JP3429881B2 - Composite type hexagonal ferrite magnetic powder and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hexagonal ferrite magnetic powder suitable for high recording density magnetic recording media, magnetic fibers, composite materials such as magnetic glass.

[0002]

2. Description of the Related Art Generally, a coating type recording medium comprises a non-magnetic substrate made of polyethylene terephthalate film or the like, and a magnetic layer containing magnetic powder and a resin binder as main components formed on the surface of the substrate. There is. In the magnetic recording medium having such a structure, the conventional γ-Fe
A magnetic recording method has been adopted in which needle-like magnetic powder such as ₂ O ₃ , Co-deposited γ-Fe ₂ O ₃ , CrO ₂ or metallic Fe is used and magnetization in the longitudinal direction of the coated surface is utilized. However, in this recording method, if an attempt is made to improve recording / reproduction in a high frequency region, the demagnetizing field in the recording medium increases, so that the recording density cannot be improved so much.

Therefore, in order to significantly improve the recording density, a perpendicular magnetic recording system utilizing magnetization in a direction perpendicular to the base of the magnetic recording medium has been proposed and is being developed. This perpendicular magnetic recording system is suitable for high-density magnetic recording because the problem of demagnetizing field in the recording medium does not occur even in the high frequency range.

As a recording medium suitable for this perpendicular magnetic recording system, there is conventionally known a recording medium in which a metal magnetic thin film such as a Co--Cr alloy is deposited on the substrate surface by a vacuum deposition method or a sputtering method. . In this type of magnetic recording medium, the magnetic layer is made of a metal thin film, so environmental stability and running durability,
There was also a problem with productivity.

Therefore, as a coating type perpendicular magnetic recording medium which is less likely to cause such a problem, there is a magnetic recording medium using hexagonal ferrite magnetic fine particles in which the easy axis of magnetization is easily oriented in the vertical direction as magnetic powder. Are known. Examples of hexagonal ferrite magnetic powder suitable for a magnetic recording medium include M-type BaFe ₁₂ O ₁₉ and W-type BaM.
e ₂ Fe ₁₆ O ₂₇ (Me is a substitutional metal element) single-phase hexagonal ferrite magnetic particles, or composite hexagonal crystal containing simultaneously M-type or W-type hexagonal ferrite and spinel ferrite in one particle Examples thereof include system ferrite magnetic particles, and hexagonal system ferrite magnetic particles obtained by substituting some of those atoms with other elements. As a method for producing such a hexagonal ferrite magnetic powder, a glass crystallization method, a coprecipitation-firing method, a hydrothermal synthesis-firing method, a flux method of firing both precipitates in a flux, etc. are generally used. Is.

Of the above-mentioned hexagonal ferrites, single-phase hexagonal ferrites generally do not have very high saturation magnetization, whereas composite hexagonal ferrites have
Magnetization has been improved by compounding spinel ferrite, and saturation magnetization of 60 emu / g or more can be easily obtained. Therefore, it has attracted particular attention for high recording density magnetic recording media.

[0007]

However, although it is recognized that the improvement of the saturation magnetization due to the compounding of the spinel ferrite of the hexagonal ferrite as described above mainly contributes to the improvement of the output in the long wavelength region, it has a short wavelength. In the region, the output tends to be lowered due to the compounding, and it has been also recognized that the coercive force of the magnetic powder varies among lots.

One of the causes for this is that the composite of spinel ferrite does not necessarily proceed uniformly for each particle. It is said that the non-uniformity of compounding of each particle is one of the controlling factors of the short wavelength characteristics of SFD (Switchin
g Field Distribution: represents the Hc distribution state of individual magnetic particles), and as a result, it is considered that the recording / reproducing characteristics of the magnetic recording medium are deteriorated.

The present invention has been made in order to solve such a problem in the composite type hexagonal ferrite, and while maintaining its high magnetization, the conventional drawback of S
It is an object of the present invention to provide a magnetic powder capable of producing a magnetic recording medium having a reduced FD and exhibiting high output characteristics even in a short wavelength region.

[0010]

The composite type hexagonal ferrite magnetic powder according to the present invention is characterized by the composition of spinel ferrite compounded with hexagonal ferrite. That is, the feature of the present invention is that in the composite hexagonal ferrite magnetic powder formed by compounding hexagonal ferrite and spinel ferrite, the spinel ferrite is
Formula _{M 1 + x Fe 2-x} O 4 ............ (1) ( where where x represents a number of 0 <x <0.1, M is C
o represents at least one element selected from Ni, Zn, Cu, Mg, and Mn). Further, the composite hexagonal ferrite magnet of the present invention
The powder manufacturing method is based on the process of manufacturing hexagonal ferrite magnetic powder.
And the hexagonal ferrite magnetic powder with the general formula M _{1 + x}
Fe _2−x O ₄ (where x is 0 <x <0.1
Represents the number, M is Co, Ni, Zn, Cu, Mg, Mn
Represents at least one element selected from)
Process to set spinel ferrite to the composition
It is characterized by having and.

In the present invention, the range of x in the spinel ferrite composition is set to be different from the range usually used so far, so that the high saturation magnetization characteristic of the composite hexagonal ferrite is maintained. At the same time, it is possible to significantly improve the SFD.

In the present invention, the first feature of the spinel ferrite composition represented by the general formula (1) is that x> 0, and it is preferable that x is smaller than 0.1. When x is 0.1 or more, the magnetization of spinel ferrite is reduced, which is not preferable.

In the present invention, the hexagonal ferrite that can be composited with the spinel ferrite having the above composition is a single-phase hexagonal ferrite such as M type (magnetoplumbite type) or W type, or already spinel ferrite. Examples include various composite hexagonal ferrites that are compounded with. These hexagonal ferrites can be represented by the following general formula.

AO.n (Fe _12-xy M1 _x M2 _y O _18-a ) (2) (wherein A is at least one element selected from Ba, Sr, and Ca, and M1 is divalent) Of at least one element selected from the group of metal elements, M2 is at least one element selected from the group of 4- to 6-valent metal elements, and a is [x
+ (3-m) y] / 2 (where m is the average valence of M2), n is 0.8 or more and 3 or less, x is 0 or more and 3 or less, and y is In the hexagonal ferrite represented by the general formula (2), particularly, the divalent metal M1 includes Co and Z.
It is effective to use at least one element selected from n and Ni. Further, among these hexagonal ferrites, M represented by n = 0.8 to 1.03 and a = 0
The type Ba ferrite is industrially the easiest to obtain, and is therefore preferable as a target for compounding with spinel ferrite.

In the present invention, the means for compounding the spinel ferrite represented by the general formula (1) and the hexagonal ferrite represented by the general formula (2) is not limited to a particular method. . As one of the means of compounding, after batch-mixing raw materials containing respective constituent elements of spinel ferrite and hexagonal ferrite,
There is a so-called batch method for producing crystals according to the above-described conventional method for producing hexagonal ferrite such as a glass crystallization method. According to this method, the ferrite having a spinel structure is bitten between the R block layers in the hexagonal ferrite crystal to grow crystals, and the magnetic powder of the present invention is obtained. At this time, part of the spinel ferrite grows on the surface of the hexagonal ferrite crystal.

As another method of forming a composite, the hexagonal ferrite magnetic particles represented by the general formula (2) are synthesized by the conventional hexagonal ferrite method, and then represented by the general formula (1). There is a method of performing it in two steps such as synthesizing the spinel ferrite. In this case, spinel ferrite grows in the form of being deposited on the surface of the hexagonal ferrite magnetic particles. The effect of the present invention is
Although it can be obtained by either of the above composite methods, in particular by the latter, by adopting a composite method of depositing spinel ferrite on the surface of the hexagonal ferrite,
The effect of the present invention can be more remarkably obtained.

In the present invention, the ratio of the spinel ferrite compounded to the matrix hexagonal ferrite is 0.2 to 5, more preferably 0.5 to 5, in terms of molar ratio.
The range of 2 is desirable. When the molar ratio is less than 0.2, the effect of improving the saturation magnetization due to compounding is reduced, which is not preferable. If it is more than 5, the uniaxial anisotropy of the obtained crystal is lost and the magnetic field orientation of the magnetic powder is lowered, or the particles are coarsened, which is also not preferable.

The magnetic powder of the present invention has a wide range of uses such as magnetic recording media and composite materials such as magnetic fibers and magnetic glass. When it is used for a magnetic recording medium, it is particularly required to be magnetically stable, so that the average particle diameter thereof is preferably within the range of 10 to 60 nm. If the coercive force is too high, the head magnetic field saturates during recording, making writing with a normal magnetic head difficult.
If it is too low, it becomes impossible to hold the recording signal.
It is desirable to adjust it to be in the range of up to 4000 Oe.

[0019]

The composition of spinel ferrite in the conventionally proposed composite type hexagonal ferrite is such that the value of x in the general formula (1) is 0 or less (x≤0), that is, the stoichiometric composition. It was an iron-rich type. Such a composition was intended to generate Fe ^{2+ in the} spinel ferrite and reduce the electric resistance by electron exchange with Fe ³⁺ .

In carrying out the present invention, the SFD, which is a drawback of the composite magnetic powder having such a composition region, is large,
Though the saturation magnetization is large, the short wavelength characteristics do not extend and the coercive force of the magnetic powder varies among lots.

The reason why such a phenomenon occurs is not always clear, but it can be considered as follows. That is the case of x ≦ 0, it easily can Fe ²⁺ ions in the spinel ferrite in the process of crystallization, whereas the Fe ²⁺ ions has a property of easily being readily oxidized to Fe ³⁺ ions. Therefore, the number thereof is likely to change due to a slight difference in oxygen concentration during crystal formation, and the magnetic characteristics of the magnetic powder are likely to change accordingly. Therefore, the reason why the magnetic powder SFD is large when x ≦ 0 is that the oxygen concentration surrounding individual magnetic particles in the crystal formation process is
It is considered that it is not always constant microscopically, and as a result, the Fe ²⁺ ion concentration formed in the spinel ferrite during the crystallization process differs for each particle. The variation in the coercive force of the magnetic powder between lots is also considered to be due to the change in the Fe ²⁺ concentration in the magnetic powder due to the subtle change in the oxygen concentration during crystal formation.

In the present invention, the above-mentioned difficulties of the conventional composite type hexagonal ferrite magnetic powder can be rephrased by setting the amount of M element x in the general formula of spinel ferrite to 0 <x and setting it larger than the stoichiometric composition. For example, an attempt was made to eliminate it by making the iron concentration lower than the stoichiometric composition and making it iron-deficient.

According to the present invention, by reducing the Fe ²⁺ concentration in the crystal by using the iron-deficient spinel ferrite, the SFD of the composite hexagonal ferrite magnetic powder is reduced, and the interparticle and lot The variation of the coercive force Hc of is improved. As a result of stable control of the coercive force of the magnetic powder,
The short wavelength characteristics of the manufactured magnetic recording medium are improved. At the same time, since the high saturation magnetization, which is an inherent feature of the composite type hexagonal ferrite magnetic powder, is not impaired, its long wavelength characteristics can be secured as before.

[0024]

EXAMPLES The present invention will be described in detail below with reference to examples.

Example 1 In producing the composite type hexagonal Ba ferrite magnetic powder of the present invention in two steps, first, a single-phase hexagonal Ba ferrite magnetic powder was produced. For the production of single-phase powder, B
Aqueous solutions of aCl ₂ , FeCl ₃ , CoCl ₂ and NbCl ₅ were prepared and mixed. Each of the aqueous solutions was prepared by mixing Ba, Fe, Co, and Nb elements with the following chemical formula _{Ba.Fe 12-2x} Co _x Nb _{x / 2} O ₁₉ (where x = 0.64) when they are mixed. ) Co-Nb substitution B represented by
a Ferrite composition ratio is included. Then, an alkali was added to this mixed solution to precipitate a coprecipitate under pH 13. Further, this mixture was heated at 120 ° C. for 4 hours to generate a precursor of the Co—Nb-substituted Ba ferrite. Then, this precursor was washed with water and mixed with BaCl ₂ (BaC was added to the dried precursor).
The weight ratio of l ₂ = 1: 1) and, after sufficiently stirring, and then dried by a spray drier. The dry mixture thus obtained was heat treated at 900 ° C. for 2 hours and then dried with BaCl ₂
The flux was removed by washing with water to obtain an M-type single-phase hexagonal Ba ferrite magnetic powder having the above composition.

Then, to the water to which 0.1 mol of the Ba ferrite magnetic powder thus obtained was added, Co spinel ferrite (chemical formula Co _{1 + x} Fe _2-x O ₄ x =
CoCl ₂ and FeCl containing 0.2 mol of Co and Fe (having a composition represented by 0.05)
The aqueous solution of ₂ was further added and mixed with stirring. An alkaline aqueous solution is mixed with the obtained mixed solution, and Ba is mixed at a pH of 13.
A spinel ferrite component was coprecipitated on the ferrite magnetic powder. Then, while performing nitrogen bubbling, the temperature of this slurry was raised to about 90 ° C., and then nitrogen bubbling was switched to nitrogen bubbling and the reaction was performed for about 4 hours.
Then, the obtained slurry was washed with water to remove alkali, and then dried to obtain magnetic fine particles.

With respect to the obtained magnetic fine particles, X-ray diffraction,
As a result of electron microscopic observation and composition analysis, it was found that this was a composite hexagonal Ba with Co spinel ferrite deposited on the surface.
It was confirmed to be ferrite magnetic powder.

Example 2 A single-phase hexagonal Ba ferrite magnetic powder was prepared in the same manner as in Example 1, and 0.1 mol of the magnetic powder was added to Co spinel ferrite (chemical formula Co _{1 + x} Fe _2-x O ₄ has a composition represented by x = 0.026)
An aqueous solution of CoCl ₂ and FeCl ₂ containing 0.2 mol of Co and Fe was further added and mixed with stirring.
An alkaline aqueous solution was mixed with the obtained mixed liquid to coprecipitate the spinel ferrite component on the Ba ferrite magnetic powder under pH 13. Then, while performing nitrogen bubbling, the temperature of this slurry was raised to about 90 ° C., and then nitrogen bubbling was switched to nitrogen bubbling and the reaction was performed for about 4 hours. Then, the obtained slurry was washed with water to remove alkali, and then dried to obtain magnetic fine particles.

The obtained magnetic fine particles were subjected to X-ray diffraction, electron microscope observation and composition analysis in the same manner as in Example 1. As a result, it was found that this was a composite hexagonal Ba ferrite magnet with Co spinel ferrite deposited on the surface. It was confirmed to be powder.

Example 3 A single-phase hexagonal Ba ferrite magnetic powder was prepared in the same manner as in Example 1, and 0.1 mol of the magnetic powder was added to water to give Example 2.
Co spinel ferrite having the same composition as used in 0.1
Magnetic fine particles were obtained in the same manner as in Example 2 except that an aqueous solution of CoCl ₂ and FeCl _{2 in} an amount corresponding to moles was further added and mixed with stirring.

The obtained magnetic fine particles were subjected to X-ray diffraction, electron microscope observation, and composition analysis in the same manner as in Example 1. As a result, it was found that this was a composite hexagonal Ba ferrite magnet with Co spinel ferrite deposited on the surface. It was confirmed to be powder.

Example 4 A single-phase hexagonal Ba ferrite magnetic powder was prepared in the same manner as in Example 1, and 0.1 mol of the magnetic powder was added to Co-Z.
n spinel ferrite {Chemical formula (Co _0.8 Zn _0.2 )
_{1 + x} Fe _2-x O ₄ has a composition represented by x = 0.026} Co, Z corresponding to 0.2 mol
An aqueous solution of CoCl ₂ , ZnCl ₂ , and FeCl ₂ containing n and Fe was further added and mixed with stirring. An alkaline aqueous solution was mixed with the obtained mixed liquid to coprecipitate the spinel ferrite component on the Ba ferrite magnetic powder under pH 13. Then, while performing nitrogen bubbling, the temperature of this slurry was raised to about 90 ° C., and then nitrogen bubbling was switched to nitrogen bubbling and the reaction was performed for about 4 hours. Then, the obtained slurry was washed with water to remove alkali, and then dried to obtain magnetic fine particles.

The obtained magnetic fine particles were subjected to X-ray diffraction, electron microscope observation and composition analysis in the same manner as in Example 1. As a result, it was found that the composite hexagonal Ba having Co-Zn spinel ferrite deposited on the surface was used. It was confirmed to be ferrite magnetic powder.

Example 5 Next, the composite powder of the present invention was produced by the batch method. Upon production, the M-type hexagonal system B used in Example 2 was used.
a aqueous solution of BaCl ₂ , FeCl ₃ , CoCl ₂ and NbCl ₅ containing Ba, Fe, Co and Nb in the same composition ratio as the a ferrite, and Co having the same composition ratio as the Co spinel ferrite used in Example 2 as well. CoCl ₂ and FeCl ₃ aqueous solutions containing Fe and Fe were added and mixed with stirring. An alkaline aqueous solution was mixed with the obtained mixed liquid, and hydrothermal treatment was performed in an autoclave at 120 ° C. and pH 13 for about 6 hours.

Next, this slurry was washed with water and then BaC
l ₂ was mixed (weight ratio of BaCl ₂ to the dried precursor = 1: 1), sufficiently stirred, and dried by a spray dryer. The dry mixture thus obtained is
After heat treatment at 900 ° C. for 2 hours, the BaCl ₂ flux was removed by washing with water to obtain magnetic fine particles.

The obtained magnetic fine particles were similarly subjected to X-ray diffraction, electron microscope observation and composition analysis. As a result, it was found that this was a spinel-encapsulated composite hexagonal Ba ferrite magnet containing spinel layers on the surface and inside. It was confirmed to be powder.

Comparative Example 1 A single-phase hexagonal Ba ferrite magnetic powder was prepared in the same manner as in Example 1, and a chemical formula Co _{1 + x} Fe _2-x representing the composition of Co spinel ferrite was prepared as a Co spinel ferrite raw material to be added thereto. A composite hexagonal Ba ferrite magnetic powder having Co ferrite adhered to the surface thereof was produced in the same manner as in Example 2 except that O ₄ with x = 0 was used.

Comparative Example 2 A single-phase hexagonal Ba ferrite magnetic powder was prepared in the same manner as in Example 1, and as a Co spinel ferrite raw material to be added thereto, a chemical formula Co _{1 + x} Fe _2-x representing the composition of Co spinel ferrite was prepared. A composite hexagonal Ba ferrite magnetic powder having Co ferrite adhered to the surface thereof was produced in the same manner as in Example 2 except that O ₄ with x = −0.4 was used.

Comparative Example 3 A single-phase hexagonal Ba ferrite magnetic powder was prepared in the same manner as in Example 1, and a chemical formula (Co _0.8 Zn ZnO) representing the composition of Co-Zn spinel ferrite was added as a Co-Zn spinel ferrite raw material. _0.2 ) In the same manner as in Example 4 except that x = 0 in _{1 + x} Fe _{2 -x} O ₄ was used, a composite hexagonal Ba ferrite magnetic powder having Co ferrite deposited on the surface was used. It was made.

Comparative Example 4 As a Co spinel ferrite raw material to be mixed together with the M-type hexagonal Ba ferrite material, x = 0 in the chemical formula Co _{1 + x} Fe _{2 -x} O ₄ representing the composition of Co spinel ferrite. A composite type hexagonal Ba ferrite magnetic powder containing Co spinel ferrite was manufactured in the same manner as in Example 5 except that the above-mentioned materials were used.

Next, with respect to each of the magnetic powders of the above-mentioned Examples and Comparative Examples thus obtained, the magnetic characteristics,
The shape characteristics and SFD values were measured. The measurement results are shown in the following Table 1 together with the kind of the substitutional metal element M, the value of x, and the molar ratio of spinel ferrite and Ba ferrite.
Shown in.

[0042]

[Table 1] As is clear from Table 1, in the magnetic fine particles in which hexagonal ferrite and spinel ferrite are compounded, the SFD of the magnetic powder is improved by making the spinel ferrite composition iron-deficient.

Further, the trial production of the composite powders of Example 2 and Comparative Example 1 was repeated 5 times, respectively, and the degree of coercive force variation was examined. In Example 2, it was ± 20 Oe, while in Comparative Example 1 In the case of, it was ± 70 Oe. From this, it can be understood that the composite magnetic powder of the present invention using the iron-deficient spinel ferrite can reduce the variation in coercive force and stably control the coercive force. Furthermore, when the electric resistances of the magnetic powders of Example 2 and Comparative Example 1 were measured, they were 4 × 10 ⁶ Ωcm and 7 × 10 ⁷ Ωcm, respectively.
Therefore, it was found that the present invention is also effective in reducing the electric resistance of the magnetic powder.

[0044]

As described above, according to the composite magnetic powder of the present invention in which the composition of the spinel ferrite is iron-deficient, compared to the magnetic powder of the conventional composition in which spinel ferrite and hexagonal ferrite are composited. As a result, the SFD, which is a controlling factor of the short wavelength characteristic, is significantly improved, and at the same time, as secondary effects, effects such as stable control of coercive force and reduction of electric resistance are recognized. Therefore, according to the present invention, a magnetic powder capable of producing a magnetic recording medium exhibiting high output characteristics even in a short wavelength region is provided.

[0045]

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Satoshi Hagiwara 5583 Kawajiri, Yoshida-cho, Hara-gun, Shizuoka 5 Toshiba Toshiba Glass Co., Ltd. (56) Reference JP-A-4-236403 (JP, A) JP-A-6 -77034 (JP, A) JP 2-40127 (JP, A) JP 60-261051 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01F 1/00- 1/117 C04G 35/26-35/40 C01G 49/00-49/08 C04B 35/00-35/22 G11B 5/62-5/82

Claims (4)

(57) [Claims] 1. A composite hexagonal ferrite magnetic powder comprising a mixture of hexagonal ferrite and spinel ferrite, wherein the spinel ferrite has a general formula of M _{1 + x} Fe _{2 -x} O ₄ (where x is the formula: Represents a number 0 <x <0.1, M is C
o, Ni, Zn, Cu, Mg, Mn, which represents at least one element selected from the above.), a composite hexagonal ferrite magnetic powder. 2. The composite according to claim 1, wherein the spinel ferrite is adhered to the surface of the single-phase hexagonal ferrite magnetic particles or the composite hexagonal ferrite magnetic particles. Type hexagonal ferrite magnetic powder. 3. An average particle size of 10 to 60 nm and a coercive force of 2
The composite hexagonal ferrite magnetic powder according to claim 1 or 2, characterized in that it is from 0 to 4000 Oe. 4. A process for producing hexagonal ferrite magnetic powder.
If, on the hexagonal ferrite magnetic powder, the general formula _{M 1 + x Fe 2-x} O 4 ( provided that where x is a number from 0 <x <0.1, M is C
selected from o, Ni, Zn, Cu, Mg, Mn
(Representing at least one element)
And the step of depositing spinel ferrite.
Production method of the characteristic composite type hexagonal ferrite magnetic powder
Law.