JP2001076919A - Ferrite magnet and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress variation in magnetic characteristics due to variation in baking condition, when a ferrite magnet having high residual flux density and high magnetic coercive force is manufactured. SOLUTION: A ferrite magnet contains A, R, Fe, M and Si as metal elements, where A contains at least one element selected from among Sr, Ba, Ca and Pb, R contains at least one element selected out of rare-earth elements (containing Y) and Bi, and M is at least one element selected from among Co, Mn, Al, Cr, Ni and Zn. When the content of each metal oxide is found by converting these metal elements into the metal oxides of stoichiometric composition, content of SiO2 is 1.3-2.0 mol%, and further the atomic ratio A+ R-(Fe+M)/12}/Si is 1.1-1.9, and hexagonal ferrite is contained as a main phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetoplumbite-type hexagonal ferrite magnet and a method for manufacturing the same.

[0002]

2. Description of the Related Art Magnetoplumbite (M type) hexagonal Sr ferrite or Ba ferrite is mainly used as an oxide permanent magnet material, and these are used as sintered magnets or bonded magnets. ing.

[0003] Of the magnet properties, particularly important are the residual magnetic flux density (Br) and the intrinsic coercive force (HcJ). Br
Is determined by the density and degree of orientation of the magnet and the saturation magnetization (4πIs) determined by its crystal structure, and is expressed by Br = 4πIs × degree of orientation × density. The 4πIs of M-type Sr ferrite and Ba ferrite is about 4.65 kG. Density and degree of orientation,
Even in the case of the sintered magnet that can obtain the highest value, 98
% Is the limit. Therefore, Br of these magnets
Is limited to about 4.46 kG, and high B of 4.5 kG or more
Obtaining r has heretofore been virtually impossible.

On the other hand, the present inventors have disclosed, for example,
Japanese Patent Application Laid-Open No. 1-154604 proposes a ferrite magnet having a high residual magnetic flux density and a high coercive force, which cannot be achieved by a conventional M-type ferrite magnet. This ferrite magnet is at least one element selected from Sr, Ba, Ca, and Pb, and always includes Sr and includes at least one element selected from rare earth elements (including Y) and Bi. When R is an element that always contains La and Co or Co and Zn is an element M, the total composition ratio of each metal element of A, R, Fe and M is represented by the total metal element amount. A: 1 to
13 at%, R: 0.05 to 10 at%, Fe: 80 to
It has a main phase of hexagonal magnetoplumbite type ferrite of 95 atomic% and M: 0.1 to 5 atomic%.

Japanese Patent Application Laid-Open No. Hei 10-149910 discloses that (Sr _1-x R _x ) On · ([Fe _{1- y My} ) ₂ O ₃ ] (where R is La, Nd and Pr). At least one, M is M
n, at least one of Co, Ni, and Zn), wherein 0.05 ≦ x ≦ 0.5, {x / (2.2n)} ≦ y ≦ {x / (1. 8n)｝, 5.70 ≦ n <6.00. In order to improve the saturation magnetization, the invention described in the publication discloses that an Fe ion corresponding to a magnetic moment oriented in the antiparallel direction is replaced with another element having a smaller magnetic moment than the Fe ion or a non-magnetic element ( The charge compensation is performed by substituting the Sr site with another element (the above R) in order to suppress the generation of a different phase while substituting with the above M).

[0006]

In the process of studying the optimum conditions for producing ferrite magnets disclosed in the above publications, the present inventors replaced the Fe site with Co, Zn or the like, and replaced the Sr site with Co, Zn or the like. It has been found that when substituted by rare earth elements, magnetic properties are greatly affected by firing conditions. That is, in a ferrite magnet that does not contain Co, Zn, or the like and a rare earth element, even if the firing conditions fluctuate to such an extent that the magnetic properties do not fluctuate to a problem,
It has been found that the magnetic properties of ferrite magnets containing Co, Zn, and the like and rare earth elements significantly fluctuate. Specifically, as shown in FIG. 5, it was found that the coercive force was significantly reduced when the oxygen partial pressure in the firing atmosphere fluctuated, particularly when the oxygen partial pressure was lower than in air. It was also found that the coercive force varied greatly even when the firing temperature varied.

In manufacturing a ferrite magnet, in the firing step, oxygen absorption due to decomposition and combustion of a binder and a dispersant, absorption and release of oxygen due to a change in the valence of a constituent element and a change in structure. For example, the oxygen partial pressure in the firing atmosphere fluctuates constantly. Since the width of the fluctuation greatly varies depending on various conditions such as the composition of the object to be fired, the amount to be charged into the firing furnace, the type and amount of the additive, and so on, the oxygen partial pressure should be controlled to be always constant. Is difficult. The firing temperature also varies depending on various factors, such as the distance of the object to be fired from the heat source, the height of the object to be fired from the hearth, and the airflow in the furnace that changes depending on the loading condition of the object to be fired. Therefore, it is difficult to control so that the temperature transition pattern is always constant. Therefore, it is difficult to stably realize the original high coercive force with a ferrite magnet having a composition whose characteristics are easily affected by the oxygen partial pressure fluctuation and the temperature fluctuation during firing.

Particularly, in a continuous furnace which is effective for improving productivity in mass production, fluctuations in the oxygen partial pressure and the temperature transition pattern are larger than in a batch furnace. For example, the temperature transition pattern in a batch furnace is clear in each of the steps of heating, stabilizing, and cooling, but in a continuous furnace, there is substantially no stable part, and there is a case where the process directly shifts from the heating step to the cooling step. Also,
In a furnace in which the cost required for firing is low, for example, a furnace of a heating type utilizing combustion of fuel such as a gas combustion furnace, oxygen is consumed when burning fuel, so that the partial pressure of oxygen in the furnace varies greatly. Therefore, when a continuous furnace, a combustion furnace, and a combustion furnace type continuous furnace are used, a ferrite magnet that is hardly affected by fluctuations in oxygen partial pressure and temperature during firing is required.

The present invention has been made in view of such circumstances, and when manufacturing a ferrite magnet having a high residual magnetic flux density and a high coercive force, it is intended to suppress fluctuations in magnetic characteristics due to fluctuations in firing conditions. With the goal.

[0010]

This and other objects are achieved by the present invention which is defined below as (1) to (8). (1) A containing at least one element selected from Sr, Ba, Ca and Pb is represented as A, R as at least one element selected from rare earth elements (including Y) and Bi, and Co, Assuming that at least one element selected from Mn, Al, Cr, Ni and Zn is M, A, R, Fe, M and Si are contained as metal elements, and these metal elements are converted to oxides. When the content of each metal oxide was determined, the content of SiO ₂ was 1.3 to 2.
A ferrite magnet having 0 mol%, an atomic ratio {A + R- (Fe + M) / 12} / Si of 1.1 to 1.9, and having hexagonal ferrite as a main phase. (2) The ratio of the total amount of each of A, R, Fe and M to the total amount of metal elements is A: 1 to 13 atomic%, R: 0.
05 to 10 atomic%, Fe: 80 to 95 atomic%, M: 0.
The ferrite magnet according to the above (1), wherein the content is 1 to 5 atomic%. (3) having at least two different Curie temperatures;
The ferrite magnet according to the above (1) or (2), wherein the Curie temperatures are in the range of 400 ° C. to 480 ° C. and the Curie temperatures are separated from each other by 5 ° C. or more. (4) A method for producing a ferrite magnet according to any one of the above (1) to (3), comprising a firing step of firing a formed body of the raw material powder to obtain a sintered magnet. A method for producing a ferrite magnet in which the oxygen partial pressure in the atmosphere fluctuates. (5) The method for producing a ferrite magnet according to (4), wherein the oxygen partial pressure in the atmosphere is 0.15 atm or less in at least a part of the firing step. (6) A method for producing a ferrite magnet according to any one of the above (1) to (3), comprising a firing step of firing a compact of a raw material powder to obtain a sintered magnet. A method for producing a ferrite magnet in which the firing temperature varies. (7) At least one compound containing at least one of the magnet constituent elements is added to the calcined material or particles each having hexagonal ferrite as a main phase, and then molded and sintered. (6) The method for producing a ferrite magnet according to any of (6). (8) The method for producing a ferrite magnet according to (7), wherein a part of the magnet constituent elements is one or more elements selected from the elements R and M.

[0011]

In the present invention, the element R and the element M are added to a magnet in order to obtain a high residual magnetic flux density and a high coercive force. As shown in the experimental results in FIG. 5, the present inventors have found that the ferrite magnet to which the elements R and M are added has higher firing conditions (oxygen partial pressure in the atmosphere and It has been found that the fluctuations in magnetic properties due to fluctuations in temperature) are significantly increased. And, in order to suppress this magnetic characteristic fluctuation,
Si content and atomic ratio {A + R- (Fe + M) / 12} /
It has been found that optimizing Si is extremely effective.

As mentioned above, ferrite magnets containing the elements R and M are known. But,
It is not known that when the element R and the element M are added, the fluctuation of the magnetic characteristics due to the fluctuation of the firing conditions becomes remarkably large. Then, in order to suppress this variation in magnetic characteristics, S
i amount and atomic ratio {A + R- (Fe + M) / 12} / S
It is not known to control i so that it is within the range defined by the present invention.

The present inventors first produced a calcined material having a main phase of hexagonal ferrite containing at least the element A, and added at least one of the magnet constituent elements to the calcined material.
When a method of adding a species, particularly at least one element selected from the elements R and M and then sintering to obtain a magnet (hereinafter referred to as a post-addition method) is used, It has been found that the effect of fluctuations in the firing conditions is particularly large. And, in the present invention, the Si content and the atomic ratio ｛A
Control of + R- (Fe + M) / 12 ° / Si has been found to be particularly effective in this case. The ferrite magnet manufactured by the post-addition method as described above usually has a Curie temperature of 2 or more. A magnet containing Co as the element M and having a Curie temperature of 2 or more has improved magnetic properties compared to a magnet having the same composition and only one Curie temperature.

The post-addition method is described in Japanese Patent Application Laid-Open No. H11-195516 (published on July 21, 1999), which was published after the filing of the basic application of the present application (Japanese Patent Application No. 11-193348). Have been. However, the publication does not disclose that when the post-addition method is used, fluctuations in magnetic properties due to fluctuations in firing conditions are further increased. The amount of Si and the atomic ratio {A + R- (Fe + M) / 12} / Si There is no description that the control is performed so as to fall within the range limited by the present invention.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Sintered Magnet The ferrite magnet of the present invention has a hexagonal magnetoplumbite (M-type) ferrite as a main phase and contains A, R, Fe, M and Si as metal elements. . Element A
Is at least one element selected from Sr, Ba, Ca and Pb. The element R is at least one element selected from rare earth elements (including Y) and Bi. The element M is at least one element selected from Co, Mn, Al, Cr, Ni, and Zn. In the magnet of the present invention, when the content of each metal oxide is determined by converting the contained metal elements into general oxides, the content of SiO ₂ is 1.3 to 2.0 mol%, Preferably, it is 1.4 to 1.9 mol%, and the atomic ratio {A + R- (Fe + M) / 12} / Si is 1.1 to 1.9, preferably 1.2 to 1.7.

As described above, in the present invention, a certain amount or more of Si is contained, A + R is made excessive with respect to (Fe + M) / 12, and the degree of this excess is made to correspond to the amount of Si. As a result, the fluctuation rate of the magnetic characteristics when the oxygen partial pressure or temperature fluctuates is reduced, and in particular, a decrease in coercive force under a low oxygen partial pressure can be significantly suppressed. On the other hand, if the content of SiO ₂ is too small, the magnetic characteristics will fluctuate significantly when the oxygen partial pressure fluctuates and / or the firing temperature fluctuates during firing. On the other hand, if the content of SiO ₂ is too large, the ratio of non-magnetic components such as glass to the magnet becomes high, and the magnetic properties, particularly the residual magnetic flux density, decrease. {A + R- (Fe + M) / 12} /
If the Si is too small or too large, the magnetic properties will fluctuate greatly when the oxygen partial pressure fluctuates and / or the firing temperature fluctuates during firing.

When calculating the content by converting the metal element contained in the magnet into a general oxide, the iron oxide, strontium oxide, barium oxide, calcium oxide, rare earth element (RE) oxide Material, bismuth oxide, cobalt oxide, manganese oxide, aluminum oxide, chromium oxide and silicon oxide are converted to Fe ₂ O ₃ , SrO, Ba, respectively.
O, CaO, RE ₂ O ₃ (where Pr is Pr ₆ O ₁₁ , C
e is CeO ₂ , Tb is Tb ₄ O ₇ ), Bi ₂ O ₃ , CoO,
It is converted into MnO, Al ₂ O ₃ , Cr ₂ O ₃ and SiO ₂ .

The atomic ratio R / M in the magnet of the present invention is
Preferably it is 0.7-1.5. When M is divalent, it is preferable that M = R in terms of valence balance as described later. However, by making R excessive relative to M, the effect of the present invention is enhanced.

The effect of the present invention is that the magnet of the present invention has at least two different Curie temperatures, these Curie temperatures are in the range of 400 ° C. to 480 ° C., and the absolute value of these differences is 5 ° C. This is particularly effective when the above is true. With such a structure having a plurality of Curie temperatures, the squareness Hk / HcJ is remarkably improved, and the contents of expensive Co and R can be reduced.

The Curie temperature (Tc) is the temperature at which a magnetic material changes from ferromagnetic to paramagnetic. There are several methods for measuring Tc. In particular, in the case of a magnetic material having a plurality of Tc, the Tc is obtained by drawing a magnetization-temperature curve while changing the temperature of the measurement sample with a heater or the like.
Find c. Here, a vibrating magnetometer (VSM) is often used for measuring magnetization. This is because it is easy to secure a space for installing a heater or the like around the measurement sample.

The measurement sample may be a powder or a sintered body. In the case of a powder, it is necessary to fix it with a heat-resistant adhesive or the like. It is preferable to make the sample as small as possible within a range where the measurement accuracy of the magnetization can be ensured so that the entire sample can be heated uniformly at the time of measurement, and it is preferable to make the heating rate relatively slow.

The sample may be anisotropic or isotropic,
In the case of an anisotropic sample, it is preferable to measure in the c-axis direction after magnetization in the c-axis direction, which is the easy axis direction. In the case of an isotropic sample, the magnetization in the same direction as the magnetization direction is measured. The magnetization of the sample is performed by applying a sufficiently large magnetic field of 1 T or more. Usually, after magnetization at room temperature, the magnetization of the sample is measured while increasing the temperature, but at this time, no magnetic field is applied, or it is preferable to measure under a weak magnetic field of 0.1 T or less even if applied. . This is because, when measurement is performed while applying a large magnetic field, a paramagnetic component is also detected at a temperature higher than the Curie temperature, and the Curie temperature tends to be unclear.

FIG. 6 shows an example in which two Curie temperatures appear. FIG. 6 is a graph showing the vicinity of the Curie temperature of a σ-T curve with temperature T as the horizontal axis and magnetization σ as the vertical axis.
In the vicinity of the temperature at which the sharp decrease of the magnetization starts, the σ-T curve is convex upward. As you increase the temperature from here,
The magnetization σ changes as follows. First, as the temperature rises, the magnetization rapidly decreases. Next, the σ-T curve changes to a convex downward, and the decrease in magnetization becomes gentle. Then, σ
The -T curve changes to a convex upward again, and the magnetization decreases rapidly. Next, the σ-T curve changes to a convex downward again, and the magnetization gradually decreases, while the magnetization finally becomes zero. In the σ-T curve, three tangents at the inflection point, that is, the point at which the projection changes from upwardly convex to the downwardly convex or the point at which the downwardly convexly changes to the upwardly convex, are represented by I, I
I and III. The intersection between the tangents I and II is the Curie temperature Tc1 on the low temperature side, and the intersection between the tangent III and the horizontal axis is the Curie temperature Tc2 on the high temperature side. Even when there are three or more Curie temperatures, each Curie temperature can be determined from the σ-T curve according to this method.

When a plurality of Curie temperatures are present, the absolute value of the difference between them is 5 ° C. or more, preferably 10 ° C. or more. These Curie temperatures are in the range of 400 to 480 ° C, preferably in the range of 400 to 470 ° C, and more preferably in the range of 430 to 460 ° C. The Curie temperature of pure M-type Sr ferrite is 465
It is about ° C.

Here, the ratio (σ1 / σRT) of the magnetization (σ1) at the Curie temperature at the lowest temperature to the magnetization (σRT) at 25 ° C. is preferably 0.5% to 30%.
%, More preferably 1% to 20%, even more preferably 2%
% To 10%. When σ1 / σRT is less than 0.5%,
It becomes difficult to detect the Curie temperature on the higher temperature side.

It is considered that the plurality of Curie temperatures appear because the structure of the ferrite crystal has a multiphase structure of M-type ferrite which is magnetically different. However, even when a plurality of Curie temperatures are present, M
A single-phase structure consisting of phases is detected. When using the post-addition method described above, there are usually a plurality of Curie temperatures,
In this case, the number of Curie temperatures is often two.

In the magnet of the present invention, the ratio of the total of each of A, R, Fe and M to the total amount of metal elements is
Preferably, A: 1 to 13 atomic%, R: 0.05 to 10 atomic%, Fe: 80 to 95 atomic%, M: 0.1 to 5 atomic%
And more preferably A: 3 to 11 atomic%, and R: 0.
2 to 6 atomic%, Fe: 83 to 94 atomic%, M: 0.3 to
4 at%, more preferably A: 3 to 9 at%,
R: 0.5 to 4 atomic%, Fe: 86 to 93 atomic%, M:
0.5 to 3 atomic%. If the content of the element A is too small, no M-type ferrite is formed or a non-magnetic phase such as α-Fe ₂ O ₃ increases. If the content of the element A is too large,
No M-type ferrite is formed, or nonmagnetic phases such as SrFeO _3-x increase. The ratio of Sr in A is preferably 5
It is 1 atomic% or more, more preferably 70 atomic% or more, and still more preferably 100 atomic%. If the ratio of Sr in the element A is too low, it is impossible to obtain both the improvement of the saturation magnetization and the remarkable improvement of the coercive force. If the content of the element R is too small, the solid solution amount of the element M will be small, and the effect of improving the magnetic properties will be insufficient. If the content of the element R is too large, a non-magnetic hetero phase such as orthoferrite increases. If the content of the element M is too small or too large, the effect of improving the magnetic properties becomes insufficient.

[0028] During the magnet of the present invention, A, the atomic ratio of R, Fe and M may be represented by formula _{I A 1-x R x (} Fe 12-y M y) z O 19. In the above formula I, x, y and z may be determined so that the above {A + R− (Fe + M) / 12} / Si falls within the above-mentioned limited range and the above-mentioned R / M falls within the above-mentioned preferred range. But 0.04 ≦ x ≦ 0.9, 0.04 ≦ y ≦ 1.0, particularly 0.04 ≦ y ≦ 0.5, 0.8 ≦ x / y ≦ 5, 0.7 ≦
It is preferable not to deviate from z <1.

In the above formula I, when x is too small, that is, when the amount of the element R is too small, the solid solution amount of the element M in the hexagonal ferrite cannot be increased, and the effect of improving the saturation magnetization and / or The effect of improving the sexual magnetic field becomes insufficient. If x is too large, the element R cannot be substituted and dissolved in the hexagonal ferrite.
Is generated and the saturation magnetization decreases. If y is too small, the effect of improving the saturation magnetization and / or the effect of improving the anisotropic magnetic field become insufficient. If y is too large, the element M cannot be substituted and solid-solved in the hexagonal ferrite. Further, even in a range where the element M can be substituted for a solid solution, the anisotropy constant (K ₁ ) and the anisotropic magnetic field (H _A ) greatly deteriorate. If z is too small, the nonmagnetic phase containing Sr and the element R increases, so that the saturation magnetization decreases. If z is too large, the α-Fe ₂ O ₃ phase or the element M
, The saturation magnetization decreases.

In the above formula I, if x / y is too small or too large, the valence of the element R and the element M cannot be balanced, and a different phase such as W-type ferrite is easily formed. When the element M is a divalent ion and the element R is a trivalent ion, it is general to set x / y = 1 in terms of valence equilibrium. Is preferred. The reason why the allowable range is large in the region where x / y exceeds 1 is that even when y is small, the valence can be balanced by the reduction of Fe ³⁺ → Fe ²⁺ .

In the above formula I representing the composition, the number of atoms of oxygen (O) is 19, because M is all divalent, R is all trivalent, and x = y, z =
It shows the stoichiometric composition ratio of oxygen at the time of 1.
The number of oxygen atoms differs depending on the types of M and R and the values of x, y, and z. Further, 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 or the like. In addition, the valence of the element M such as Co may change, and the ratio of oxygen to the metal element changes accordingly. In this specification, the number of oxygen atoms is indicated as 19 regardless of the type of R and the values of x, y, and z. However, the actual number of oxygen atoms may be a value slightly deviated from this.

The magnet composition can be measured by, for example, fluorescent X-ray quantitative analysis. The presence of the main phase can be confirmed by X-ray diffraction, electron beam diffraction, or the like.

In order to increase the saturation magnetization and coercive force of the magnet, it is preferable to use at least one of Sr and Ca as the element A, and it is particularly preferable to use Sr. The proportion of Sr + Ca in A is preferably at least 51 atomic%, more preferably at least 70 atomic%,
More preferably, it is 100 atomic%.

As the element R, preferably at least one kind of lanthanoid, more preferably at least one kind of light rare earth, more preferably at least one kind of La, Nd and Pr, particularly preferably La is used. The proportion of La occupied in R is preferably 40
It is at least 70 atomic%, more preferably at least 70 atomic%, and it is most preferable to use only La as R for improving the saturation magnetization. This is because, when comparing the solid solution limit amount to hexagonal M-type ferrite, La is the largest.
Therefore, if the ratio of La in R is too low, the amount of solid solution of R cannot be increased, and as a result, the amount of solid solution of element M cannot be increased, and the effect of improving magnetic properties is reduced. I will. When Bi is used in combination, the calcining temperature and the sintering temperature can be lowered, which is advantageous in production.

As the element M, at least Co and Z
It is preferable to use at least one kind of n, particularly Co.
The proportion of Co in M is preferably at least 10 atomic%, more preferably at least 20 atomic%. If the proportion of Co in M is too low, the coercive force is insufficiently improved.

The magnet may contain B ₂ O ₃ .
By including B ₂ O ₃ , the calcining temperature and the sintering temperature can be lowered, which is advantageous in production. The content of B ₂ O ₃ is preferably 0.5% by weight or less based on the whole magnet powder. If the B ₂ O ₃ content is too large, the saturation magnetization will be low.

The magnet powder may contain at least one of Na, K and Rb. These when converted into Na ₂ O, K ₂ O and Rb ₂ O, respectively, the total content thereof is preferably not more than 3 wt% of the total magnetic powder. If these contents are too large, the saturation magnetization will be low. When these elements expressed in M ^I, M ^I in ferrite is contained, for example, in the form of ^{_{Sr 1.3-2a R a M I a-}} 0.3 Fe 11.7 M 0.3 O 19. In this case, 0.3 <a ≦ 0.
It is preferably 5. When a is too large, in addition to the saturation magnetization becomes low, a problem that the element M ^I is thus a large amount of evaporation occurs during firing.

In addition to these, for example, Ga, In,
Li, Mg, Cu, Ti, Zr, Ge, Sn, V, N
b, Ta, Sb, As, W, Mo, etc. may be contained as an oxide. These contents are converted into oxides having a stoichiometric composition in terms of gallium oxide of 5% by weight or less, indium oxide of 3% by weight or less, lithium oxide of 1% by weight or less, magnesium oxide of 3% by weight or less, and copper oxide of 3% or less. Weight% or less, titanium oxide 3 weight% or less, zirconium oxide 3
Weight% or less, germanium oxide 3 weight% or less, tin oxide 3 weight% or less, vanadium oxide 3 weight% or less, niobium oxide 3 weight% or less, tantalum oxide 3 weight% or less, antimony oxide 3 weight% or less, arsenic oxide 3 weight %, 3 wt% or less of tungsten oxide, and 3 wt% or less of molybdenum oxide.

Manufacturing Method Next, a method for manufacturing a magnet will be described.

The production method of the present invention has a firing step of firing a compact of the raw material powder to obtain a sintered magnet.

The method for producing the raw material powder is not particularly limited. For example, the raw material powder may be produced by a so-called calcination by a solid phase reaction, or may be produced by a coprecipitation method or a hydrothermal synthesis method.
Hereinafter, a case in which the calcination step is provided will be mainly described.

First, the starting materials are mixed and then calcined to obtain a calcined body. The calcined body is pulverized by pulverization or pulverization to obtain the raw material powder. Then, after the raw material powder is formed, it is fired.

The magnet of the present invention having the above-mentioned composition can be used even when the oxygen partial pressure in the atmosphere fluctuates and / or the firing temperature (stable temperature) fluctuates in the firing step.
Fluctuations in magnetic properties, particularly fluctuations in coercive force, are small. The present invention exhibits a remarkably high effect when the oxygen partial pressure in the firing atmosphere is 0.15 atm or less, particularly when it is 0.10 atm or less. Therefore, the present invention is suitable for the case of using a gas continuous furnace in which the oxygen partial pressure in the furnace is low. Further, in the present invention, even if the stable temperature fluctuates within a range of, for example, 60 ° C. or less, fluctuations in magnetic properties, particularly fluctuations in coercive force, can be suppressed to a small level.

Next, preferred conditions for manufacturing the magnet of the present invention will be described.

As a starting material, an oxide powder or a compound which becomes an oxide upon firing, such as a powder of a carbonate, a hydroxide or a nitrate, is used. The average particle size of the starting material is not particularly limited, but is usually preferably about 0.1 to 2 μm. In particular, it is preferable to use fine powder for iron oxide, and specifically, the average particle size of primary particles is preferably 1 μm.
Hereafter, more preferably, those having a size of 0.5 μm or less are used.
In addition, as the starting material containing the element A, it is preferable to use a hydroxide or a carbonate because the stability at the time of stock is good.

The calcination may be usually performed in an oxidizing atmosphere such as air. The calcination conditions are not particularly limited, but usually,
The stabilization temperature is 1000-1350 ° C, and the stabilization time is 1 second
The time may be set to 10 hours, more preferably 1 second to 3 hours. The calcined body has a substantially magnetoplumbite-type ferrite structure, and the average particle size of its primary particles is preferably 2 μm or less, more preferably 1 μm or less, still more preferably 0.1 to 1 μm, and most preferably. 0.1-0.5
μm. The average particle size can be measured by a scanning electron microscope.

In the present invention, it is preferable to use SiO ₂ as a starting material for supplying Si. SiO ₂
It may be mixed with other starting materials before calcination, mixed after calcination, or the addition of SiO ₂ may be divided between before and after calcination. The effect of the present invention is realized at least if SiO ₂ is added before firing. However, in order to further improve the effects of the present invention, it is preferable to add at least a part, and preferably all, of SiO ₂ after calcination.

The starting compounds other than SiO ₂ are also
It is not necessary to mix all of them before calcination, and it may be configured to add a part or all of each compound after calcination.

In the method of adding starting material compounds other than SiO ₂ after calcination, that is, the post-addition method, first, a calcined material having a hexagonal ferrite containing at least the element A as a main phase is produced. Then, after crushing this calcined material,
Alternatively, at the time of pulverization, a compound to be added later (post-additive) is added to the calcined material, and then molded and sintered. In order to obtain a magnet having a plurality of Curie temperatures as described above, one or two or more elements selected from the elements R and M, preferably both the elements R and M are added to the post-additive. The compound to be added later is selected so as to be contained at least.

The amount of the post-additive is preferably 1 to
It is 100% by volume, more preferably 5 to 70% by volume, still more preferably 10 to 50% by volume. As the compound containing the element R, an R oxide can be used. However, since the R oxide has relatively high solubility in water, there is a problem that the R oxide flows out during wet molding. In addition, since it has hygroscopicity, it tends to cause a weighing error. for that reason,
As the R compound, a carbonate or a hydroxide is preferable. Post-additives of other elements may be added as oxides or compounds that become oxides upon firing, such as carbonates and hydroxides.

The post-additive may be added after calcination and before sintering, but is preferably added during pulverization described below. However, in the present invention, not the calcined material, but produced by a coprecipitation method or a hydrothermal synthesis method, and at least the element A
A post-additive may be added to the particles containing hexagonal ferrite containing as a main phase.

As for the element R or the element M, it is desirable that at least 30%, more preferably at least 50%, of the total amount contained in the magnet is added as a post-additive. For other elements, the amount added as a post-additive is not particularly limited. The average particle size of the post-additive is preferably about 0.1 to 2 μm.

Here, the addition amount of the post-additive will be specifically described. For example, Sr: La: Fe: Co = 0.8: 0.2: 11.8:
For the purpose of producing a sintered magnet having a ratio of 0.2, the raw materials are mixed at a ratio of Sr: Fe = 0.8: 9.6 (= 1: 12) and calcined. By adding a post-additive of La: Fe: Co = 0.2: 2.2: 0.2 to the calcined material and calcining, a sintered magnet having the above-described target composition is obtained. Further, for example, Sr: Fe = 0.8: 11.8 (= 1: 14.75) is mixed and calcined (at this time, the calcined material is M-type Sr ferrite and α-Fe ₂ O ₃ And the resulting calcined material is sintered by adding a post-additive of La: Co = 0.2: 0.2 to the resultant calcined material, followed by firing. Is obtained.

The reason why the sintered magnet produced by the post-addition method has a plurality of Curie temperatures is not clear, but is considered as follows. At the time of sintering, a reaction between the calcined material particles having the M-type ferrite phase and the post-additive occurs.
It is considered that M-type ferrite portions having low concentrations are generated. That is, assuming that La and Co in the post-additive diffuse toward the center of the calcined material particles during sintering, the concentration of La and Co in the crystal grains after sintering is higher than that in the center. It is thought that the surface layer tends to be high. Since the Curie temperature depends on the replacement amount of La and Co, particularly the replacement amount of La, it is considered that the presence of a plurality of Curie temperatures reflects the existence of the La and Co concentration distribution in the crystal grains.

Next, molding and pulverization which is a preceding step will be described.

It is preferable to use a wet molding method for molding the raw material powder. In wet molding, it is preferable to use a molding slurry containing a raw material powder, water as a dispersion medium, and a dispersant. In order to further enhance the effect of the dispersant, it is preferable to provide a wet pulverization step before the wet molding step. When the calcined body powder is used as the raw material powder, the calcined body powder is generally composed of granules. Therefore, in order to roughly pulverize or pulverize the calcined body powder, a dry coarse pulverization step is performed before the wet pulverization step. Is preferably provided. When the raw material powder is manufactured by a coprecipitation method, a hydrothermal synthesis method, or the like, usually, a dry coarse grinding step is not provided, and a wet grinding step is not essential. It is preferable to provide a pulverizing step. The case where the calcined particles are used as a raw material powder and a dry coarse pulverizing step and a wet pulverizing step are provided will be described below.

In the dry coarse pulverization step, pulverization is usually performed until the BET specific surface area becomes about 2 to 10 times. After pulverization, the average particle size is preferably about 0.1 to 1 μm,
The specific surface area is preferably about 4 to 10 m ² / g. The pulverizing means is not particularly limited. For example, a dry vibrating mill, a dry attritor (medium stirring type mill), a dry ball mill and the like can be used, and it is particularly preferable to use a dry vibrating mill. The pulverization time may be appropriately determined according to the pulverization means. In addition, when adding some starting materials after calcination, it is preferable to add in this dry coarse pulverization process. For example, it is preferable that at least a part of each of SiO ₂ and CaCO ₃ which becomes CaO by firing is added in the dry coarse pulverization step.

Dry coarse pulverization also has the effect of introducing crystal strain into the calcined particles to reduce the coercive force HcB. Due to the decrease in coercive force, aggregation of particles is suppressed, and dispersibility is improved. In addition, the degree of orientation is also improved by softening. The softened particles return to their original hard magnetism in a subsequent sintering step.

After the dry coarse pulverization, a pulverization slurry containing the pulverized particles and water is prepared, and wet pulverization is performed using the slurry. The content of the raw material powder in the slurry for pulverization is 10 to
It is preferably about 70% by weight. The grinding means used for wet grinding is not particularly limited, but is usually a ball mill,
It is preferable to use an attritor, a vibration mill or the like. The pulverization time may be appropriately determined according to the pulverization means.

After the wet pulverization, the pulverization slurry is concentrated to prepare a molding slurry. Concentration may be performed by centrifugation or the like. The content of the raw material powder in the molding slurry is preferably about 60 to 90% by weight.

In the wet molding step, molding in a magnetic field is performed using a molding slurry. Molding pressure is 0.1 ~ 0.5t / cm ²
And the applied magnetic field may be about 5 to 15 kOe.

When a non-aqueous dispersion medium is used for the molding slurry, a high degree of orientation can be obtained. However, in order to reduce the load on the environment, it is preferable to use an aqueous dispersion medium. In order to compensate for the decrease in the degree of orientation due to the use of the aqueous dispersion medium, it is preferable that a dispersant is present in the molding slurry. The dispersant used in this case is an organic compound having a hydroxyl group and a carboxyl group, a neutralized salt thereof, or its lactone, an organic compound having a hydroxymethylcarbonyl group, or an acid. It is preferable that the compound is an organic compound having a dissociable enol-type hydroxyl group or a neutralized salt thereof.

When a non-aqueous dispersion medium is used,
For example, as described in JP-A-6-53064, a dispersion medium is prepared by adding a surfactant such as oleic acid to an organic solvent such as toluene or xylene. By using such a dispersion medium, it is possible to obtain a high degree of magnetic orientation of about 98% at the maximum even when ferrite particles having a submicron size that are difficult to disperse are used.

Each of the above organic compounds has 3 to 20 carbon atoms,
It is preferably 4 to 12, and a hydroxyl group is bonded to 50% or more of carbon atoms other than the carbon atom double-bonded to the oxygen atom. When the number of carbon atoms is 2 or less, the effect of improving the degree of orientation becomes insufficient. Even if the number of carbon atoms is 3 or more, the effect is still insufficient if the bonding ratio of the hydroxyl group to carbon atoms other than the carbon atom double-bonded to the oxygen atom is less than 50%. The bonding ratio of the hydroxyl group is limited for the above-mentioned organic compound, and is not limited for the dispersant itself. For example, when a lactone of an organic compound having a hydroxyl group and a carboxyl group (hydroxycarboxylic acid) is used as a dispersant,
The limitation on the bonding ratio of hydroxyl groups applies to hydroxycarboxylic acids themselves, not lactones.

The basic skeleton of the organic compound may be linear or cyclic, and may be saturated or contain an unsaturated bond.

As the dispersant, specifically, hydroxycarboxylic acid or a neutralized salt thereof or a lactone thereof is preferable. Particularly, gluconic acid (C = 6; OH = 5; COOH
= 1) or a neutralized salt thereof or a lactone thereof, lactobionic acid (C = 12; OH = 8; COOH = 1), tartaric acid (C = 4; OH = 2; COOH = 2) or a neutralized salt thereof, glucoheptone Acid γ-lactone (C = 7; OH
= 5) is preferred. Among these, gluconic acid or its neutralized salt or its lactone is preferable because it has a high effect of improving the degree of orientation and is inexpensive.

As the organic compound having a hydroxymethylcarbonyl group, sorbose is preferred.

Ascorbic acid is preferred as the organic compound having an enol-type hydroxyl group which can be dissociated as an acid.

In the present invention, citric acid or a neutralized salt thereof can also be used as a dispersant. Citric acid has a hydroxyl group and a carboxyl group, but does not satisfy the condition that a hydroxyl group is bonded to 50% or more of carbon atoms other than a carbon atom double-bonded to an oxygen atom. However, the effect of improving the degree of orientation is recognized.

For some of the above preferred dispersants,
The structure is shown below.

[0071]

Embedded image

The degree of orientation by magnetic field orientation is determined by the pH of the slurry.
Affected by Specifically, if the pH is too low, the degree of orientation decreases, which affects the residual magnetic flux density after sintering. When a compound exhibiting an acid property in an aqueous solution, such as hydroxycarboxylic acid, is used as the dispersant, the pH of the slurry becomes low. Therefore,
For example, it is preferable to adjust the pH of the slurry by adding a basic compound together with the dispersant. As the basic compound, ammonia and sodium hydroxide are preferable. Ammonia may be added as aqueous ammonia. In addition, by using the sodium salt of hydroxycarboxylic acid, the pH can be prevented from lowering.

As a raw material, SiO_TwoAnd CaCO_ThreeUsing
If used, hydroxycarboxylic acid or its lactide
Tons are used mainly when preparing slurry for molding.
SiO with rally supernatant_TwoAnd CaCO_ThreeLeaked
And the desired performance, such as a decrease in HcJ, cannot be obtained.
Become. In addition, the pH is adjusted by adding the above basic compound.
Is increased, the SiO_TwoAnd CaCO_ThreeOutflow
Will be more. In contrast, hydroxycarboxylic acids
If a calcium salt is used as a dispersant, SiO _Twoand
CaCO_ThreeOutflow is suppressed. However, the above basification
Compound was added or sodium salt was used as dispersant
In the case of_TwoAnd CaCO_ThreeTo target composition
On the other hand, if it is added in excess, SiO_TwoQuantity and Ca
Insufficiency of the amount of O can be prevented. In addition, ascorbic acid
When used, SiO_TwoAnd CaCO_ThreeOutflow
Almost not.

For the above reasons, the pH of the slurry is preferably 7 or more, more preferably 8 to 11.

The kind of the neutralizing salt used as the dispersant is not particularly limited, and may be any of a calcium salt and a sodium salt. For the above-mentioned reason, the calcium salt is preferably used. When a sodium salt is used as the dispersant or when ammonia water is added, there is a problem that, in addition to the outflow of subcomponents, cracks are easily generated in the formed body and the sintered body.

Incidentally, two or more dispersants may be used in combination.

The amount of the dispersant added is preferably 0.05 to 3.0% by weight, more preferably 0.10% by weight, based on the raw material powder.
~ 2.0% by weight. If the amount of the dispersant is too small, the degree of orientation will not be sufficiently improved. On the other hand, if the amount of the dispersing agent is too large, cracks are likely to occur in the molded body and the sintered body.

When the dispersant is ionizable in an aqueous solution, for example, an acid or a metal salt, the amount of the dispersant added is an ion equivalent. That is, the amount of addition is determined in terms of organic components excluding hydrogen ions and metal ions.
When the dispersant is a hydrate, the amount of addition is determined excluding water of crystallization. For example, when the dispersant is calcium gluconate monohydrate, the amount to be added is calculated in terms of gluconate ions.

When the dispersant is made of lactone or contains lactone, the amount of addition is determined in terms of hydroxycarboxylic acid ions, assuming that all of the lactone is opened to form hydroxycarboxylic acid.

The timing of adding the dispersant is not particularly limited, and may be added during dry coarse pulverization, may be added during the preparation of a slurry for wet pulverization, and may be partially added during dry coarse pulverization. And the remainder may be added during wet grinding. Alternatively, it may be added by stirring after wet pulverization. In any case, since the dispersant is present in the molding slurry, the effect of the addition of the dispersant is realized. However, it is better to add at the time of grinding, especially at the time of dry coarse grinding,
The effect of improving the degree of orientation increases. In a vibration mill or the like used for dry coarse pulverization, larger energy is given to the particles than in a ball mill or the like used for wet pulverization, and the temperature of the particles increases, so that the chemical reaction is likely to proceed. Therefore, if a dispersant is added at the time of dry coarse pulverization, the amount of the dispersant adsorbed on the particle surface increases, and as a result, a higher degree of orientation is considered to be obtained. Actually, when the residual amount of the dispersing agent in the molding slurry (which is considered to be almost equal to the adsorption amount) is measured, the amount of the dispersing agent added during the dry coarse grinding is larger than that when the dispersing agent is added during the wet grinding. The ratio of the residual amount to is increased. In addition, when the dispersant is added in a plurality of times,
What is necessary is just to set the addition amount of each time so that the total addition amount may be in the preferable range described above.

After the wet molding, the molded body is dried.
Preferably 100 to 500 in air or nitrogen
By applying heat treatment at a temperature of ° C., the added dispersant is sufficiently decomposed and removed. Drying and the heat treatment may be performed continuously, but if the molded body is rapidly heated without being sufficiently dried, cracks occur in the molded body,
It is preferable that the temperature is slowly increased from room temperature to about 100 ° C., and that drying is sufficiently performed in this temperature range. After the heat treatment, firing is performed to obtain a sintered ferrite magnet.
The stable temperature during firing is preferably 1150 to 1250.
° C, more preferably 1160 to 1220 ° C, and the time for maintaining the temperature at a stable temperature is preferably 0.5 to 3 hours. As described above, for example, a stabilization process may not be provided in a continuous furnace or the like, but even in such a case, sufficient performance is obtained with the ferrite magnet of the present invention.

The average crystal grain size of the magnet of the present invention is preferably 2 μm or less, more preferably 1 μm or less, and still more preferably 0.5 to 1.0 μm. In the present invention, the average crystal grain size exceeds 1 μm. However, a sufficiently high coercive force can be obtained. The crystal grain size can be measured by a scanning electron microscope. The specific resistance is usually a 10 ⁰ [Omega] m or more.

The compact was crushed using a crusher or the like, and the average particle size was reduced to 100 to 700 μm by sieving or the like.
The magnets may be obtained by classifying the granules so as to have a particle size of about m to obtain magnetic-field-oriented granules, subjecting them to dry magnetic field molding, and sintering them.

In the ferrite magnet of the present invention, a high coercive force and a high saturation magnetization are realized by containing the element R and the element M. Therefore, if it has the same shape as a conventional ferrite magnet that does not contain these elements, the generated magnetic flux density can be increased, and when applied to a motor, high torque can be realized, and it can be applied to speakers and headphones. In this case, the magnetic circuit can be strengthened to obtain sound quality with good linearity, thereby contributing to higher performance of applied products. If the same function as that of a conventional ferrite magnet is sufficient, the size (thickness) of the magnet can be reduced (thinned), which contributes to reduction in size and weight (thinness). Also,
Conventionally, even in a motor in which the field magnet is a winding type electromagnet, this can be replaced with a ferrite magnet, which contributes to weight reduction, shortening of the production process, and cost reduction. In addition, because of its excellent coercive force (HcJ) temperature characteristics, it can be used even in low-temperature environments where there was a risk of low-temperature demagnetization (permanent demagnetization) of ferrite magnets, especially in cold regions and in the sky. The reliability of the manufactured product can be significantly increased. Further, in the present invention, even if the firing conditions are unstable, ferrite magnets having the above-described excellent characteristics can be stably mass-produced. Large contribution to

The magnet of the present invention is processed into a predetermined shape and is used for a wide range of applications as described below.

For example, motors for vehicles such as fuel pumps, power windows, ABSs, fans, wipers, power steering, active suspensions, starters, door locks, electric mirrors, etc .; FDD
For spindle, VTR capstan, VTR rotary head, VTR reel, VTR loading, VTR
For camera capstan, VTR camera rotating head, V
Motors for OA and AV equipment such as TR camera zoom, VTR camera focus, boombox capstan, CD, LD, MD spindle, CD, LD, MD loading, CD, LD optical pickup, etc .; Air conditioner compressor Motors for household appliances such as refrigerator compressor, electric tool drive, electric fan, microwave oven fan, microwave oven plate rotation, mixer drive, dryer fan drive, shaver drive, electric toothbrush, etc .;
Motors for FA equipment such as robot axes, joint drive, robot main drive, machine tool table drive, machine tool belt drive, etc .; motor generators, magnets for speakers and headphones, magnetron tubes, magnetic field generation for MRI It can be used for devices, CD-ROM clampers, distributor sensors, ABS sensors, fuel and oil level sensors, magnet latches, and the like.

[0087]

EXAMPLE 1 SrCO ₃ , Fe ₂ O ₃ , SiO ₂ and CaC
Each powder of O ₃ was blended, mixed and pulverized by a wet attritor for 2 hours, and then dried and sized to obtain granules.

The granules were calcined in air at 1250 ° C. for 3 hours to obtain a calcined material. The composition of the calcined material (analytical value by fluorescent X-ray analysis) is shown in Table 1-1.

Next, as post-additives, SiO ₂ , Ca
CO ₃ , lanthanum carbonate [La ₂ (CO ₃ ) ₃ .8H ₂ O],
Cobalt oxide (a mixture of Co ₃ O ₄ and CoO) was added to the calcined material, and calcium gluconate was further added at 0.6% by weight.
The mixture was added and dry-pulverized by a batch vibrating rod mill for 20 minutes to obtain a coarsely pulverized powder. Next, Fe ₂ O ₃ was added to the coarsely pulverized powder.
, And wet-pulverized by a ball mill for 40 hours, and then dehydrated and concentrated to a concentration of about 78% to obtain a molding slurry.

Next, the molding slurry was compression-molded while dewatering to obtain a molded body having a diameter of 30 mm and a height of 18 mm. At the time of compression molding, a magnetic field of about 13 kOe was applied in the compression direction. The molding pressure was 0.4 t / cm ² .

Next, the compact is fired to obtain a sintered magnet.
After processing the upper and lower surfaces, the relationship between the magnetic properties and sintered body properties of the sintered magnet and the oxygen partial pressure in the firing atmosphere was examined. The firing was performed in a mixed gas atmosphere (1 atm) of oxygen gas and nitrogen gas, and the oxygen partial pressure in the firing atmosphere was controlled by controlling the flow rates of both gases. The heating rate and the cooling rate during firing were 5 ° C./min, and the firing temperature was 122 ° C.
The temperature was set to 0 ° C., and the time for maintaining the temperature at the firing temperature (stabilization time) was set to 1 hour.

Table 1-2 shows the composition of the sintered magnet (analytical value by fluorescent X-ray) whose magnetic properties were evaluated. Table 1
The composition shown in FIG.
The value is for a measurement sample obtained by baking at 00 ° C. for 1 hour.

[0093]

[Table 1]

FIG. 1 shows magnets having the compositions shown in Table 1-2.
In addition, the oxygen partial pressure pO ₂ during firing and the magnetic properties ｛coercive force (Hc
J), residual magnetic flux density (Br) and squareness ratio (Hk / Hc)
J) Indicates the relationship with｝.

As shown in FIG. 1, the composition of the example of the present invention, that is, the atomic ratio {A + R- (Fe + M) / 12} /
In a composition in which the content of Si and SiO ₂ is within the above-mentioned limited range, even when fired in an atmosphere having an oxygen partial pressure of 0.05 atm, magnetic properties equivalent to or higher than those fired in air are obtained, Even when firing in an atmosphere having an oxygen partial pressure of 0.01 atm, almost no decrease in magnetic properties is observed. Specifically, when the oxygen partial pressure was reduced from 0.20 atm to 0.01 atm, the composition of the comparative example, that is, ΔA + R− (Fe
+ M) / 12｝ / Si and a composition in which one of the content of SiO ₂ is out of the above-mentioned range, a decrease of about 400 Oe or more is observed. In the composition of the comparative example in which a higher coercive force is obtained, the coercive force is reduced by about 1500 Oe due to a decrease in the oxygen partial pressure. On the other hand, in the composition of the example, the decrease in the coercive force was within about 150 Oe or less, and no decrease in the residual magnetic flux density was observed at this time. From these results, the effect of the present invention is clear.

Example 2 A sinter having the composition shown in Table 2-2 (analytical value by fluorescent X-ray analysis) was performed in the same manner as in Example 1 except that the calcined material having the composition shown in Table 2-1 was used. A magnet was made. However, during firing, the oxygen partial pressure in the atmosphere was fixed at 0.05 atm.
Various firing temperatures were used.

[0097]

[Table 2]

FIG. 2 shows the relationship between the firing temperature and the magnetic properties of the magnets having the compositions shown in Table 2-2.

As shown in FIG. 2, in the composition of the comparative example,
While the coercive force fluctuates greatly when the firing temperature is changed,
Example composition, that is, atomic ratio ΔA + R− (Fe + M) /
In the composition in which the content of 12% / Si and SiO ₂ is within the above-mentioned limited range, the composition of the comparative example, that is, {A + R− (Fe
+ M) / 12 ° / Si, the variation in coercive force is smaller than a composition in which one of the content of Si and SiO ₂ is out of the above-mentioned limited range.

Example 3 A sinter having the composition shown in Table 3-2 (analytical value by fluorescent X-ray analysis) was performed in the same manner as in Example 1 except that the calcined material having the composition shown in Table 3-1 was used. A magnet was made. However, during firing, the oxygen partial pressure in the atmosphere was fixed at 0.05 atm.
The firing temperature was fixed at 1220 ° C. A group consisting of Example 3A-1, Example 3A-2, and Comparative Example 3A (hereinafter, group A), a group consisting of Example 3B-1, Example 3B-2, and Comparative Example 3B (hereinafter, group B) ) And Example 3C-1, Example 3C-2, Comparative Example 3C In each of the groups (hereinafter, group C), the elements other than Ca are made substantially equal in amount, and the amount of A is changed by changing the amount of Ca. And ΔA + R- (Fe + M) / 1
2｝ / Si was changed.

[0101]

[Table 3]

FIG. 3 shows the relationship between the atomic ratio {A + R- (Fe + M) / 12} / Si and the magnetic characteristics, and FIG. 4 shows the relationship between the CaO content and the magnetic characteristics for the magnets having the compositions shown in Table 3-2. Are shown below.

In FIG. 3, a comparison of the magnetic characteristics in each of the groups A, B, and C reveals that the coercive force is significantly increased when the atomic ratio is within the range defined by the present invention. That is, it is understood that a high coercive force can be obtained under a low oxygen partial pressure according to the present invention. On the other hand, FIG.
Paying attention to the coercive force graph, it can be seen that the CaO amount of Comparative Example 3C is smaller than the composition of the examples of Group A and larger than the composition of Examples of Groups B and C. That is, it is understood that the CaO amount of Comparative Example 3C is neither excessive nor too low as compared with the compositions of the other Examples.

Conventionally, in the Sr ferrite magnet, it has been considered that the content of CaO as an additive has a great effect on the coercive force. However, from FIGS. 3 and 4, under low oxygen partial pressure, the CaO content does not increase. No ｛A + R- (Fe + M)
It is apparent that the coercive force changes greatly depending on / 12 ° / Si.

In the Sr ferrite produced in each of the above embodiments, when a part of La was replaced with Bi,
It was found that the calcination temperature could be lowered by the addition. That is, the calcination temperature at which the best properties were obtained was shifted to the lower temperature side, and the coercive force was hardly deteriorated. Also,
When a sintered magnet was manufactured with a composition in which La was partially replaced by another rare earth element, the same effect as in the above examples was observed.

In each of the above examples, lanthanum carbonate and cobalt oxide were added to the calcined material as post-additives. However, even if the same amounts were added to the starting materials without post-addition,
The same effects as in the above examples were observed. However, the effect was slightly lower than in the case where it was added later.

The Curie temperature of the sintered magnet produced in each of the above examples was measured in the following procedure. First, the sintered magnet was processed into a columnar shape having a diameter of 5 mm and a height of 6.5 mm so that the height direction was the c-axis direction, to obtain a measurement sample. Next, at 25 ° C., the sample was magnetized by applying a magnetic field of about 20 kOe in the c-axis direction of the sample using a VSM.
Next, with the VSM magnetic field generation current set to zero (however, a magnetic field of about 50 Oe is generated due to the residual magnetization of the magnetic pole),
By simultaneously measuring the remanent magnetization in the c-axis direction of the sample and the sample temperature, σ-T as shown in FIG.
A curve was obtained. The temperature of the sample was raised by a heater arranged around the sample. The heating rate was about 10 ° C./min. The Curie temperature was determined from the obtained σ-T curve by the method described above. As a result, the magnets manufactured in the above examples have two Curie temperatures, the Curie temperature on the low temperature side is between 430 and 445 ° C, and the Curie temperature on the high temperature side is between 450 and 460 ° C. all right. The magnetization (σ1) at the Curie temperature on the low temperature side is 2
Ratio (σ1 / σRT) to magnetization (σRT) at 5 ° C
Was 2-10%. When each sample was analyzed by X-ray diffraction, it was found that each sample was a single phase of M-type ferrite.

Reference Example A sintered ferrite magnet having the composition shown in Table 4 below was produced. The Sr ferrite magnet containing La and Co was produced by the above-described post-addition method. The firing was performed in a mixed gas atmosphere (1 atm) of oxygen gas and nitrogen gas, and the flow rate of both gases was controlled to control the oxygen concentration in the firing atmosphere. Figure 5 shows the oxygen concentration in the firing atmosphere.
Shown in The coercive force (HcJ) of these sintered magnets was measured. FIG. 5 shows the results.

[0109]

[Table 4]

FIG. 5 shows that Sr containing La and Co
In the case of ferrite magnets, the coercive force changes significantly depending on the oxygen concentration in the firing atmosphere, whereas in the case of conventional Sr ferrite magnets containing neither La nor Co, the coercive force depends on the oxygen concentration in the firing atmosphere. It turns out that the property is low. The LaCo-containing magnet shown in FIG. 5 has an atomic ratio {A + R- (Fe + M) / 12} / Si outside the range limited by the present invention.

From the results shown in FIG. 5 and the results of each of the above examples, the Si content and the atomic ratio ΔA + R− (Fe
It is clear that controlling (+ M) / 12 ° / Si exerts a specific effect only on the ferrite magnet containing the elements R and M.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the oxygen partial pressure in a firing atmosphere and the magnetic properties of a sintered magnet.

FIG. 2 is a graph showing a relationship between a firing temperature and magnetic properties of a sintered magnet.

FIG. 3 Atomic ratio {A + R- (Fe + M) / 12} / Si
6 is a graph showing the relationship between the magnetic properties of a sintered magnet.

FIG. 4 is a graph showing the relationship between the CaO content and the magnetic properties of a sintered magnet.

FIG. 5 shows the oxygen concentration in the firing atmosphere and the coercive force H of the sintered magnet.
It is a graph which shows the relationship with cJ.

FIG. 6 is a reference graph for explaining how to determine two Curie temperatures.

Claims (8)

[Claims] 1. A is a material containing at least one element selected from Sr, Ba, Ca and Pb, R is at least one element selected from a rare earth element (including Y) and Bi, When at least one element selected from Co, Mn, Al, Cr, Ni and Zn is M, the metal elements include A, R, Fe, M and Si, and these metal elements are converted to oxides. Then, when the content of each metal oxide was determined, the content of SiO ₂ was 1.3 to
A ferrite magnet having 2.0 mol% and an atomic ratio {A + R- (Fe + M) / 12} / Si of 1.1 to 1.9, and having hexagonal ferrite as a main phase. 2. The ratio of the total amount of each of A, R, Fe and M to the total amount of metal elements is as follows: A: 1 to 13 atom%, R: 0.05 to 10 atom%, Fe: 80 to 95 atom %, M: 0.1 to 5 atomic%. 3. The method according to claim 1, which has at least two different Curie temperatures, wherein the Curie temperatures are in the range of 400 ° C. to 480 ° C., and wherein the Curie temperatures are at least 5 ° C. apart from each other. Ferrite magnet. 4. The method for producing a ferrite magnet according to claim 1, further comprising a firing step of firing a molded body of the raw material powder to obtain a sintered magnet. A method for producing a ferrite magnet in which the oxygen partial pressure varies. 5. The method for producing a ferrite magnet according to claim 4, wherein in at least a part of the firing step, the oxygen partial pressure in the atmosphere is 0.15 atm or less. 6. The method for producing a ferrite magnet according to claim 1, further comprising a firing step of firing a molded body of the raw material powder to obtain a sintered magnet. A method for manufacturing ferrite magnets that fluctuate in temperature. 7. A calcined material or particles each having hexagonal ferrite as a main phase, at least one compound containing at least one magnet constituent element is added, and then molded and sintered. 7. The method for producing a ferrite magnet according to any one of items 1 to 6. 8. A part of the magnet constituent element is the element R
8. The method for manufacturing a ferrite magnet according to claim 7, wherein the ferrite magnet is at least one element selected from the group consisting of the element M and the element M.