CN114956801B - High-squareness permanent magnet strontium ferrite magnetic material and preparation method thereof - Google Patents
High-squareness permanent magnet strontium ferrite magnetic material and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of magnetic materials, and discloses a high-squareness permanent magnetic strontium ferrite magnetic material and a preparation method thereof. The invention has the chemical formula of SrFe according to the formula 11.8 O 19 Weighing SrCO 3 、Fe 2 O 3 Performing primary ball milling and presintering on raw materials; secondly, adding CaCO with a certain mass fraction in a secondary ball milling stage 3 、La(OH) 3 、Co 3 O 4 Raw materials and additives are added; and finally, performing wet magnetic field orientation molding, setting the heating rate by adopting echelon temperature, and sintering to obtain the magnetic field. The permanent magnetic strontium ferrite obtained by the invention is especially widely applied to various controllers, electrical instruments, automobiles, motors and the like, and is suitable for large-scale popularization and application.
Description
Technical Field
The invention relates to the technical field of magnetic materials, in particular to a high-squareness permanent magnetic strontium ferrite magnetic material and a preparation method thereof.
Background
In recent years, with the continuous improvement of economic level and the rapid development of electronic information technology industry, permanent magnetic ferrites cannot be separated from the magnetic materials in the fields of generators, motors and nuclear magnetic resonance of medical industry, electrical instruments, industrial equipment and the like in the field of electric machines.
In large-scale industrial production, the requirements of J-H demagnetization curve squareness of a magnet in practical application need to be considered besides high magnetic energy product, high coercive force and low temperature coefficient, and H is commonly used k /H cj In this way, the squareness of the demagnetization curve is one of the important indexes of the permanent magnet material. Maximum magnetic energy product (BH) of squareness degree permanent magnet material max Having a positive correlation, i.e. at the same B r Under the condition, the larger the squareness is, the maximum magnetic energy product (BH) max The larger the square, the material resists the influence factors of external magnetic field, environmental temperature and the likeThe stronger the interference capability, the better its stability. At present, in the research aspect of magnetic properties, on one hand, the research on the improvement of coercive force, residual magnetism and magnetic energy product is focused, for example, CN113248246A is researched through additive components and proportion, and the prepared strontium ferrite has higher residual magnetism B r Magnetic coercive force H cb Intrinsic coercive force H cj And maximum magnetic energy product (BH) max Thereby improving the magnetic performance of the strontium ferrite; CN104591744A improves magnetic performance by exploring dispersant such as boric acid and calcium gluconate. On the other hand, the method aims at optimizing the process and reducing the cost. For example, CN101870579A utilizes a microwave sintering process, so that the sintering time is shortened, and the production efficiency is improved; CN104211388A is used for preparing low-temperature sintered ferrite by a sol-gel method, so that green emission reduction, energy conservation and environmental protection are realized. However, the squareness of the J-H demagnetization curve of the magnet has been rarely studied. Therefore, development of a magnetic material which can improve the squareness of the J-H demagnetization curve of the magnet, is simple in preparation process and low in cost becomes urgent in the field.
Disclosure of Invention
In view of this, the invention provides a high-squareness permanent magnetic strontium ferrite magnetic material and a preparation method thereof, and solves the problem that the prior art is blank in the research on the squareness of a J-H demagnetization curve of a magnet.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a preparation method of a high-squareness permanent magnetic strontium ferrite magnetic material, which comprises the following steps:
(1) Primary ball milling: mixing iron oxide red, strontium carbonate and water, and then sequentially carrying out ball milling, drying, presintering, crushing and sieving to obtain presintering material particles;
(2) Secondary ball milling: mixing the pre-sintered material particles, calcium carbonate, lanthanum hydroxide, cobaltosic oxide and an additive, and then carrying out secondary ball milling to obtain slurry after secondary ball milling;
(3) Shaping: carrying out magnetic field orientation molding on the slurry subjected to secondary ball milling to obtain a green body;
(4) And (3) sintering: and sintering the green body at a gradient temperature to obtain the high-squareness permanent magnetic strontium ferrite magnetic material.
Preferably, in the step (1) and the step (2), the iron red, the strontium carbonate, the calcium carbonate, the lanthanum hydroxide and the cobaltosic oxide are independently dried at 70-90 ℃ for 3-5 hours and then mixed.
Preferably, in the step (1), the molar ratio of the iron oxide red to the strontium carbonate is 5.5 to 6:1; the mass ratio of the mixture of water, iron oxide red and strontium carbonate to the ball milling medium is 1: 8 to 12, and the diameter of the ball milling medium is 5.5 to 6.5mm.
Preferably, in the step (1), the drying temperature is 110-130 ℃, and the drying time is 1-3 h.
Preferably, in the step (1), the pre-sintering temperature is 1200-1300 ℃, and the pre-sintering time is 1.5-3 h; the mesh number of the screen used for crushing and sieving is 100-140 meshes.
Preferably, in the step (2), the molar ratio of calcium carbonate, lanthanum hydroxide and cobaltosic oxide is 0.2-0.35: 0.2 to 0.35:0.24 to 0.36; the additive is SiO 2 And sorbitol, siO 2 The addition amount of the sorbitol is 0.5 to 1 weight percent of the total mass of the iron red, the strontium carbonate, the calcium carbonate, the lanthanum hydroxide and the cobaltosic oxide, and the addition amount of the sorbitol is 0.1 to 0.5 weight percent of the total mass of the iron red, the strontium carbonate, the calcium carbonate, the lanthanum hydroxide and the cobaltosic oxide.
Preferably, in the step (2), the secondary ball milling is performed in a rolling ball mill, the time of the secondary ball milling is 15 to 18 hours, and the size of crystal grains in the slurry after the secondary ball milling is 0.6 to 0.7 μm.
Preferably, in the step (3), the slurry after the secondary ball milling is dehydrated before the magnetic field orientation molding, and the water content of the dehydrated slurry is 30-40%; the pressure of magnetic field orientation molding is 14-14.5 MPa; the diameter of the green body is 28-32 mm.
Preferably, in the step (4), the step-by-step sintering is to perform sintering for 40-80 min by raising the temperature from room temperature to 280-320 ℃ to obtain a first sintered product; sintering the first sintering product at 580-600 ℃ for 40-80 min to obtain a second sintering product; sintering the second sintered product at 900-920 ℃ for 40-80 min to obtain a third sintered product; sintering the third sintered product at 1150-1200 ℃ for 80-100 min to obtain the high squareness permanent magnetic strontium ferrite magnetic material;
the time for heating from room temperature to 280-320 ℃ is 140-160 min, the time for heating the first sintering product from 280-320 ℃ to 580-600 ℃ is 110-130 min, the time for heating the second sintering product from 580-600 ℃ to 900-920 ℃ is 90-110 min, and the time for heating the third sintering product from 900-920 ℃ to 1150-1200 ℃ is 80-100 min.
The invention also provides a high-squareness permanent magnetic strontium ferrite magnetic material prepared by the preparation method of the high-squareness permanent magnetic strontium ferrite magnetic material.
According to the technical scheme, compared with the prior art, the invention has the following beneficial effects:
the invention adds corresponding raw material CaCO according to the formula during secondary ball milling 3 、La(OH) 3 、Co 3 O 4 Obtaining the sintered permanent magnetic ferrite with high squareness;
the invention adopts the step-by-step temperature setting sintering during the sintering, adopts different heating rates in the initial sintering stage, the intermediate sintering stage and the high-temperature sintering stage, controls the appearance and the diameter/thickness ratio of crystal grains, and simultaneously ensures that a sample has higher density so as to ensure that the sample has good comprehensive performance.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the prior art descriptions will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is an SEM image of a high squareness permanent magnetic strontium ferrite magnetic material obtained in example 1 of the present invention;
fig. 2 is an SEM image of the high squareness permanent magnetic strontium ferrite magnetic material obtained in embodiment 2 of the present invention;
fig. 3 is a demagnetization curve of the high squareness permanent magnetic strontium ferrite magnetic material obtained in embodiment 1 of the present invention;
fig. 4 is a demagnetization curve of the high squareness permanent magnetic strontium ferrite magnetic material obtained in embodiment 2 of the present invention;
fig. 5 is an SEM image of the permanent magnetic strontium ferrite magnetic material obtained in comparative example 1 of the present invention;
fig. 6 is a demagnetization curve of the permanent magnetic strontium ferrite magnetic material obtained in comparative example 1 of the present invention.
Detailed Description
The invention provides a preparation method of a high-squareness permanent magnetic strontium ferrite magnetic material, which comprises the following steps of:
(1) Primary ball milling: mixing iron oxide red, strontium carbonate and water, and then sequentially carrying out ball milling, drying, presintering, crushing and sieving to obtain presintering material particles;
(2) Secondary ball milling: mixing the pre-sintered material particles, calcium carbonate, lanthanum hydroxide, cobaltosic oxide and an additive, and then carrying out secondary ball milling to obtain slurry after secondary ball milling;
(3) Shaping: carrying out magnetic field orientation molding on the slurry subjected to secondary ball milling to obtain a green body;
(4) And (3) sintering: and sintering the green body at a gradient temperature to obtain the high-squareness permanent magnetic strontium ferrite magnetic material.
In the invention, in the step (1) and the step (2), the iron oxide red, the strontium carbonate, the calcium carbonate, the lanthanum hydroxide and the cobaltosic oxide are independently dried at 70-90 ℃ for 3-5 h and then mixed.
In the invention, the drying temperature of the iron oxide red, the strontium carbonate, the calcium carbonate, the lanthanum hydroxide and the cobaltosic oxide is preferably 75-85 ℃, and more preferably 78-82 ℃; the drying time is preferably 3.5 to 4.5 hours, and more preferably 4 hours.
In the present invention, in the step (1), the molar ratio of the iron red to the strontium carbonate is preferably 5.5 to 6:1, more preferably 5.7 to 5.8:1; the mass ratio of the mixture of water, iron oxide red and strontium carbonate to the ball milling medium is preferably 1: 8 to 12, more preferably 1.5:9 to 11; the diameter of the ball-milling medium is preferably 5.5 to 6.5mm, more preferably 5.8 to 6.2mm.
In the present invention, in the step (1), the drying temperature is preferably 110 to 130 ℃, and more preferably 115 to 120 ℃; the drying time is preferably 1 to 3 hours, more preferably 1.5 to 2.5 hours.
In the present invention, in the step (1), the temperature of the pre-firing is preferably 1200 to 1300 ℃, and more preferably 1250 to 1280 ℃; the pre-sintering time is preferably 1.5 to 3 hours, and more preferably 2 to 2.5 hours; the mesh number of the screen used for crushing and sieving is preferably 100 to 140 meshes, and more preferably 120 meshes.
In the present invention, in the step (2), the molar ratio of calcium carbonate, lanthanum hydroxide and cobaltosic oxide is preferably 0.2 to 0.35:0.2 to 0.35:0.24 to 0.36, more preferably 0.22 to 0.28:0.25 to 0.3:0.28 to 0.32; the additive is SiO 2 And sorbitol; siO 2 2 The addition amount of (b) is preferably 0.5-1% of the total mass of iron red, strontium carbonate, calcium carbonate, lanthanum hydroxide and cobaltosic oxide, and more preferably 0.6-0.8% of the total mass of iron red, strontium carbonate, calcium carbonate, lanthanum hydroxide and cobaltosic oxide; sorbitol and SiO 2 The mass ratio of (b) is preferably 0.1 to 0.5:0.5 to 1, more preferably 0.2 to 0.4:0.8 to 0.9.
In the present invention, in the step (2), the secondary ball milling is performed in a rolling ball mill, and the time of the secondary ball milling is preferably 15 to 18 hours, and more preferably 16 to 17 hours; the crystal grain size in the slurry after the secondary ball milling is preferably 0.6 to 0.7 μm, and more preferably 0.65 μm.
In the present invention, in the step (3), the slurry after the secondary ball milling is dehydrated before the magnetic field orientation molding, and the water content of the dehydrated slurry is preferably 30 to 40%, and more preferably 32 to 38%; the pressure for magnetic field orientation molding is preferably 14 to 14.5MPa, and more preferably 14.2 to 14.4MPa; the diameter of the green compact is preferably 28 to 32mm, more preferably 29 to 31mm.
In the invention, in the step (4), the echelon sintering is carried out by heating from room temperature to 280-320 ℃ for 40-80 min to obtain a first sintered product; sintering the first sintering product at 580-600 ℃ for 40-80 min to obtain a second sintering product; sintering the second sintered product at 900-920 ℃ for 40-80 min to obtain a third sintered product; and sintering the third sintering product at 1150-1200 ℃ for 80-100 min to obtain the high squareness permanent magnetic strontium ferrite magnetic material.
In the invention, the sintering temperature required for obtaining the first sintering product is preferably 290-310 ℃, and more preferably 300-305 ℃; the sintering temperature required by the second sintered product is preferably 585-595 ℃, and is further preferably 590 ℃; the sintering temperature required for obtaining the third sintering product is preferably 905-915 ℃, and is further preferably 910 ℃; the sintering temperature required by the obtained high squareness permanent magnet strontium ferrite magnetic material is preferably 1152-1190 ℃, and more preferably 1155-1158 ℃.
In the invention, the time for raising the temperature from room temperature to 280-320 ℃ is preferably 140-160 min, and more preferably 145-155 min; the time for heating the first sintering product from 280-320 ℃ to 580-600 ℃ is preferably 110-130 min, and more preferably 115-125 min; the time for heating the second sintering product from 580-600 ℃ to 900-920 ℃ is preferably 90-110 min, and more preferably 95-105 min; the time for heating the third sintered product from 900-920 ℃ to 1150-1200 ℃ is preferably 80-100 min, and more preferably 85-95 min.
In the initial stage of sintering, the temperature is raised at a low rate, and a wet-process molding sample can be directly placed into a sintering furnace, so that not only is the effective evaporation of water ensured and the sample is prevented from cracking, but also the production time can be greatly shortened compared with the traditional mode of standing, drying and sintering the sample; in the intermediate stage of sintering, solid-phase reaction is promoted to be carried out; and in the high-temperature sintering stage, the sample is ensured to have higher density.
The invention also provides a high-squareness permanent magnetic strontium ferrite magnetic material prepared by the preparation method of the high-squareness permanent magnetic strontium ferrite magnetic material.
The technical solutions provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.
Example 1
(1) Drying materials: iron oxide red (Fe) serving as a required raw material 2 O 3 ) Strontium carbonate (SrCO) 3 ) Calcium carbonate (CaCO) 3 ) Lanthanum hydroxide (La (OH) 3 ) Cobaltosic oxide (Co) 3 O 4 ) Placing the sample in a drying oven to dry for 4 hours at 80 ℃ to fully evaporate water and ensure the accuracy of the weighed mass of the sample;
(2) Primary ball milling: according to the formula SrFe 11.8 O 19 Weighing Fe 2 O 3 And SrCO 3 According to the water: raw materials: ball =1.5, ball milling is carried out at a weight ratio of 1;
(3) Drying the slurry: placing the slurry after ball milling and mixing in an experimental disc, standing, filtering, and placing in a drying oven, and drying at the temperature of 120 ℃;
(4) Pre-burning: the dried slurry is formed into blocks, the block samples are directly put into a box type furnace for presintering, the temperature is kept at 1250 ℃ for 2h, then the block samples are naturally cooled to room temperature along with the box type furnace, the presintering materials are taken out, and XRD and VSM tests are carried out after grinding;
(5) Crushing: pre-burning the sample block, crushing for 5min by using a sealed assay sample preparation crusher, and passing through a 120-mesh screen;
(6) Secondary ball milling: putting the powder passing through the screen into a ball milling tank, and adding Sr according to the chemical formula of the formula 1-x- y Ca y La x Co z Fe 2n-z O 19 (x =0.22, y =0.25, z =0.3, n = 5.55) CaCO was added 3 、La(OH) 3 、Co 3 O 4 And SiO with the total mass of 0.8wt percent of iron red, strontium carbonate, calcium carbonate, lanthanum hydroxide and cobaltosic oxide is added 2 Sorbitol accounting for 0.3wt% of the total mass of the iron red, the strontium carbonate, the calcium carbonate, the lanthanum hydroxide and the cobaltosic oxide is subjected to ball milling for 16 hours by using a rolling ball mill; measuring the granularity by a laser granularity analyzer, wherein the grain size is required to be less than the critical grain size of a single domain and reaches 0.6 mu m;
(7) And (3) dehydrating: taking out the secondary ball-milling slurry, placing the secondary ball-milling slurry on filter cloth, standing for 8 hours, and controlling the water content to be 30%;
(8) Shaping: adopting magnetic field orientation molding, wherein the pressure is 14.1MPa, and pressing into a round cake green body with the diameter of 30 mm;
(9) And (3) sintering: sintering the green body in a high-temperature sintering furnace at 1200 ℃, adopting gradient temperature sintering, heating to 300 ℃ for 150min at room temperature, preserving heat for 60min, heating to 600 ℃ for 120min, preserving heat for 60min, heating to 900 ℃ for 100min, preserving heat for 60min, heating to 1200 ℃ for 90min, preserving heat for 90min, and finally naturally cooling to obtain the high-squareness permanent magnet strontium ferrite magnetic material;
(10) Grinding a sample: and (4) polishing the surface of the high-squareness permanent magnetic strontium ferrite magnetic material until the surface is smooth and the upper surface and the lower surface are parallel.
Example 2
The difference from example 1 is that: performing secondary ball milling in the step (6): putting the powder passing through the screen mesh into a ball milling tank, and adding Sr according to a formula 1-x-y Ca y La x Co z Fe 2n-z O 19 (x =0.34, y =0.25, z =0.3, n = 5.55) CaCO was added 3 、La(OH) 3 、Co 3 O 4 And SiO with the total mass of 0.8wt percent of iron red, strontium carbonate, calcium carbonate, lanthanum hydroxide and cobaltosic oxide is added 2 Sorbitol accounting for 0.3wt% of the total mass of the iron red, the strontium carbonate, the calcium carbonate, the lanthanum hydroxide and the cobaltosic oxide is subjected to ball milling for 16 hours by using a rolling ball mill; measuring the granularity by a laser granularity analyzer, wherein the grain size is required to be smaller than the critical grain size of a single domain and reaches 0.6 mu m; otherwise, the same procedure as in example 1 was repeated.
Comparative example 1
The differences from example 1 are: performing primary ball milling in the step (2): according to the formula Sr 0.41 Ca 0.25 La 0.34 Co 0.3 Fe 10.8 O 19 Weighing Fe 2 O 3 、SrCO 3 、CaCO 3 、La(OH) 3 、Co 3 O 4 According to the water: raw materials: ball =1.5, ball milling is carried out according to the weight ratio of (1); and (5) secondary ball milling in the step (6): putting the powder passing through the screen into a ball milling tank, and directly adding iron red, strontium carbonate, calcium carbonate, lanthanum hydroxide and cobaltosic oxideSiO in an amount of 0.3wt% based on the total mass 2 CaCO with the total mass of iron oxide red, strontium carbonate, calcium carbonate, lanthanum hydroxide and cobaltosic oxide accounting for 0.5wt percent 3 Sorbitol accounting for 0.3wt% of the total mass of the iron red, the strontium carbonate, the calcium carbonate, the lanthanum hydroxide and the cobaltosic oxide is subjected to ball milling for 16 hours by using a rolling ball mill; the grain size is measured by a laser grain size analyzer, and the grain size is required to be smaller than the critical grain size of a single domain and reaches 0.6 mu m. Otherwise, the same procedure as in example 1 was repeated.
Samples were cut using a small-sized cutter to meet the sample test requirements, and the properties of the materials obtained in examples 1 to 2 and comparative example 1 were measured and analyzed by XRD, an automatic permanent magnet property measuring instrument, versalab and the like.
From the above test results, it can be seen that, according to the formulation, caCO was added as a raw material during the secondary ball milling according to the present invention 3 、La(OH) 3 、Co 3 O 4 According to the SEM results, the average grain diameter/thickness ratios of the sintered magnets were 1.5 and 2.3, respectively, the crystal grains were uniform in size, free from sharp corners, and flaky, and the H content of the obtained material was found to be small k /H cj Not less than 90 percent. While comparative example 1 gave a grain average diameter/thickness ratio of 1.3,H k /H cj It is only 76%.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (7)
1. A preparation method of a high-squareness permanent magnetic strontium ferrite magnetic material is characterized by comprising the following steps:
(1) Primary ball milling: mixing iron oxide red, strontium carbonate and water, and then sequentially performing ball milling, drying, presintering, crushing and sieving to obtain presintering material particles;
(2) Secondary ball milling: mixing the pre-sintered material particles, calcium carbonate, lanthanum hydroxide, cobaltosic oxide and an additive, and then carrying out secondary ball milling to obtain slurry after secondary ball milling;
(3) Shaping: carrying out magnetic field orientation molding on the slurry subjected to secondary ball milling to obtain a green body;
(4) And (3) sintering: sintering the green body at a gradient temperature to obtain a high squareness permanent magnetic strontium ferrite magnetic material;
in the step (4), the echelon temperature sintering is carried out for 40 to 80min by heating the room temperature to 280 to 320 ℃ to obtain a first sintering product; sintering the first sintering product at 580-600 ℃ for 40-80min to obtain a second sintering product; sintering the second sintering product at 900-920 ℃ for 40-80min to obtain a third sintering product; sintering the third sintering product at 1150-1200 ℃ for 80-100min to obtain a high squareness permanent magnetic strontium ferrite magnetic material;
the temperature of the first sintered product is raised from the room temperature to 280 to 320 ℃ for 140 to 160min, the temperature of the first sintered product is raised from 280 to 320 ℃ to 580 to 600 ℃ for 110 to 130min, the temperature of the second sintered product is raised from 580 to 600 ℃ to 900 to 920 ℃ for 90 to 110min, and the temperature of the third sintered product is raised from 900 to 920 ℃ to 1150 to 1200 ℃ for 80 to 100min;
in the step (1), the molar ratio of the iron red to the strontium carbonate is 5.5 to 6:1; the mass ratio of the mixture of water, iron oxide red and strontium carbonate to the ball milling medium is 1 to 2:8 to 12, and the diameter of the ball milling medium is 5.5 to 6.5mm;
in the step (2), the molar ratio of calcium carbonate, lanthanum hydroxide and cobaltosic oxide is 0.2-0.35: 0.2 to 0.35:0.24 to 0.36; the additive is SiO 2 And sorbitol, siO 2 The addition amount of the sorbitol is 0.5 to 1wt% of the total mass of the iron red, the strontium carbonate, the calcium carbonate, the lanthanum hydroxide and the cobaltosic oxide, and the addition amount of the sorbitol is 0.1 to 0.5wt% of the total mass of the iron red, the strontium carbonate, the calcium carbonate, the lanthanum hydroxide and the cobaltosic oxide.
2. The method for preparing the high squareness permanent magnetic strontium ferrite magnetic material according to claim 1, wherein in the steps (1) and (2), iron oxide red, strontium carbonate, calcium carbonate, lanthanum hydroxide and cobaltosic oxide are independently dried at 70 to 90 ℃ for 3 to 5 hours and then mixed.
3. The method for preparing the high squareness permanent magnetic strontium ferrite magnetic material according to claim 1, wherein in the step (1), the drying temperature is 110 to 130 ℃ and the drying time is 1 to 3 hours.
4. The method for preparing the high squareness permanent magnetic strontium ferrite magnetic material according to claim 2, wherein in the step (1), the pre-sintering temperature is 1200-1300 ℃, and the pre-sintering time is 1.5-3h; the mesh number of the screen used for crushing and sieving is 100 to 140 meshes.
5. The method for preparing a highly squareness permanent magnetic strontium ferrite magnetic material according to claim 1, wherein in the step (2), the secondary ball milling is performed in a rolling ball mill for 15 to 18h, and the grain size in the slurry after the secondary ball milling is 0.6 to 0.7 μm.
6. The method for preparing the high squareness permanent magnetic strontium ferrite magnetic material according to any one of claims 1 to 4, wherein in the step (3), the slurry after the secondary ball milling is dehydrated before the magnetic field orientation molding, and the water content of the dehydrated slurry is 30 to 40%; the pressure for magnetic field orientation molding is 14 to 14.5MPa; the diameter of the green body is 28 to 32mm.
7. The high-squareness permanent magnetic strontium ferrite magnetic material prepared by the preparation method of the high-squareness permanent magnetic strontium ferrite magnetic material according to any one of claims 1 to 6.
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