JP2023027860A - Magnetic powder material and method for producing permanent magnet and magnetic powder material - Google Patents

Abstract

To provide a method for producing a magnetic powder material having a high coercive force in a hexagonal ferrite by a simple method.SOLUTION: A method for producing a magnetic powder material executes: a step of mixing an alkaline solution with an aqueous solution in which ions of A and iron ions in proportions constituting hexagonal ferrite and lithium ions are dissolved to generate a coprecipitate when A is an element selected from Ba, Sr, and Pb; a step of adding a flux while the coprecipitate is in a suspension state; a heat treatment step of heating a flux-added coprecipitate to grow crystals; and a step of removing the flux from a heat-treated substance to obtain the magnetic powder material composed of hexagonal ferrite particles in which a part of iron is replaced with lithium.SELECTED DRAWING: Figure 2

Description

The present invention relates to a magnetic powder material that can be used as a material for a permanent magnet, a permanent magnet, and a method for producing a magnetic powder material. The present invention relates to a magnetic powder material composed of hexagonal ferrite particles having a structure such as a magnetoplum type or a ferrox planar type, a permanent magnet, and a method for producing a magnetic powder material.

As a high-performance magnetic powder material for permanent magnets, it is well known that magnetic powders using rare earth elements such as Nd--Fe--B and Sm--Co as main constituent elements are currently mainstream. Vigorous studies are ongoing for improvement. However, in these Nd--Fe--B and Sm--Co magnets, the use of a large amount of rare earth elements, which are rare elements, poses a serious problem.

On the other hand, as a magnetic powder material for permanent magnets, an iron oxide-based magnetic powder material is used in large quantities other than the above-mentioned Nd--Fe--B-based and Sm--Co-based magnetic powder materials. This iron oxide-based magnetic powder material has low manufacturing costs because the raw materials are inexpensive, and its performance as a permanent magnet is inferior to that of rare earth-based magnets. ing.
In iron oxide magnets using iron oxide magnetic powder materials, the most widely used magnetic powder materials at present are hexagonal ferrite magnetic powders such as barium ferrite and strontium ferrite. This hexagonal ferrite magnetic powder has been known as a permanent magnet material for a long time, and a huge number of patent applications and paper reports have been made so far.

Further, in order to further improve the properties of this hexagonal ferrite magnetic powder, studies on substitution elements and compositions have been made vigorously. For example, it is known that magnetic properties can be improved by substituting barium, strontium, and part of iron with other elements (for example, JP-A-10-149910, JP-A-2000-323317, JP-A-2000-323317, and JP-A-2000-323317. Japanese Laid-Open Patent Publication No. 2001-052912). In particular, substituting a portion of Ba or Sr with lanthanum (La), which is a rare earth element, and further substituting a portion of iron with cobalt, which is a transition metal element, significantly improves magnetic properties such as coercive force and saturation magnetization. is publicly known (for example, JP-A-2000-331813, JP-A-2001-068319, JP-A-2005-259751, JP-A-2005-268784). Replacing some of the main elements such as barium, strontium, and iron constituting the hexagonal ferrite magnetic powder with other elements is an extremely effective technique for improving the magnetic properties of the magnetic powder.

Non-Patent Document 1 describes that in an iron oxide magnetic powder having a spinel ferrite structure with a crystal structure different from that of hexagonal ferrite, the charge balance of cations and anions in the magnetic powder deviates from the stoichiometric ratio. A technique for substituting a portion of iron with elements such as cobalt, nickel, and lithium is described as follows.

JP-A-10-149910 JP-A-2000-323317 Japanese Patent Application Laid-Open No. 2001-052912 JP-A-2000-331813 Japanese Patent Application Laid-Open No. 2001-068319 JP-A-2005-259751 Japanese Patent Laid-Open No. 2005-268784)

M. Kishimoto, et al., "Coercive force of Co-Ni-Li spinel ferrite particles synthesized through co-precipitation, hydrothermal treatment, and etching in hydrochloric acid", Japan. J. Appl. Phys, Vol. 59 (2020) 085002.

(Problem of conventional technology)
As described in Patent Documents 1 to 7, hexagonal ferrite magnetic powders represented by barium ferrite and strontium ferrite are widely used as materials for permanent magnets with excellent cost performance, and further improvements have been made. ing. As a means of improvement, a method of substituting a part of barium, strontium, iron, etc. with other elements such as cobalt or lanthanum has become mainstream.
When element substitution is performed to improve magnetic properties, for example, in the above-described method of partially substituting barium, strontium, or iron with lanthanum or cobalt, in order to develop the desired properties, the element to be substituted must be specified. The problem is that it is necessary to place them in a precise position, and it is difficult to control them.

Non-Patent Document 1 describes a technique for increasing the coercive force by substituting part of the iron with cobalt, nickel-lithium, or the like in iron oxide magnetic powder of spinel ferrite instead of hexagonal ferrite. ing. However, the crystal structure of the spinel ferrite of Non-Patent Document 1 is a relatively simple structure, and it is possible to add Li by heat treatment at about 200 ° C., but the structure of hexagonal ferrite is complicated. However, even if the manufacturing method of spinel ferrite is directly applied to hexagonal ferrite, there is a problem that it is impossible to obtain a magnetic powder substituted with cobalt, nickel-lithium, or the like.

A technical object of the present invention is to obtain a magnetic powder material having a high coercive force in a hexagonal ferrite by a simple method.

In order to solve the technical problem, the magnetic powder material of the invention according to claim 1 is
When A is any element of Ba, Sr, and Pb, and x is 0.12 or more and 1.8 or less, a part of the iron generally represented by the chemical formula AFe _12-x Li _x O ₁₉ is lithium. It is characterized by comprising substituted hexagonal ferrite particles.

The invention according to claim 2 is the magnetic powder material according to claim 1,
It is characterized by a coercive force of 443 to 787 kA/m when measured with an applied magnetic field of 1350 kA/m.

The invention according to claim 3 is the magnetic powder material according to claim 1 or 2,
The particles are characterized by having a plate-like shape.

The invention according to claim 4 is the magnetic powder material according to any one of claims 1 to 3,
It is a hexagonal ferrite with a magnetoplum-type or ferrox-planar-type crystal structure.

The invention according to claim 5 is the magnetic powder material according to any one of claims 1 to 4,
It is characterized by being subjected to magnetic field orientation treatment.

In order to solve the technical problem, the permanent magnet of the invention according to claim 6 is
A magnetic powder material according to any one of claims 1 to 5 is used.

In order to solve the technical problem, the method for producing a magnetic powder material of the invention according to claim 7 comprises:
When A is any element of Ba, Sr, and Pb, an alkaline solution is mixed with an aqueous solution in which ions of A and iron ions in proportions constituting hexagonal ferrite and lithium ions are dissolved, creating a coprecipitate;
adding a flux while the coprecipitate is in suspension;
a heat treatment step of heating the coprecipitate to which the flux has been added to grow crystals;
a step of removing the flux from the heat-treated material to obtain a magnetic powder material consisting of hexagonal ferrite particles in which a portion of the iron is replaced with lithium;
is characterized by executing

The invention according to claim 8 is the method for producing a magnetic powder material according to claim 7,
It is characterized in that the heat treatment step is performed at a temperature higher than the melting point by 0° C. to 200° C.

According to the inventions of claims 1, 6, and 7, hexagonal ferrite in which a portion of iron is substituted with lithium can be obtained, and a magnetic powder material with high coercive force can be obtained by a simple method. .
According to the second aspect of the invention, a magnetic powder material having a coercive force of 443 to 787 kA/m can be obtained.
According to the third aspect of the invention, a plate-shaped magnetic powder material can be obtained, and the orientation treatment for aligning the axes of easy magnetization in one direction facilitates obtaining a magnet with high magnetic force.
According to the fourth aspect of the invention, hexagonal ferrite represented by magnetoplum type or ferrox planar type can be obtained.
According to the fifth aspect of the invention, a powder material with a high squareness ratio can be obtained.
According to the eighth aspect of the invention, a magnetic powder material having a larger particle size can be obtained by heat treatment at a temperature 0° C. to 200° C. higher than the melting point.

1 is a transmission electron micrograph of particles that are precursors of lithium-substituted strontium ferrite particles before heat treatment in flux in Example 1. FIG. 1 is a transmission electron micrograph of lithium-substituted strontium ferrite particles subjected to heat treatment in a flux in Example 1. FIG. 2 is an X-ray diffraction diagram of lithium-substituted strontium ferrite particles subjected to heat treatment in a flux in Example 1. FIG. 3 is a magnetization curve of lithium-substituted strontium ferrite particles subjected to heat treatment in a flux in Example 1. FIG. 4 is a transmission electron micrograph of lithium-substituted barium ferrite particles subjected to heat treatment in a flux in Example 2. FIG.

Embodiments of the present invention will now be described with reference to the drawings, but the present invention is not limited to the following embodiments.
It should be noted that in the following explanation using the drawings, illustration of members other than those necessary for the explanation is omitted as appropriate for ease of understanding.

The magnetic powder material of the present invention is a hexagonal ferrite particle such as barium ferrite or strontium ferrite in which part of the iron is replaced with lithium, and generally has a plate-like shape and has an extremely large coercive force. , it becomes the optimum magnetic powder material for permanent magnets.

As a basic method for producing the magnetic powder material of the present invention, a coprecipitate containing iron, barium, and strontium, which are basic constituent elements of hexagonal ferrite, and lithium, which is a substituting element, is prepared. is added to dissolve a flux such as potassium bromide (KBr) in a state containing the Heat treatment is performed at a temperature higher than the melting point of (KBr). When the temperature is raised to the melting point of the flux (KBr), the oxide particles are dispersed in the KBr in the liquid phase. By this treatment (molten salt treatment, flux treatment), coprecipitates of elements such as iron, barium, strontium, and lithium crystal grow into hexagonal ferrite particles in the liquid flux. After that, when the temperature is lowered to room temperature, KBr changes from a liquid to a solid, but since KBr is water-soluble, the flux can be removed by washing with water. By removing the flux in this way, it is possible to obtain hexagonal ferrite particles in which part of the iron is replaced with lithium.

As the crystal structure of such hexagonal ferrite particles, many different crystal structures such as the magnetoplum type and the ferrox planer type are known. Depending on the composition ratio of ions, hexagonal ferrite particles with various crystal structures can be handled. The substitution amount of lithium is preferably 1 to 15 mol % expressed as Li/(Li+Fe). When the amount of lithium substituted is less than 1 mol %, it is difficult to obtain a sufficient effect of improving the coercive force. On the other hand, if the substitution amount of lithium is more than 15 mol %, it becomes difficult to completely substitute Li for Fe, and as a result, Li that cannot be completely substituted remains as an oxide, which tends to lower the saturation magnetization. Therefore, the substitution amount of lithium is preferably in the range of 1 to 15 mol %.
When A is any element of Ba, Sr, and Pb, and hexagonal ferrite particles in which iron is partially substituted with lithium are represented by the chemical formula AFe _12-x Li _x O ₁₉ , lithium is 1 to 15. The mol % substituted state corresponds to x being between 0.12 and 1.8.

Lithium can replace alkaline earth metals such as barium and strontium, but it is most effective to replace iron in order to obtain a high coercive force. Furthermore, it is also possible to replace lithium with other elements such as cobalt and nickel at the same time. Even in such a case, it is preferable to substitute lithium within the above-mentioned range for the element existing at the site originally occupied by iron.

(Detailed description of manufacturing method)
In order to produce the lithium-substituted hexagonal ferrite particles as the magnetic powder material of the embodiment of the present invention, starting materials are basic constituent elements such as barium, strontium and iron, and hydroxides of lithium.
First, to an aqueous solution containing these element ions (Ba, Sr, Fe, Li ions), an alkaline aqueous solution with the number of moles required to convert these ions into hydroxides is added to produce hydroxides of these ions. is prepared as a coprecipitate. The ion source is not particularly limited, and metal salts such as chlorides, nitrates and sulfates of these metal elements (Ba, Sr, Fe, Li) can be used.

The concentration of alkali is preferably 1.5 to 5 times the number of moles required to form the hydroxide of the metal ion, that is, excess alkali. The alkali source is not particularly limited, and sodium hydroxide, potassium hydroxide, and the like can be used as preferred alkali sources. In addition, since iron ions become trivalent when hexagonal ferrite particles are formed, it is preferable to use trivalent iron ions when preparing a coprecipitate.
Lithium ions are usually monovalent, but this is an important finding discovered for the first time by the present invention. For the purpose, monovalent lithium with the lowest possible valence is the optimum substitution element.

The thus-obtained coprecipitate is washed with water to remove alkaline components, and then dissolved in a suspension state by adding a flux. It is very important to use the suspension in this way. Once dried, the particles are strongly agglomerated, and it is extremely difficult to redisperse them. As a result, the grains tend to have a wide grain size distribution when crystals are grown by heat treatment in the next step. As the flux, for example, KBr, FK, NaCl, LiBr, etc. can be preferably used. However, since these fluxes are used for the purpose of crystallizing particles to an arbitrary size, they are limited to these types. Various fluxes can be used depending on the desired particle size.

Next, the coprecipitate in which the flux is dissolved is heated for heat treatment for crystal growth. Generally, the higher the heat treatment temperature in the flux, the greater the degree of crystal growth, and various fluxes with different melting points can be selected according to the desired particle size. The temperature of this heat treatment is a temperature higher than the melting point of the flux, and the flux is melted by heat, the particles flow in the flux, and the particles coalesce to grow crystals. The heat treatment temperature is preferably set within a range of about 0° C. to 200° C. higher than the melting point. A higher temperature relative to the melting point is preferable because it promotes crystal growth and makes it easier to obtain large-sized particles. There is fear. On the other hand, if the heat treatment temperature is close to the melting point (melting point+0° C.), the fluidity may be insufficient. Therefore, the heat treatment temperature is preferably +0°C to 200°C, more preferably +100°C. Therefore, for example, when potassium bromide (KBr) is used as a flux, it is preferably used within a temperature range of about 734 to 934°C because its melting point is 734°C.

Next, the particles obtained by crystal growth by the heat treatment in the flux are washed with water to remove the flux. For example, when KBr is used as a flux, since KBr is easily dissolved in water, it can be easily removed by immersing the crucible in water to dissolve KBr and then repeating decantation.

Next, after removing the flux by washing with water, the remaining particles are removed by filtering and drying. By performing the heat treatment in the flux at such a high temperature, it is possible to obtain particles having a hexagonal structure substituted with an element such as lithium grown to a particle size of 100 to 500 nm depending on the heat treatment temperature. The grains crystallized in the flux in this way usually have a hexagonal plate shape reflecting the crystal structure. The ability to obtain particles having such a plate-like shape is an extremely important feature of the present invention in parallel with obtaining a large coercive force, and was obtained for the first time by the production method of the present invention. Having such a plate-like shape is extremely useful, for example, when performing an orientation treatment for aligning the axis of easy magnetization in a permanent magnet or the like. This is because the mechanical orientation is also added by having.

(Action of Embodiment)
The lithium-substituted hexagonal ferrite particles thus obtained have a coercive force of 443 to 787 kA/m and a magnetization of about 58 Am ² /kg when measured in an applied magnetic field of 1350 kA/m (17000 Oe). A magnetic powder having a particle size in the range of 100 to 500 nm and having a generally plate-like shape is obtained. A permanent magnet having a high coercive force and moderate saturation magnetization at the same time, and having an optimal shape and particle size for magnetic field and mechanical orientation. It becomes the optimum magnetic powder material for use. In the production method of the embodiment, it is expected that a magnetic powder having a coercive force of 300 to 1000 kA/m, a magnetization amount of 45 to 70 Am ² /kg, and a squareness ratio of about 0.80 to 1.0 can be obtained. be.

It was generally difficult to obtain a coercive force of 400 kA/m or more with a magnetic material produced by a conventional manufacturing method, but the magnetic material of the embodiment can easily achieve a coercive force of 400 kA/m or more. , it is possible to obtain a magnetic material having a higher coercive force than the conventional one. In particular, in the embodiment, the substitution of lithium can be performed only by performing heat treatment after adding the flux to the coprecipitate, and the element to be substituted can be There is no need for control to precisely place the to a specific position. Therefore, in the embodiment, a magnetic material with high coercive force can be easily obtained.
Further, in the embodiment, flux treatment is performed to obtain hexagonal ferrite particles in which part of iron is replaced with lithium. Since the spinel ferrite described in Non-Patent Document 1 has a simple structure, it is possible to add Li by heat treatment at about 200° C. using an autoclave. On the other hand, since the hexagonal ferrite of the embodiment has a complicated structure, a high temperature treatment of about 800° C. is indispensable, and the flux treatment of the embodiment is necessary. That is, in the embodiment, unlike the treatment method described in Non-Patent Document 1, by performing the flux treatment, which is a treatment method first discovered by the present application, for the first time, a hexagonal It was possible to realize crystal ferrite particles.

Next, a detailed manufacturing method (example) will be described with respect to the manufacturing method of the embodiment. Values are shown when measured with an applied magnetic field of 1350 kA/m (17000 Oe).
Hereinafter, the present invention will be described more specifically by describing examples, but it goes without saying that the present invention is not limited to the examples described here. In particular, in this example, the method of lithium replacement will be described by taking a composition for obtaining a magnetoplum-type hexagonal ferrite as an example, but it goes without saying that the structure is not limited to this. As the constituent elements, an example using strontium, barium, and iron, which are the basic elements that make up the hexagonal ferrite, was shown. It goes without saying that it is possible.

(Example 1)
<Preparation example 1 of lithium-substituted strontium ferrite particles>
Using a 1000 mL beaker, 0.05 mol of strontium chloride salt, 0.57 mol of ferric chloride salt, 0.03 mol of lithium chloride salt were dissolved in 500 g of water. Next, 5.7 moles of sodium hydroxide was dissolved in 1000 g of water using a 2500 mL beaker. This aqueous solution of strontium chloride, ferric chloride and lithium chloride was added to an aqueous solution of sodium hydroxide and stirred for 10 minutes to form a coprecipitate of strontium, iron and lithium.
Next, this coprecipitate was washed with water by decantation until it became neutral. After that, the mixture was allowed to stand for about 1 hour to precipitate a coprecipitate, and after removing the supernatant liquid, 1.8 mol of potassium bromide was added as a flux to this suspension, and the potassium bromide was dissolved and mixed with stirring. .

The mixture was then spread on a metal vat and placed in an oven and dried at 90°C for about 1 day to remove moisture. After pulverizing this dry mixture, it was placed in a crucible and heat-treated at 830° C. for 1 hour using a muffle furnace. By this heat treatment in the flux, the coprecipitate particles crystallize into lithium-substituted strontium ferrite particles having a hexagonal crystal structure.
Finally, the heat-treated product was immersed in water together with the crucible, and the potassium bromide was dissolved and removed by washing with water.
The particles thus obtained were subjected to particle shape observation by a transmission electron microscope, structural analysis by X-ray diffraction, and magnetic properties by a sample vibrating magnetometer.

FIG. 1 shows a transmission electron micrograph of a coprecipitate composed of hydroxides of strontium, iron and lithium.
FIG. 2 shows a transmission electron micrograph of lithium-substituted strontium ferrite particles obtained by subjecting this coprecipitate to heat treatment in a flux to allow crystal growth.
FIG. 3 shows an X-ray diffraction pattern of the lithium-substituted strontium ferrite particles.
FIG. 4 shows the magnetization curve of the lithium-substituted strontium ferrite particles.
From FIG. 1, it can be seen that it is an aggregate of fine particles with a size of several nanometers.
Further, from FIG. 2, it can be seen that the particles are composed of approximately hexagonal tabular particles with a particle size of about 100 nanometers.
The diffraction peaks in the X-ray diffraction diagram shown in FIG. 3 coincide with the peaks of known magnetoplum-type hexagonal ferrite, indicating that the particles are magnetoplum-type hexagonal ferrite.
From FIG. 4, the coercive force measured at the maximum applied magnetic field of 1350 kA/m (17000 Oe) is 468 kA/m (5870 Oe), and the magnetization at 1350 kA/m is 59.5 Am ² /kg (59.5 emu/g). Met. The squareness ratio (magnetization amount at zero applied magnetic field/magnetization amount at 1350 kA/m) at an applied magnetic field of 1350 kA/m was 0.550.

Although the reason why such a high coercive force is obtained is not clear, as described above, by substituting a portion of the trivalent iron with monovalent lithium ions, the charges of the cations and anions in the particles are reduced. It is considered that the balance deviates from the stoichiometric ratio, resulting in the formation of vacancies and lattice defects in the particles, which act to prevent magnetization reversal and increase the coercive force. be. In any case, the phenomenon that the coercive force remarkably increases in such an unbalanced state of valences was found for the first time in the present invention.

(Example 2)
<Preparation example 2 of lithium-substituted strontium ferrite particles>
In the production of lithium-substituted strontium ferrite particles in Example 1, except that 0.57 mol of ferric chloride salt was changed to 0.56 mol and lithium chloride salt was changed from 0.03 mol to 0.04 mol. A coprecipitate was prepared in the same manner as in 1, a flux was added, heat treatment was performed in the flux, and lithium-substituted strontium ferrite particles were prepared. It was confirmed by X-ray diffraction that these particles were also substantially magnetoplum-type hexagonal ferrite. Further, it was found from the transmission electron micrograph that the particles were approximately hexagonal tabular particles with a particle size of about 100 nanometers. As for the magnetic properties, the coercive force was 485 kA/m (6080 Oe) and the magnetization amount at 1350 kA/m was 57.7 Am ² /kg (57.7 emu/g). The squareness ratio (magnetization amount at zero applied magnetic field/magnetization amount at 1350 kA/m) at an applied magnetic field of 1350 kA/m was 0.556.

(Example 3)
<Preparation of lithium-substituted barium ferrite particles>
A coprecipitate was produced in the same manner as in Example 1, except that 0.05 mol of barium chloride was used instead of 0.05 mol of strontium chloride in the preparation of lithium-substituted strontium ferrite particles in Example 1. Then, a flux was added and heat treatment was performed in the flux to prepare lithium-substituted barium ferrite particles. It was confirmed by X-ray diffraction that these particles were also substantially magnetoplum-type hexagonal ferrite. FIG. 5 shows a transmission electron micrograph of the lithium-substituted barium ferrite particles. It can be seen from the photograph that the particles are approximately hexagonal tabular particles with a particle size of about 120 nanometers.
As for the magnetic properties, the coercive force was 443 kA/m (5550 Oe) and the magnetization amount at 1350 kA/m was 59.0 Am ² /kg (59.0 emu/g). The squareness ratio (magnetization amount at zero applied magnetic field/magnetization amount at 1350 kA/m) at an applied magnetic field of 1350 kA/m was 0.545.

In these examples, an example is shown in which a part of the iron is replaced with lithium in the basic composition of the hexagonal ferrite magnet composed of alkaline earth elements such as divalent strontium and barium and trivalent iron. Needless to say, it is possible to perform complex replacement such as replacing part of the alkaline earth elements with lanthanum, part of iron with cobalt, and further replacing part of iron with lithium.

(Example 4)
<Magnetic orientation treatment of lithium-substituted strontium ferrite particles>
The lithium-substituted strontium ferrite particles obtained in Example 2 were subjected to magnetic field orientation treatment. As a method, 1 g of this particle, 0.3 g of vinyl chloride resin (MR-104, manufactured by Kaneka) as a binder, and 380 g of toluene as a solvent are placed in a zirconia pot with a capacity of 100 cc, and dispersed as beads. 100 g of zirconia beads with a diameter of 0.1 mm were added and dispersed for 5 hours using a planetary ball mill to prepare a magnetic paint.
Magnetic field orientation was performed by the following procedure. The magnetic paint was coated onto the base film using a glass rod. Next, this film was inserted near the center of a pole piece of an electromagnet generating a magnetic field of 400 kA/m, left to stand for about 10 minutes, and naturally dried to prepare a magnetic film. A portion of about 1 mm×1 mm was cut out from the vicinity of the center of this magnetic film and used as a sample for magnetic measurement. The magnetic field orientation direction squareness ratio (magnetization amount at zero applied magnetic field/magnetization amount at 1350 kA/m) of this magnetic film was 0.918, confirming extremely high orientation. The coercive force at this time was 787 kA/m (9860 Oe). Such a high coercive force is due to the effect of aligning the anisotropy direction and the effect of reducing the anisotropy due to the demagnetizing field of the plate-like particles due to the laminated orientation of the plate-like particles. it is conceivable that.

As described above, the lithium-substituted hexagonal ferrite particles of the present invention not only have a remarkable increase in coercive force due to the partial replacement of iron with lithium, but are also excellent due to the plate-like shape of the particles. magnetic field orientation. Such a plate-like shape results from the crystal growth of the particles in the flux, and is one of the major features of the present invention as well as the high coercive force due to substitution with lithium. Such high coercive force and orientation are extremely useful as permanent magnets.

(Comparative example 1)
<Preparation of Strontium Ferrite Particles Not Substituted with Lithium>
In Comparative Example 1, strontium ferrite particles were prepared under the same conditions as in Example 1, except that lithium was not added and 0.57 mol of ferric chloride salt was changed from 0.57 mol to 0.60 mol. made. That is, strontium ferrite particles, which are hexagonal ferrite with a standard composition, were produced without substitution with lithium.
The coercivity of this particle when measured at a maximum applied magnetic field of 1350 kA/m (17000 Oe) was 376 kA/m (4710 Oe) and the magnetization at 1350 kA/m was 61.1 Am ² /kg (61.1 emu/g). there were. The squareness ratio (magnetization amount at zero applied magnetic field/magnetization amount at 1350 kA/m) at an applied magnetic field of 1350 kA/m was 0.541. It was found to consist of plate-like particles with a particle size of about 120 nanometers.

(Comparative example 2)
<Preparation of Barium Ferrite Particles Not Substituted with Lithium>
In Comparative Example 2, barium ferrite particles were produced under the same conditions as in Example 3, except that lithium was not added and the ferric chloride salt was changed from 0.57 mol to 0.60 mol. That is, barium ferrite particles, which are hexagonal ferrite with a standard composition, were produced without substitution with lithium.
The coercivity of this particle when measured at a maximum applied magnetic field of 1350 kA/m (17000 Oe) was 362 kA/m (4540 Oe) and the magnetization at 1350 kA/m was 59.3 Am ² /kg (59.3 emu/g). there were. The squareness ratio (magnetization amount at zero applied magnetic field/magnetization amount at 1350 kA/m) at an applied magnetic field of 1350 kA/m was 0.538. It was found to consist of tabular particles with a particle size of about 150 nanometers.

Next, the results of Examples and Comparative Examples will be described. In Examples 1 and 2, lithium-substituted strontium ferrite particles with different amounts of substitution were described. In both examples, it was confirmed that the coercive force was greatly increased by the lithium substitution. In Example 2, in which the amount of lithium substitution is large, the saturation magnetization amount is slightly decreased as compared with Example 1, but the coercive force is larger.

Example 3 describes the lithium-substituted barium ferrite particles. Compared with the lithium-substituted strontium ferrite particles of Examples 1 and 2, the coercive force and saturation magnetization are slightly lower, but part of the iron of the hexagonal ferrite particles It was confirmed that the phenomenon of obtaining high coercive force by replacing with lithium is the same for both strontium ferrite and barium ferrite. Although not explained in the examples, the coercive force increasing effect by lithium substitution can be applied not only to the magnetoplum type structure but also to all hexagonal ferrite particles such as the ferrox planar type.
Furthermore, in Example 4, the lithium-substituted strontium ferrite particles obtained in Example 2 were subjected to a magnetic field orientation treatment, and it was confirmed that the coercive force was further increased significantly. Such a large increase in coercive force due to the magnetic field orientation treatment is due to the effect of aligning the axis of easy magnetization of the magnetic powder in one direction and the plate-like shape of the magnetic powder obtained by the present invention. is also caused. That is, it is considered that the lamination of the plate-like particles suppresses the decrease in the anisotropy due to the demagnetizing field of the plate-like particles, and as a result, the anisotropy is further increased and the coercive force is increased.

On the other hand, in Comparative Examples 1 and 2, strontium ferrite particles and barium ferrite particles, which are standard hexagonal ferrites without lithium replacement, were described. Since these particles were not subjected to lithium replacement, the coercive force was obviously smaller than the particles of Examples 1 to 3, which were subjected to lithium replacement.

As described above, the magnetic powder obtained in this example was found to be magnetoplum-type hexagonal ferrite particles from the results of X-ray diffraction, and had an approximately hexagonal plate-like shape from the results of electron microscope observation. I found out.
The particle size of this magnetic powder greatly depends on the heat treatment conditions in the flux. In general, the higher the heat treatment temperature, the larger the particle size, which can be controlled within the range of 100 to 500 nanometers.
As for the magnetic properties, the coercive force when measured at an applied magnetic field of 1350 kA/m (17000 Oe) usually increases as the amount of lithium substitution increases, and is in the range of 443 to 787 kA/m compared to the comparative example of less than 400 kA/m. A powder with a high coercive force is obtained. Also, ^{the magnetization amount tends to decrease as the amount of lithium substitution increases, and the magnetization amount is in the range of 57.7 to 59.5 Am 2 /} kg. It has little effect on comparison. In addition, the magnetic powder of this example has a squareness ratio of 0.918, which is large due to the orientation treatment of Example 4, compared to the comparative example, which had a squareness ratio of about 0.538 to 0.541. A powder is obtained. As the squareness ratio increases, the axis of easy magnetization tends to align in one direction.

In any case, hexagonal ferrite particles having a high coercive force can be obtained by using lithium as a basic substituting element. The phenomenon that the coercive force is significantly increased by substituting lithium for a portion of the iron in the magnetic powder having the hexagonal ferrite structure as described above was discovered for the first time by the present invention.

Therefore, the magnetic powder of this example is lithium-substituted hexagonal ferrite particles, and has a coercive force of 443 to 787 kA/m and a magnetization amount of 58 Am ² / when measured with an applied magnetic field of 1350 kA/m (17000 Oe). It is a magnetic powder of generally plate-like shape with a particle size of about 100 to 120 nm, having a high coercive force and moderate saturation magnetization, and having an optimal shape and particle size for magnetic field and mechanical orientation. It becomes the optimum magnetic powder material for permanent magnets.

As described above, the magnetic powder of this example is a hexagonal ferrite particle in which a portion of iron is substituted with lithium, and has a coercive force of 443 to 787 kA/m when measured in an applied magnetic field of 1350 kA/m (17000 Oe). 58 Am ² /kg as saturation magnetization, generally plate-shaped magnetic powder with particle size in the range of 100 to 120 nm, high coercive force and moderate saturation magnetization, magnetic field and mechanical orientation. It is the most suitable magnetic powder for permanent magnets, and its practical value is extremely high.

Claims (8)

When A is any element of Ba, Sr, and Pb, and x is 0.12 or more and 1.8 or less, a part of the iron generally represented by the chemical formula AFe _12-x Li _x O ₁₉ is lithium. A magnetic powder material comprising substituted hexagonal ferrite particles. 2. The magnetic powder material according to claim 1, having a coercive force of 443 to 787 kA/m when measured with an applied magnetic field of 1350 kA/m. 3. The magnetic powder material according to claim 1, wherein the particles are plate-shaped. 4. The magnetic powder material according to any one of claims 1 to 3, which is a hexagonal ferrite having a magnetoplum-type or ferrox-planar-type crystal structure. 5. The magnetic powder material according to any one of claims 1 to 4, wherein the magnetic powder material is magnetically oriented. A permanent magnet using the magnetic powder material according to any one of claims 1 to 5. When A is any element of Ba, Sr, and Pb, an alkaline solution is mixed with an aqueous solution in which ions of A and iron ions in proportions constituting hexagonal ferrite and lithium ions are dissolved, creating a coprecipitate;
adding a flux while the coprecipitate is in suspension;
a heat treatment step of heating the coprecipitate to which the flux has been added to grow crystals;
a step of removing the flux from the heat-treated material to obtain a magnetic powder material consisting of hexagonal ferrite particles in which a portion of the iron is replaced with lithium;
A method for producing a magnetic powder material, characterized by performing 8. The method for producing a magnetic powder material according to claim 7, wherein the heat treatment step is performed at a temperature higher than the melting point by 0° C. to 200° C.

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