grain boundary phase 4 mainly containing Nd is formed on the outer periphery of the Nd ₂ Fe ₁₄ B crystal grains 1. As the concentration of unevenly distributed heavy rare earth elements increases, the structure changes from (1) to (2), (3), (4), and the FeCo-based alloy crystal grains 5 have heavy rare earth element-containing FeCo. The system alloy 6 grows, and the heavy rare earth element-containing oxide 2 grows in the vicinity of the crystal grains 5 of the FeCo alloy. In any structure, the concentration of heavy rare earth elements in the vicinity of the crystal grains 5 of the FeCo alloy is higher than the average concentration of the sintered magnet.

  The sintered magnet of this example is formed with oxides containing rare earth elements, oxyfluorides, bcc-structure Fe-based alloys, bct-structured NdFeB-based alloys, and heavy rare earth elements such as Tb and Dy in the vicinity of the grain boundaries. Is unevenly distributed. A typical uneven width is 1 to 200 nm from the center of the grain boundary. Further, a magnetic coupling occurs between the bcc-structured Fe-based alloy and the bct-structured NdFeB-based alloy, and anisotropy is also added to the bcc- and bct-structured Fe-based alloys. This anisotropy depends on the direction and magnitude of the magnetic field applied at a temperature higher than the Curie point of the NdFeB alloy. Confirm the easy axis direction of magnetization by measuring the angular dependence of the magnetization curve in the temperature range higher than the Curie point of the NdFeB alloy and below the sintering temperature, particularly below the temperature including the Curie point of the Fe alloy. Can do. The easy magnetization direction of the Fe-based alloy has an angle difference of 5 to 90 degrees from the easy magnetization direction of the NdFeB-based alloy. When the angle difference is less than 5 degrees, the squareness of the demagnetization curve is lower than when the angle difference is 5 to 90 degrees. An angle difference of 90 to 175 degrees is almost equivalent to an angle difference of 5 to 90 degrees.

  In the case where the residual magnetic flux density is equal and the purpose is to reduce the rare earth usage, apart from the compatibility of the increase in the residual magnetic flux density and the reduction of the rare earth usage as in this embodiment, the saturation magnetization of the Fe-based alloy is 170 to 240 emu / g. It can be achieved within the range, and cost reduction can be realized. When the saturation magnetization of the Fe-based alloy is less than 170 emu / g, the effect of increasing the residual magnetic flux density is less than 1%, which is very small. In addition, it is difficult to produce an Fe-based alloy exceeding 240 emu / g in consideration of the oxidation prevention step and the thermal stability during sintering. Even if impurity elements such as carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus which are inevitably mixed in are contained in the grain boundaries or grains, the magnet characteristics can be improved if the basic configuration does not change.

  In addition to the pulverization method as in the present embodiment, the Fe-based alloy powder exhibiting saturation magnetization as described above can be electroplating, wet methods such as ion dropping, plasma-based methods, and various spraying methods such as vacuum deposition. , Techniques using organisms and bacteria can be adopted.

After vacuum melting the 60% Fe35% Co5% Dy alloy, is injected the molten metal that is dissolved in copper rotating roll surface was reduced dissolved in Ar + 30% H ₂ gas atmosphere, the cooling rate 100 ° C. / sec of about 700 ° C. / sec After cooling at a speed, it was pulverized in an inert gas to obtain a flat or amorphous 60% Fe35% Co5% Dy alloy powder. The particle size of the 60% Fe35% Co5% Dy alloy powder can be controlled depending on the jet mill grinding time, and the average particle size can be controlled in the range of 0.1 to 1000 μm. In order to coat fluoride on the surface of 60% Fe35% Co5% Dy alloy powder having a saturation magnetic flux density of 2.2T, a TbF alcohol solution and 60% Fe35% Co5% Dy alloy powder are mixed and the alcohol is evaporated. A TbF-based film is formed on the surface of 60% Fe35% Co5% Dy alloy powder. Mixing ratio of 60% Fe35% Co5% Dy alloy powder and Nd ₂ Fe ₁₄ B powder coated with a TbF-based film having an average film thickness of 2 nm to 60% Fe 35% Co 5% Dy alloy powder 5: Nd ₂ Fe ₁₄ B powder 5 Mix with. The average particle size of the Nd ₂ Fe ₁₄ B powder is 1 μm. To improve the sinterability, about 2% of Fe-60% Nd-5% Co gold powder having an average particle size smaller than the average particle size of Nd ₂ Fe ₁₄ B powder was added to the mixed powder as a sintering aid. After forming in a magnetic field (20 kOe), sintering was performed at 1100 ° C., and a magnetic field (10 kOe) was applied in a direction perpendicular to the forming magnetic field during liquid phase formation. The aging heat treatment after sintering was set to a temperature higher than the Curie point of Nd ₂ Fe ₁₄ B at 400 to 700 ° C., and a magnetic field (20 kOe) was applied in the same direction as the magnetic field direction of molding in the magnetic field.

When the average particle size of 60% Fe35% Co5% Dy alloy powder is 2 μm, the compact after sintering in magnetic field and aging treatment in magnetic field has a residual magnetic flux density (Br) of 1.64 T (16.4 kG). The coercive force was 19.5 kOe. The value of Br exceeds 1.61T which is the theoretical value of Nd ₂ Fe ₁₄ B, and the 60% Fe 35% Co 5% Dy alloy powder has a low rare earth element concentration, so the amount of rare earth element used can be reduced. In order to obtain a value of Br exceeding the theoretical value of Nd ₂ Fe ₁₄ B, the following conditions are required as in this embodiment.

[1] Use a rare earth element-containing Fe-based alloy having a saturation magnetization higher than that of Nd ₂ Fe ₁₄ B.
[2] Since Fe-based alloys are unlikely to form a liquid phase below the sintering temperature, a sintering aid in which a part of the rare earth element is unevenly distributed is added near the grain boundary.
[3] Applying a magnetic field perpendicular to the forming magnetic field during sintering.
[4] Applying a magnetic field in a direction parallel to the forming magnetic field during the aging and quenching treatment.
[5] The average particle size of the Fe-based alloy having high saturation magnetization is larger than the average particle size of Nd ₂ Fe ₁₄ B.
[6] Fluoride and oxyfluoride can be confirmed at the grain boundary triple point.

The conditions [1] to [6] will be described in detail below.
Condition [1]: A rare earth element-containing Fe-based alloy having a saturation magnetization higher than that of Nd ₂ Fe ₁₄ B is a material having a saturation magnetic flux density exceeding 1.6 T, such as an FeCo-based alloy. When a heavy rare earth element is added to Nd ₂ Fe ₁₄ B, the saturation magnetic flux density of the rare earth element-containing Fe-based alloy may also be reduced by the decrease in magnetic flux density due to the addition of the heavy rare earth element. In addition to the FeCo system, various Fe-M systems such as FeNi system, FeAl system, FeSi system, FeMn system, and FeCr system (M is one or a plurality of metal elements or metalloid elements other than Fe) may be used.

  Condition [2]: It is desirable to use an alloy that becomes a liquid phase at a temperature of 1100 ° C. or less as the sintering aid. Fe, FeCo, and Fe-M alloys containing 30 wt% to 90 wt% rare earth elements can be used. Alternatively, when a metal binder is used, a nonmagnetic metal such as low melting point Zn, CuZn, Ga, or Al can be used.

Condition [3]: Applying a magnetic field in a direction perpendicular to the forming magnetic field at the time of sintering continuously aligns the continuity of a material with a high Curie point such as FeCo in a direction different from the orientation direction of Nd ₂ Fe ₁₄ B. This is because the direction of high continuity is set to a direction different from the magnetization direction by enhancing the property, and the sintering heat treatment may be performed by applying a magnetic field in a direction different from the forming magnetic field at 5 to 90 degrees. When the difference between the magnetic field direction during sintering and the magnetic field direction during molding is less than 5 degrees, the squareness index Hk (the value of the demagnetizing field that is 90% of Br) is reduced by 1 to 5 kOe, and the magnetization It becomes easy to reverse.

Condition [4]: Magnetic anisotropy energy in the vicinity of the grain boundary of Nd ₂ Fe ₁₄ B is increased by applying a magnetic field in a direction parallel to the forming magnetic field during the aging and quenching treatment. The rapid cooling rate is to cool the temperature near the Curie point of Nd ₂ Fe ₁₄ B at a cooling rate of 50 ° C./min or more. With this cooling rate, cubic crystals in which the oxyfluoride is a metastable phase at room temperature are formed, and a part thereof forms a matching interface with Nd ₂ Fe ₁₄ B and Fe-based alloys.

Condition [5]: High if the average particle size of the Fe-based alloy having a saturation magnetization is smaller than the average particle size of the Nd ₂ Fe ₁₄ B, increases the interfacial area between the Fe-based alloy and Nd ₂ Fe ₁₄ B, various Since the crystals of the Fe-based alloy grown in the orientations have the respective easy magnetization directions, magnetization reversal is likely to occur and the coercive force is significantly reduced. When the mixing ratio of the Fe-based alloy and Nd ₂ Fe ₁₄ B in the sintered magnet is 5: 5 or the mixing ratio of the Fe-based alloy is smaller than this ratio, the number of crystal grains of the average grain size Fe-based alloy is Nd ₂ The number is less than the number of Fe ₁₄ B crystal grains. The grain size of the Fe-based alloy is about 50% of grains having an average grain size or larger, and about 50% of grains having a grain size less than the average grain size. The average value of the distribution is Nd ₂ Fe ₁₄ B. If the value is greater than the average particle size, the effect of magnetization reversal suppression or coercivity increase due to exchange coupling, magnetostatic coupling, interface anisotropy, and stress-induced anisotropy between the Fe-based alloy and Nd ₂ Fe ₁₄ B Can be confirmed.

Condition [6]: Fluoride is required to prevent the Fe-based alloy from reacting with Nd ₂ Fe ₁₄ B and deteriorating the magnetic properties. The fluoride film applied to the Fe-based alloy partially agglomerates during sintering and becomes an oxyfluoride and grows on the grain boundary triple point or the magnet surface. It is also observed in some biphasic grain boundaries. Fluoride partially reacts with the sintering aid, and further reacts with the liquid phase formed during sintering to form an oxyfluoride containing a rare earth element, and a part thereof aggregates. When the average crystal grain size of the Fe-based alloy is smaller than the average grain size of Nd ₂ Fe ₁₄ B, the amount of fluoride applied to the Fe-based alloy increases, and the residual magnetic flux density greatly decreases. This is because in the sintered magnet, fluoride and oxyfluoride do not have magnet properties, and therefore the proportion of the ferromagnetic material decreases as the amount of fluoride used increases.

The volume of fluoride or oxyfluoride which is a fluorine-containing phase is preferably 0.001 to 2% by volume. If the volume fraction is less than 0.001%, it becomes difficult to suppress the reaction during sintering of the Fe-based alloy and Nd ₂ Fe ₁₄ B, and the coercive force is greatly reduced. If 0.0001%, the coercive force is less than 5 kOe. Become. On the other hand, if it exceeds 2% by volume, the sinterability deteriorates, and in order to ensure a density of 7 g / cm ³ or more, the volume of the sintering aid needs to be 5% or more, and the residual magnetic flux density starts to decrease. . Therefore, it is desirable that the low melting point sintering aid is 5% or more and the volume fraction of the fluorine-containing material is 0.001 to 2% by volume.

It is necessary to suppress as much oxygen as possible in the raw material powder and the process up to the sintering process, and an Nd ₂ Fe ₁₄ B powder production process employs an oxygen removal process by hydrogen reduction. On the other hand, when the average particle size of the Fe-based alloy is equal to or smaller than the average particle size of the Nd ₂ Fe ₁₄ B powder, the Fe-based alloy surface is easily oxidized and the saturation magnetization of the Fe-based alloy is reduced. This decrease in saturation magnetization is suppressed by the formation of a fluoride film and its reduction reaction, but when the average particle size of the Fe-based alloy is less than the average particle size of the Nd ₂ Fe ₁₄ B powder, the amount of fluoride used is reduced from 2 Reduction to 5 wt% is necessary to ensure high saturation magnetization, and since 5% sintering aid is used to improve sinterability, the residual magnetic flux density is 1.6T or more. It is difficult.

When the oxygen amount exceeds 2000 ppm, the heavy rare earth element forms an oxide or an oxyfluoride rather than unevenly distributed in Nd ₂ Fe ₁₄ B, and the coercive force does not increase. If the oxygen content is less than 300 ppm, the oxyfluoride is difficult to grow, and the Fe-based alloy and Nd ₂ Fe ₁₄ B powder react easily during sintering, resulting in a composition variation of Nd ₂ Fe ₁₄ B and a composition variation of the rare earth-rich phase. The coercive force becomes 7 kOe or less due to the structural change of the rare earth-rich phase. Therefore, the optimum oxygen concentration is in the range of 300 to 2000 ppm.

In this example, since a rare earth element is added to the Fe-based alloy, it is possible to confirm the uneven distribution of the rare earth element in a part of the grain boundary in both the Fe-based alloy and Nd ₂ Fe ₁₄ B crystal grains. The growth of oxides and oxyfluorides containing rare earth elements in the part can be confirmed. R ₂ Fe ₁₄ B or R ₂ Co ₁₇ containing a plurality of rare earth elements (R) can be used in place of Nd ₂ Fe ₁₄ B, and the same applies even if various metal elements other than iron and rare earth elements are added. The characteristics can be confirmed. Furthermore, monoclinic or orthorhombic Sm ₂ Fe ₁₄ B in which the lattice of Sm ₂ Fe ₁₄ B, which is a compound of light rare earth elements, is deformed may be used.

The Fe-Co alloy in which two types of compositions of Fe-10% Co and Fe-40% Co are modulated contains various trace metal elements and has a modulation period of 1 to 100 nm. This composition-modulated alloy has an average crystal grain size of 1 μm and can be prepared by mixing with an Nd ₂ Fe ₁₄ B-based crystal having an average crystal grain size of less than 1 μm, followed by temporary molding in a magnetic field and sintering in a magnetic field. The magnetic field application direction in the sintering heat treatment is applied in parallel to the direction parallel to the easy magnetization direction of the Nd ₂ Fe ₁₄ B-based crystal, that is, the direction perpendicular to the composition modulation direction. The mixing ratio of the composition-modulated alloy and the Nd ₂ Fe ₁₄ B-based crystal is 9: 1. As a sintering aid, 5% Fe-65% Nd alloy is added to increase the density after sintering to 7 g / cm ³ or more and to ensure a coercive force of 15 kOe or more. A sintered magnet having a residual magnetic flux density of 1.5 T to 1.7 T is obtained in which the direction perpendicular to the composition modulation direction is substantially parallel to the easy magnetization direction of the Nd ₂ Fe ₁₄ B-based crystal.

  In addition to Fe-10% Co / Fe-40% Co, the composition modulation alloy includes FeCo alloy / FeAl alloy, FeCo alloy / NiAl alloy, FeCo alloy / MnAl alloy, FeCo alloy / MnGa alloy FeCo alloy / FeCoO alloy, Fe alloy / FeCoNiTi alloy can be applied. Confirmed increase in magnetic anisotropy due to introduction of various defects such as magnetostriction, shape memory, lattice distortion, stacking fault, two-dimensional metastable phase, etc. near the interface due to composition modulation or structural modulation when the modulation period is 100 nm or less it can. In these combinations, when the modulation period is 1 nm or less, an increase in coercive force is recognized, the residual magnetic flux density is 1.0 T or more when the modulation period is 0.1 to 1 nm, the modulation composition concentration difference is 10 to 90%, A rare earth-free alloy having a coercive force of 10 kOe or more can be provided.

In this example, when the average crystal grain size of the Nd ₂ Fe ₁₄ B-based crystal is 1 μm or more, the surface area of the Nd ₂ Fe ₁₄ B-based crystal grain is decreased, and the crystal grains of the Nd ₂ Fe ₁₄ B-based crystal and the composition-modulated alloy are reduced. Therefore, the magnetic coupling such as exchange coupling is reduced, and the coercive force is reduced. For this reason, the average crystal grain size of the Nd ₂ Fe ₁₄ B-based crystal needs to be smaller than the crystal grain size of the composition-modulated alloy.

Addition of 0.01 to 2% by volume of a fluoride containing a rare earth element such as NdF ₃ as a sintering aid grows an unevenly distributed phase of the rare earth element in the vicinity of the grain boundary, thereby increasing the coercive force due to the reduction effect of fluoride. In addition, the effect of increasing the residual magnetic flux density can be confirmed. At this time, the added fluoride is combined with oxygen and becomes an oxyfluoride after sintering. When the oxyfluoride is gradually cooled after sintering, it becomes rhombohedral or orthorhombic, but it becomes cubic by rapidly cooling the vicinity of the Curie point of the Fe-based alloy at a cooling rate of 100 to 300 ° C./min. Part of the cubic oxyfluoride forms a matching interface with the bcc phase of the Fe-based alloy, thereby suppressing the reaction between the Nd ₂ Fe ₁₄ B-based crystal and the Fe-based alloy. The crystal plane (h, k, l) with NdOF is parallel to (n, m, l) of bcc structure Fe. Here, h, k, l, n, m, and l are integers.

When the volume of the fluoride added exceeds 2% by volume, the sinterability deteriorates. This is sintered when not increase the liquid phase for some rare earth-rich phase part of oxyfluoride at 1000 ° C. is sintering temperature is there liquid phase number phase is reacted 7 g / cm ³ or more It will not be high density. Therefore, the amount of fluoride added is preferably 2% by volume or less.

Stress is applied to the composition-modulated alloy of the present embodiment during the sintering process, and anisotropy induced by the stress is generated to increase the coercive force. In particular, since Nd ₂ Fe ₁₄ B-based crystals exhibit a shrinkage dependent on the crystal orientation during sintering, anisotropic stress is also applied to the composition-modulated alloy, resulting in stress-induced anisotropy. Magnetic force increases.

An Nd ₂ Fe ₁₄ B-based powder having an average particle diameter of 1 μm and an Fe-based powder having an average particle diameter of 1.5 μm are reduced in a hydrogen atmosphere and then mixed with TbF ₃ beads. The temperature during mixing is 200 ° C., and the mixing ratio is 5: 5 for Nd ₂ Fe ₁₄ B powder: Fe powder. The bead material TbF ₃ partially adheres and diffuses on the outermost surface of the Nd ₂ Fe ₁₄ B-based powder or Fe-based powder, and fluoride or oxyfluoride is formed on the outermost surface of the Nd ₂ Fe ₁₄ B-based powder. . Then, after adding shape anisotropy to the powder by adding Fe-70% Nd alloy powder, which is a sintering aid, and kneading in a magnetic field, preliminary molding in a magnetic field and sintering / aging processes After that, a sintered magnet is created. The sintering temperature is 900 ° C., and by applying a magnetic field of 20 kOe at a temperature higher than 400 ° C. during the sintering aging heat treatment, the magnetic coupling between the Nd ₂ Fe ₁₄ B crystal and the Fe crystal is strengthened and maintained. Increase the magnetic force.

When the average particle size of the Fe-based powder is smaller than the average particle size of the Nd ₂ Fe ₁₄ B-based powder consists of Nd ₂ Fe ₁₄ B-based powder periphery as Fe-based powder is coated continuously, the coercive force is 1 Decrease by ~ 5%. Therefore, it is desirable that the average particle size of the Fe-based powder is equal to or larger than the average particle size of the Nd ₂ Fe ₁₄ B-based powder. Part of the Fe-based powder aggregates to form an aggregate of 50 to 100 μm, which is confirmed in the sintered body, part of which comes into contact with the Fe-based crystal, and part of the rare earth oxide or rare earth oxyfluoride. In contact. It is possible to obtain a sintered body having a density of 7 g / cm ³ or more by adding 1 to 10% of a sintering aid that forms a liquid phase at a low temperature below the sintering temperature, and Br (residual magnetic flux density) is A sintered magnet with 1.65 T, Hc (coercive force) of 19 kOe is obtained.

In the sintered body of this example, a part of the Fe-based crystal is in contact with a part of the Nd ₂ Fe ₁₄ B-based crystal, and the magnetization of both is ferromagnetically coupled. The magnetization of the Fe-based powder crystal is not reversed by the corresponding magnetic field. Magnetization reversal of Fe-based crystal, Nd ₂ Fe ₁₄ B system depends on the value of the crystals of the coercive force, Nd ₂ Fe ₁₄ B system should hardly reversed crystal coercive force is large. Therefore, it is necessary to increase the coercivity of the Nd ₂ Fe ₁₄ B-based crystal in the vicinity of the Fe-based crystal. A part of TbF ₃ diffuses in the vicinity of the grain boundary of the Nd ₂ Fe ₁₄ B-based crystal, thereby increasing the magnetocrystalline anisotropy energy and contributing to an increase in coercive force. Therefore, the magnetization reversal of the Fe-based crystal is also suppressed by Tb diffusion, and the maximum energy product can be increased if the magnetization increase exceeding the magnetization decrease by Tb diffusion can be secured in the Fe-based crystal.

In this embodiment, a plurality of rare earth elements can be used in place of Nd in the Nd ₂ Fe ₁₄ B-based powder, and various metal elements and metalloid elements other than boron may be added. In addition, Fe and Fe-M (M is one or more metals or metalloid elements other than Fe) having a saturation magnetization of 180 emu / g or more can be used for the Fe-based powder. The crystal structure of Fe-based powder is either bcc or fcc, which is the same structure as pure Fe, or bct or hcp structure with expanded lattice volume. Nd ₂ Fe ₁₄ B-based crystal or oxyfluoride and Fe-based crystal The interface has a misfit of 0.1 to 20% in the lattice constant, and magnetic anisotropy due to lattice distortion based on the difference in lattice constant appears. The M-rich phase containing 50% to 99% of the M element grows near the grain boundary, and the M-rich phase has a metastable bcc or bct structure. Near some grain boundaries, FexMyOz (x, y, z are positive numbers) or FelMmOnFk (l, m, n, k are positive numbers) grows and contributes to an increase in coercive force. The presence of crystal lattice strain affects the magnetic moment and Curie point in addition to magnetic anisotropy, and the Fe-Fe interatomic distance or Fe-M or MM interatomic distance has a small strain effect. As a result, the saturation magnetization and the Curie point increase by 5% and 20 ° C., respectively.

The lattice of the Fe-based crystal is easier to deform than the Nd ₂ Fe ₁₄ B-based crystal. However, since the metastable Fe-based crystal deformed by lattice deformation easily returns to the stable phase when the volume is small, the volume of the crystal grains containing the metastable phase is increased to increase the Nd ₂ Fe ₁₄ B-based crystal and the Fe-based crystal. It is necessary to increase the stability of lattice distortion in the vicinity of the interface. For this reason, the average crystal grain size of the Fe-based crystal is set larger than the average crystal grain size of the Nd ₂ Fe ₁₄ B-based crystal. In this example, when the average crystal grain size of the Fe-based crystal is less than 1 μm, the lattice strain in the Fe-based crystal is easily relaxed, and no increase in magnetocrystalline anisotropy energy is observed, and the effect of increasing the saturation magnetization and the Curie point is observed. There is almost no.

Solution frequency plasma Nd ₂ Fe ₁₄ B system and Fe powder having an average particle size of 60nm and Nd ₂ Fe ₁₄ B-based powder having an average particle diameter of 50nm was prepared by Method powder: Fe powder 5: After mixing in a ratio of 5, grain After adding a Fe-80% Nd alloy having a diameter of 20 nm and preliminarily forming in a magnetic field, the surface fluorination with the decomposition gas of ammonium fluoride proceeds, and then the sintered compact is sintered at 900 ° C., and the temperature is 500 to 900 ° C. Anisotropy was added to the Fe powder by applying a magnetic field of 10 to 100 kOe in a direction perpendicular to the magnetic field direction applied by temporary forming in the magnetic field. The solution used in the high-frequency plasma method in solution is a transparent liquid in which DyF ₃ is dissolved in an alcohol solvent. The coercive force is increased by 5 kOe compared to the case of a solution not using fluoride. The amount of fluorine is in the range of 0.001 to 1 atomic% with respect to the sintered body, and fluorine is unevenly distributed at the grain boundaries. Moreover, Dy can be confirmed in the vicinity of the uneven distribution location of fluorine.

  The sintered magnets produced by this method have a magnetic property of Br of 1.6 T, a coercive force of 18 kOe, and the amount of rare earth elements used is 6 atomic%, so that about 50% of rare earth elements can be reduced. In order to reduce the amount of rare earth elements used, the following conditions are necessary.

Condition [1]: In addition to the Nd ₂ Fe ₁₄ B crystal, Fe or Fe crystal, boride, carbide and fluoride or oxyfluoride are observed in the sintered magnet, and the oxyfluoride is cubic. The oxyfluoride contains rare earth elements and carbon, and a part of the crystal lattice is in a consistent relationship with the Fe-based crystal.

Condition [2]: Fe or Fe-based crystals have anisotropy, and show magnetic characteristics depending on the direction of magnetic field application during sintering heat treatment. When a magnetic field of 10 to 100 kOe is applied in the sintering heat treatment process in a direction perpendicular to the magnetic field direction applied in the temporary forming in the magnetic field, the direction in which the magnetization of Fe is likely to be saturated is the Nd ₂ Fe ₁₄ B-based crystal in the sintering process. It becomes almost parallel to the direction of the magnetic field applied in the temperature range above the Curie point. Since the magnetization direction of the sintered magnet and the easy magnetization direction of Fe have an angle difference of 5 degrees to 175 degrees, the magnetization reversal of Fe is suppressed.

Condition [3]: The average particle size of Fe or Fe-based crystals is larger than the average particle size of Nd ₂ Fe ₁₄ B-based crystals. In order to increase the magnetocrystalline anisotropy energy by diffusing Dy around the periphery of the Nd ₂ Fe ₁₄ B-based crystal by impregnation with DyF _3, the larger the outer peripheral area of the Nd ₂ Fe ₁₄ B-based crystal, the greater the coercive force. It is remarkable. Therefore, any finer grain size of the Nd ₂ Fe ₁₄ B-based crystal, average particle size of Fe or Fe-based crystal can be larger than the average particle diameter of the Nd ₂ Fe ₁₄ B-based crystal becomes a condition of high coercivity .

Condition [4]: Heavy rare earth elements are unevenly distributed near the grain boundaries of the Nd ₂ Fe ₁₄ B-based crystal. Instead of heavy rare earth elements, Fe or Fe-based crystals are formed by unevenly distributing metal elements such as Cu, Ga, Nb, Zr, Mn, Al, Ti, Ta, Ag, and Bi other than Fe and Co. The coercive force is increased by increasing the crystal stability and forming a coherent interface. The uneven distribution width of metal elements other than Fe and Co having a bcc structure is preferably 2 to 10 nm from the center of the grain boundary.

Condition [5]: A part of the Fe-based crystal is aggregated and sintered to form a crystal having a coarse particle diameter of 500 nm or more. Oxides and oxyfluorides of rare earth elements are formed in part of the aggregated crystals, and FehCoiMjOkFl (M is a metal element other than Fe or Co, h, i, j, k, l is a positive number), and the oxyfluoride grows in a layered manner to increase the coercive force. This oxyfluoride is either ferromagnetic, antiferromagnetic, or ferrimagnetic, and grows along grain boundaries and also grows at grain boundary triple points. The effect of increasing the coercive force can be confirmed when the grain boundary coverage of the oxyfluoride is 0.1% or more, and the coercive force is increased by 1 kOe at 1%. This oxyfluoride grows in layers along the grain boundary, thereby suppressing magnetization reversal in the vicinity of the grain boundary of the Nd ₂ Fe ₁₄ B-based crystal and magnetic anisotropy energy in the vicinity of the grain boundary of the Fe or Fe-based crystal. Will increase. The optimum grain boundary coverage of oxyfluoride is 1 to 50%, and when it exceeds 80%, the magnetization of the magnet decreases.

Condition [6]: Nd ₂ Fe ₁₄ B-based crystal grains or part of Fe-based crystal grains are aggregated to grow crystal grains 10 to 100 times as large as the raw material powder. Such coarse crystal grains have crystal orientations that are substantially aligned in one direction, and magnetization reversal occurs in the vicinity of grain boundaries or various intragranular precipitates. Therefore, FehCoiMjOkFl (M is a metal element other than Fe or Co, h, i, j, k, and l are positive numbers) to suppress magnetization reversal.

In this embodiment, fluoride or nitride, boride, oxide, or carbide containing rare earth elements or alkali metals can be used in place of DyF ₃ . The fluoride whose coercive force increase is 3 kOe or more is a fluoride containing a heavy rare earth element, and the volume fraction of fluoride in the sintered body is smaller than the volume fraction of oxyfluoride.

In this embodiment, Sm ₂ Fe ₁₄ B or RnMm can be used instead of the Nd ₂ Fe ₁₄ B-based crystal. Here, R is a rare earth element or a plurality of rare earth elements, M is one or more of Fe, Co, Mn, and Cr, and n and m are positive numbers. Sm ₂ Fe ₁₄ B is formed in the vicinity of the grain boundary, and by making the a axis parallel to the orientation magnetic field or the magnetic field direction during sintering, magnetic coupling with the Fe-based alloy occurs and the coercive force is set to 10 to 30 kOe. Is possible. When some Sm ₂ Fe ₁₄ B has a monoclinic or orthorhombic structure, the coercive force can be further increased.

An NdF ₃ film is formed by solution treatment on the surface of an Fe-35% Co powder having an average particle diameter of 30 nm prepared by a high frequency plasma method. The average film thickness of the NdF ₃ film is 1 nm. Fe-35% Co powder coated with 80 to 95% of the surface area with this NdF ₃ film was heat-molded at 500 ° C. under the condition of 5 t / cm ² , and then Nd ₂ Fe ₁₄ B-based nanoparticles and sintering aid nano Impregnate the particles. The average particle diameter of the Nd ₂ Fe ₁₄ B-based nanoparticles and the sintering aid nanoparticles is 10 nm, and the Nd ₂ Fe ₁₄ B-based nanoparticles are impregnated by impregnating the crystal grain gap of the heat-molded Fe-35% Co. Enter and sinter at 800 ° C. When the ratio of Nd ₂ Fe ₁₄ B-based nanoparticles: Fe-35% Co powder is 1:20, the sintered magnet has Br of 1.9 T, coercive force of 9 kOe, and a coercive force temperature coefficient of −0.1% / ° C. Is obtained.

  A magnet in which the amount of the rare earth element-containing alloy is smaller than the amount of the alloy not containing the rare earth element as in this embodiment has the following characteristics. 1) The average grain size of Fe-based crystal grains not containing rare earth elements is larger than the average grain diameter of crystals containing rare earth elements. 2) The rare earth element used for the sintered magnet is 5% or less and 0.1% or more. If it is less than 0.1%, it is difficult to ensure a coercive force of 5 kOe or more. 3) Fluoride or oxyfluoride is observed at a part of the triple point of the grain boundary. 4) In addition to the disordered phase, Fe—Co alloys have crystals with an ordered phase and a lattice strain of 0.1 to 10%. When the lattice strain exceeds 1%, the coercive force is increased without using rare earth elements. 5 to 20 kOe can be realized.

In this example, since the Nd ₂ Fe ₁₄ B-based nanoparticles are impregnated, the average particle size needs to be smaller than that of the Fe-35% Co powder, and the average particle size of the Nd ₂ Fe ₁₄ B-based nanoparticles is required. However, impregnation cannot be carried out if the average particle diameter is twice or more of the Fe-35% Co powder. Instead of Nd ₂ Fe ₁₄ B-based nanoparticles, SmCo-based nanoparticles, AlNiCo-based nanoparticles, MnGa-based nanoparticles, MnBi-based nanoparticles, MnAlC-based nanoparticles, and FeCoCr-based nanoparticles can be used. In addition to the sintering method, molding methods such as hot thermoforming, cold spray method, shock wave molding, energized plasma molding, electromagnetic wave heating molding, stirring friction molding, and strong magnetic field molding can also be used.

An NdF-based film is formed by solution treatment on the surface of Fe-40% Co powder having an average particle diameter of 10 nm prepared by a high frequency plasma method. The average film thickness of the NdF-based film is 1 nm. NdF ₂ and NdOF are recognized in addition to NdF _{3 in the} NdF-based film. An Fe-40% Co powder coated with 80 to 99% of the surface area with this NdF-based film is molded under the condition of 1 t / cm ² , and then sintered by applying electromagnetic waves and causing NdF ₃ to generate heat. By applying a unidirectional magnetic field (20 kOe) during application of electromagnetic waves, an FeCo-based sintered body having anisotropy in the magnetic field direction is obtained, and the residual magnetic flux density is 1.2 to 1.7 T, the coercive force is 5 to 15 kOe. Thus obtained sintered body is obtained.

In order to further increase the coercive force of the magnet as described above, 1% by volume of Nd ₂ Fe ₁₄ B-based nanoparticles are impregnated before heating the electromagnetic wave, and Nd ₂ Fe ₁₄ B remains at the grain boundary triple point after sintering. And a coercive force of 20 to 25 kOe can be realized. Adding a low melting point phase having a melting point of 900 ° C. or lower together with Nd ₂ Fe ₁₄ B-based nanoparticles to improve density after sintering also contributes to an increase in coercive force. Prior to the impregnation treatment, the surface can be cleaned by exposure to various reducing gases, and the magnetic properties after the impregnation can be improved. The same effect can be obtained by using SmCo-based compounds or MnBi-based, AlNiCo-based, or MnAl-based alloy particles instead of Nd ₂ Fe ₁₄ B.

The magnet material as in this example has the following features [1] to [6].
Characteristic [1]: The rare earth element usage is 0.1 to 5 atomic%. The volume fraction of crystals that do not contain rare earth elements is greater than the volume fraction of crystals that contain rare earth elements.

  Feature [2]: Anisotropy is observed in the FeCo-based crystal grains, and the magnetization curve is anisotropic. After heating to a temperature range between the Curie temperature and the sintering temperature of crystals containing rare earth elements, the magnet magnetic properties are restored to the magnetic properties before heating by rapid cooling, and the magnetization curve is measured at a temperature above the Curie temperature. It can be confirmed that the magnetization curve is dependent on the magnetic field application direction.

  Characteristic [3]: Fluoride and oxyfluoride are observed in part of the crystal grain boundary. The oxyfluoride has a crystal orientation relationship with the FeCo crystal to form a matching interface, and the (a, b, c) FeCo crystal and the (l, m, n) crystal plane of the oxyfluoride are parallel. Here, a, b, c, l, m, and n are positive numbers. This orientation relationship is established because the lattice constant of the oxyfluoride is almost equal to twice that of the FeCo crystal (1.8 to 2.2 times), and the lattice strain due to the difference in lattice constant is the FeCo crystal. When introduced into the crystal, the magnetocrystalline anisotropy increases. Even if the FeCo crystal contains a metal element other than FeCo or an element that can be arranged at the intrusion position, there is no significant change.

  Characteristic [4]: A part of the FeCo-based crystal is aggregated to form a coarse crystal having a maximum size of 500 to 1000 nm. In order to suppress the growth of such a coarse crystal, the coarse crystal grain size can be set to 100 to 200 nm by increasing the average film thickness of the NdF-based film to 1.5 to 2 nm.

  Feature [5]: A part of the FeCo-based crystal has a lattice strain, and the strain amount is 0.1 to 10%. The lattice energy and the crystal grain shape anisotropy increase the anisotropy energy of the FeCo-based crystal. Lattice strain is related to the grain growth process by applying a magnetic field, and there is a difference in strain between the magnetic field direction and the perpendicular direction of the magnetic field, and this difference affects the magnetic property anisotropy.

Characteristic [6]: Curie point is 700-1000 degreeC. Regarding the temperature dependence of magnetization, when Nd ₂ Fe ₁₄ B and FeCo crystals are grown on a sintered magnet, a temperature change in magnetization corresponding to the Curie points of at least two ferromagnetic phases is observed. That is, in the relationship between magnetization and temperature, at least two inflection points can be confirmed at a temperature of 20 ° C. or higher. In the measurement of the magnetic specific heat, at least two peaks can be confirmed.

An NdF-based film is formed by solution treatment on the surface of an Fe powder having an average particle diameter of 5 nm and an Fe-30% Co powder prepared by a high frequency plasma method. The average film thickness of the NdF-based film is 0.1 nm. NdF ₂ and NdOF are recognized in addition to NdF _{3 in the} NdF-based film. Fe powder coated with 80-99% of the surface area with this NdF-based film and Fe-30% Co powder were mixed at a volume ratio of 1: 1, molded under the condition of 1 t / cm ² , and then applied with electromagnetic waves. Sinter ₃ by generating heat. By applying a unidirectional magnetic field (20 kOe) during application of electromagnetic waves, an FeCo-based sintered body having anisotropy in the magnetic field direction is obtained, and the residual magnetic flux density is 1.2 to 1.7 T, the coercive force is 5 to 15 kOe. Thus obtained sintered body is obtained.

In order to further increase the coercive force of the magnet as described above, 1% by volume of Nd ₂ Fe ₁₄ B-based nanoparticles are impregnated before heating the electromagnetic wave, and Nd ₂ Fe ₁₄ B remains at the grain boundary triple point after sintering. And a coercive force of 20 to 25 kOe can be realized. Adding a low melting point phase having a melting point of 900 ° C. or lower together with Nd ₂ Fe ₁₄ B-based nanoparticles to improve density after sintering also contributes to an increase in coercive force. Instead of Nd ₂ Fe ₁₄ B, (Nd, Dy) ₂ (Fe, Co) ₁₄ B, Sm ₂ Fe ₁₄ B, SmCo compounds, MnBi, AlNiCo, MnAl, MnGa, MnGe, spinel ferrite Similar effects can be obtained by using alloy particles such as CuFeF.

The magnet material of the present embodiment has the following features [1] to [6].
Characteristic [1]: The rare earth element usage is 0.01 to 1 atomic%. The volume fraction of crystals that do not contain rare earth elements is greater than the volume fraction of crystals that contain rare earth elements. When the rare earth element usage is less than 0.01%, it is difficult to make the density 6 g / cm ³ or more, the coercive force is less than 5 kOe, and the magnetic properties are low. If the amount of rare earth element used exceeds 1 atomic%, the residual magnetic flux density decreases and the temperature dependence of the coercive force increases, so it is desirable to make it less than 1 atomic%.

  Feature [2]: FeCo-based crystal grains have anisotropy and composition modulation or a structure in which the crystal structure is modulated, and the magnetization curve has anisotropy. The saturation magnetic flux density is high in the direction perpendicular to the composition modulation period. In a magnetic field of 20 kOe, a magnetic flux density difference of 10% or more is recognized between the composition modulation period, the parallel direction, and the perpendicular direction. Further, the coercive force is 5 kOe or more in the direction parallel to the direction of the composition modulation period, and the coercive force is small in the direction perpendicular to the direction of the composition modulation period. Some of the metal elements contained in the FeCo crystal grains form clusters, and elements having an fcc structure such as Cu and Ag form clusters of the bcc or bct structure.

  Characteristic [3]: Fluoride and oxyfluoride or oxide are observed in part of the crystal grain boundary. Even if these fluorine-containing compounds contain impurities such as carbon, nitrogen, phosphorus, boron, sulfur, and hydrogen, the same effect can be obtained. Even when there are more oxygen-containing compounds than fluorine-containing compounds, there is no significant change.

  Characteristic [4]: A part of the FeCo-based crystal is aggregated to form a coarse crystal having a maximum size of 500 to 1000 nm. In order to suppress the growth of such a coarse crystal, the coarse crystal grain size can be set to 10 to 100 nm by increasing the average film thickness of the NdF-based film to 1.5 to 2 nm. When the size of the coarse crystal exceeds 500 nm, the squareness of the demagnetization curve is lowered. For this reason, it is desirable that coarse crystals have a particle size of 100 nm or less.

  Feature [5]: A part of the FeCo-based crystal has a lattice strain, and the strain amount is 0.01 to 10%. The anisotropy energy of the FeCo-based crystal is increased by increasing the anisotropy due to the lattice distortion and the crystal grain shape anisotropy, compositional modulation or regularity modulation. Lattice strain is related to the grain growth process by applying a magnetic field, and there is a difference in strain between the magnetic field direction and the perpendicular direction of the magnetic field, and this difference affects the magnetic property anisotropy. In the FeCo-based crystal, two types of lattice constants are recognized on average, and lattice strain based on the difference in lattice constant is locally recognized at the matching interface or the non-matching interface. Further, as a crystal other than bcc, at least one kind of growth of bct, orthorhombic, hexagonal, monoclinic, face-centered cubic, and rhombohedral is observed. When crystals other than bcc are formed together with bcc, lattice distortion and interfacial magnetic anisotropy increase and coercive force increases. If the lattice strain is less than 0.001%, the effect of increasing the coercive force is small, but if it is 0.01% or more, a coercive force of 5 kOe or more can be secured.

  Characteristic [6]: Curie point is 700-1000 degreeC. The composition modulation structure is stable up to this temperature range.

  In this example, it is possible to make the composition modulation period 10 nm or less by setting the crystal grain size of the FeCo-based particles having two kinds of compositions to less than 5 nm, and magnetic anisotropy accompanying lattice distortion due to the difference in lattice constant. It is possible to increase sexual energy. In addition to Fe / Fe-30% Co, the two types of compositions are Fe / Fe-5% Co, Fe / Fe-90% Co, Fe / Co, Fe / FeAl alloy, Fe / FeMn alloy, Fe / FeNi alloy, Fe / FeSi alloy, and other combinations of Fe / Fe-M (where M is a metal or metalloid element other than Fe) can confirm compositional modulation and lattice distortion associated with the modulation structure, and shape anisotropy and crystal magnetism An increase in anisotropy or interfacial magnetic anisotropy can be realized, and fluoride or oxyfluoride is observed in part of the grain boundary. In particular, in the combination of FeCo alloy and Co, a part of the FeCo alloy has an hcp structure and exhibits higher magnetocrystalline anisotropy than when it has a bcc structure, and the crystal structure can create a structure whose composition is modulated by hcp. The residual magnetic flux density is higher than that of Co. In addition to the above two types of combinations, three or more types of similar combinations can be realized, and NdFeB-based and SmCo-based compounds containing rare earth elements at the grain boundary triple points may be formed.

  Co nanoparticles having an average particle diameter of 5 nm are prepared by a high-frequency plasma method, and an FeCo alloy is formed on the surface of the Co nanoparticles without being exposed to the atmosphere in the same apparatus. In Co nanoparticles in which an Fe—Co alloy having a thickness of 1 to 10 nm is formed on the outer peripheral side, the crystal structure of the FeCo alloy also has an hcp structure, and there is a difference in magnetic properties between the c-axis direction and the c-plane. Co particles coated with such an FeCo alloy (FeCo / Co) maintain the Co crystal structure even in the FeCo alloy, and can form particles having different compositions and lattice constants at the central portion and the outer peripheral side. Uniaxial magnetic anisotropy occurs. Since the outer peripheral side of the FeCo / Co particles is easily oxidized, a fluoride is formed to a thickness of 1 nm by solution treatment. The particles were oriented in a magnetic field and then heat compression molded to obtain a magnet compact. The magnetic characteristics of the magnet are a residual magnetic flux density of 1.7 T and a coercive force of 20 kOe. When the rare earth element is not contained in the fluoride, a magnet not using the rare earth element is obtained.

  In this example, the hcp structure changes to the bcc structure depending on the composition and thickness of the FeCo alloy. Even if the bcc structure is mixed, if the volume ratio of the bcc structure is 50% or less, a large difference in coercive force is not recognized. The Co concentration of the FeCo alloy is preferably in the range of 0.1% to 60%, and the average thickness is preferably 1 to 50 nm or less. If the Co concentration is less than 0.1%, the bcc structure exceeds 50%, and the coercive force is significantly reduced. On the other hand, if it exceeds 60%, it becomes difficult to set the residual magnetic flux density of the compact to 1.7 T. If the average thickness is less than 1 nm, it is difficult to increase the residual magnetic flux density. If the average thickness exceeds 50 nm, the bcc phase becomes stable and the bcc volume exceeds 60%, and the coercive force is small. If the Co concentration of the FeCo alloy is in the concentration range of 0.1% to 60% and the average thickness is 1 to 50 nm or less, matching strain is introduced at the interface between the Co particles and the FeCo alloy, and in the vicinity of the interface. A crystal orientation relationship is established. The coercive force can be increased by increasing the magnetocrystalline anisotropy energy by unevenly distributing metal elements and metalloid elements other than Fe and Co, which are the third elements, in the vicinity of the matching interface.

  As the fluoride, any fluoride capable of solution processing can be used, and an oxyfluoride is formed at the time of thermoforming. Further, when the molding temperature exceeds 900 ° C., a part of the FeCo alloy having the hcp structure undergoes a phase transition to the bcc structure. Therefore, it is necessary to add an additional element that stabilizes the hcp structure or to perform the molding temperature at a low temperature.

  An oxyfluoride containing Fe and Co represented by FeaCobOcFd (a, b, c and d are positive numbers) grows at or near the grain boundary of Co or FeCo alloy. This oxyfluoride can contain a metal element other than Fe or Co, and the metal element can be unevenly distributed in the vicinity of the oxyfluoride. This oxyfluoride grows in a layered or granular form, and contributes to an increase in coercive force by introducing lattice strain into the crystal of Co or FeCo alloy near the interface.

  In this embodiment, part of the hcp structure may be an fcc or bct structure. A ferromagnetic alloy or a ferromagnetic compound having uniaxial anisotropy can be used in place of Co in this embodiment.

  An alcohol solvent fluoride solution obtained by mixing a fluoride solution containing Co and a fluoride solution containing Fe is evaporated in a magnetic field of 10 kOe to precipitate Fe and Co from the solution. By heating to 350 ° C. or higher, FeCo alloy crystals continuous in the magnetic field direction are formed. Fluoride grows on the outer periphery of the FeCo crystal and suppresses oxidation of the FeCo crystal. The ratio of Co and Fe can be arbitrarily controlled. When Co: Fe = 1: 1, FeCo particles having an average particle diameter of 10 nm can be created, and magnet powder having a magnetic field direction that can be easily magnetized can be created. The inside of the powder having a particle size of 10 nm has an hcp structure around Co and a bcc structure around Fe, and both structures are confirmed, and uniaxial magnetic anisotropy is recognized as a whole. By placing various high coercivity alloys such as various rare earth-containing compounds, AlNiCo alloys, MnGa alloys, MnAl alloys in the gaps between the magnetic particles having high continuity of the magnetic particles in the direction parallel to the magnetic field direction, A magnet having a coercive force of 10 kOe or more and a residual magnetic flux density of 1.6 T can be obtained, and the amount of rare earth used can be reduced.

  In this example, the easy magnetization direction is parallel to the magnetic field direction, and the crystal structure of the FeCo alloy includes bct structure in addition to hcp and bcc. Further, in the fluorine-containing compound, an amorphous structure containing Fe or Co or a crystal structure of orthorhombic, rhombohedral, hexagonal, monoclinic and tetragonal can be confirmed. Thus, a powder or crystal in which a plurality of ferromagnetic phases are observed in the crystal at a particle size of 10 nm and a plurality of ferromagnetic phases exhibiting uniaxial magnetic anisotropy is formed is not FeCo alloy as in this example. Fe-M alloy (M is a metal element other than Fe), Mn-M alloy (M is a metal element other than Mn), Co-M (M is a metal element other than Co), Cr-M (M is An alloy system such as a metal element other than Cr can be realized by a precipitation process from a solution, and a magnet material having a coercive force of 10 kOe can be produced.

  In the said Example, when an average particle diameter exceeds 50 nm, a stable bcc structure will exceed 50%, and a coercive force will fall to 1 kOe or less. The average particle diameter with a coercive force exceeding 5 kOe is 20 nm or less, and becomes 10 kOe when it is 10 nm or less. In addition, the coercive force tends to decrease below 2 nm. For this reason, the average particle size is desirably in the range of 2 to 20 nm. The particle shape has a shape anisotropy extending in the direction of applying a magnetic field, but uniaxial anisotropy can be added even to particles having an indefinite shape, a spherical shape or a plate shape.

  In addition to the above methods, the magnetic particles for magnets of 20 nm or less as in this example can use various synthesis methods such as sol-gel method, coprecipitation method, precipitation method using carbon nanotubes, and synthesis method using organisms (bacteria). .

Pure Fe (purity 99.99%) and pure Co (purity 99.99%) were weighed and an Fe-40% Co alloy was prepared in an Ar + 10% H ₂ atmosphere. Using this mother alloy, a powder was prepared by gas atomization. Ar + 10% H ₂ gas was used for gas atomization, created at an injection pressure of 15 MPa, and classified to a powder diameter of 50 μm or less. The average particle size is 30 μm. This powder was subjected to a TbF-based solution treatment to form an amorphous fluoride film on the powder surface with a film thickness of 2 nm, and then the solvent was removed by heat treatment to obtain a magnetic powder having a saturation magnetization of 210 emu / g. After inserting this powder into a WC die, applying an alternating magnetic field of 10 kOe and applying a load of 1 t / cm ² , impregnation with a slurry of Nd ₂ Fe ₁₄ B fine powder (average particle size 0.1 to 1 μm) and a solvent. Then, after applying a magnetic field of 20 kOe orthogonal to the magnetic field application direction, a load of ² t / cm ² was applied and the resultant was molded by discharge plasma sintering. The ratio of FeCo alloy to Nd ₂ Fe ₁₄ B is 9: 1. The temperature was increased at a rate of 200 ° C./min and maintained at 800 ° C., then a load of ² t / cm ² was applied, and the mixture was cooled at a cooling rate of 300 ° C./min. A TbCuAgF-based treatment liquid was applied to this molded body and then diffused at 700 ° C., so that Tb, Cu, and Ag were unevenly distributed in the vicinity of the grain boundaries. The magnetic properties of this molded body were Br of 1.7 T and Hc of 18 kOe.

A magnet having a residual magnetic flux density exceeding 1.6 T as in this embodiment can be realized by magnetically coupling an FeCo alloy having a large saturation magnetization with the magnetization of Nd ₂ Fe ₁₄ B, and Nd ₂ Fe ₁₄ B is impregnated. Therefore, the average particle size of Nd ₂ Fe ₁₄ B needs to be smaller than the average particle size of the FeCo alloy. At the grain boundary triple point, Nd ₂ Fe ₁₄ B, boride, or rare earth oxide is recognized in addition to the acid fluoride. In addition to the FeCo alloy, an FeM alloy having a saturation magnetization of 170 emu / g or more (M is one or more of metals or metalloid elements other than Fe) can be used. In addition to Nd ₂ Fe ₁₄ B, SmCo, AlNiCo, FeCoCr, CoPt, FePt, MnBi, MnAs, MnCo, MnAlC, MnN, MnC, MnF, MnFe, CrMn Alloy systems such as MnNiF and MnGaF can be used.

When the material to be impregnated in this example is a TbF-based alcohol solution, a magnet having a coercive force of 5 to 10 kOe after molding is obtained when the TbF-based film is 0.1 wt%, and the amount of rare earth elements contained in the magnet Is less than 0.1 wt%. In this magnet, the FeCo alloy has a bcc structure, and TbF ₃ , TbF ₂ , TbOF, and Tb ₂ O ₃ can be confirmed as the TbF-based film. Further, a TbFe, TbCo-based intermetallic compound is locally formed. When the load at the time of thermoforming exceeds 1 t / cm ² , the increase in coercive force and the increase in residual magnetic flux density become remarkable, and the maximum energy product increases by 10 to 20% by changing from 1 t / cm ² to 2 t / cm ^2. . The cooling rate after molding is 300 ° C./min, and the coercive force is increased by 10% as compared with no magnetic field by cooling in a magnetic field of 10 kOe or more. When the magnetic field application direction and the magnetization direction for cooling in the magnetic field are the same, the direction connecting the magnetic poles (S pole and N pole) is substantially perpendicular to the magnetization direction.

  The coercivity of the FeCo alloy is influenced by the magnetic properties of the interface, in addition to the magnetocrystalline anisotropy of the FeCo alloy itself. The magnetic properties of the interface depend on the partner material in contact with the grain boundary or interface and the crystal structure and atomic arrangement in the vicinity. Such grain boundaries and interfaces are nearly two-dimensional and are very different from bulk stable three-dimensional crystals. At such a low-dimensional interface, the atomic arrangement of Co, Fe, and Tb is anisotropic. Such anisotropic atomic arrangement, strain (stress), lattice matching, and interface discontinuity affect the magnetic structure near the interface. In order to control the magnetic structure, it is important to design and create the grain boundary phase artificially. Co, Fe, Tb two-dimensional structure, low-dimensional (one-dimensional, two-dimensional) arrangement, low-dimensional stress at the interface By forming the additional structure, the magnetic coupling structure with the adjacent main phase through the interface, and the Tb uneven structure near the interface, the anisotropic energy can be increased.

  When a metal element such as Co, Fe or Tb forms a one-dimensional structure in a specific direction of the interface at the interface, the metastable phase of the interface can be achieved by cooling in a magnetic field. The metastable phase at the interface is a compound such as an oxide, fluoride, carbide, nitride or boride or an intermetallic compound, and grows adjacent to a compound such as metallic glass or quasicrystal or an unevenly distributed phase. That is, two types of metastable phases grow adjacent to each other, so that the metastable phase is stabilized, the lattice strain and the matching interface remain stably up to a high temperature, the magnetic anisotropy energy increases, and the coercive force increases.

  In addition, the structure of the above metal elements arranged two-dimensionally in a lattice shape, hexagonal shape, rhombus shape, or triangular shape is the concentration and arrangement position (structure or orientation) of oxygen, carbon and fluorine or boron arranged at the interface, surface Since it depends on reconstruction, dislocations, defect structures, etc., it is necessary to use preparation conditions that can control the concentration and structure of these elements.

  Since these structural controls involve movement and rearrangement of atoms, it is necessary to add thermal energy to move them. The temperature must be 100 ° C or higher, preferably 400 ° C or higher. The structure control is an interface structure that reacts to external magnetic fields, external stresses, and external factors in addition to powder production conditions such as composition, particle size, and grain shape. Must be created.

  In this embodiment, a two-dimensional structure mainly composed of Tb and F or O is formed at the interface, and Fe or Co is bonded with a specific adjacent atomic structure in the vicinity thereof, and this Fe or Co and the main phase FeCo phase. Are magnetically coupled to suppress magnetization reversal. In the vicinity of the local grain boundary having this adjacent atomic structure, the distance between Fe-Fe, Fe-Co, and Co-Co atoms in a specific direction is 0.1% to 20% on average than the distance between atoms in the bulk stable state. long. The magnetic anisotropy in the vicinity of the grain boundary increases due to the expansion and contraction of interatomic positions of the low coordination number atoms.

  As described above, as the magnetic anisotropy in the vicinity of the grain boundary increases, the magnetic anisotropy of the unit cell in contact with the grain boundary or the magnetic anisotropy of the atomic plane in contact with the grain boundary is different from the average crystal magnetic anisotropy in the grain. It becomes 2 to 100 times the value of the directionality. Further, the direction in which the magnetic anisotropy energy becomes maximum rotates by 10 to 90 degrees from the direction in which the magnetic anisotropy energy in the grains becomes maximum. The direction in which the magnetic anisotropy energy is maximized is less likely to cause magnetization reversal when the angle difference from the intra-granular direction is smaller, and is preferably 45 degrees or less, but the ratio of the magnetic anisotropy energy exceeds 5 times. In this case, the energy of the system is lowered when the magnetic anisotropy in the grain is strongly influenced by the magnetic anisotropy in the vicinity of the grain boundary and the magnetic anisotropy in the grain boundary is aligned in the direction of the magnetic anisotropy. There is no particular limitation as long as the angle difference is within 90 degrees.

Fe ²⁺ , Fe ³⁺ , Co ²⁺ using ferrous chloride (FeCl ₂ .4H ₂ O), ferric chloride (FeCl ₃ .6H ₂ O), cobalt chloride (CoCl ₂ .6H ₂ O) After preparing an aqueous solution, ammonia water is added, and further a fluoride solution is mixed, and FeCo alloy, (Fe, Co) ₃ O ₄ , (Fe, Co) F compound, (Fe, Co) OF compound A slurry consisting of In this slurry, FeCo-based alloy particles are mixed with a particle diameter of 2 to 50 nm. By magnetic separation, ferromagnetic particles having a saturation magnetization of 50 to 230 emu / g can be separated and extracted. By subjecting the extracted slurry to magnetic field orientation and heating by electromagnetic waves, oxides, fluorides or oxyfluorides are selectively heated and sintered, and at the same time, residual stress can be induced in the compact. Further, when the particle diameter is 10 nm or less, the ratio of the volume of crystal lattices arranged on the particle surface to the total number of crystal lattices increases to about 10% or more, so the influence of the interface greatly affects the structure and magnetic properties. .

  In particular, as in this example, magnetostriction due to electromagnetic wave heating in a magnetic field, manifestation of stress, shape anisotropy and interface anisotropy due to thermal stress, growth of fluorine-containing metastable phase and manifestation of lattice strain remaining at the interface As a result, the crystal lattice near the interface is locally distorted and the magnetocrystalline anisotropy energy is increased. By increasing the magnetocrystalline anisotropy, a molded magnet mainly composed of a FeCo alloy having a coercive force of 5 to 10 kOe can be formed. Pulsed electromagnetic heating is effective for high coercivity, and it is possible to sinter while suppressing the growth of crystal grains by applying electromagnetic waves for a time of 1 ms or less and applying and heating at high frequencies. The direction of anisotropy can be controlled by application.

In this example, when the FeCo-based alloy is Fe ₅₀ Co ₅₀ , when the average particle size of the Fe ₅₀ Co ₅₀ particles is 5 nm, the lattice strain of the crystal lattice within 1 nm from the interface and the lattice strain at the center are averaged. Thus, a difference of 1% or more occurs, and oxides and oxyfluorides grow on a part of the particle surface. Some fluorine-containing phases exhibit antiferromagnetism. In addition, a difference is observed in the magnetization curve between the magnetic field application direction and the perpendicular direction, and the magnetocrystalline anisotropy energy increases and the coercive force increases due to the occurrence of strain due to the magnetic field application. When the applied magnetic field is small, sufficient distortion does not appear and the coercive force does not increase. Therefore, when a coercive force is required, it is necessary to apply a magnetic field of a certain value or more. When the material of this embodiment is used in a magnetic circuit such as a rotating machine, it is desirable to apply a bias magnetic field using a general permanent magnet or the like. By controlling the bias magnetic field, the case where coercive force is required as a permanent magnet and the case where the permanent magnet characteristic is unnecessary can be realized by the same material system, so that high torque and high efficiency can be achieved.

  In the magnet of this embodiment, oxides and oxyfluorides grow at the grain boundaries or in the vicinity of the grain boundaries. In particular, the growth of CokFelOmFn (k, l, m, and n are positive numbers) and the composition near the oxyfluoride. And the structure (crystal structure and strain) affect the coercive force.

  In this embodiment, by adding a rotational component in the direction of applying a magnetic field, particles connected in a spiral shape, screw shape, or spring shape can be created, and shape anisotropy can be added.

Fe-25 atom% Co particles are made into a fiber-shaped powder by a rapid cooling method. A FeCo alloy melted at high frequency in an Ar gas atmosphere is pressed into a water bath to obtain a fibrous powder. The FeCo alloy powder has a diameter of 2 to 200 μm and a length of 5 to 500 μm. This powder is treated with an NdTbF-based solution to form an NdTbF-based film on the surface of the FeCo alloy powder, and then mixed with an NdFeB-based sintered powder having an average particle size of 0.5 to 5 μm. The mixing ratio of the FeCo alloy powder and the NdFeB-based sintered powder is 2: 8. In the temporary forming step after mixing, the NdFeB-based sintered powder has an average c-axis direction parallel to the magnetic field application direction, and the length direction of the FeCo alloy powder (the 5-500 μm direction) is parallel to the magnetic field application direction. Become. The conditions of the temporary forming process are a magnetic field of 10 kOe and a pressure of 1 t / cm ² . This temporary molded body is put in a heat treatment furnace and heated to 1050 ° C., and then a magnetic field of 20 kOe is applied in a direction parallel to the magnetic field application direction at the time of forming the temporary molded body, and FeCo and NdFeB system at a cooling rate of 1 to 10 ° C./second. The temperature range including the Curie temperature of the magnetic powder (850 ° C. to 300 ° C.) is cooled. Furthermore, a sintered magnet having a density of 7.0 to 7.6 g / cm ³ is obtained through an aging treatment at 300 to 600 ° C.

  The characteristics of the sintered magnet material manufactured in this example will be described below. The ferromagnetic phases that bear the magnetic flux density of the sintered body are FeCo alloy and NdFeB alloy, and magnetic coupling or strain acts between these ferromagnetic phases. For the FeCo alloy, a composition higher than the saturation magnetization of the NdFeB alloy is selected, and various 3d or 4d transition metal elements or rare earth elements are contained in an amount of 0.1 to 20 atomic% in order to increase the magnetocrystalline anisotropy.

  When the FeCo alloy is an Fe-25% -1% Zr alloy containing 1 atomic percent of Zr, the mixing ratio of the FeCoZr alloy powder and the NdFeB-based sintered powder is 2: 8, and the above-mentioned preparation conditions are obtained by using the NdFeF-based treatment liquid. The magnet characteristics of the magnet sintered below have a maximum energy product of 67 MGOe and a coercive force of 2 MA / m. When the transition metal element such as Zr is contained exceeding 20 atomic%, the residual magnetic flux density is remarkably lowered. On the other hand, when the content is less than 1%, the coercive force decrease and the squareness decrease remarkably.

  The features of the sintered magnet of this example are as follows. 1) The average grain size of the FeCo alloy is larger than the average crystal grain size of the NdFeB alloy. 2) The uneven distribution of metal elements added to part of the grain boundaries or constituent elements of the fluoride treatment film, oxygen, and carbon can be confirmed. 3) The saturation magnetization of the FeCo-based alloy is larger than the saturation magnetization of the NdFeB-based sintered powder. 4) The grain growth direction of the FeCo alloy is not isotropic and is anisotropic. 5) Ferromagnetic phases having different degrees of order are observed in the FeCo alloy. 6) The shape anisotropy of the FeCo alloy is larger than that of the NdFeB alloy.

  In this example, a magnetic coupling acts between the FeCo-based alloy and the NdFeB-based alloy, and any of oxides, oxyfluorides, borides, carbides, etc. can be confirmed at the grain boundaries. The iron content in the grains is higher than the center of the grain boundary, and the concentrations of heavy rare earth elements and additive elements tend to be high at the ends of the ferromagnetic phase crystal grains in contact with the grain boundaries. In particular, (Fe, Co) mCn, (Fe, Co) m (C, F) n, (Fe, Co, M) mCn, (Fe, Co, M) m (C, F) n Or, (Fe, Co, M) m (C, F, O) n grows to increase the coercive force by 1 to 5 kOe (m and n are positive numbers, and M is a transition metal element other than Fe and Co). In addition, lattice strain is introduced into a part of the crystal in the FeCo alloy. This lattice strain is introduced because the thermal expansion coefficient differs between the FeCo-based alloy and the NdFeB-based alloy in the cooling process after sintering. By introducing lattice strain, the magnetocrystalline anisotropy of the FeCo alloy increases and the coercive force increases.

Fe-30 atomic% Co powder prepared by the water atomization method is mixed with Nd ₂ Fe ₁₄ B-based powder, and after hot forming, hot-formed and sintered. The mixing ratio of the FeCo-based powder and the NdFeB-based powder is 4: 6, and the average particle diameter is 10 μm and 4 μm, respectively. The FeCo-based powder prevents diffusion into the liquid phase during sintering by NdF-based solution treatment. Various kinds of transition metal elements (transition metal elements other than Fe and Co) are added to the FeCo-based powder in the range of 0.1 to 10 atomic% as an additive element, and the magnets are unevenly distributed near the grain boundaries after sintering. It is possible to improve the heat resistance. Preformed in a temperature range performed in a magnetic field of 10kOe under a load of 2t / cm ^2, heat molding after 1000 to 1100 ° C. the preformed body in the temperature range of 300 to 900 ° C. under a load of 1~10t / cm ² Sinter. After sintering, an aging treatment was performed to obtain a sintered magnet. The squareness of the demagnetization curve is reduced when the pre-sintering heat forming process is not used, but by using the heat forming process, the squareness is increased and a maximum energy product of 60 to 80 MGOe is obtained. It is done. By applying a magnetic field of 10 to 100 kOe at the time of heat forming, the degree of orientation can be increased to improve the squareness. The growth of carbides, borides, oxides or oxyfluorides can be confirmed in part of the grain boundaries, and the uneven distribution of the transition metal elements or elements such as Ga and Al can be confirmed in the vicinity of these grain boundary products.

  In the above production process, when sintering is performed without introducing the pre-sintering heat forming step, the maximum energy product is 40 to 55 MGOe, and the effect of adding the FeCo-based powder is difficult to obtain. Even when a low melting point sintering aid is added to facilitate sintering, it is 50-60 MGOe, and the effect of increasing the maximum energy product is small. When the thermoforming is performed at a low temperature of less than 300 ° C., the magnetic properties are not improved because the crack orientation of the powder is disturbed. Molding in the temperature range exceeding 900 ° C. is remarkably consumed by the mold and is difficult to mass-produce. Also, in such a high temperature range, the fluoride film is easily peeled off, and mutual diffusion occurs easily, resulting in deterioration of magnetic characteristics.

  The FeCo powder prepared by the water atomization method contains 1000 ppm of oxygen, and an oxyfluoride or oxide such as NdOF is formed on the powder surface after the NdF treatment. Such surface products do not diffuse easily and some of them remain at the grain boundaries after sintering. By making the oxygen concentration of the FeCo-based powder less than 500 ppm, the growth of such oxygen-containing materials is suppressed, and carbides grow. The coercive force increases when a metastable phase of (Fe, Co) mCn and (Fe, Co, M) m (C, F) n grows in the vicinity of the grain boundary among carbides. In the above, m and n are positive numbers, and M is a transition metal element other than Fe and Co.

1 Nd ₂ Fe ₁₄ B crystal grains 2 Heavy rare earth element-containing oxide 3 Oxide fluoride 4 Rare earth rich grain boundary phase 5 FeCo alloy crystal grains 6 Heavy rare earth element-containing FeCo alloy

Claims (8)

In sintered magnets containing iron alloys, rare earth iron boron alloys and oxyfluorides,
The iron-based alloy has a saturation magnetization larger than that of the rare earth iron boron-based alloy,
Heavy rare earth elements are unevenly distributed in the vicinity of grain boundaries between the iron-based alloy and the rare-earth iron boron-based alloy,
The average crystal grain size of the iron-based alloy is (a), the average crystal grain size of the rare earth iron-boron alloy is (b), and the average crystal grain size ratio of the iron-based alloy to the rare earth iron-boron alloy is (a) / B), a sintered magnet having a relationship of 1 <(a / b) <100. The sintered magnet according to claim 1, wherein
A sintered magnet characterized in that the crystal structure of the iron-based alloy is a bcc or bct structure. The sintered magnet according to claim 1, wherein
A sintered magnet characterized in that a saturation magnetic flux density of the iron-based alloy is higher than a saturation magnetic flux density of the rare earth iron boron-based alloy. The sintered magnet according to claim 1, wherein
A sintered magnet, wherein a magnetic coupling occurs between the iron-based alloy and the rare earth iron boron-based alloy, and anisotropy of a shape or a magnetization curve is added to the iron-based alloy. The sintered magnet according to claim 1, wherein
A sintered magnet, wherein the crystal structure of the oxyfluoride is a cubic structure. The sintered magnet according to claim 1, wherein
A sintered magnet, wherein the rare earth iron boron alloy and the iron alloy crystals are adjacent to each other through a grain boundary. The sintered magnet according to claim 1, wherein
A sintered magnet, wherein the orientation of the rare earth iron boron alloy is higher than the orientation of the iron alloy. The sintered magnet according to claim 1, wherein
The sintered magnet characterized in that the saturation magnetization of the iron-based alloy is 170 emu / g to 240 emu / g.