JP4983619B2 - permanent magnet - Google Patents

Description

  The present invention relates to a permanent magnet used in a rotating device such as a motor, a voice coil motor (VCM) for a hard disk drive (HDD), and the like.

  Rare earth magnets, for example, R-TM-B magnets (R is a rare earth element, TM is a transition metal element containing Fe as a main component, and B is boron) are electric / electronic because of their excellent magnetic properties and economy. Widely used in the field of equipment. Among them, Nd-Fe-B magnets have high magnetic properties, show high energy products, are rich in Fe as the main material and are inexpensive, and Nd is resource-friendly and inexpensive compared to Sm. For this reason, it has become the mainstream of rare earth magnets instead of Sm—Co permanent magnets.

  However, the Nd-Fe-B magnet contains a rare earth element that oxidizes (rusts) relatively easily as a main component, and is disadvantageous in that it is very easily corroded as compared with general steel materials and Sm-Co magnets. Therefore, various surface treatments have been proposed conventionally.

  For example, in Patent Document 1, a uniform corrosion-resistant double layer composed of a Cu layer and a Ni-P layer is formed on the surface of a rare earth sintered magnet body as a protective layer by, for example, electrolytic plating or electroless plating. Has been proposed.

Japanese Patent Publication No.7-12005

  However, even when a protective layer as shown in Patent Document 1 is formed, red rust (spot rust) occurs in some after several hours, and rust and blisters occur after the next day. It is in the present situation that has not been obtained corrosion resistance.

  In addition, when the application of the permanent magnet is, for example, for HDD, in-vehicle use, or portable use, the magnet becomes smaller and thinner, the ratio of the protective layer such as a plating layer to the magnet volume increases, and the high temperature environment is severe. More cases are used under certain conditions. Under such conditions, a thermal demagnetization phenomenon occurs in which the magnetic flux density of the magnet becomes smaller than the initial magnetic flux density, and the ability as a magnet is reduced. However, Patent Document 1 does not consider measures for demagnetization.

  This invention is made | formed in view of the above, Comprising: It aims at providing the permanent magnet which can implement | achieve an improvement in corrosion resistance and reduced magnetization.

  In order to solve the above-described problems and achieve the object, the permanent magnet according to the present invention has a Ni-P-Cu with an addition amount x of Cu <0 ≦ x ≦ 0.1 wt% on the surface of the metal magnet body. It has the protective layer which consists of a layer, It is characterized by the above-mentioned.

  The permanent magnet according to the present invention is characterized in that, in the above invention, the amount x of Cu added is 0.01 ≦ x ≦ 0.1 wt%.

  The permanent magnet according to the present invention is characterized in that, in the above invention, a buffer layer is provided between the surface of the metal magnet body and the protective layer.

  The permanent magnet according to the present invention is characterized in that, in the above invention, the buffer layer is made of a Cu layer.

  The permanent magnet according to the present invention is characterized in that, in the above-mentioned invention, the metal magnet element is a rare earth magnet containing a rare earth element.

  The permanent magnet according to the present invention is provided with a protective layer made of a Ni-P-Cu layer to which a predetermined amount of Cu is added on the surface of the metal magnet body, thereby suppressing demagnetization and improving corrosion resistance. There is an effect that can be made. It is confirmed that when a small amount of Cu is added to the Ni-P layer, the film stress (residual stress) after the heat treatment is reduced, and the protective layer by adding an appropriate amount of such Cu. This is presumably because the decrease in film stress contributes to the suppression of thermal demagnetization and the improvement of corrosion resistance in some form.

  The best mode for carrying out the permanent magnet according to the present invention will be described below with reference to the drawings. The permanent magnet of the present invention is not particularly limited as long as it is a metal magnet. In the present embodiment, as a suitable example, a configuration example using an R-TM-B permanent magnet will be shown.

  FIG. 1 is a perspective view showing a configuration example of a permanent magnet according to the present embodiment, and FIG. 2 is a central longitudinal side view thereof. The permanent magnet 1 of the present embodiment includes a magnet body 2 that is a metal magnet body that forms a magnet body, a buffer layer 3 formed on the surface of the magnet body 2, and the surface of the buffer layer 3, that is, The protective layer 4 is formed on the outermost layer on the surface of the magnet body 2.

[Magnet body 2]
The magnet body 2 is a sintered body containing R (R is composed of at least one rare earth element including Y), TM (transition element containing Fe as a main component), and B (boron) as main components. is there. That is, the magnet body 2 is composed of a rare earth magnet containing a rare earth element.

  Here, the contents of R, TM, and B are preferably 5.5 ≦ R ≦ 30 atomic%, 42 ≦ TM ≦ 90 atomic%, and 2 ≦ B ≦ 28 atomic%, respectively. It is preferable that TM is basically composed of Fe as a main component, a substitution element thereof, and inevitable impurities, and 11.7 ≦ R ≦ 13.5 atomic%, 42 ≦ TM ≦ 90 atomic%, 5 More preferably, ≦ B ≦ 7 atomic%.

  When the magnet body 2 in the present embodiment is manufactured by powder metallurgy, the following composition is preferable. First, the rare earth element R includes at least one of Nd, Pr, Ho, and Tb, or one or more of La, Sm, Ce, Gd, Er, Dy, Eu, Pm, Tm, Yb, and Y. Those are preferred.

  In addition, when using 2 or more types of elements as R, a mixture, such as a misch metal, can be used as a raw material. It is preferable that the element R always contains Nd and / or Pr. The ratio between Nd and Pr is not particularly limited. The total amount of elements other than both Nd and Pr is preferably 10 atomic% or less of the entire element R. Furthermore, it is preferable to add Dy and / or Tb.

  The content of R is particularly preferably from 5.5 to 30 atomic%. When the R content is less than 5.5 atomic%, the crystal structure is a cubic structure having the same structure as α-Fe, so that a high coercive force (Hcj) cannot be obtained, and the R content is 30 atomic%. If it exceeds, the R-rich nonmagnetic phase increases, and the residual magnetic flux density (Br) decreases. When 11.7 ≦ R ≦ 13.5 atomic%, the maximum energy product can be increased, which is preferable for the present embodiment. More preferably, the content of R is 12.2 to 13.5 atomic%.

  The TM content is preferably 42 to 90 atomic%. When the TM content is less than 42 atomic%, the residual magnetic flux density (Br) decreases, and when the TM content exceeds 90 atomic%, the coercive force (Hcj) decreases. By substituting a part of Fe with Co, the temperature characteristics can be improved without impairing the magnetic characteristics. However, when the Co substitution amount exceeds 50% of Fe, the magnetic characteristics are lowered. 50% or less is preferable.

  The content of B (boron) is preferably 2 to 28 atomic%. If the B content is less than 2 atomic%, a rhombohedral structure is obtained, and the coercive force (Hcj) is insufficient. If the B content exceeds 28 atomic%, a B-rich nonmagnetic phase increases, Magnetic flux density (Br) decreases. The content of B is further preferably 5 to 7 atomic%, more preferably 5.5 to 6.5 atomic%.

  Further, in addition to the above R, TM, and B, Ni, Si, Cu, Ca, O, C, and the like as unavoidable impurities may be contained in 3 atomic% or less of the whole.

  Furthermore, by replacing a part of B with one or more of C, P, S, and Cu, productivity can be improved and costs can be reduced. In this case, the amount of substitution is preferably 4 atomic% or less.

  In addition, Al, Ti, V, Cr, Mn, Bi, Nb, Ta, Mo, W, Sb, Ge, Sn, Zr, Ni, Si are used to improve coercivity, improve productivity, and reduce costs. One or more of Hf, Ga, Cu and the like may be added. In this case, the total amount added is preferably 10 atomic% or less.

  The magnet body 2 made of the R-TM-B system has a main phase having a substantially tetragonal crystal structure. The particle size of the main phase is preferably about 0.5 to 100 μm. Furthermore, it usually contains a nonmagnetic phase of 0.5 to 50% by volume. Such a magnet body 2 is preferably manufactured by a powder metallurgy method as described below.

  First, an alloy having a desired composition is produced by a process such as a casting method or a strip casting method. The obtained alloy is roughly pulverized to a particle size of about 10 to 800 μm by a jaw crusher, brown mill, stamp mill or the like, and then finely pulverized to a particle size of about 0.5 to 10 μm by a jet mill, an attritor or the like.

The obtained powder is preferably molded in a magnetic field. In this case, the magnetic field strength is preferably 600 kA / m or more, and the molding pressure is preferably about 0.5 to ⁵ ton / cm ² . The obtained molded body is sintered at a temperature of 900 to 1200 ° C. for 0.5 to 24 hours and rapidly cooled. The sintering atmosphere is preferably an inert gas such as Ar gas or a vacuum. Thereafter, an aging treatment is preferably performed at 500 to 900 ° C. for 1 to 24 hours in an inert gas atmosphere or in a vacuum. Further, the sintering treatment and the aging treatment may be performed in a plurality of times.

[Buffer layer 3]
The buffer layer 3 is formed on the surface of the magnet body 2 formed in this way. The purpose of the buffer layer 3 is to protect the magnet body 2 during the electroless plating process to form the protective layer 4. Since electroless plating has low deposition efficiency, a large amount of hydrogen is generated. In the electroless plating reaction, comparing the metal precipitation reaction that is the main reaction and the hydrogen generation reaction that is the side reaction, the hydrogen generation efficiency is higher than the metal precipitation efficiency (about 30%). However, a large amount of hydrogen is generated due to the main hydrogen generation reaction. As a result, the magnet body 2 made of a rare earth magnet having a high hydrogen storage property absorbs hydrogen and becomes powdery, so that the magnetic properties of the magnet, the adhesion properties and the corrosion resistance properties of the protective layer 4 are deteriorated. Further, the surface component of the magnet body 2 is eluted by a substitution reaction by the electroless plating bath.

  For the buffer layer 3, from the viewpoint of hydrogen blocking and substitution reaction suppression, metals and alloys such as Cu, Ni, Co, Ag, Sn, Al, Si, Fe, Mo, Ti, Zr, V, Nb, Mn, Or these oxides, nitrides, carbides and the like are not particularly limited, and among them, Cu and Ni are preferable, and Cu is more preferable. Moreover, there is no restriction | limiting in particular about the formation method of Cu layer as the buffer layer 3, Wet plating methods, such as electroplating, Mechanical plating methods, Vacuum film-forming methods, such as vapor deposition, a sputter | spatter, ion plating, CVD Any method such as (Chemical Vapor Deposition) method or PVD (Physical Vapor Deposition) method may be used.

  The buffer layer 3 will be described in detail below by taking an electroplating method as an example of a typical Cu layer forming method.

  Prior to plating the Cu layer as the buffer layer 3 on the magnet body 2 obtained as described above, it is preferable to perform a predetermined pretreatment as described below. That is, before the plating process, barrel polishing is performed to remove burrs and the like on the processed surface of the magnet body 2. Further, degreasing treatment is performed to remove dirt on the surface of the magnet body 2, and chemical etching with acid is performed to clean the surface. The degreasing solution used in the degreasing treatment may be any one that is used for ordinary steel. In general, it is mainly composed of NaOH, and other additives are not specified. Nitric acid is preferably used as the acid used in the chemical etching.

  When plating a general steel material, non-oxidizing acids such as hydrochloric acid and sulfuric acid are often used. However, in the case where the magnet body 2 contains a rare earth element as in the present embodiment, when the treatment is performed using a non-oxidizing acid such as hydrochloric acid or sulfuric acid, hydrogen generated by the acid is generated in the magnet body 2. Occluded on the surface of the material, the occlusion site becomes brittle and a large amount of powder undissolved material is generated. This powder undissolved material causes surface roughness, defects and poor adhesion after plating. For this reason, it is preferable that these acids are not contained in the chemical etching treatment solution. Therefore, it is preferable to use nitric acid, which is an oxidizing acid that generates little hydrogen. Furthermore, it is more preferable to use nitric acid containing aldonic acid or a salt thereof at the same time because unevenness of a level that cannot be visually confirmed is formed on the surface and the adhesion of the film is improved.

  Such an improvement in adhesion is selectively realized by aldonic acid or a salt thereof, but not by other organic acids such as citric acid or tartaric acid.

  It is more preferable that the concentration of nitric acid in the treatment liquid used for the pretreatment is 1 N or less, particularly 0.5 N or less. When the concentration of nitric acid exceeds 1N, the dissolution rate of the magnet body 2 is extremely fast, and it becomes difficult to control the amount of dissolution. In particular, the amount of dissolution increases in a large amount of processing such as barrel processing, and the product dimensions The accuracy cannot be maintained. Moreover, when the nitric acid concentration becomes too thin, the amount of dissolution becomes insufficient. For this reason, the nitric acid concentration is desirably 1 N or less, particularly 0.5 to 0.05 N as described above. The amount of Fe dissolved at the end of the treatment is about 1 to 10 g / L.

  Furthermore, in order to completely remove a small amount of undissolved substances and residual acid components from the surface of the magnet body 2 that has been subjected to pretreatment, it is preferable to perform cleaning using ultrasonic waves. This ultrasonic cleaning is preferably performed in ion-exchanged water with very few chlorine ions that generate rust on the surface of the magnet body 2. Moreover, you may perform the same water washing before and after such ultrasonic cleaning, and in each process of pre-processing as needed.

  A Cu layer is formed as a buffer layer 3 by electroplating on the surface of the magnet body 2 subjected to the above pretreatment. By forming the Cu layer by electroplating, a high performance corrosion resistant film excellent in mass productivity can be formed particularly in the case of small objects.

  In addition, when forming a Cu layer directly on the surface of the magnet body 2 by electroplating, in order to prevent substitution deposition of Cu on the surface of the magnet body 2, the treatment may be performed in a weak alkaline bath having a pH of 7 to 10. preferable. At this time, the plating bath preferably contains any of an organic phosphonic acid compound, EDTA, and cyan in the bath. In particular, an organic phosphonic acid compound and EDTA are preferable because they have a small environmental load. Note that the thickness of the Cu layer is 0.1 to 50 μm, preferably 1 to 10 μm.

[Protective layer 4]
A Ni—P—Cu electroless plating film is formed as the protective layer 4 on the surface of the buffer layer 3 formed in this way. In electroless plating, metal ions in the plating bath are deposited on the surface of the substrate as a metal using a chemical reaction of a reducing agent. The Ni-P-Cu electroless plating solution contains 100 g / L or less of at least one nickel metal salt among nickel chloride, nickel sulfate, and nickel hypophosphite, and copper chloride, sulfuric acid are used as the copper metal source. At least one of copper, copper pyrophosphate, copper porphyrin complex, copper phthalocyanine complex is contained in an amount of 20 g / L or less, hypophosphite is contained as a reducing agent in an amount of 100 g / L or less, and hydroxide is used as a pH adjusting agent. What contains 150 g / L or less of at least 1 sort (s) among basic compounds, such as sodium and ammonium hydroxide, an inorganic acid, and an organic acid is preferable.

  150 g / L or less of at least one of oxycarboxylic acids such as sodium citrate and sodium acetate as buffering agents, or inorganic acids such as boric acid and carbonic acid, sodium citrate, sodium acetate, ammonium hydroxide as complexing agents, 100 g / L or less of at least one of ethylene glycol and further alkali salts of organic acids (acetic acid, glycolic acid, citric acid, tartaric acid, gluconic acid, etc.), thioglycolic acid, ammonia, triethanolamine, ethylenediamine, glycine, and pyridine In addition, 10 g / L or less of sulfide, chloride, fluoride, and surfactant can be contained as an accelerator and a stabilizer, respectively.

  This plating solution is used in the range of pH 3 to 13, and the bath temperature during plating is in the range of 20 to 100 ° C.

  The method of immersing the magnet body 2 in the plating solution may be either a barrel method or a hooking jig method, and is appropriately selected depending on the size and shape of the magnet body 2.

The deposited plating film is composed of Ni and P as main components, and P is composed of an amorphous phase in which Ni is supersaturated in Ni, or a fine mixed phase of Ni and a nickel phosphide phase such as Ni ₃ P. The content of P is not particularly limited, but the P content is preferably 0.1 to 14% by weight, and more preferably 7 to 12% by weight. Further, the content x of Cu is preferably 0 <x ≦ 0.1 wt%, and more preferably 0.01 ≦ x ≦ 0.1 wt%. In terms of corrosion resistance, the plating thickness of the protective layer 4 is preferably 0.5 to 20 μm, and more preferably 1 to 10 μm.

  In the present embodiment, since the surface layer of the magnet body 2 has a two-layer structure of the buffer layer 3 and the protective layer 4, the corrosion resistance is improved. For example, even if pinholes exist when the buffer layer 3 is formed as a Cu layer by an electroplating method, the penetrating state of the pinholes is interrupted by forming and covering the protective layer 4 on the surface layer. Even if pinholes are present in the protective layer 4 formed by electroless plating on the surface layer, the presence of the buffer layer 3 in the base layer does not penetrate the magnet body 2 and keeps the corrosion resistance. In particular, when the buffer layer 3 is formed as a Cu layer, the protective layer 4 (Ni—P—Cu layer) having a higher ionization tendency than the buffer layer 3 (Cu layer) is present on the surface of the buffer layer 3. Corrosion proceeds when the base protective layer 4 (Ni—P—Cu layer) dissolves in an anodic manner, and the noble buffer layer 3 (Cu layer) is cathodic-proofed. Since the layer 3 is protected, the corrosion resistance is further improved.

  In addition, in electroless plating film formation, a base layer serving as a catalyst is necessary in principle, and a known palladium catalyst or the like can also be used in this embodiment. However, the magnet body 2 itself may have catalytic activity without performing the catalyst application treatment as a normal pretreatment for electroless plating. Moreover, the plating film deposited by electrolytic plating may act as a catalyst. Furthermore, the protective layer 4 is not limited to electroless plating film formation, and may be formed by a thin film formation method such as sputtering. In these cases, the buffer layer 3 may be omitted, and the protective layer 4 may be formed directly on the surface of the magnet body 2. Moreover, in this Embodiment, although the protective layer 4 was formed in the outermost layer of the surface of the magnet element | base_body 2, after forming the protective layer 4 in order to improve the corrosion resistance improvement and the intensity | strength with an adhesive agent, Another layer may be provided on the surface, or the protective layer 4 may be subjected to post-treatment such as chromate treatment.

  Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to the examples.

[Production of magnet sample]
(14.1) Nd- (0.4) Dy- (78.8) Fe- (0.6) Co- (6.1) A coarsely pulverized ingot of composition B is further jetted with an inert gas. A fine powder having an average particle size of about 3.5 μm was obtained by milling. This fine powder was molded in a magnetic field, and sintered and heat-treated to obtain a sintered magnet. Next, this sintered magnet was cut into a length of 20 mm, a width of 10 mm, and a thickness of 2 mm to obtain a magnet body 2.

  The processed magnet body 2 was subjected to Cu electroplating through the steps of barrel polishing, degreasing, and etching, and a 7 μm-thick Cu layer was formed as a buffer layer 3 on the surface of the magnet body 2.

A protective layer 4 was formed by electroless plating on the surface of the magnet body 2 on which the buffer layer 3 made of the Cu layer was formed. At this time, the electroless plating bath is
Hypophosphite Na 30g / L
Lactic acid 28g / L
Sulfuric acid Ni 20g / L
Phthalocyanine copper 0-1g / L
pH = 4.5, 90 ° C
It was. The formed protective layer 4 by electroless plating is a Ni—P—Cu layer, the composition of which is Cu content x [wt%] x = 0, 0.005, 0.01, 0.05, By changing to 0.1 and 0.15, Ni-12 wt% P-0 to 0.15 wt% Cu was obtained, and the film thickness was 5 μm. After the protective layer 4 was formed, it was washed with pure water, substituted with alcohol, and then air-dried to produce six samples with different Cu contents x in the protective layer 4.

[Measurement for characterization]
And the salt spray test for the stress measurement of the electroless plating film | membrane, the thermal demagnetization measurement for magnetic flux change evaluation, and corrosion resistance evaluation was done.

  The stress measurement of the electroless plating film is performed in the same process as in the case of 6 samples on a copper plate, and electroless plating with a film thickness of 5 μm corresponding to the protective layer 4 is performed, and is performed at 150 ° C. in a hot air circulation oven. After maintaining the time, the sample was gradually cooled to room temperature, and the stress was measured with a stress tester which is a strip electrodeposition stress measuring instrument (manufactured by Electrochemical Co., USA). The following results were obtained by such stress measurement. In addition, FIG. 3 is a graph which shows the result of the film | membrane stress measurement after such heat processing.

Cu content x [% by weight] Stress [kg / mm ² ]
x = 0 18
x = 0.005 6.1
x = 0.01 4.2
x = 0.05 7.8
x = 0.1 12
x = 0.15 23

In addition, the magnetic flux change (demagnetization) with respect to the initial magnetic flux is evaluated by measuring the open flux before the heat treatment after magnetizing the five samples prepared as described above, and then measuring the stress of the above-described film. As in the case, hold at 150 ° C. for 2 hours in a hot air circulating oven, slowly cool to room temperature, re-magnetize, measure the open flux after heat treatment, and evaluate the rate of change of magnetic flux before and after heat treatment It is a thing. Here, the rate of change of magnetic flux is
Magnetic flux change rate = (open flux after heat treatment−open flux before heat treatment) / open flux before heat treatment. The following results were obtained by such thermal demagnetization measurement.

Cu content x [wt%] Magnetic flux change rate [%]
x = 0-1.45
x = 0.005-0.95
x = 0.01-0.87
x = 0.1-0.99
x = 0.15 -1.55

  Furthermore, the corrosion resistance evaluation is performed by conducting a salt spray test (JIS Z2371) under the conditions of a temperature of 35 ° C. and a 5% neutral NaCl solution on the five samples prepared as described above, and visually measuring and evaluating the rusting area. It is a thing. The results shown in Table 1 were obtained by the salt spray test, where ◯ indicates no rust generation, Δ indicates partial red rust generation (spot rust), and X indicates rust and blister generation.

[Characteristic evaluation]
Since the magnetic flux change rate indicates the degree of deterioration due to demagnetization of the magnetic flux with respect to the initial magnetic flux, it can be said that the smaller the value of the magnetic flux change rate, the better. According to the result of the thermal demagnetization measurement of this example, when the Cu content x in the protective layer 4 is x = 0.005, x = 0.01, x = 0.1, Cu is not included It can be seen that the rate of change in magnetic flux is small compared to (x = 0), and reduced magnetism is obtained. On the other hand, it can be seen that when the Cu content x in the protective layer 4 is x = 0.15, the rate of change in magnetic flux is larger and demagnetization is greater than when Cu is not included (x = 0). Here, according to the stress measurement result of the film after the heat treatment, when the Cu content x in the protective layer 4 is x = 0.005 to 0.1, the film stress is decreased, whereas the protective layer When the Cu content x in FIG. 4 is x = 0.15, the film stress is greater than when the Cu content x is not included (x = 0). That is, it can be said that the magnitude of the magnetic flux change rate corresponds to the stress measurement result of the film after the heat treatment. Therefore, it is presumed that the decrease in the film stress of the protective layer 4 due to the addition of an appropriate amount of Cu contributes in some way to the effect of suppressing thermal demagnetization.

  Further, according to the corrosion resistance evaluation results shown in Table 1, when the protective layer 4 does not contain Cu (x = 0), some red rust (spot rust) occurs in several hours, and after 48 hours, 96 hours After the next day such as later, the occurrence of rust and blistering has been confirmed, indicating that the corrosion resistance is not sufficient. On the other hand, when the protective layer 4 containing Cu is formed, it can be seen that rust does not occur in several hours and the corrosion resistance is improved. In particular, when the Cu content x is x = 0.01 or x = 0.1, no rust occurs even after 24 hours, and some red rust (spot rust) occurs even after the next day. It can be seen that the corrosion resistance is greatly improved.

  Therefore, when these measurement results are comprehensively evaluated, the Cu content x is set to 0 <x ≦ 0.0 as the protective layer 4 formed of the Ni—P—Cu layer formed on the outermost layer of the surface of the magnet body 2. It can be seen that if it is 1% by weight, both reduced magnetism and improved corrosion resistance can be achieved. In particular, it can be seen that if the Cu content x is 0.01 ≦ x ≦ 0.1 wt%, the reduced magnetism and corrosion resistance can be greatly improved.

It is a perspective view which shows the structural example of the permanent magnet of embodiment of this invention. It is a center longitudinal cross-sectional side view of FIG. It is a graph which shows the result of the film stress measurement after heat processing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Permanent magnet 2 Magnet base body 3 Buffer layer 4 Protective layer

Claims (4)

On the surface of the metal magnet body, a protective layer made of a Ni—P—Cu layer in which the addition amount x of Cu is 0 <x ≦ 0.1 wt% ;
A buffer layer between the surface of the metal magnet body and the protective layer;
A permanent magnet comprising:   2. The permanent magnet according to claim 1, wherein the additive amount x of Cu is 0.01 ≦ x ≦ 0.1 wt%. The buffer layer is, the permanent magnet according to claim 1 or 2, characterized in that a Cu layer. The permanent magnet according to any one of claims 1 to 3 , wherein the metal magnet body is made of a rare earth magnet containing a rare earth element.

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