JPH04356719A - Magnetic recording medium and production thereof - Google Patents

Abstract

PURPOSE:To provide the magnetic recording medium of a ferromagnetic metallic thin film type which can attain an improvement in reproduced output and C/N in a particularly high frequency range, i.e., short wavelength in order to obtain the high reproduced output and C/N over a wide recording frequency range. CONSTITUTION:A nonmagnetic substrate layer 2 formed by a vacuum film forming method and a high magnetic energy layer 3 which is so formed as to increase the quantity of the oxygen to be introduced into the vapor flow of a ferromagnetic metal in the late period of film formation are successively laminated on a nonmagnetic base body 1. The above-mentioned high magnetic energy layer 3 is the high magnetic energy layer having >=6.5X10<6> (gauss oersted) product of the residual magnetic flux density and antimagnetic force thereof. In addition, this high magnetic energy layer contains oxygen and the oxygen concn. on the front surface side thereof is higher than the oxygen concn. on the nonmagnetic base body side.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to the improvement of so-called ferromagnetic metal thin film type magnetic recording media, which are formed by forming a ferromagnetic metal thin film as a magnetic layer on a non-magnetic substrate by a vacuum evaporation method, and particularly for high-definition use. The present invention relates to a ferromagnetic metal thin film type magnetic recording medium suitable for broadband signal recording and high-density recording such as the above.

0002

2. Description of the Related Art High-density recording continues to be a strong trend in magnetic recording media. In order to achieve high-density recording, it is necessary to increase the reproduction output, reduce noise, or achieve both to increase the so-called C/N (ratio of reproduction output C to noise). .

In addition to changing the magnetic material used in coating-type magnetic recording media, which has been widely used in the past, such as changing from iron oxide powder to ferromagnetic metal powder, the magnetic properties of each material have also changed. We have achieved magnetic recording and reproducing characteristics with high density and high S/N by making improvements such as improving the particle size and making the particles finer.

However, despite these efforts, coating-type recording media are beginning to reach their limits in high-density recording, and development of metal thin-film media is progressing as a new material to achieve the next high-density recording. ing. Methods for creating metal magnetic thin films include vacuum deposition methods in which a thin film is formed in a vacuum such as sputtering, ion plating, and electron beam evaporation of ferromagnetic metals on a substrate such as a polymer film, and methods in which a thin film is formed in a vacuum in an aqueous solution. A so-called plating method is known in which a thin film is formed on a substrate.

Among these, some magnetic tape media produced by electron beam evaporation have begun to be put into practical use as magnetic tapes for 8 mm video systems, so-called "Hi-8ME." However, in recent years, there has been an extremely strong desire to achieve even higher recording densities, and the demand for large-capacity recording, for example as a recording medium for high-definition systems, has become increasingly strong. In order to meet such demands, research has been carried out to improve the characteristics of ferromagnetic metal thin film magnetic recording media.

Conventional methods for improving the characteristics of metal thin film type recording media include electron beam evaporation using Co-Ni; Technology that increases magnetic force, reduces noise, and improves corrosion resistance (for example,
It is disclosed in Japanese Patent Application Laid-open No. 23931 and Japanese Patent Application Laid-open No. 58-32234. ), ■ Oblique incidence evaporation method in which a ferromagnetic metal vapor flow is introduced obliquely onto a non-magnetic substrate to form a film.
Methods for improving magnetic properties (for example, Japanese Patent Publication No. 41-148
This method is disclosed in Japanese Patent Publication No. 12 and Japanese Patent Publication No. 56-52377. ), ■ A method of reducing noise by creating a multilayer structure of multiple vapor-deposited films and improving recording and reproducing characteristics by improving the magnetic properties of a magnetic film (including providing a non-magnetic intermediate layer) (for example, Japanese Patent Publication No. 57 (Disclosed in Japanese Patent Publication No. 3133), ■ Technology to eliminate the directional dependence of recording and reproducing characteristics by forming a film formed by oblique incidence deposition into a multilayer structure and controlling the growth direction of magnetic particles (for example, Publication No. 54-141608, Japanese Patent Publication No. 57-32
It is disclosed in Publication No. 23. ), etc. have been attempted.

Among these attempts, the method of introducing oxygen into a ferromagnetic thin film and the oblique incidence evaporation method have attracted particular attention as techniques for creating magnetic recording media for high-density recording with improved magnetic properties and excellent electromagnetic conversion characteristics. has been done.

However, these techniques are insufficient to improve the reproduction output and C/N over a wide frequency band of recorded signals, and when the recording wavelength is 0.4 μm or less, such as in a high-definition system, Over a wide frequency range, that is, a wide recording wavelength range, necessary for recording high-density recording signals of 1 μm2/bit or less and digital signals with high transfer rates with a track width of 5 μm or less,
This was not sufficient to obtain a magnetic recording medium that could provide high reproduction output.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the conventional situation, and an object of the present invention is to provide high playback output and high C/R over a wide recording frequency range.
The object of the present invention is to provide a ferromagnetic metal thin film type magnetic recording medium that can improve reproduction output and C/N ratio particularly in a high frequency region, that is, in a short wavelength.

0010

[Means for Solving the Problems] An object of the present invention is to have a layer structure in which two or more thin films formed by a vacuum film forming method are laminated on a non-magnetic substrate, and the layer structure is one layer structure. In a magnetic recording medium that includes a ferromagnetic thin film of more than one layer, the uppermost thin film of the layer structure has a ferromagnetic thin film whose residual magnetic flux density (Br (Gauss)) and coercive force (Hc (Oersted)) are multiplied by the product (Br×
Hc) is 6.5 x 106 (Gauss Oersted) or more, and the high magnetic energy layer contains oxygen, and the oxygen concentration on the surface side is higher than the oxygen concentration on the nonmagnetic substrate side. After forming at least one ferromagnetic thin film or nonmagnetic thin film on a nonmagnetic substrate by a vacuum film forming method, the ferromagnetic thin film or the nonmagnetic thin film is The angle of incidence of the ferromagnetic metal vapor flow on the non-magnetic substrate varies from the maximum angle of incidence (θmax) to the minimum angle of incidence (θmi).
n ), and the maximum incident angle (θm
A high magnetic energy layer is formed by an oblique incidence evaporation method in which an oxidizing gas is introduced into the ferromagnetic metal air flow so that the amount of oxygen introduced is larger near the minimum incidence angle (θmin) than near the minimum incident angle (θmin). This can be achieved by a method of manufacturing a magnetic recording medium.

That is, in the present invention, at least one nonmagnetic thin film layer or ferromagnetic thin film layer is previously provided on a nonmagnetic substrate by a vacuum film forming method, and then oxygen is removed in the film thickness direction by a vacuum film forming method. By providing a ferromagnetic thin film whose distribution is controlled so that the oxygen concentration on the surface side is higher than the oxygen concentration on the non-magnetic substrate side, the product of Br and Hc of the ferromagnetic thin film is 6.5 x 106. (Gauss-Oersted) or more.

In other words, the magnetic recording medium of the present invention:
Since it has a high magnetic energy layer with large Br×Hc,
It is compatible with broadband signal recording and can maintain high output even in a magnetic recording system where the recording wavelength is small, for example, about 0.4 μm or less. This is based on the principle of magnetic recording.

Although the details of the mechanism by which such a high magnetic energy layer is formed are unknown, it is thought to be approximately as follows. When a ferromagnetic thin film is directly deposited on a non-magnetic substrate, the ferromagnetic crystal grains are damaged by low molecular weight components and gas components such as moisture generated from the surface of the polymer film such as polyethylene phthalate when the surface is exposed to high temperatures. Although this growth is disturbed by inducing some kind of fluctuation in the initial growth, this can be prevented by providing a ferromagnetic thin film or a nonmagnetic thin film under the high magnetic energy layer as in the present invention; This is thought to be due to the fact that by defining the oxygen distribution in this high magnetic energy layer as described above, disturbances in the initial growth of ferromagnetic crystal grains can be minimized in the same way as described above.

[0014] There is no particular restriction on the specific method for producing a magnetic recording medium having such a high magnetic energy layer, but the high magnetic energy layer may be formed in the late stage of film formation (at the time of surface formation of the high magnetic energy layer). It can be produced by increasing the amount of oxygen introduced. Specifically, as described above, the incident angle of the ferromagnetic metal vapor flow forming the high magnetic energy layer with respect to the nonmagnetic substrate changes continuously from the maximum incidence angle (θmax) to the minimum incidence angle (θmin), and The minimum incident angle (θmin) is smaller than the vicinity of the maximum incidence angle (θmax).
) It can be manufactured by an oblique incidence evaporation method in which an oxidizing gas is introduced into the ferromagnetic metal air flow so that the amount of oxygen introduced is larger in the vicinity of the ferromagnetic metal.

In the process of arriving at the present invention, the present applicant discovered that various layers such as a single magnetic layer, underlayer + magnetic layer, lower magnetic layer + nonmagnetic intermediate layer + upper magnetic layer, etc., were formed on the same nonmagnetic substrate. We have produced many ferromagnetic metal thin film magnetic recording media with a layered structure,
The relationship between Br×Hc of the ferromagnetic thin film layer A that is farthest from the substrate, the oxygen distribution state in the film, and the C/N in a short wavelength region was investigated. As mentioned above, the present invention has a ferromagnetic thin film layer A, that is, at least one ferromagnetic thin film or a nonmagnetic thin film between the high magnetic energy layer and the nonmagnetic substrate, and the residual magnetic flux density Br of the high magnetic energy layer is (Gauss) and coercive force Hc (
Br×Hc is 6.5×106 (
Gauss-Oersted) or higher, and it is important for the oxygen concentration contained on the surface side of the high magnetic energy layer to be higher than the oxygen concentration contained on the substrate side in order to obtain a high C/N in the short wavelength region. I discovered that.

That is, when the substrate side of the ferromagnetic thin film layer A contains a large amount of oxygen, an effective method for increasing Br×Hc is to reduce the amount of oxygen introduced during film formation to increase Br. However, when the amount of introduced oxygen decreases, the size of the particles forming the magnetic layer increases, and the noise level increases rapidly, and even if the output level increases due to an increase in Br, the C/N does not increase. On the other hand, when there is at least one ferromagnetic thin film or non-magnetic thin film between the ferromagnetic thin film layer A and the substrate, such as the high magnetic energy layer in the present invention, and the amount of oxygen contained on the substrate side is small, the introduction It is relatively easy to reduce Br without particularly reducing the amount of oxygen.
As a result, the output level can be increased without increasing the noise level, and the C/N ratio can be increased.

To measure the magnetic properties of the high magnetic energy layer in the magnetic recording medium of the present invention, a nonmagnetic layer is formed on a nonmagnetic substrate by a vacuum deposition method, and a layer having the same structure as the high magnetic energy layer is deposited on top of the nonmagnetic layer. A measurement sample with a magnetic layer formed under the same conditions was
I created it separately. The magnetic properties were measured using a vibrating sample magnetometer (VSM).

In the present invention, the oxygen distribution in the uppermost ferromagnetic thin film layer of the constituent layers (that is, the high magnetic energy layer which is the magnetic layer located farthest from the substrate) is as follows: It is sufficient that the oxygen concentration contained in the layer is higher than the oxygen concentration contained in the substrate side of the layer, and the absolute value of the oxygen concentration is not limited. In order to obtain good durability, the oxygen concentration on the surface side of the magnetic layer is preferably 10 at % to 50 at %, and the oxygen concentration on the substrate side is preferably 5 at % to 30 at %. Here, the oxygen concentration on the surface side and the substrate side means, for example, if the thickness of the magnetic layer is d, the average oxygen concentration at a thickness of d/10 from the surface is the oxygen concentration on the surface side of the magnetic layer. The average oxygen concentration at a thickness of d/10 from the interface between the substrate and the layer adjacent thereto may be used as a guideline for the oxygen concentration on the substrate side or the interface side, respectively.

In the magnetic recording medium of the present invention, the product (Br x Hc) of the high magnetic energy layer is 6.5 x 106 or more, preferably 7.0 x 106 or more, more preferably 8
．． 0x106 It is more than Ørsted Gauss.

There are no particular limitations on other magnetic properties, but if Br is too small (3000 Gauss or less), sufficient output for high-density recording cannot be obtained, and if Hc is too small (800 Oe or less), high-density recording cannot be achieved. Insufficient output for recording. Therefore, Br is preferably 3000 Gauss or more, particularly preferably 4500 Gauss or more. Further, Hc is preferably 800 Oe or more, particularly preferably 1300 Oe or more.

The thickness of the high magnetic energy layer is not particularly limited, but in order to obtain a ferromagnetic thin film with the above characteristics, the thickness is 300 to 5000 Å, preferably 600 to 3500 Å, and more preferably 800 to 2500 Å.

[0022] It is substantially difficult to ensure magnetic properties with a film thinner than 300 Å in thickness. Also, the thickness is 300
When it is 0 Å or more, the surface roughness becomes rough and the output decreases due to an increase in spacing loss, and the size of the columnar particles increases and noise during reproduction increases, making it impractical.

[0023] The layer structure in which the high magnetic energy layer is the uppermost layer in the present invention has at least one magnetic and/or nonmagnetic thin film layer between the nonmagnetic substrate and the high magnetic energy layer. As long as it is formed by a vacuum film forming method, there are no restrictions on the number of layers to be laminated, the material and thickness of each layer, and the manufacturing method. For example, in extreme cases, the layer previously provided to form the high magnetic energy layer may be compositionally the same as the high magnetic energy layer. That is, at least two or more thin films are formed on a nonmagnetic substrate, and at least one nonmagnetic layer is provided between the high magnetic energy layer located farthest from the substrate and the nonmagnetic substrate. Alternatively, the condition that a magnetic layer formed by a vacuum film forming method is present may be satisfied.

Specific examples of the layer structure of the magnetic recording medium according to the present invention include the structures shown in FIGS. 1 and 2. In the example of FIG. 1, after forming the nonmagnetic underlayer 2 on the nonmagnetic substrate 1,
It has a structure in which a high magnetic energy layer 3 is formed, and the example shown in FIG.
, high magnetic energy layers 6 are sequentially laminated.

Examples of means for forming the ferromagnetic metal thin film include vapor phase plating, sputtering, vapor deposition, ion plating, and CVD. In order to more effectively achieve the object of the present invention, oblique incidence deposition is preferred as a means for forming the high magnetic energy layer, and a ferromagnetic metal thin film made of orthorhombic columnar particles formed by this method is preferred.

Specifically speaking, the orthorhombic columnar particles include those in which columnar particles, which are aggregates of microcrystals, are arranged in a diagonally folded manner. Oblique incidence deposition refers to evaporating metal atoms from an evaporation source onto a moving substrate while continuously changing the angle of incidence from the maximum angle of incidence (θmax) to the minimum angle of incidence (θmin). When the substrate is transported along a cylindrical can, the deposited ferromagnetic metal thin film is made of curved columnar ferromagnetic metal crystals.

In the manufacturing method of the present invention, the θmax
The range is 60 to 90 degrees, preferably 80 to 90 degrees.
The range of θmin is 20 to 60 degrees, preferably 30 to 50 degrees.

Further, in the magnetic recording medium and the manufacturing method thereof of the present invention, an oxidizing gas containing oxygen or a mixed gas of an oxidizing gas and an inert gas is introduced into the vacuum chamber during the oblique incidence deposition. A film containing an oxide in the form of columnar particles can be formed.

In addition to oxygen, the oxidizing gas includes ozone,
Hydrogen peroxide etc. can be used. Further, examples of the inert gas include helium, argon, and the like. In particular, by increasing the amount of oxygen introduced from the vicinity of θmin of the ferromagnetic metal vapor flow than from the vicinity of θmax, the distribution of oxygen in the high magnetic energy layer is changed closer to the surface than closer to the substrate. This is preferable because it can be made to increase in number. The vicinity of θmax and the vicinity of θmin refer to θmax
The meaning also includes x and θmin.

Here, the θmax and the θmin
The specific amount of oxygen introduced into the ferromagnetic metal vapor flow is not particularly limited, and is appropriately adjusted depending on the size and scale of the vapor deposition apparatus.

Therefore, when forming the high magnetic energy layer by oblique incidence deposition, the oxidizing gas may be introduced only from the low incidence angle side. In particular, films obtained by introducing these oxidizing gases have excellent magnetic properties, excellent reproduction output and nozzle performance, and can improve durability when used as a magnetic tape.

On the other hand, the method of forming the ferromagnetic thin film layer or nonmagnetic layer other than the high magnetic energy layer is not particularly limited as long as it is a vacuum film forming method. Examples include a vacuum evaporation method, a sputtering method, an ion plating method, a CVD method, and the like.

[0033] The layer structure for forming a film on a non-magnetic substrate in the present invention is preferably carried out continuously in a vacuum chamber, and a method that can form a film on a continuous non-magnetic substrate at high speed is desirable. When forming the nonmagnetic layer between the high magnetic energy layer and the nonmagnetic substrate by a vapor deposition method, a vacuum vapor deposition apparatus basically used for producing a ferromagnetic metal thin film can be used. That is,
The metal material to be evaporated may be, for example, Cu, Pt, Ti, Al,
It can be manufactured by using non-magnetic metal materials such as Cr and Bi, or by evaporating these metal materials while introducing an oxygen-containing gas. Alternatively, in carrying out the present invention, the nonmagnetic layer only needs to be substantially nonmagnetic, so if a magnetic metal material is used, it can be formed as a nonmagnetic oxide by introducing an oxygen-containing gas during vapor deposition. It can be made. Preferred metals include:
Preferred metal oxides include Cu, Ti, Au, Al, etc., and oxides of Co, Ni, Si, Ti, etc. can be mentioned.

FIG. 3 schematically shows an example of a vacuum evaporation apparatus that can be used in the production of the present invention. This device uses a vacuum pump (not shown) to maintain a predetermined degree of vacuum, e.g., 1 x 10-4 Torr.
Do the following. When introducing oxygen gas to form a magnetic film, the pressure is set to 1.times.10@-3 Torr or less. Further, when the nonmagnetic layer is formed of a metal oxide, the pressure is set to 1×10 −3 Torr or more. Inside the vacuum chamber 7, an evaporation source 9 heated by a heating means such as an electron beam heating device 8 of about 20 KeV, a shielding plate 10 for regulating the incident angle θmin of the evaporated atoms, a cylindrical can 11 for cooling, A glow discharge treatment chamber 12 used for surface cleaning and charge removal of the substrate, gas introduction sections 13 and 14 for gas such as oxygen, an unwinding roll 15, a take-up reel 16, and the like are arranged. Unwinding roll 1
While the non-magnetic substrate 1 supplied from 5 is continuously run along the can 11, evaporated atoms from the evaporation source 9 are deposited on the substrate, and a continuous film of the evaporated atoms is formed into a magnetic layer or Formed as a nonmagnetic layer.

Therefore, when manufacturing the present invention using only the above-mentioned vacuum evaporation method, a magnetic recording medium having a structure as shown in FIG. 1 or 2 can be obtained by repeating the evaporation several times using the same apparatus. be able to. In this case, the metal type of the evaporation source 9 may or may not be replaced.

Materials for the ferromagnetic metal thin film used in the present invention include metals such as Fe, Co, and Ni, alloys thereof, and alloys in which Cu, Pt, Cr, etc. are added to these metals. desirable.

[0037] The nonmagnetic substrate used in the present invention includes:
Bases such as polyethylene terephthalate film (PET), polyethylene naphthalate film (PEN), polyaramid film, polyimide film, polyamide film, etc. are used. For magnetic tape applications, those having a thickness of several microns to more than ten microns are mainly used. These materials, their thickness, etc. are matters to be selected that are compatible with the magnetic recording medium system, and do not define the present invention. The surface of these bases may be provided with one or more types of protrusions such as mountain-like protrusions and wrinkle-like protrusions. By providing these, minute protrusions can be formed on the surface of the magnetic layer, thereby improving the durability of the magnetic recording medium. The above-mentioned mountain-like or granular protrusions can be obtained by adding organic particles or inorganic particles internally during the formation of a polymer film, or by coating the film surface with organic particles or inorganic particles. The wrinkle-like protrusions can be formed, for example, by applying and drying a dilute resin solution. The height, distribution, density, etc. of these may be selected appropriately, but the height of the protrusion is 30 to 200 Å, and the density is 1×
It is preferable that the number is about 104 to 3×107 pieces/mm2.

Due to the heat generated during vacuum film formation, many components are degassed from the nonmagnetic layer substrate. In the present invention, since other layers are formed on the nonmagnetic substrate before forming the high magnetic energy layer, this outgassing is not affected by the formation of the high magnetic energy layer. Therefore, the magnetic recording medium of the present invention is particularly advantageous when the coating layer is formed on a nonmagnetic substrate as described above.

The outermost surface of the high magnetic energy layer of the present invention can be provided with a protective film, a lubricant, or both in order to improve the corrosion resistance and durability of the magnetic film. Examples of the protective film include an oxide thin film, a nitride thin film, and a carbon-based thin film. Examples of lubricants include various fatty acids, their esters, perfluoropolyethers, etc.
Usually 2-40mg/m2, preferably 3-20m
It can be applied as is or diluted with an organic solvent or the like in a range of g/m2.

Although the surface shape of the magnetic layer is not particularly defined,
When it has protrusions with a height of 10 to 500 angstroms, it has particularly excellent runnability and durability.

The shape of the magnetic recording medium is tape, sheet,
It may be a card, a disk, or the like, but tapes and disks are particularly preferred. In order to further improve the running durability of the magnetic recording medium of the present invention, a back layer made of non-magnetic particles and a binder resin can be provided on the surface opposite to the surface on which the magnetic layer is located.

[0042]

[Examples] The present invention will be explained in more detail with reference to Examples below. It will be readily understood by those skilled in the art that the ingredients, proportions, order of operations, etc. shown herein may be modified without departing from the spirit of the invention.

[0043] Therefore, the present invention should not be limited to the following examples. An embodiment of the configuration whose cross-sectional view is shown in FIG. 1 will be described using a vapor deposition apparatus whose outline is shown in FIG. 3. The nonmagnetic substrate 1 is a 10 μm thick substrate on which microprotrusions made of SiO2 particles with a height of about 200 Å and a density of 1.2×10 7 particles/mm 2 are provided on the surface on which the ferromagnetic metal thin film is deposited. Polyethylene terephthalate film was used.

First, in order to form the lower magnetic layer, the nonmagnetic substrate 1 is passed through a glow discharge treatment chamber 12 using oxygen plasma for removing moisture contained therein and cleaning the surface of the substrate. A film forming section composed of an electron beam heating device 8, an evaporation source 9, a shielding plate 10, and gas introduction sections 13 and 14 was passed along a cylindrical can 11 for cooling. Using Cu as the evaporation source 9, it is evaporated by electron beam heating, and a thickness of about 20 mm is deposited on the substrate.
A 0 Å nonmagnetic underlayer was deposited.

Next, in order to form the high magnetic energy layer 3, while transporting the substrate provided with the nonmagnetic underlayer 2 in the same manner as described above, an alloy having a composition of 80% Co and 20% Ni was used as an evaporation source. A lower magnetic layer was deposited on the substrate by evaporation by electron beam heating. At this time, the intensity of the electron beam, the amount of oxygen gas introduced from the two gas introduction sections 13 and 14, the conveyance speed of the nonmagnetic substrate, the shielding plate 10
and the relative position of the evaporation source 9, i.e. θmax, θmin
By appropriately selecting , the thickness of the high magnetic energy layer was approximately 1000 to 2000 Å, and the magnetic properties and oxygen distribution in the film were adjusted. The amount of oxygen gas introduced at this time is 500 to 150
0SCCM (Standard Cubic cc p
er Minutes) are listed in Table 1. Also,
The intensity of the electron beam was 20 keV, the transport speed of the nonmagnetic substrate was 0.5 m/sec, θmax was 90 degrees, and θmin was 40 degrees.

By the above procedure, magnetic tape samples #1 to #7 having two-layered magnetic films having the same non-magnetic underlayer 2 and high magnetic energy layer 3 having different magnetic properties and oxygen distribution in the film were prepared. Created. #1, 2, 3, and 4 are made by introducing oxygen only from the gas introduction part 13 when producing the high magnetic energy layer, and #5, 6, and 7 are made by introducing oxygen from the gas introduction part 13 and 14 when producing the high magnetic energy layer. It was created by introducing. For comparison, a ferromagnetic single layer film without the non-magnetic underlayer 2 and having a thickness of about 2000 Å was prepared by introducing oxygen into sample #8 through the gas introduction portions 13 and 14. #2, 3, 4 are examples of the present invention, #1, 5, 6,
7 and 8 are comparative examples.

The characteristics of the high magnetic energy layers of samples #1 to #7 or the ferromagnetic single layer film of sample #8 are as follows:
Thickness, in-plane longitudinal magnetic properties, average oxygen concentration at 100 Å near the surface and at 100 Å near the interface with the non-magnetic underlayer 2 (in the case of #1 to #7) or the non-magnetic substrate (in the case of #8). It is shown in Table 1.

A vibrating sample magnetometer (T
VSMP-1) manufactured by OEI was used. Here, the in-plane longitudinal direction is a direction within the film plane and parallel to the substrate transport direction. The average oxygen concentration is measured by Auger electron spectroscopy.
The concentration distribution of Co, Ni, O, and Cu contained in the fabricated film in the depth direction was determined, and the oxygen concentration among them was determined by 1 from the surface.
The average value was calculated at 00 Å and 100 Å from the interface with the nonmagnetic underlayer or nonmagnetic substrate. For the measurement, a PHI660 model manufactured by ULVAC-PHI was used, and the primary electron acceleration voltage was 3 kV and the current value was 50 nA. For etching with argon ions, the acceleration voltage was 3.5 kV and the current value was 0.5.
A raster scan of 2 mm x 2 mm was performed using μA.

Next, a back layer was applied to the substrate surface opposite to the magnetic layer of Samples #1 to #8, and 20 m of KRYTOX-K157SL manufactured by Maruwa Bussan Co., Ltd. was coated on the surface of the magnetic layer.
g/m2
It was dissolved in ZS-100 and applied. Next, it was cut into 8 mm width and assembled into an 8 mm video cassette, and the electromagnetic conversion characteristics were measured.

The electromagnetic conversion characteristics were measured using a modified Fuji Photo Film Hi-8 Movie M870HR.
A single wavelength signal of MHz was recorded at the optimum recording current, and the playback level and noise level at 6MHz were measured using a Hewlett-Packard Spectrum Analyzer 3585A.
The difference was determined as C/N. Table 1 shows the results using the C/N of sample #8 as the measurement standard (0 dB).

[0051]

[Table 1]

The results in Table 1 are expressed as Br×Hc and C/N of the magnetic layer.
When paying attention to the relationship, it can be seen that the larger Br×Hc is, the higher the C/N can be obtained. Especially when Br×Hc is 6.
In a range larger than 5×106 Oe・G (Oersted Gauss), even if the values of Br×Hc are the same, the example in which the oxygen concentration on the surface side is higher than the oxygen concentration on the interface side is better. The C/N is about 2 dB higher than that of the comparative example in which the oxygen concentration on the surface side is higher than the oxygen concentration on the surface side. This can be explained by the oxygen distribution in the film. That is, when a large amount of oxygen is contained on the interface side as in the comparative example, Br
In order to increase ×Hc, it is effective to reduce the amount of oxygen introduced during vapor deposition and increase Br, but when the amount of introduced oxygen decreases, the size of the particles forming the magnetic layer increases, and As a result, the noise level increases rapidly, and B
Although the C/N does not increase even if the output level increases due to an increase in r, when there is a non-magnetic underlayer and the amount of oxygen contained on the interface side is small as in the example, the amount of introduced oxygen can be particularly reduced. Even without this, Br can be increased relatively easily, and as a result, the output level can be increased without increasing the noise level, and the C/N becomes larger than that of the comparative example.

Although the details of the mechanism by which the magnetic properties change due to the oxygen distribution in the film are still unknown, the presence of gas such as oxygen at the interface influences crystal growth in the early stages of forming a ferromagnetic thin film. However, it is thought that this induces some kind of fluctuation, leading to deterioration of the magnetic properties. On the other hand, in a ferromagnetic thin film that does not introduce oxygen near the interface and is formed on a thin film layer such as a Cu underlayer, such fluctuations are small and it is thought that good magnetic properties can be obtained.

In the above embodiments of the present invention, Cu is used for the non-magnetic underlayer, but any material can be used for the non-magnetic underlayer as long as it has properties close to non-magnetic. is possible. Further, in the embodiments of the present invention, it is also possible to provide a ferromagnetic layer in place of the non-magnetic underlayer, or to provide one or more ferromagnetic layers or non-magnetic layers under the non-magnetic underlayer. What is required is a configuration that has at least one magnetic and/or nonmagnetic thin film layer between a nonmagnetic substrate and a ferromagnetic layer located farthest from the nonmagnetic substrate, and the nonmagnetic The oxygen concentration on the surface side of the ferromagnetic thin film layer located farthest from the substrate, that is, the high magnetic energy layer, is higher than the oxygen concentration on the interface side, and Br×Hc is 6.5×106 (Gauss-Oersted). It's bigger than that.

[0055]Although the case where the apparatus shown in Fig. 3 is used as an embodiment of the present invention has been described, it is also possible to deposit two or three layers at once using a vapor deposition apparatus having two or three cylindrical cans. It is also possible to produce the magnetic recording medium of the present invention by forming a magnetic recording medium.

[0056]

Effects of the Invention In the magnetic recording medium according to the present invention, the ferromagnetic metal thin film layer farthest from the nonmagnetic substrate has a Br×Hc of 6.
．． 5×106 (Gauss Oersted) or more,
By having the thin film layer have a higher oxygen concentration on the surface side than the oxygen concentration on the substrate side, it is possible to obtain high output and low noise, especially in the short wavelength region, and to improve the C/N. The ratio can be dramatically improved. Furthermore, this allows high-definition video tapes to be manufactured at low cost.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing an example of a cross section of a magnetic recording medium of the present invention.

FIG. 2 is a diagram schematically showing an example of a cross section of a magnetic recording medium of the present invention.

FIG. 3 is a diagram for explaining a specific example of a vacuum evaporation apparatus used to manufacture the magnetic recording medium of the present invention.

[Explanation of symbols]

1 Non-magnetic substrate 2 Non-magnetic underlayer 3 High magnetic energy layer 4 Lower magnetic layer 5 Nonmagnetic intermediate layer 6 High magnetic energy layer 7 Vacuum chamber 8　Electron beam heating device 9 Evaporation source 10 Shielding plate 11 Cylindrical can 12 Glow discharge treatment chamber 13 Gas introduction part 14 Gas introduction part 15 Unwinding roll 16 Take-up roll

Claims (2)

[Claims] Claim 1: A magnetic material having a layered structure consisting of two or more layers of thin films formed by vacuum deposition on a non-magnetic substrate, and the layered structure includes one or more ferromagnetic thin films. In the recording medium, the topmost thin film of the layer structure has a product (Br×Hc) of residual magnetic flux density (Br (Gauss)) and coercive force (Hc (Oersted)) of 6.5×106 (Gauss Oersted). ) A magnetic recording medium, characterized in that the high magnetic energy layer contains oxygen, and the oxygen concentration on the surface side is higher than the oxygen concentration on the nonmagnetic substrate side. 2. After forming at least one ferromagnetic thin film or nonmagnetic thin film on a nonmagnetic substrate by a vacuum film forming method, a ferromagnetic metal vapor flow is applied onto the ferromagnetic thin film or the nonmagnetic thin film. The angle of incidence with respect to the non-magnetic substrate changes continuously from the maximum angle of incidence (θmax) to the minimum angle of incidence (θmin), and the angle of incidence near the minimum angle of incidence (θmin) is higher than the angle of incidence near the maximum angle of incidence (θmax). A method for manufacturing a magnetic recording medium, comprising forming a high magnetic energy layer by an oblique incidence deposition method in which an oxidizing gas is introduced into the ferromagnetic metal stream so as to increase the amount of oxygen introduced.