Magnetic body

Abstract

According to the present invention, a magnetic body contains a plurality of magnetic particles, is cylindrical, and comprises an end surface extending in the radial direction and an outer circumferential surface extending in the axial direction, wherein the outer circumferential surface comprises a plurality of magnetic poles in the circumferential direction, the end surface forms a reference plane, the residual flux density of the end surface in the axial direction is greater than the residual flux density of the outer circumferential surface in the radial direction, and the relative density of the magnetic particles exceeds 95%. Also, the magnetic body contains a plurality of magnetic particles, is ring-shaped, and comprises an end surface extending in the radial direction and outer and inner circumferential surfaces extending in the axial direction, wherein the outer circumferential surface and / or the inner circumferential surface comprises a plurality of magnetic poles in the circumferential direction, the end surface forms a reference plane, the residual flux density of the end surface in the axial direction is greater than the residual flux density of the outer circumferential surface in the radial direction, and the relative density of the magnetic particles exceeds 95%.

Description

magnetic material

[0001] The present invention relates to a magnetic body.

[0002] Patent Document 1 describes a rare earth magnet comprising, by atomic percentage, 9% to 14% R (where R is a rare earth element consisting primarily of one or both of Nd and Pr), 4% to 8% B, and the balance being Fe and unavoidable impurities, and the structure of the rare earth magnet is comprised of a crystal grain aggregate (X) comprising 8% to less than 13% R, 4% to 8% B, and the balance being Fe and unavoidable impurities, and a crystal grain aggregate (Y) comprising 13% to 20% R, 4% to 8% B, and the balance being Fe and unavoidable impurities, the volume percentage of the crystal grain aggregate (Y) being 5% to 50% of the rare earth magnet, and the density of the rare earth magnet being 95% or more of the true density of the crystal grain aggregate (X).

[0003] Japanese Unexamined Patent Publication No. 2-288305

[0004] However, the rare earth magnet of Patent Document 1 has room for improvement in magnetization characteristics when magnetized in multiple poles from the circumferential direction.

[0005] SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetic body that is multi-polar magnetized from the circumferential direction and has significantly improved magnetization characteristics.

[0006] In order to solve the above-mentioned problems and achieve the object, a magnetic body according to one aspect of the present invention includes a plurality of magnetic particles, is cylindrical, and has an end face extending in a radial direction and an outer peripheral surface extending in an axial direction, the outer peripheral surface has a plurality of magnetic poles in the circumferential direction, the end face forms a reference plane, the residual magnetic flux density of the end face in the axial direction is greater than the residual magnetic flux density of the outer peripheral surface in the radial direction, and the relative density of the magnetic particles exceeds 95%. The magnetic body according to one aspect of the present invention is a magnetic body magnetized in multiple poles from the circumferential direction, and has significantly improved magnetization characteristics.

[0007] FIG. 1 is a diagram illustrating the magnetic body of embodiment 1. FIG. 2 is a diagram illustrating the magnetic body of embodiment 1. FIG. 3 is a diagram illustrating the magnetic body of embodiment 2. FIG. 4 shows the results of measuring the J-H curve for the hot-worked magnet obtained in step (b1) of Example 1. FIG. 5-1 is a diagram illustrating the evaluation magnetic body (A1) after magnetization. FIG. 5-2 is a diagram illustrating the evaluation magnetic body (A2) after magnetization. FIG. 6 shows the results of measuring the surface magnetic flux density for the evaluation magnetic bodies (A1) and (A2) obtained in Example 1. FIG. 7 shows the results of measuring the J-H curve for the hot-worked magnet obtained in step (b2) of Example 2. FIG. 8 shows the results of measuring the surface magnetic flux density for the evaluation magnetic bodies (A3) and (A4) obtained in Example 2. FIG. 9 shows the results of measuring the J-H curve for a Nd sintered magnet and a Nd bonded magnet. FIG. 10 shows the results of measuring the surface magnetic flux density of the magnetic materials (A5) and (A6) for evaluation obtained in Comparative Example 1.

[0008] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are easily replaceable by those skilled in the art, or those that are substantially the same.

[0009] 1 and 2 are diagrams illustrating the magnetic body of the first embodiment. The magnetic body 1 includes a plurality of magnetic particles and is a magnet known as a binderless magnet or a bulk magnet. The magnetic body 1 is cylindrical. Specifically, the magnetic body 1 has an end face 11 extending in the radial direction X and an outer peripheral surface 12 extending in the axial direction Z. The outer peripheral surface 12 has a plurality of magnetic poles in the circumferential direction. For example, as shown in FIG. 2 , the magnetic body 1 has 12 magnetic poles, and preferably has four or more magnetic poles. For this reason, the magnetic body 1 is suitable for use in a radial gap motor. The end face 11 also forms a reference surface. In this specification, the reference surface refers to a flat surface (plane). The residual magnetic flux density of the end face 11 in the axial direction Z is greater than the residual magnetic flux density of the outer peripheral surface 12 in the radial direction X. The magnetic body 1 has a relative density of magnetic particles exceeding 95%.

[0010] Patent Document 1 describes that when Nd—Fe—B alloy powder is hot-formed under compressive stress by hot pressing, plastic flow occurs within the compact, and the crystal rotation associated with this plastic flow tends to orient the axis of easy magnetization (C-axis) parallel to the pressing direction. For this reason, it was known that magnetization characteristics would be poor when magnetized in a direction perpendicular to the C-axis. Furthermore, it was common technical knowledge that, if magnetization in a direction perpendicular to the C-axis is desired, it is not possible to simultaneously improve magnetic properties by increasing density and minimize degradation of magnetic properties by suppressing anisotropy level unless the relative density is kept at 95%.

[0011] In contrast, magnetic body 1 is binderless, can be produced through a hot densification process as described below, has a relative density of magnetic particles exceeding 95%, and the residual magnetic flux density of the end face 11 in the axial direction Z is greater than the residual magnetic flux density of the outer peripheral surface 12 in the radial direction X. However, magnetic body 1 has significantly improved magnetization characteristics even when multi-pole magnetized from the circumferential direction.

[0012] In magnetic body 1, the plurality of magnetic particles usually have portions oriented in a direction intersecting with the axial direction Z. For this reason, it is believed that magnetic body 1 has significantly improved magnetization characteristics, even when multi-pole magnetized from the circumferential direction. Arrow A in FIG. 1 indicates the orientation direction of the above-mentioned portions of the plurality of magnetic particles. The fact that the plurality of magnetic particles have portions oriented in a direction intersecting with the axial direction Z can be confirmed from the static magnetic characteristics. That is, when the J-H curve of magnetic body 1 is measured, where H is the magnetic field and J is the magnetization of the magnet, this can be confirmed by the difference in characteristics depending on the measurement direction and the gentle curve.

[0013] Furthermore, the magnetic body 1 usually contains carbon, which is due to the polystyrene used in the compound preparation step (step (a)) in the manufacturing method of the magnetic body 1, as will be described later.

[0014] Here, we will explain the method for manufacturing the magnetic body 1. The method for manufacturing the magnetic body 1 includes, for example, steps (a) to (c).

[0015] In step (a), rare earth iron-based magnet powder (magnetic particles) and polystyrene are mixed to prepare a compound.

[0016] The rare earth iron-based magnet powder (magnetic particles) used is a rare earth iron-based magnet powder obtained by pulverizing a magnetically isotropic rare earth iron-based magnet ribbon produced by the rapid cooling method. The rare earth iron-based magnet powder produced by the rapid cooling method is usually flat in shape. The obtained rare earth iron-based magnet powder is also magnetically isotropic. The rare earth iron-based magnet powder preferably contains at least Nd as a rare earth element, and is, for example, an Nd—Fe—B-based magnet. The Nd—Fe—B-based magnet is a ternary tetragonal compound, Nd2Fe 14 The Nd—Fe—B magnet contains a B-type compound phase as the main phase. Furthermore, Nd—Fe—B magnets usually further contain a rare earth-rich phase (Nd-rich phase), etc. The Nd—Fe—B magnets may be used singly or in combination of two or more types.

[0017] The rare earth iron-based magnet powder (specifically, Nd—Fe—B-based magnet) may contain rare earth elements other than Nd. Examples of rare earth elements other than Nd include praseodymium (Pr), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The rare earth elements other than Nd may be used alone or in combination of two or more.

[0018] In Nd—Fe—B magnets, a portion of the Fe (usually less than 50 atomic %) may be substituted with Co. Furthermore, Nd—Fe—B magnets may contain other elements. Examples of such other elements include titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), copper (Cu), and gallium (Ga). The other elements may be used alone or in combination of two or more.

[0019] The rare earth iron-based magnet powder is mixed with polystyrene to produce a compound. Since polystyrene does not contain oxygen atoms, it is unlikely to deteriorate the magnetic properties of the resulting magnetic body 1. In step (a), specifically, polystyrene is dissolved in an organic solvent to produce a resin solution. Here, any organic solvent can be used as long as it can dissolve polystyrene and evaporate during drying, as described below. Methyl ethyl ketone is preferably used as the organic solvent. The rare earth iron-based magnet powder and this resin solution are kneaded. Next, the kneaded mixture obtained by kneading is dried, the organic solvent is evaporated, and then the mixture is crushed. The crushed mixture obtained by crushing is classified to obtain a compound.

[0020] In step (a), the polystyrene is preferably mixed in an amount of 2 wt% or less, more preferably 1 wt% to 2 wt%, relative to 100 wt% of the rare earth-iron-based magnet powder. If the amount exceeds 2 wt%, carbide is generated in step (b1), resulting in a large amount of residual carbon in the sintered magnet body, which may result in excessive degradation of the magnetic properties. If the amount is less than 1 wt%, the improvement in packing efficiency in step (b1) may be insufficient.

[0021] In step (b1) (hot densification step), the compound obtained in step (a) is filled into a first mold and hot densified. Specifically, in step (b1), a first mold is prepared. The first mold is composed of a hollow cylindrical die and cylindrical upper and lower punches inserted inside the die. The die, upper and lower punches are made of a conductive material (e.g., graphite, cemented carbide, etc.).

[0022] Next, the compound is filled into the first mold, and the mold is set in a sintering apparatus (SPS apparatus: spark plasma sintering apparatus) for sintering, and the sintered magnet body (hot-pressed magnet body) is removed from the first mold.

[0023] The compound filled in the cavity of the first die is compressed by the upper and lower punches through pressure applied between the upper and lower electrodes. Current flows from the upper electrode to the upper punch, then through the die and compound, and then through the lower punch to the lower electrode, generating Joule heat and generating discharge plasma within the compound, which heats the compound. For example, the compound is heated to 600-700°C while being pressurized at 30-50 MPa (hot press). Sintering is preferably performed under reduced pressure in an inert atmosphere, specifically, an argon or nitrogen atmosphere.

[0024] After heating, the sintering machine is turned off and cooled. After cooling to a predetermined temperature, the first mold is removed from the sintering machine. Specifically, the cylindrical sintered magnet body formed by debinding and sintering is removed from the first mold. Although the sintered magnet body is debound, it usually contains carbon.

[0025] In step (b2) (hot plastic working step), the sintered magnet body obtained in step (b1) is packed into a second mold and subjected to hot plastic working. Specifically, in step (b2), a second mold is first prepared. The second mold may be prepared in parallel with the preparation of the first mold, or may be prepared before the first mold. Next, the sintered magnet body produced in the hot densification step is placed in the second mold, and the second mold is then placed in a sintering apparatus for hot plastic working.

[0026] In the sintering apparatus, an upper electrode is disposed on the upper end of the punch, and a lower electrode is disposed on the lower end of the die. The upper and lower electrodes are formed of a conductive material (e.g., graphite, cemented carbide, etc.). The sintering apparatus is equipped with a power supply device and a control device that apply a predetermined voltage between the upper and lower electrodes to supply a predetermined current. The sintering apparatus may also be used as the sintering apparatus in the hot densification process, or may be a separate device.

[0027] The sintered magnet body, positioned between the die and punch of the second die, is pressed by the upper and lower punches. It is also heated by discharge plasma and Joule heat generated by current flowing through the upper electrode → punch → sintered magnet body → die → lower electrode. Hot plastic working begins with the application of a pressure of 30 to 100 MPa, followed by heating. The sintered magnet body is pressurized while being heated, for example, to a temperature of 600°C to 700°C. During heating, an ON-OFF DC pulse current is applied to the sintered magnet body. During hot plastic working, the pressure is adjusted to prevent the working speed from increasing, preferably to maintain a constant working speed. Hot plastic working is preferably performed under reduced pressure or in an inert atmosphere, specifically, an argon or nitrogen atmosphere. Hot plastic working is preferably performed from the start of displacement to its completion while monitoring the displacement. Here, the displacement is typically monitored by monitoring the displacement of a servo motor controlling the pressure.

[0028] After heating, the current is cut off and the sintering machine is cooled. After cooling to a predetermined temperature, the second die is removed from the sintering machine, and the cylindrical hot-plastically processed magnet obtained from the sintered magnet body by hot plastic working is taken out from the second die.

[0029] In the hot-processed magnet obtained in step (b2), the relative density of the magnetic particles typically exceeds 95%. Therefore, the hot-processed magnet is then subjected to step (c). That is, in step (c), the hot-processed magnet obtained in step (b2) is magnetized (e.g., pulse magnetized) to provide multiple magnetic poles in the circumferential direction of the outer circumferential surface. This results in the magnetic body 1. By undergoing steps (b1) and (b2) of the above-described manufacturing method, the end faces of the magnetic body 1 form reference surfaces. Furthermore, by undergoing steps (b1) and (b2) of the above-described manufacturing method, the residual magnetic flux density of the end faces 11 in the axial direction Z is also greater in the magnetized magnetic body 1 than the residual magnetic flux density of the outer circumferential surface 12 in the radial direction X. Furthermore, the multiple magnetic particles have portions oriented in a direction intersecting the axial direction Z. Similar to the hot-processed magnet, the relative density of the magnetic particles in the magnetized magnetic body 1 typically exceeds 95%.

[0030] If the relative density of the magnetic particles in the sintered magnet body obtained in step (b1) exceeds 95%, step (b2) does not need to be performed. That is, the sintered magnet body obtained in step (b1) may be subjected to step (c). In this case, the same magnetic body 1 as that obtained by performing step (b2) can be obtained.

[0031] The hot densification and hot plastic working processes cause crystal grains to grow into flattened shapes, and the flat surfaces of the particles tend to mechanically align in the direction of pressure. In other words, the direction of pressure (the minor axis direction of the crystal grains) and the axis of easy magnetization tend to align. As a result, the axis of easy magnetization of the crystal grains within the magnet tends to align in the thickness direction of the sintered magnet body and hot plastic working magnet. Therefore, sintered magnet bodies and hot plastic working magnets have magnetic anisotropy.

[0032] However, in sintered magnet bodies and hot-processed magnets with a relative density of magnetic particles exceeding 95%, the magnetic particles also have portions oriented in a direction intersecting the axial direction Z. Therefore, these sintered magnet bodies and hot-processed magnets are believed to have excellent magnetization characteristics, even when magnetized in multipolar fashion from the circumferential direction. The presence of portions of the magnetic particles oriented in a direction intersecting the axial direction can be confirmed by their static magnetic properties. Specifically, when measuring the J-H curves of these sintered magnet bodies and hot-processed magnets, this can be confirmed by the difference in characteristics depending on the measurement direction and the gentle curves.

[0033] Furthermore, even after magnetization, the magnetic body 1 has a portion oriented in a direction intersecting the axial direction Z. The portion of the magnetic body 1 oriented in a direction intersecting the axial direction Z is magnetized. When the J-H curve is measured, it can be confirmed that the magnetic body 1 has a portion oriented in a direction intersecting the axial direction, as it shows a difference in characteristics depending on the measurement direction and a gentle curve. For this reason, it is considered that the magnetic body 1 has significantly improved magnetization characteristics, even though it is multi-polarly magnetized from the circumferential direction. The magnetization characteristics are improved more by performing steps (b1) and (b2) than by performing only step (b1).

[0034] <Magnetic Body of Embodiment 2> Figure 3 is a diagram illustrating a magnetic body of embodiment 2. The magnetic body 2 is ring-shaped and includes an end face 21 extending in the radial direction X and an outer peripheral surface 22 and an inner peripheral surface 23 extending in the axial direction Z. The outer peripheral surface 22 has multiple magnetic poles in the circumferential direction. For example, as shown in Figure 2, the magnetic body 2 has 12 magnetic poles, and preferably has four or more magnetic poles. Apart from these points, the magnetic body 2 is similar to the magnetic body 1 described in embodiment 1. Therefore, the magnetic body 2 is also binderless and can be produced through a hot densification process or a hot plastic working process. Furthermore, the relative density of the magnetic particles exceeds 95%, and the residual magnetic flux density of the end face 21 in the axial direction Z is greater than the residual magnetic flux density of the outer peripheral surface 22 in the radial direction X. However, even though the magnetic body 2 is magnetized with multiple poles in the circumferential direction, the magnetic properties are significantly improved.

[0035] The method for producing magnetic body 2 is the same as the method for producing magnetic body 1, except that the first mold used in step (b1) (hot densification step) is different. Here, step (b1) in the method for producing magnetic body 2 will be described.

[0036] In step (b1) (hot densification step), the compound obtained in step (a) is filled into a first mold and hot densified. Specifically, in step (b1), a first mold is prepared. The first mold is composed of a hollow cylindrical die, hollow cylindrical upper and lower punches inserted inside the die, and cylindrical cores placed inside the upper and lower punches. The die, upper and lower punches, and core are made of a conductive material (e.g., graphite, cemented carbide, etc.).

[0037] Next, the compound is filled into the first mold, and the mold is set in a sintering apparatus (SPS apparatus: spark plasma sintering apparatus) for sintering, and the sintered magnet body (hot-pressed magnet body) is removed from the first mold.

[0038] The compound filled in the cavity of the first mold is compressed by the upper and lower punches through pressure applied between the upper and lower electrodes. Furthermore, current flows from the upper electrode to the upper punch, then through the die, core, and compound, and then to the lower electrode via the lower punch. This generates Joule heat and generates discharge plasma within the compound, heating the compound. For example, the compound is heated to 600-700°C while being pressurized at 30-50 MPa (hot press). Furthermore, sintering is preferably performed under reduced pressure in an inert atmosphere, specifically, an argon or nitrogen atmosphere.

[0039] After heating, the sintering machine is turned off and cooled. After cooling to a predetermined temperature, the first mold is removed from the sintering machine. Specifically, the ring-shaped sintered magnet body formed by debinding and sintering is removed from the first mold. Although the sintered magnet body is debound, it usually contains carbon.

[0040] <Modified Magnetic Body> In the magnetic body 2, the outer peripheral surface 22 has a plurality of magnetic poles in the circumferential direction. This is not limiting, and both the outer peripheral surface 22 and the inner peripheral surface 23 may have a plurality of magnetic poles in the circumferential direction, or only the inner peripheral surface 23 may have a plurality of magnetic poles in the circumferential direction. That is, it is sufficient that at least one of the outer peripheral surface 22 and the inner peripheral surface 23 has a plurality of magnetic poles in the circumferential direction.

[0041] The present invention will be explained in more detail below based on examples, but the present invention is not limited to these examples.

[0042] [Examples] [Example 1] In Example 1, the magnetic body 1 described in Embodiment 1 was produced. Step (a): 200 g of Nd—Fe—B magnetic powder (magnetic particles, product name: MQU-M, manufactured by Magnequench) was mixed with 4 g of polystyrene dissolved in 20 g of methyl ethyl ketone (MEK). Next, the mixture was kneaded for 15 minutes in a laboratory mill while evacuating the air in a draft chamber to obtain a kneaded mixture. The kneaded mixture was placed in an oven heated to 80°C and dried for 30 minutes to volatilize the MEK. The powder from which the MEK had volatilized was crushed in a mortar to obtain a compound. Step (b1): The compound obtained in Step (a) was filled into a first mold and hot densified. The first mold consisted of a hollow cylindrical die and cylindrical upper and lower punches inserted inside the die. The die, upper and lower punches were made of conductive material. The compound was filled into the first mold and placed in a sintering apparatus (SPS apparatus: spark plasma sintering apparatus) for sintering. After heating, the sintering apparatus was turned off and cooled. After cooling to a predetermined temperature, the first mold was removed from the sintering apparatus. A cylindrical sintered magnet body (hot-pressed magnet body) formed by sintering the magnet powder was removed from the first mold. Its relative density was 98.4%. The sintered magnet body measured 9 mm in diameter and 7 mm in height. Step (c): The sintered magnet body obtained in step (b1) was pulse-magnetized to provide multiple magnetic poles (18 poles) in the circumferential direction of the outer periphery. This resulted in magnetic body 1. The end faces of magnetic body 1 formed reference planes. Magnetic body 1 contained carbon. The relative density and size of magnetic body 1 remained the same as those of the sintered magnet body. The relative density was 98.4%. Carbon was also present, but the amount was 2000 ppm or less. The relative density was calculated from the ratio of the density of the sintered body to the true density of the alloy. The density of the sintered body was determined by the buoyancy method. Here, the true density of the alloy is, for example, 7.6 g / cm 3 The carbon content was measured by a combustion method using a CS analyzer.

[0043] <Static Magnetic Properties> Figure 4 shows the results of measuring the J-H curve for the hot-worked magnet obtained in step (b1) of Example 1. The measurements were performed on the outer peripheral surface in the radial direction X and the end surface in the axial direction Z. It was found that the residual magnetic flux density at the end surface in the axial direction Z was greater than the residual magnetic flux density at the outer peripheral surface in the radial direction X. This indicated a difference in characteristics depending on the measurement direction. The J-H curve also showed a gentle curve. Therefore, it was confirmed that multiple magnetic particles have portions oriented in a direction intersecting the axial direction Z. It is believed that similar results would be obtained if the J-H curve were measured for the magnetic body 1 obtained in step (c). In other words, it is believed that the residual magnetic flux density at the end surface in the axial direction Z is greater than the residual magnetic flux density at the outer peripheral surface in the radial direction X. It is believed that this indicates a difference in characteristics depending on the measurement direction. The J-H curve also shows a gentle curve. Therefore, it is believed that it is confirmed that multiple magnetic particles have portions oriented in a direction intersecting the axial direction Z. Here, the J-H curve was measured using a B-H curve tracer.

[0044] <Magnetic Properties> To evaluate the magnetic properties, cubic (7 mm per side) sintered magnet bodies for evaluation (A1) and (A2) were produced in the same manner as Magnetic Body 1 above, except that the first mold was changed. The four side faces of the cube can be considered the outer circumferential surfaces of Magnetic Body 1, and the top and bottom faces of the cube can be considered the end faces of Magnetic Body 2. One side face of the sintered magnet body for evaluation (A1) was subjected to pulse magnetization (four poles) with a pole pitch of 1.57 mm. In this manner, Magnetic Body for Evaluation (A1) was obtained. Furthermore, the top face of the sintered magnet body for evaluation (A2) was subjected to pulse magnetization (four poles) with a pole pitch of 1.57 mm. In this manner, Magnetic Body for Evaluation (A2) was obtained. Note that FIG. 5-1 shows the magnetic body for evaluation (A1) after magnetization, and FIG. 5-2 shows the magnetic body for evaluation (A2) after magnetization. FIG. 6 shows the results of measuring the surface magnetic flux density for the evaluation magnetic bodies (A1) and (A2) obtained in Example 1. Here, the surface magnetic flux density was measured on the magnetized surfaces of the evaluation magnetic bodies (A1) and (A2). FIG. 6 also shows calculated values ​​along with the measured values. As can be seen from FIG. 6, the magnetic properties of the evaluation magnetic body (A1), which was magnetized on the side, were significantly improved compared to the calculated values. Thus, magnetic properties equivalent to those of the evaluation magnetic body (A2), which was magnetized on the top surface, were obtained. This is presumably due to the presence of a plurality of magnetic particles oriented in a direction intersecting the axial direction Z. It is believed that the magnetic properties of the magnetic body 1, which was magnetized on the outer peripheral surface, were also significantly improved, similar to those of the evaluation magnetic body (A1). Here, the surface magnetic flux density was measured using a magnet analyzer.

[0045] Example 2 In Example 2, the magnetic body 1 described in Embodiment 1 was produced. Steps (a) and (b1) were performed in the same manner as in Example 1. Step (b2): The sintered magnet body obtained in step (b1) was packed into a second mold and subjected to hot plastic processing. Specifically, the sintered magnet body produced in the hot densification step was placed in the second mold, and the second mold was then placed in a sintering apparatus for hot plastic processing. After heating, the sintering apparatus was turned off and cooled. After cooling to a predetermined temperature, the second mold was removed from the sintering apparatus. A cylindrical hot plastic processed magnet obtained by hot plastic processing from the sintered magnet body was removed from the second mold. The relative density was 98.4%. The hot plastic processed magnet had a diameter of 9 mm and a height of 7 mm. Step (c): The hot plastic processed magnet obtained in step (b2) was pulse-magnetized to have multiple magnetic poles (12 poles) circumferentially on its outer periphery. This resulted in the production of magnetic body 1. The end faces of magnetic body 1 formed reference surfaces. Magnetic body 1 contained carbon. The relative density and size of magnetic body 1 remained the same as those of the hot plastic processing magnet.

[0046] <Static Magnetic Properties> Figure 7 shows the results of measuring the J-H curve for the hot-formed magnet obtained in step (b2) of Example 2. The measurements were performed on the outer peripheral surface in the radial direction X and the end surface in the axial direction Z. It was found that the residual magnetic flux density at the end surface in the axial direction Z was greater than the residual magnetic flux density at the outer peripheral surface in the radial direction X. The J-H curve also exhibited a gentle curve. This confirmed that multiple magnetic particles have portions oriented in a direction intersecting the axial direction Z. It is believed that similar results would be obtained if the J-H curve were measured for the magnetic body 1 obtained in step (c). In other words, it is believed that the residual magnetic flux density at the end surface in the axial direction Z is greater than the residual magnetic flux density at the outer peripheral surface in the radial direction X. The J-H curve also exhibits a gentle curve. This confirmed that multiple magnetic particles have portions oriented in a direction intersecting the axial direction Z.

[0047] <Magnetic Properties> To evaluate the magnetic properties, cubic (7 mm per side) sintered magnet bodies for evaluation (A3) and (A4) were produced in the same manner as magnetic body 1 above, except that the first mold was changed. The four side surfaces of the cube can be considered to be the outer peripheral surfaces of magnetic body 2, and the top and bottom surfaces of the cube can be considered to be the end faces of magnetic body 2. One side surface of sintered magnet body for evaluation (A3) was subjected to pulse magnetization (four poles) with a pole pitch of 1.57 mm. In this manner, magnetic body for evaluation (A3) was obtained. Furthermore, the top surface of sintered magnet body for evaluation (A4) was subjected to pulse magnetization (four poles) with a pole pitch of 1.57 mm. In this manner, magnetic body for evaluation (A4) was obtained. The magnetic poles of magnetic bodies for evaluation (A3) and (A4) after magnetization were formed in the same manner as magnetic bodies for evaluation (A1) and (A2) shown in FIGS. 5-1 and 5-2, respectively. FIG. 8 shows the results of measuring the surface magnetic flux density for the evaluation magnetic bodies (A3) and (A4) obtained in Example 2. Here, the surface magnetic flux density was measured on the magnetized surfaces of the evaluation magnetic bodies (A3) and (A4). FIG. 8 also shows the calculated values ​​along with the measured values. As can be seen from FIG. 8, the magnetic properties of the evaluation magnetic body (A3), which was magnetized on the side, were significantly improved compared to the calculated values. Thus, magnetic properties equivalent to those of the evaluation magnetic body (A4), which was magnetized on the top surface, were obtained. This is presumably due to the fact that multiple magnetic particles have portions oriented in a direction intersecting the axial direction Z. It is believed that the magnetic properties of the magnetic body 1, which was magnetized on the outer circumferential surface, were also significantly improved, similar to those of the evaluation magnetic body (A3).

[0048] Comparative Example 1 <Static Magnetic Properties> The static magnetic properties were evaluated for a sintered Nd magnet (cylindrical, 10 mm diameter, 7 mm height, anisotropic magnet) and a bonded Nd magnet (cylindrical, 10 mm diameter, 7 mm height, isotropic magnet). Figure 9 shows the results of measuring the J-H curves for the sintered Nd magnet and the bonded Nd magnet. For the sintered Nd magnet, measurements were performed on the outer peripheral surface in the radial direction X and the end surface in the axial direction Z. For the bonded Nd magnet, measurements were performed on the outer peripheral surface in the radial direction X. It was found that the residual magnetic flux density of the end surface in the axial direction Z of the sintered Nd magnet was greater than the residual magnetic flux density of the outer peripheral surface in the radial direction X. The residual magnetic flux density of the outer peripheral surface in the radial direction X was lower than that of the bonded Nd magnet. Furthermore, the J-H curve for the end surface in the axial direction Z is not a smooth curve, indicating that the sintered Nd magnet is an almost completely anisotropic magnet.

[0049] <Magnetic Properties> The magnetic properties were evaluated for a Nd sintered magnet (cubic, 7 mm per side, anisotropic magnet) and a Nd bonded magnet (cubic, 7 mm per side, isotropic magnet). Pulse magnetization (four poles) was performed on one side of the Nd sintered magnet with a pole pitch of 1.57 mm. In this manner, a magnetic body for evaluation (A5) was obtained. Furthermore, pulse magnetization (four poles) was performed on one side of the Nd bonded magnet with a pole pitch of 1.57 mm. In this manner, a magnetic body for evaluation (A6) was obtained. The magnetic poles of the magnetic bodies for evaluation (A5) and (A6) after magnetization were formed in the same manner as for the magnetic body for evaluation (A1) shown in FIG. 5-1. FIG. 10 shows the results of measuring the surface magnetic flux density of the magnetic bodies for evaluation (A5) and (A6) obtained in Comparative Example 1. Here, the surface magnetic flux density was measured on the magnetized surfaces of the magnetic bodies for evaluation (A5) and (A6). Furthermore, Figure 10 shows the calculated values ​​for the Nd bonded magnet along with the measured values. As can be seen from Figure 10, the Nd bonded magnet is an almost completely isotropic magnet, with the calculated values ​​and the measured values ​​generally agreeing. Furthermore, even if a Nd sintered magnet is magnetized in multiple poles from the side, no improvement in magnetic properties is observed. Therefore, it is presumed that in multi-pole magnetization from the side, it is necessary to have a portion in which multiple magnetic particles are oriented in a direction that intersects with the axial direction Z.

[0050] Here, in the magnetic body 1 according to Example 1 and Example 2, the relative density of the magnetic particles exceeds 95%, and therefore the magnetic bodies of Example 1 and Example 2 have the property of high electrical conductivity. Due to this property, it is thought that an eddy current is induced inside the magnetic body when a magnetic flux is applied by pulse magnetization, and that this eddy current magnetizes the magnetic particles oriented in a direction intersecting the axial direction.

[0051] The following will be described with reference to the second quadrant (so-called demagnetization curve) of the J-H curve in Fig. 7 . Auxiliary lines 1, 2, 3, and 4 are drawn in Fig. 7 . Auxiliary line 1 is defined as a line in the first quadrant that is parallel to the horizontal axis of the graph and passes through the maximum point of the graph showing the end face in the axial direction Z. Auxiliary line 2 is defined as a line in the second quadrant that is parallel to the vertical axis of the graph and passes through the point where the graph showing the end face in the axial direction Z intersects with the horizontal axis of the graph. Auxiliary line 3 is defined as a line in the third quadrant that is parallel to the horizontal axis of the graph and passes through the minimum point of the graph showing the end face in the axial direction Z. Auxiliary line 4 is defined as a line in the fourth quadrant that is parallel to the vertical axis of the graph and passes through the point where the graph showing the end face in the axial direction Z intersects with the horizontal axis of the graph.

[0052] In the second and fourth quadrants, the graph showing the end face in the axial direction Z is within the area surrounded by the auxiliary lines, but in the first and third quadrants, part of the graph showing the end face in the axial direction Z is outside the area surrounded by the auxiliary lines. Furthermore, in the second quadrant, the rate of change of H (kA / m) when J(T) is from 0 to -1000 is 16%, and the rate of change in the comparative example is approximately 1% as shown in FIG. 9 , so the range is 1%≦rate of change≦16%. Similarly, auxiliary lines 1, 2, 3, and 4 are shown in FIG. 4 for Example 1. The rate of change in Example 1 falls within the above range.

[0053] The second quadrant is the so-called demagnetization curve, and as in Examples 1 and 2, the gentler the slope, the more isotropic the magnet contains. On the other hand, as in Comparative Example 1, the steeper the slope, the more anisotropic the magnet contains. Since Examples 1 and 2 contain obliquely oriented components, they are considered to be magnets that contain more isotropic components than Comparative Example 1. As shown above, the range of the rate of change is shown, and it can be said that the larger this rate of change, the more obliquely oriented the magnet contains.

[0054] 1, 2 magnetic material, 11, 21 end surface, 12, 22 outer peripheral surface, 23 inner peripheral surface

Claims

1. A magnetic body comprising a plurality of magnetic particles, being cylindrical, having an end face extending in the radial direction and an outer peripheral face extending in the axial direction, the outer peripheral face having a plurality of magnetic poles in the circumferential direction, the end face forming a reference plane, the residual magnetic flux density of the end face in the axial direction being greater than that of the outer peripheral face in the radial direction, and the relative density of the magnetic particles exceeding 95%.

2. A magnetic body comprising a plurality of magnetic particles, being ring-shaped, having an end face extending in the radial direction and an outer peripheral face and an inner peripheral face extending in the axial direction, at least one of the outer peripheral face and the inner peripheral face having a plurality of magnetic poles in the circumferential direction, the end face forming a reference plane, the residual magnetic flux density of the end face in the axial direction being greater than that of the outer peripheral face in the radial direction, and the relative density of the magnetic particles exceeding 95%.

3. The magnetic body according to claim 1 or 2, wherein the plurality of magnetic particles have a portion oriented in a direction intersecting the axial direction.

4. The magnetic body according to claim 1 or 2, wherein the reference plane is a flat surface.

5. The magnetic body according to claim 1 or 2, which contains carbon.

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