JPH0647469B2 - Ferrite powder for high density recording - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high density magnetic recording medium, particularly a perpendicular magnetic recording medium, and more particularly to a ferrite powder suitable for use in a coating type perpendicular magnetic recording medium.

[Conventional technology]

As the magnetic material used for the coating type magnetic recording medium,
Conventionally, γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , and fine particles of metal powder have been used. For a recording medium using these magnetic materials, a method of magnetizing in the in-plane longitudinal direction of the recording medium is adopted, but with this method, the demagnetizing field in the recording medium increases and the magnetization of the medium is strong. Since it is subject to demagnetization, it is difficult to achieve higher density. In contrast to such a longitudinal recording method, as a high-density recording method, a perpendicular magnetic recording method characterized by magnetizing in a direction perpendicular to the surface of a recording medium layer has been proposed and put into practical use.

According to this perpendicular recording method, in the adjacent magnetization in the medium,
Since the N and S different poles are arranged side by side, the demagnetizing field is reduced and strong remanent magnetization can be maintained. Therefore, the shorter the recording wavelength, the smaller the demagnetizing field and the magnetization between the adjacent different poles. At this point, the attractive force acts on each other, so that the magnetizations are mutually strengthened.

Thus, the perpendicular magnetic recording method is essentially a method suitable for high density recording. The recording medium used in this method is, for example, a Co-Cr alloy sputtering method, a vacuum vapor deposition method for forming a thin film, or a thin plate having a hexagonal ferrite powder having an easy axis of magnetization in the c-axis direction. The method of coating on the support has been proposed. In particular, the coating method is more advantageous than the former in terms of productivity and durability, and therefore, earnestly developed for practical use. In the recording medium by this coating method, since the performance strongly depends on the magnetic body forming the magnetic layer, it is strongly demanded to improve the characteristics of the magnetic body. Since there is a remarkable progress in improving the characteristics, it is strongly desired to develop a magnetic material that can withstand high density recording even more than conventional hexagonal ferrite powder.

[Problems to be Solved by the Invention]

As described above, the saturation magnetization (σ _s ) and the residual magnetization (σ) of the magnetic material are required to sufficiently withstand higher density recording as compared with the conventional coating type perpendicular magnetic recording medium using the hexagonal ferrite powder. It is necessary to improve _r ).

Generally, the average particle size of hexagonal ferrite powder used in perpendicular magnetic recording media is 0.3 μm or less, and the BET value is 30 to 80 m ²
/ G. As the particles become finer, the σ of the magnetic powder
_s is reduced to about 54 emu / g at most, and the squareness ratio (SQ = σ _r / σ _s ) is reduced to less than 0.47, resulting in a reduction in σ _r .

As a method for improving the σ _s of such hexagonal ferrite fine particles, JP-A-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, the soft magnetic layer formed on the grain surface layer inevitably lowers the squareness ratio (SQ), and as a result, an improvement in σ _r cannot be expected.

Further, in JP-A-61-136923, by burning hexagonal ferrite powder in a reducing atmosphere, Fe (III) contained in the ferrite is replaced with Fe (II) to obtain σ _s
Are disclosed.

However, in this case, since the substitution amount of Fe (II) increases, the stoichiometric valence balance of the Fe (III) -Fe (II) -O system is impaired and the Fe (III) -Fe system becomes magnetically unstable. Will be deteriorated.

As described above, in the methods of improving σ _s by the known techniques up to now, it is unavoidable that the SQ is lowered, and as a result, the improvement of σ _r cannot be expected.

Therefore, it is a problem to be solved by the invention to develop a novel ferrite powder having improved σ _s without lowering SQ.

[Means for Solving the Problems]

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

The hexagonal ferrite that has been conventionally used in the perpendicular magnetic recording medium has a general formula: MO.n (Fe _{1-x M'x} ) ₂ O ₃ ... [where M is a metal element composed of Ba, Sr, Pb, and Ca. One or more of them. M'is a metal element for adjusting coercive force. n =
6], and had a coercive force adjusted by substituting Fe (III) of the magnetoplumbite ferrite with another metal element.

However, it has the above composition and the average particle size is 0.3μ.
In ferrite powders of m or less, it is difficult to improve σ _s, and it is only about 50 to 54 emu / g at most. On the other hand, the method disclosed in the above-mentioned JP-A-60-255629 and JP-A-61-136923 as a method for further improving σ _s results in a decrease in SQ as described above. Therefore, improvement of σ _r cannot be expected. The present inventors have conducted research to solve these problems,
A ferrite powder having a novel composition specified by the following formula was prepared and the test was repeated, and it was confirmed that these were novel ferrite powders showing high saturation magnetization and high remanent magnetization without SQ reduction. Achieved the invention.

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

The method for producing the ferrite powder of the present invention may be any of the coprecipitation method, the flux method, the hydrothermal synthesis method and the glass crystallization method as long as the composition represented by the formula is obtained. For example, the manufacturing method by the hydrothermal synthesis method is shown below.

First, the raw materials are adjusted by the general formula: [However, 6.3 ≦ n ≦ 9, M is at least one metal element selected from Ba, Sr, Pb, and Ca. M'is Zr, Ti,
One or more metal elements selected from V, Sn, W and Nb.
M ″ is one or more metal elements selected from Co, Cu, Zn, Mn, Mg, and Ni. X, y, and z are ranges defined as follows: 0.01 <x ≦ 0.03, 0 <y ≦ 0.2, 0 <z ≤ 0.2
] A mixture in which metal components having a predetermined ratio are uniformly mixed is prepared in an N ₂ atmosphere based on the ferrite composition represented by

In the composition formula, 6.3 ≦ n ≦ 9 means that n is 6.3
If it is less than the above, it is impossible to achieve both the saturation magnetization of the magnetic powder and the improvement of the squareness ratio (SQ), which are the objects of the present invention.

When n> 9, the particles become coarser and the particle size becomes 0.5 μm.
This is because the above becomes unsuitable as magnetic powder for high density magnetic recording. Further, regarding the Fe (II) content, 0.01 <
x ≦ 0.3 means that when x is 0.01 or less, the effect of improving the saturation magnetization cannot be expected, and Fe becomes so large that x becomes larger than 0.3.
This is because when (II) is excessive, non-plate-like irregularly shaped particles that are considered to be soft magnetic are generated and the saturation magnetization is improved, but the squareness ratio (SQ) is decreased.

Further, as a metal element added for the purpose of controlling the coercive force of the magnetic powder, that is, M ', Zr, Ti, V, Sn,
One or more metal elements selected from W and Nb, and M ″ is selected from Co, Cu, Zn, Mn, Mg and Ni.
The coercive force can be controlled by combining at least one kind of metal element.

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

The content of the metal element added for the purpose of controlling the coercive force is 0.
The reason for limiting to <y ≤ 0.2 and 0 <z ≤ 0.2 is that the coercive force is greater than 1500 (Oe) and the requirement of the present invention cannot be satisfied without addition, while 0.2 <y and 0.2 <z This is because the coercive force is less than 400 (Oe).

The source material that provides these metal components may be a halide, nitrate or other water-soluble metal salt or hydroxide. In that case, when all the raw materials are water-soluble metal salts, the raw material mixture is an aqueous solution containing a predetermined ratio of metal ions, while the raw material mixture carrying hydroxide as the raw material is a slurry-like mixture. . When a water-soluble metal salt and a hydroxide are allowed to coexist, a slurry containing metal ions and a metal hydroxide is formed. In addition, Fe (II
Iron oxyhydroxide can also be used as a raw material to give component I).

Next, the raw material mixture adjusted to this predetermined ratio is brought into contact with an alkali (alkali solution containing an alkali substance) in an N ₂ atmosphere. As a result, a precipitate is usually formed to obtain an alkaline slurry-like substance. 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. In the absence of acid radicals, the above raw material mixture and alkaline solution are mixed with N ₂
The amount of alkali is such that the pH of the alkaline slurry-like substance obtained by contact in the atmosphere becomes 11.0 or higher. 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 therein. The reason for defining the amount of alkali in such a range is that if the amount of alkali is outside this range, the amount of ferrite phase produced is significantly reduced. The alkaline solution used is selected from a solution of NaOH, LiOH, NH ₄ OH or a mixed solution thereof, or a solution containing a substance having a strong alkalinity.

Moreover, although all of these operations are performed in an N ₂ atmosphere,
The reason is to prevent Fe (II) from being oxidized to become Fe (III).

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

An alkaline slurry-like substance containing a predetermined ratio of metal components represented by the above compositional formula was prepared in an H ₂ O medium exceeding 100 ° C. and in the presence of an alkali having an alkali equivalent ratio of more than 1.0 to an acid radical, or in a reaction system. Ferrite particles are produced by hydrothermal treatment in the presence of an alkali having a pH of 11 or more, and further in an atmosphere of O ₂ -free N ₂ . Here, the hydrothermal treatment means performing a ferrite synthesis reaction using water as a medium in the autoclave.

Regarding the reaction temperature of the ferrite formation reaction in the autoclave, the temperature exceeds 100 ° C, preferably 120 to 400 ° C.
Is appropriate. If the temperature inside the autoclave exceeds 400 ° C, it becomes economically disadvantageous because of the extremely high pressure. Similarly 120 ° C
If it is less than the above, the amount of ferrite produced is too small to reach the object of the invention. The holding time of the temperature and pressure is 10 hours or less, and in some cases even about 1 hour may be sufficient for the purpose.

Further, the reason for carrying out the hydrothermal synthesis reaction in N ₂ atmosphere is that Fe
This is to prevent the oxidation of (II) into Fe (III).

The ferrite powder thus obtained is a plate-like particle having a mean particle size of 0.01 to 0.3 μm, satisfying the composition ratio of the metal elements shown in the above compositional formula from the result of chemical analysis, and the result of VSM measurement. Therefore, the saturation magnetization value of the ferrite powder was 55 emu / g or more and the squareness ratio was 0.47 or more. As described above, it was confirmed that it is possible to produce a ferrite powder having a high remanent magnetization satisfying the target characteristic condition of the present invention in which the saturation magnetization is increased without lowering the squareness ratio.

An example will be described below.

[Example 1] Composition formula Where M = Ba, M '= Ti, M "= Zn + Ni,
n = 7, x = 0.1, y = 0.1, z = 0.1,
3.37Mol / of FeCl ₃ solution 259 ml, 3.37mol / of FeCl ₂ solution 37ml, 2.45mol / of BaCl ₂ solution 37
ml, water 1000 ml, titanium tetrachloride 24.20 g, zinc chloride 8.60
g, an aqueous solution of 8.87 g of anhydrous nickel chloride was thoroughly mixed in an N ₂ atmosphere, and this mixed solution was added at room temperature.
645 ml of 18.45 mol / NaOH aqueous solution was added to obtain a brown precipitate.

This mixture is then placed in an autoclave under N ₂ atmosphere.
The reaction was carried out at 400 ° C for 5 hours. After sufficiently washing the reaction product thus obtained to remove impurities,
Dry granulation was performed to obtain magnetic powder. This powder was plate-shaped and had an average particle diameter of 0.12 μm. Also, from the VSM measurement with the maximum applied magnetic field of 10 kOe, its saturation magnetization is
The remanent magnetization was 57.5 emu / g, the remanence was 27.2 emu / g, and the coercive force was 680 (Oe).

Example 2 In the composition formula, the content of Fe (II), that is, x =
The same operation and evaluation as in Example 1 were performed except that the composition of the raw material was changed so that 0.1 was x = 0.05. The compositional conditions and characteristics of these are shown in Table 1.

[Example 3] In the composition formula, the same operations and evaluations as in Example 1 were performed except that the composition of the raw material was changed so that n = 7 became n = 8. The compositional conditions and characteristics of these are shown in Table 1.

Example 4 In the composition formula, y = 0. 1 was changed to y = 0.12 and z = 0.
Other than changing the composition of the raw materials so that 1 becomes z = 0.12.
The same operation and evaluation as in Example 1 were performed. The compositional conditions and characteristics of these are shown in Table 1.

Example 5 Composition formula Where M = Ba, M '= Zr, M "= Zn + Cu,
n = 7, x = 0.1, y = 0.1, z = 0.1,
3.37Mol / of FeCl ₃ solution 259 ml, 3.37mol / of FeCl ₂ solution 37 ml, 1.38 mol / of BaCl ₂ solution 65
N, an aqueous solution of 43.29 g of zirconium oxychloride, 8.60 g of zinc chloride and 10.62 g of cupric chloride dissolved in 1000 ml of water.
After mixing well in ₂ atmosphere, add 607 ml of 18.45 mol / NaOH aqueous solution to this mixed solution at room temperature,
A brown precipitate was obtained.

This mixture is then placed in an autoclave under N ₂ atmosphere.
The reaction was carried out at 400 ° C for 5 hours. After sufficiently washing the reaction product thus obtained to remove impurities,
Dry granulation was performed to obtain magnetic powder. This powder was plate-shaped and had an average particle size of 0.06 μm. Also, from the VSM measurement with the maximum applied magnetic field of 10 kOe, its saturation magnetization is
56.8emu / g, remanent magnetization 28.1emu / g, coercive force 625 (Oe)
Met.

Example 6 In the composition formula, the content of Fe (II), that is, x =
The same operation and evaluation as in Example 5 were carried out except that the composition of the raw material was changed so that 0.1 was x = 0.05. The compositional conditions and characteristics of these are shown in Table 1.

[Example 7] The same operation and evaluation as in Example 5 were performed, except that the composition of the raw material was changed so that n = 7 became n = 8 in the composition formula. The compositional conditions and characteristics of these are shown in Table 1.

[Example 8] In the composition formula, y = 0.1 was changed to y = 0.12, and z = 0.
Other than changing the composition of raw materials so that 1 becomes z = 0.12.
The same operation and evaluation as in Example 5 were performed. The compositional conditions and characteristics of these are shown in Table 1.

[Example 9] The same operation and evaluation as in Example 5 were performed except that the composition of the raw material was changed so that M ″ = Co + Cu in the composition formula. The composition conditions and characteristics are shown in Table 1. Indicated.

[Comparative Example 1] In the composition formula MO.nFe ₂ O ₃ , M is 3.37 mol / n so that Ba and n = 6.
FeCl ₃ aqueous solution of 296 ml and 0.0706 mol / BaC of
After thoroughly mixing 1181 ml of 1 ₂ aqueous solution under N ₂ atmosphere,
18.45mol / NaOH solution 52 in this mixture at room temperature
0 ml was added to obtain a highly alkaline slurry substance containing a brown precipitate. Then, this slurry-like substance was reacted in an autoclave under N ₂ atmosphere at 400 ° C. for 5 hours. The reaction product thus obtained was thoroughly washed to remove impurities, and then dried and disintegrated to obtain a ferrite powder.

As a result of observation with a transmission electron microscope, the obtained ferrite powder was composed of plate-like particles and had an average particle size of 0.45 μm.

Further, the VSM measurement with the maximum applied magnetic field of 10 kOe revealed that the saturation magnetization was 34.2 emu / g, the residual magnetization was 13.7 emu / g, and the coercive force was 1730 (Oe).

[Comparative Example 2] In the composition formula MO · n (Fe _1-xy M ′ _x M ″ _y ) ₂ O ₃ , M = Ba, M ′ = Ti, M ″ = Zn + Cu,
3.37 mol / so that n = 6, x = 0.1, y = 0.1
296 ml of FeCl ₃ solution, 3.35 mol / BaCl ₂
Solution 31ml, water 1000ml titanium tetrachloride 24.20g, zinc chloride
An aqueous solution in which 8.60 g and cupric chloride 10.62 g were dissolved was thoroughly mixed in an N ₂ atmosphere, and then 18.45 mol / NaOH aqueous solution 650 ml was added to this mixed solution at room temperature to obtain a brown precipitate. .

This mixture is then placed in an autoclave under N ₂ atmosphere.
The reaction was carried out at 400 ° C for 5 hours. After sufficiently washing the reaction product thus obtained to remove impurities,
Dry granulation was performed to obtain magnetic powder. This powder was plate-shaped and had an average particle diameter of 0.12 μm. Also, from the VSM measurement with the maximum applied magnetic field of 10 kOe, its saturation magnetization is
53.5emu / g, remanent magnetization 24.2emu / g, coercive force 810
It was (Oe).

[Comparative Example 3] Composition formula Where M = Ba, M '= Ti, M "= Zn + Ni,
n = 6, x = 0.1, y = 0.1, z = 0.1,
259 ml of 3.37 mol / FeCl ₃ solution, 37 ml of 3.37 mol / FeCl ₂ solution, 3.35 mol / BaCl ₂ solution 31
ml, water 1000 ml, titanium tetrachloride 24.20 g, zinc chloride 8.60
g, an aqueous solution of 8.87 g of anhydrous nickel chloride was thoroughly mixed in an N ₂ atmosphere, and this mixed solution was added at room temperature.
650 ml of 18.45 mol / NaOH aqueous solution was added to obtain a brown precipitate.

This mixture is then placed in an autoclave under N ₂ atmosphere.
The reaction was carried out at 400 ° C for 5 hours. After sufficiently washing the reaction product thus obtained to remove impurities,
Dry granulation was performed to obtain magnetic powder. This powder had a plate-like shape and had an average particle diameter of 0.09 μm. Also, from the VSM measurement with the maximum applied magnetic field of 10 kOe, its saturation magnetization is
55.6emu / g, remanent magnetization 24.5emu / g, coercive force 755 (Oe)
Met.

〔effect〕

Conventionally, a hexagonal ferrite having a general formula used for a coating type perpendicular magnetic recording medium has the composition and can improve σ _s when manufactured as a ferrite powder having an average grain size of 0.3 μm or less. Difficult and at most 50 ~
Only 54 emu / g was obtained. Various methods developed to increase its σ _s by special processing are S
Along with the decrease in Q, the improvement in σ _r could not be expected as a result. On the other hand, the ferrite powder of the present invention, which is a ferrite powder having a novel composition specified by the above general formula, is a ferrite powder having an increased σ _s obtained without a decrease in SQ and has a high density. This is a ferrite powder suitable for recording. The ferrite powder of the present invention having such characteristics can be easily produced by various known methods by blending the raw materials so that the target composition becomes the composition represented by the general formula, 100 ° C in an autoclave under particularly controlled reaction conditions
It can be conveniently prepared by hydrothermal synthesis carried out at temperatures above.

Claims (2)

[Claims] 1. A general formula: [Wherein M represents one or more metal elements selected from the group consisting of Ba, Sr, Pb and Ca, and M'is selected from the group consisting of V, Sn, Ti, Zr, W and Nb. Represents one or more metallic elements, M ″ is Mn, Zn
, Cu, Co, Ni and Mg represent one or more kinds of metal elements selected from the group consisting of n, 6.3 and n represent numerical values of 6.3 ≦ n ≦ 9, and x, y and z respectively represent the following formulas: 0.01 <x
Represents a numerical value that satisfies ≦ 0.3, 0 <y ≦ 0.2, 0 <z ≦ 0.2. ] A ferrite powder for high density recording having a composition represented by: 2. The ferrite powder according to claim 1, wherein M'in the general formula (1) is Zr and M "is at least one metal element selected from the group consisting of Co, Cu and Zn.