JPH05258932A - Magnetism recording magnetic powder - Google Patents

Abstract

PURPOSE:To make the title high density magnetism recording magnetic powder optimum by providing the same with the saturated magnetism in high value, the coercive force controlled at pertinent value, the narrow distribution and the small temperature coefficient of coercive force without aging at all. CONSTITUTION:The title magnetism recording magnetic powder is composed of single crystalline particles represented by a structural formula of MM' (wherein M represents at least one kind selected from Ba and Sr, M' represents at least one kind selected from Co, Ni and Zn, x is 0.2-1.5) as well as the structure comprising magnet plumbite type structure (RS block) and spinel type structure (S block) laminated in the axial direction. At this time, it is recommended that a part of Fe is equivalently substituted with another kind of element, trivalent in average, represented by Coy1Niy2Zny3Tiy(y1+y2+y3=y).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high density magnetic recording, and more particularly to magnetic powder useful as a coating type high density magnetic recording medium.

[0002]

2. Description of the Related Art In the field of magnetic recording, with the advent of video and digital audio, the demand for high density recording is increasing. In the in-plane magnetic recording which is the mainstream at present, when an attempt is made to increase the recording density, the demagnetizing field in the magnetic layer increases, so that the improvement of the recording density is limited. Therefore, perpendicular magnetic recording is promising for high density recording.

As a method of forming a magnetic layer having an easy axis of magnetization in the vertical direction, Co--C is formed by a sputtering method or an evaporation method.
There is a method of forming a thin film such as r on the substrate and a method of applying magnetic powder such as barium ferrite together with a binder on the substrate, but the coating method is currently the mainstream technology,
Since it is well established, it can be said that the coating type recording medium is more practical.

Coating type perpendicular magnetic recording was realized by using barium ferrite particles, particularly hexagonal plate-shaped barium ferrite particles. First, the magnetic particles used in this case are preferably so fine that their particle size does not exhibit superparamagnetism. Generally, particles having an average particle size of 0.01 to 0.3 μm are required. This fact is described, for example, in Japanese Patent Laid-Open No.
Japanese Patent No. 125219 discloses that "... perpendicular magnetic recording has an advantage over in-plane magnetic recording when the recording wavelength is 1 .mu.m.
It is an area of m or less. However, in order to perform sufficient recording and reproduction in this wavelength region, the crystal grain size of the ferrite is preferably 0.3 μm or less. However, 0.01μ
Since a desired ferromagnetism is not exhibited when the thickness is about m, an appropriate crystal grain size is required to be about 0.01 to 0.3 μm. Can also be understood from the description.

Next, it is desirable that the dispersibility of the magnetic particles is as excellent as possible. This fact, for example,
JP-A-56-155022 discloses "...
A good recording medium cannot be obtained unless it has a property of being uniformly dispersed. Therefore, it is also necessary that at least individual particles do not sinter and aggregate at the time of producing the magnetic powder. Can also be seen from the description.

The saturation magnetization of the magnetic particles needs to be as large as possible. This fact is also described in, for example, Japanese Patent Laid-Open No. 56-149328, "... the magnetoplumbite ferrite used in the magnetic recording medium material is required to have as large a saturation magnetization as possible." It can be understood. Especially 60 emu / g
Those having the above saturation magnetization are desired.

Further, regarding the coercive force of the magnetic particles, the coercive force is 300 to 1500 in relation to the reproduction output and the head characteristics.
Oe is required, and it is desirable that its temperature coefficient is as small as possible. This fact is described in, for example, Japanese Unexamined Patent Publication No. 56-149328, "... Coercive force when miniaturized shows a value of about 500 to 1500 Oe ... It is necessary to obtain magnetoplumbite ferrite. It is desirable that the density is high and the output is large from the viewpoint of reproduction output, but about 1500-
Oe is the practical limit. ",
Further, in Japanese Patent Application Laid-Open No. 62-132732, "... The coercive force of a magnetic recording medium has a great influence on the electromagnetic conversion characteristics. However, when the electromagnetic conversion characteristics change, the recording, reproducing and erasing characteristics also change. That is, if a magnetic recording medium with a large temperature change is used in a place where the environmental temperature is significantly different, recording failure,
The reproduction output is reduced, or the recording erasure failure occurs, so that the function as a magnetic recording medium is significantly reduced. It can be understood from the fact that it is described as "...". In particular, a material having a temperature coefficient of coercive force of 1-Oe / ° C or less is strongly desired.

Further, in order to obtain good recording / reproducing characteristics in the region where the recording wavelength is 1 μm or less, the coercive force distribution of the magnetic powder needs to be as small as possible. Barium ferrite is C
Since the coercive force distribution is smaller than that of acicular magnetic powders such as o-γFe ₂ O ₃ and metallic iron, an attempt has been made recently to obtain high output in the short wavelength region by utilizing the coercive force distribution. There is. S ^*, which is one of the indices of coercive force distribution (given by S ^* = Hc / H ^*, where H ^* is the H value at the intersection of the tangent line at Hc value and M = Mr in the hysteresis loop) In terms of the value of, it must be 0.6 or more in a non-oriented coating film.

The following three methods are known as typical methods for producing hexagonal plate-shaped barium ferrite particles for magnetic recording. (1) An alkali and an alkali carbonate are mixed into an aqueous solution containing a ferric salt and a barium salt while stirring, and a coprecipitate of ferric hydroxide and barium carbonate is mixed under the condition that the pH value is 10 or more. After the coprecipitate was completely washed with water and dried,
A method of obtaining barium ferrite particles by heat treatment at around 0 ° C. (coprecipitation-firing method: JP-A-56-60002).

(2) An alkaline solution having a pH value of 10 or more in which Fe ⁺³ or Ba ²⁺ is dissolved or coprecipitated is heated to a temperature of 100 to 374 ° C. in an autoclave to obtain a barium ferrite precursor (crystallinity). , Barium ferrite having incomplete magnetic properties is generated by reaction, and then washed, dried, and fired (usually 800 ° C. or higher) to obtain barium ferrite particles (hydrothermal synthesis method: for example, M. Kiyama, Bul).
l. Chem. Soc. Jpa. , 49 (1976),
1855 and JP-A-60-12973).

(3) A barium ferrite constituent raw material such as BaO or Fe ₂ O ₃ and a glass forming material such as B ₂ O ₃ are mixed, and the melted material is rapidly cooled and solidified, and then heat treated to produce barium in a glass substance. A method of precipitating ferrite, dissolving a matrix to extract barium ferrite particles, washing with water, and drying (glass crystallization method: for example, Miki, Well Nikkei New Material, April 28, 1986, 52).
Page and JP-A-56-67904). By the production method represented by the above-mentioned method, it is possible to supply barium ferrite particles for magnetic recording whose average particle diameter and dispersibility satisfy desired conditions.

Regarding the coercive force, part of Fe constituting barium ferrite is replaced with another element represented by Co-Ti (for example, J. Smit, HPJ.W.
ijn; Ferrites, 1959, p. 208;) to obtain a desired value. Furthermore, the coexistence of spinel ferrite phase represented by the magnetoplumbite type and MO · Fe ₂ O ₃ represented by MO · nFe ₂ O _3, a method of controlling the coercive force (JP 56
(-118304) or a method of controlling the magnetic characteristics by modifying only the surface of magnetoplumbite type ferrite particles with spinel type ferrite (Japanese Patent Laid-Open No. 62-139123).

[0013]

However, in the method of controlling the coercive force by substituting Fe of barium ferrite mentioned in the preceding paragraph, the inconvenient situation that the saturation magnetization is lower than that of barium ferrite before the substitution occurs. It had the drawback of inviting. Further, regarding the temperature stability of the coercive force, the barium ferrite itself before substitution shows a characteristic temperature characteristic that the coercive force increases with a rise in temperature, but when Fe substitution is performed, the temperature coefficient further increases. However, in some of the examples described in JP-A No. 62-155504, some reach 5.4-Oe / ° C. Deterioration of the magnetic properties, such as accompanying the replacement operation, makes magnetic recording extremely difficult, and has been a major obstacle to practical use.

Further, since it is extremely difficult to realize a homogeneous metamorphic treatment with the one in which only the surface of the magnetoplumbite type ferrite particles as in Japanese Patent Laid-Open No. 62-139123 is metamorphosed, it is extremely difficult to realize a magnetic powder. Has a drawback that the coercive force distribution is wide and that the magnetic properties change with time because the metamorphic portion is chemically unstable. In view of such problems, the object of the present invention is that the saturation magnetization has a high value, and the coercive force is controlled to an appropriate value.
Another object of the present invention is to provide a magnetic powder that exhibits excellent magnetic properties such as a small coercive force distribution and a small temperature coefficient of coercive force, and whose magnetic properties do not change with time.

[0015]

In order to overcome the above-mentioned problems, the inventors of the present invention have conducted intensive studies and found that in the conventional magnetoplumbite ferrite single-phase particles, a part of Fe was replaced with a different element. Without composition formula MM ' _x Fe
_{12 + 2x} O _{19 + 4x} (M is at least one element or combination of elements selected from Ba and Sr, and M ′ is C
and at least one element or combination of elements selected from o, Ni and Zn, x represents a number of 0.2 to 1.5), and a magnetoplumbite structure represented by RS. The magnetic powder composed of single crystal particles having a crystal structure in which the spinel type structure represented by S is laminated in the c-axis direction, and the magnetic powder in which a part of Fe is replaced with a different element have a high saturation magnetization. It was found that the coercive force was controlled to an appropriate value, the coercive force distribution was small, and the temperature coefficient of the coercive force was small, which showed excellent magnetic properties, and the magnetic properties did not change with time.

The magnetic powder of the present invention will be described in detail below. In the composition formula showing the magnetic powder of the present invention, M is Ba
And at least one selected from Sr and M '
Is at least one selected from Co, Ni and Zn, and x represents a number in the range of 0.2 to 1.5. That is, in the ferrite magnetic powder of the present invention, one type selected from Ba and Sr is used as the divalent element (M) that constitutes the magnetoplumbite-type ferrite, and as the element (M ′) that constitutes the spinel-type ferrite. Co, Ni
And at least one selected from Zn is used. When these elements (M, M ′) are used in a ratio that satisfies the above composition formula, a magnetic material having a desired high saturation magnetization can be obtained. This is because it has a crystal structure in which S blocks (spinel structure) having a magnetic moment per unit weight larger than that of RS blocks (magnetoplumbite structure) are inserted and stacked. M'is Co, Ni,
One of the reasons for selecting from Zn is to make the magnetic moment per unit weight of the S block larger than that of the RS block. In addition, the uniaxial anisotropy of particles is reduced by inserting an S block composed of at least one divalent element selected from Co, Ni and Zn and having a large magnetic moment per unit weight. Therefore, the coercive force decreases. At the same time, the temperature dependence of the uniaxial anisotropy also changes, and the temperature coefficient of coercive force decreases. When x is less than 0.2, it is difficult to obtain the desired high saturation magnetization value and temperature stability. Further, when x exceeds 1.5, giant particles that are not hexagonal plate-shaped are mixed in the generated ferrite particles, or the amount of spinel type structure (block) varies among particles, resulting in a large coercive force distribution.

When a lower coercive force of 1500-Oe or less is required, it is preferable to replace part of Fe with an equal amount of a different element. As a substituting element, S to be inserted
Co, Ni, which is a divalent metal element constituting the block,
A combination of Zn and Ti which is a tetravalent non-magnetic element so as to be trivalent on average [Co _y1 Ni _y2 Zn _y3 Ti
_y (y ₁ + y ₂ + y ₃ = y)] is preferable. This is because the saturation magnetization value of the magnetic powder is not reduced. Regarding the amount of substitution, the value of y must be 1 or less when 2 y mol of Fe is substituted per composition formula. This is because when the value of y exceeds 1, the uniaxial anisotropy of single crystal particles is lost. When the value of y exceeds 1, the uniaxial anisotropy of the single crystal particles is lost and the coercive force required for magnetic recording cannot be obtained.

The magnetic powder of the present invention generally contains from 0.01 to
It has an average particle size of 0.2 μm. In order to inexpensively supply the magnetic powder of the present invention, for example, it is preferable to base the coprecipitation-firing flux method disclosed in JP-A-64-5914. However, in the magnetic powder of the present invention, the uniformity of each particle is particularly severely required, and therefore some measures must be taken to obtain the desired magnetic powder with good reproducibility and reliability.

That is, as the raw material aqueous solution, M,
An aqueous solution prepared by dissolving M ′, Fe and a water-soluble salt of Fe and a substitution element of Fe, preferably chloride in pure water at a desired mixing ratio, and an alkali and an alkali carbonate in excess of equivalents, preferably sodium hydroxide. Prepare an aqueous solution prepared by dissolving and sodium carbonate. By mixing these, a coprecipitation reaction occurs and a precursor is obtained. At this time, unless special attention is paid to the mixing method, it becomes difficult to obtain magnetic powder having desired uniformity with good reproducibility. The present inventors have found that it is possible to obtain magnetic powder having desired uniformity with good reproducibility by continuously mixing both liquids using a line mixer. It is difficult to obtain a uniform precursor by the droplet dropping or simultaneous mixing suggested by JP-A-64-5914 for the following reason. In the dropping of droplets, the pH changes with the progress of the reaction, and the conditions are different in the early and late stages of the reaction. Further, in the simultaneous mixing, since the mixing conditions depend on the reaction tank used and the stirring device, it is difficult to expect reproducibility when changing them, and in the present invention particularly when production on an industrial scale is assumed. Obtaining the required uniformity is virtually impossible. By continuously supplying both solutions to the line mixer, the coprecipitation reaction field can be limited within the line mixer, and the pH value during the coprecipitation reaction can be kept constant, so that a uniform precursor can be obtained. You can get it.

The liquid temperature during the reaction is from room temperature to 75
Temperatures up to about ° C are preferred. The pH value of the obtained alkaline suspension is adjusted to 7 to 10 with a dilute acid, preferably hydrochloric acid, and then filtered and dried to recover a solid. This solid substance contains a neutral salt mainly composed of NaCl generated during the coprecipitation reaction and pH adjustment, and heat treatment at 750 to 950 ° C. for about 0.5 to 10 hours with the neutral salt coexisting. After crystallizing the ferrite by applying
The magnetic powder of the present invention can be obtained by washing and removing impurity salts such as 1 and drying.

As a conventional technique in which a magnetoplumbite type ferrite and a spinel type ferrite are allowed to coexist in some form, there are magnetic powders disclosed in JP-A-56-118304 and JP-A-56-118305. However, this magnetic powder is for a magnetic card which originally requires a coercive force of 1,000-Oe or more, and has a technical problem completely different from that of the present invention. Furthermore, since this magnetic powder is supplied by a dry method using an oxide as a starting material and undergoes a pulverizing step, it is not a single crystal particle having a hexagonal plate shape and has an average particle size of 0.6 to 0. 7
It is as coarse as μm, which is completely different from the ferrite particles specified in the present invention.

It is also part of the main objective of the invention,
As a conventional technique for improving the temperature stability of the coercive force of hexagonal plate-shaped ferrite particles for magnetic recording, Japanese Patent Laid-Open No. 62-1391 has been proposed.
The plate-like Ba ferrite fine particles disclosed in Japanese Patent No. 24 are listed as BaO.n {(Fe _{1-a Ra} ) ₂ O ₃ } (4 ≦ n
≦ 6, 0 <a ≦ 0.2, R represents a divalent metal ion other than Co (II), Ti (IV) or Co (II))
o Ferrite (Co ²⁺ _x Fe ²⁺ _y · Fe ₂ O ₃ , provided that
O <x ≤ 1, 0 ≤ y <1, 0 <x + y ≤ 1) is used for the transformation, that is, the magnetoplumbite ferrite single-phase magnetic powder is used, and only the particle surface is modified to obtain the magnetic properties. In order to improve the characteristics, the magnetoplumbite type structure (RS block) and the spinel type structure (S block) are c-axis without using the magnetoplumbite type ferrite single phase magnetic powder of the present invention. The technical idea is completely different from the single crystal ferrite particles having a crystal structure laminated in the direction.

Since it is extremely difficult to carry out the surface modification uniformly, the coercive force distribution of the surface-modified magnetic powder as described in the above-mentioned patent publication is large, but a simple composition having the composition and structure defined in the present invention is used. The coercive force distribution of the magnetic powder composed of crystalline particles is small and is equivalent to the coercive force distribution of the magnetic powder composed of magnetoplumbite type ferrite single phase particles. Further, in the above-mentioned patent publication, there is no description about the change with time of magnetic characteristics, but the magnetic powders described in the examples contain divalent Fe ²⁺ , and the final step is 100 ° C. at most.
Since it is a hot water treatment of a certain degree, it is chemically extremely unstable, and it is unavoidable that the magnetic characteristics deteriorate with the passage of time. In contrast to this, the ferrite particles of the present invention do not contain divalent Fe ²⁺ and undergo a heat treatment at 750 ° C. or higher in the final step, so that they are chemically very stable and have a magnetic characteristic. The problem of aging does not occur.

A similar case is disclosed in JP-A-62-265122,
JP-A-62-265123, JP-A-63-14411
7, JP-A-63-144118, JP-A-63-1441
19 and JP-A-63-144120, all of which utilize magnetoplumbite-type ferrite single-phase particles and modify or modify only the particle surface. The specified magnetic powder can be clearly discriminated. Incidentally, JP-A-63-
In the claims of Japanese Patent No. 252930, "Hexagonal ferrite magnetic powder characterized by containing a magnetoplumbite type crystal structure phase and a spinel type crystal structure phase"
However, it is only described that the surface of the magnetoplumbite type ferrite single phase particles is modified in the Examples, and the magnetoplumbite / spinel like the magnetic powder of the present invention is described. No laminated structure is suggested.

Further, Japanese Patent Laid-Open No. Sho 6-26 previously proposed by the present inventors.
In the magnetic powder described in Japanese Patent Publication No. 4-5914, since the spinel structure is too large in proportion, the saturation magnetization has a high value, but it is extremely difficult to reduce the coercive force distribution.

[0026]

The magnetic powder of the present invention exhibits higher saturation magnetization than the magnetoplumbite single-phase particles because the S block (spinel type structure) has a larger magnetic moment per unit weight than the RS block (magnetoplumbite structure). This is because it has a crystal structure in which is inserted. C
The uniaxial anisotropy of the particles is reduced by inserting an S block composed of at least one divalent element selected from o, Ni and Zn and having a large magnetic moment per unit weight, so that the coercive force is reduced. Decreases, and at the same time, the temperature coefficient of coercive force decreases. In particular, since the amount of S block inserted is 0.2 or more as the value of x in the composition formula, the temperature coefficient is sufficiently small in practical use. The value of x in the composition formula is 1.
Since it is 5 or less, the coercive force distribution does not become large.
Part of Fe in the magnetic powder is a different element, especially S that is inserted.
Co, Ni, which is a divalent metal element constituting the block,
The coercive force is controlled to a further lower value by substituting Zn and Ti, which is a tetravalent non-magnetic element, so as to be trivalent on average.

[0027]

EXAMPLES The magnetic powder of the present invention will be specifically described below with reference to examples. Example 1 0.1 mol of BaCl ₂ .2H ₂ O, CoCl ₂ .6H ₂
O 0.1 mol, ZnCl ₂ 0.055 mol, NiCl ₂
An aqueous solution of 0.025 mol of 6H ₂ O, 0.08 mol of TiCl ₄ and 1.24 mol of 1.24 mol of FeCl ₃ .6H ₂ O dissolved in 3 liters of distilled water and NaOH 6.
Mol and an aqueous solution of 0.1 mol of Na ₂ CO ₃ dissolved in 3 liters of distilled water were mixed using a line mixer to obtain a coprecipitate slurry. 1N-HCl was added dropwise to this alkaline slurry to adjust the pH to 9.0, followed by filtration, drying and pulverization to obtain a coprecipitate fine powder containing NaCl. This powder was heat treated in air at 820 ° C. for 2 hours and then washed with distilled water to obtain NaC.
Impurity salts such as 1 are removed, filtered and dried to obtain the composition formula BaC.
Magnetic powder consisting of single crystal particles represented by oNi _0.25 Zn _0.55 Ti _0.8 Fe _12.4 O ₂₃ was obtained.

As a result of observing this magnetic powder with a transmission electron microscope, the average particle diameter was 0.06 μm. High-resolution observation of one of the grains confirmed that it was a single crystal grain having a structure in which the RS block and the S block were laminated in the c-axis direction. When the magnetic characteristics of this magnetic powder were measured by VSM (maximum applied magnetic field 10 kOe), it was 10 kOe.
Value was 60.0 emu / g, coercive force was 800-Oe, and the temperature coefficient of coercive force from 20 ° C to 120 ° C was 0.3-Oe / ° C. The magnetic properties did not change over time. The value of S ^* , which is an index of the coercive force distribution, was 0.62 in the non-oriented coating film.

Examples 2 to 6 Magnetic powder was produced in the same manner as in Example 1 except that the compounding ratio of the metal chloride was adjusted to the composition shown in Table 1, and the characteristics were measured. The characteristics are as shown in Table 1.

Comparative Example A metal chloride aqueous solution was added with 0.1 mol of BaCl ₂ .2H ₂ O,
CoCl ₂ .6H ₂ O 0.08 mol, TiCl ₄ 0.0
A composition formula BaCo _0.8 Ti _0.8 Fe _10.4 O was obtained by performing the same operation as in Example except that 8 mol and 1.04 mol of FeCl ₃ .6H ₂ O were dissolved in 3 liters of distilled water.
Magnetic powder consisting of single crystal particles shown by ₁₉ was obtained.

As a result of observing this magnetic powder with a transmission electron microscope, the average particle diameter was 0.06 μm. As a result of high resolution observation of one of the grains, it was confirmed to be a single crystal grain having a magnetoplumbite type structure composed of only the RS block. When the magnetic characteristics of this magnetic powder were measured by VSM (maximum applied magnetic field 10 kOe), the magnetization value at 10 kOe was 59.5 emu / g, and the coercive force was 8
It was 70-Oe, and the temperature coefficient of coercive force from 20 to 120 ° C was 3.9-Oe / ° C. The magnetic properties did not change over time. The value of S ^* , which is an index of the coercive force distribution, was 0.67 in the non-oriented coating film.

[0032]

INDUSTRIAL APPLICABILITY The magnetic powder composed of single crystal particles having a structure in which the RS block (magnetoplumbite type structure) and the S block (spinel type structure) of the present invention have a high saturation magnetization and a coercive force. Is controlled to an appropriate value, the coercive force distribution is small, and the temperature coefficient of the coercive force is small, showing excellent magnetic characteristics, and the magnetic characteristics do not change with time. Therefore, this magnetic powder is most suitable for high density magnetic recording.

[0033]

[Table 1]

Claims (3)

[Claims] 1. A composition formula MM ' _x Fe _{12 + 2x} O _{19 + 4x} (M
Is at least one element or a combination of elements selected from Ba and Sr, and M ′ is Co, Ni and Zn.
At least one element or a combination of elements selected from x is represented by 0.2 to 1.5),
A magnetic powder for magnetic recording comprising a single crystal particle having a structure in which a magnetoplumbite structure (RS block) and a spinel structure (S block) are laminated in the c-axis direction. 2. A composition formula wherein 2y (y represents a number of 1 or less) moles of Fe is _added to Co _y1 Ni _y2 Zn _y3 Ti _y (y ₁ + y).
_{2. The} magnetic powder for magnetic recording according to claim 1, wherein the magnetic powder for magnetic recording is replaced by an equivalent amount of a hetero element represented by ₂ + y ₃ = y) and having an average of trivalence. 3. The magnetic powder for magnetic recording according to claim 1, which has an average particle size of 0.01 to 0.2 μm.