JP2006165364A - Ferrite permanent magnet and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a ferrite permanent magnet with a high coercive force (HcJ) approximately without reducing a magnetic characteristic potential. <P>SOLUTION: A ferrite permanent magnet that is mainly composed of Wurzite M-type ferrite and contains F: 10 to 400 ppm. It is preferable that the Wurzite M-type ferrite includes a composition represented by a formula (I): A<SB>1-x</SB>R<SB>x</SB>(Fe<SB>12-y</SB>Me<SB>y</SB>)<SB>z</SB>O<SB>19</SB>. In such a case, however, A is at least one kind of element selected from Sr, Ba, Ca and Pb and surely contains Sr, R is at least one kind of element selected from rare earth elements (including Y) and Bi and surely contains La, and Me is Co or Co and Zn. Furthermore, the conditions of 0.04≤x≤0.9, 0.04≤y≤1.0, 0.4≤x/y≤5.0 and 0.7≤z≤1.2 are established. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement in magnetic properties of a ferrite permanent magnet, and particularly provides a ferrite permanent magnet capable of adjusting the balance of residual magnetic flux density (Br) and coercive force (HcJ) without reducing the magnetic property potential.

Ferrite permanent magnets include hexagonal Sr ferrite and Ba ferrite. Currently, magnetoplumbite (M type) structure Sr ferrite or Ba ferrite is mainly used, and these ferrite sintered bodies Bonded magnets are manufactured.
When designing a motor using a ferrite permanent magnet and other rotating machines, two magnetic characteristics of residual magnetic flux density (Br) and coercive force (HcJ) are considered. That is, a high residual magnetic flux density (Br) may be required, and a high coercive force (HcJ) may be required. Usually, when a high residual magnetic flux density (Br) is to be obtained, the coercive force (HcJ) is reduced, and conversely, when a high coercive force (HcJ) is to be obtained, the residual magnetic flux density (Br) tends to be reduced.

Until now, in ferrite permanent magnets, in order to adjust the balance of residual magnetic flux density (Br) and coercive force (HcJ), aluminum oxide (Al ₂ O ₃ ), chromium oxide (Cr ₂ O ₃ ), silicon oxide (SiO ₂₎ ), A method of adding a trace amount of oxide such as calcium oxide (CaO) has been conventionally performed (for example, JP-A-55-138204 (Patent Document 1), JP-A-60-152009 ( Patent Document 2)).

JP-A-55-138204 Japanese Patent Laid-Open No. 60-152009

Conventionally used aluminum oxide and chromium oxide are additives for suppressing sinterability, and as a result, a high coercive force (HcJ) can be realized.
Here, the magnetic characteristic potential will be described with reference to FIG.
Even in the case of ferrite permanent magnets having the same composition, the values of residual magnetic flux density (Br) and coercive force (HcJ) can be changed by adjusting the firing temperature. For example, a line segment a in FIG. 2 shows an example. A line segment a indicates fluctuations in the residual magnetic flux density (Br) and the coercive force (HcJ) when a certain ferrite sintered magnet is manufactured by changing the firing temperature, for example. The same applies to the line segments b and c in FIG.

  Since the higher the residual magnetic flux density (Br) and the coercive force (HcJ) can be obtained as the line segment is at the upper right of the graph, it can be said that the magnetic characteristic potential is higher.

  Since there is a limit to increasing the coercive force (HcJ) by adjusting the firing temperature, a method of adding aluminum oxide or the like is used. According to this method, the magnetic characteristic indicated by the line segment a can be shifted to the line segment b, but the magnetic characteristic potential is usually lowered. Therefore, it is desired to increase the coercive force (HcJ) without reducing the magnetic characteristic potential as in the line segment c. Therefore, an object of the present invention is to enable the production of a ferrite permanent magnet having a high coercive force (HcJ) without substantially reducing the magnetic characteristic potential.

For this purpose, the above problem can be solved by using the hexagonal M-type ferrite of the present invention as a main component and containing F: 10 to 400 ppm.
In the present invention, the hexagonal M-type ferrite preferably has a composition represented by the following formula (I).
A _1-x R _x (Fe _12-y Me _y ) _z O ₁₉ (I)
However, A is at least one element selected from Sr, Ba, Ca and Pb, and necessarily contains Sr, and R is at least one element selected from rare earth elements (including Y) and Bi. La must be included, and Me is Co or Co and Zn.
0.04 ≦ x ≦ 0.9
0.04 ≦ y ≦ 1.0
0.4 ≦ x / y ≦ 5.0
0.7 ≦ z ≦ 1.2
Moreover, it is preferable that the ferrite permanent magnet of this invention is F: 50-300 ppm.

The above ferrite permanent magnet includes a step (a) of obtaining a molded body by pressure-molding a composition containing hexagonal M-type ferrite raw material powder and a fluorine compound: 0.01 to 0.45 wt%, and a molded body And a step (b) of obtaining a sintered body by heating and holding at a predetermined temperature, and a method for producing a ferrite permanent magnet.
Here, the fluorine compound is preferably SrF ₂ .

  According to the present invention, a ferrite permanent magnet having a high coercive force (HcJ) can be manufactured with almost no decrease in magnetic characteristic potential.

Hereinafter, the present invention will be described in detail.
By containing F (fluorine), the ferrite permanent magnet of the present invention can obtain a ferrite permanent magnet having a high coercive force (HcJ) without lowering the magnetic characteristic potential. However, if the F content is less than 10 ppm, it is difficult to enjoy the effect of improving the coercive force (HcJ). On the other hand, when the content of F exceeds 400 ppm, the coercive force (HcJ) is reduced. Therefore, the ferrite permanent magnet of the present invention has an F content of 10 to 400 ppm. A preferable F content is 50 to 300 ppm, and a more preferable F content is 80 to 200 ppm.

  In the present invention, the reason why the above-described effect can be obtained by containing F is not clear, but as shown in Examples described later, aluminum oxide conventionally used for improving coercive force (HcJ) is used. Decreases the saturation magnetization (σs), while the inclusion of F increases the saturation magnetization (σs). In addition, the ferrite permanent magnet containing F has a larger crystal grain size than the case where aluminum oxide is added, although the crystal grain size of the sintered body is reduced as compared with the case where F is not contained. Therefore, the residual magnetic flux density (Br) is higher than that of a ferrite permanent magnet containing aluminum oxide, and a decrease in magnetic characteristic potential can be prevented.

The ferrite permanent magnet to which the present invention can be applied is not particularly limited, and can be applied to all ferrite permanent magnets having hexagonal M-type ferrite as a main phase.
Here, if the hexagonal M-type ferrite is mentioned as a precaution, it is represented by the general formula of A ²⁺ O.6Fe ₂ O ₃ or AFe ₁₂ O ₁₉ . A is generally one or more of Sr, Ba, Ca and Pb.

The present invention is preferably applied to an La-Co-containing M-type ferrite in which a part of A is substituted with La and a part of Fe is substituted with Co. This La-Co-containing M-type ferrite preferably has a main component represented by the following formula (I).
A _1-x R _x (Fe _12-y Me _y ) _z O ₁₉ (I)
However, A is at least one element selected from Sr, Ba, Ca and Pb, and necessarily contains Sr, and R is at least one element selected from rare earth elements (including Y) and Bi. La must be included, and Me is Co or Co and Zn.
0.04 ≦ x ≦ 0.9
0.04 ≦ y ≦ 1.0
0.4 ≦ x / y ≦ 5.0
0.7 ≦ z ≦ 1.2
More preferably,
0.04 ≦ x ≦ 0.5,
0.04 ≦ y ≦ 0.5,
And more preferably
0.1 ≦ x ≦ 0.4,
0.04 ≦ y ≦ 0.4,
It is.

Element A:
In order to increase the saturation magnetization and the coercive force of the ferrite permanent magnet according to the formula (I), it is preferable to use at least one of Sr and Ca as the element A, and particularly preferably Sr. The ratio of Sr + Ca in element A, particularly the ratio of Sr, is preferably 51 atomic% or more, more preferably 70 atomic% or more, and further preferably 100 atomic%. If the ratio of Sr in the element A is too low, it is difficult to increase both the saturation magnetization and the coercive force.

R (x):
In the formula (I), if x indicating the amount of the element R is too small, that is, if the amount of the element R is too small, the amount of the element Me dissolved in the hexagonal M-type ferrite cannot be increased, thereby improving the saturation magnetization. And / or the anisotropic magnetic field improvement effect becomes insufficient. If x is too large, the element R cannot be substituted and dissolved in the hexagonal M-type ferrite. For example, orthoferrite containing the element R is generated, and the saturation magnetization is lowered. Therefore, x in formula (I)
Is preferably 0.04 ≦ x ≦ 0.9.

  The rare earth elements used as the element R are Y, Sc and lanthanoid elements. As element R, La must be used, and when other elements are used, preferably at least one of lanthanoid elements, more preferably at least one of light rare earth elements, more preferably at least one of Nd and Pr. Use. The proportion of La in the element R is preferably 40 atomic% or more, more preferably 70 atomic% or more, and it is most preferable to use only La as the element R in order to improve saturation magnetization. This is because La is the largest when the solid solution limit amount for hexagonal M-type ferrite is compared. Therefore, if the ratio of La in the element R is too low, the solid solution amount of the element R cannot be increased. As a result, the solid solution amount of the element Me cannot be increased, and the effect of improving the magnetic characteristics is small. turn into. If Bi is used in combination, the calcination temperature and the sintering temperature can be lowered, which is advantageous in production.

Me (y):
In the formula (I), when y indicating the amount of the element Me is too small, the saturation magnetization improvement effect and / or the anisotropic magnetic field improvement effect becomes insufficient. If y is too large, the element Me cannot be substituted and dissolved in the hexagonal M-type ferrite. Even in the range where the element Me can be substituted and dissolved, the deterioration of the anisotropy constant (K1) and the anisotropy magnetic field (Ha) increases. Therefore, y in the present invention is preferably 0.04 ≦ y ≦ 1.0.

  The proportion of Co in the element Me is preferably 20 atomic% or more, more preferably 50 atomic% or more, and still more preferably 100 atomic%. When the ratio of Co in the element Me is too low, the coercive force is not sufficiently improved.

z:
In formula (I), if z is too small, the nonmagnetic phase containing Sr and element R increases, so that the saturation magnetization becomes low. If z is too large, the α-Fe ₂ O ₃ phase or the nonmagnetic spinel ferrite phase containing the element Me increases, so the saturation magnetization becomes low. Therefore, z in the present invention is preferably 0.7 ≦ z ≦ 1.2.

In the formula (I), if x / y is too small or too large, the valence of the element R and the element Me cannot be balanced, and a different phase such as W-type ferrite is easily generated. When the element M is a divalent ion and the element R is a trivalent ion, x / y = 1 should be set from the viewpoint of valence balance, but it is preferable to make the element R excessive. The reason why the allowable range is large in the region of x / y> 1 is that the valence is balanced by the reduction of Fe ³⁺ → Fe ²⁺ even if y is small.

In the formula (I), the number of atoms of oxygen O is 19, which means that the elements Me are all divalent, the elements R are all trivalent, and x = y and z = 1. The stoichiometric composition ratio of oxygen is shown. The number of oxygen atoms varies depending on the types of the elements Me and R and the values of x, y, and z. For example, when the firing atmosphere is a reducing atmosphere, oxygen deficiency (vacancy) may occur. Further, Fe is usually trivalent in M-type ferrite, but this may change to divalent. In addition, the valence of the element Me such as Co may change, and the ratio of oxygen to the metal element changes accordingly. In the present invention, the number of oxygen atoms is displayed as 19 regardless of the type of element R and the values of x, y, and z. However, the actual number of oxygen atoms may be slightly deviated from this.

  The composition of the ferrite permanent magnet according to the present invention can be measured by fluorescent X-ray quantitative analysis or the like, but does not exclude the inclusion of components other than the main component and subcomponents.

The ferrite permanent magnet according to the present invention may contain a Si component and further a Ca component. The Si component and the Ca component are added for the purpose of improving the sinterability of the hexagonal M-type ferrite, controlling the magnetic properties, and adjusting the crystal grain size of the sintered body. Although it is preferable to use SiO ₂ as the Si component and CaCO ₃ as the Ca component, it is not limited to this example. The amount added is preferably 0.15 to 1.35 wt% in terms of Si ₂ , and the ratio Ca / Si molar ratio of the Ca component to the Si component is 0.35 to 2.10. More preferably, it is 0.30 to 0.90 wt% in terms of SiO ₂ , Ca / Si is 0.70 to 1.75, more preferably 0.45 to 0.90 wt%, and Ca / Si is 1.05 to 1.05. 1.75.

The ferrite permanent magnet of the present invention may contain Al ₂ O ₃ and / or Cr ₂ O ₃ as subcomponents. Al ₂ O ₃ and Cr ₂ O ₃ improve the coercive force but reduce the residual magnetic flux density. Therefore, the total content of Al ₂ O ₃ and Cr ₂ O ₃ is preferably 3 wt% or less in order to suppress a decrease in residual magnetic flux density. In order to sufficiently exhibit the effect of the Al ₂ O ₃ and / or Cr ₂ O ₃ addition, it is preferable that the total content of Al ₂ O ₃ and Cr ₂ O ₃ and 0.1 wt% or more .

The ferrite permanent magnet of the present invention preferably contains no alkali metal element such as Na, K, Rb, etc., but may contain it as an impurity. When these are converted into oxides such as Na ₂ O, K ₂ O, Rb ₂ O and the content is determined, the total of these contents is preferably 3 wt% or less of the entire ferrite permanent magnet. If these contents are too large, the saturation magnetization will be low.

  In addition to these, for example, Ga, In, Li, Mg, Ti, Zr, Ge, Sn, V, Nb, Ta, Sb, As, W, and Mo may be contained as oxides. These contents are converted into oxides of stoichiometric composition, respectively, gallium oxide 5 wt% or less, indium oxide 3 wt% or less, lithium oxide 1 wt% or less, magnesium oxide 3 wt% or less, titanium oxide 3 wt% or less, oxidation Zirconium 3 wt% or less, germanium oxide 3 wt% or less, tin oxide 3 wt% or less, vanadium oxide 3 wt% or less, niobium oxide 3 wt% or less, tantalum oxide 3 wt% or less, antimony oxide 3 wt% or less, arsenic oxide 3 wt% or less, tungsten oxide 3 wt% % Or less, and molybdenum oxide is preferably 3 wt% or less.

  When the present invention is applied to a ferrite sintered magnet, the average crystal grain size is preferably 1.5 μm or less, more preferably 1 μm or less, and further preferably 0.5 to 1.0 μm. The crystal grain size can be measured with a scanning electron microscope.

<Application>
The ferrite permanent magnet of the present invention can constitute a ferrite sintered magnet, a ferrite magnet powder, a bonded magnet as a ferrite magnet powder dispersed in a resin, and a magnetic recording medium as a film-like magnetic phase.
The sintered ferrite magnet and bonded magnet according to the present invention are processed into a predetermined shape and used for a wide range of applications as described below. For example, automotive motors for fuel pumps, power windows, ABS (anti-lock brake systems), fans, wipers, power steering, active suspension, starters, door locks, electric mirrors, etc. Can be used as Also for FDD spindle, VTR capstan, VTR rotary head, VTR reel, VTR loading, VTR camera capstan, VTR camera rotary head, VTR camera zoom, VTR camera focus, radio cassette etc. It can be used as a motor for OA / AV equipment such as a CD / LD / MD spindle, a CD / LD / MD loading, and a CD / LD optical pickup. Furthermore, it can be used as a motor for home appliances such as an air conditioner compressor, a freezer compressor, an electric tool drive, a dryer fan, a shaver drive, an electric toothbrush, and the like. Furthermore, it can also be used as a motor for FA devices such as a robot shaft, joint drive, robot main drive, machine tool table drive, and machine tool belt drive. Other applications include motorcycle generators, speaker / headphone magnets, magnetron tubes, MRI magnetic field generators, CD-ROM clampers, distributor sensors, ABS sensors, fuel / oil level sensors, magnet latches, isolators. Etc. are preferably used.

When the ferrite magnet powder according to the present invention is used for a bonded magnet, the average particle size is preferably 0.1 to 5.0 μm. The more desirable average particle size of the bonded magnet powder is 0.1 to 2.0 μm, and the more desirable average particle size is 0.1 to 1.0 μm. When manufacturing a bonded magnet, ferrite magnet powder is kneaded with various binders such as resin, metal, rubber, etc., and molded in a magnetic field or in the absence of a magnetic field. As the binder, NBR (acrylonitrile butadiene rubber), chlorinated polyethylene, polyamide resin and the like are preferable. After molding, it is cured to form a bonded magnet.
A magnetic recording medium having a magnetic layer can be produced using the ferrite permanent magnet of the present invention. This magnetic layer includes the M-type ferrite phase described above. For example, a vapor deposition method or a sputtering method can be used to form the magnetic layer. When the magnetic layer is formed by sputtering, the sintered ferrite magnet according to the present invention can be used as a target. Examples of the magnetic recording medium include a hard disk, a flexible disk, and a magnetic tape.

<Manufacturing method>
Next, the suitable manufacturing method of the ferrite sintered magnet by this invention is demonstrated. The method for producing a sintered ferrite magnet of the present invention includes a blending step, a calcination step, a pulverization step, a pulverization step, a forming step in a magnetic field, and a firing step. The pulverization process is divided into a coarse pulverization process and a fine pulverization process.
<Mixing process>
In the blending step, the raw material powder is weighed so as to have a predetermined ratio, and then mixed and pulverized by a wet attritor, a ball mill or the like for about 1 to 20 hours. As a starting material, a compound containing one of ferrite constituent elements (Fe, element A, element R, element Me, etc.) or a compound containing two or more of these may be used. As the compound, an oxide or a compound that becomes an oxide by firing, for example, carbonate, hydroxide, nitrate, or the like is used. Although the average particle diameter of the starting material is not particularly limited, it is usually preferable to be about 0.1 to 2 μm. It is not necessary to mix all starting materials in this step before calcination, and a part or all of each compound may be post-added. For example, some or all of the element M component such as Co is preferably added after calcination.

In the present invention, in the blending step, a supply source of F (fluorine) can be blended as one of the starting materials. As a supply source of F, an F compound is used. For example, the F _{compounds, SrF 2, FeF 2, FeF} 3, ClF, F 2 O are listed.
Furthermore, in this invention, the Si component and / or Ca component as an additive can be added in a predetermined amount in the blending step.

  In the present specification, the act of adding additives such as subcomponents before the calcination step is referred to as pre-addition, and the act of adding after the calcination step is referred to as post-addition. An example in which a Si component and / or a Ca component is added in advance is shown. However, in the present invention, the F compound, the Si component and / or the Ca component are not limited to the pre-addition, but can be added later. Moreover, one part can be pre-added and another part can also be post-added.

<Calcination process>
The raw material composition obtained in the blending step is calcined. Calcination is usually performed in an oxidizing atmosphere such as air. The calcining conditions are not particularly limited, but usually, the stable temperature may be 1000 to 1350 ° C., and the stable time may be 1 second to 10 hours. The calcined body has a substantially magnetoplumbite (M) type ferrite structure, and its primary particle diameter is preferably 2 μm or less, more preferably 1 μm or less.

<Crushing process>
The calcined body is generally in the form of granules, lumps, etc., and cannot be formed into a desired shape as it is, and is pulverized. In addition, a pulverization step is necessary to mix the raw material powder for adjusting to a desired final composition, additives, and the like. Adding raw material powder or the like in this step corresponds to post-addition. The pulverization process is divided into a coarse pulverization process and a fine pulverization process. In addition, it can also be set as the ferrite magnet powder for bonded magnets by grind | pulverizing a calcined body to predetermined particle size.

<Coarse grinding process>
As described above, since the calcined body is generally in the form of granules, lumps, etc., it is preferable to coarsely pulverize it. In the coarse pulverization step, a vibration mill or the like is used, and processing is performed until the average particle size becomes 0.5 to 10 μm. The powder obtained here will be referred to as coarsely pulverized powder.
<Fine grinding process>
The coarsely pulverized powder is pulverized by a wet attritor, ball mill, jet mill or the like, and pulverized to an average particle size of 0.08 to 2 μm, preferably 0.1 to 1 μm, more preferably about 0.2 to 0.8 μm. The fine pulverization step is performed for the purpose of eliminating coarsely pulverized powder, thoroughly mixing post-additives, and refining the crystal grains of the sintered body to improve magnetic properties. The specific surface area (determined by the BET method) of the finely pulverized powder obtained is preferably about 7 to 12 m ² / g. Depending on the pulverization method, the pulverization time may be, for example, 30 minutes to 10 hours for a wet attritor and 10 to 40 hours for wet pulverization with a ball mill.

In the present invention, it is preferable to add a polyhydric alcohol represented by the general formula Cn (OH) nHn ⁺² in the pulverization step in order to increase the degree of magnetic orientation of the sintered body. Here, in the said general formula, the preferable value of n showing carbon number is 4-100, More preferably, it is 4-30, More preferably, it is 4-20, More preferably, it is 4-12. For example, sorbitol is desirable as the polyhydric alcohol, but two or more polyhydric alcohols may be used in combination. Further, other known dispersants may be used in addition to the polyhydric alcohol used in the present invention.

  The above general formula is a general formula in the case where the skeleton is all a chain formula and does not contain an unsaturated bond. The number of hydroxyl groups and the number of hydrogen in the polyhydric alcohol may be slightly smaller than the number represented by the general formula. That is, it is not limited to saturated bonds, and may include unsaturated bonds. The basic skeleton may be chain or cyclic, but is preferably chain. Moreover, if the number of hydroxyl groups is 50% or more of the carbon number n, the effect of the present invention is realized. However, it is preferable that the number of hydroxyl groups is large, and the number of hydroxyl groups and the number of carbons are most preferable. The polyhydric alcohol may be added in an amount of 0.05 to 5 wt%, preferably 0.1 to 3 wt%, more preferably about 0.3 to 2 wt% with respect to the object to be added. The added polyhydric alcohol is thermally decomposed and removed in the baking step after the molding step in the magnetic field.

<Molding process in magnetic field>
The forming step in a magnetic field can be performed by either dry forming or wet forming, but is preferably performed by wet forming in order to increase the degree of magnetic orientation. Therefore, in the following, after the preparation of the slurry for wet forming, the forming step in the magnetic field will be described.
When wet molding is performed, the fine pulverization step is performed wet, and the resulting slurry is concentrated to a predetermined concentration to obtain a wet molding slurry. Concentration may be performed by centrifugation or a filter press. In this case, it is preferable that the finely pulverized powder accounts for about 30 to 80 wt% in the wet forming slurry. The dispersion medium is preferably water, and it is preferable to add a surfactant such as gluconic acid and / or gluconate, sorbitol. Next, molding is performed in a magnetic field using the slurry for wet molding. The molding pressure may be about 0.1 to 0.5 ton / cm ² and the applied magnetic field may be about 5 to 15 kOe. The dispersion medium is not limited to water, and a non-aqueous solvent may be used. When a non-aqueous dispersion medium is used, an organic solvent such as toluene or xylene can be used. In this case, it is preferable to add a surfactant such as oleic acid.

<Baking process>
The obtained molded body is fired to obtain a sintered body. Firing is usually performed in an oxidizing atmosphere such as air. The firing conditions are not particularly limited, but the temperature is usually raised at about 5 ° C./hour, for example, the stable temperature is 1100 to 1300 ° C., more preferably 1150 to 1250 ° C., and the stable time is about 0.5 to 3 hours. It ’s fine.
When a molded body is obtained by wet molding, cracks may occur in the molded body if the molded body is heated rapidly without being sufficiently dried. In that case, it is preferable to sufficiently dry the molded body and suppress the generation of cracks by setting a slow temperature increase rate from room temperature to about 100 ° C., for example, about 10 ° C./hour. In addition, when a surfactant (dispersant) or the like is added, degreasing treatment is performed at a temperature rising rate of about 2.5 ° C./hour, for example, in a range of about 100 to 500 ° C. It is preferable to remove.

  The manufacturing method of the ferrite sintered magnet has been described above, but the same process can be appropriately employed when manufacturing the ferrite magnet powder. There are two processes for producing the ferrite magnet powder according to the present invention from a calcined body and from a sintered body. That is, a ferrite magnet powder can be obtained by pulverizing the calcined body and subjecting it to a necessary heat treatment. Moreover, a ferrite magnet powder can also be obtained by grind | pulverizing a sintered compact and performing the heat processing required for this. That is, the ferrite magnet powder includes any form of calcined powder, powder pulverized after calcination, and powder pulverized after calcination and firing. This ferrite magnet powder can be used for a bonded magnet.

As starting materials, iron oxide (Fe ₂ O ₃ ), strontium carbonate (SrCO ₃ ), and lanthanum hydroxide (La (OH) ₃ ) were prepared. The starting materials constituting these main components were weighed so that the main composition after firing was Sr _0.8 La _0.2 Co _0.15 Fe _11.85 O ₁₉ . This mixed raw material was mixed and pulverized with a wet attritor for 2 hours to obtain a slurry-like raw material composition. After the slurry was dried, calcination was performed in the atmosphere at 1100 to 1150 ° C. for 2.5 hours. The obtained calcined powder was coarsely pulverized with a small rod vibration mill for 10 minutes.

To the obtained coarsely pulverized powder, silicon oxide (SiO ₂ ) was added to 0.6 wt% with respect to the main component, and calcium carbonate (CaCO ₃ ) was added to 1.4 wt%. Further, the additive shown in Table 1 and 0.5 wt% sorbitol were added, and pulverization was performed with a wet ball mill until the specific surface area (BET value 8.5 m ² / g) was reached. The solid content concentration of the obtained finely pulverized slurry was adjusted to 70 to 75%, and using a wet magnetic field molding machine, a cylindrical molded body having a diameter of 30 mm and a thickness of 15 mm was obtained in an applied magnetic field of 12 kOe. The molded body was sufficiently dried at room temperature in the air, and then fired by holding at 1180 to 1220 ° C. for 1 hour in the air.

Among the obtained sintered bodies, those containing SrF ₂ were each measured for F content by ion chromatography. The results are shown in Table 1.
Next, the average crystal grain size of the obtained sintered body was measured. The results are also shown in Table 1.
Furthermore, about the obtained sintered compact, saturation magnetization ((sigma) s), residual magnetic flux density (Br), and coercive force (HcJ) were measured. The results are also shown in Table 1. FIG. 1 shows the relationship between the saturation magnetization (σs) and the residual magnetic flux density (Br) at each firing temperature. “Ref.” In FIG. 1 indicates a sintered body not containing the additive shown in Table 1. The saturation magnetization (σs) is obtained based on a magnetization curve in the easy axis direction and a magnetization curve in the hard axis direction measured with a maximum applied magnetic field of 20 kOe using a VSM (Vibrating Sample Magnetometer). ing. However, for convenience of measurement, the saturation magnetization (σs) is the maximum magnetization value on the magnetization curve in the easy axis direction. Further, the residual magnetic flux density (Br) and the coercive force (HcJ) were measured with a BH tracer having a maximum applied magnetic field of 25 kOe.

As shown in Table 1, F (fluorine) remained from the ferrite permanent magnet to which SrF ₂ was added.
Further, it can be seen from Table 1 that the crystal grains can be refined by adding SrF ₂ , but the degree of refinement is smaller than that in the case of adding Al ₂ O ₃ .

As for the saturation magnetization (σs), the saturation magnetization (σs) decreases when Al ₂ O ₃ is added, whereas the saturation magnetization (σs) does not decrease even when SrF ₂ is added. Recognize.

Next, referring to FIG. 1, the ferrite permanent magnet added with Al ₂ O ₃ can obtain a high coercive force (HcJ) of about 5000 Oe, but the residual magnetic flux density (Br) is about 4100 G. Further, the range of residual magnetic flux density (Br) and coercive force (HcJ) that can be adjusted is extremely narrow, and the magnetic characteristic potential is low. In contrast, the ferrite permanent magnet added with 0.1 wt% and 0.3 wt% SrF ₂ has a residual magnetic flux density (Br) and a coercive force (HcJ) higher than those of the ferrite permanent magnet added with Al ₂ O _3. Also exists in the upper right, and its variation is linear and wide. A ferrite permanent magnet containing 90 ppm and 260 ppm of F can obtain a residual magnetic flux density (Br) of 4150 G or more and a coercive force (HcJ) of 4700 Oe or more by adjusting the heat treatment temperature.
As described above, a ferrite permanent magnet having a high magnetic characteristic potential and a high coercive force (HcJ) can be obtained by adding a predetermined amount of SrF _{2 as} a fluorine compound.

It is a graph which shows the relationship between the saturation magnetization ((sigma) s) and the residual magnetic flux density (Br) for every firing temperature of the ferrite permanent magnet obtained in the Example. It is a graph explaining magnetic characteristic potential.

Claims (5)

  A ferrite permanent magnet comprising hexagonal M-type ferrite as a main component and containing F: 10 to 400 ppm. The ferrite permanent magnet according to claim 1, wherein the hexagonal M-type ferrite has a composition represented by the following formula (I).
A _1-x R _x (Fe _12-y Me _y ) _z O ₁₉ (I)
However, A is at least one element selected from Sr, Ba, Ca and Pb, and necessarily contains Sr, and R is at least one element selected from rare earth elements (including Y) and Bi. La must be included, and Me is Co or Co and Zn.
0.04 ≦ x ≦ 0.9
0.04 ≦ y ≦ 1.0
0.4 ≦ x / y ≦ 5.0
0.7 ≦ z ≦ 1.2   The ferrite permanent magnet according to claim 1 or 2, wherein F: 50 to 300 ppm. A step (a) of obtaining a molded body by pressure-molding a composition containing hexagonal M-type ferrite raw material powder and a fluorine compound: 0.01 to 0.45 wt%;
A step (b) of obtaining a sintered body by heating and holding the molded body at a predetermined temperature;
A method for producing a ferrite permanent magnet. The method for producing a ferrite permanent magnet according to claim 4, wherein the fluorine compound is SrF ₂ .

Images