JPH04362020A - Ferritic magnetic powder and its production - Google Patents

Abstract

PURPOSE:To offer ferritic magnetic powder remarkably improved in saturation magnetization compared to that of the conventional one, furthermore small in the temp. change of coercive force, excellent in dispersibility and usable as the magnetic recording material for high density recording. CONSTITUTION:This is ferritic magnetic powder having features of being expressed by a general formula AO.n(Fe12-XMx(O18-z) (where A denotes one or more kinds of elements selected from Ba, Sr, Ca and Pb and M denotes one or more kinds of elements selected from Co, Ni, Zn, Cu, Mg, Mn, Fe(II), Bi, Si, Ti, Zr, Sn, Ta, Nb, Mo, V and W as well as the numerical value of n=1.2 to 3.0, x=0>l to 4.0 and 0<z<2 is satisfied) and constituted of hexagonal system ferritic grains showing a hexagonal sheet shape.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel ferrite magnetic powder and a method for producing the same. More specifically, the present invention has a coercive force of 200 to 2000 Oe, which is suitable for use in magnetic recording media for high-density recording, and has improved saturation magnetization compared to conventional ones. The present invention relates to a ferrite magnetic powder that exhibits small temperature changes and a method for producing the same. In recent years, with the demand for higher density magnetic recording, the development of a perpendicular magnetic recording method using magnetoplumbite-type ferrite magnetic powder as a magnetic recording medium has been progressing, and it has been used for applications such as DAT tape, 8 mm tape, and high-definition tape. It is considered. The magnetoplumbite type ferrite magnetic powder used in the perpendicular magnetic recording system has a coercive force of an appropriate value (200 to 2000 Oe).
Therefore, it is desired that the saturation magnetization is as high as possible, the coercive force changes little with temperature, and the orientation is good.

0002

[Prior art and its problems] Conventionally, various methods have been known for producing magnetoplumbite type ferrite magnetic powder, such as coprecipitation, glass crystallization, and hydrothermal synthesis. Regarding the conversion law, the special public interest law of 1983
Regarding the hydrothermal synthesis method, see Japanese Patent Application Laid-open No. 59-175707 and Japanese Patent Publication No. 60-1297.
Publication No. 3, Japanese Patent Publication No. 15576/1983, Japanese Patent Application Publication No. 1983
This is proposed in Publication No.-137002, etc. However, the magnetoplumbite type ferrite magnetic powder obtained by any of the above methods has a saturation magnetization of 60 em.
There were disadvantages in that the coercive force was low at less than u/g and the coercive force varied greatly with temperature.

0003

[Object of the invention] The object of the present invention is to solve the above problems,
The object of the present invention is to provide a ferrite magnetic powder that is fine particles, has a coercive force of 200 to 2000 Oe, has a high saturation magnetization, has a small change in coercive force with temperature, and has excellent orientation, and a method for producing the same.

0004

[Means for solving the problems] The present invention provides the general formula
AO・n(Fe12-xMx O18-z) (However,
A represents one or more elements selected from Ba, Sr, Ca and Pb, and M represents Co, Ni, Zn, Cu, Mg,
Mn, Fe(II), Bi, Si, Ti, Zr, Sn,
Indicates one or more elements selected from Ta, Nb, Mo, V and W, n = 1.2 ~ 3.0, x = 0.1 ~
4.0, a numerical value of 0<z<2. ) and is characterized by being hexagonal ferrite particles having a hexagonal plate shape. The ferrite magnetic powder of the present invention has the general formula AO・n(Fe12-xMx
O18-z) A in the general formula represents one or more elements selected from Ba, Sr, Ca and Pb, and M represents Co, Ni, Zn, Cu, Mg, Mn.
, Fe(II), Bi, Si, Ti, Zr, Sn, Ta
, Nb, Mo, V and W, and n = 1.2 to 3.0, preferably 1.4.
~2.5, and x=0.1~4.0. In addition, when z is the average valence of M, z=(
3-m) A numerical value expressed as x/2, where 0<z<2,
Preferably 0.2<z<1.5. In the present invention, as shown in the above general formula, by replacing a part of Fe with M and setting n in the range of 1.2 to 3.0, compared to the conventional magnetoplumbite type ferrite, Ferrite magnetic powder with improved saturation magnetization and small temperature change in coercive force can be obtained. Further, in order to increase the density of magnetic recording, it is preferable that the particle diameter is 50 nm or less.

The ferrite magnetic powder of the present invention is produced by the following method. A and F that constitute ferrite magnetic powder
A solution containing e and M and alkali hydroxide are mixed to form a precipitate such that the alkali hydroxide concentration in the mixed solution is 3M or more, and the slurry containing the precipitate is heated to 120%
After hydrothermal treatment at ~300°C, the slurry containing the precipitate is washed, and then Co, Ni, Zn, Mg, M
One or more metal ions selected from n and Cu and Fe
2+-containing aqueous solution and alkaline aqueous solution are added, the resulting mixed suspension is heat-treated at 50 to 200°C, and the resulting precipitate is fired at 700 to 950°C to form the ferrite magnetic powder. can get. As the compound A, nitrates, chlorides, hydroxides, etc. are used. In order to obtain particles with good crystallinity, it is desirable to use the amount of A such that the concentration of A is in the range of 0.03 to 0.50M. As the Fe compound, nitrates, chlorides, etc. are used. The amount of Fe used is 8 to 12 A per 1 gram atom.
Gram atoms are preferred. If the amount of Fe is too small, the amount of ferrite magnetic powder produced will be small and the crystallinity will be poor. Furthermore, if the amount of Fe is too large, hematite will be produced as a by-product, and the particles of ferrite magnetic powder will become large, resulting in poor magnetic properties. As the compound M, chloride, nitrate, ammonium salt, etc. are used. As the alkali hydroxide, sodium hydroxide, potassium hydroxide, etc. are used. The amount of alkali hydroxide used must be such that the alkali hydroxide concentration in the solution after mixing the alkali hydroxide is 3M or more, and is preferably in the range of 4 to 8M. If the amount of alkali hydroxide is too small, the particles become large, the particle size distribution becomes wide, and hematite is generated. Further, it is not economical to increase the amount of alkali hydroxide excessively. There are no particular restrictions on the method of mixing the solution containing A, Fe, and M with the alkali hydroxide, but for example, A,
There is a method of adding an aqueous alkali hydroxide solution to a solution containing Fe and M.

[0006] Next, the slurry containing the obtained precipitate is hydrothermally treated to generate and precipitate fine crystals. The temperature of the hydrothermal treatment is 120 to 300°C. If the temperature is too low, crystal formation will not be sufficient, and if the temperature is too high, the particle size of the ferrite powder ultimately obtained will become large, which is not preferable. Hydrothermal treatment time is usually 0.5 to 20
The hydrothermal treatment typically takes an autoclave. In the present invention, before the hydrothermal treatment,
The slurry containing the precipitate is heated to 0.5 to 4 at a temperature below 50°C.
After aging for 8 hours, a solution containing Bi may be added. The amount of Bi added is 1 to 5 with respect to the total amount of Fe and M.
mol %, preferably 2 to 4 mol %. By adding Bi, the particle size of the ferrite magnetic powder can be made 50 nm or less, and the plate ratio can be made 5 or less.

Next, after washing the fine crystal precipitate produced by the hydrothermal treatment with water to remove free alkali,
An aqueous solution and an alkaline aqueous solution containing one or more metal ions selected from Co, Ni, Zn, Mg, Mn, and Cu and Fe2+ are added to the slurry, and the resulting mixed suspension is heat-treated at 50 to 200 °C. . Co, Ni, Zn,
As compounds of Mg, Mn and Cu, those soluble in water such as their nitrates, chlorides, and sulfates are used, and Fe
As the compound, ferrous sulfate and ferrous chloride are generally used. Next, the obtained precipitate is washed with water and then fired to obtain ferrite magnetic powder. In the calcination, it is preferable to mix a flux into the precipitate obtained in advance. As the flux, at least one of sodium chloride, barium chloride, potassium chloride, strontium chloride, and sodium fluoride is used. The amount of flux used is 10 to 1
80% by weight, especially 30-120% by weight is preferred. If the amount of flux is too small, sintering of the particles will occur, and if it is too large, there will be no benefit from increasing the amount and it is not economical. There are no particular restrictions on the method of mixing the precipitate and flux; for example, a flux may be added to a slurry of the precipitate, wet-mixed, and then the slurry may be dried, or a flux may be added after drying the precipitate. It may be dry mixed. The firing temperature is 700-950°C, preferably 800-930°C. If the temperature is too low, crystallization will not proceed and the saturation magnetization will become low. Furthermore, if the temperature is too high, the particles become large and sintering occurs, which is not preferable. Appropriate firing time is about 10 minutes to 30 hours.

[0008]

[Examples] The present invention will be explained in more detail by showing Examples and Comparative Examples below. Example 1 Ferric nitrate 2.580 mol, cobalt nitrate 0.061
0.061 mol of nickel nitrate, 0.123 mol of titanium tetrachloride and 0.123 mol of zinc nitrate were dissolved in 1800 ml of deionized water, and separately, 0.368 mol of barium hydroxide and 36 mol of caustic soda were dissolved in 2000 ml of deionized water. Both solutions were mixed to form a precipitate. Next, the slurry containing the generated precipitate was
After aging at 0°C for 6 hours, 0.092 mo of bismuth nitrate
1 in 50 ml of deionized water was added. The resulting slurry containing the precipitate was placed in an autoclave;
Hydrothermal treatment was performed at 140°C for 6 hours. Next, after thoroughly washing the obtained precipitate with water, 200 ml of water was added to the slurry.
0.061 mol of cobalt chloride, 0.122 mol of zinc chloride
After adding a solution containing 0.549 mol of ferrous chloride and 0.549 mol of ferrous chloride and mixing thoroughly, add 1.7 mol of caustic soda.
A solution of 300 ml of water was added, and the mixture was aged at 80°C. After thoroughly washing the obtained precipitate with water, it was filtered and dried, and NaCl and BaCl2 .2H2 were added as fluxing agents to the precipitate.
Add a mixture of O to precipitate in a weight ratio of 1:1 to 100
% by weight and mixed. This mixture was heated under nitrogen atmosphere.
It was baked at 860°C for 2 hours. The obtained fired product was thoroughly washed with water, filtered and dried to obtain ferrite magnetic powder. As a result of compositional analysis, the obtained ferrite magnetic powder was found to contain BaO
・1.6 (Fe10.2Co0.4Ni0.2Zn0.
8Ti0.4O17.5). Further, the characteristics of this ferrite magnetic powder were as follows: Particle diameter: 0.043 μm Plate ratio: 3.8 Coercive force: 560 Oe Saturation magnetization: 64.5 emu/g Temperature change in coercive force: 0.2 Oe/°C.

Example 2 Ferric nitrate 2.700 mol, cobalt nitrate 0.061
0.061 mol of nickel nitrate, 0.061 mol of titanium tetrachloride, and 0.061 mol of zinc nitrate were dissolved in 1800 ml of deionized water, and separately, 0.368 mol of barium hydroxide and 36 mol of caustic soda were dissolved in 2000 ml of deionized water. , both solutions were mixed to form a precipitate. Next, the slurry containing the generated precipitate was aged at 20° C. for 6 hours, and then a solution of 0.092 mol of bismuth nitrate dissolved in 50 ml of deionized water was added. The slurry containing the obtained precipitate was placed in an autoclave and subjected to hydrothermal treatment at 140°C for 6 hours. Next, the obtained precipitate was thoroughly washed with water, and a solution of 0.061 mol of cobalt chloride, 0.123 mol of zinc chloride, and 0.552 mol of ferrous chloride dissolved in 200 ml of water was added to the slurry and thoroughly mixed. After that, add 1.7 mol of caustic soda to 300 ml of water.
A solution dissolved in was added, and the mixture was aged at 80°C. The obtained precipitate was thoroughly washed with water, filtered and dried, and a flux of NaCl and BaCl2.2H2O was added at a weight ratio of 1.
:1 was added in an amount of 100% by weight based on the precipitate and mixed. This mixture was calcined at 870° C. for 2 hours under a nitrogen atmosphere. The obtained fired product was thoroughly washed with water, filtered and dried to obtain ferrite magnetic powder. As a result of compositional analysis, the obtained ferrite magnetic powder was found to contain BaO 2.0 (Fe
10.6Co0.4Ni0.2Zn0.6Ti0.2O
17.5). Further, the characteristics of this ferrite magnetic powder were as follows: Particle size: 0.045 μm Plate ratio: 3.9 Coercive force: 560 Oe Saturation magnetization: 63.4 emu/g Temperature change in coercive force: 0.3 Oe/°C.

Example 3 Ferrite magnetic powder was obtained in the same manner as in Example 1 except that bismuth nitrate was not added. As a result of compositional analysis, the obtained ferrite magnetic powder was found to contain BaO.
1.6 (Fe10.2Co0.4Ni0.2Zn0.8
Ti0.4O17.5). Further, the characteristics of this ferrite magnetic powder were as follows: Particle size: 0.063 μm Plate ratio: 7.8 Coercive force: 550 Oe Saturation magnetization: 64.3 emu/g Temperature change in coercive force: 0.2 Oe/°C.

Example 4 Ferrite magnetic powder was obtained in the same manner as in Example 2 except that bismuth nitrate was not added. As a result of compositional analysis, the obtained ferrite magnetic powder was found to contain BaO.
2.0 (Fe10.6Co0.4Ni0.2Zn0.6
Ti0.2O17.5). Further, the characteristics of this ferrite magnetic powder were as follows: Particle size: 0.065 μm Plate ratio: 7.9 Coercive force: 550 Oe Saturation magnetization: 63.1 emu/g Temperature change in coercive force: 0.3 Oe/°C.

Comparative Example 1 Ferric nitrate 3.129 mol, cobalt nitrate 0.123
0.061 mol of nickel nitrate, 0.123 mol of titanium tetrachloride and 0.245 mol of zinc nitrate were dissolved in 1800 ml of deionized water, and separately, 0.460 mol of barium hydroxide and 37 mol of caustic soda were dissolved in 2000 ml of deionized water. Both solutions were mixed to form a precipitate. The slurry containing the obtained precipitate was placed in an autoclave and subjected to hydrothermal treatment at 140°C for 6 hours. Next, the obtained precipitate was thoroughly washed with water, filtered and dried, and NaCl and BaCl2 .2H2 were added as fluxing agents.
Add a mixture of O to precipitate in a weight ratio of 1:1 to 100
% by weight and mixed. This mixture was heated under nitrogen atmosphere.
It was baked at 860°C for 2 hours. The obtained fired product was thoroughly washed with water, filtered and dried to obtain ferrite magnetic powder. As a result of compositional analysis, the obtained ferrite magnetic powder was found to contain BaO
・0.99 (Fe10.2Co0.4Ni0.2Zn0
．． 8Ti0.4O17.5). In addition, the characteristics of this ferrite magnetic powder are that the particle size is 0.061
μm Plate ratio 7.7 Coercive force 560 Oe Saturation magnetization 60.2 emu/g Temperature change in coercive force 2.3 Oe/°C.

Comparative Example 2 Ferric nitrate 3.252 mol, cobalt nitrate 0.123
0.061 mol of nickel nitrate, 0.061 mol of titanium tetrachloride, and 0.184 mol of zinc nitrate were dissolved in 1800 ml of deionized water, and separately, 0.460 mol of barium hydroxide and 37 mol of caustic soda were dissolved in 2000 ml of deionized water. , both solutions were mixed to form a precipitate. The resulting slurry containing the precipitate was placed in an autoclave;
Hydrothermal treatment was performed at 140°C for 6 hours. Next, the obtained precipitate was thoroughly washed with water, filtered and dried, and a flux of NaCl and BaCl2.2H2O was added in a weight ratio of 1.
:1 was added in an amount of 100% by weight based on the precipitate and mixed. This mixture was calcined at 870° C. for 2 hours under a nitrogen atmosphere. The obtained fired product was thoroughly washed with water, filtered and dried to obtain ferrite magnetic powder. As a result of compositional analysis, the obtained ferrite magnetic powder was found to contain BaO 1.0 (Fe
10.6Co0.4Ni0.2Zn0.6Ti0.2O
17.5) The properties of the obtained ferrite magnetic powder are as follows: Particle size: 0.066 μm Plate ratio: 7.8 Coercive force: 540 Oe Saturation magnetization: 60.1 emu/g Temperature change in coercive force: 2.4 Oe/℃ there were.

[0014]

Effects of the Invention The ferrite magnetic powder obtained by the present invention has dramatically improved saturation magnetization compared to conventional ones, has small temperature change in coercive force, has excellent dispersibility, and is capable of high-density recording. It is suitably used as a magnetic recording material for.

Claims (4)

[Claims] [Claim 1] General formula AO・n(Fe12-xM
xO18-z) (However, A represents one or more elements selected from Ba, Sr, Ca, and Pb, and M represents Co.
, Ni, Zn, Cu, Mg, Mn, Fe(II), Bi
, Si, Ti, Zr, Sn, Ta, Nb, Mo, V and W, n = 1.2
~3.0, x=0.1~4.0, 0<z<2. ), and is characterized by being hexagonal ferrite particles having a hexagonal plate shape. [Claim 2] The particle size of the ferrite magnetic powder is 50 nm.
2. The ferrite magnetic powder according to claim 1, wherein the ferrite magnetic powder has a plate ratio of 5 or less. 3. A solution containing each element constituting the ferrite magnetic powder and an alkali hydroxide are mixed so that the alkali hydroxide concentration in the mixed solution is 3M or more to form a precipitate. The slurry containing the precipitate is heated to 120-300℃.
After hydrothermal treatment with
Add an aqueous solution containing one or more metal ions selected from Fe2+ and an alkaline aqueous solution, heat-treat the resulting mixed suspension at 50 to 200°C, and then sinter the resulting precipitate at 700 to 950°C. The method for producing ferrite magnetic powder according to claim 1, characterized in that: 4. A solution containing each element constituting the ferrite magnetic powder and an alkali hydroxide are mixed so that the alkali hydroxide concentration in the mixed solution is 3M or more to form a precipitate, and then aged. After that, a solution containing Bi is added, and the slurry containing the precipitate is hydrothermally treated at 120 to 300°C, the slurry containing the precipitate is washed, and then Co, Ni, Zn, Mg, An aqueous solution and an alkaline aqueous solution containing one or more metal ions selected from Mn and Cu and Fe2+ are added, and the resulting mixed suspension is
After heat treatment at 00°C, the resulting precipitate was heated to 700-9
3. The method for producing ferrite magnetic powder according to claim 2, wherein the ferrite magnetic powder is fired at 50°C.