Magnetic particles containing manganese-aluminum alloy, and method for producing such magnetic particles

Abstract

The present invention provides magnetic particles containing a manganese-aluminum alloy with suitable magnetic field orientation. The present invention pertains to magnetic particles containing a manganese-aluminum alloy, wherein the magnetic particles have a substantially spherical shape with a particle diameter in the range of 0.1-1000 μm, a twin structure, and a plurality of parallel streaks on the surfaces thereof, the manganese-aluminum alloy has a τ phase, the magnetic particles further include alumina, the abundance ratio of the alumina included in the magnetic particles is in the range of 0.1-30 mass%, the abundance ratio of the manganese-aluminum alloy included in the magnetic particles is in the range of 70-99 mass%, and the abundance ratio of the τ phase included in the magnetic particles is in the range of 10-99 mass%.

Description

Magnetic particles comprising manganese-aluminum alloys and methods for producing such magnetic particles

[0001] The present invention relates to magnetic particles comprising manganese-aluminum alloys and to methods for making such magnetic particles.

[0002] It has been known that magnetic particles of manganese-aluminum alloys containing the ferromagnetic τ phase can be used as magnetic materials.

[0003] Manufacturing Rev.8,10(2021),VVPopov Jr.et al.,Published by EDP Sciences 2021,Special Issue The emerging materials and processing Technologies Radu Piticescu and Ioana Vlaicu(Eds.)

[0004] In general, the crystal structure of manganese-aluminum alloy particles containing the τ phase contains twins as impurities, and it is known that such twins have a negative effect on the magnetic field orientation of the alloy particles (Non-Patent Document 1). Furthermore, if the magnetic field orientation is poor, it becomes difficult to develop magnetic anisotropy in the magnetic particles, which makes it difficult to improve the magnetic properties.

[0005] The present invention has been made in view of the above background, and an object of the present invention is to provide magnetic particles containing a manganese-aluminum alloy that have better magnetic field orientation, and a method for producing such magnetic particles.

[0006] The present invention provides magnetic particles comprising a manganese-aluminum alloy, the magnetic particles having a substantially spherical shape with a particle diameter in the range of 0.1 μm to 1000 μm, a twin crystal structure, and a plurality of parallel stripes on the surface, the manganese-aluminum alloy having a τ phase, and the magnetic particles further containing alumina, the abundance of the alumina contained in the magnetic particles being in the range of 0.1 mass % to 30 mass %, the abundance of the manganese-aluminum alloy contained in the magnetic particles being in the range of 70 mass % to 99 mass %, and the abundance of the τ phase contained in the magnetic particles being in the range of 10 mass % to 99 mass %.

[0007] The present invention also provides a method for producing magnetic particles containing a manganese-aluminum alloy, comprising: (1) mixing manganese particles having a maximum particle diameter of 1000 μm or less, an aluminum source, carbon particles, an activator containing a halide, and a sintering inhibitor having a maximum particle diameter that is 0.0002 to 3 times that of the manganese particles to obtain a mixed powder; (2) calorifying the mixed powder, wherein the mixed powder is heated to a maximum temperature of 1000°C to 1235°C; and (3) cooling the calorified treated body from the maximum temperature to a first temperature at a first cooling rate, wherein the first temperature is in the range of 500°C to 400°C, and the first cooling rate is in the range of 100°C / h to 400°C / h. (4) cooling the treated body from the first temperature to a temperature of 300°C or less at a second cooling rate, the second cooling rate being 600°C / h or more; and after (4), magnetic particles containing a manganese-aluminum alloy are obtained, in which the ratio of aluminum to manganese (Al / Mn) in the manganese-aluminum alloy is in the range of 25 / 75 to 35 / 65 in mass ratio.

[0008] The present invention can provide magnetic particles containing a manganese-aluminum alloy that have better magnetic field alignment properties, and can also provide a method for producing such magnetic particles.

[0009] 1 is a perspective view schematically showing one form of magnetic particles containing a manganese-aluminum alloy according to one embodiment of the present invention. It is a diagram schematically showing a cross section taken along line A-A in FIG. 1. It is a diagram schematically showing one example of a flow of a method for producing magnetic particles according to one embodiment of the present invention. It is a diagram schematically showing a state in which mixed powder is filled into a reaction vessel in a method for producing magnetic particles according to one embodiment of the present invention. It is a graph schematically showing cooling conditions for a treated body in a method for producing magnetic particles according to one embodiment of the present invention. It is a photograph showing an example of the surface morphology of magnetic particles contained in a powder (Powder 1) according to one embodiment of the present invention. It is a photograph showing an example of the surface morphology of magnetic particles contained in a powder (Powder 2) according to another embodiment of the present invention. It is a photograph showing an example of the surface morphology of magnetic particles contained in a powder (Powder 5) according to yet another embodiment of the present invention. It is a photograph showing an example of the cross-sectional morphology of magnetic particles contained in a powder (Powder 2) according to one embodiment of the present invention. It is a photograph showing an example of the surface morphology of magnetic particles according to a comparative example. It is a photograph showing an example of the surface morphology of magnetic particles according to a comparative example. It is a photograph showing an example of the cross-sectional morphology of magnetic particles according to a comparative example. It is a photograph showing an example of the distribution of twin boundaries of magnetic particles contained in a powder (Powder 1) according to one embodiment of the present invention. 13A is a SEM photograph of a cross section, and FIG. 13B is an image highlighting the twin boundary. It is a graph showing the hysteresis curve obtained for a powder (Powder 1) according to one embodiment of the present invention.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] In one embodiment of the present invention, there is provided magnetic particles comprising a manganese-aluminum alloy, the magnetic particles having a substantially spherical shape with a particle diameter in the range of 0.1 μm to 1000 μm, a twin crystal structure, and a plurality of parallel stripes on the surface, the manganese-aluminum alloy having a τ phase, and the magnetic particles further containing alumina, the abundance of the alumina contained in the magnetic particles being in the range of 0.1 mass % to 30 mass %, the abundance of the manganese-aluminum alloy contained in the magnetic particles being in the range of 70 mass % to 99 mass %, and the abundance of the τ phase contained in the magnetic particles being in the range of 10 mass % to 99 mass %.

[0012] As mentioned above, the crystalline structure of manganese-aluminum alloy particles containing the τ phase usually contains twins as impurities, and it is known that such twins have a negative effect on the magnetic orientation of the alloy particles. Furthermore, if the magnetic orientation is poor, it becomes difficult to develop magnetic anisotropy in the magnetic particles, which makes it difficult to improve the magnetic properties.

[0013] In contrast, magnetic particles according to one embodiment of the present invention contain a manganese-aluminum alloy containing the τ phase and have a fine spherical shape with a particle diameter ranging from 0.1 μm to 1000 μm. The magnetic particles according to one embodiment of the present invention also have a twin crystal structure. Furthermore, the magnetic particles containing a manganese-aluminum alloy according to one embodiment of the present invention are characterized by having a plurality of parallel "stripe" on the surface of the sphere.

[0014] As will be described later, it has been found from the results of cross-sectional observation of the magnetic particles that these "streaks" correspond to the "order" of the crystalline structure formed inside the spherical particles.

[0015] Due to the presence of such "order" in the crystal structure, magnetic particles containing a manganese-aluminum alloy according to one embodiment of the present invention can exhibit good magnetic field orientation, despite the inclusion of twins in the crystal structure. As a result, when magnetic particles according to one embodiment of the present invention are magnetically oriented, better magnetic properties can be obtained.

[0016] (Magnetic Particles According to an Embodiment of the Present Invention) Next, with reference to FIGS. 1 and 2, magnetic particles containing a manganese-aluminum alloy according to an embodiment of the present invention will be described in more detail.

[0017] 1 and 2 are schematic diagrams showing one form of the surface and cross section, respectively, of a magnetic particle containing a manganese-aluminum alloy according to one embodiment of the present invention (hereinafter also simply referred to as a "first magnetic particle").

[0018] Fig. 1 shows a schematic representation of the surface morphology of the first magnetic particle, and Fig. 2 shows a schematic representation of the cross-sectional morphology taken along line AA in Fig. 1.

[0019] As shown in FIG. 1, the first magnetic particle 100 is generally spherical in shape and has a surface 110 .

[0020] In this application, "substantially spherical" or "substantially spherical shape" is not limited to a pure sphere, but also means a shape such as an ellipsoid, in which the dimensional difference in any two directions arbitrarily selected from the mutually orthogonal X-axis direction, Y-axis direction, and Z-axis direction is within ±20%.

[0021] The particle diameter of the first magnetic particles 100 is in the range of 0.1 μm to 1000 μm, preferably in the range of 0.1 μm to 75 μm, and more preferably in the range of 0.1 μm to 38 μm.

[0022] The first magnetic particle 100 also has a twin structure. The locations where the twins are contained are not particularly limited. The twins may be arranged randomly within the crystal, or the twins may be arranged orderly, or the first magnetic particle 100 may have both a portion where the twins are arranged randomly and a portion where the twins are arranged orderly.

[0023] The first magnetic particle 100 also has a plurality of parallel streaks 112 on the surface 110. The number of streaks 112 is not particularly limited, but may be, for example, four or more, six or more, or ten or more.

[0024] 1, the streaks 112 are formed over almost the entire surface 110 of the first magnetic particle 100. However, this is merely an example, and the streaks 112 may be formed over only a portion of the surface 110.

[0025] 1 may vary depending on the location. The minimum value of the pitch q of the streaks 112 is not particularly limited, but may be in the range of 0.1 μm to 50 μm, for example. In other words, the spacing between the streaks may be in the range of 0.1 μm to 50 μm.

[0026] 2, the first magnetic grain 100 has an "ordered" crystalline structure inside, i.e., a large number of groups of layered crystals 122 extending in parallel are found inside the first magnetic grain 100.

[0027] The first magnetic particle 100 preferably has layered crystals 122. Twin crystals contained in the first magnetic particle 100 are preferably oriented to form an "ordered" crystal structure inside the first magnetic particle 100, and the "order" of the twin crystals forms layered crystals 122, and a group of layered crystals formed by stacking the layered crystals 122 forms streaks 112 on the surface of the first magnetic particle 100. The twin crystals contained in the first magnetic particle 100 are thought to be oriented to form an "ordered" crystal structure by controlling the heat transfer during cooling and by performing a two-stage cooling process using a manufacturing method described below, with the alumina abundance rate, manganese-aluminum alloy abundance rate, and τ phase abundance rate each within a specific range.

[0028] 2, the layered crystals 122 are formed over almost the entire cross section of the first magnetic particle 100. However, this is merely an example, and the layered crystals 122 may be formed over only a portion of the cross section.

[0029] Here, the extension direction of each layer crystal 122 in Figure 2 corresponds to the extension direction of the streaks 112 in Figure 1. It has also been confirmed that as the number of surface streaks 112 increases, the number of internal layer crystals 122 also increases. In this case, the number of layer crystals 122 inside the particle may be greater than the number of surface streaks 112.

[0030] In this way, the first magnetic particle 100 has an "order" in the crystal structure that corresponds to the morphology of the surface streaks 112. The existence of such an "order" in the crystal structure allows the first magnetic particle 100 to exhibit high magnetic field orientation despite the inclusion of twin crystals.

[0031] When the first magnetic particles 100 are magnetically oriented, the direction of the magnetic field is parallel to the extension direction of the layered crystals 122 in most particles.

[0032] (Other Features of the First Magnetic Particles 100) The first magnetic particles 100 contain a manganese-aluminum alloy containing the τ phase and alumina.

[0033] The ratio of the manganese-aluminum alloy contained in the first magnetic particles 100 is in the range of 70% by mass to 99% by mass, and the ratio of alumina is in the range of 0.1% by mass to 30% by mass.

[0034] The proportion of the τ phase contained in the first magnetic particles 100 is in the range of 10% by mass to 99% by mass. The proportion of the τ phase contained in the first magnetic particles 100 is preferably at least 30% by mass, and more preferably at least 50% by mass, with the lower limit set forth above. By setting the proportion of the τ phase contained in the first magnetic particles 100 within the above range, magnetization of the magnetic powder is more easily manifested. This also makes it easier to improve the magnetic flux density of the magnet.

[0035] Alumina tends to be unevenly distributed on the surfaces 110 of the first magnetic particles 100 .

[0036] The manganese-aluminum alloy may further contain at least one of an ε phase, a β phase, and a γ phase, but the ε phase contained in the manganese-aluminum alloy is preferably 10 mass % or less.

[0037] In the first magnetic particles 100, the manganese-aluminum alloy may contain 65% to 75% by mass of manganese and 25% to 35% by mass of aluminum.

[0038] The manganese-aluminum alloy may further contain 0.1 atm % to 10 atm % of at least one of carbon and boron atoms.The manganese-aluminum alloy may contain 0.1% to 10% carbon in atomic ratio.

[0039] Additionally or alternatively, the manganese-aluminum alloy may contain at least one metal selected from the group consisting of silicon, titanium, niobium, molybdenum, tin, vanadium, iron, zinc, bismuth, copper, nickel, and chromium. These metals are hereinafter collectively referred to as "additive metals." The additive metal may be contained in an amount ranging from 0.1% to 10% by mass, for example, relative to the entire first magnetic particle 100.

[0040] When the first magnetic particles 100 contain such an additive metal, better magnetic properties can be obtained than when no additive metal is contained.

[0041] The first magnetic particles 100 may further contain 0.1% to 30% by mass of at least one of aluminum carbide and manganese aluminum carbide.

[0042] The first magnetic particles 100 having such characteristics exhibit magnetic properties when magnetized, even when they are individual particles, and therefore can be used as micromagnets.

[0043] Alternatively, the first magnetic particles 100 may be used as a powder containing a large number of first magnetic particles 100 .

[0044] Such a powder may, for example, contain 100 or more first magnetic particles 100. For example, the powder may contain 500 or more first magnetic particles 100, and in particular 1000 or more first magnetic particles 100.

[0045] Such powders may also have a maximum particle diameter of 1000 μm or less, for example, a maximum particle diameter of 500 μm or less or 100 μm or less.

[0046] Furthermore, when the value expressed by Mr / Ms is referred to as the remanent magnetic susceptibility P of the powder, the remanent magnetic susceptibility P may be 0.35 or more, where Mr is the remanent magnetization (emu / g) and Ms is the maximum magnetization (emu / g) measured by applying 10 kOe with a VSM.

[0047] As mentioned above, it has been understood that twins in manganese-aluminum alloy particles have a negative effect on magnetic field orientation, and therefore it is preferable to eliminate them as much as possible.

[0048] In contrast, in one embodiment of the present invention, twins are not actively eliminated in each manganese-aluminum alloy particle contained in the powder. Nevertheless, a powder containing first magnetic particles 100 according to one embodiment of the present invention can achieve a remanence P of 0.35 or more. In one embodiment of the present invention, by performing a two-stage cooling treatment and setting the abundance ratio of alumina, the abundance ratio of manganese-aluminum alloy, and the abundance ratio of τ phase within specific ranges, a twin structure of fine crystal grains can be formed, improving the coercivity and, as a result, improving the remanence P. The remanence P may be 0.40 or more.

[0049] In the powder according to one embodiment of the present invention, the configuration and effect of the first magnetic particles 100 described above allows for good magnetic field orientation.

[0050] (Method for Producing Magnetic Particles According to One Embodiment of the Present Invention) Next, a method for producing magnetic particles according to one embodiment of the present invention will be described with reference to FIG.

[0051] FIG. 3 is a schematic diagram showing an example of the flow of a method for producing magnetic particles containing a manganese-aluminum alloy according to one embodiment of the present invention.

[0052] As shown in FIG. 3 , a method for producing magnetic particles containing a manganese-aluminum alloy according to one embodiment of the present invention (hereinafter referred to as the “first production method”) includes the following steps: (1) obtaining a mixed powder by mixing manganese particles having a maximum particle diameter of 1000 μm or less, an aluminum source, carbon particles, an activator containing a halide, and a sintering inhibitor having a maximum particle diameter that is 0.0002 to 3 times that of the manganese particles (step S110); (2) calorifying the mixed powder, in which the mixed powder is heated to a maximum temperature of 1000° C. to 1235° C. (step S120); and (3) cooling the calorified treated body from the maximum temperature to a first temperature at a first cooling rate, in which the first temperature is in the range of 500° C. to 400° C. and the first cooling rate is in the range of 100° C. / h to 400° C. / h (step S130). (4) A step (step S140) of cooling the treated body from the first temperature to a temperature of 300°C or less at a second cooling rate, wherein the second cooling rate is 600°C / h or more.

[0053] Each step will be described in more detail below.

[0054] (Step S110) First, a mixed powder is prepared.

[0055] The mixed powder contains manganese particles, an aluminum source, carbon particles, an activator, and a sintering inhibitor. Each component will be described below.

[0056] (Manganese Particles) The manganese particles have a maximum particle diameter of 1000 μm or less.

[0057] The maximum particle diameter of the manganese particles may be, for example, in the range of 5 μm to 500 μm, preferably in the range of 10 μm to 200 μm, and more preferably in the range of 10 μm to 50 μm.

[0058] The smaller the maximum particle diameter of the manganese particles, the shorter the diffusion distance of aluminum during the calorifying treatment (step S120), and the shorter the heat treatment time.

[0059] Furthermore, if the maximum particle diameter of the magnetic particles containing manganese-aluminum alloy after calorizing treatment is reduced, the bulk density during molding can be easily increased, and molding into a desired shape becomes easier.

[0060] In the present application, the "maximum particle diameter" refers to the value at which the particle diameter is the largest. The "maximum particle diameter" can be obtained, for example, by classification using a sieve method. Alternatively, the "maximum particle diameter" may be actually measured by observation using a microscope, etc. In the examples of the present application, the "maximum particle diameter" was determined by classification using a sieve method.

[0061] (Aluminum Source) The aluminum source may be aluminum metal particles or aluminum alloy particles.

[0062] The maximum particle diameter of the aluminum source is selected to be smaller than the maximum particle diameter of the sintering inhibitor. For example, the maximum particle diameter of the aluminum source may be 0.29 times or less the maximum particle diameter of the sintering inhibitor.

[0063] The maximum particle diameter of the aluminum source may be, for example, in the range of 0.1 μm to 300 μm, preferably in the range of 1 μm to 200 μm, and more preferably in the range of 1 μm to 100 μm. The smaller the maximum particle diameter of the aluminum source, the more easily the aluminum source can enter the gaps between the sintering inhibitors, thereby shortening the heat treatment time.

[0064] (Carbon Particles) Carbon particles are known to stabilize the crystal structure of the τ phase, and in the present application, they play a role in synthesizing powder having a high τ phase fraction.

[0065] The carbon particles are selected from, for example, carbon black, graphite or carbon fibers.

[0066] The maximum particle diameter of the carbon particles is not particularly limited, but may be, for example, in the range of 0.1 μm to 100 μm.

[0067] The carbon particles are added in an amount of, for example, 0.1% by mass to 10% by mass relative to the total amount of the manganese powder and the aluminum powder, or 0.5% by mass to 1.5% by mass or 0.75% by mass to 1.25% by mass relative to the total amount of the manganese powder and the aluminum powder.

[0068] (Activator) The activator has the role of forming metal halide vapor during the calorification treatment of manganese particles and accelerating the calorification treatment.

[0069] The activator may include, for example, at least one of ammonium chloride, aluminum chloride, and aluminum fluoride, and is added in an amount ranging from 0.1% by mass to 10% by mass with respect to the total amount of the mixed powder.

[0070] (Sintering inhibitor) The sintering inhibitor may include at least one of alumina, kaolin, and silicon oxide.

[0071] The sintering inhibitor may have at least one shape selected from the group consisting of, for example, a sphere, a triangular pyramid, a triangular prism, a tetrahedron, a cone, and a cylinder.

[0072] The sintering inhibitor has a maximum particle diameter that is sufficiently larger than the manganese particles and the aluminum source. For example, the maximum particle diameter of the sintering inhibitor may be selected to be 3.4 times or more the maximum particle diameter of the manganese particles or the maximum particle diameter of the aluminum source.

[0073] The sintering inhibitor preferably has a maximum particle diameter that is 0.0002 to 3 times larger than that of the manganese particles.

[0074] The maximum particle diameter of the sintering inhibitor may be, for example, in the range of 50 μm to 5000 μm.

[0075] Two types of sintering inhibitors may be used: a first sintering inhibitor having a first average particle diameter and a second sintering inhibitor having a second average particle diameter. When two types of sintering inhibitors with different average particle diameters are used, it is preferable to use sintering inhibitors whose maximum particle diameters differ at a specific ratio based on sphere packing in Euclidean space (e.g., the average particle diameter of one sintering inhibitor is preferably 0.29 times or less), which is a reference for heterogeneous sphere packing. Accordingly, the ratio of the two sintering inhibitors used is preferably such that the sintering inhibitor with the smaller average particle diameter is 1 / 4 or less of the sintering inhibitor with the larger average particle diameter.

[0076] In the present application, the "average particle diameter" refers to the median diameter, which is the particle diameter with a cumulative frequency of more than 50%, measured by a particle size measurement method such as a wet laser light scattering method. In the present application, the measurement was carried out using the laser light scattering method.

[0077] (Mixed Powder) The above components are mixed to prepare a mixed powder.

[0078] The amount of manganese particles contained in the entire mixed powder is, for example, in the range of 3% by mass to 45% by mass. The amount of aluminum source contained in the entire mixed powder is, for example, in the range of 1% by mass to 15% by mass. The amount of sintering inhibitor contained in the entire mixed powder can be appropriately adjusted based on the amount of manganese particles and the amount of aluminum source, but is, for example, in the range of 40% by mass to 96% by mass.

[0079] In the mixed powder, the aluminum source is added so that the mass ratio of aluminum to manganese (Al / Mn) contained in the manganese-aluminum alloy particles to be produced falls within the range of 25 / 75 to 35 / 65.

[0080] If necessary, the mixed powder may further contain boron in an atomic ratio of 0.1% to 5%.

[0081] Furthermore, in addition to or alternatively, the mixed powder may contain at least one metal selected from the group consisting of silicon, titanium, niobium, molybdenum, tin, vanadium, iron, zinc, bismuth, copper, nickel, and chromium as an "additive metal."

[0082] The additive metal may be added in the form of metal particles, for example, in which case the size (maximum particle diameter) of the additive metal particles may be in the range of 0.1 μm to 100 μm, for example.

[0083] The additive metal may be added in a range of 0.1% by mass to 10% by mass relative to the entire mixed powder. The content of the additive metal may be 0.1% by mass to 5% by mass, or may be 0.1% by mass to 3% by mass, relative to the entire mixed powder. For example, when the mixed powder contains silicon as an additive metal, from the viewpoint of suppressing decomposition of the τ phase, the content of silicon is preferably 2% by mass or less, more preferably 1.5% by mass or less, even more preferably 1.0% by mass or less, and particularly preferably 0.5% by mass or less, relative to the entire mixed powder.

[0084] (Step S120) Next, the mixed powder prepared in step S110 is heat-treated. For this purpose, the mixed powder may be filled into a reaction vessel.

[0085] The reaction vessel is heated to calorify the manganese particles, i.e., aluminum produced from the aluminum source diffuses into the manganese particles, forming magnetic particles containing a manganese-aluminum alloy.

[0086] When the reaction vessel is heated, a large amount of heat is generated by the thermite reaction between the mixed powders, as aluminum reacts with the trace amounts of oxygen contained in the manganese particles.

[0087] When such a thermite reaction occurs, the temperature inside the reaction vessel becomes extremely high, and the treated mixture, i.e., the "treated mixture," may become agglomerated, with all particles firmly adhering to one another. Once such an agglomerated treated mixture is produced, it may become impossible to separate the sintering inhibitor from the treated mixture.

[0088] In contrast, in the first production method, the formation of a lumpy mixture can be significantly suppressed.

[0089] This feature will be described below with reference to FIG.

[0090] 4 is a schematic diagram showing an example of the state of the mixed powder when it is filled into a reaction vessel. As shown in FIG. 4, the components of the mixed powder, that is, manganese particles 352, aluminum source 354, carbon particles, activator, and sintering inhibitor 358, are each filled into the reaction vessel.

[0091] It should be noted that the carbon particles and the activator are omitted in Fig. 4. Also, it is assumed here that each component of the mixed powder is spherical.

[0092] Here, when the diameter of the sintering prevention agent 358 is sufficiently larger than the diameter of the manganese particles 352 and the diameter of the aluminum source 354, gaps 365 are formed between adjacent sintering prevention agents 358. Furthermore, the manganese particles 352 and the aluminum source 354 are disposed in the gaps 365 formed by the sintering prevention agent 358.

[0093] When the reaction vessel is heated with the components of the mixed powder arranged in this manner, even if a thermite reaction occurs in the reaction vessel, the possibility of manganese particles 352 adhering to sintering inhibitor 358 and / or other manganese particles 352 can be greatly reduced because voids 365 serve to provide numerous reaction "small compartments" for the calorification process.

[0094] As a result, the treated mixture produced after the heat treatment is not in the form of aggregated lumps, but rather the magnetic particles containing manganese-aluminum alloy are separated from the sintering inhibitor 358. This makes it possible to recover the magnetic particles containing manganese-aluminum alloy from the treated mixture in a subsequent step.

[0095] The filling rate of the sintering inhibitor 358 in the reaction vessel is preferably in the range of 50% to 80%.

[0096] In this way, in the first manufacturing method, the calorification treatment of the manganese particles 352 can be carried out by utilizing the gaps 365 that are generated between the sintering inhibitors 358 .

[0097] The treatment atmosphere for the calorifying treatment may be an inert atmosphere that does not contain oxygen, such as an argon gas atmosphere.

[0098] The processing temperature of the calorification process (hereinafter referred to as the "maximum temperature (T ｍａｘ The maximum temperature is, for example, in the range of 1000°C to 1235°C, and may be in the range of 1180°C to 1220°C. If the maximum temperature is low, the amount of τ phase produced is small, and if the temperature is too high, the τ phase will aggregate into clumps.

[0099] The treatment time is not particularly limited, but is, for example, in the range of 1 hour to 10 hours.

[0100] (Steps S130 to S140) Next, the calorified treated body is cooled.

[0101] In the first manufacturing method, two cooling steps, a first cooling step (corresponding to step S130) and a second cooling step (corresponding to step S140), are performed.

[0102] FIG. 5 shows a schematic diagram of the cooling conditions for the treated body.

[0103] A two-stage cooling process is shown schematically in Fig. 5. In Fig. 5, the horizontal axis represents the processing time, and the vertical axis represents the temperature of the processed body.

[0104] As shown in FIG. 5, when the treated body is cooled, first, the calorified treated body is cooled to the maximum temperature T ｍａｘ to the first temperature T １ It is cooled to.

[0105] Here, the first temperature T １ is in the range of 500°C to 400°C, and the first cooling rate is in the range of 100°C / h to 400°C / h.

[0106] First temperature T １is preferably in the range of 470°C to 400°C, more preferably in the range of 450°C to 400°C. The first cooling rate is preferably in the range of 150°C / h to 350°C / h, more preferably in the range of 150°C / h to 250°C / h.

[0107] Thereafter, the temperature of the treatment object is increased to the first temperature T １ When the temperature drops to 0°C, a second cooling treatment (II) is carried out for further cooling.

[0108] In the second cooling treatment (II), the treatment body is cooled to the first temperature T １ to the second temperature T ２ The alloy is cooled at a second cooling rate until the temperature reaches a temperature of 1000.degree.

[0109] Here, the second cooling rate is 600° C. / h or more. Therefore, in the second cooling treatment (II), the treated body is “rapidly cooled”.

[0110] Also, the second temperature T ２ is preferably 300° C. or less, may be 250° C. or less, may be 200° C. or less, for example, 100° C. or room temperature.

[0111] In the first manufacturing method, after step S140, spherical particles containing a manganese-aluminum alloy can be formed that have a characteristic morphology as shown in FIGS. 1 and 2 above. That is, spherical magnetic particles are obtained that have multiple streaks 112 on their surfaces, contain τ phase, and have a crystal structure that includes twins. That is, magnetic particles are obtained that contain a specific amount of τ phase and have a twin structure. Furthermore, by orienting the twins through the two-stage cooling treatment, layered crystals 122 are stacked to form an "ordered" crystal structure group, and multiple parallel streaks are generated on the surface, resulting in magnetic particles containing a manganese-aluminum alloy that have good magnetic field orientation.

[0112] The sintering inhibitor is then removed from the treated body, which may be done, for example, by sieving the treated mixture using a sieve.

[0113] This makes it possible to produce magnetic particles containing a manganese-aluminum alloy.

[0114] In the manganese-aluminum alloy of the resulting magnetic particles, the ratio of aluminum to manganese (Al / Mn) may be in the range of 25 / 75 to 35 / 65 by mass ratio.

[0115] The first manufacturing method is characterized in that the magnetic particles obtained contain small amounts of alumina and carbon or carbide.

[0116] Of these, alumina is thought to be produced as a result of part of the aluminum constituting the manganese-aluminum alloy being oxidized during the calorifying treatment.

[0117] The amount of alumina contained in the produced magnetic particles is in the range of 0.1% by mass to 30% by mass, and may be in the range of 1% by mass to 10% by mass, relative to the mass of the magnetic particles.

[0118] The carbon or carbide is derived from carbon particles contained in the mixed powder of raw materials.

[0119] That is, if some carbon particles react with the aluminum source contained in the mixed powder during the calorification treatment, aluminum carbide and / or manganese aluminum carbide is produced. On the other hand, if some carbon particles are dissolved in the manganese-aluminum alloy, carbon is detected in the alloy.

[0120] The amount of manganese-aluminum alloy contained in the magnetic particles is in the range of 85% by mass to 99% by mass, and may be in the range of 86% by mass to 98% by mass.

[0121] Furthermore, in the manganese-aluminum alloy contained in the magnetic particles, the τ phase may be in the range of 25% by mass to 99% by mass relative to the manganese-aluminum alloy, and the τ phase is preferably, for example, 30% by mass or more, and more preferably 50% by mass or more, relative to the manganese-aluminum alloy.

[0122] The manganese-aluminum alloy contained in the magnetic particles may contain at least one of the ε phase, β phase, and γ phase in addition to the τ phase.

[0123] In this application, the τ phase means a tetragonal structure of MnAl, the ε phase means a hexagonal structure of MnAl, and the β phase means a hexagonal structure of MnAl. ３ Al ２ means a Cubic structure, and the γ phase means Mn ５ Al ８ means a rhombohedral structure.

[0124] However, the ε phase is preferably present in an amount of 10 mass % or less based on the total mass of the manganese-aluminum alloy.

[0125] The maximum particle diameter of the obtained powder is, for example, 1000 μm or less, and preferably 500 μm or less.

[0126] Furthermore, the remanent magnetic susceptibility P of the obtained powder, expressed by the above-mentioned Mr / Ms, is 0.35 or more, and preferably 0.4 or more.

[0127] Although not fully understood at present, the following is thought to be the reason why, in the first manufacturing method, a powder containing a sufficient amount of τ phase can be manufactured by performing such a two-stage cooling treatment on the treated body.

[0128] In the first cooling process, the first temperature T １ is in the range of 500° C. to 400° C. Therefore, during cooling of the workpiece, the workpiece passes through a solidus (approximately 870° C.) that is lower than the ε-phase stable region in the binary phase diagram of MnAl.

[0129] Here, when the object to be treated is cooled relatively slowly (gradual cooling), the object to be treated can be supercooled to the metastable region of the τ phase (about 600° C. or less) while leaving the ε phase.

[0130] Next, in the second cooling process, the first temperature T １ to the second temperature T ２ Therefore, during the second cooling treatment, the generated τ phase is not decomposed and is maintained at room temperature.

[0131] Therefore, by carrying out a two-stage cooling treatment as in the first manufacturing method, it is believed that it is possible to produce MnAl powder (magnetic particles containing manganese-aluminum alloy) with a significantly high τ-phase content. Furthermore, it is believed that the MnAl powder contains a twin structure, and that the two-stage cooling treatment controls the heat transfer during cooling, thereby orienting the twins, forming an "ordered" crystal structure and resulting in layered crystals. Furthermore, it is believed that the layered crystals, formed by stacking layered crystals, produce multiple parallel stripes on the surface, making it possible to produce magnetic particles containing a manganese-aluminum alloy with good magnetic field orientation.

[0132] Examples of the present invention will be described below. In the following description, Examples 1 to 6 are Examples. Examples 11 and 12 are Comparative Examples. Examples 21 to 24 are Examples.

[0133] Example 1 A powder was prepared in the following manner.

[0134] First, 69 g of manganese particles (maximum particle diameter 100 μm, average particle diameter 10 μm) and 31 g of aluminum particles (200 mesh) as an aluminum source were thoroughly mixed by ball milling (10 mmφ monomalon balls) to obtain a first powder.

[0135] Next, carbon particles (0.25% by mass), an activator (0.5% by mass), and a sintering inhibitor (74.6% by mass) were added to this first powder (24.9% by mass), and then they were thoroughly mixed to prepare a mixed powder.

[0136] Ammonium chloride particles were used as the activator. Two types of spherical alumina particles with different diameters were used as the sintering inhibitor. The first alumina particles had a maximum particle diameter of 1.1 mm and an average particle diameter of 1 mm, while the second alumina particles had a maximum particle diameter of 0.3 mm and an average particle diameter of 0.2 mm. The mass ratio of the first alumina particles to the second alumina particles was 5:1 (first alumina particles:second alumina particles).

[0137] In the mixed powder, the content ratio of aluminum particles to manganese particles (Al / Mn) was 29 / 71 in mass ratio.

[0138] Next, this mixed powder was packed into a heat-resistant container. The calculated packing ratio of the alumina particles was 74 volume %. The manganese particles, aluminum particles, carbon particles, and ammonium chloride particles were packed so as to occupy 80% of the remaining 26% of voids.

[0139] Next, the inside of the heat-resistant container was evacuated and replaced with an argon atmosphere, and then the heat-resistant container was heated to 1215° C. After being held at 1215° C. for 10 hours, the treated body was cooled in two stages.

[0140] In the first cooling treatment, the treated body was cooled from 1215° C. to 400° C. at a cooling rate of 200° C. / h. In the second cooling treatment, the treated body was rapidly cooled from 400° C. to 200° C. at a cooling rate of 600° C. / h.

[0141] Thereafter, the treated body was taken out of the heat-resistant container and sieved to remove the alumina powder, thereby obtaining a powder containing approximately spherical particles (hereinafter referred to as "powder 1").

[0142] (Examples 2 to 6) Powders were produced in the same manner as in Example 1. However, in Examples 2 to 6, the composition of the mixed powder, the conditions for the calorification treatment, and the conditions for cooling were changed from those in Example 1.

[0143] The resulting powders are referred to as "Powder 2" to "Powder 6," respectively.

[0144] Example 11 Powder was prepared in the same manner as in Example 5.

[0145] However, in Example 11, the treated body after the calorification treatment was cooled to room temperature at a cooling rate of 200° C. / h (single-stage cooling).

[0146] Hereinafter, the obtained powder is referred to as "powder 11."

[0147] Example 12 Powder was prepared in the same manner as in Example 11.

[0148] However, in Example 11, the treated body after the calorifying treatment was cooled to room temperature at a cooling rate of 600° C. / h.

[0149] Hereinafter, the obtained powder will be referred to as "powder 12."

[0150] Table 1 below shows the powder production conditions for each example.

[0151]

[0152] (Evaluation) The following evaluations were carried out using each powder.

[0153] (X-ray Diffraction Analysis) X-ray diffraction analysis of each powder was performed using an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation). From the obtained diffraction patterns, the mass fraction of each phase contained in the powder was determined by Rietveld analysis.

[0154] Rietveld refinement was performed using the program RIETAN-FP.

[0155] The profile function used was Toratani's extended split Pseude-Voigt function. Fitting was performed so that the reliability factor Rwp (R-weighted pattern), which is generally considered a guideline, was less than 10% for the entire analysis range.

[0156] The analysis range was 2θ=10° to 120°.

[0157] Table 2 below shows the calculated abundance ratios of each phase in Powders 1 and 2.

[0158]

[0159] These results confirmed that Powders 1 and 2 contained at least 50 wt % of the τ phase. Similar results were obtained for Powders 3 to 6.

[0160] (Observation of Particles) Particles contained in each powder were observed using an electron microscope (SUI510 manufactured by Hitachi High-Technologies Corporation).

[0161] 6 to 8 show examples of the surface morphology of particles contained in Powder 1, Powder 2, and Powder 5, respectively. FIG. 9 shows an example of the cross-sectional morphology of particles contained in Powder 2. FIGS. 10 and 11 show examples of the surface morphology of particles contained in Powder 11 and Powder 12, respectively. FIG. 12 shows an example of the cross-sectional morphology of particles contained in Powder 12.

[0162] Comparing these results, it can be seen that the particles in Powders 1, 2, and 5 have multiple parallel streaks formed on the spherical surface, whereas the particles in Powders 11 and 12 do not have such streaks.

[0163] 9, it was found that layered crystals were formed inside the particles of Powder 2. Similar observation results were obtained for the particles of Powder 1 and Powder 5.

[0164] In contrast, as can be seen from Figure 12, no such layered crystals were observed in the cross section of Powder 12. Similar results were obtained in the cross section of Powder 11.

[0165] Furthermore, multiple parallel streaks were observed on the spherical surfaces of the particles in Powders 3, 4, and 6, and it was also found that layered crystals were formed inside the particles in the cross sections of Powders 3, 4, and 6.

[0166] As a result of elemental mapping of the cross section of each particle using EPMA, it was found that alumina was unevenly distributed on the outer surface of the particle.

[0167] (Measurement of Twin Structure) Using an electron microscope (JEOL: JSM-IT800HL) and an electron backscatter diffraction (EBSD) detector (EDAX: Velocity), the distribution of twins in the particles contained in the powder was observed.

[0168] A particle was selected from the powder, embedded in resin, and polished to prepare a cross section for observation. The accelerating voltage during observation was 15.0 kV, and the probe current was 70 nA. In analyzing the twin boundary, the crystal plane was assumed to be the (111) plane, the rotation axis was normal to the {111} plane, and the rotation angle was assumed to be 180 degrees. The rotation angle and the threshold value for the twin plane (K1) were set to 5° and 1°, respectively.

[0169] Figure 13 shows an example of the distribution of twin boundaries in particles contained in Powder 1. In Figure 13, (A) is an SEM photograph of a cross section, and (B) is an image in which the twin boundaries are highlighted. In (B), the white lines correspond to the twin boundaries.

[0170] Thus, it was confirmed that the particles contained in Powders 1 to 6 according to one embodiment of the present invention contain twin crystal structures.

[0171] (Magnetic Properties) The remanent magnetic susceptibility P of each powder was evaluated in an applied magnetic field of 10 kOe using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.).

[0172] As an example, Fig. 14 shows the hysteresis obtained for Powder 1. In Fig. 14, the horizontal axis represents the external magnetic field, and the vertical axis represents the magnetization.

[0173] From the obtained results, the residual magnetic susceptibility P (=Mr / Ms) was calculated and found to be 0.57.

[0174] Table 3 below shows the values ​​of remanence P obtained for each powder.

[0175]

[0176] As a result of the measurement, it was found that Powders 1 to 6, which have a twin crystal structure and multiple parallel streaks on their surfaces, have significantly higher remanent magnetic susceptibility P than Powders 11 and 12, which do not have any streaks observed on their surfaces.

[0177] (Example 21) A powder was prepared in the same manner as in Example 1. However, in this Example 21, silicon particles (maximum particle diameter 10 μm) were further added to the first powder. The amount of silicon particles added was 0.5 mass% relative to the total (total of the first powder and the silicon particles).

[0178] The resulting powder is referred to as "Powder 21."

[0179] Example 22 A powder was produced in the same manner as in Example 21. However, in this Example 22, the amount of silicon particles added was 1.5 mass % relative to the total (total of the first powder and the silicon particles).

[0180] The resulting powder is referred to as "Powder 22."

[0181] Example 23: A powder was prepared in the same manner as in Example 1. However, in Example 23, titanium particles (maximum particle diameter: 10 μm) were further added to the first powder. The amount of titanium particles added was 0.5 mass% based on the total (total of the first powder and the titanium particles).

[0182] The resulting powder is referred to as "Powder 23."

[0183] Example 24: A powder was prepared in the same manner as in Example 1. However, in Example 24, chromium particles (maximum particle diameter: 10 μm) were further added to the first powder. The amount of the chromium particles added was 0.5 mass% based on the total (total of the first powder and the chromium particles).

[0184] The resulting powder is referred to as "Powder 24."

[0185] (Evaluation) The aforementioned X-ray diffraction analysis was performed on Powders 21 to 24, and it was confirmed that each contained 50 wt % or more of the τ phase. Furthermore, observation of the particles contained in each powder confirmed that all particles were approximately spherical, with multiple parallel lines formed on the spherical surface. It was also confirmed that each contained a twin structure. (Evaluation of Heat Resistance) The heat resistance of Powder 1 and Powders 21 to 24 was evaluated. Specifically, the change in magnetic properties of each powder before and after heat treatment was evaluated. The heat treatment was performed by holding each powder in an Ar atmosphere at 650°C for 1 hour.

[0186] The magnetic properties were measured using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) to measure the remanent magnetic susceptibility P, maximum magnetization Ms, and coercive force iHC of each powder in an applied magnetic field of 10 kOe.

[0187] The evaluation results are shown in Table 4 below.

[0188]

[0189] For comparison, Table 4 also shows the results obtained for the above-mentioned Powder 1.

[0190] Generally, manganese-aluminum alloy magnets are produced by sintering powder prepared by crushing manganese-aluminum alloy particles. The crushing process reduces the size of the manganese-aluminum alloy particles and introduces microstructures, such as crystal defects and dislocations, that are significant for their magnetic properties.

[0191] However, conventional sintered bodies of manganese-aluminum alloy particles have the problem that the microstructure introduced in the micronization process is lost during the heat sintering process, making it difficult to maintain the high magnetic properties at the powder stage.

[0192] However, the results show that the magnetic properties of Powder 1 and Powders 21 to 24 did not change significantly even after heat treatment. This indicates that the magnetic particles of the manganese-aluminum alloy according to one embodiment of the present invention, which have a twin crystal structure and multiple parallel streaks on their surfaces, have significantly higher thermal stability. In particular, Powders 21 to 24, which contain an additive element such as silicon, exhibit significantly higher magnetic properties in the powder state than Powder 1, and it was confirmed that these properties were maintained even after heat treatment.

[0193] (Aspects of the Invention) The present invention may have the following aspects.

[0194] (Aspect 1) Magnetic particles containing a manganese-aluminum alloy, the magnetic particles having a substantially spherical shape with a particle diameter in the range of 0.1 μm to 1000 μm, a twin crystal structure, and a plurality of parallel streaks on the surface, the manganese-aluminum alloy having a τ phase, the magnetic particles further containing alumina, the abundance of the alumina contained in the magnetic particles being in the range of 0.1 mass % to 30 mass %, the abundance of the manganese-aluminum alloy contained in the magnetic particles being in the range of 70 mass % to 99 mass %, and the abundance of the τ phase contained in the magnetic particles being in the range of 10 mass % to 99 mass %.

[0195] (Embodiment 2) The magnetic particles according to embodiment 1, further comprising at least one metal selected from the group consisting of silicon, titanium, niobium, molybdenum, tin, vanadium, iron, zinc, bismuth, copper, nickel, and chromium.

[0196] (Aspect 3) The magnetic particles according to aspect 2, wherein the at least one metal is contained in an amount ranging from 0.1% by mass to 10% by mass relative to the magnetic particles.

[0197] (Aspect 4) The magnetic particles according to any one of aspects 1 to 3, wherein the spacing between the streaks is in the range of 0.1 μm to 50 μm.

[0198] (Embodiment 5) The magnetic particles according to any one of embodiments 1 to 4, wherein the manganese-aluminum alloy further includes at least one of an ε phase, a β phase, and a γ phase.

[0199] (Aspect 6) The magnetic particles according to aspect 5, wherein the manganese-aluminum alloy contains 10 mass % or less of the ε phase.

[0200] (Aspect 7) The magnetic particles according to any one of aspects 1 to 6, wherein the manganese-aluminum alloy contains 65% to 75% by mass of manganese and 25% to 35% by mass of aluminum.

[0201] (Embodiment 8) The magnetic particles according to any one of embodiments 1 to 7, wherein the manganese-aluminum alloy contains 0.1% to 10% of carbon by atomic ratio.

[0202] (Aspect 9) The magnetic particles according to any one of aspects 1 to 8, further comprising 0.1% by mass to 30% by mass of at least one of aluminum carbide and manganese aluminum carbide.

[0203] (Aspect 10) The magnetic particle according to any one of aspects 1 to 9, wherein the alumina is unevenly distributed on the surface.

[0204] (Embodiment 11) The magnetic particle according to any one of embodiments 1 to 10, wherein the magnetic particle is a micromagnet.

[0205] (Aspect 12) A powder containing magnetic particles according to any one of aspects 1 to 11, wherein the maximum particle diameter is 1000 μm or less, and when the value expressed by Mr / Ms is referred to as the remanent magnetic susceptibility P, the remanent magnetic susceptibility P of the powder is 0.35 or more, where Mr is the remanent magnetization (emu / g) and Ms is the maximum magnetization (emu / g) when a magnetization of 10 kOe is applied.

[0206] (Aspect 13) A method for producing magnetic particles containing a manganese-aluminum alloy, comprising: (1) mixing manganese particles having a maximum particle diameter of 1000 μm or less, an aluminum source, carbon particles, an activator including a halide, and a sintering inhibitor having a maximum particle diameter that is 0.0002 to 3 times that of the manganese particles to obtain a mixed powder; (2) calorifying the mixed powder, wherein the mixed powder is heated to a maximum temperature of 1000°C to 1235°C; (3) cooling the calorified treated body from the maximum temperature to a first temperature at a first cooling rate, wherein the first temperature is in the range of 500°C to 400°C, and the first cooling rate is in the range of 100°C / h to 400°C / h; (4) cooling the treated body from the first temperature to a temperature of 300°C or less at a second cooling rate, the second cooling rate being 600°C / h or more; and after (4), magnetic particles containing a manganese-aluminum alloy are obtained, in which the ratio of aluminum to manganese (Al / Mn) in the manganese-aluminum alloy is in the range of 25 / 75 to 35 / 65 in mass ratio.

[0207] (Aspect 14) The method according to aspect 13, wherein the mixed powder further comprises at least one metal selected from the group consisting of silicon, titanium, niobium, molybdenum, tin, vanadium, iron, zinc, bismuth, copper, nickel, and chromium.

[0208] (Aspect 15) The method according to aspect 13 or 14, wherein the activator comprises at least one selected from the group consisting of ammonium chloride, aluminum chloride, and aluminum fluoride.

[0209] (Aspect 16) The method according to any one of aspects 13 to 15, wherein the amount of the activator is in the range of 0.1% by mass to 10% by mass based on the total mixed powder.

[0210] (Aspect 17) The method according to any one of aspects 13 to 16, wherein the maximum particle diameter of the aluminum source is 0.1 μm to 300 μm.

[0211] (Aspect 18) The method according to any one of Aspects 13 to 17, wherein a powder containing the magnetic particles is obtained by the method, and the powder has a maximum particle diameter of 1000 μm or less.

[0212] (Aspect 19) The method according to Aspect 18, wherein the remanent magnetic susceptibility P of the powder is 0.35 or more, where Mr is remanent magnetization (emu / g) and Ms is maximum magnetization (emu / g) when a magnetization of 10 kOe is applied, when the value represented by Mr / Ms is referred to as remanent magnetic susceptibility P.

[0213] According to the present invention, it is possible to provide magnetic particles containing a manganese-aluminum alloy that have better magnetic field alignment properties, and also to provide a method for producing such magnetic particles.

[0214] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese patent applications filed on June 4, 2024 (Patent Application No. 2024-090654) and November 12, 2024 (Patent Application No. 2024-197321), the contents of which are incorporated herein by reference.

[0215] 100 First magnetic particle 110 Surface 112 Streaks 122 Layered crystal 352 Manganese particle 354 Aluminum source 358 Sintering inhibitor 365 Void

Claims

1. Magnetic particles containing a manganese-aluminum alloy, the particles having a generally spherical shape with a particle diameter in the range of 0.1 μm to 1000 μm, a twin crystal structure, and a plurality of parallel streaks on the surface, the manganese-aluminum alloy having a τ phase, the magnetic particles further containing alumina, the abundance of the alumina contained in the magnetic particles being in the range of 0.1% by mass to 30% by mass, the abundance of the manganese-aluminum alloy contained in the magnetic particles being in the range of 70% by mass to 99% by mass, and the abundance of the τ phase contained in the magnetic particles being in the range of 10% by mass to 99% by mass.

2. The magnetic particles of claim 1, further comprising at least one metal selected from the group consisting of silicon, titanium, niobium, molybdenum, tin, vanadium, iron, zinc, bismuth, copper, nickel, and chromium.

3. The magnetic particle according to claim 2, wherein the at least one metal is contained in the magnetic particle in an amount ranging from 0.1% by mass to 10% by mass.

4. The magnetic particle according to claim 1, wherein the spacing between the stripes is in the range of 0.1 μm to 50 μm.

5. The magnetic particles according to claim 1, wherein the manganese-aluminum alloy further comprises at least one of an ε phase, a β phase, and a γ phase.

6. The magnetic particles according to claim 5, wherein the manganese-aluminum alloy contains 10 mass % or less of the ε phase.

7. Magnetic particles according to claim 1, wherein the manganese-aluminum alloy contains 65% to 75% by weight of manganese and 25% to 35% by weight of aluminum.

8. The magnetic particles according to claim 1, wherein the manganese-aluminum alloy contains 0.1% to 10% carbon by atomic ratio.

9. The magnetic particles according to claim 1, further comprising 0.1% to 30% by mass of at least one of aluminum carbide and manganese aluminum carbide.

10. The magnetic particle according to claim 1, wherein the alumina is unevenly distributed on the surface.

11. The magnetic particle of claim 1, wherein the magnetic particle is a micromagnet.

12. A powder containing magnetic particles as defined in claim 1, wherein the maximum particle diameter is 1000 μm or less, and when the value expressed by Mr / Ms is called the residual magnetic susceptibility P, the residual magnetic susceptibility P of the powder is 0.35 or more, where Mr is the residual magnetization (emu / g) and Ms is the maximum magnetization (emu / g) when a magnetization of 10 kOe is applied.

13. A method for producing magnetic particles containing a manganese-aluminum alloy, comprising: (1) mixing manganese particles having a maximum particle diameter of 1000 μm or less, an aluminum source, carbon particles, an activator containing a halide, and a sintering inhibitor having a maximum particle diameter that is 0.0002 to 3 times that of the manganese particles to obtain a mixed powder; (2) calorifying the mixed powder, wherein the mixed powder is heated to a maximum temperature of 1000°C to 1235°C; and (3) cooling the calorified treated body from the maximum temperature to a first temperature at a first cooling rate, wherein the first temperature is in the range of 500°C to 400°C, and the first cooling rate is in the range of 100°C / h to 400°C / h. (4) cooling the treated body from the first temperature to a temperature of 300°C or less at a second cooling rate, the second cooling rate being 600°C / h or more; and after (4), magnetic particles containing a manganese-aluminum alloy are obtained, in which the ratio of aluminum to manganese (Al / Mn) in the manganese-aluminum alloy is in the range of 25 / 75 to 35 / 65 in mass ratio.

14. The method of claim 13, wherein the mixed powder further comprises at least one metal selected from the group consisting of silicon, titanium, niobium, molybdenum, tin, vanadium, iron, zinc, bismuth, copper, nickel, and chromium.

15. The method of claim 13, wherein the activator comprises at least one selected from the group consisting of ammonium chloride, aluminum chloride, and aluminum fluoride.

16. The method of claim 13, wherein the amount of the activator is in the range of 0.1% to 10% by weight based on the total weight of the mixed powder.

17. The method of claim 13, wherein the maximum particle diameter of the aluminum source is 0.1 μm to 300 μm.

18. The method of claim 13, wherein the method results in a powder containing the magnetic particles, the powder having a maximum particle diameter of 1000 μm or less.

19. The method according to claim 18, wherein the remanent magnetic susceptibility P of the powder is 0.35 or more, where Mr is the remanent magnetization (emu / g) and Ms is the maximum magnetization (emu / g) when a magnetization of 10 kOe is applied.

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