JP2004281492A - Permanent magnet material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small or thin permanent magnet having S/V=6 mm<SP>-1</SP>or above representing good magnetic characteristics without performing a heat treatment for recovering the characteristics after grinding. <P>SOLUTION: The permanent magnet material produces a sintered magnet having an R-Fe-B based composition (R is one kind or more than one kinds being selected from rare earth elements including Y) having mean crystal grain size in main phase of 5 μm or less determined from surface integral rate, ground to have a specific surface area of 6 mm<SP>-1</SP>or above, and having a volume integral rate (%) in the surface deterioration layer not higher than 0.5×S/V (S/V is specific surface area and the unit is mm<SP>-1</SP>). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３６】
［実施例２］
比表面積Ｓ／Ｖが２０ｍｍ^−１となるように全面研削加工された磁石体Ｍ１をアルカリ溶液で洗浄した後、酸洗浄して乾燥させた。これを磁石体Ｍ２と称する。各洗浄の前後には純水による洗浄工程が含まれている。磁石体Ｍ２の磁気特性及び表面劣化層の平均厚さと体積分率を表２に示した。磁石体Ｍ１と比較して、磁気特性が全く劣化していないことがわかる。
【００３７】
［実施例３］
比表面積Ｓ／Ｖが２０ｍｍ^−１となるように全面研削加工され、アルカリ洗浄に次いで酸洗浄された磁石体Ｍ２に対し、無電解銅メッキにより厚さ約５μｍの銅皮膜を被着した。これを磁石体Ｍ３と称する。磁石体Ｍ３の磁気特性及び表面劣化層の平均厚さと体積分率を表２に併記した。磁石体Ｍ１及びＭ２と比較して、磁気特性が殆ど劣化していないことがわかる。
【００３８】
【表２】

【００３９】
【発明の効果】
本発明によれば、研削加工後に特性を回復させるための熱処理を施すことなく良好な磁気特性を示すＳ／Ｖ＝６ｍｍ^−１以上の小型あるいは薄型の永久磁石を提供することができる。
【図面の簡単な説明】
【図１】本発明による磁石体の減磁曲線（曲線Ｈ）及び従来技術による磁石体の減磁曲線（曲線Ｋ）を示した図である。
【図２】本発明による磁石体の結晶粒径分布を示した図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an R—Fe—B permanent magnet material in which deterioration of magnetic properties due to grinding of the surface of a sintered magnet body is reduced, and in particular, specific surface area (S (surface area) / V (volume) of the magnet body. ) Is about 6 mm ⁻¹ or more for small or thin high-performance permanent magnet materials.
[0002]
[Prior art]
Nd-Fe-B-based permanent magnets have been increasingly used because of their excellent magnetic properties. In recent years, Nd-Fe-B magnets, especially high-performance, have been developed with computer-related equipment using magnets, CD players, DVD players, mobile phones, and other electronic devices that are becoming lighter, thinner, smaller, more efficient, and more energy efficient. There is a demand for smaller and thinner Nd-Fe-B based sintered magnets, and the demand for small or thin magnets whose specific surface area S / V exceeds 6 mm ^-1 is also increasing. .
[0003]
In order to process a small or thin Nd-Fe-B based sintered magnet into a practical shape and mount it on a magnetic circuit, it is necessary to grind a shaped and sintered block-shaped sintered magnet. An outer edge cutting machine, an inner edge cutting machine, a surface grinding machine, a centerless polishing machine, a lapping machine and the like are used.
[0004]
However, it is known that when the Nd-Fe-B based sintered magnet is ground by the above-mentioned apparatus, the magnetic properties are deteriorated as the magnet body becomes smaller. This deterioration is considered to be due to the grain boundary structure required for the expression of a high coercive force of the present magnet being lost on the surface of the magnet due to processing or due to processing strain. In order to prevent the magnetic properties from deteriorating, for example, by preventing the growth of crystal grains in the sintering process of the magnet, the magnetic properties are degraded even when the grinding process is performed until the specific surface area S / V becomes 2.6 mm ^−1. There is proposed a magnet material that does not use it (see Patent Document 1: Japanese Patent No. 2514155). However, when the S / V exceeds 6 mm ⁻¹ , there is a problem that the magnetic characteristics are significantly deteriorated.
[0005]
As a method of preventing the characteristic deterioration of such an extremely small magnet body, for example, a thin film layer mainly composed of a rare earth element is formed on the surface to be ground by sputtering or the like, and further subjected to a heat treatment to modify the deteriorated surface to be ground. Thus, there has been proposed a method for preventing the deterioration of the characteristics of the magnet body (see Patent Document 2: Japanese Patent Publication No. 5-60241 and Patent Document 3: Japanese Patent Publication No. 6-63086). However, it is difficult to apply the above method to mass production because of extremely low productivity, there is little deterioration in magnetic properties, and it is practically impossible to produce an extremely small magnet having an S / V exceeding 6 mm ^−1. Was considered possible.
[0006]
[Patent Document 1]
Japanese Patent No. 2514155 [Patent Document 2]
Japanese Patent Publication No. 5-60241 [Patent Document 3]
Japanese Patent Publication No. 6-63086
[Problems to be solved by the invention]
An object of the present invention is to provide an R-Fe-B-based sintered magnet material in which deterioration of magnetic properties due to grinding is reduced in view of the above-described conventional problems.
[0008]
Means for Solving the Problems and Embodiments of the Invention
The present inventors have conducted various studies on the coercive force in the vicinity of the surface of the R—Fe—B based sintered magnet. As a result, when the effect of the processing strain is suppressed as much as possible while paying attention to the processing speed, the deterioration in the surface to be ground is deteriorated. It has been found that the average thickness t (unit: μm) of the layer is approximately the same as the average crystal grain size D (unit: μm) obtained from the area ratio of the magnet main phase.
From the relationship between the average thickness t of the deteriorated layer and the average crystal grain size D, the average grain size of the deteriorated layer on the surface to be ground can be reduced by making the crystal grain size of the main phase as small as possible. That is, it has been found that deterioration of characteristics of a small or thin permanent magnet can be reduced. In order to achieve this, it is necessary to make the magnet raw material particles sufficiently fine in the pulverizing step in the manufacturing step of the sintered magnet, and to suppress the coarsening of the main phase crystal grains in the sintering step. Although the present process is not easily achieved, the present inventors have conducted intensive studies on the atmosphere, processing temperature, alloy composition, and the like in the process of producing a sintered magnet, and have found that the average crystal grain size of R-Fe-B is 5 μm or less. By producing a system-based sintered magnet, the volume fraction (%) of the surface deteriorated layer of the sintered magnet body is 0.5 × S / V (S / V is specific surface area and the unit is mm ⁻¹ ) or less. The maximum energy product of the sintered magnet body is 85% or more of the bulk energy of the sintered magnet, that is, 85% or more of the maximum energy product of the magnet body having a specific surface area of approximately less than 0.6 mm ⁻¹ , which causes deterioration of magnetic characteristics. It has been found that the present invention can be significantly reduced, and the present invention has been completed. It is.
[0009]
That is, the permanent magnet material according to the present invention is a sintered magnet having an R—Fe—B-based composition (R is one or more selected from rare earth elements including Y), and is a main component determined from the area fraction. The average crystal grain size of the phase is 5 μm or less, and the specific surface area is ground to 6 mm ⁻¹ or more, and the volume fraction (%) of the surface deteriorated layer of the sintered magnet body is 0.5 × S / V (S / V is a specific surface area, and the unit is mm- ¹ ) or less.
[0010]
Furthermore, the maximum energy product of the sintered magnet body is 85% or more of the maximum energy product of the bulk state of the sintered magnet, that is, the maximum energy product of the magnet body whose specific surface area before grinding is less than 0.6 mm ^−1. It is characterized by the following.
[0011]
In addition to the above aspect, after the grinding processing, the sintered magnet body is washed with at least one of an alkali, an acid, and an organic solvent, and the volume fraction (%) of the surface deteriorated layer of the sintered magnet body is 0.5 × S / V. (S / V is specific surface area and the unit is mm ⁻¹ ) or less, and the maximum energy product of the sintered magnet body is 85% or more of the maximum energy product in the bulk state of the sintered magnet. And
Further, the present invention is characterized in that the permanent magnet body is subjected to surface treatment by plating or painting.
[0012]
Hereinafter, the present invention will be described in more detail.
The present invention reduces the deterioration of magnetic properties due to the grinding of the surface of an R—Fe—B sintered permanent magnet body and has a high performance for small or thin magnets having a specific surface area S / V of 6 mm ⁻¹ or more. It relates to a permanent magnet material.
Here, the R-Fe-B-based sintered permanent magnet can be obtained by coarsely pulverizing, finely pulverizing, molding, and sintering the master alloy according to a conventional method.
In this case, the master alloy contains R, Fe, and B. R is one or more selected from rare earth elements including Y, and specifically, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu Nd, Pr, and Dy are preferred. The content of the rare earth element containing Y is preferably 10 to 20 atomic%, more preferably 12 to 15 atomic%, and more preferably 10% or more of Nd and Pr or any one of them in R. It is preferable that the content be 50 atomic% or more. B is preferably contained in an amount of 3 to 15 atomic%, particularly 4 to 8 atomic%. In addition, Al, Cu, Zn, In, Si, P, S, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta, One or more selected from W may be contained in an amount of 0 to 11 atomic%, particularly 0.1 to 5 atomic%. The balance is Fe or inevitable impurities such as C, N, and O, but Fe is preferably contained at 50 at% or more, particularly at least 65 at%. Further, a part of Fe, for example, 0 to 40 atomic%, particularly 0 to 15 atomic% of Fe may be replaced with Co.
[0013]
The mother alloy is obtained by melting a raw metal or alloy in a vacuum or an inert gas, preferably an Ar atmosphere, and then casting it in a flat mold or a book mold, or casting it by strip casting. It should be noted that an alloy close to the R ₂ Fe ₁₄ B compound composition, which is the main phase of the present alloy, and an R-rich alloy, which is a liquid phase aid at the sintering temperature, are separately prepared, weighed and mixed after coarse pulverization. The two-alloy method is also applicable to the present invention. However, for an alloy having a composition close to the main phase, α-Fe tends to remain depending on the cooling rate during casting and the alloy composition, and is homogenized as necessary for the purpose of increasing the amount of the R ₂ Fe ₁₄ B compound phase. A chemical treatment is performed. The heat treatment is performed at 700 to 1,200 ° C. for 1 hour or more in a vacuum or Ar atmosphere. For an R-rich alloy serving as a liquid phase aid, a so-called liquid quenching method can be applied in addition to the casting method.
[0014]
The above alloy is usually coarsely pulverized to 0.05 to 3 mm, particularly 0.05 to 1.5 mm. In the coarse grinding step, a brown mill or hydrogen grinding is used. In the case of an alloy produced by strip casting, hydrogen grinding is preferable.
The coarse powder obtained in this manner is finely pulverized by, for example, a jet mill using high-pressure nitrogen. At this time, the weight-median particle size of the fine powder measured by using a laser diffraction method is 5 μm or less, Pulverization is preferably performed so as to be 0.2 to 5 μm, and more preferably 0.5 to 4.5 μm. However, powders having a weight median particle size of 5 μm or less are very active, and when exposed to the air, oxidation proceeds rapidly with heat generation. Therefore, it is necessary to prevent the fine powder from coming into contact with the atmosphere during the period from the pulverization step to the sintering step through compression molding in a magnetic field. For this purpose, the fine powder recovery container is filled with a solvent capable of inhibiting the oxidation of the fine powder such as mineral oil to make the fine powder into a slurry, wet-molded and put into a sintering furnace, or the entire apparatus or a mold is used. Dry molding is performed by a compression molding machine in which the vicinity is an inert gas atmosphere, and the resultant is put into a sintering furnace. In the latter case, the container is kept in an inert gas atmosphere even when the fine powder and the molded body are moved to the next step, or all the paths in which the fine powder and the molded body are moved, including the apparatus, are placed in an inert gas atmosphere. Even with the above-described means for preventing oxidation, it is difficult to completely prevent the oxidation of the fine powder, and if the weight-median particle size of the fine powder is less than 0.2 μm, the influence of unavoidable oxidation is large. In some cases, good magnetic characteristics cannot be obtained.
[0015]
The fine powder is formed by a compression molding machine in a magnetic field, and is put into a sintering furnace. The sintering is performed in a vacuum or in an atmosphere of an inert gas such as Ar or He at a temperature of usually 900 to 1,250 ° C, particularly 1,000 to 1,100 ° C.
Further, after sintering, at a low temperature lower than the sintering temperature, preferably 200 to 900 ° C, more preferably 350 to 750 ° C, in a vacuum or an inert gas atmosphere such as Ar or He for 10 minutes to 5 hours, particularly The heat treatment is preferably performed for about 30 minutes to 2 hours, and a magnetic material having high coercive force and good squareness can be obtained by this heat treatment.
[0016]
The sintered magnet obtained here contains the tetragonal R ₂ Fe ₁₄ B compound as a main phase in an amount of 60 to 99% by volume, particularly preferably 80 to 98% by volume, and the balance is 0.5 to 20% by volume. R-rich phase, 0 to 10% by volume of B-rich phase and at least one of carbides, nitrides, oxides and hydroxides formed by unavoidable impurities, or a mixture or composite thereof.
[0017]
The obtained sintered block is ground into a practical shape. However, in order to minimize the influence of processing strain, it is preferable to reduce the processing speed within a range where productivity is not reduced. In this case, the grinding method can be performed according to a conventional method, but the processing speed is specifically 0.1 to 20 mm / min, particularly preferably 0.5 to 10 mm / min.
[0018]
In this case, as a grinding amount, the specific surface area S / V (surface area mm ² / volume mm ³ ) of the sintered block is 6 mm ⁻¹ or more, preferably 10 mm ⁻¹ or more. The upper limit is appropriately selected and is not particularly limited, but is usually 40 mm ^-1 or less, particularly 30 mm ^-1 or less.
[0019]
In the above-described grinding process, when a water-based coolant is used for the grinding machine, or when the ground surface is exposed to a high temperature during the processing, an oxide film is likely to be formed on the surface to be ground. In order to remove this, washing is performed using at least one of an alkali, an acid and an organic solvent. When a surface treatment by plating or painting is required, this treatment is a pretreatment.
[0020]
Incidentally, as the alkali, potassium pyrophosphate, sodium pyrophosphate, potassium citrate, sodium citrate, potassium acetate, sodium acetate, potassium oxalate, sodium oxalate, etc., as the acid, hydrochloric acid, nitric acid, sulfuric acid, acetic acid, Citric acid, tartaric acid and the like can be used, and as an organic solvent, acetone, methanol, ethanol, isopropyl alcohol and the like can be used. In this case, the alkali or acid can be used as an aqueous solution having an appropriate concentration that does not corrode the magnet body.
[0021]
In the sintered magnet of the present invention, the average crystal grain size D of the main phase determined from the area fraction is 5 μm or less, preferably 0.5 to 5 μm, and more preferably 1 to 4.5 μm. As described above, the average thickness t (μm) of the surface-deteriorated layer on the surface to be ground is approximately the same as the average crystal grain size (μm) obtained from the area ratio of the magnet main phase. The volume fraction (%) of the surface-deteriorated layer is 0.5 × S / V (S / V is a specific surface area, the unit is mm ⁻¹ ) or less, preferably 0.4 × S / V or less, more preferably 0 × S / V. 0.3 × S / V or less. Although the lower limit may be 0, it is usually at least 0.01 × S / V, especially at least 0.03 × S / V.
[0022]
Here, the average thickness t of the deteriorated layer is calculated according to the following procedure.
First, a demagnetization curve (JH curve) of the ground magnet body is measured. When the slope of the demagnetization curve is plotted against the applied magnetic field (dJ / dH-H curve), two peaks are recognized. Among them, the peak position at the peak with the applied magnetic field having a large absolute value corresponds to the magnetization reversal of the crystal grains in the magnet body whose characteristics have not deteriorated. The peak position at the other peak (referred to as _Hdmg ) corresponds to the coercive force of the surface deteriorated layer of the magnet body, and the magnetic polarization of the deteriorated layer is zero at that position. Therefore, the value of magnetic polarization (referred to as J _blk ) corresponding to H _dmg in the JH curve can be defined as the magnetic polarization of undegraded particles inside the magnet. Using the saturation magnetic polarization (J _s ) of the magnet body and J _blk , the volume fraction (referred to as V _dmg , the unit is percent) of the area deteriorated by the grinding is calculated by the following equation.
V _dmg = _{[(J s -J blk) / J} s ] × 100
[0023]
On the other hand, for example, assuming that the magnet body is a rectangular parallelepiped and its size is A × B × C (unit: μm), V _dmg can be expressed as the following equation using the average thickness t of the deteriorated layer. , T is calculated from the following equation.
V _dmg = [1- (A-2t) × (B-2t) × (C-2t) / ABC] × 100
[0024]
Even when the magnet body has an arbitrary shape, an equation similar to the above equation can be easily described according to the shape.
[0025]
Further, the average crystal grain size D of the magnet main phase is determined as follows. First, after the magnet body is mirror-polished, the grain boundaries are contrasted with a corrosive liquid. The area of each particle is measured from an optical microscope image or a scanning electron microscope image taken of the arbitrary field of view, and the diameter of a circle equivalent to this is defined as the crystal particle size of each particle. Subsequently, when creating a histogram showing the particle size distribution, the ratio of the area occupied by the crystal grains is plotted instead of the number of crystal grains existing in the range with respect to the range of the particle size. An example is shown in FIG. The area median grain size obtained from this histogram is defined as the average crystal grain size.
[0026]
The volume fraction (%) of the surface-deteriorated layer in the present invention is 0.5 × S / V or less as described above. The reason for this limitation is as follows.
If the average thickness of the surface deteriorated layer is constant, the volume fraction occupied by the deteriorated layer increases as the specific surface area increases. The dimensional limit that can be ground by the current technology is about S / V = 30 mm ^{−1 in} specific surface area. When the volume fraction of the deteriorated layer exceeds 0.5 × S / V in the magnet body of S / V = 30 mm ⁻¹ , that is, when the volume fraction of the magnet layer is 15% or more, the maximum energy obtained is reduced to 4MGOe or less. In order to make full use of the high magnetic properties of the R-Fe-B based sintered magnet represented by the Fe-B based sintered magnet, the volume fraction of the surface-deteriorated layer should be 0.5 × S / V or less. I do. To achieve this, as described above, the average crystal grain size of the main phase of the sintered magnet needs to be 5 μm or less.
[0027]
Further, a decrease in the squareness of the demagnetization curve due to the processing leads to a decrease in the maximum energy product. However, when the volume fraction of the surface-deteriorated layer is set to 0.5 × S / V or less, the sintered magnet body The maximum energy product can be increased to 85% or more of the maximum energy product of the magnet body before grinding, in which the sintered magnet has a bulk state, that is, the specific surface area is less than 0.6 mm ^-1 .
[0028]
Therefore, according to the present invention, a small or thin permanent magnet with less characteristic deterioration can be provided. In this case, as an example of a specific size of the permanent magnet, 1 mm × 1 mm × 1 mm (S / V = 6 mm ⁻¹ ), 0.8 mm × 0.8 mm × 0.25 mm (S / V = 13 mm ⁻¹⁾ ), 0.8 mm × 0.8 mm × 0.13 mm (S / V = 20 mm ⁻¹ ), 0.8 mm × 0.3 mm × 0.13 mm (S / V = 25 mm ⁻¹ ), and the like.
[0029]
In the present invention, the magnet may be subjected to surface treatment by plating or painting. In this case, the plating may be performed as a single layer or a laminate of a single substance or an alloy of Ni, Cu, Sn, Zn, Au, and Ag, and the thickness of the plating film is 0.1 to 30 μm, particularly 1 to 30 μm. It is preferably 20 μm. Examples of the coating include an inorganic coating such as water glass, a resin coating such as an epoxy resin and an acrylic resin, or a treatment such as a zinc rich paint, and the thickness is 0.1 to 100 μm, particularly 1 to 50 μm. Is preferred.
[0030]
【Example】
Hereinafter, specific embodiments of the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.
[0031]
[Example 1, Comparative Example 1]
Strip casting method in which a predetermined amount of Nd, Dy, Co, Al, Fe metal and ferroboron having a purity of 99% by weight or more and ferroboron are weighed in a high frequency and melted in an Ar atmosphere, and the molten alloy is poured into a copper single roll in an Ar atmosphere. Thus, a thin plate-shaped alloy was obtained. The composition of the obtained alloy is such that Nd is 11.0 atomic%, Dy is 2.3 atomic%, Co is 1.0 atomic%, Al is 1.0 atomic%, B is 4.5 atomic%, and Fe is The remainder is referred to as alloy A. After absorbing hydrogen in the alloy A, the alloy A was heated to 500 ° C. while performing evacuation to partially release hydrogen, so-called hydrogen pulverization to obtain coarse powder of 30 mesh or less. Further, a predetermined amount of Nd, Dy, Fe, Co, Al, Cu metal and ferroboron having a purity of 99% by weight or more was weighed, and after high frequency melting in an Ar atmosphere, casting was performed. The composition of the obtained alloy is 20 atomic% of Nd, 10 atomic% of Dy, 24 atomic% of Fe, 6 atomic% of B, 1 atomic% of Al, 2 atomic% of Cu, and the balance of Co, This is referred to as alloy B. The alloy B was coarsely pulverized to 30 mesh or less using a brown mill in a nitrogen atmosphere.
[0032]
Subsequently, 90% by weight of the alloy A powder and 10% by weight of the alloy B powder were weighed and mixed in a nitrogen-purged V blender for 30 minutes. This mixed powder was finely pulverized by a jet mill using high-pressure nitrogen gas to a powder having a median particle diameter of 4 μm. The obtained mixed fine powder was molded at a pressure of about 1 ton / cm ² while being oriented in a magnetic field of 15 kOe under a nitrogen atmosphere without being exposed to the atmosphere. Next, the molded body was put into a sintering furnace in an Ar atmosphere without being exposed to the air, sintered at 1,060 ° C. for 2 hours, further aged at 510 ° C. for 1 hour, and rapidly cooled to 10 mm × 20 mm × A magnet block having a thickness of 15 mm was manufactured. The magnet block was entirely ground into a rectangular parallelepiped having a predetermined size so that the specific surface area S / V became 20 mm ⁻¹ by an inner peripheral cutting machine, thereby obtaining a magnet body of the present invention. This is called a magnet M1.
[0033]
For comparison, the mixed powder having the same composition was finely pulverized by a jet mill into a powder having a weight median particle diameter of 8 μm. The obtained mixed fine powder was molded at a pressure of about 1 ton / cm ² while being oriented in a magnetic field of 15 kOe in the atmosphere. Then, it was put into a sintering furnace in an Ar atmosphere, sintered at 1,080 ° C. for 2 hours, further aged at 510 ° C. for 1 hour, and quenched to prepare a magnet block having dimensions of 10 mm × 20 mm × 15 mm in thickness. The magnet block was entirely ground into a rectangular parallelepiped of a predetermined size so that the specific surface area S / V became 20 mm ⁻¹ by an inner peripheral blade cutting machine. This is called a magnet P1.
[0034]
FIG. 1 shows the demagnetization curves of the magnet bodies M1 and P1 as curves H and K, respectively. Table 1 shows the average crystal grain size, the magnetic properties before and after the processing, the average thickness of the surface-deteriorated layer, and the volume fraction. In the prior art, when processed to S / V = 20 mm ⁻¹ , the volume fraction of the degraded layer reached close to 40%, and the maximum energy product was only 10% or less of the bulk magnet. And a high energy product far exceeding
[0035]
[Table 1]

[0036]
[Example 2]
The magnet body M1 whose entire surface was ground so that the specific surface area S / V became 20 mm ^-1 was washed with an alkali solution, then washed with an acid, and dried. This is called magnet body M2. Before and after each cleaning, a cleaning step using pure water is included. Table 2 shows the magnetic properties of the magnet M2, the average thickness of the surface-deteriorated layer, and the volume fraction. It can be seen that the magnetic properties are not deteriorated at all as compared with the magnet body M1.
[0037]
[Example 3]
The magnet body M2, which was entirely ground so that the specific surface area S / V became 20 mm ^-1 and washed with alkali and then with acid, was coated with a copper film having a thickness of about 5 μm by electroless copper plating. This is called magnet body M3. Table 2 also shows the magnetic properties of the magnet M3, the average thickness of the surface-deteriorated layer, and the volume fraction. It can be seen that the magnetic properties are hardly deteriorated as compared with the magnet bodies M1 and M2.
[0038]
[Table 2]

[0039]
【The invention's effect】
According to the present invention, it is possible to provide a small or thin permanent magnet of S / V = 6 mm ⁻¹ or more that exhibits good magnetic properties without performing a heat treatment for restoring the properties after grinding.
[Brief description of the drawings]
FIG. 1 is a diagram showing a demagnetization curve (curve H) of a magnet body according to the present invention and a demagnetization curve (curve K) of a magnet body according to the prior art.
FIG. 2 is a view showing a crystal grain size distribution of a magnet body according to the present invention.

Claims (5)

A sintered magnet having an R-Fe-B composition (R is one or more selected from rare earth elements including Y), wherein the average crystal grain size of the main phase determined from the area fraction is 5 µm or less. , the specific surface area is machined on or ^{6 mm -1,} in sintered volume fraction of the magnet body surface deterioration layer (%) is 0.5 × S / V (S / V is the specific surface area, the unit is mm ^{- 1} ) A permanent magnet material characterized by the following. A sintered magnet having an R-Fe-B composition (R is one or more selected from rare earth elements including Y), wherein the average crystal grain size of the main phase determined from the area fraction is 5 µm or less. And the maximum energy product of the sintered magnet body is ground to 6 mm ⁻¹ or more, and the maximum energy product of the sintered magnet body is less than 0.6 mm ⁻¹ before the grinding. Permanent magnet material characterized by not less than 85% of the product. A sintered magnet having an R-Fe-B composition (R is one or more selected from rare earth elements including Y), wherein the average crystal grain size of the main phase determined from the area fraction is 5 µm or less. After being ground to have a specific surface area of 6 mm ^-1 or more, the surface area of the sintered magnet body is reduced by washing with at least one of an alkali, an acid and an organic solvent (%). Is 0.5 × S / V (S / V is a specific surface area and a unit is mm ⁻¹ ) or less. A sintered magnet having an R-Fe-B composition (R is one or more selected from rare earth elements including Y), wherein the average crystal grain size of the main phase determined from the area fraction is 5 µm or less. After being ground to a specific surface area of 6 mm ⁻¹ or more, the sintered body is washed with at least one of an alkali, an acid, and an organic solvent, thereby increasing the maximum energy product of the sintered magnet body. A permanent magnet material characterized in that the specific energy is 85% or more of the maximum energy product of the magnet body having a specific surface area of less than 0.6 mm ^-1 before grinding. 5. The permanent magnet material according to claim 1, wherein the permanent magnet material is subjected to a surface treatment by plating or painting.

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