JPS6046932A - Production of hexagonal ferrite magnetic powder - Google Patents

Abstract

PURPOSE:To produce the titled magnetic powder having extremely fine particle size and sharp particle size distribution, by mixing the solutions of metallic ions and an alkali solution under specific condition at specific ratios to form a hexagonal ferrite, heating the mixture, and calcining the produced precipitate. CONSTITUTION:The objective hexagonal ferrite of formula I (A is Ba, Sr or Ca; M is Co, Ti, Ni, Mn, Cu, Zn, In, Ge, Nb and/or Zr; 0.08<=m<=0.1; 5<=n<=6) can be produced as follows. (A) A solution containing the ions of the above metals at the ratios to form the above ferrite is mixed with (B) an alkali solution. The mixture is heated, and the produced precipitate is washed with water, dried and baked to obtain the titled magnetic powder. The above process is carried out under a condition satisfying the formula 1<=x<=8, and the formula IIand formula III, or formula IV and formula V, or formula VI and formula VII, or formula VIII and formula IX, wherein x is the ratio of the alkali equivalent of the solution A to each of the metallic ion equivalent in the solution B, and y is heating temperature ( deg.C).

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for producing hexagonal ferrite magnetic powder that is effective for use in perpendicular magnetic recording media. The present invention relates to a method for producing hexagonal ferrite magnetic powder.

[Technical background of the invention and its problems]

Conventionally, 1-Fe20H1CrO2 was used for magnetic recording and reproduction.
A generally used method is to orient magnetic powder made of acicular crystals such as , CO-coated r-Fe2O, etc. in the in-plane longitudinal direction of the recording medium and utilize residual magnetization in the in-plane longitudinal direction.

However, this recording medium has the property that the demagnetizing field within the magnetic recording medium increases as the recording density increases, and there is a drawback that the recording and reproducing characteristics are particularly poor in the short wavelength region. In order to overcome this demagnetizing field and perform high-density recording,
While increasing the coercive force of the recording medium, it is necessary to make the magnetic recording layer thinner. However, at present, it is difficult to increase the coercive force of the magnetic recording layer, and making the magnetic recording layer thinner is not preferable because it causes problems such as deterioration of characteristics of reproduced signals.

For these reasons, it has been difficult to increase the density of magnetic recording using a method in which acicular magnetic powder is oriented in the in-plane longitudinal direction and residual magnetization in this direction is utilized.

In order to completely solve this problem, a method has been proposed that uses residual magnetization in the direction perpendicular to the surface of the magnetic recording medium. In this perpendicular magnetic recording method, as the recording density increases, the demagnetizing field in the recording medium decreases, so it can be said that it is essentially a recording method suitable for high-density recording. Here, the residual magnetization in the direction perpendicular to the surface of the recording medium may be achieved by oriented the magnetic powder entirely over the entire recording medium so that the residual magnetization is perpendicular, or by applying the magnetic powder without orientation. A portion of the residual magnetization may remain in the vertical direction.

As such a recording medium, for example, the recording layer is made of Co-
It has been proposed that a Cr alloy is formed into a film by the sintering method, or that it is a coated layer of magnetic powder that is flat in shape and has an axis of easy magnetization perpendicular to the plate surface.

In the latter case, the magnetic powder to be applied is, for example, BaFe
xz 019, monocrystalline ferrite is used. This is because hexagonal ferrite has a flat plate shape and an axis of easy magnetization in the direction perpendicular to the plate surface, so the plate surface can be easily aligned parallel to the tape surface after one cloth, and it can be easily aligned by magnetic field orientation treatment or mechanical orientation treatment. This is based on the reason that vertical alignment can be achieved.

When forming a coating layer using such hexagonal ferrite, the ferrite itself has a high coercive force He, which saturates the head during recording. It is necessary to reduce the magnetic force, and it is also necessary to select the crystal grain size in the range of 0.01 to 0.3 μm. Control of particle size is particularly important, because if the particle size is less than 0.101 μm, strong magnetism necessary for magnetic recording cannot be obtained, and if it exceeds 0.3 μm, it will be difficult to perform high-density recording advantageously. be.

For this reason, various hexagonal ferrite magnetic powders have been developed. Among them, the following formula 2AO・n(Fe
1-mMm)! 03. (In the formula, A is /? Liu A (Ba)
.

Full representation of at least one element selected from the group of strontium (Sr) and calcium (Ca); M is cobalt (Co), titanium (Tl), pnickel (Ni)
, mango y (Mn) + copper (Cu), zinc (Zn)
, indium (In).

Represents at least one element selected from the group of germanium (Ge), niobium (Nb), and zirconium (Zr); m and n are each 0.08≦m≦0.2
．． Substituted hexagonal ferrite fine powder represented by the number satisfying the relationship 5≦n≦6 is useful for the above-mentioned uses (see % Japanese Patent Publication No. 56-61101).

The hexagonal ferrite magnetic powder is generally manufactured as follows. That is, it is a method in which a solution of metal salts and an alkaline solution are mixed so that each metal has the above-mentioned composition, a hydrothermal synthesis reaction is performed to obtain an F coprecipitate, and this is calcined at a predetermined temperature. (Unexamined Japanese Patent Publication No. 56-16032
(see issue). It can also be produced by the glass crystallization method disclosed in JP-A No. 56-67904. The former method is particularly useful because it can produce hexagonal ferrite magnetic powder of the required particle size at a relatively high yield.

However, the magnetic powder produced by this coprecipitation-sintering method does not necessarily have a sharp particle size distribution, and it cannot fully satisfy the demands for higher densities in today's magnetic recording. Yes.

Therefore, it is desired to develop a method for stably mass-producing hexagonal ferrite magnetic powder having a particle size of 0.01 to 0.3 μm with a sharp particle size distribution at a low cost.

[Purpose of the invention]

An object of the present invention is to provide a method for stably producing magnetic powder with a sharp particle size distribution when producing hexagonal ferrite magnetic powder by a coprecipitation-sintering method.

[Summary of the invention]

In order to achieve the above object, the present inventors have made the above fc
A detailed study of the relationship between the ratio of the two types of reaction solutions and the hydrothermal synthesis temperature revealed that when the two satisfy a certain relationship, the magnetic powder of 0.01 to 0.3 μm is completely stable and sharp. The present invention has been completed based on the fact that it can be manufactured with a uniform particle size distribution.

That is, the method of the present invention has the following formula: AO-n(, Fe,
-mMm) 203 (wherein A is Ba, Sr, C
Represents at least one element selected from the group a:
MViCo, Ti, Ni, Mn.

Cu, Zn, In, Ge, Nb, Z
represents at least one element selected from the group r;
m and n are 0.08≦m≦0.2 and 5≦n, respectively
A solution (I) containing each of the above metal ions selected in a proportion constituting a hexagonal ferrite represented by a number satisfying the relationship of ≦6) and an alkaline solution (■) are mixed; Heating to form a precipitate; Next, the precipitate is completely washed with water, dried, and fired to produce a macrogonal ferrite magnetic powder. The ratio to the sum of ion equivalents is X,
When the heating temperature is taken as the y-plane, X is a number that satisfies 1≦X≦8, and 1≦x (when 1,9, 5x+30≦y≦180; 1
．． When 9≦x<2.2, 5x+30≦y≦=20
0x+560; 2.2≦x (when 4, 5x+30≦
y≦100x-100; when 4≦X≦8, 5x+30
It is characterized by satisfying the relationship ≦y≦300.

The hexagonal ferrite magnetic powder produced by the method of the present invention has the general formula: AO-n (Fel-mMm)203 (A
, , M.

n and m each have the same meaning as above).

This magnetic powder is made of a solution (I) containing ions of each metal constituting the ferrite in a predetermined ratio and an alkaline solution (If
) is the starting material. Here, the solution (2) may be anything as long as it is alkaline, such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate,
Examples include aqueous solutions of ammonium hydroxide and ammonium carbonate.

Hydroxylation is usually used due to its low price and easy availability)
An aqueous solution of IJum is used. In addition, the solution is prepared by dissolving a predetermined amount of a metal salt necessary to form a magnetic powder having a desired composition in water.

In the method of the present invention, first, solution (1) and solution (2) are mixed in the commercial ratio described below. Next, the mixed solution is heated at a temperature described later to cause coprecipitation of each metal ion. At this time,
When the applied temperature is 100° C. or higher, the entire reaction is carried out in a pressure-tight closed container such as an autoclave. Preferably, the reaction is carried out under stirring. Thereafter, the obtained precipitate is thoroughly washed with water to remove the alkali equivalent, and then dried and calcined. If water washing is insufficient and alkali remains, agglomerated particle agglomerates, which are thought to be caused by the alkali, are formed, and the particle size distribution of the magnetic powder obtained after firing becomes broad, making it impossible to achieve the entire purpose. Firing may be performed in air using a common heating furnace such as an electric furnace. The firing temperature is 700-950°C. Preferably 700-85
It is 0°C.

In the above steps, the greatest feature of the method of the present invention is that the ratio of the alkali equivalent of solution beating to the sum of the equivalents of each metal ion in solution (I) is set to X, and the temperature during the hydrothermal synthesis reaction of the mixed solution is set to y. (
6), the purpose is to manage x r Y as follows.

That is, first, X satisfies the relationship 1≦X≦8. Then, the relationship between X and y is 1≦x (when 1, 9, 5x+
30≦y≦180; When 1.9≦x<2.2, 5x+
30≦y≦-200x+560: 2.2≦x (when 4, 5x+30≦y≦100x-100; 4≦X≦
8, the relationship satisfies 5x+30≦y≦300.

This relationship with xy is shown in the figure. In the figure, x, y are the coordinates a
(1,,35), b(1,180), c(1,9,
180).

d(2,2,120), e(4,300), f(8,3
00) and g(8,70)ffi in this order straight i1M'
It is shown as a coordinate point within the range indicated by diagonal lines connected by e. Area outside this shape (not including the border)
Both are unsuitable areas for the method of the present invention.

In other words, the magnetic powder manufactured under the conditions of Territory has very low saturation magnetization and coercive force, and cannot be used as a magnetic powder for magnetic recording media. Under the conditions of region B, the obtained magnetic powder has a particle size larger than 0.3 μm, and the particle size distribution is uneven and broad. Since region C is a high temperature region and therefore a high pressure region, the equipment used becomes large and the manufacturing cost becomes high, and mass productivity is poor and it is not practical from an industrial perspective. Furthermore, since a large amount of alkali IJ' is used in region D, a large amount of water and a lot of time are required for washing the precipitate. Moreover, if the water washing is insufficient, there is a risk that the residual alkali during firing may have an adverse effect as described above. Finally, under the conditions of region E, the particle size of the obtained precipitate becomes ultrafine, about 100^ or less. Therefore, the sedimentation rate is extremely low, and washing the precipitate with water to remove alkali and other unnecessary components requires an extremely large amount of water and time, which is not preferable.

When X + Y is within the shaded range in the figure, the obtained magnetic powder has a saturation magnetization of 586 rnu/y or more and a coercive force of 7.
It has a large particle size distribution of 50 to 8100e, and above all, its particle size distribution is in the range of 0.01 to 0.3 μm, making it suitable as a magnetic powder for high-density recording.

[Embodiments of the invention]

2.0%/l/FeC6316I%O aqueous solution 1000
mg, 1.0%/l/206 m7 of Ba C10.2 H20 aqueous solution! , 1.0 mol Co C14., H
167 mg of 2O aqueous solution and 167 tn1.0 molar TiC4 aqueous solution. , the above four types of solutions are mixed and the solution and 1
1 1 11 2+2+4', that is, 1 m.

A sodium hydroxide aqueous solution was used as solution (2). For solution beating, weigh out an equivalent amount of sodium hydroxide so that the equivalent ratio with solution (1) is as shown in the table, and add it to 1,500 ml of pure water.
- It was prepared by dissolving it in -.

First, the solution (II) was cooled to about 20° C., and the solution (I) was added dropwise thereto and mixed with stirring. After stirring for 30 minutes, an aqueous solution containing a precipitate was obtained.

The whole was heat-treated for 1 hour at the temperature shown in the table to carry out a hydrothermal synthesis reaction. In the case of heat treatment at 100°C or higher, the precipitate obtained was heated for 3°C using an autoclave.
It was baked at 0°C for 3 hours.

The composition is BaOH5-67 (("eo, 5eo
COo, o71sTio, o7x5) 20g
-Ti-substituted Ba ferrite powder was obtained.

For each powder obtained, the saturation magnetization and coercive force were measured using a sample vibrating magnetometer with a maximum magnetic field strength of 10 KOe, and the particle size and its distribution were observed using a transmission electron microscope and a scanning electron microscope. /Hi. The above results are summarized in Table 1.

〔Effect of the invention〕

As is clear from the above explanation, according to the method of the present invention, the obtained hexagonal ferrite magnetic powder has ■ particle size distribution of 0.
．． It has a large saturation magnetization and a large coercive force within the range of 0.01 to 0.3 μm, making it extremely useful as a magnetic powder for high-density recording.

[Brief explanation of drawings]

The figure is a diagram showing the relationship between the sum of equivalents of alkaline earth metal ions applied in the method of the present invention and the hydrothermal synthesis temperature.

Claims (1)

[Claims] Primary formula: A O-n (Fe1-m Mm)20
3 (wherein A represents at least one element selected from the group of barium, strontium, and calcium; M
iCobalt, titanium, nickel, manganese. Represents at least one element selected from the group of copper, zinc, indium, germanium, niobium, and zirconium; m and n are 0.08≦m≦0.2, 5, respectively.
Mixing a solution (1) containing the above-mentioned metal ions selected in proportions constituting hexagonal ferrite i represented by a number that satisfies the relationship ≦n≦6, and an alkaline solution (■);
The mixed solution is completely heated to form a precipitate; the precipitate is then washed with water, dried, and fired to produce a hexagonal ferrite magnetic powder, in which the alkali equivalent of the solution (II) and the solution (I ) is the ratio k x + heating temperature to the sum of the equivalents of each metal ion eaten by y (
C), then X is a number that fully satisfies 1≦X≦8, and X and y are 1≦x (when 1, 9, 5x+30≦y≦180; 1.
9≦x (when 2,2, 5x+30≦y≦-200x
+560: 2.2≦x (when 4, 5x+30≦y
≦100x-100; When 4≦X≦8, 5x+30≦
A method for producing hexagonal ferrite magnetic powder, characterized in that the number satisfies the relationship y≦300. 2. The method for producing hexagonal 7-elite magnetic powder according to claim 1, wherein the firing temperature is 700 to 950°C. 3. The method for producing hexagonal thread ferrite magnetic powder according to claim 1 or 2, wherein the firing temperature is 700 to 850°C.