JPH04349214A - Magnetic recording medium for digital recording - Google Patents

Abstract

PURPOSE:To provide the magnetic recording medium for digital recording which has the lesser asymmetry and distortion of isolated reproducing waveforms, has the uniform reproducing waveforms in spite of the execution of forward and backward rotations at the time of recording and reproducing, has a lower error rates, obviate the degradation in S/N, does not require equalization or allows the use of a simple equalization circuit. CONSTITUTION:This recording medium has a 1st ferromagnetic metallic thin film and 2nd ferromagnetic metallic thin film deposited by diagonal evaporation from different directions. The total thickness of the 1st ferromagnetic thin film is 0.7 to 1.3 times the total thickness of the 2nd ferromagnetic thin film and the total sum of t. theta of the respective layers constituting the 1st ferromagnetic thin film is 0.7 to 1.3 times the tn theta of the respective layers constituting the 2nd ferromagnetic thin film when the max. incident angle is designated as thetamax., the min. incident angle as thetamin, theta=thetamax-thetamin, and the thickness of the ferromagnetic metallic thin film as t.

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 for digital recording.

0002

2. Description of the Related Art Toward the practical application of HDTV, a magnetic tape capable of high-density recording is required in order to record a huge amount of digital image signals onto a small cassette.

[0003] In order to realize this, the Technical Report of the Television Society vol. 13, No. 59, PP19-24
(1989) reported experimental results of digital image recording using a coated magnetic tape using metal magnetic powder.

[0004] Also, in IEICE technical research report (IEICE technical report) PP39-44 MR90-15, Co-
Experiments have been conducted using a Cr-deposited perpendicular magnetic tape.

On the other hand, a magnetic tape whose magnetic layer is a ferromagnetic metal thin film mainly composed of Co and further containing Ni etc. and formed by an oblique evaporation method has a high saturation magnetic flux density and a high coercive force, making it an excellent magnetic tape. Shows electromagnetic conversion characteristics.

[0006] Therefore, IEICE Technical Report PP43-49 MR9
In 0-7, in order to investigate isolated reproduction waves using this obliquely deposited magnetic tape, we recorded rectangular waves, conducted experiments and analysis of the dependence on the running direction, and considered the recording mechanism. There is.

[0007] In this case, as shown in Figure 1 on page 43 of the report, the vapor deposition tape is a single-layer vapor deposition film in which columnar crystal grains grow in one direction, which is obliquely vapor-deposited from one direction. Used as a magnetic layer.

As a result, in this paper, by recording solitary wave signals in the forward and reverse directions at the optimum recording current, and observing four types of isolated reproduced waveforms in the forward and reverse directions for each, As shown in Figure 4 on page 45, the ratio of the time from the zero cross point to the peak point and the time from the peak point to the zero cross point is extremely large, less than 1/5, or more than 5 times, resulting in asymmetry of the reproduced waveform. is extremely large.

[0009] Furthermore, there is little overlap between the four types of reproduced waveforms, and among the most different reproduced waveforms, the overlap of peaks above 0 points is less than 60%.

[0010] If the isolated reproduced waveform is asymmetric and distorted as described above, and if waveform irregularities occur due to forward/reverse reversal of recording and reproduction, the error rate will increase in actual recording and reproduction, and the S/N will decrease.
In addition, a complicated equalization circuit is required, or equalization becomes extremely difficult, and depending on the degree of distortion of the reproduced waveform, it becomes difficult to maintain compatibility with so-called metal tapes.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the asymmetry and distortion of an isolated reproduced waveform, to ensure that the reproduced waveform is uniform even when forward/reverse rotation is performed during recording and reproduction, and to have a low error rate.
It is an object of the present invention to provide a magnetic recording medium for digital recording that does not cause a decrease in S/N, does not require equalization, or can use a simple equalization circuit.

0012

[Means for Solving the Problems] Such objects are achieved by the present invention as described in (1) to (6) below. (1) A magnetic recording medium for digital recording,
A magnetic layer is provided on a non-magnetic substrate, and this magnetic layer is formed by an oblique evaporation method and includes at least one first ferromagnetic metal thin film containing Co as a main component, and at least one layer of the first ferromagnetic metal thin film.
a second ferromagnetic metal thin film mainly composed of Co, which is formed by oblique evaporation from a direction different from that of the ferromagnetic metal thin film of The angle formed by the surface normal is the incident angle, the maximum value of the incident angle is θmax, the minimum value of the incident angle is θmin,
When Δθ=θmax −θmin and t is the film thickness of the layers constituting the first and second ferromagnetic metal thin films, the total film thickness of the first ferromagnetic metal thin film is equal to the second ferromagnetic metal thin film. The thickness is 0.7 to 1.3 times the total thickness of the magnetic metal thin film, and the sum of t and Δθ of each layer constituting the first ferromagnetic metal thin film constitutes the second ferromagnetic metal thin film. t・Δ of each layer
A magnetic recording medium for digital recording, characterized in that the value of θ is 0.7 to 1.3 times the sum of θ.

(2) A magnetic recording medium for digital recording, which has a magnetic layer on a non-magnetic substrate, and this magnetic layer is formed by an oblique evaporation method, and includes at least one layer of Co.
a first ferromagnetic metal thin film whose main component is at least one
and a second ferromagnetic metal thin film whose main component is Co, which is formed by oblique deposition from a direction different from that of the first ferromagnetic metal thin film, and which optimizes positive and negative solitary wave signals. 1. A magnetic recording medium for digital recording, wherein the time from a zero cross point to a peak point is 0.5 to 2 times the time from a peak point to a zero cross point when recorded and reproduced using a recording current.

(3) A magnetic recording medium for digital recording, which has a magnetic layer on a non-magnetic substrate, and this magnetic layer is formed by an oblique evaporation method, and includes at least one layer of Co.
a first ferromagnetic metal thin film whose main component is at least one
The first ferromagnetic metal thin film of the layer is formed by oblique deposition from a direction different from that of the first ferromagnetic metal thin film, and has a second ferromagnetic metal thin film mainly composed of Co, and runs in the forward and reverse directions. When a solitary wave signal is recorded at the optimum recording current, reproduced by running in the forward direction and reverse direction, and the reproduced waveforms are superimposed, the overlap between the reproduced waveforms is 7.
A magnetic recording medium for digital recording, characterized in that the magnetic recording medium is 0% or more.

(4) The angle between the direction in which the ferromagnetic metal is incident during vapor deposition and the normal to the surface of the non-magnetic substrate is defined as the incident angle, the maximum value of the incident angle is θmax, and the minimum value of the incident angle is θm.
in, Δθ=θmax −θmin, and the first
And, when the thickness of the layers constituting the second ferromagnetic metal thin film is t, the total thickness of the first ferromagnetic metal thin film is 0.0% of the total thickness of the second ferromagnetic metal thin film. 7 to 1.3 times, and t・Δ of each layer constituting the first ferromagnetic metal thin film.
(2) above, wherein the sum of θ is 0.7 to 1.3 times the sum of t and Δθ of each layer constituting the second ferromagnetic metal thin film;
Or the magnetic recording medium for digital recording according to (3).

(5) The angle between the direction in which the ferromagnetic metal is incident during vapor deposition and the normal to the surface of the non-magnetic substrate is defined as the incident angle, the maximum value of the incident angle is θmax, and the minimum value of the incident angle is θm.
in, Δθ=θmax −θmin, and the first
And, when the thickness of the layers constituting the second ferromagnetic metal thin film is t, the total thickness of the first ferromagnetic metal thin film is 0.0% of the total thickness of the second ferromagnetic metal thin film. 7 to 1.3 times, and t・Δ of each layer constituting the first ferromagnetic metal thin film.
The sum of θ is 0.7 to 1.3 times the sum of t and Δθ of each layer constituting the second ferromagnetic metal thin film, and positive and negative solitary wave signals are recorded at the optimum current. When played,
The magnetic recording medium for digital recording according to (3) above, wherein the time from the zero cross point to the peak point is 0.5 to 2 times the time from the peak point to the zero cross point.

(6) The magnetic recording medium for digital recording according to any one of (1) to (5) above, wherein digital recording is performed using a signal having a half-width of 50 to 500 nsec and a recording wavelength of 0.35 to 0.80 μm.

[0018]

[Operation] In forming a ferromagnetic metal thin film on an oblique evaporation type magnetic recording medium, a nonmagnetic substrate is placed on the surface of a rotating cylindrical cooling drum and transported, while an electron beam or the like is directed at a stationary ferromagnetic metal source. Vapor deposition is performed by irradiating the

At this time, the angle between the direction in which the ferromagnetic metal is incident and the normal to the surface of the non-magnetic substrate is called the angle of incidence, and the deposition is normally performed so that the angle of incidence gradually decreases from the start to the end of the deposition. Therefore, the columnar crystal grains in the ferromagnetic metal thin film formed on the non-magnetic substrate are approximately parallel to the non-magnetic substrate surface on the non-magnetic substrate side, and grow in an arc shape as they move away from the non-magnetic substrate surface.

[0020] The maximum and minimum values of the incident angle during vapor deposition are
Maximum incident angle θmax and minimum incident angle θmi respectively
It is called n. Note that θmax is 90 degrees or less,
θmin is a predetermined angle greater than 0 degrees.

Then, a ferromagnetic metal thin film is deposited at Δθ=θmax −θmin from θmax to θmin.

In the present invention, two or more layers of such ferromagnetic metal thin films are used as a magnetic layer, and the substrate is transported in the forward direction during vapor deposition to form one or more layers with crystal grains oriented in one direction. 1
The ferromagnetic metal thin film is laminated with one or more second ferromagnetic metal thin films whose crystal grains are oriented in the opposite direction by transporting the substrate in the opposite direction.

Then, the first and second ferromagnetic metal thin films are laminated, and preferably the Δθ and film thickness of each thin film are controlled within a predetermined range to improve the symmetry of the isolated reproduced waveform, It also eliminates the distortion and further eliminates waveform irregularities caused by forward/reverse recording/reproduction.

[0024]

[Specific Configuration] The specific configuration of the present invention will be explained in detail below. [Nonmagnetic Substrate] There are no particular restrictions on the material of the nonmagnetic substrate used in the present invention, and various films that can withstand the heat during deposition of a ferromagnetic metal thin film, such as polyethylene terephthalate, can be used. Further, various materials described in Japanese Patent Application Laid-Open No. 10315/1988 can be used. Note that various dimensions such as film thickness may be appropriately determined depending on the application.

[Magnetic Layer] The magnetic layer formed on the nonmagnetic substrate is composed of two or more ferromagnetic metal thin films containing Co as a main component and formed by oblique evaporation.

[0026] θmax during deposition of each ferromagnetic metal thin film is 8
The angle is preferably 0 to 90 degrees, and θmin is 10 to 90 degrees.
Preferably, the angle is 60 degrees.

In this case, in calculating Δθ, θma
x and θmin shall not be given positive or negative signs, but more precisely, θmax of the first ferromagnetic metal thin film
, θmin are positive values, θmax and θmin of the second ferromagnetic metal thin film are negative values.

[0028] This is because the ferromagnetic metal is deposited between the layers constituting the first and second ferromagnetic metal thin films so that the direction of incidence of the ferromagnetic metal intersects the normal line of the non-magnetic substrate. . Between the layers constituting the first and second ferromagnetic metal thin films, the growth directions of the columnar crystal grains of the ferromagnetic metal intersect with the normal line to the surface of the nonmagnetic substrate interposed therebetween.

[0029] Such a structure can be obtained by diagonally depositing the non-magnetic substrate with its running direction reversed.

There is no particular restriction on the total number of laminated ferromagnetic metal thin films, and a configuration of two, three, or four or more layers may be selected depending on the purpose.

In these cases, the stacking order of the first ferromagnetic metal thin film layer and the second ferromagnetic metal thin film layer is arbitrary.

That is, in the case of a two-layer structure, either layer may be located on the upper layer with respect to the medium running direction.

In the case of a multilayer structure of three or more layers, the layers may be laminated in any order, but usually the first and second ferromagnetic metal thin film layers are alternately laminated.

Under this assumption, when the thickness of each ferromagnetic metal thin film layer is t, the total thickness of the first ferromagnetic metal thin film is 0 of the total thickness of the second ferromagnetic metal thin film. .7~1.
3 times, especially 0.8 to 1.2 times.

Further, the sum of t and Δθ of each layer constituting the first ferromagnetic metal thin film is 0.7 to 1.3 times the sum of t and Δθ of each layer constituting the second ferromagnetic metal thin film. , especially 0.
It is 8 to 1.2 times.

[0036] Such a laminated body improves the symmetry of the reproduced waveform, reduces distortion, and provides a uniform waveform response even when recording and reproduction are performed in forward and reverse directions.

Each ferromagnetic metal thin film constituting the magnetic layer is made of N
A Co--Ni alloy containing i is preferable, and an alloy containing about 80% Co and about 20% Ni in molar ratio is particularly suitable.

[0038] Further, if necessary, it may contain 10% or less of Cr, and may also contain various metals described in JP-A-63-10315 and other metal components.

Furthermore, if necessary, corrosion resistance etc. can be improved by incorporating a small amount of oxygen into the surface layer of each layer or by interposing a non-magnetic layer.

The thickness of each ferromagnetic metal thin film layer is about 300 to
Preferably it is 1500A.

[0041] The total thickness of the magnetic layer is 1200 to 3000 mm.
It is preferable that it is about A. This allows the output to be sufficiently increased.

Each ferromagnetic metal thin film layer is formed by an oblique vapor deposition method. Since the oblique vapor deposition apparatus and method are described in the various documents mentioned above, any one may be adopted from among them.

In the oblique vapor deposition method, for example, a long film-like nonmagnetic substrate unwound from a supply roll is fed along the surface of a rotating cooling drum, while oblique vapor deposition is performed from one or more stationary metal sources. It is wound onto a take-up roll. In this case, the incident angle changes continuously from θmax at the initial stage of evaporation to θmin at the final stage, and columnar crystal grains of ferromagnetic metal mainly composed of Co are grown on the surface of the nonmagnetic substrate in an arc shape in one direction and aligned. It is.

When the magnetic layer has a multilayer structure, this step is repeated.

When forming two ferromagnetic metal thin film layers in which the direction of incidence of the ferromagnetic metal crosses the normal line of the nonmagnetic substrate, the running direction of the nonmagnetic substrate is reversed and diagonally Vapor deposition may be performed.

Preferably, various known top coat layers are provided on the magnetic layer of the magnetic recording medium of the present invention in order to protect the magnetic layer and improve corrosion resistance. Furthermore, in order to ensure runnability when formed into a tape, it is preferable that various known back coat layers be provided on the side of the nonmagnetic substrate opposite to the magnetic layer.

[Characteristics] Such a magnetic recording medium has a coercive force Hc in the longitudinal direction of the tape of about 800 to 1700 Oe, a residual magnetic flux density Br of about 2500 to 5000 G,
The maximum magnetic flux density Bm may be approximately 3000 to 7000G.

[0048] Also, (half width 50 to 500n
sec) When a rectangular wave positive and negative solitary wave pulse signal train having a recording wavelength of about 0.35 to 0.80 μm is recorded at the optimum recording current, the time from the zero cross point to the peak point of the reproduced waveform (rise time) is the time (fall time) from the peak point to the zero cross point.
It is preferably 5 to 2 times, particularly 0.8 to 1.5 times. Note that the optimum recording current is a recording current that provides the maximum output.

Furthermore, using a fixed head type head tester, the above-mentioned solitary wave signal was recorded in the forward and reverse directions at the optimum recording current, and then reproduced in the forward and reverse directions, respectively. When the reproduction waveforms of seeds are superimposed, the overlap of the peaks of 0 or more points of each reproduction waveform is 7
It is preferably 0% or more, particularly 80% or more, and even 90 to 100%.

[0050] In this way, when the reproduced waveform becomes symmetrical, distortion disappears, and the waveforms are aligned during forward/reverse recording/reproduction, the error rate decreases, the S/N ratio improves, and equalization becomes easier. It can also be omitted, improving compatibility with other tapes.

[Recording and Reproduction] Digital recording and reproduction may be performed in various known formats according to the various reports mentioned above. At this time, the half width of the recording signal is usually 50 to 500.
The recording wavelength is approximately 0.35 to 0.80 μm.

[0052]

EXAMPLES Hereinafter, specific examples of the present invention will be shown and the present invention will be explained in more detail. [Example 1] In an Ar atmosphere of 10-4 Torr, a polyethylene terephthalate (PET) film with a thickness of 7 μm was fed out from a supply roll and moved along the circumferential surface of a rotating cylindrical cooling drum. C
A ferromagnetic metal thin film was formed by diagonally depositing the O alloy, and the film was wound onto a take-up roll.

Next, using this winding roll as a supply roll, a ferromagnetic metal is obliquely vapor-deposited in an incident direction that intersects the incident direction during the above-mentioned oblique vapor deposition, with the normal direction of the PET film surface in between, to form a two-layer structure. A magnetic recording medium having a magnetic layer was obtained.

Both θmin and θmax during vapor deposition of the upper and lower ferromagnetic metal thin films are 4, respectively.
0° and 90°, Δθt and Δθu of the upper layer and lower layer are respectively 50°, and the thickness of the upper layer tt
was 1000A, and the thickness tu of the lower layer was 1000A.

This sample has tu /tt =1, t
u Δθu /tt Δθu =1.

[0056] This sample was cut into a tape with a width of 8 mm using a slitter to make a video cassette.

Separately, for comparison, θmin = 4
A 20 at % Ni--Co alloy thin film having a single layer structure of a 2000A film was formed at 0° and θmax = 90° to produce a comparative cassette.

Each cassette was loaded into an actual machine (S900 manufactured by Sony Corporation) equipped with an MIG head, and 1 MHz positive and negative isolated square waves were recorded at the optimum recording current, and the zero cross-peak time Tl and peak- Zero cross time Tr was measured.

Furthermore, using a drum-type head tester, the above-mentioned isolated rectangular wave was recorded in the forward and reverse directions at the optimum recording current, and these were reproduced in the forward and reverse directions, respectively, to digitally reproduce the four types of waveforms. It was measured with an oscilloscope, averaged 16 times, and plotted. These plots were superimposed, and the one with the smallest overlapping area of 0 or more peaks was determined as the degree of overlap. These results are shown in Table 1 below.

[0060]

[Table 1]

Next, using each of these cassettes, we measured the error rate on an actual machine (modified digital audio tape recorder), and found that the cassette of the present invention had an error rate of 10-4 compared to the comparative cassette. It became 10-5.

[0062]

[Effects of the Invention] When the magnetic recording medium of the present invention is used for digital recording, the error rate is low, the S/N is high, equalization can be simplified, and compatibility with other media is excellent.
Extremely high quality digital recording can be performed.

Claims (6)

[Claims] 1. A magnetic recording medium for digital recording, comprising a magnetic layer on a non-magnetic substrate, the magnetic layer being formed of at least one layer by an oblique evaporation method, and comprising at least one layer containing Co as a main component. a ferromagnetic metal thin film, and at least one second ferromagnetic metal thin film, which is formed by oblique evaporation from a direction different from that of the first ferromagnetic metal thin film, and whose main component is Co. , the angle between the direction in which the ferromagnetic metal is incident during vapor deposition and the normal to the surface of the non-magnetic substrate is defined as the incident angle, the maximum value of the incident angle is θmax, and the minimum value of the incident angle is θ
min, Δθ=θmax −θmin, and the thickness of the layer constituting the first and second ferromagnetic metal thin films is t.
When, the total film thickness of the first ferromagnetic metal thin film is 0.7 to 1.3 times the total film thickness of the second ferromagnetic metal thin film, and the first ferromagnetic metal thin film t・ of each layer constituting
A magnetic recording medium for digital recording, characterized in that the sum of Δθ is 0.7 to 1.3 times the sum of t·Δθ of each layer constituting the second ferromagnetic metal thin film. 2. A magnetic recording medium for digital recording, comprising a magnetic layer on a non-magnetic substrate, the magnetic layer comprising at least one layer formed by an oblique evaporation method and comprising Co as a main component. a ferromagnetic metal thin film, and at least one second ferromagnetic metal thin film, which is formed by oblique evaporation from a direction different from that of the first ferromagnetic metal thin film, and whose main component is Co. , when positive and negative solitary wave signals are recorded and reproduced at the optimum recording current, the time from the zero cross point to the peak point is 0.5 to 2 times the time from the peak point to the zero cross point. A magnetic recording medium for digital recording. 3. A magnetic recording medium for digital recording, comprising a magnetic layer on a non-magnetic substrate, the magnetic layer comprising at least one layer formed by an oblique evaporation method and comprising Co as a main component. a ferromagnetic metal thin film, and at least one second ferromagnetic metal thin film, which is formed by oblique evaporation from a direction different from that of the first ferromagnetic metal thin film, and whose main component is Co. , when traveling in the forward and reverse directions to record a solitary wave signal at the optimum recording current, reproducing by traveling in the forward and reverse directions, and superimposing each reproduced waveform, each reproduced waveform The overlap is 70
% or more. 4. The angle between the direction in which the ferromagnetic metal is incident during vapor deposition and the normal to the surface of the non-magnetic substrate is defined as the incident angle,
The maximum value of the incident angle is θmax, the minimum value of the incident angle is θmi
n, Δθ=θmax −θmin, and when the film thickness of the layers constituting the first and second ferromagnetic metal thin films is t, the total film thickness of the first ferromagnetic metal thin film is the second ferromagnetic metal thin film. is 0.7 to 1.3 times the total film thickness of the ferromagnetic metal thin film, and t·Δθ of each layer constituting the first ferromagnetic metal thin film.
4. The magnetic recording medium for digital recording according to claim 2, wherein the sum of t and Δθ of each layer constituting the second ferromagnetic metal thin film is 0.7 to 1.3 times. 5. The angle between the direction in which the ferromagnetic metal is incident during vapor deposition and the normal to the surface of the non-magnetic substrate is defined as the incident angle,
The maximum value of the incident angle is θmax, the minimum value of the incident angle is θmi
n, Δθ=θmax −θmin, and when the film thickness of the layers constituting the first and second ferromagnetic metal thin films is t, the total film thickness of the first ferromagnetic metal thin film is the second ferromagnetic metal thin film. is 0.7 to 1.3 times the total film thickness of the ferromagnetic metal thin film, and t·Δθ of each layer constituting the first ferromagnetic metal thin film.
is 0.7 to 1.3 times the sum of t and Δθ of each layer constituting the second ferromagnetic metal thin film, and positive and negative solitary wave signals are recorded and reproduced at the optimum current. 4. The magnetic recording medium for digital recording according to claim 3, wherein the time from the zero cross point to the peak point is 0.5 to twice the time from the peak point to the zero cross point. 6. The magnetic recording medium for digital recording according to claim 1, wherein digital recording is performed using a signal having a half-width of 50 to 500 nsec and a recording wavelength of 0.35 to 0.80 μm.