JPH01164008A - Magnetic powder for high density magnetic recording and magnetic recording medium employing same - Google Patents

Abstract

PURPOSE:To suitably enlarge an aspect ratio and to remarkably decrease the temperature dependency of a coercive force, by substituting a predetermined amount of Zr or Hf, and other elements for controlling the valency number, for a part of Fe as a constitutive element. CONSTITUTION:At least one kind of elements which are selected from Zr and Hf which have the number of atoms of 0.05-0.5per chemical formula, and at least one kinds of elements which are selected from the elements other than Zr and Hf, are substituted for Fe atoms contained in a substitute hexagonal system ferrite which has an average particle size of 0.01-0.2mum and a coercive force of 200-2000Oe. On the other hand, for the magnetic recording medium employing the magnetic powder described above, the magnetic powder is coated on the surface of a supporting body. When the average particle size of the uniaxial anisotropy of hexagonal system ferrite crystal is less than 0.02mum, both the magnetization and coercive force are reduced, and therefore the play back output of the magnetic recording medium is lowered, while when the average particle size thereof is above 0.2mum, the coercive force is reduced and the noise in playback is remarkably increased during high density recording.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic powder for high-density magnetic recording and a magnetic recording medium using the same.

(Prior Art) A coated or cloth-type magnetic recording medium is composed of a non-magnetic support such as polyethylene terephthalate, and a magnetic layer provided on the support, the main components of which are magnetic powder and a resin binder. There is.

Conventionally, γ-Fe20 is used as magnetic powder for magnetic recording.
, CrO, Co-'y-Fe203, and other acicular magnetic powders have been widely used.

On the other hand, in recent years, in order to significantly improve magnetic recording density, there has been a strong desire for magnetic recording media that can perform perpendicular magnetization recording, and ultrafine particle magnetism of hexagonal ferrite is a suitable magnetic recording medium for this purpose. Research has been done on using powder,
It has been found that high density recording is possible.

In addition, some of the Fe atoms in the hexagonal ferrite are replaced with a divalent element such as Co, a tetravalent element selected from TI and Ge, or a 5-valent element selected from V, Nb%sb and Ta.
Magnetic powder for high-density magnetic recording substituted with valent elements is also known (US Pat. No. 4,341.848).

(Question to be solved by the invention) By the way; in the above-mentioned hexagonal ferrite, in order to improve the vertical orientation, it is better to have the platelet ratio (particle size/thickness) of the particles as large as possible. When the plate ratio is increased, the packing density when used as a medium decreases, and the saturation magnetization of the magnetic powder also decreases, so the plate ratio is approximately 3.5 to 3.5.
It is necessary to control it within the range of 5.0.

Furthermore, even in a magnetic recording medium using the above-mentioned hexagonal ferrite as magnetic powder, its magnetic properties must be stable against temperature changes. In other words, if the magnetic properties change significantly with temperature, the recording and reproducing characteristics of the magnetic recording medium will vary significantly with changes in the ambient temperature during use, causing a practical problem.

However, magnetic recording media using hexagonal ferrite are
Even around room temperature, the coercive force (Hc) value shows a characteristic temperature change in that it increases as the temperature rises. Therefore, from a practical standpoint, the development of hexagonal ferrite with excellent temperature stability is desired. Ta.

In response to these conventional circumstances, the present inventors have conducted various studies on methods for controlling the plate ratio of hexagonal ferrite within an appropriate range and improving the temperature stability of coercive force (He). As a result, by replacing a part of the purchased element Pe with a predetermined amount of 2' or Hf' and other elements for valence adjustment, the plate ratio becomes moderately large.
We also found that the temperature dependence of coercive force was significantly reduced.

The present invention has been made based on this knowledge, and includes a magnetic powder for high-density magnetic recording in which the platelet ratio of particles is increased within an appropriate range and temperature characteristics are improved, and a magnetic recording medium using the same. is intended to provide.

[Structure of the Invention] (Means for Solving the Problems) The magnetic powder for high-density magnetic recording of the present invention has an average particle size of 01 mm.
μa+ ~0.2μm, coercive force 200Oe~2000
a substituted hexagonal ferrite having Oe, the Fe atom of the substituted hexagonal ferrite is at least one element selected from Zr and H in the number of atoms per chemical formula of 0.05 to 0.5. Zr and Hf'
and at least one element selected from other elements, and a magnetic recording medium using the magnetic powder is characterized in that the magnetic powder is coated on the surface of a support. It is characterized by “.

Examples of the hexagonal ferrite used in the present invention include M type (Magnetoplus ferrite type).
, W-type uniaxially anisotropic hexagonal Ba ferrite, sr ferrite, Pb ferrite, Ca ferrite, or a part of Ba in Ba ferrite with other Sr, pb, C
Examples include uniaxially anisotropic ferrites such as those substituted with a or ion-substituted products thereof.

In the present invention, the average grain size of the hexagonal ferrite crystals with -axis anisotropy is limited to the range of 0.02 μm to 0.2 μm because magnetization and coercive force decrease below 0.02 μm. As a result, the reproduction output of the magnetic recording medium decreases, and conversely, the reproduction output of the magnetic recording medium decreases to 0.
This is because if the amount exceeds 2 μl, the coercive force decreases and noise during reproduction becomes significant during high-density recording.

Moreover, the reason why the coercive force is limited to the range of 200 Oe to 2000 Oe is because if it is less than 200 Oe, the recording medium will not have sufficient green signal remaining, and if it exceeds 20000 Oe, it will not be possible to record or reproduce the recording medium made of ferrite, sendust, amorphous alloy, etc. This is because it becomes difficult for the head to record and erase signals.

As a means for reducing the coercive force in the present invention, for example, a method of substituting a part of the constituent element Fe with the following divalent to hexavalent metals is used, but in particular, the combination of Co and TI is used. and a combination of Co and Nb is preferred.

Bivalent --- Co, NI, Zn trivalent...
・Mn, In quadrivalent・---・TI, 5nSGe pentavalent・・・・・・vSNb1Sb1Ta hexavalent・・・・・・
・Cr, MoSne These elements are replaced with trivalent Fe ions, so
In order to match the valence of the Fe atom to be replaced with 3, it is necessary to use them in combination so that the average valence becomes 3. And the amount of substitution per chemical formula of these substitution elements is 2
Although it varies depending on the valence and the combination of tetravalent to hexavalent metal elements, the number of atoms per 1 chemical formula is suitably 0.2 to 1.2.

In the present invention, Fe atoms of hexagonal ferrite are
It is substituted with at least one element selected from Zr and H in an amount of 0.05 to 0.5 atoms per 1 chemical formula, and is represented by the following general formula.

AFe Ha Mb 0 12-x-y x y 19 (wherein, A is at least one element selected from Ba5SrSPb and Ca, and Ha is Co, ZnSNi
, In, Mn.

Ti5Sn, Ge5V 5NbSSb, Ta, C
Mb represents at least one element selected from r, No and V; Mb represents at least one element selected from Zr and Iff; X and y are 0.2≦X≦1.2.0. 05≦y≦0.5. ) In the magnetic powder of the present invention, the appropriate range of the substitution amount of the element selected from Zr and Hf' is 0.05 to 0.5 in number of atoms per chemical formula, because the substitution amount is 0.05 to 0.5. 05
If it is less than 0.5, the magnitude of the plate ratio and the temperature dependence of coercive force (He) will not be sufficiently improved, and if it exceeds 0.5, the saturation magnetization of the magnetic powder will drop significantly, making it difficult to use it as a magnetic recording medium. This is because proper output characteristics cannot be obtained.

In addition, since Zr and Hf are tetravalent elements, it is not possible to replace the Pc atom of hexagonal ferrite with these elements alone, and when combined with the other replacement elements mentioned above, the average valence as a whole increases. It is necessary to adjust it so that it is trivalent.

Suitable substituted hexagonal ferrites of the present invention include two types of substituted hexagonal ferrites represented by the following general formulas.

APe MaT-HaWMb 012-2x
x x-y y 19 (in the formula, ^ is Ba,
At least one element selected from Sr, pb, and Ca, MaIC at least one element selected from Co, Ni, and Zn, and MaM at least one element selected from TI and Sn.

At least one element selected from Ge, Mb is Z
At least one element selected from r and llf is shown, and X and y are 0.2≦X≦1.2.0.05≦y≦0.5. ) (In the formula, A is at least one element selected from Bas 5rSPb and Ca, and Mal is Co, Ni
q At least one element selected from Zn, Ma
T is Nb, Sb.

At least one element selected from Ta, Mb is Z
and H, respectively, and X and y are 0.2≦X, 51.2.0.05≦y≦0.5.

) Among these, Co is particularly suitable for Haπ, TI for MaW, and Nb for Mar.

The method for producing the magnetic powder of the present invention includes, for example, melting oxides, carbonates, etc. of each element necessary to form the desired hexagonal ferrite together with a glass-forming substance such as boric acid; The obtained melt is rapidly cooled to form a glass, then this glass is heat-treated at a predetermined temperature to precipitate the desired hexagonal ferrite crystal powder, and finally the glass component is removed by heat treatment to form a hexagonal ferrite. In addition to the glass crystallization method for obtaining the ferrite-based ferrite, a coprecipitation-calcination method, a hydrothermal method, etc. can be applied.

However, among these methods, the glass crystallization method is particularly suitable for the present invention in view of the characteristics of the magnetic powder produced.

The hexagonal ferrite magnetic powder of the present invention is usually applied together with a binder resin to the surface of a support made of a plastic film such as a polyester film or a metal plate such as an aluminum plate to form a magnetic recording medium.

Binder resins that constitute the magnetic layer together with the magnetic fine particles include, for example, vinyl chloride-vinyl acetate copolymers, vinylidene chloride copolymers, acrylic ester copolymers, polyvinyl butyral resins, polyurethane resins, and cellulose derivatives. , epoxy resin, or a mixture of these with 2FR or more is used.

Further, in addition to the magnetic powder and binder resin described above, additives such as a dispersant, a lubricant, an abrasive, an antistatic agent, and the like can be appropriately contained in the magnetic layer as necessary.

(Function) The magnetic powder for high-density magnetic recording of the present invention has an average particle size of 0.02
Since it is μIn~0.2 μm, it has sufficient reproduction output when used as a magnetic recording medium, and noise during reproduction of high-density magnetic recording is small.

Also, for example, some of the constituent Fe atoms may be replaced with Co.
- By replacing with Tl etc., the coercive force can be increased to 200 Oe ~
Since it is set to 2000 Oe, a recording signal remains sufficiently, and the signal can be recorded and erased using a normal magnetic head.

Furthermore, the Pc atoms of the hexagonal ferrite are
At least one element selected from Zr and 11
Since it is substituted with at least one element selected from elements other than f, the plate-like ratio of the particles is appropriately increased, and not only is the effect of improving the media output due to vertical alignment, but also the coercive force is increased. Temperature dependence is reduced, allowing stable recording and playback even when the environmental temperature changes.

(Example) Next, examples of the present invention will be described.

Examples 1-6 Chemical formula Babe Co TI M
O(M=Zr,l1f)12-x x x-y
Ba ferrite magnetic powder in which X in y19 was set to 0.85 and H atom substitution ff1y was controlled in the range of 0.05 to 0.50 was produced by the glass crystallization method as follows.

First, Fe2O3, C
od, TiO5ZrO (or) If'02) were added at the same time, melted at 1350°C, and rapidly cooled by rolling to produce a glass containing the above components.

Next, this glass was heated at 800° C. for 4 hours to precipitate Ba ferrite substituted with C01TiSZr (or 1(r)) in the matrix.

Finally, this glass was washed with acetic acid to obtain Ba ferrite magnetic powder. The obtained magnetic powder was fine particles with a particle size of approximately 0.1 μm.

Next, using these Ba ferrite particles, a magnetic paint having the following composition was prepared (where parts indicate parts by weight).

Ba ferrite particles 100 parts Vinyl chloride-vinyl acetate copolymer 10/・Polyurethane
10 Aluminum oxide
2 // Lubricant
1.5” Dispersant (lecithin)
2 No I methyl ethyl ketone 70/l
Toluene 70/l cyclohexanone 401/hardening agent
5 // The paint thus obtained was applied onto a polyethylene terephthalate film with a thickness of 15 μm, vertically aligned in a 5KOe magnetic field, dried in a magnetic field, and then calendered and slit processed. A magnetic tape was manufactured by forming a magnetic layer with a thickness of 3.5 μm.

The plate ratio of each magnetic powder thus produced, the coercive force (He) and saturation magnetization (σ) at room temperature of each magnetic tape produced using these magnetic powders, and 20°C to 100°C.
Temperature change in coercive force (He) between ΔHe/ΔT1
The electromagnetic characteristics of the medium were measured. The measurement results are shown in Table 1.

In addition, the comparative examples in the table are magnetic powders and magnetic tapes manufactured in the same manner as in the above examples except that in the general formula described above, y is O, which is outside the range of the present invention, and 80. This is shown for comparison with the present invention.

(Left below) Examples 7 to 12 In the chemical formula, X is 0.85, and the substitution my of the X atom is 0.0.
Sr ferrite magnetic powder controlled in the range of 5 to 0.50 was mixed with B O-8rO glass and Pc0qCoOsNbO1, which was formulated to constitute the above Sr ferrite composition.
Magnetic powder was produced by glass crystallization using Zr02 (or HfO2) under the same conditions as in Example 1.

Further, a magnetic tape was produced in the same manner as in Example 1 using these magnetic powders.

The properties of these magnetic powders and magnetic tapes were also measured in the same manner as in Example 1. The results are shown in Table 2.

Note that the comparative examples in the table were also produced under the same conditions as the above-mentioned comparative examples.

(The following is a blank space) [Effects of the Invention] As is clear from the above examples, the magnetic powder of the present invention has a fine particle size, a moderately large plate-like ratio, and is capable of high-density recording through vertical orientation. In addition, the temperature characteristics of coercive force (He) are improved without reducing the magnetization of the medium, effectively improving the electromagnetic conversion characteristics of magnetic powder for high-density magnetic recording and recording media using it. and the temperature characteristics of coercive force can be improved.

Applicant: Toshiba Corporation Agent Patent Attorney Suyama Sa

Claims (1)

[Claims] (1) Average particle size 0.02 μm to 0.2 μm, coercive force 20
It consists of a substituted hexagonal ferrite having 0 Oe to 2000 Oe, and the Fe atom of the substituted hexagonal ferrite is
At least one element selected from Zr and Hf having an atomic number of 0.05 to 0.5 per chemical formula and Z
A magnetic powder for high-density magnetic recording, characterized in that it is substituted with at least one element selected from elements other than r and Hf. (2) The substituted hexagonal ferrite is AFe_1_2_−_2_xMa^II_xMa^IV_x
_-_yMb_yO_1_9 (wherein A is Ba, Sr,
At least one element selected from Pb and Ca,
Ma^II is at least one selected from Co, Ni, and Zn
Ma^IV represents at least one element selected from Ti, Sn, and Ge; Mb represents at least one element selected from Zr and Hf; x and y are 0. 2≦x≦1.2, 0.05≦y≦0.5. )
The magnetic powder for high-density magnetic recording according to claim 1, characterized in that it is represented by: (3) The substituted hexagonal ferrite is AFe_{_1_2_-_(_(_3_/_2_)_+
＿(＿１＿／＿２＿)＿y＿）＿｝Ma＾II_xMa＾
V_(_x_−_y_)_/_2Mb_yO_1_9(
In the formula, A is at least one element selected from Ba, Sr, Pb, and Ca, Ma^II is at least one element selected from Co, Ni, and Zn, and Ma^V is Nb,
At least one element selected from Sb and Ta, Mb
represents at least one element selected from Zr and Hf, and x and y are 0.2≦x≦1.2, 0.05≦y≦0.5. )
The magnetic powder for high-density magnetic recording according to claim 1, characterized in that it is represented by: (4) The magnetic powder for high-density magnetic recording according to any one of claims 1 to 3, wherein the substituted hexagonal ferrite is produced by a glass crystallization method. (5) Average particle size 0.01 μm to 0.2 μm, coercive force 20
0 Oe to 2000 Oe, the Fe atoms of the substituted hexagonal ferrite have Z of 0.05 to 0.5 in number per chemical formula.
At least one element selected from r and Hf and Zr
and at least one element selected from elements other than Hf, which is coated on the surface of a support. (6) The substituted hexagonal ferrite is AFe_1_2_-_2_xMa^II_x_-_yMa
^IV_x_-_yMb_yO_1_9 (in the formula, A is Ba
, Sr, Pb, and Ca, Ma^II is at least one element selected from Co, Ni, and Zn, and Ma^IV is Ti, Sn, and Ge. At least one element, Mb, Zr and H
each represents at least one element selected from f,
x and y are 0.2≦x≦1.2, 0.05≦y≦0.5. )
6. The magnetic recording medium according to claim 5, wherein the magnetic recording medium is represented by: (7) The substituted hexagonal ferrite is AFe_{_1_2_-_(_(_3_/_2_)_x
＿＋＿(＿１＿／＿２＿）＿y＿｝Ma＾II_xMa＾
V_(_x_−_y_)_/_2Mb_yO_1_9(
In the formula, A is at least one element selected from Ba, Sr, Pb, and Ca, Ma^II is at least one element selected from Co, Ni, and Zn, and Ma^V is Nb,
At least one element selected from Sb and Ta, Mb
represents at least one element selected from Zr and Hf, and x and y are 0.2≦x≦1.2, 0.05≦y≦0.5. )
6. The magnetic recording medium according to claim 5, wherein the magnetic recording medium is represented by: (8) The magnetic recording medium according to any one of claims 5 to 7, wherein the substituted hexagonal ferrite is produced by a glass crystallization method.