JPH05159263A - Magnetic recording medium - Google Patents

Abstract

(57) [Abstract] [Purpose] For magnetic recording media such as magnetic tapes or magnetic disks used in computers and the like, solving the problem of high cost of substrate materials such as polymer substrates, and solving various substrate materials. A magnetic recording medium having excellent magnetic characteristics and inexpensive is obtained by forming the combined magnetic layers. [Structure] Co and Cr or C in order from the polymer substrate 4 side
First magnetic layer 11 containing o, Cr and Ni as main components
And a second magnetic layer containing Co and O or Co, Ni and O as main components, and the coercive force x (Oe) in the in-plane direction of the first magnetic layer 11 is 200 or more. Magnetic layer 12
The coercive force in the film in-plane direction is larger than the coercive force in the first magnetic layer 11 only, and the coercive force in the film in-plane direction after lamination is (-9 / 20x + 340)
% Or more. [Effect] It is possible to obtain excellent recording / reproducing characteristics according to the material of the inexpensive polymer substrate used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium comprising a laminated thin film such as a magnetic tape used in audio equipment, video equipment or the like or a magnetic disk used in computers or the like.

[0002]

2. Description of the Related Art With the progress of information society, information recording carriers have been increased in capacity and density. Also in the field of magnetic tapes, research and development aiming at increasing the density of recording media have been actively conducted, and some thin film media have been proposed to meet this demand. Co-Cr and the like have been widely studied as an ultra-high density magnetic recording material.
Research and development using (Ni-Cr thin film) and the like are being conducted.
In addition, a recording medium (hereinafter referred to as “2”) in which a magnetic Co—O (or Co—Ni—O thin film) is laminated on a Co—Cr thin film
A layered medium) is also being researched to achieve both recording density characteristics and practical durability.

Further, as a method for producing these thin film magnetic recording media, the continuous winding vacuum vapor deposition method is particularly superior in productivity and is very effective as a practical mass production method.

FIG. 2 shows an outline of a vapor deposition apparatus for manufacturing a magnetic recording medium. As shown in FIG.
The long polymer substrate 4 unwound from the unwinding roll 3 in the rotation direction shown by the arrow in the vacuum chamber 2 evacuated by is formed along the circumferential surface of the cylindrical can 5 for forming the magnetic layer. After the electron beam evaporation source 7 which is being irradiated with the electron beam 6 during the traveling receives the vapor deposition of the magnetic layer from the opening 9 of the mask 8, the magnetic layer is taken up by the take-up roll 10 to manufacture a magnetic tape. For example, Co—Cr may be used as an evaporation material in forming the Co—Cr magnetic thin film, and Co may be formed in an oxygen atmosphere in forming the Co—O thin film.
Can be evaporated.

[0005]

However, the optimum structure of the two-layer structure medium has not been fully clarified, and the structure of the medium for realizing high C / N has been demanded. Further, in practical use of a thin film type magnetic recording medium, it is important to keep the material cost low as well as the characteristics of the medium. Polymer substrates account for a large proportion of the material cost, and inexpensive substrate materials are required. Polyamide or polyimide substrates have been used so far in Co-Cr based magnetic recording media formed by vacuum deposition.
These ultra-heat-resistant polymer substrates are expensive, and a medium design using a relatively inexpensive polyethylene naphthalate substrate or a more inexpensive polyethylene terephthalate substrate was also necessary for practical use.

The present invention is intended to solve such a problem, and an object of the present invention is to provide a magnetic recording medium having excellent recording and reproducing characteristics by forming a magnetic layer according to the type of polymer substrate material. To do.

[0007]

In order to achieve the above object, the present invention provides a magnetic recording medium having a magnetic layer directly on a polymer substrate or via an underlayer, in which the magnetic layers are sequentially arranged from the polymer substrate side. A first magnetic layer containing Co and Cr or Co, Cr and Ni as main components, and a second magnetic layer containing Co and O or Co, Ni and O as main components. The coercive force x in the in-plane direction of the first magnetic layer when removed is 200 oersteds or more, and the coercive force in the in-plane direction of only the second magnetic layer is in the in-plane direction of only the first magnetic layer. Is larger than the coercive force of the first magnetic layer in the in-plane direction of the first magnetic layer (−).
9 / 20x + 340)% or more.

[0008]

Therefore, according to the present invention, by strengthening the magnetic coupling between the first magnetic layer and the second magnetic layer, the noise from the first magnetic layer can be reduced and a high C / N can be obtained. it can.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
Will be explained. As shown in FIG. 1, a Co-Cr having a saturation magnetization of 550 emu / cc was formed as a first magnetic layer 11 on a supporting substrate 4 made of a polymer substrate by an electron beam evaporation method.
Layers were formed. Subsequently, a Co—O layer was formed as the second magnetic layer 12 by an electron beam evaporation method to obtain a magnetic recording medium (hereinafter referred to as a medium). The saturation magnetization of the second magnetic layer 12 is also 550 emu / cc. The obtained medium was cut into a tape and the recording / reproducing characteristics were evaluated with a ring head. The relative speed between the medium and the ring head was 3.8 m / s. The carrier (C) and noise (N) levels were measured under the above conditions. The measurement bandwidth was 30 KHz.
The coercive force was measured by a vibrating sample magnetic force system.

In FIG. 3, the peripheral surface temperature of the cylindrical can 5 and the coercive force in the film surface direction when the peripheral surface temperature of the cylindrical can 5 is changed to form only the first magnetic layer 11 (Co-Cr). (Hc ₁ in the figure or table). In the present invention, the coercive force in the in-plane direction of the film is an in-plane coercive force in the traveling direction of the polymer substrate 4 (direction orthogonal to the substrate width direction). In FIG. 3, a circle indicates a case where a polyethylene terephthalate substrate is used, a triangle indicates a case where a polyethylene naphthalate substrate is used, and a square indicates a case where a polyimide substrate is used. At the same peripheral surface temperature, the same coercive force is obtained regardless of which substrate is used, but when the polyethylene terephthalate substrate is used, the peripheral surface temperature of the cylindrical can 5 is 60 ° C. The molecular substrate 4 was thermally damaged, and the surface of the film became rough so that the film could not be stably formed. Further, when the peripheral surface temperature was 70 ° C., the heat damage to the polymer substrate 4 was more severe, and film formation was impossible. Further, when a polyethylene naphthalate substrate is used, when the peripheral surface temperature is 120 ° C., the polymer substrate 4 is thermally damaged during vapor deposition,
The surface of the film became rough and it was not possible to form a stable film. Further, when the peripheral surface temperature was 130 ° C., the heat damage to the polymer substrate 4 was more serious, and film formation was impossible. On the other hand, when the polyimide substrate was used, film formation was possible up to a peripheral surface temperature of 300 ° C. Therefore, in the case of a polyethylene terephthalate substrate, the coercive force within the film surface of the first magnetic layer 11 is 300 oersted or less, and in the case of a polyethylene naphthalate substrate, it is 400 oersted or less. Optimal design of the medium in is required.

FIG. 4 shows the film of the entire laminated film after forming the second magnetic layer 12 (Co-O) to a thickness of 80 nm on the coercive force of the first magnetic layer 11 (Co-Cr) as a parameter. The ratio of the in-plane coercive force (denoted as Hc ₂ in the figure or in the table) to the coercive force of the first magnetic layer 11 and the recording wavelength of 0.5 μm.
FIG. 6A is a diagram showing a relationship with a carrier level in m, and FIG. 8B is a diagram showing a relationship with a noise level. In FIG. 4, 200% on the horizontal axis means that the in-plane coercive force after lamination is twice the coercive force of the first magnetic layer 11. The peripheral surface temperature of the cylindrical can 5 when forming the Co—O layer is 20 ° C., and the second magnetic layer 12 is formed directly on the polymer substrate 4 without providing the first magnetic layer 11. Has a coercive force of 1400 Oersted. The in-plane coercive force of the laminated film was adjusted by changing the film thickness of the first magnetic layer 11. As can be seen from FIGS. 4A and 4B, the noise level decreases as the rate of increase of the in-plane coercive force after lamination increases, and the in-plane coercive force 400 of only the first magnetic layer 11 increases. 160% for Oersted, 200% for 300 Oersted, 250 for 200 Oersted
%, The noise reduction is almost saturated. On the other hand, when the in-plane coercive force of only the first magnetic layer 11 is 100 oersted, the degree of increase in coercive force due to stacking has almost no effect on noise. Further, generally, the larger the in-plane coercive force of the first magnetic layer 11 is, the smaller the noise of the laminated medium is. Therefore, it is desirable that the in-plane coercive force of the first magnetic layer 11 is as high as possible.

5A and 5B show the in-plane coercive force of 2 when the second magnetic layer 12 is formed directly on the polymer substrate 4.
FIG. 5 shows the results of an experiment similar to FIG. 4 in the case of 000 Oersted. The thickness of the second magnetic layer 12 is 10
It was set to 0 nm. In FIG. 5, the noise level is slightly lower than that of FIG. 4, but in this case as well, the first magnetic layer 1
In the in-plane coercive force of 400 oersted with only 1, 160
%, 300 Oersted at 200%, and 200 Oersted at 250%, the noise reduction is almost saturated. When the in-plane coercive force of only the first magnetic layer 11 is 100 Oersted, the degree of increase in coercive force due to lamination has almost no effect on noise reduction, as in the case of FIG.

Therefore, from the results of FIGS. 4 and 5, when the coercive force in the film in-plane direction after lamination is 250 with respect to the coercive force in the film in-plane direction when only the first magnetic layer 11 is formed, it is 250. It can be seen that it is desirable to have a medium structure in which the content is at least%, in the case of polyethylene naphthalate, at least 200%, and in the case of polyimide, at least 160%.

The reason why a medium with low noise can be obtained when the increase in coercive force after lamination is large is considered as follows. That is, when the second magnetic layer 12 is formed on the first magnetic layer 11, the two magnetic layers are ferromagnetically coupled, and the low coercive force component in the first magnetic layer 11 has a large coercive force. It is restrained by the magnetic layer 12 to have a high coercive force. The degree of high coercive force is determined by the relationship between the two magnetic layers. If the first magnetic layer 11 becomes too thick, the effect of the second magnetic layer 12 becomes small, and many low coercive force components remain as noise sources. The first magnetic layer 11 is distant from the magnetic head, and particularly when the in-plane component thereof has a low coercive force, read noise is likely to occur, and an increase in the in-plane coercive force by the second magnetic layer 12 reduces noise. It is valid.

FIG. 6 shows an in-plane coercive force of 1500 oersted and a film thickness of 100 n when directly formed on the polymer substrate 4.
m of the second magnetic layer 12, 200, 300, and 40
FIG. 6 is a diagram showing the relationship between the film thickness of the first magnetic layer 11 and the coercive force in the in-plane direction of the laminated film when the first magnetic layer 11 is laminated on the 0 Oersted first magnetic layer 11. As can be seen from FIG. 6, as the thickness of the first magnetic layer 11 increases, the coercive force of the laminated film decreases, and FIGS. 4 (a), 4 (b), 5
The coercive force decrease below the in-plane coercive force required for noise reduction in the results of (a) and (b) is caused when the in-plane coercive force of the first magnetic layer 11 is 200, 300, 400 oersted. It occurs at 140, 170, and 200 nm or more, respectively.

FIG. 7 shows an in-plane coercive force of 2000 oersted and a film thickness of 100 n when directly formed on the polymer substrate 4.
m of the second magnetic layer 12, 200, 300, and 40
7 is a diagram showing the relationship between the film thickness 11 of the first magnetic layer and the coercive force in the in-plane direction of the laminated film when the first magnetic layer 11 of 0 Oersted is laminated on the first magnetic layer 11. As in the case, as the first magnetic layer 11 becomes thicker, the coercive force of the laminated film lowers, and as shown in FIGS. 4 (a), 4 (b), 5 (a),
The decrease in coercive force below the in-plane coercive force required for noise reduction in the result of (b) is 180, when the coercive force in the in-plane direction of the first magnetic layer 11 is 200, 300, 400 oersted, respectively. Occurs above 200,210 nm.

Therefore, in order to realize the magnetic recording medium of the present invention by using a concrete means, a polymer substrate 4 made of a long polyethylene terephthalate substrate in vacuum is provided along the circumferential surface of a cylindrical can 5. While traveling, the first magnetic layer 11 containing Co and Cr or Co, Cr and Ni as main components is directly deposited on the polymer substrate 4 or via the underlayer by the vacuum deposition method, and Co and O or Co and Ni.
When the magnetic recording medium is manufactured by sequentially forming the second magnetic layer 12 containing O and O as main components, the peripheral surface temperature of the cylindrical can 5 is set to 0 ° C. or higher when forming the first magnetic layer 11. ℃
The film thickness is set as follows, and the coercive force in the in-plane direction after lamination is 250% or more of the in-plane coercive force of only the first layer.
Magnetic layer 11 is formed on the polymer substrate 4 by vacuum vapor deposition while moving the polymer substrate 4 made of a long polyethylene naphthalate substrate in vacuum along the peripheral surface of the cylindrical can 5. The first magnetic layer 11 containing Co and Cr or Co, Cr and Ni as main components, directly or through an underlayer, and Co and O or Co and N.
When a magnetic recording medium is manufactured by sequentially forming the second magnetic layer 12 containing i and O as main components, the first magnetic layer 11
When forming the film, the peripheral surface temperature of the cylindrical can 5 is set to 60 ° C. or higher and 110 ° C. or lower, and the coercive force in the film in-plane direction after lamination is 200% or more of the in-plane coercive force of only the first layer The first magnetic layer 11 is formed to have a film thickness such that the film thickness becomes, or the polymer substrate 4 made of a long polyimide substrate is run in vacuum along the peripheral surface of the cylindrical can 5 by a vacuum deposition method. A first magnetic layer 11 containing Co and Cr or Co, Cr and Ni as main components on the polymer substrate 4 directly or via an underlayer, and a first magnetic layer 11 containing Co and O or Co, Ni and O as main components. When the magnetic recording medium is manufactured by sequentially forming the second magnetic layer 12 and the second magnetic layer 12, the peripheral surface temperature of the cylindrical can 5 is set to 120 ° C. or more and 300 ° C. or less when forming the first magnetic layer 11, and the layers are stacked. The film surface where the coercive force in the subsequent film surface direction is only the first layer Made by forming a first magnetic layer 11 a thickness equal to or larger than 160% of the direction coercive force.

Table 1 shows optimum medium design conditions when each polymer substrate 4 is used.

[0019]

[Table 1]

FIG. 8 is a summary of the results described in the above-described examples. The in-plane coercive force of only the first magnetic layer 11 and the lamination required to obtain high C / N. The relationship of the multiplication factor of the in-plane coercive force afterwards is shown. If the multiplication factor of the in-plane coercive force required to obtain a high C / N from FIG. 8 is y (%) and the in-plane coercive force of only the first magnetic layer 11 is x (Oe),
It was found that y> -9 / 20 + 340, and the in-plane coercive force was 200 oersted or more (x ≧ 20
0), and the in-plane coercive force of the second magnetic layer 12 is larger than the in-plane coercive force of the first magnetic layer 11 (y> 10).
It can be seen that together with 0), it becomes an index of a high C / N medium.

Although only the case where Co--Cr is used as the first magnetic layer 11 has been described as an example, the case where Co--Ni--Cr is used and the case where the second magnetic layer 1 is used are described.
Similar results were obtained when Co-Ni-O was used instead of Co-O as 2.

In the present invention, the second magnetic layer 12 may be made of the same material in multiple layers.
In the present invention, only the magnetic tape-shaped embodiment is described, but it goes without saying that the invention can be applied to a disk-shaped medium.

[0023]

As is apparent from the above embodiments, according to the magnetic recording medium of the present invention, the medium is composed of the first magnetic layer and the second magnetic layer which are matched to the material of the polymer substrate used. Thus, a magnetic recording medium having excellent recording / reproducing characteristics can be obtained at low cost.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration of a magnetic recording medium according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a vapor deposition apparatus used to manufacture the magnetic recording medium.

FIG. 3 is a characteristic diagram showing the relationship between the peripheral surface temperature of a cylindrical can and the coercive force in the in-plane direction of the film.

FIG. 4A and FIG. 4B are characteristic diagrams showing the relationship between the change in coercive force in the in-plane direction of the film after lamination and the recording / reproducing characteristics.

5A and 5B are another characteristic diagrams showing the relationship between the change in coercive force in the in-plane direction of the film after lamination and the recording / reproducing characteristics.

FIG. 6 is a characteristic diagram showing the relationship of coercive force in the in-plane direction after lamination when the film thickness of the first magnetic layer is changed.

FIG. 7 is another characteristic diagram showing coercive force in the in-plane direction after lamination when the film thickness of the first magnetic layer is changed.

FIG. 8 is a characteristic diagram showing the relationship between the coercive force of the first magnetic layer and the coercive force multiplication factor required for high C / N after lamination.

[Explanation of symbols]

 4 Polymer Substrate 11 First Magnetic Layer 12 Second Magnetic Layer

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer on a polymer substrate directly or via an underlayer, wherein the magnetic layer is Co and Cr or Co and Cr in order from the polymer substrate side.
And a first magnetic layer containing Ni as a main component, and a second magnetic layer containing Co and O or Co, Ni and O as a main component, and the first magnetic layer when the second magnetic layer is removed. Has a coercive force x (Oe) in the in-plane direction of the magnetic layer of 200 or more, and a coercive force in the in-plane direction of only the second magnetic layer is in the in-plane direction of only the first magnetic layer. Greater than magnetic force,
A magnetic recording medium characterized in that the coercive force in the in-plane direction after lamination is (-9 / 20x + 340)% or more of the coercive force in the in-plane direction of the first magnetic layer.