Magnetic powder material, permanent magnet, and method for manufacturing magnetic powder material

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

[Technical Field]

[0001] 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 manufacturing the magnetic powder material, and in particular to a magnetic powder material, a permanent magnet, and a method for manufacturing the magnetic powder material, which are made of hexagonal ferrite particles having a structure such as a magnetoplumb type or a ferroplanar type, and which have basic constituent elements such as barium (Ba), strontium (Sr), lead (Pb), etc. [Background technology]

[0002] It is well known that the current mainstream high-performance magnetic powder materials for permanent magnets are Nd-Fe-B and Sm-Co magnetic powders that use rare earth elements as their main constituent elements, and vigorous research is still ongoing to improve their magnetic properties. However, a major issue with these Nd-Fe-B and Sm-Co magnets is the use of large amounts of rare earth elements, which are scarce elements.

[0003] On the other hand, in addition to the above-mentioned Nd-Fe-B and Sm-Co magnetic powder materials, iron oxide magnetic powder materials are also widely used as magnetic powder materials for permanent magnets. These iron oxide magnetic powder materials have low manufacturing costs because the raw materials are inexpensive, and although their performance as permanent magnets is inferior to rare earth magnets, they are currently used in the largest quantities due to their low manufacturing costs. Among the iron oxide magnets using this iron oxide magnetic powder material, the magnetic powder material currently used most widely is hexagonal ferrite magnetic powder such as barium ferrite or strontium ferrite. This hexagonal ferrite magnetic powder has long been known as a permanent magnet material, and a huge number of patent applications and research papers have been published on it.

[0004] In addition, in order to further improve the properties of this hexagonal ferrite magnetic powder, substitution elements and compositions have been vigorously investigated. For example, it is known that magnetic properties can be improved by substituting barium, strontium, or even part of the iron with other elements (e.g., JP-A-10-149910, JP-A-2000-323317, JP-A-2001-052912). In particular, it is known that substituting part of the Ba and Sr with the rare earth element lanthanum (La) and further substituting part of the iron with the transition metal element cobalt significantly improves magnetic properties such as coercivity and saturation magnetization (e.g., JP-A-2000-331813, JP-A-2001-068319, JP-A-2005-259751, JP-A-2005-268784). In this way, substituting some of the main elements constituting the hexagonal ferrite magnetic powder, such as barium, strontium, and iron, with other elements is an extremely effective method for improving the magnetic properties of the magnetic powder.

[0005] Non-Patent Document 1 describes a technology in which, in an iron oxide magnetic powder having a spinel ferrite structure, which has a different crystal structure from hexagonal ferrite, part of the iron is replaced with elements such as cobalt, nickel, or lithium so that the charge balance between cations and anions in the magnetic powder deviates from the stoichiometric ratio. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-149910 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-323317 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-052912 [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-331813 [Patent Document 5] Japanese Patent Application Laid-Open No. 2001-068319 [Patent Document 6] Japanese Patent Application Laid-Open No. 2005-259751 [Patent Document 7] JP 2005-268784 A [Non-patent literature]

[0007] [Non-Patent Document 1] M. Kishimoto, and 2 others, "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. Summary of the Invention [Problem to be solved by the invention]

[0008] (Problems with the prior art) As described in Patent Documents 1 to 7, hexagonal ferrite magnetic powders, such as barium ferrite and strontium ferrite, are used in large quantities as cost-effective permanent magnet materials, and further improvements have been made. The main method of improvement is to replace a portion of the barium, strontium, or iron with other elements, such as cobalt or lanthanum. When element substitution is performed to improve magnetic properties, for example, in the above-mentioned method of substituting part of the barium, strontium, or iron with lanthanum or cobalt, it is necessary to accurately place the substituting element at a specific position in order to achieve the desired properties, and this control is difficult, which is an issue.

[0009] Non-Patent Document 1 describes a technique for increasing the coercive force by substituting part of the iron in an iron oxide magnetic powder of spinel ferrite, rather than hexagonal ferrite, with cobalt, nickel lithium, etc. However, the crystal structure of the spinel ferrite in Non-Patent Document 1 is relatively simple, and Li can be added by heat treatment at about 200°C, whereas hexagonal ferrite has a complex structure, and there is a problem that even if the manufacturing method for spinel ferrite is applied directly to hexagonal ferrite, it is not possible to obtain a magnetic powder substituted with cobalt, nickel lithium, etc.

[0010] The present invention has as its technical object to obtain a magnetic powder material with high coercivity from hexagonal ferrite by a simple method. [Means for solving the problem]

[0011] In order to solve the above technical problem, the magnetic powder material of the invention described in claim 1 is A Ba,Pb When x is 0.12 or more and 1.8 or less, the chemical formula is generally AFe 12-x Li x O 19 The hexagonal ferrite particles are characterized in that a part of the iron is substituted with lithium.

[0012] The invention described in claim 2 is the magnetic powder material described in claim 1, It is characterized by a coercive force of 443 to 787 kA / m when measured in an applied magnetic field of 1350 kA / m.

[0013] The invention described in claim 3 is the magnetic powder material described in claim 1 or 2, The particles are characterized by their plate-like shape.

[0014] In order to solve the above technical problem, the magnetic powder material of the invention described in claim 4 is When x is between 0.12 and 1.8, the general chemical formula is SrFe 12-x Li x O 19 The iron is partly substituted with lithium in the hexagonal ferrite particles, It is characterized by a coercive force of 443 to 787 kA / m when measured in an applied magnetic field of 1350 kA / m.

[0015] In order to solve the above technical problem, the magnetic powder material of the invention described in claim 5 is When x is between 0.12 and 1.8, the general chemical formula is SrFe 12-x Li x O 19 The iron is partly substituted with lithium in the hexagonal ferrite particles, The particles are characterized by their plate-like shape.

[0016] Claim 6 The invention described in claims 1 to 5 In the magnetic powder material according to any one of the preceding claims, The crystal structure is a hexagonal ferrite of the magnetoplum or ferroplanar type.

[0017] Claim 7 The invention described in claims 1 to 6 In the magnetic powder material according to any one of the preceding claims, It is characterized by having undergone magnetic field orientation treatment.

[0018] In order to solve the above technical problems, Claim 8 The permanent magnet of the invention described in Claims 1 to 7 The magnetic powder material according to any one of the preceding items is used.

[0019] In order to solve the above technical problems, Claim 9 The method for producing a magnetic powder material of the invention described in a step of mixing an alkaline solution with an aqueous solution in which ions of A, iron ions, and lithium ions are dissolved in a ratio that constitutes hexagonal ferrite, where A is any one of Ba, Sr, and Pb, to form a coprecipitate; adding a flux to the coprecipitate in suspension; a heat treatment step of heating the coprecipitate to which the flux has been added to grow crystals; 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 has been substituted with lithium; The present invention is characterized by carrying out the following.

[0020] Claim 10 The invention described in Claim 9 In the method for producing a magnetic powder material according to the present invention, The heat treatment step is carried out at a temperature 0°C to 200°C higher than the melting point. [Effects of the Invention]

[0021] Claim 1 ,4,5,8,9 According to the invention described in the above, it is possible to obtain hexagonal ferrite in which part of the iron is substituted with lithium, and to obtain a magnetic powder material with high coercivity by a simple method. Claim 2 ,4 According to the invention described in the above, it is possible to obtain a magnetic powder material having a coercive force of 443 to 787 kA / m. Claim 3 ,5 According to the invention described in the above, a plate-shaped magnetic powder material can be obtained, and by carrying out an orientation treatment to align the axis of easy magnetization in one direction, it becomes easier to obtain a magnet with high magnetic force. Claim 6 According to the invention described in the above, it is possible to obtain hexagonal ferrites such as magnetoplum type and ferroplanar type. Claim 7 According to the invention described in the above, a powder material with a high squareness ratio can be obtained. Claim 10 According to the invention described in the above, a magnetic powder material with a larger particle size can be obtained by heat treatment at a temperature 0°C to 200°C higher than the melting point. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a transmission electron microscope photograph of particles that will become precursors of lithium-substituted strontium ferrite particles before being subjected to heat treatment in a flux in Example 1. [Figure 2] 1 is a transmission electron microscope photograph of lithium-substituted strontium ferrite particles subjected to a heat treatment in a flux in Example 1. [Figure 3]1 is an X-ray diffraction diagram of lithium-substituted strontium ferrite particles subjected to a heat treatment in a flux in Example 1. [Figure 4] 1 shows the magnetization curve of the lithium-substituted strontium ferrite particles subjected to heat treatment in a flux in Example 1. [Figure 5] 1 is a transmission electron microscope photograph of lithium-substituted barium ferrite particles subjected to a heat treatment in a flux in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0023] Next, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiment. In the following description using the drawings, illustrations of components other than those necessary for the description are omitted as appropriate to facilitate understanding.

[0024] 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 has been replaced with lithium, and is a magnetic powder material that usually has a plate-like shape and has extremely large coercive force, making it an ideal magnetic powder material for permanent magnets.

[0025] The basic method for producing the magnetic powder material of the present invention involves preparing a coprecipitate containing the basic constituent elements of hexagonal ferrite—iron, barium, and strontium—as well as the substitution element lithium. This coprecipitate is dissolved in water by adding a flux such as potassium bromide (KBr). The water is then dried and removed, and the mixture of the coprecipitate and flux of elements such as iron, barium, strontium, and lithium is heated at a temperature above the melting point of the flux (KBr). When heated to the melting point of the flux (KBr), oxide particles are dispersed in the liquid KBr. This process (molten salt treatment, flux treatment) allows the coprecipitate of elements such as iron, barium, strontium, and lithium to crystallize into hexagonal ferrite particles in the liquid flux. When the temperature is then lowered to room temperature, the KBr changes from liquid to solid. However, because KBr is water-soluble, the flux can be removed by washing with water. By removing the flux in this manner, hexagonal ferrite particles in which some of the iron has been substituted with lithium can be obtained.

[0026] Many different crystal structures, such as magnetoplumb and ferroplanar types, are known for such hexagonal ferrite particles, but they are not particularly limited. Various crystal structures can be achieved by varying the composition ratio of each metal ion during coprecipitate preparation. The lithium substitution amount, expressed as Li / (Li+Fe), is preferably 1 to 15 mol %. If the lithium substitution amount is less than 1 mol %, it is difficult to achieve a sufficient improvement in coercivity. On the other hand, if the lithium substitution amount is more than 15 mol %, it becomes difficult to completely replace Fe with Li. As a result, the remaining Li remains as an oxide, which tends to reduce saturation magnetization. Therefore, the lithium substitution amount is preferably in the range of 1 to 15 mol %. The hexagonal ferrite particles in which A is one of the elements Ba, Sr, or Pb and part of the iron is replaced by lithium are represented by the chemical formula ABe 12-x Li x O 19 When expressed as above, a state in which 1 to 15 mol % of lithium is substituted corresponds to x being 0.12 to 1.8.

[0027] Lithium can also be substituted with alkaline earth metals such as barium and strontium, but substituting iron is the most effective way to obtain high coercivity. Furthermore, it is also possible to simultaneously substitute lithium with other elements such as cobalt and nickel. Even in such cases, it is preferable to substitute lithium within the above-mentioned range for the elements present in the sites originally occupied by iron.

[0028] (Detailed description of manufacturing method) To produce lithium-substituted hexagonal ferrite particles as the magnetic powder material of the embodiment of the present invention, basic constituent elements such as barium, strontium, and iron and hydroxides of lithium are used as starting materials. First, an alkaline solution with the number of moles required to convert these ions into hydroxides is added to an aqueous solution containing these element ions (Ba, Sr, Fe, and Li ions), and the hydroxides of these ions are coprecipitated. Note that the ion source is not particularly limited, and metal salts such as chlorides, nitrates, and sulfates of these metal elements (Ba, Sr, Fe, and Li) can be used.

[0029] The alkali concentration is preferably 1.5 to 5 times the molar equivalent of the number of moles required to produce the hydroxide of the metal ions, resulting in an excess of alkali. The alkali source is not particularly limited, and sodium hydroxide, potassium hydroxide, etc. are preferred. Furthermore, since iron ions become trivalent when forming hexagonal ferrite particles, it is preferable to use trivalent iron ions when preparing the coprecipitate. Furthermore, lithium ions are usually monovalent, which is an important finding that was first discovered by the present invention. In order to deviate the charge balance between cations and anions in the magnetic powder from the stoichiometric ratio, monovalent lithium with as small a valence as possible is the optimal substitution element.

[0030] The coprecipitate thus obtained is washed with water to remove the alkali components, and then dissolved in suspension by adding a flux. Using the precipitate in this suspension state is crucial, because once dried, the particles aggregate strongly and are extremely difficult to redisperse. As a result, the crystal growth process by heat treatment in the next step tends to result in particles with a wide particle size distribution. Suitable fluxes include KBr, FK, NaCl, and LiBr. However, because these fluxes are used to crystallize particles to a desired size, the flux is not limited to these types; various fluxes can be used depending on the desired particle size.

[0031] Next, the coprecipitate containing the dissolved flux is heated for crystal growth. The degree of crystal growth generally increases with increasing heat treatment temperature in the flux; therefore, various fluxes with different melting points can be selected depending on the desired particle size. The heat treatment temperature is set at or above the melting point of the flux, where the flux melts due to heat, causing particles to flow and coalesce within the flux, resulting in crystal growth. The heat treatment temperature is preferably set between 0°C and 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 particles. However, a temperature above 200°C above the melting point requires more energy for heating and may alter the flux itself. On the other hand, a heat treatment temperature close to the melting point (melting point + 0°C) may result in insufficient fluidity. Therefore, the heat treatment temperature is preferably between 0°C and 200°C above the melting point, with a temperature of approximately 100°C above the melting point being particularly preferable. Therefore, for example, when potassium bromide (KBr) is used as a flux, since its melting point is 734°C, it is preferable to use it in a temperature range of about 734 to 934°C.

[0032] Next, the particles obtained by crystal growth through heat treatment in a flux are washed with water to remove the flux. For example, if KBr is used as the flux, KBr is easily soluble in water, so the crucible is immersed in water to dissolve the KBr, and then the KBr can be easily removed by repeated decantation.

[0033] Next, the flux is removed by washing with water, and the remaining particles are filtered, dried, and extracted. This high-temperature flux heat treatment produces particles with a hexagonal crystal structure substituted with elements such as lithium, which grow to particle sizes of 100 to 500 nm depending on the heat treatment temperature. These particles crystallized in the flux typically have a hexagonal plate shape, reflecting their crystal structure. Obtaining particles with such a plate-like shape, along with the large coercive force, is an extremely important feature of the present invention and was first achieved by the manufacturing method of the present invention. Having such a plate-like shape is extremely useful, for example, when performing an orientation process to align the easy axis of magnetization in a single direction in a permanent magnet, because the plate-like shape not only provides the orientation of the easy axis of magnetization due to the magnetic field, but also provides mechanical orientation.

[0034] (Operation of the embodiment) The lithium-substituted hexagonal ferrite particles thus obtained have a coercive force of 443 to 787 kA / m and a magnetization of 58 Am when measured in an applied magnetic field of 1350 kA / m (17000 Oe). 2 At a concentration of about 1000 kA / kg, a magnetic powder having a normal plate-like shape with a particle size in the range of 100 to 500 nm is obtained, which simultaneously has high coercivity and moderate saturation magnetization, and furthermore, is an optimal magnetic powder material for permanent magnets having a shape and particle size optimal for magnetic field and mechanical orientation. 2 It is expected that magnetic powder with a squareness ratio of about 0.80 to 1.0 can be obtained.

[0035] While it is generally difficult to obtain a coercive force of 400 kA / m or more with magnetic materials produced by conventional manufacturing methods, the magnetic materials of the present invention can easily achieve a coercive force of 400 kA / m or more, making it possible to obtain magnetic materials with higher coercive forces than conventional materials. In particular, the present invention allows lithium substitution to be performed simply by adding a flux to the coprecipitate and then performing a heat treatment, eliminating the need for precise control of the placement of the substitution element at specific positions, as is the case with conventional methods of substitution with lanthanum or cobalt. Therefore, the present invention makes it easy to obtain magnetic materials with high coercive forces. In addition, in the embodiment, a flux treatment is performed to obtain hexagonal ferrite particles in which a portion of the iron is substituted with lithium. The spinel ferrite described in Non-Patent Document 1 has a simple structure, so it is possible to add Li by heat treatment at about 200°C using an autoclave. In contrast, the hexagonal ferrite of the embodiment has a complex structure, so high-temperature treatment at about 800°C is essential, 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 flux treatment, which is a treatment method discovered for the first time by the present application, it is possible to realize, for the first time, hexagonal ferrite particles in which a portion of the iron is substituted with lithium. [Example]

[0036] Next, a detailed manufacturing method (example) for the manufacturing method of the embodiment will be described. In the following examples, the coercive force and saturation magnetization of the magnetic powder are shown as values ​​measured using a sample vibrating magnetometer at room temperature with a maximum applied magnetic field of 1350 kA / m (17000 Oe). The present invention will be described in more detail below with reference to examples, but it goes without saying that the present invention is not limited to the examples described here. In particular, in this example, a lithium substitution method will be described using a composition for obtaining a magnetoplumb-type hexagonal ferrite as an example, but it goes without saying that the present invention is not limited to this structure. Furthermore, although an example has been shown in which strontium, barium, and iron, which are the basic elements constituting hexagonal ferrite, are used as constituent elements, it goes without saying that lithium substitution can also be performed on substitution elements such as lanthanum and cobalt in addition to these elements.

[0037] Example 1 <Preparation Example 1 of Lithium-Substituted Strontium Ferrite Particles> In a 1000 mL beaker, 0.05 mol of strontium chloride salt, 0.57 mol of ferric chloride salt, and 0.03 mol of lithium chloride salt were dissolved in 500 g of water. Next, in a 2500 mL beaker, 5.7 mol of sodium hydroxide was dissolved in 1000 g of water. This aqueous solution of strontium chloride, ferric chloride, and lithium chloride was added to the aqueous solution of sodium hydroxide and stirred for 10 minutes to form a coprecipitate of strontium, iron, and lithium. The coprecipitate was then washed with water by decantation until neutral, and then left to settle for about an hour. After removing the supernatant, 1.8 mol of potassium bromide was added to the suspension as a flux, and the potassium bromide was dissolved and mixed with stirring.

[0038] The mixture was then spread on a metal tray and placed in an oven, where it was dried at 90°C for about a day to remove moisture. After crushing the dried mixture, it was placed in a crucible and heated in a muffle furnace at 830°C for one hour. This heat treatment in the flux causes the coprecipitate particles to grow into lithium-substituted strontium ferrite particles with a hexagonal crystal structure. Finally, the heat-treated product together with the crucible was immersed in water, and the potassium bromide was dissolved and removed by washing with water. The lithium-substituted particles were taken out and dried in air to obtain lithium-substituted strontium ferrite particles. The particles thus obtained were examined for particle shape by a transmission electron microscope, structural analysis by X-ray diffraction, and magnetic properties by a sample vibrating magnetometer.

[0039] Figure 1 shows a transmission electron microscope photograph of a coprecipitate consisting of hydroxides of strontium, iron, and lithium. FIG. 2 shows a transmission electron microscope photograph of lithium-substituted strontium ferrite particles that were grown by subjecting this coprecipitate to heat treatment in a flux and then crystal growth. FIG. 3 shows the X-ray diffraction pattern of the lithium-substituted strontium ferrite particles. FIG. 4 shows the magnetization curve of the lithium-substituted strontium ferrite particles. Figure 1 shows that it is an aggregate of minute particles measuring a few nanometers in size. Furthermore, Figure 2 shows that the particles are composed of roughly hexagonal plate-like particles with a particle size of about 100 nanometers. The diffraction peaks in the X-ray diffraction pattern shown in FIG. 3 coincide with those of known magnetoplum-type hexagonal ferrite, and it is clear that the particles are magnetoplum-type hexagonal ferrite. From Figure 4, the coercive force measured at a maximum applied magnetic field of 1350 kA / m (17000 Oe) was 468 kA / m (5870 Oe), and the magnetization at 1350 kA / m was 59.5 Am 2 The squareness ratio (magnetization amount at zero applied magnetic field / magnetization amount at 1350 kA / m) in an applied magnetic field of 1350 kA / m was 0.550.

[0040] The reason why such a high coercive force is obtained is not clear, but as mentioned above, it is thought that by substituting a portion of the trivalent iron with monovalent lithium ions, the charge balance between the cations and anions in the particles deviates from the stoichiometric ratio, resulting in the formation of vacancies or lattice defects within the particles, which act to hinder magnetization reversal and increase the coercive force. In any case, this phenomenon of a significant increase in coercive force in a state of valence imbalance was discovered for the first time by the present invention.

[0041] Example 2 <Preparation Example 2 of Lithium-Substituted Strontium Ferrite Particles> In the preparation of lithium-substituted strontium ferrite particles in Example 1, a coprecipitate was prepared in the same manner as in Example 1, except that the ferric chloride salt was changed from 0.57 mol to 0.56 mol and the lithium chloride salt was changed from 0.03 mol to 0.04 mol. A flux was then added and heat treatment in the flux was carried out to prepare lithium-substituted strontium ferrite particles. X-ray diffraction confirmed that these particles were also approximately magnetoplume-type hexagonal ferrite. Transmission electron microscope photographs also revealed that the particles were approximately hexagonal plate-like particles with a particle size of approximately 100 nanometers. The magnetic properties were a coercive force of 485 kA / m (6080 Oe) and a magnetization at 1350 kA / m of 57.7 Am. 2 The squareness ratio (magnetization amount at zero applied magnetic field / magnetization amount at 1350 kA / m) in an applied magnetic field of 1350 kA / m was 0.556.

[0042] Example 3 <Preparation of lithium-substituted barium ferrite particles> A coprecipitate was prepared in the same manner as in Example 1, except that 0.05 moles of barium chloride salt was used instead of 0.05 moles of strontium chloride salt in the preparation of lithium-substituted strontium ferrite particles in Example 1. A flux was added, and the mixture was heat-treated in the flux to prepare lithium-substituted barium ferrite particles. X-ray diffraction confirmed that these particles were also approximately magnetoplume-type hexagonal ferrite. Figure 5 shows a transmission electron microscope photograph of these lithium-substituted barium ferrite particles. The photograph reveals that the particles are roughly hexagonal plate-like particles with a particle size of approximately 120 nanometers. The magnetic properties are a coercive force of 443kA / m (5550Oe) and a magnetization of 59.0A at 1350kA / m. 2 The squareness ratio (magnetization amount at zero applied magnetic field / magnetization amount at 1350 kA / m) in an applied magnetic field of 1350 kA / m was 0.545.

[0043] In these examples, we have shown examples in which lithium has been substituted for part of the iron in the basic composition of a hexagonal ferrite magnet consisting of an alkaline earth element such as divalent strontium or barium and trivalent iron. However, it goes without saying that it is also possible to make complex substitutions, such as substituting part of the alkaline earth element with lanthanum, part of the iron with cobalt, and then substituting part of the iron with lithium.

[0044] Example 4 <Magnetic field orientation treatment of lithium-substituted strontium ferrite particles> A magnetic field orientation treatment was performed on the lithium-substituted strontium ferrite particles obtained in Example 2. 1 g of these particles, 0.3 g of vinyl chloride resin (MR-104, manufactured by Kaneka) as a binder, and 380 g of toluene as a solvent were placed in a 100 cc zirconia pot, and 100 g of zirconia beads with a diameter of 0.1 mm were added as dispersing beads, and the mixture was dispersed for 5 hours using a planetary ball mill to produce a magnetic paint. The magnetic field orientation was performed as follows. The magnetic paint was coated onto a base film using a glass rod. The film was then inserted near the center of the pole piece of an electromagnet generating a magnetic field of 400 kA / m and left to dry naturally for approximately 10 minutes to produce a magnetic film. A 1 mm x 1 mm sample was cut from the center of the magnetic film for magnetic measurement. The squareness ratio of the magnetic film in the magnetic field orientation direction (magnetization amount at zero applied magnetic field / magnetization amount at 1350 kA / m) was 0.918, confirming extremely high orientation. The coercive force at this time was also 787 kA / m (9860 Oe). This high coercive force is thought to be due to the effect of the anisotropy being aligned and the reduction in the anisotropy-decreasing effect of the platelet-shaped particles due to the stacked orientation of the platelet-shaped particles.

[0045] As described above, the lithium-substituted hexagonal ferrite particles of the present invention not only exhibit a significant increase in coercive force due to the substitution of a portion of the iron with lithium, but also exhibit excellent magnetic field orientation due to the plate-like particle shape. This plate-like shape is due to the crystal growth of the particles in a flux, and is one of the major features of the present invention, along with the high coercive force due to the substitution with lithium. Such high coercive force and orientation are extremely useful as permanent magnets.

[0046] (Comparative Example 1) <Preparation of strontium ferrite particles without lithium substitution> In Comparative Example 1, strontium ferrite particles were produced under the same conditions as in Example 1, except that lithium was not added and the 0.57 mol of ferric chloride salt was changed from 0.57 mol to 0.60 mol in Example 1. In other words, strontium ferrite particles, which were hexagonal ferrite of the standard composition, were produced without substitution with lithium. The coercivity of this particle measured at a maximum applied magnetic field of 1350 kA / m (17,000 Oe) was 376 kA / m (4,710 Oe), and the magnetization at 1350 kA / m was 61.1 Am 2 / kg (61.1 emu / g). The squareness ratio (magnetization amount at zero applied magnetic field / magnetization amount at 1350 kA / m) in an applied magnetic field of 1350 kA / m was 0.541. It was found to be composed of plate-shaped particles with a particle size of approximately 120 nanometers.

[0047] (Comparative Example 2) <Preparation of barium ferrite particles without lithium substitution> 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 amount of ferric chloride was changed from 0.57 mol to 0.60 mol in Example 3. In other words, barium ferrite particles, which were hexagonal ferrite of the standard composition, were produced without substitution with lithium. The coercivity of this particle 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). The squareness ratio (magnetization amount at zero applied magnetic field / magnetization amount at 1350 kA / m) in an applied magnetic field of 1350 kA / m was 0.538. It was found to be composed of plate-shaped particles with a particle size of approximately 150 nanometers.

[0048] Next, the results of Examples and Comparative Examples will be explained. In Examples 1 and 2, lithium-substituted strontium ferrite particles with different substitution amounts were described. In both examples, it was confirmed that the coercive force increased significantly due to lithium substitution. In Example 2, which has a higher lithium substitution amount, the saturation magnetization was slightly reduced compared to Example 1, but the coercive force was greater.

[0049] Example 3 describes lithium-substituted barium ferrite particles, and although the coercive force and saturation magnetization are slightly lower than those of the lithium-substituted strontium ferrite particles of Examples 1 and 2, it was confirmed that the phenomenon of obtaining high coercive force by substituting part of the iron in hexagonal ferrite particles with lithium is the same for both strontium ferrite and barium ferrite. Although not described in the examples, this effect of increasing coercive force by lithium substitution can be applied not only to magnetoplume-type structures but also to hexagonal ferrite particles in general, such as ferroplanar-type structures. 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. This significant increase in coercive force due to the magnetic field orientation treatment is due to the effect of aligning the easy axis of magnetization of the magnetic powder in one direction and also due to the plate-like shape of the magnetic powder obtained in the present invention. In other words, it is believed that the stacking of the plate-like particles suppresses the decrease in anisotropy due to the demagnetizing field of the plate-like particles, resulting in a further increase in anisotropy and an increase in coercive force.

[0050] On the other hand, strontium ferrite particles and barium ferrite particles, which are standard hexagonal ferrites without lithium substitution, were described in Comparative Examples 1 and 2. Since these particles were not subjected to lithium substitution, their coercive force was clearly smaller than that of the particles of Examples 1 to 3, which were subjected to lithium substitution.

[0051] As described above, the magnetic powder obtained in this example was found to be magnetoplume-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. The particle size of this magnetic powder depends greatly on the heat treatment conditions in the flux; generally, the higher the heat treatment temperature, the larger the particle size, which can be controlled within the range of 100 to 500 nanometers. In terms of magnetic properties, the coercive force measured in an applied magnetic field of 1350 kA / m (17000 Oe) generally increases with an increase in the amount of lithium substitution, and powders with high coercive force in the range of 443 to 787 kA / m are obtained compared to comparative examples with coercive force of less than 400 kA / m. Also, the magnetization tends to decrease with an increase in the amount of lithium substitution, reaching 57.7 to 59.5 kA / m. 2 / kg, and the comparative example (59.3 to 61.1 Am 2 / kg), there is almost no effect. Furthermore, with the magnetic powder of this example, by performing the orientation treatment as in Example 4, powder with a high squareness ratio of 0.918 can be obtained, compared to the comparative example, which had a squareness ratio of approximately 0.538 to 0.541. As the squareness ratio increases, the easy axis of magnetization tends to align in one direction, so the squareness ratio is preferably 0.8 or more (0.8 to 1.0).

[0052] In any case, by using lithium as a basic substitution element, it is possible to obtain hexagonal ferrite particles with high coercivity. This phenomenon of a significant increase in coercivity by substituting part of the iron in magnetic powder having a hexagonal ferrite structure with lithium was discovered for the first time by the present inventors.

[0053] Therefore, the magnetic powder of this example is a lithium-substituted hexagonal ferrite particle, and when measured in an applied magnetic field of 1350 kA / m (17000 Oe), the coercive force is 443 to 787 kA / m and the magnetization is 58 Am 2 / kg, and has a particle size in the range of 100 to 120 nm, and is a magnetic powder with a normal plate shape. It has high coercivity and moderate saturation magnetization, and furthermore, has a shape and particle size that are optimal for magnetic fields and mechanical orientation, making it an ideal magnetic powder material for permanent magnets.

[0054] As described above, the magnetic powder of this example is a hexagonal ferrite particle in which part of the iron is replaced with lithium, and when measured in an applied magnetic field of 1350 kA / m (17000 Oe), the coercive force is 443 to 787 kA / m and the saturation magnetization is 58 Am 2 / kg, and has a particle size in the range of 100 to 120 nm, and is a magnetic powder with a normal plate shape. It has high coercivity and moderate saturation magnetization, and furthermore, it has a plate shape and particle size that are optimal for magnetic fields and mechanical orientation, making it an ideal magnetic powder for permanent magnets, and its practical value is extremely great.

Claims

1. When A is either Ba or Pb and x is 0.12 or more and 1.8 or less, the general chemical formula is AFe 12-x Li x O 19 A magnetic powder material characterized by comprising hexagonal ferrite particles represented by the formula (I) in which part of the iron is substituted with lithium.

2. 2. The magnetic powder material according to claim 1, wherein the coercive force is 443 to 787 kA / m when measured in an applied magnetic field of 1350 kA / m.

3. 3. The magnetic powder material according to claim 1, wherein the particles are plate-like.

4. When x is 0.12 or more and 1.8 or less, the chemical formula is generally SrFe 12-x Li x O 19 The iron is partly substituted with lithium in the hexagonal ferrite particles, A magnetic powder material characterized in that the coercive force when measured in an applied magnetic field of 1350 kA / m is 443 to 787 kA / m.

5. When x is 0.12 or more and 1.8 or less, the chemical formula is generally SrFe 12-x Li x O 19 The iron is partly substituted with lithium in the hexagonal ferrite particles, A magnetic powder material characterized in that the particles are plate-like in shape.

6. 6. A magnetic powder material according to claim 1, wherein the crystal structure is a magnetoplum or ferroplanar hexagonal ferrite.

7. 7. The magnetic powder material according to claim 1, which has been subjected to a magnetic field orientation treatment.

8. A permanent magnet, characterized in that the magnetic powder material according to any one of claims 1 to 7 is used.

9. a step of mixing an alkaline solution with an aqueous solution in which ions of A, iron ions, and lithium ions are dissolved in a ratio that constitutes hexagonal ferrite, where A is any one of Ba, Sr, and Pb, to form a coprecipitate; adding a flux to the coprecipitate in suspension; a heat treatment step of heating the coprecipitate to which the flux has been added to grow crystals; 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 has been substituted with lithium; A method for producing a magnetic powder material, comprising:

10. 10. The method for producing a magnetic powder material according to claim 9, wherein the heat treatment step is carried out at a temperature 0° C. to 200° C. higher than the melting point.

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