JPH02120235A - Ferrite powder for high density recording - Google Patents

Abstract

PURPOSE:To improve saturation magnetization and remanent magnetization of a ferrite powder for high density recording by specifying the composition of the above-mentioned powder with the general formula containing Ba, V, Mn, O and Fe, etc. CONSTITUTION:The aimed ferrite powder for high density recording formed of a composition expressed by the general formula (M is a metal element selected from Ba, Sr, Pb and Ca; M' is a metal element selected from V, Sn, Ti, Zr, W and Nb; M'' is a metal element selected from Mn, Zn Cu, Co, Ni and Mg; n is 6.3-9; x is 0.01-0.3; y is 0-0.2; z is 0-0.2). The aimed ferrite powder is obtained by blending raw material substances so as to provide the composition expressed by the general formula. The above-mentioned powder has high saturation magnetization and remanent magnetization and is used for vertical magnetic recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferrite powder suitable for use in a high-density magnetic recording medium, particularly a perpendicular magnetic recording medium, and more particularly, a ferrite powder suitable for use in a coated perpendicular magnetic recording medium.

[Conventional technology]

Magnetic materials used in coated magnetic recording media include:
Conventionally, 'y-Fc203. Co-containing r-Fc203
Microparticles of powder and metal powder have been used. For recording media using these magnetic 4-O materials, a method is adopted in which the recording medium is magnetized in the in-plane longitudinal direction, but when this method is used, the demagnetizing field within the recording medium increases and the magnetization of the medium is Since it is subject to strong demagnetization, it is difficult to further increase the density. In contrast to such longitudinal recording methods, a perpendicular magnetic recording method, which is characterized by magnetization in a direction perpendicular to the surface of the recording medium layer, has been proposed as a high-density recording method, and is being put into practical use.

According to this perpendicular recording method, adjacent magnetizations within the medium are
Since the N and S different poles are arranged side by side, the demagnetizing field is reduced and a strong residual magnetization can be maintained. Therefore, as the recording wavelength becomes shorter, the demagnetizing field decreases and the difference between the magnetization of adjacent different poles decreases. Since an attractive force acts on them, their mutual magnetization becomes stronger.

In this way, the perpendicular magnetic recording method can be said to be essentially a method suitable for high-density recording. The recording medium used in this method can be manufactured by, for example, using a Co-Cr alloy sputtering method, a thin film forming method using a vacuum evaporation method, or a thin film using hexagonal ferrite powder having an easy magnetization axis in the C-axis direction. A method of coating on a support has been proposed. In particular, the coating method is said to be advantageous in terms of productivity and durability compared to the former method, and therefore, intensive development is underway with a view to putting it into practical use. Since the performance of recording media using this coating method strongly depends on the magnetic material forming the magnetic layer, there is a strong demand for improving the characteristics of the magnetic material. Since remarkable progress has been made in improving properties, there is a strong desire to develop a magnetic material that can withstand even higher density recording than conventional hexagonal ferrite powder.

[Problem to be solved by the invention]

In this way, compared to conventional coated perpendicular magnetic recording media using hexagonal ferrite powder, it is necessary to increase the saturation magnetization (σ ) and residual magnetization (σ ) to improve S
``It is necessary to do so.

Generally, the average particle size of hexagonal ferrite powder used in perpendicular magnetic recording media is 0.3 or less, and the BET value is 30 to 8.
(W/g. As the particle size progresses in this way, the σ of the magnetic powder decreases to about 54 etsu/g at most, and the squareness ratio (SQ-σ/σ) is less than 0.47. This results in a decrease in S σ .

As a method for improving the growth of such hexagonal ferrite fine particles, Japanese Patent Laid-Open No. 60-255629 discloses a method of modifying the surface of barium ferrite particles with a magnetite layer. However, in this case, although the saturation magnetization is improved, a decrease in squareness ratio (SQ) is unavoidable due to the soft magnetic layer formed on the grain surface layer, and as a result, no improvement in σ can be expected.

Furthermore, in JP-A-61-138923, Fe(Illr) contained in hexagonal ferrite powder is converted to Fe(II) by firing hexagonal ferrite powder in a reducing atmosphere.
) to improve σ is disclosed.

However, in this case, as the amount of Fe(II) substitution increases, Fe(In)-Fe(II)
The stoichiometric valence balance of the -0 series is impaired and becomes magnetically unstable, leading to deterioration of SQ.

As described above, with the methods of improving σ using conventional techniques, a decrease in SQ cannot be avoided, and as a result, no improvement in σ can be expected.

Therefore, the problem to be solved by the present invention is to develop a new ferrite powder with improved σ without a decrease in SQ.

[Means to solve the problem]

An object of the present invention is to provide a novel ferrite powder suitable for perpendicular magnetic recording media and having high saturation magnetization and residual magnetization.

The hexagonal ferrite conventionally used in perpendicular magnetic recording media has the general formula: MO-n (Fet-, M;)2 o3-
...■ [However, M is one or more of the metal elements consisting of Ba, Sr, Pb, and Ca. M' is a metal element for coercive force adjustment.

n-6], and the coercive force was adjusted by replacing Fe(m) of magnetoblanbite type ferrite with another metal element.

However, it has the above composition and an average particle size of 0.3
It is difficult to improve the σ of ferrite powder with a particle size of 50 to 54 e■u/g at most. On the other hand, as a method for further improving σ, the above-mentioned Japanese Patent Application Laid-Open No. Sho S Go-255629 and Japanese Patent Laid-Open No. 61-13692
In the method disclosed in 3, as already described, S
As Q decreases, no improvement in σ can be expected as a result.

The present inventors conducted research to solve these problems, prepared ferrite powder having a new composition specified by the following formula 0, and repeated tests.
The present invention was achieved by confirming that this is a new ferrite powder that exhibits high saturation magnetization and high residual magnetization without any decrease in magnetization.

Next, the novel ferrite powder of the present invention will be explained in more detail.

The method for producing the ferrite powder of the present invention may be any of the coprecipitation method, flux method, hydrothermal synthesis method, and glass crystallization method as long as the composition shown in formula (1) can be obtained. For example, a manufacturing method using a hydrothermal synthesis method is shown below.

First, the raw materials are prepared according to the general formula: % formula % One or more metal elements selected from Ca. M′ is Zr,
Ti, V, Sn, W, Nb One or more metal elements. M' is Co, Cu, and Zn.

One or more metal elements selected from Mn, Mg, and Ni. x, y, z are within the range specified below.
01<x≦0.03. Q<y≦0.2.0<z≦
A mixture in which metal components are uniformly mixed in a predetermined ratio based on the ferrite composition expressed as [0.2] is prepared in an N2 atmosphere.

In composition formula (■), 6.3≦n≦9 means that n is 6.3≦n≦9.
This is because if it is less than 3, it is not possible to achieve both the saturation magnetization and improvement of squareness ratio (SQ) of the magnetic powder, which are the objectives of the present invention.

In addition, when n>9, the particles become coarser and the particle size becomes 0.5
This is because the particle size exceeds m, making it unsuitable as a magnetic powder for high-density magnetic recording. Furthermore, 0.0 for Fe(n) content
The reason for setting 1<x≦0.3 is that if X is 0601 or less, no effect of improving saturation magnetization can be expected, and if X is larger than 0.3 and Fe(II) is excessive, soft magnetism This is because non-plate-like irregularly shaped particles are produced, and the saturation magnetization (although the saturation magnetization is improved considerably, the squareness ratio (SQ) is reduced).

Further, the metal elements added for the purpose of controlling the coercive force of the magnetic powder, ie, M', include Zr and TI.

One or more metal elements selected from V, Sn, W, and Nb, and M' is Co, Cu, Zn, and Mn.

Coercive force can be controlled by combining one or more metal elements selected from Mg and Ni.

Zr is selected as M′, and Co, Cu and Z are selected as M′.
It was confirmed that when a combination of one or more selected from n is used as an additive metal element for coercive force control, the effect is particularly good and stable.

The content of metal elements added for the purpose of coercive force control is O
The reason for limiting <y≦0.2.0<z≦0.2 is that without additives, the coercive force would be greater than 1500 (Oe) and the requirements of the present invention could not be satisfied. y,
This is because when 0.2<z, the coercive force becomes less than 40 (i (Oe)).

The raw materials providing these metal components may be halides, nitrates, other water-soluble metal salts, or hydroxides. At this time, when all the raw materials are water-soluble metal salts, the raw material mixture is an aqueous solution containing metal ions in a predetermined ratio, whereas when hydroxide is selected as the raw material, the raw material mixture is a slurry-like mixture. . Moreover, when a water-soluble metal salt and a hydroxide are allowed to coexist, a slurry containing metal ions and metal hydroxide is obtained. Note that iron oxyhydroxide can also be used as a raw material for providing the Fe(m) component.

Next, the raw material mixture adjusted to a predetermined ratio is brought into contact with an alkali (an alkaline solution containing an alkaline substance) in an N2 atmosphere. This typically results in the formation of a precipitate, resulting in an alkaline slurry-like material. The amount of alkali used is such that when acid radicals are present in the slurry, the alkali equivalent ratio to acid radicals exceeds 1.0. When no acid radical is present, the amount of alkali is such that the pH of the alkaline slurry material obtained by contacting the raw material mixture and the alkaline solution in an N2 atmosphere is 11.0 or more. In any case, the alkaline slurry-like substance is a slurry containing metal hydroxide and iron oxyhydroxide, or a slurry-like substance containing metal ions in these. The reason for specifying the amount of alkali within this range is that outside this range, the amount of ferrite phase produced will be significantly reduced.

The alkaline solutions used are NaOH and LiOH.

The solution is selected from a solution of NH4OH, a mixed solution thereof, or a solution containing another substance exhibiting strong alkalinity.

In addition, all of these operations are performed in an N2 atmosphere,
The reason for this is to prevent Fe(II) from being oxidized to Fe(III).

Next, the alkaline slurry material thus obtained is subjected to hydrothermal treatment. The method is performed as follows.

An alkaline slurry-like material containing a predetermined ratio of metal components represented by the above composition formula
In the medium and in the presence of two alkalis with an alkali equivalent ratio of more than 1.0 to acid radicals, or in the presence of an alkali that makes the pH of the reaction system 11 or more, and furthermore, N2 that does not contain 0.
Ferrite particles are generated by hydrothermal treatment in an atmosphere. Here, hydrothermal treatment means performing a ferrite synthesis reaction using water as a medium in an autoclave.

Regarding the reaction temperature of the ferritization reaction in the autoclave, the temperature is higher than 100°C, preferably 120°C to 4°C.
00°C is appropriate. The temperature inside the autoclave is 400℃.
If the temperature exceeds ℃, the pressure becomes extremely high, which is economically disadvantageous. If the temperature is lower than <120° C., the amount of ferrite produced is small and the object of the invention can no longer be achieved. It is sufficient to maintain this temperature and pressure for less than 10 hours, and in some cases even about 1 hour may be sufficient to achieve the purpose.

Furthermore, the reason why the hydrothermal synthesis reaction is performed in an N2 atmosphere is that Fe
This is to prevent oxidation of (II) to Fe(m).

According to the results of chemical analysis, the ferrite powder thus obtained satisfies the composition ratio of the metal elements shown in the above composition formula (2) and is plate-shaped particles with an average particle size of 0.01 to 0.04 m,
Further, from the results of V SM al determination, the saturation magnetization value of the ferrite powder is 55ca+u/g or more, and the squareness ratio is 0.
It was 47 or higher. It has thus been confirmed that it is possible to produce a ferrite powder with high residual magnetization that satisfies the target characteristic conditions of the present invention and has increased saturation magnetization without reducing the squareness ratio.

This will be explained below using examples.

[Example 1] F e C of 3.37111 oI/fl so that the composition formula % formula %
II a solution 259 ml, 347mofI/1) of F e CI 2 solution 37ml 1° 2.45IDoj7/
After thoroughly mixing 37 ml of B a CI 2 solution of D, an aqueous solution of 24.20 g of titanium tetrachloride, 8.0 Og of zinc chloride, and 8.87 g of anhydrous nickel chloride dissolved in 10,100 O of water in an N2 atmosphere, the mixture was prepared at room temperature. 18 in the mixed solution
．． 45a+oj! III NaOH aqueous solution 845ml
was added to obtain a brown precipitate.

This mixture was then reacted for 5 hours at 400° C. under N2 atmosphere in an autoclave. The reaction product thus obtained was thoroughly washed to remove impurities, and then dried and granulated to obtain magnetic powder. This powder had a plate-like shape and an average particle size of 0.124. Also, from VSM measurement with a maximum applied magnetic field of 10 kOe, its saturation magnetization is 57.5 emu/g1 residual magnetization is 27.2 emu.
u/g-, coercive force was fi80 (Oe).

[Example 2] In the compositional formula (■), the content of Fe(II), that is, x
The same operations and evaluation as in Example 1 were performed except that the composition of the raw materials was changed so that -0,1 became x-0,05. The composition conditions and properties of these are shown in Table 1.

[Example 3] The same operations and evaluation as in Example 1 were performed except that in the composition formula (2), the composition of the raw materials was changed so that n-7 became n-8. , their compositional conditions and properties are shown in Table 1.

[Example 4] Same as Example 1 except that in the composition formula (■), the composition of the raw materials was changed so that yo, t became y-0,12, and zmo, l became z=0.12. The same operations and evaluations were performed.

The composition conditions and properties of these are shown in Table 1.

[Example 5] In M-Ba, M'-Zr, M'-Zn
+Cu, n-7,x-0,1,7=(1,1,
F of 3.371+loΩ/Ω so that z-0,1
e CI) a solution 259 ml, 347 moff
/Ω FeCΩ2 solution 37ml1゜1.38IIloi
J/l of B a Cf) 2 solution 85 ml. water 101
After thoroughly mixing an aqueous solution in which 43.29 g of zirconium oxychloride, 8.60 g of zinc chloride, and 10.02 g of cupric chloride were dissolved in 00O in an N2 atmosphere, 18.45 mojl/D of the mixed solution was added at room temperature. 607 ml of NaOH aqueous solution was added to obtain a brown precipitate.

This mixture was then reacted for 5 hours at 400° C. under N2 atmosphere in an autoclave. The reaction product thus obtained was thoroughly washed to remove impurities, and then dried and granulated to obtain magnetic powder. This powder had a plate-like shape and an average particle diameter of 0.06 μs. Also, from the VSM11'Pl constant with the maximum applied magnetic field of 10 kOe, its saturation magnetization is 5B, and the residual magnetization of 8Bmu/g1 is 2.
The magnetic field was 8.1 Bmu/g, and the coercive force was 625 (Oe).

[Example 6] In the composition formula (■), the content of Fe (If), that is, x
The same operations and evaluation as in Example 5 were performed except that the composition of the raw materials was changed so that mO,l became x-0.05. The composition conditions and properties of these are shown in Table 1.

[Example 7] The same operations and evaluation as in Example 5 were performed except that in compositional formula (1), the composition of the raw materials was changed so that n=7 was nmg. The composition conditions and properties of these are shown in Table 1.

[Example 8] Same as Example 5 except that in the composition formula (■), the composition of the raw materials was changed so that Y-0,1 was changed to y-0,12 and ZaO,l was changed to z-0,12. The same operations and evaluations were performed.

The composition conditions and properties of these are shown in Table 1.

[Example 9] The same operation and evaluation as in Example 5 were performed except that in the composition formula (2), the composition of the raw materials was changed so that M'=Co+Cu. The composition conditions and properties of these are shown in Table 1.

[Comparative Example 1] B a Cj of composition formula % formula % mol/I! 2 solution 1181ml with N
After thoroughly mixing under 2 atmospheres, add LB, 45IIof)/II NaOH solution 520 to this mixture at room temperature.
ml was added to obtain a highly alkaline slurry containing a brown precipitate. This slurry material was then reacted in an autoclave at 400°C under N2 atmosphere for 5 hours.

The reaction product thus obtained was thoroughly washed to remove impurities, and then dried and granulated to obtain ferrite powder.

As a result of observation using a transmission electron microscope, the obtained ferrite powder was found to consist of plate-shaped particles with an average particle size of 0.45 mm.

Also, from VSM measurement with the maximum applied magnetic field of 10 kOc,
Its saturation magnetization is 34.2 ctsu/gs, residual magnetization is 13.7 cfllu/g1, and coercive force is 1730 (Oc
)Met.

[Comparative Example 2] Composition Formula % Formula % An aqueous solution in which 24.20 g of titanium chloride, 8.130 g of zinc chloride, and 10.62 g of cupric chloride were dissolved was thoroughly mixed in an N2 atmosphere, and then the mixture was heated at room temperature. 18.45 in solution
Add 850ml of NaOH aqueous solution,
A brown precipitate was obtained.

This mixture was then reacted for 5 hours at 400° C. under N2 atmosphere in an autoclave. The reaction product thus obtained was thoroughly washed to remove impurities, and then dried and granulated to obtain magnetic powder. This powder had a plate-like shape and an average particle size of 0612ρ. Also, from the VSMal11 constant due to the maximum applied magnetic field LOkOe,
Its saturation magnetization is 53.5 emu/g1 and its residual magnetization is 24.
2 emu/g, and its coercive force was 810 (Oe).

[Comparative Example 3] Fe of 3.37tnoll/fl was added so that the composition formula %formula%
Cj! a solution 259 ml, 3.37 mojJ /
(l of FeCΩ2 solution 37ml 1゜3J5mojJ /1
'B a CI) 2 solution 31 ml. Water 10100O
After thoroughly mixing an aqueous solution in which 24.20 g of titanium tetrachloride, 8.60 g of zinc chloride, and 8.87 g of anhydrous nickel chloride were dissolved in N2 atmosphere, 1% of this mixed solution was added at room temperature.
8.45+noff/fl NaOH aqueous solution 650ml
1 was added to obtain a brown precipitate.

This mixture was then reacted for 5 hours at 400° C. under N2 atmosphere in an autoclave. The reaction product thus obtained was thoroughly washed to remove impurities, and then dried and granulated to obtain magnetic powder. This powder has a plate-like shape, and its average particle size is 0.0! It was llum. Further, VSM measurement with a maximum applied magnetic field of 10 kOe revealed that the saturation magnetization was 55.8eIIlu/g1, the residual magnetization was 24.5etnu/gs, and the coercive force was 755 (Oe).

〔effect〕

The hexagonal ferrite having the general formula (2), which has been conventionally used in coated perpendicular magnetic recording media, has this composition and improves σ when manufactured as a ferrite powder with an average particle size of 0.3- or less. It is difficult to
Only ~54 emu/g was obtained. Various methods developed to increase σ through special treatments have resulted in a decrease in SQ, and as a result, no improvement in σ can be expected.On the other hand, the new method specified by the general formula The ferrite powder of the present invention, which is a ferrite powder with a composition such as The ferrite powder of the present invention can be easily produced by various known methods by blending raw materials so that the target composition becomes the composition represented by the general formula 100 in an autoclave under the same reaction conditions.
They may be conveniently prepared by hydrothermal synthesis carried out at temperatures above .degree.

Claims (2)

[Claims] 1. General formula: MO・n(Fe^(III)_1_-_x_-_y_-_
zFe^(II)_xM'_yM″_z)_2O_3...
・(1) [However, M in the formula is Ba, Sr, Pb and C
M′ represents one or more metal elements selected from the group consisting of a, M′ represents one or more metal elements selected from the group consisting of V, Sn, Ti, Zr, W and Nb, and M″ represents M
represents one or more metal elements selected from the group consisting of n, Zn, Cu, Co, Ni and Mg, where n is 6.3≦n
Represents a numerical value of ≦9, and x, y, and z are each expressed by the following formula:
0.01<x≦0.3, 0<y≦0.2, 0<z≦0.
Represents a numerical value that satisfies 2. ] A ferrite powder for high-density recording having a composition expressed by: 2. M′ in the general formula (1) is Zr, and M″
The ferrite powder according to claim 1, wherein is one or more metal elements selected from the group consisting of Co, Cu and Zn.