JPH05159269A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium which has recording and reproducing characteristics excellent over the entire wavelength region and is decreased in spacing losses is the magnetic recording medium to be used for a high-density recording and reproducing device, such as digital VTR. CONSTITUTION:The recording material is constituted by laminating a 1st magnetic layer 2 which consists essentially of Co and Cr or Co, Ni and Cr and has the direction 4 of the axis of easy magnetization in nearly an intra-film plane direction and a 2nd magnetic layer 3 which consists essentially of Co and O or Co, Ni and O and has the direction 5 of the axis of easy magnetization in the direction rising diagonally from the inside of the film plane on a nonmagnetic substrate 1. As a result, the recording and reproducing characteristics excellent over the entire wavelength region are obtd. in order to efficiently pass the magnetic fluxes from recording magnetization. Since the direction 5 of the axis of easy magnetization is in a diagonal direction, the spacing losses are decreased.

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 used in a high density recording / reproducing apparatus such as a digital video tape recorder 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 are attracting attention as a material that exceeds the limit of high 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, the oblique deposition method is used to improve the high-density recording / reproducing characteristics as compared with the conventional coating type medium due to the contribution of the magnetization component in the direction perpendicular to the film surface of the magnetic layer. However, next-generation VTRs such as home digital VTRs and high definition VTRs
Further excellent high-density recording / reproducing characteristics are required for the magnetic recording medium corresponding to the above, and as a candidate thereof, Co-C
A perpendicular magnetic recording medium containing r, Co-Ni-Cr, Co-O, Co-Ni-O or the like as a main component is expected.

[0003]

However, the perpendicular magnetic recording medium has a low reproduction output in the long wavelength recording region.
There is a problem that the digital signal processing is difficult because the isolated reproduction waveform has a dipulse shape. Another problem with the perpendicular magnetic recording medium is that the spacing loss in recording / reproducing with the ring type magnetic head is larger than that in the conventional magnetic recording medium.

The present invention solves the above problems, and an object of the present invention is to provide a magnetic recording medium having excellent recording / reproducing characteristics in the entire wavelength region and reduced spacing loss, and a method for manufacturing the same. To do.

[0005]

To achieve the above object, the magnetic recording medium of the present invention comprises Co and Cr or C.
The first magnetic layer containing o, Ni and Cr as main components and having an easy axis of magnetization in the substantially in-plane direction, and Co and O or rising from the inside of the film containing Co, Ni and O as main components The magnetic recording medium of the present invention has a structure in which a second magnetic layer having an easy axis of magnetization in the direction is sequentially laminated. Further, in the method for manufacturing a magnetic recording medium of the present invention, a Cr thin film is formed on a non-magnetic substrate, and the Cr Co and Cr or C on the thin film
A first magnetic layer containing o, Ni, and Cr as main components is formed by a vacuum vapor deposition method with almost normal incidence, and Co and O or Co, Ni, and O containing main components are formed on the first magnetic layer. The second magnetic layer is formed by an oblique incident reaction vacuum deposition method.

[0006]

With this structure, since the direction of the easy axis of magnetization of the second magnetic layer rises obliquely with respect to the film surface, the spacing loss is extremely reduced, and the direction of the easy axis of magnetization is present in the film surface. Since the first magnetic layer functions to efficiently pass the magnetic flux from the recording magnetization, the recording / reproducing characteristics are improved over the entire wavelength region. Further, in the manufacturing method, the Cr thin film layer is formed on the non-magnetic substrate, and the first and second magnetic layers are formed on the Cr thin film layer by vapor deposition to manufacture a magnetic recording medium having excellent characteristics with high mass productivity. be able to.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing the basic structure of the magnetic recording medium of the present invention. In FIG. 1, reference numeral 1 denotes a non-magnetic substrate, on which a first magnetic layer 2 is formed and a second magnetic layer 3 is further formed. 4 is the first magnetic layer 2
The magnetization easy axis direction of 5 indicates the magnetization easy axis direction of the second magnetic layer 3. α indicates the rising angle from the film surface of the second magnetic layer 3 in the easy axis direction 5 of magnetization. The easy magnetization axis direction 4 of the first magnetic layer 2 is substantially in the plane of the film. The recording efficiency associated with spacing loss strongly depends on the rising angle α. The spacing loss sharply increases as α approaches 90 °. Further, the spacing loss increases even when α approaches 0 °. Therefore, there is an appropriate α value.

Further, α also affects the reproduced waveform. α is 9
As it approaches 0 °, a dipulse-shaped waveform is obtained. However, with only the second magnetic layer 3,
Although the spacing loss is reduced, sufficient recording / reproducing characteristics cannot be obtained. Therefore, there is the first magnetic layer 2.

The easy magnetization axis direction 4 of the first magnetic layer 2 is substantially in the film in-plane direction and directly contributes to a great improvement of the recording / reproducing characteristics in the long wavelength region. 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 magnetic recording medium. At this time, the surface layer of the magnetic recording medium is mainly magnetized. The second is the magnetic recording medium of the present invention.
Of the magnetic layer 3 corresponds to the surface layer portion. The function of the first magnetic layer 2 is to make the recording magnetization of the surface layer portion exist more stably.
That is, in the deep layer portion of the magnetic recording medium, the easy axis direction 4 is substantially in the film plane, and therefore, it functions as a closed magnetic path that efficiently connects the magnetic flux from the recording magnetization.

As described above, the constitution of the first magnetic layer 2 in which the easy magnetization axis direction 4 is substantially in the film plane and the second magnetic layer 3 in which the easy magnetization axis direction 5 rises obliquely from the film plane. By doing so, a magnetic recording medium with a small spacing loss and improved recording / reproducing characteristics can be obtained.

Next, a desirable state of the magnetic recording medium of the present invention will be described. The film thickness and the saturation magnetization of each magnetic layer of the first magnetic layer 2 and the second magnetic layer 3 are 50, respectively.
More preferably, it is in the range of 300 nm and 300 to 700 kA / m. If the film thickness is less than 50 nm, the magnetic characteristics are not always sufficient in both magnetic layers. Also 300 nm
If it exceeds, noise tends to increase. However, 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 magnetic recording 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. When a head having a relatively high saturation magnetic flux density such as a metal head is used, the first magnetic layer 2 is thinned and the second magnetic layer 3 is thinned.
S / N is improved by increasing the thickness.

The saturation magnetization also needs to be determined in consideration of the ring head used, but generally 300 k
If it is less than A / m, reproduction output is low, and if it exceeds 700 kA / m, noise tends to be high. Therefore, when the saturation magnetization is 300 to 700 kA / m, it is possible to obtain the one in which both characteristics are more excellent.

Next, a method of manufacturing a magnetic recording medium according to an embodiment of the present invention will be described with reference to the schematic sectional view showing the film structure of FIG. In FIG. 2, 6 is a non-magnetic substrate on which a Cr thin film layer 7 is formed. In comparison with FIG. 1, the nonmagnetic substrate 1 in FIG. 1 comprises the nonmagnetic substrate 6 and the Cr thin film layer 7 in FIG. The first magnetic layer 2 is formed on the Cr thin film layer 7. Further, the second magnetic layer 3 is formed on the first magnetic layer 2.

Each thin film is formed by a vacuum evaporation method which is excellent in mass productivity. The method of forming the first magnetic layer 2 containing Co and Cr or Co, Ni and Cr as the main components on the Cr thin film layer 7 by the sputtering method with almost vertical incidence is widely used in the manufacture of hard disks. According to this method, Co and Cr or Co, Ni and C
The c-axis of the dense hexagonal structure, which is the easy magnetization axis of the first magnetic layer 2 containing r as a main component, grows parallel to the film surface by epitaxial growth. As a result, the easy axis of magnetization can be made substantially parallel to the film surface. Then, a high coercive force in the in-plane direction of the film is obtained, and the generation of noise is suppressed.

However, as it is, the conventional in-plane magnetic recording medium cannot be obtained, and further required high-density recording characteristics cannot be obtained. Therefore, on the first magnetic layer 2, a second layer containing Co and O or Co, Ni and O as main components is formed.
The magnetic layer 3 is formed by the oblique incident reactive vacuum deposition method. The thickness of the Cr thin film layer 7 in the magnetic recording medium manufacturing method of the present invention is preferably 10 to 100 nm.
More preferably, it is 20 to 50 nm. Generally, a film thickness of about 10 nm or more is required for the thin film to completely cover the substrate surface. Furthermore, a film thickness of 20 nm or more is desired in order to obtain an excellent crystalline film by epitaxial growth.
This is because the Cr thin film layer 7 itself also increases in crystallinity as the film thickness increases due to self-epitaxial growth. However, if the film thickness exceeds 100 nm, the crystal grains become large and the surface of the Cr thin film layer 7 becomes rough. In order to avoid roughening, it is desirable that the thickness be 50 nm or less.

When a magnetic thin film having high crystallinity is generally laminated on the first magnetic layer 2 containing Co and Cr or Co, Ni and Cr as a main component, the laminated magnetic thin film serves as an underlying first magnetic layer. The crystallinity of 2 is succeeded, and it becomes difficult to control the inclination of the crystal axis. That is, it is difficult to freely control the direction of the easy magnetization axis. C
In the second magnetic layer 3 containing o and O or Co, Ni and O as the main components, the origin of the magnetic anisotropy is not the crystallinity but the grain shape. It is possible to control the easy magnetization axis direction by selecting it. The saturation magnetization of each magnetic layer can be controlled by adjusting the Cr content in the case of the first magnetic layer 2 and the oxygen content in the case of the second magnetic layer 3.

As described above, in order to realize the magnetic recording medium of the present invention, it is necessary to stack at least three kinds of thin films on the non-magnetic substrate 6. It is disadvantageous in terms of productivity to form the three kinds of thin films separately and sequentially. However, it is also difficult to form all thin films at the same time. Therefore, in the method of manufacturing the magnetic recording medium of the present invention, a method was devised in which a long polymer film is used as the non-magnetic substrate 6 and the Cr thin film layer 7 and the first magnetic layer 2 are formed thereon almost at the same time. ..

FIG. 3 is a schematic view of a manufacturing apparatus used in one embodiment of this method. In FIG. 3, a long polymer film 9 unwound from a supply roll 8 travels along the circumferential surface of a rotating cylindrical can 10, and during this period, evaporated atoms supplied from two evaporation sources 11 and 12 are supplied. Are deposited. Then, the polymer film on which the layers 7 and 2 have been formed is wound on the winding roll 13. Evaporation source 11 is Cr
For forming the thin film layer 7, the evaporation source 12 is Co and Cr.
Alternatively, it is for forming the first magnetic layer 2 containing Co, Ni and Cr as main components. A shielding plate 14 is provided between the evaporation sources 11 and 12 and the cylindrical can 10 so that a film is not formed in an unnecessary portion. The evaporated atoms pass through the opening formed in the shield plate 14 and reach the polymer film 9 almost vertically. No shield is required between the two evaporation sources. Due to their mutual vapor pressure, the vaporized atoms do not mix badly. Some mixing does not affect the properties of the membrane. Since Cr is a substance that is easily oxidized, it is very advantageous that the next film is formed immediately after the formation. The fact that the surface of the Cr thin film layer 7 is not oxidized means that the epitaxial growth is efficiently realized. Further, if the shielding plate 14 is cooled, the oxygen partial pressure in the vicinity of the vapor deposition portion is remarkably lowered by the getter action of Cr, which is very useful for improving the film characteristics. It is well known that oxygen deteriorates the film characteristics in the growth of the first magnetic layer 2 containing Co and Cr or Co, Ni and Cr as the main components.

Next, the formation of the second magnetic layer 3 will be described. FIG. 4 shows Co and O or Co, Ni and O.
2 is a schematic view of a manufacturing apparatus used in an embodiment of the present invention for forming the second magnetic layer 3 containing as a main component. In FIG. 4, the long polymer film 16 unwound from the supply roll 15 travels along the circumferential surface of the rotating cylindrical can 17, and during this period, evaporated atoms supplied from the evaporation source 18 are accumulated. .. Here, the polymer film 16 has the Cr thin film layer and the first magnetic layer already formed. This polymer film 16 is wound around a winding roll 19 after forming the second magnetic layer.

The material charged in the evaporation source 18 is Co or Co and Ni. Oxygen for reactive vapor deposition is introduced from the outside in the vicinity of the vapor deposition section. When forming the second magnetic layer, the shielding plate 20 is provided to change the incident angle of the vaporized atoms to the polymer film 16 from the initial incident angle φi to the final incident angle φf with respect to the substrate normal. Initial incident angle φ
The range of i is 50 to 90 °, and the range of the final incident angle φf is 30.
The rising angle α of the axis of easy magnetization of the second magnetic layer from the film surface is 20 to 60 °.

Co and O or Co, Ni and O
The magnetic characteristics of the second magnetic layer containing as a main component are almost determined by the arrangement of the microcrystalline particles. This arrangement depends on the angle of incidence. The array is curved because the incident angle changes continuously, and the average tilt direction has the easy axis direction of magnetization. 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,
For a head that generates a relatively strong vertical magnetic field in the vertical direction, such as a metal in-gap head (MIG head), a high S / N is obtained by increasing α within a limited range, and a small α is used for a ferrite ring head or the like. Is good.

Here, a magnetic recording method for the magnetic recording medium of the present invention using a ring type magnetic head will be described. In the magnetic recording medium of the present invention, in order to make it smaller than the spacing loss, the relative movement directions of the magnetic recording medium and the ring type magnetic head are set such that the easy magnetization axis direction of the second magnetic layer and the leading edge of the ring type magnetic head. It is desirable that the direction is such that the direction of the head magnetic field in the vicinity substantially coincides. That is, the direction of the easy axis of magnetization of the second magnetic layer is close to the direction of the head magnetic field near the leading edge, and the magnetization reversal is mainly determined by the head magnetic field on the leading core side. The head magnetic field direction in the vicinity of the trailing edge is close to the hard axis direction 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.

Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention and comparison. Example 1 A Co—Cr film was formed as a Cr thin film layer and a first magnetic layer using the continuous vapor deposition apparatus shown in FIG. Co
-The saturation magnetization of the Cr film is about 500 kA / m, and the film thickness is about 10
It is 0 nm. The temperature of the cylindrical can 10 during vapor deposition is 25
It was set to 0 ° C. The thickness of the Cr thin film layer was about 30 nm. Next, a Co—O film was formed as the second magnetic layer using the continuous vapor deposition device shown in FIG. Co− as the second magnetic layer
In the O film, Co is evaporated from the evaporation source 18 and the incident angle of the evaporated atoms to the nonmagnetic substrate is changed from the initial incident angle of 80 ° to the final incident angle of
It was changed to 0 °. Co-O film (strictly speaking, Co and C
O was introduced into the Co vapor stream in order to form a mixed film with the oxide of o). The saturation magnetization of the Co-O film is about 600 k
A / m, film thickness is about 150 nm. The temperature of the cylindrical can 17 during vapor deposition was 150 ° C. Non-magnetic substrate has thickness 1
In order to examine the spacing loss, four kinds of 0 μm polyimide films having different protrusion heights provided with surface protrusion shapes were used.

Comparative Example 1 Using the continuous vapor deposition apparatus shown in FIG. 3, in order to investigate the performance of only the first magnetic layer, only a Cr thin film layer and a Co--Cr film were formed as the first magnetic layer. C
The saturation magnetization of the o-Cr film is about 500 kA / m, and the film thickness is about 1
00 nm. The temperature of the cylindrical can 10 during vapor deposition is 2
It was set to 50 ° C. The thickness of the Cr thin film layer was about 30 nm.
As the non-magnetic substrate, a polyimide film having a thickness of 10 μm was used, and in order to examine the spacing loss, four types having different protrusion heights provided with surface protrusion shapes were used.

Comparative Example 2 Using the continuous vapor deposition apparatus shown in FIG. 4, in order to investigate the performance of only the second magnetic layer, only the Co—O film was directly formed on the non-magnetic substrate as the second magnetic layer. .. In the Co—O film as the second magnetic layer, Co was evaporated from the evaporation source, and the incident angle of the evaporated atoms on the nonmagnetic substrate was changed from the initial incident angle of 80 ° to the final incident angle of 40 °. Co
Oxygen was introduced into the Co vapor stream to form a -O film (strictly speaking, a mixed film of Co and an oxide of Co). Co-
The saturation magnetization of the O film is about 600 kA / m and the film thickness is about 150 n.
m. The temperature of the cylindrical can 17 during vapor deposition is 150 ° C.
And As the non-magnetic substrate, a polyimide film having a thickness of 10 μm was used, and in order to examine the spacing loss, four types having different protrusion heights provided with surface protrusion shapes were used.

The estimated values of the spacing loss and C / N of the magnetic recording medium obtained for the above three examples are shown in Table 1 below.
Shown in. However, 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 a spacing length between the head and the magnetic recording medium, and λ is a recording wavelength. Also,
K is a proportional coefficient called a spacing loss factor, which mainly depends on the type of magnetic recording 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. The C / N value was evaluated based on the results of Example 1. The evaluation was performed at recording wavelengths of 3.5 μm and 0.5 μm. In Table 1, the K value represents the relative movement direction of the magnetic recording medium and the ring magnetic head, the easy axis of magnetization of the second magnetic layer and the relative movement direction of the ring magnetic head, and the second value. In the case where the direction of the easy axis of magnetization of the magnetic layer and the magnetic field direction of the head near the leading edge of the ring type magnetic head are substantially aligned with each other. The head is a metal in-gap head.

[0028]

[Table 1]

As shown in (Table 1), in the magnetic recording medium of the present invention of Example 1, not only a K value smaller than that of the other two Comparative Examples 1 and 2 was obtained, but also excellent recording / reproduction was performed. It can be seen that the characteristics can be obtained. It is considered that such an improvement in the characteristics is realized because the functions of both the first and second magnetic layers described above act synergistically and exceed the performance of each magnetic layer alone.

Even when Ni is added to one or both of the first magnetic layer and the second magnetic layer in a proportion of 30% by weight or less, the effects of the present invention can be sufficiently obtained in the same manner as described above. It was

[0031]

According to the present invention, the direction of the easy axis of magnetization is specified.
It is possible to provide a magnetic recording medium which has excellent recording / reproducing characteristics in all wavelength regions and has reduced spacing loss, which is a magnetic recording medium having a magnetic layer. That is, the magnetic recording medium of the present invention can exhibit excellent recording / reproducing characteristics even in practical characteristics, such as when minute protrusions or grooves are formed on the surface for stable recording / reproducing.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing the basic structure of a magnetic recording medium of the present invention.

FIG. 2 is a sectional view schematically showing a film structure of a magnetic recording medium according to an embodiment of the present invention.

FIG. 3 shows C used in the manufacturing method in one embodiment of the present invention.
Schematic of a continuous vapor deposition apparatus for simultaneously forming an r thin film layer and a first magnetic layer

FIG. 4 is a schematic view of a continuous vapor deposition apparatus for forming a second magnetic layer used in the manufacturing method in one embodiment of the present invention.

[Explanation of symbols]

 1 Non-Magnetic Substrate 2 First Magnetic Layer 3 Second Magnetic Layer 4, 5 Easy Magnetization Axis Direction 6 Non-Magnetic Substrate (Polymer Film) 7 Cr Thin Film Layer 9 Polymer Film 10, 17 Cylindrical Can 11, 12, 18 evaporation sources

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuro Ishida 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (8)

[Claims] 1. Co and Cr or C on a non-magnetic substrate
a first magnetic layer containing o, Ni and Cr as main components and having an easy axis of magnetization substantially in the in-plane direction, and Co and O or rising up obliquely from the inside of the film containing Co, Ni and O as main components. A magnetic recording medium comprising: a second magnetic layer having an easy axis of magnetization in a vertical direction. 2. The film thickness and the saturation magnetization of each magnetic layer of the first magnetic layer and the second magnetic layer are 50 to 300 nm, respectively.
And the magnetic recording medium according to claim 1, having a range of 300 to 700 kA / m. 3. The magnetic recording medium according to claim 1, wherein the rising angle of the second magnetic layer in the direction of the easy axis from the film surface is in the range of 20 to 60 °. 4. A Cr thin film is formed on a non-magnetic substrate, and Co and Cr or Co, Ni and C are formed on the Cr thin film.
A first magnetic layer containing r as a main component is formed by a vacuum vapor deposition method with almost normal incidence, and a second magnetic layer containing Co and O or Co, Ni and O as a main component is formed on the first magnetic layer. Is formed by an oblique incident reaction vacuum deposition method. 5. The method for manufacturing a magnetic recording medium according to claim 4, wherein the thickness of the Cr thin film is 10 to 100 nm. 6. A polymer film is used as a non-magnetic substrate, a Cr thin film is formed on the polymer film running on the peripheral surface of a cylindrical can, and immediately after that, a first magnetic layer is formed. A method of manufacturing a magnetic recording medium according to claim 4. 7. A non-magnetic substrate comprising a polymer film, C
6. The method for manufacturing a magnetic recording medium according to claim 4, wherein the second magnetic layer is formed while the polymer film having the r thin film and the first magnetic layer formed thereon is run on the circumferential surface of the cylindrical can. 8. When the angle formed by the incident direction of vaporized atoms to the non-magnetic substrate and the normal direction of the non-magnetic substrate is defined as the incident angle, the incident angle at the initial stage of formation of the second magnetic layer is the formation angle. The incident angle is larger than the final incident angle and is 50 at the initial stage of formation.
8. The method for manufacturing a magnetic recording medium according to claim 4, 5, 6 or 7, wherein the incident angle at the final stage of formation is 30 to 70 °.