JPH05342551A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To improve high-density recording and reproducing characteristic by forming magnetic layers having the coercive force larger in the front surface side part in the substrate than the side part on the substrate. CONSTITUTION:This magnetic recording medium is constituted by forming the first magnetic layer 2 consisting of Co-Ni-O on the nonmagnetic substrate 1 and the second magnetic layer 3 consisting of Co-O film thereon. The magnetic layers are larger in saturation magnetization and larger in magnetic anisotropy when these layers are formed of the Co alone, but the Co-Ni contg. 20wt.% Ni is used in order to improve corrosion resistance. Then, the second magnetic layer 3 has the larger coercive force than the coercive force of the first magnetic layer 2. The direction 4 of the axis of easy magnetization of the first magnetic layer 2 has the rising angle alpha1 from the film plane and the direction 5 of the axis of easy magnetization of the second magnetic layer 3 has the rising angler alpha2 from the film plane. The angle alpha1 is preferably 5 to 30 deg. and the angle alpha2 is preferably 10 to 40 deg. in order to lessen the spacing loss and to obtain the sufficient recording and reproducing characteristics.

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, such as a digital VTR and a high definition VTR, which is compatible with high density recording and reproducing, and a method for manufacturing the same.

[0002]

2. Description of the Related Art At present, magnetic recording / reproducing devices tend to be smaller and have higher densities, and metal thin film type media have been attracting attention as exceeding the limit of higher density of conventional coating type media.
In this regard, a metal thin film medium containing Co—Ni—O as a main component has been put to practical use as a magnetic tape for VTR. In order to form such a magnetic recording medium with high productivity, for example, a web coater type continuous vapor deposition apparatus may be used to continuously deposit a magnetic layer on a long polymer substrate while moving it. .. At this time, by using the method of oblique vapor deposition, a high coercive force is obtained and the high density recording / reproducing characteristics are improved as compared with the conventional coating type medium. However, home digital VTR, high definition V
For magnetic recording media compatible with next-generation VTRs such as TR,
Further excellent high-density recording / reproducing characteristics are required, and magnetic recording media containing Co—O, Co—Ni—O, etc. as a main component are expected as candidates thereof.

[0003]

However, Co-O and Co-Ni- formed by the above-mentioned oblique vacuum deposition method.
In the single-layer magnetic recording medium composed of a magnetic layer containing O or the like as a main component, the coercive force of the initial formation layer formed at a high incident angle, that is, the final formation layer formed at a low incident angle, that is, , Higher than the magnetic layer surface layer. Therefore, when recording a signal with the magnetic head, the recording is insufficient in the deep portion of the magnetic layer where the recording magnetic field is weakened. If the magnetomotive force of the head is increased in order to prevent this, recording demagnetization occurs in the surface portion of the magnetic layer having a low coercive force. There is also a magnetic recording medium in which two magnetic films having the same material composition are formed as a magnetic layer, but in this case, the magnetic layers having substantially the same magnetic characteristics are in the deep portion and the surface portion. .. Also in this case, if the magnetomotive force of the magnetic head is increased so that the deep layer portion can be sufficiently recorded, the recording demagnetization occurs in the surface layer portion.

As described above, when the entire magnetic layer of the medium cannot be recorded sufficiently or there is recording demagnetization, sufficient reproduction output cannot be obtained, and excellent high density recording / reproduction characteristics are required. There is a problem that it is not sufficient as a magnetic recording medium compatible with next-generation VTRs such as home digital VTRs and high-definition VTRs.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a magnetic recording medium capable of increasing the recording efficiency of a magnetic film and excellent in high-density recording / reproducing characteristics, and a manufacturing method thereof. Is.

[0006]

According to the present invention of claim 1, there is provided a magnetic recording medium in which a magnetic film having a coercive force larger on a surface side portion than on a substrate side portion is formed on a substrate.

According to a fifth aspect of the present invention, a first magnetic layer having a predetermined coercive force is formed on a traveling substrate, and the coercive force of the first magnetic layer is formed on the formed first magnetic layer. It is a method of manufacturing a magnetic recording medium in which a second magnetic layer having a larger coercive force is formed.

[0008]

In the present invention, since the surface side portion is a magnetic film having a larger coercive force than the substrate side portion, recording demagnetization is less likely to occur and recording efficiency is increased.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments.

FIG. 1 is a sectional view schematically showing the basic structure of a magnetic recording medium of one embodiment according to the present invention. That is, the magnetic recording medium is a Co—Ni—O on the non-magnetic substrate 1.
A first magnetic layer 2 made of a film is formed, and C is further formed on the first magnetic layer 2.
A second magnetic layer 3 made of an o-O film is formed. Here, Co has a large magnetic anisotropy due to the crystal magnetic anisotropy, and thus is often used as a magnetic material of a magnetic recording medium. C
Since Ni is contained in o-Ni, the saturation magnetization is small and the magnetic anisotropy is smaller than Co. However, in order to improve the corrosion resistance, commercially available magnetic recording media use Co—Ni containing 20 wt% of Ni. Comparing the Co—O film obtained by reacting with oxygen when forming the film and the Co—Ni—O film, the former Co—O
The film has a larger magnetic anisotropy and a higher coercive force can be obtained. The magnetic recording medium of the present embodiment realizes a magnetic recording medium having high recording efficiency by utilizing the difference in magnetic characteristics of these two films.

Reference numeral 4 in FIG. 1 indicates the direction of the easy axis of magnetization of the first magnetic layer 2, and reference numeral 5 indicates the direction of the easy axis of magnetization of the second magnetic layer 3. Angles α1 and α2 represent rising angles of the easy axes of magnetization of the first magnetic layer 2 and the second magnetic layer 3 from the film surface, respectively. The recording efficiency related to the spacing loss strongly depends on the inclination angle α2 of the easy axis of the second magnetic layer 3. The spacing loss rapidly increases as α2 approaches 90 °. In addition, spacing loss increases even when α2 approaches 0 °. That is, there is an appropriate α2 value. Further, α2 also affects the reproduced waveform. As α2 approaches 90 °, a dipulse-shaped waveform is obtained. The desirable range of α2 is 10 to 40 °. However, with only the second magnetic layer 3, sufficient recording and reproducing characteristics cannot be obtained although the spacing loss is reduced. Therefore, there is the first magnetic layer 2. The rising angle α1 of the first magnetic layer 2 from the film surface in the easy magnetization axis direction 4 is smaller than α2, which directly contributes to a great improvement of the recording / reproducing characteristics in the long wavelength region and is deeper than the medium surface layer. In the part, it is adapted to the direction of the magnetic field produced by the magnetic head in which the in-plane component increases more. The desirable range of α1 is 5 to 30 °. Further, the coercive force of the first magnetic layer 2 is smaller than that of the second magnetic layer 3, and it is easy to record even with a recording magnetic field which becomes weaker apart from the magnetic head. Further, the first magnetic layer 2 indirectly contributes to the improvement of the recording / reproducing characteristics in the short wavelength region. In the short wavelength region, the head magnetic field has a surface that is difficult to penetrate into the deep layer of the medium. At this time, the surface layer of the medium is mainly magnetized. In the medium of the present invention, the second magnetic layer 3 corresponds to the surface layer portion. The first magnetic layer 2 has a function of allowing the recording magnetization of the surface layer portion to exist more stably. That is, in the deep portion of the medium, it is a function of a closed magnetic circuit that efficiently connects the magnetic flux from the recording magnetization.

The film thickness and saturation magnetization of both the first magnetic layer 2 and the second magnetic layer 3 are 30 to 300 n, respectively.
m and a range of 300 to 700 kA / m are desirable. If the film thickness is 30 nm or less, sufficient magnetic characteristics cannot be obtained in both magnetic layers. Further, when the thickness is 300 nm or more, noise becomes significantly high. The film thickness of each magnetic layer may be appropriately changed depending on the capability of the magnetic head used and the specifications of the medium.
For example, when a head such as a ferrite ring head whose saturation magnetic flux density is not so high is used, it is better to make the first magnetic layer 2 thicker and the second magnetic layer 3 thinner. Further, when using a head having a relatively high saturation magnetic flux density such as a metal head, the S / N is improved by making the first magnetic layer 2 thinner and the second magnetic layer 3 thicker. The saturation magnetization must also be determined in consideration of the ring head to be used, but generally, it is difficult to obtain a high reproduction output at 300 kA / m or less, and noise becomes extremely high at 700 kA / m or more. Will end up.

FIG. 2 is a sectional view schematically showing the film structure of the above embodiment. As described above, the first layer is formed on the non-magnetic substrate 1.
Magnetic layer 2 is formed, and the second magnetic layer 3 is formed on the first magnetic layer 2. The thin film of each magnetic layer is formed by a continuous vacuum deposition method which is excellent in mass productivity. Therefore, the columnar particles forming each layer are curved and inclined as shown in FIG. The easy axis of magnetization is further inclined toward the film surface side than the average inclination direction of the columnar particles. The easy axis of magnetization is determined by the combination of the magnetic anisotropy originally possessed by the columnar particles and the shape anisotropy of the film proportional to the saturation magnetization. Co-
In the Ni—O film and the Co—O film, the easy axis of magnetization can be controlled by the incident angle at the time of film formation.

FIG. 3 shows an example of a schematic of a continuous vacuum deposition apparatus used for forming a Co-Ni-O film and a Co-O film. The long polymer film 1 unwound from the supply roll 6 travels along the peripheral surface of the rotating cylindrical can 11, during which vaporized atoms supplied from the vaporization source 9 are accumulated. The polymer film after the film formation is wound on a winding roll 7. In order to form two magnetic layers on the polymer film 1, it is necessary to run the polymer film twice, and when the first magnetic layer is formed on the evaporation source 9, C is used.
o-Ni is charged, and Co is charged when the second magnetic layer is formed. A shielding plate 8 is provided between the evaporation source 9 and the cylindrical can 11 so that a film is not formed in an unnecessary portion. The vaporized atoms reach the polymer film 1 through the opening formed in the shielding plate 8. Oxygen is introduced through the introduction pipe 10 for reactive vapor deposition. The saturation magnetization of each magnetic layer can be controlled by adjusting the oxygen content. The incident angle of vaporized atoms to the substrate is the initial incident angle φ with respect to the substrate normal.
Change from i to the final incident angle φf. The range of the initial incident angle φi is 70 to 90 °, and the range of the final incident angle φf is 40 to 6
When the angle is 0 °, the rising angle of the axis of easy magnetization of the film formed from the film surface can be 5 to 30 °. Further, when the range of the initial incident angle φi is 50 to 70 ° and the range of the final incident angle φf is 30 to 50 °, the rising angle of the easy axis of the film formed from the film surface may be 10 to 40 °. I can.

As described above, in order to realize the magnetic recording medium of the above embodiment, it is necessary to stack two kinds of thin films on the non-magnetic substrate. It is disadvantageous in terms of productivity to form the two thin films separately and sequentially. Therefore, as a manufacturing method of another embodiment, a method of continuously and simultaneously forming the first magnetic layer and the second magnetic layer on a long polymer film is used. FIG. 4 is a schematic view showing a manufacturing apparatus of this method.
In this manufacturing apparatus, the long polymer film 1 unwound from the supply roll 6 runs along the peripheral surface of the rotating cylindrical can 11, and two evaporation sources 12 are placed on the running polymer film 1. Vaporized atoms provided by and 13 are deposited. The polymer film 1 after the film formation is wound on a winding roll 7. The evaporation source 12 is for forming the first magnetic layer and is charged with Co—Ni, and the evaporation source 13 is for forming the second magnetic layer and is charged with Co. A shielding plate 8 is provided between the evaporation sources 12 and 13 and the cylindrical can 11 so that a film is not formed in an unnecessary portion. The vaporized atoms reach the polymer film 1 through the opening formed in the shielding plate 8. A shield plate 1 is provided between the two evaporation sources 12 and 13.
4 prevents mixture of two kinds of steam. Further, oxygen introducing pipes 15 and 16 are provided near the openings. When forming the magnetic film, the respective incident angles are set by the two openings. The incident angle is very important in the formation of the second magnetic layer, and it is important to consider the head magnetic field to be used when determining the incident angle.
For example, in a head such as a MIG head which generates a relatively strong vertical head magnetic field, a high S / N can be obtained by increasing α2 within a limited range, and in a ferrite ring head or the like, it is better to reduce α2. Good.

Now, a magnetic recording method for the magnetic recording medium of the present invention using a ring type magnetic head will be described. In order to further reduce the spacing loss in the magnetic recording medium of the present invention, the direction of relative movement between the magnetic recording medium and the ring type magnetic head is set to the easy magnetization axis direction 5 of the second magnetic layer.
It is desirable that the head magnetic field direction in the vicinity of the leading edge of the ring type magnetic head be substantially the same.
That is, the easy magnetization axis direction 5 of the second magnetic layer is close to the head magnetic field direction near the leading edge, and the magnetization reversal is mainly determined by the head magnetic field on the leading core side. The direction of the head magnetic field near the trailing edge is close to the direction of the hard axis of the second magnetic layer, and it is difficult to receive the demagnetizing action from the head magnetic field on the trailing core side. Therefore, it is considered that the recording efficiency is high and the spacing loss is sufficiently small.

Next, a specific manufacturing method of the above embodiment will be described together with a comparative example.

(Example) Two magnetic layers were simultaneously formed using the continuous vapor deposition apparatus shown in FIG. The film thickness, incident angle and saturation magnetization of the first magnetic layer made of a Co—Ni—O film are 50 nm, 80 to 50 ° and 500 k, respectively.
A / m. The weight composition ratio of Co and Ni is 4: 1.
Is. The film thickness, incident angle, and saturation magnetization of the second magnetic layer made of a Co—O film are 50 nm and 60 to 40, respectively.
And 530 kA / m. The rising angles α1 and α2 from the film surface of the easy axis of magnetization of the resulting film were 20 ° and 30 °, respectively. The coercive force is 95 kA / m and 1 in the first and second magnetic layers, respectively.
It was 27 kA / m. In addition, the cylindrical can 1 at the time of vapor deposition
The temperature of 1 was 100 ° C. The substrate was a polyethylene naphthalate film having a thickness of 10 μm, and in order to examine the spacing loss, four kinds of protrusions having surface protrusions and having different protrusion heights were used.

Comparative Example 1 Two magnetic layers were simultaneously formed using the continuous vapor deposition apparatus shown in FIG. For comparison with the example, the two magnetic layers were both Co—Ni—O films. The weight composition ratio of Co and Ni is 4: 1.
The film thickness, incident angle and saturation magnetization of the first magnetic layer are 50 nm, 80 to 50 ° and 500 kA / m, respectively. The film thickness, incident angle and saturation magnetization of the second magnetic layer are 50 nm, 60-40 ° and 510 kA / m, respectively.
Is. The rising angles α1 and α2 from the film surface of the easy axis of magnetization of the resulting film were 20 ° and 28 °, respectively. The coercive force was 95 kA / m and 80 kA / m in the first and second magnetic layers, respectively. The temperature of the cylindrical can 11 during vapor deposition was 100 ° C. The substrate was a polyethylene naphthalate film having a thickness of 10 μm, and in order to examine the spacing loss, four kinds of protrusions having surface protrusions and having different protrusion heights were used.

Comparative Example 2 Two magnetic layers were simultaneously formed using the continuous vapor deposition apparatus shown in FIG. For comparison with the example, the two magnetic layers were both Co—O films.
The film thickness, incident angle and saturation magnetization of the first magnetic layer are 50 nm, 80 to 50 ° and 510 kA / m, respectively. The film thickness, incident angle and saturation magnetization of the second magnetic layer are 50 nm, 60-40 ° and 530 kA / m, respectively.
Is. The rising angles α1 and α2 from the film surface of the easy axis of magnetization of the resulting film were 22 ° and 30 °, respectively. The coercive force was 143 kA / m and 127 kA / m in the first and second magnetic layers, respectively.
The temperature of the cylindrical can 11 during vapor deposition was 100 ° C. The substrate was a polyethylene naphthalate film having a thickness of 10 μm, and in order to examine the spacing loss, four kinds of protrusions having surface protrusions and having different protrusion heights were used.

Table 1 shows the measured values of spacing loss and C / N of the magnetic recording media obtained in the above Examples and Comparative Examples. Since the spacing loss is generally expressed by K · d / λ (dB), the spacing loss was evaluated by measuring the K value. Here, d is the spacing length between the head and the medium, and λ is the recording wavelength. K is a proportional coefficient called a spacing loss factor, which mainly depends on the type of medium. The K value was obtained from the reproduction output at the recording wavelength of 0.5 μm of the magnetic recording media having different protrusion heights produced in each example. C / N
The value was evaluated based on the result of the example. The evaluation was performed at recording wavelengths of 3.5 μm and 0.5 μm. In Table 1, the K value indicates the direction of relative movement between the magnetic recording medium and the ring type magnetic head, and the direction of the easy axis of magnetization of the second magnetic layer and the head magnetic field direction near the leading edge of the ring type magnetic head are substantially the same. This is when the orientations match. The head is a MIG head.

[0022]

[Table 1]

As shown in Table 1, in the magnetic recording medium of the example, not only the K value smaller than that of the other two comparative examples is obtained, but also excellent recording / reproducing characteristics are obtained. The improvement of such characteristics is that the above-mentioned functions of both magnetic layers act synergistically to exceed the performance of each magnetic layer alone,
It is considered to have been realized.

In the above examples, the polyethylene naphthalate film was used as the polymer film as the substrate, but the invention is not limited to this, and other films such as a heat resistant film such as a polyimide film or a polyamide film may be used. Good.

In the above embodiment, the vapor deposition temperature is 100.
However, the magnetic layer may be formed by using a polyethylene terephthalate film or the like at a vapor deposition temperature of room temperature or lower.

Further, in the above embodiment, the magnetic film is formed by the first magnetic layer and the second magnetic layer, but the invention is not limited to this, and the coercive force of the surface side portion of the magnetic film is the coercive force of the substrate side portion of the magnetic film. The magnetic film may be formed as a single layer as long as it can be formed to have a larger magnetic force.

Further, in the above embodiment, Co is used for the first magnetic layer.
And a magnetic material containing Ni and O as main components and a magnetic material containing Co and O as main components were used for the second magnetic layer. However, the present invention is not limited to this, and the coercive force of the second magnetic layer is the first magnetic layer. Another magnetic material may be used as long as it is a material larger than the coercive force of the layer.

[0028]

As is apparent from the above description, the present invention has the advantages that the recording efficiency of the magnetic film is high and the high density recording / reproducing characteristics are excellent.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing the basic structure of a magnetic recording medium according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing the film structure of the magnetic recording medium of the same example.

FIG. 3 is a schematic view of a continuous vapor deposition apparatus used in a manufacturing method according to an embodiment of the present invention.

FIG. 4 is a schematic view of a continuous vapor deposition apparatus that continuously and simultaneously forms a first magnetic layer and a second magnetic layer used in a manufacturing method of another embodiment.

[Explanation of symbols]

 1 non-magnetic substrate (polymer film) 2 first magnetic layer 3 second magnetic layer 4 easy axis of magnetization of first magnetic layer 5 easy axis of magnetization of second magnetic layer 6 supply roll 7 winding roll 8 shielding Plate 9 Evaporation source 10 Oxygen introducing pipe 11 Cylindrical can 12 Evaporation source for forming first magnetic layer 13 Evaporation source for forming second magnetic layer 14 Shielding plate 15 Oxygen introducing pipe 16 Oxygen introducing pipe

Claims (7)

[Claims] 1. A magnetic recording medium, wherein a magnetic film having a coercive force larger on a surface side portion than on the substrate side portion is formed on a substrate. 2. The magnetic film has a first magnetic layer and a second magnetic layer, the first magnetic layer is formed on the substrate, and the second magnetic layer is formed on the first magnetic layer. The magnetic recording medium according to claim 1, wherein the coercive force of the second magnetic layer is larger than that of the first magnetic layer. 3. The magnetic recording medium according to claim 2, wherein the main components of the first magnetic layer are Co, Ni and O, and the main components of the second magnetic layer are Co and O. 4. The rising angles of the easy axes of magnetization of the first magnetic layer and the second magnetic layer are in the range of 5 to 30 ° and 10 to 40 ° with respect to the magnetic film surface, respectively, and the easy axes of magnetization are The magnetic recording medium according to claim 2, wherein the magnetic recording medium is inclined in the same direction with respect to the film normal. 5. The film thickness and the saturation magnetization of the first magnetic layer and the second magnetic layer are 30 to 300 nm and 300 to 300, respectively.
3. The range is 700 kA / m.
Or the magnetic recording medium described in 3. 6. A first magnetic layer having a predetermined coercive force is formed on a traveling substrate, and a coercive force larger than the coercive force of the first magnetic layer is formed on the formed first magnetic layer. A method of manufacturing a magnetic recording medium, comprising forming the second magnetic layer having the same. 7. The formation of the magnetic layer is a reaction vacuum deposition method,
When the angle formed by the direction of incidence of vaporized atoms on the substrate and the direction of the substrate normal is defined as the angle of incidence, the formation of the magnetic layer is such that the incidence angle at the initial stage of magnetic layer formation is larger than the incidence angle at the final stage of formation. In the formation of one magnetic layer, the incident angle at the initial stage of formation is 70 to 90.
And the incident angle at the final stage of formation is in the range of 40 to 60 °, and the incident angle at the initial stage of formation is 5 in the formation of the second magnetic layer.
7. The method of manufacturing a magnetic recording medium according to claim 6, wherein the angle of incidence is 0 to 70 [deg.] And the incident angle at the final stage of formation is 30 to 50 [deg.].