JP2007207936A - Rare earth permanent magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare earth permanent magnet having sufficient corrosion resistance. <P>SOLUTION: The rare earth permanent magnet 1 consists of a magnet element 3, and a protective layer 5 formed to cover the entire surface of the magnet element 3 wherein the protective layer 5 includes a first layer 2, a second layer 4 and a third layer 6 sequentially from the magnet element 3 side. The first layer is a layer containing at least a rare earth element, iron and oxygen. The second layer contains at least a rare earth element and oxygen wherein the content ratio of rare earth element to iron is larger than that in the first layer. The third layer contains at least iron and oxygen and the content ratio of rare earth element to iron is smaller than that in the first layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rare earth magnet, and more particularly to a rare earth magnet having a protective layer formed on the surface.

  In recent years, so-called rare earth magnets (for example, R—Fe—B magnets; R represents a rare earth element; the same applies hereinafter) have been developed as permanent magnets exhibiting a high energy product of 25 MGOe or more. As such a rare earth magnet, for example, Patent Document 1 discloses a magnet formed by sintering, and Patent Document 2 discloses a magnet formed by rapid quenching.

  Although this rare earth magnet exhibits a high energy product, it has a relatively low corrosion resistance because it contains a rare earth element that is relatively easily oxidized as a main component.

In order to improve the corrosion resistance of such rare earth magnets, it has been proposed to form a protective layer on the surface. For example, Patent Document 3 proposes forming a protective layer by heating a rare earth magnet at 200 to 500 ° C. in an oxidizing atmosphere.
JP 59-46008 A JP-A-60-9852 JP-A-5-226129

  However, even with the rare earth magnet of Patent Document 3, it has still been difficult to obtain sufficient corrosion resistance. For example, when a rare earth magnet is heat-treated in an oxidizing atmosphere, there is a problem that dusting or weight reduction occurs in the corrosion resistance test.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a rare earth magnet having sufficient corrosion resistance.

  In order to achieve the above object, a rare earth magnet of the present invention comprises a magnet element containing a rare earth element and iron, and a protective layer formed on the surface of the magnet element. A first layer containing at least a rare earth element, iron and oxygen, and covering the first layer, containing at least a rare earth element and oxygen, and having a higher content of the rare earth element relative to iron than the first layer The second layer includes a second layer, a third layer that covers the second layer, contains at least iron and oxygen, and has a rare earth element content ratio relative to iron that is smaller than that of the first layer.

  In the rare earth magnet having the above structure, the three layers constituting the protective layer are layers containing oxygen in addition to the constituent elements of the magnet body. Each of these layers has a higher oxygen content and is more stable than the magnet body, and is less susceptible to corrosion by the external environment. Since the rare earth magnet of the present invention is provided with a protective layer having three layers which are not easily corroded in this manner, the rare earth magnet has excellent corrosion resistance as compared with the prior art. In particular, the third layer in the protective layer is particularly excellent in corrosion resistance because the content of rare earth elements that are likely to be corroded is small compared to other layers. Therefore, by providing the third layer as the outermost layer, the rare earth magnet of the present invention can exhibit extremely excellent corrosion resistance.

  In the rare earth magnet of the present invention, the third layer is more preferably a layer that does not substantially contain a rare earth element. Thereby, the third layer becomes more difficult to be corroded, and the corrosion resistance of the rare earth magnet is further improved.

  According to the present invention, it is possible to provide a rare earth magnet having sufficient corrosion resistance.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as necessary.

FIG. 1 is a perspective view showing a rare earth magnet according to a preferred embodiment. FIG. 2 is a diagram schematically showing a cross-sectional configuration along the II-II line of the rare earth magnet shown in FIG. As shown in FIGS. 1 and 2, the rare earth magnet 1 of the present embodiment includes a magnet element body 3 and a protective layer 5 formed so as to cover the entire surface of the magnet element body 3.
[Rare earth magnet]

  Hereinafter, first, preferred embodiments of each configuration of the rare earth magnet 1 will be described.

(Magnet body)
The magnet body 3 is a permanent magnet containing a rare earth element (R) and iron (Fe). Here, the rare earth element refers to scandium (Sc), yttrium (Y), and a lanthanoid element belonging to Group 3 of the long-period periodic table. Examples of lanthanoid elements include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium. (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) and the like are included.

  Among these, as the rare earth element, at least one element selected from the group consisting of Nd, Sm, Dy, Pr, Ho and Tb is preferable, and these elements include La, Ce, Gd, Er, Eu, Tm, Yb and More preferably, it further contains at least one element selected from the group consisting of Y. As the rare earth element mainly contained in the magnet body 3, Nd is particularly preferable because it can exhibit excellent magnetic properties and the like.

  The rare earth elements include transition elements other than iron, such as cobalt (Co), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), It may further include at least one element selected from the group consisting of zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W).

  More specifically, the constituent material of the magnet body 3 is preferably an R—Fe—B based material. Such a material has a main phase of a substantially tetragonal crystal structure, and a rare earth-rich phase having a high mixing ratio of rare earth elements in the grain boundary portion of the main phase and a mixing of boron atoms. It has a high proportion of boron-rich phase. These rare earth-rich phase and boron-rich phase are nonmagnetic phases that do not have magnetism, and such a nonmagnetic phase is usually contained in an amount of 0.5 to 50% by volume in the magnet constituting material. Moreover, the particle size of the main phase is usually about 1 to 100 μm.

  In such R—Fe—B-based constituent materials, the rare earth element content is preferably 8 to 40 atomic%. When the rare earth element content is less than 8 atomic%, the crystal structure of the main phase becomes almost the same as that of α-iron, and the coercive force (iHc) tends to decrease. On the other hand, if it exceeds 40 atomic%, a rare earth-rich phase is excessively formed, and the residual magnetic flux density (Br) tends to be small.

  The Fe content is preferably 42 to 90 atomic%. When the Fe content is less than 42 atomic%, the residual magnetic flux density decreases, and when it exceeds 90 atomic%, the coercive force tends to decrease. Furthermore, the B content is preferably 2 to 28 atomic%. When the B content is less than 2 atomic%, a rhombohedral structure is likely to be formed, and this tends to reduce the holding force. When it exceeds 28 atomic%, a boron-rich phase is excessively formed. The residual magnetic flux density tends to be small.

  In the constituent materials described above, a part of Fe in the R—Fe—B system may be substituted with Co. Thus, if a part of Fe is replaced by Co, the temperature characteristics can be improved without deteriorating the magnetic characteristics. In this case, it is desirable that the amount of substitution of Co not be larger than the content of Fe. If the Co content exceeds the Fe content, the magnetic properties of the magnet body 3 tend to be small.

  A part of B in the constituent material may be substituted with an element such as carbon (C), phosphorus (P), sulfur (S), or copper (Cu). By replacing a part of B in this way, the magnet body can be easily manufactured and the manufacturing cost can be reduced. At this time, the substitution amount of these elements is desirably an amount that does not substantially affect the magnetic properties, and is preferably 4 atomic% or less with respect to the total amount of constituent atoms.

  Further, from the viewpoint of improving the holding power and reducing the manufacturing cost, in addition to the above-described structure, aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), bismuth (Bi ), Niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), antimony (Sb), germanium (Ge), tin (Sn), zirconium (Zr), nickel (Ni), silicon (Si) ), Gallium (Ga), copper (Cu), hafnium (Hf) and the like may be further included. These contents are also preferably in a range that does not affect the magnetic properties, and preferably 10 atomic% or less with respect to the total amount of constituent atoms. In addition, oxygen (O), nitrogen (N), carbon (C), calcium (Ca), etc. are conceivable as components that are inevitably mixed. These may be contained in an amount of about 3 atomic% or less with respect to the total amount of constituent atoms.

(Protective layer)
The protective layer 5 includes a first layer 2, a second layer 4, and a third layer 6 in order from the magnet body 3 side. These layers are layers containing oxygen in addition to the rare earth magnet and / or iron. Specifically, an oxide layer mainly containing a rare earth metal oxide and / or an iron oxide is preferable.

  The rare earth magnet and / or iron contained in the first to third layers 2, 4, 6 are preferably derived from the magnet element body 3. That is, the first to third layers 2, 4, and 6 constituting the protective layer 5 are not layers separately formed on the surface of the magnet body 3, but change due to oxidation of the magnet body 3 itself. It is preferable that it is a layer formed by doing. The first to third layers 2, 4, and 6 may include, for example, B, Bi, Si, Al, or the like derived from the magnet element body in addition to the rare earth element and / or iron. In addition, each layer in the protective layer 5 may contain nitrogen or the like derived from atmospheric components. The total thickness of the protective layer 5 is preferably about 0.1 to 20 μm.

  The first layer 2 is a layer containing rare earth elements, iron and oxygen. More specifically, the first layer 2 is preferably a layer containing a rare earth element oxide and an iron oxide. When the magnet body 3 contains Co or the like, the first layer 2 may further contain these elements. The film thickness of the first layer 2 is preferably 0.1 to 20 μm.

  The second layer 4 is a layer containing at least a rare earth element and oxygen. More specifically, a layer containing a rare earth element oxide is preferable. This second layer 4 may or may not contain iron. When iron is contained, it is preferably included in the form of iron oxide. The second layer 4 is a layer in which the content ratio of the rare earth element to iron is larger than that of the first layer 2. The thickness of this layer is preferably 1 to 300 nm.

  Here, the content of each element contained in each layer of the protective layer 5 is, for example, EPMA (X-ray microanalyzer method), XPS (X-ray photoelectron spectroscopy), AES (Auger electron spectroscopy) or EDS ( It can be measured using a known composition analysis method such as energy dispersive X-ray fluorescence spectroscopy. The content ratio of the rare earth element to the iron is, for example, “the rare earth element content (atomic%) / the iron content (atomic%) from the content (atomic%) of each element obtained by the above composition analysis. ) ". The second layer 4 may not contain iron (the iron content is 0%). However, as described above, the first layer 2 contains at least iron. This also applies to the case where “the content of the rare earth element relative to iron in the second layer 4 is larger than that in the first layer 2”.

The third layer 6 is a layer containing iron and oxygen. When the third layer 6 contains a rare earth element, the content ratio of the rare earth element to the iron is smaller than that of the first layer 2. The third layer 6 preferably has a rare earth element content itself less than that of the first and second layers 2 and 4, and more preferably a layer that does not substantially contain a rare earth element. preferable. This is because rare earth elements are very easily oxidized and easily corroded by elution into an acidic solution. The content ratio and content of elements in the third layer 6 can be measured in the same manner as described above. Note that “substantially free of rare earth elements” means a case where rare earth elements are not detected by the composition analysis as described above. The film thickness of the third layer 6 is preferably 5 to 1000 nm.
[Rare earth magnet manufacturing method]

  Next, a preferred method for manufacturing the rare earth magnet 1 having the above-described configuration will be described.

In manufacturing the rare earth magnet 1, first, the magnet body 3 is formed. The magnet body 3 can be manufactured by powder metallurgy. In this method, first, an alloy having a desired composition is produced by a known alloy production process such as a casting method or a strip casting method. Next, this alloy was pulverized to a particle size of 10 to 100 μm using a coarse pulverizer such as a jaw crusher, a brown mill, or a stamp mill, and then further pulverized by a fine pulverizer such as a jet mill or an attritor. The particle size is 5 to 5 μm. The powder thus obtained is preferably molded at a pressure of 0.5 to ⁵ t / cm ² in a magnetic field having a magnetic field strength of 600 kA / m or more.

  Thereafter, the obtained compact is preferably sintered in an inert gas atmosphere or under vacuum at 1000 to 1200 ° C. for 0.5 to 10 hours and then rapidly cooled. Furthermore, this sintered body is subjected to heat treatment at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere or vacuum, and if necessary, the sintered body is processed into a desired shape (practical shape). A magnet body 3 is obtained.

  The magnet body 3 obtained in this manner is preferably subjected to acid cleaning before performing a step of forming a protective layer 5 described later. Nitric acid is preferably used as the acid used in the acid cleaning. When plating a general steel material, non-oxidizing acids such as hydrochloric acid and sulfuric acid are often used. However, when a rare earth element is included as in the magnet body 3 in the present embodiment, when processing is performed using these acids, hydrogen generated by the acid is easily occluded on the surface of the magnet body 3, The occlusion site may become brittle and a large amount of powdery undissolved material may be generated. This powdery undissolved product may cause surface roughness, defects and poor adhesion after the surface treatment. For this reason, it is preferable not to contain the non-oxidizing acid as described above in the acid cleaning treatment liquid in the present embodiment. Therefore, in the acid cleaning, it is preferable to use nitric acid, which is an oxidizing acid that generates little hydrogen.

  The amount of dissolution of the surface of the magnet body 3 by such acid cleaning is preferably 5 μm or more, preferably 10 to 15 μm in average thickness from the surface. By doing so, the altered layer and the oxide layer due to the processing of the surface of the magnet body 3 can be almost completely removed, and the desired protective layer 5 (oxide layer) can be formed more accurately by the heat treatment described later. Can do.

  The concentration of nitric acid in the treatment solution used for the acid cleaning is preferably 1 N or less, particularly preferably 0.5 N or less. If the nitric acid concentration is too high, the dissolution rate of the magnet body 3 is extremely fast, and it becomes difficult to control the amount of dissolution, especially in large-scale processing such as barrel processing, and it becomes difficult to maintain the dimensional accuracy of the product. Tend. Moreover, when the nitric acid concentration is too low, the dissolved amount tends to be insufficient. For this reason, the nitric acid concentration is preferably 1 N or less, and particularly preferably 0.5 to 0.05 N. The amount of Fe dissolved at the end of the treatment is about 1 to 10 g / l.

  When acid cleaning is performed, a small amount of undissolved matter and residual acid components may remain from the surface of the magnet body 3 after acid cleaning. Therefore, in order to completely remove these undissolved materials and the like, it is preferable that the magnet body 3 is further cleaned using ultrasonic waves. This ultrasonic cleaning is preferably performed in pure water with very few chlorine ions that generate rust on the surface of the magnet body 3. Moreover, you may perform the same water washing before and after the said ultrasonic cleaning, and in each process of acid cleaning as needed.

  Next, the protective layer 5 is formed on the surface of the magnet body 3. The protective layer 5 can be formed by, for example, heat-treating (heating) the magnet body 3 in an oxidizing atmosphere containing an oxidizing gas. During the heat treatment, at least one of the oxidizing gas partial pressure, the processing temperature, and the processing time is adjusted so that the first to third layers 2, 4, and 6 described above are formed. It is preferable to adjust the three conditions of the oxidizing gas partial pressure, the processing temperature, and the processing time.

  Here, the oxidizing atmosphere is not particularly limited as long as it contains an oxidizing gas. For example, the atmosphere, oxygen atmosphere (preferably oxygen partial pressure adjustment atmosphere), water vapor atmosphere (preferably water vapor partial pressure adjustment atmosphere) ) And the like. The oxidizing gas is not particularly limited, and examples thereof include oxygen and water vapor.

  For example, the oxygen atmosphere is an atmosphere having an oxygen concentration of 0.1% or more, and an inert gas may coexist with oxygen in the atmosphere. Such inert gas includes nitrogen. That is, as an aspect of the oxygen atmosphere, there is an atmosphere composed of oxygen and an inert gas.

  Further, the water vapor atmosphere is an atmosphere having a water vapor partial pressure of 10 hPa or more, for example, and an inert gas may coexist with the water vapor. Such an inert gas includes nitrogen, and an embodiment of the water vapor atmosphere includes an atmosphere containing water vapor and an inert gas. By making the oxidizing atmosphere a water vapor atmosphere, the protective layer can be formed more easily. Furthermore, the oxidizing atmosphere may be an atmosphere containing oxygen, water vapor, and an inert gas.

  The treatment temperature in the heat treatment is preferably adjusted from the range of 200 to 550 ° C, and more preferably adjusted from the range of 250 to 500 ° C. When the processing temperature exceeds the upper limit, the magnetic properties tend to deteriorate. On the other hand, when it is less than the lower limit, it tends to be difficult to form the protective layer 5 having the three-layer structure.

  The treatment time is preferably adjusted from the range of 1 minute to 24 hours, and more preferably adjusted from the range of 5 minutes to 10 hours. When the processing time exceeds the upper limit, the magnetic characteristics tend to deteriorate. On the other hand, if it is less than the lower limit, it tends to be difficult to form the desired protective layer 5.

  When the oxidizing atmosphere is an oxygen atmosphere, the oxygen concentration is preferably 25 to 100%, and more preferably 25 to 50%. If the oxygen concentration is less than 25%, the protective layer 5 having the above-described three-layer structure tends to be difficult to obtain. On the other hand, if it exceeds 50%, the magnetic properties of the rare earth magnet 1 may be deteriorated.

  Moreover, when the oxidizing atmosphere is a water vapor atmosphere, the water vapor partial pressure is preferably adjusted from the range of 10 to 2000 hPa. When the water vapor partial pressure is less than 10 hPa, the protective layer 5 tends not to have a three-layer structure as described above. On the other hand, when the pressure exceeds 2000 hPa, the protective layer 5 is unlikely to have the three-layer structure as described above, and the high pressure is likely to make the device configuration complicated, and condensation tends to occur. is there.

  The conditions for obtaining the protective layer 5 having the three-layer structure are obtained by, for example, obtaining a correlation between the configuration of the protective layer 5 and at least one of the oxidizing gas partial pressure, the processing temperature, and the processing time in advance. Alternatively, it can be determined based on the obtained correlation. And in the case of heat processing, oxidizing gas partial pressure, processing temperature, and processing time are adjusted to the suitable conditions calculated | required from the said correlation.

  Although the rare earth magnet 1 according to the preferred embodiment has been described above, the rare earth magnet 1 is referred to as the first, second, and third layers 2, 4, and 6 that are excellent in oxidation resistance as described above. Since the protective layer 5 having a three-layer structure is provided, it has excellent corrosion resistance.

  Further, the protective layer 5 includes the second layer 4 having a large content ratio of the rare earth element with respect to the iron between the first layer 2 and the third layer 6. The adhesion between each layer is very good. For this reason, for example, peeling between layers constituting the protective layer 5 hardly occurs, and corrosion of the rare earth magnet due to destruction or corrosion of the protective layer 5 itself tends to be greatly reduced.

  The reason why the adhesion is improved by the second layer 4 is not necessarily clear, but is estimated as follows. That is, rare earth elements have a strong binding force with oxygen, as can be seen from the fact that the standard free energy for oxide formation is negatively large. For this reason, it is considered that a layer containing a large amount of rare earth element has a high effect of preventing the adjacent layer from being wedged. In addition, since rare earth elements are active metals with an atomic radius larger than that of iron, they can form a kind of complex with excess vacancies, thereby forming voids at the film interface. It is thought that it works to hold down. Also due to such factors, it is considered that the layer having a high rare earth element content has good adhesion to the adjacent layer. In addition, an effect | action is not necessarily limited to these.

  Furthermore, it is considered that the protective layer 5 can suppress corrosion of the rare earth magnet 1 due to the intrusion of a substance from the outside by having the second layer 4, which is also excellent corrosion resistance of the rare earth magnet 1. It is thought that it contributes to. Although this is not necessarily clear, it is presumed that a layer containing a large amount of rare earth element is less likely to transmit corrosive ions or the like than a layer containing no such element.

  The rare earth magnet of the present invention is not limited to the structure of the embodiment described above. For example, the rare earth magnet may further include another layer for protecting the rare earth magnet on the surface of the protective layer 5 described above. Examples of such a layer include a resin layer and a plating layer. In addition, the rare earth magnet is not limited to the rectangular parallelepiped shape as described above, and can take various forms such as a spherical shape and a ring shape.

EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.
[Manufacture of rare earth magnets]

Example 1
First, an ingot having a composition of 10.8Nd-2.5Dy-79.6Fe-1.0Co-6.1B (numbers represent atomic percentage) was prepared by powder metallurgy, and this was coarsely pulverized. . Thereafter, jet milling with an inert gas was performed to obtain a fine powder having an average particle size of about 3.5 μm. The obtained fine powder was filled in a mold and molded in a magnetic field. Next, after sintering in vacuum, heat treatment was performed to obtain a sintered body. The obtained sintered body was cut into a size of 20 mm × 10 mm × 2 mm and processed to obtain a magnet body. Next, the obtained magnet body was immersed in a 2% HNO ₃ aqueous solution for 2 minutes and then subjected to ultrasonic water washing.

  Then, the magnet body after acid cleaning (acid treatment) is heat-treated at 380 ° C. for 10 minutes in an oxidizing atmosphere with an oxygen concentration of 30% to form a protective layer on the surface of the magnet body. A magnet was obtained.

  The rare earth magnet having the protective layer formed on the surface of the magnet body as described above was sliced using a focused ion beam processing apparatus, and the film structure near the surface was observed with a transmission electron microscope. Note that JEM-2100F manufactured by JEOL Ltd. was used for the transmission electron microscope. The electron micrograph showing the laminated structure of the protective layer obtained by such observation is shown in FIG.

  In FIG. 3, the lower side is a magnet body side not shown in the photograph. From FIG. 3, the obtained rare earth magnet has a first layer A, a second layer B, and a first layer having thicknesses of 1 μm, 10 nm, and 40 nm, respectively, in order from the magnet body side. 3 layers C were confirmed to be formed. The white layer P on the third layer C is a platinum-palladium film used for observation.

  Furthermore, as a result of analyzing elements contained in the film structure in the vicinity of the surface using EDS (JED-2300T manufactured by JEOL Ltd.), Nd, Dy, Fe and O as main components from the first layer A. , Nd, Dy, Fe and O were detected from the second layer B, and Fe and O were detected from the third layer C. Further, based on the content of each element obtained by the above analysis, the content ratio of the rare earth element to the iron in each layer (the rare earth element content (atomic%) / iron content (atomic%)) was calculated. The first layer A, the second layer B, and the third layer C were 0.147, 0.342, and 0.013, respectively.

(Example 2)
After applying an epoxy resin paint to the surface of the rare earth magnet obtained in Example 1 by spray coating, the epoxy resin paint was cured by heating at 180 ° C. for 30 minutes. Thereby, the rare earth magnet further provided with the resin layer of thickness 10 micrometers on the surface of the rare earth magnet of Example 1 was obtained.

(Comparative Example 1)
After producing a magnet body and performing an acid treatment in the same manner as in Example 1, a rare earth magnet having no protective layer without heat treatment was obtained.

(Comparative Example 2)
A resin layer was further formed on the surface of the rare earth magnet obtained in Comparative Example 1 in the same manner as in Example 2 to obtain a rare earth magnet having a resin layer on the surface.
[Evaluation of corrosion resistance]

(Pressure cooker test)
A pressure cooker test was performed on each of the rare earth magnets of Examples 1-2 and Comparative Examples 1-2. The test conditions were left at 100 ° C., 0.2 MPa, 100% RH for 100 hours. As a result, the rare earth magnets of Examples 1 and 2 did not show changes in appearance such as powder fall and color change after the test. In contrast, the rare earth magnet of Comparative Example 1 turned black after the test, and in the rare earth magnet of Comparative Example 2, the resin layer was peeled off.

  Further, when the change in magnetic flux before and after the test of these rare earth magnets was measured, the permanent demagnetization of each rare earth magnet was 0.2% in Example 1, 0.1% in Example 2, and 0 in Comparative Example 1. 8%.

(Salt spray test)
First, cross cuts were applied to the resin layers of the rare earth magnets of Example 2 and Comparative Example 2, respectively. Then, each of the rare earth magnets after cross-cutting was subjected to a salt spray test at 35 ° C. for 96 hours using 5% salt water in accordance with JIS K5600-7-1. As a result, in the rare earth magnet of Example 2, although rusting was observed in the crosscut portion, corrosion from this portion did not occur. On the other hand, in the rare earth magnet of Comparative Example 2, it was confirmed that corrosion progressed from the cross cut portion to the inside, and that the resin layer was blistered.

It is a perspective view which shows the rare earth magnet which concerns on suitable embodiment. It is a figure which shows typically the cross-sectional structure which follows the II-II line | wire of the rare earth magnet shown in FIG. 3 is a transmission micrograph showing the cross-sectional structure of the protective layer of Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rare earth magnet, 2 ... 1st layer, 3 ... Magnet body, 4 ... 2nd layer, 5 ... Protective layer, 6 ... 3rd layer.

Claims (2)

A magnet body containing a rare earth element and iron, and a protective layer formed on the surface of the magnet body,
The protective layer is
A first layer covering the magnet body and including at least a rare earth element, iron and oxygen;
A second layer covering the first layer, containing at least a rare earth element and oxygen, and having a content ratio of the rare earth element to iron larger than that of the first layer;
A third layer covering the second layer, containing at least iron and oxygen, and having a rare earth element content ratio relative to iron smaller than that of the first layer;
A rare earth magnet characterized by comprising: The rare earth magnet according to claim 1, wherein the third layer is a layer substantially not containing a rare earth element.

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