JP3009943B2 - Magnetic recording media for digital recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-plane recording type magnetic recording medium for digital recording having a ferromagnetic metal thin film composed of columnar crystal grains formed by oblique evaporation as a magnetic layer.

[0002]

2. Description of the Related Art To put HDTV to practical use, a magnetic tape capable of high-density recording is required to record a huge amount of digital image signals on a small cassette.

[0003] To achieve this, the technical report of the Institute of Television Engineers of Japan vol.13, No. 59, PP19-24 (1989) includes an experiment of digital image recording using a coated magnetic tape using metal magnetic powder. The results have been reported.

Further, in the IEICE Technical Report (IEICE Technical Report) PP39-44 MR90-15, an experiment is carried out using a perpendicular magnetic tape of Co-Cr evaporation type.

On the other hand, a magnetic tape containing Co as a main component, further containing Ni or the like, and using a ferromagnetic metal thin film formed by an oblique vapor deposition method as a magnetic layer has a high saturation magnetic flux density, a high coercive force, and is excellent. Shows electromagnetic conversion characteristics. In the oblique deposition method, a ferromagnetic metal vapor is incident on the surface of a nonmagnetic substrate at a specific angle by a vapor phase method such as vapor deposition to form a ferromagnetic metal thin film composed of columnar crystal grains.

In the IEICE Technical Report PP43-49 MR90-7, using this obliquely deposited magnetic tape, a rectangular wave is recorded in order to investigate an isolated reproduction wave, and an experiment on the running direction dependency and the like are performed and analyzed. We are studying the recording mechanism. In this report, as shown in FIG. 1 on page 43, a single layer deposited film in which columnar crystal grains are grown obliquely from one direction and grown in one direction is used as the magnetic layer.

As a result, in this report, the solitary wave signal is recorded at the optimum recording current in the forward direction and the reverse direction, and four types of isolated reproduction waveforms in the forward direction and the reverse direction are observed for each of them. As shown in FIG. 4 on page 45, the ratio of the time from the zero crossing point to the peak point and the time from the peak point to the zero crossing point is extremely large, 1/5 or less, or 5 times or more, and the asymmetry of the reproduced waveform Is very large.

When the isolated reproduction waveform is asymmetric, the error rate increases in actual recording and reproduction. In particular, in a consumer standard, there is a small margin for error correction, for example, when band compression is used. Therefore, reducing the error rate is an important issue.

If the reproduced waveform is asymmetric, it is necessary to increase the width (window margin) per unit waveform in order to keep the error rate low, so that high-density recording becomes impossible. Also, since the sampling frequency cannot be increased, a high S / N cannot be obtained.

Although the asymmetry of the reproduced waveform can be corrected by an equalizing circuit, equalization is extremely difficult or impossible if the asymmetry is significant. In addition, compatibility with the coating type metal tape cannot be obtained. This is because the coating-type metal tape has good symmetry of the reproduced waveform because the axis of easy magnetization exists in the in-plane direction of the magnetic layer.

A magnetic recording medium for digital recording is required to have a high output in addition to the symmetry of the reproduced waveform. If the output is low, the error rate will increase.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnetic recording medium for digital recording in which the asymmetry of an isolated reproduction waveform is low and a high output can be obtained. And

[0013]

This and other objects are achieved by the present invention which is defined below as (1) to (4).

(1) A magnetic layer having a ferromagnetic metal thin film composed of columnar crystal grains formed by an oblique vapor deposition method is formed on a substrate surface, and the magnetic layer is formed of at least one ferromagnetic metal thin film. A lower layer, and an upper layer made of at least one ferromagnetic metal thin film, wherein an average growth direction of the columnar crystal particles in the lower layer and an average growth direction of the columnar crystal particles in the upper layer sandwich a normal line of the base. Intersect, and the thickness of the lower layer is 1.2 to less than the thickness of the upper layer.
A magnetic recording medium for digital recording, wherein the digital recording is performed by a magnetic head having a magnification of 5.0 times and relatively moving in the growth direction of the columnar crystal grains in the upper layer.

(2) When the 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 of the reproduced signal is equal to the time from the peak point to the zero cross point. The magnetic recording medium for digital recording according to the above (1), wherein the medium is 5 to 1.5 times.

(3) The magnetic recording medium for digital recording according to the above (1) or (2), wherein digital recording is performed by a signal having a half width of 50 to 500 nsec and a wavelength of 0.35 to 0.80 μm.

(4) The coercive force in the plane of the magnetic layer is 800 Oe or more, and the residual magnetic flux density is 2500 G
The magnetic recording medium for digital recording according to any one of (1) to (3) above.

[0018]

As shown in FIG. 1, in the magnetic layer 3 of the magnetic recording medium 1 for digital recording of the present invention, the average growth direction of the columnar crystal grains in the lower layer 31 and the average growth direction of the columnar crystal grains in the upper layer 32 are different. The magnetic head 10 intersects across the normal line of the base 2, and the relative movement direction of the magnetic head 10 during recording and reproduction is on the growth direction side of the columnar crystal grains in the upper layer 32.

In such a configuration, by setting the ratio of the thickness of the lower layer 31 to the thickness of the upper layer 32 within the above range, the symmetry of the isolated reproduction waveform is improved, and a sufficient output is obtained. This results in lower error rates,
Since a window margin required per unit waveform can be narrowed, high-density digital recording can be performed, and a high sampling frequency can be obtained and a good S / N can be obtained. Further, the equalization becomes easy or the equalization can be omitted, and the compatibility with the coating type metal tape is improved.

[0020]

[Specific Configuration] Hereinafter, a specific configuration of the present invention will be described in detail.

In the magnetic recording medium for digital recording of the present invention, a magnetic layer having a ferromagnetic metal thin film composed of columnar crystal grains formed by an oblique vapor deposition method is formed on the surface of a substrate. The magnetic layer has a lower layer made of at least one ferromagnetic metal thin film and an upper layer made of at least one ferromagnetic metal thin film, and is laminated in the order of a base, a lower layer, and an upper layer.

FIG. 1 shows a preferred embodiment of a magnetic recording medium for digital recording according to the present invention. The magnetic recording medium 1 for digital recording shown in FIG. 1 has a magnetic layer 3 on a base 2.
The lower layer 31 and the upper layer 32 constituting the magnetic layer 3 are each composed of one ferromagnetic metal thin film, and the average growth direction of the columnar crystal particles 311 in the lower layer 31 and the average growth direction of the columnar crystal particles 321 in the upper layer 32 are as follows. They intersect with the normal line of the base 2 interposed therebetween.

The same applies to the case where the lower layer and / or the upper layer is composed of a plurality of ferromagnetic metal thin films. That is, the average growth direction of the columnar crystal grains of all the ferromagnetic metal thin films belonging to the lower layer is interposed between the average growth direction of the columnar crystal particles of all the ferromagnetic metal thin films belonging to the upper layer and the normal line of the base 2. Intersect.

As described above, by forming the lower layer and / or the upper layer from a plurality of ferromagnetic metal thin films, the particle diameter of the columnar crystal grains of each ferromagnetic metal thin film can be reduced, and a good S / N ratio can be obtained. It is possible to obtain.

In FIG. 1, the relative movement direction of the magnetic head 10 during recording and reproduction is on the growth direction side of the columnar crystal grains in the upper layer 32. The growth direction side of the columnar crystal particles is a direction substantially matching the direction in which the growth direction of the columnar crystal particles is projected on the main surface of the substrate 2 (the direction indicated by the arrow in the figure). When recording is performed, the recording angle falls within a range of about ± 10 ° or less within the main surface of the base with respect to the projected direction.

The thickness of the lower layer 31 is 1.times.
It is 2 to 5.0 times, preferably 1.5 to 4.0 times. When the magnetic head relatively moves in the above-described direction, the symmetry of the reproduced waveform is critically improved by setting the thickness of both layers in such a relationship. Specifically, the half width is 50 to 500.
When a pulse signal train of positive and negative solitary waves of, for example, a rectangular wave having a recording wavelength of about 0.35 to 0.80 μm is recorded in nsec, the time (rise time) from the zero cross point to the peak point of the reproduced waveform is defined as the peak time. The time (fall time) from the point to the zero cross point (fall time) can be reduced to about 0.5 to 1.5 times, particularly about 0.8 to 1.2 times. In this case, the ratio between the rise time and the fall time is at the optimum recording current (the recording current at which the maximum output is obtained).

When the thickness of the lower layer is less than 1.2 times the thickness of the upper layer, the above effect is insufficient. When the thickness exceeds 5.0 times, the thickness of the upper layer becomes insufficient. The strength is insufficient, and the output is also insufficient.

The total thickness of the magnetic layer is 1000 to 3000
A, particularly preferably 1500 to 2500 A.
If the thickness of the magnetic layer is less than the above range, the strength of the entire magnetic layer is insufficient and the reliability is reduced. On the other hand, if it exceeds the above range, the recording magnetization forms a rotation mode, and the reproduction output decreases.

When the lower layer and / or the upper layer is composed of a plurality of ferromagnetic metal thin films, the thickness of each ferromagnetic metal thin film is not particularly limited, and is appropriately set according to the thickness of the entire magnetic layer and the number of layers. do it.

The inclination of the columnar crystal grains of each ferromagnetic metal thin film is not particularly limited, and depends on the required in-plane coercive force and residual magnetic flux density, or the position of the ferromagnetic metal thin film in the magnetic layer. However, in order to obtain a high coercive force and a high residual magnetic flux density, the angle θ between the average growth direction of the columnar crystal grains and the main surface of the substrate is set to 40 to 80.
°, particularly preferably 50 to 70 °. When the lower layer and / or the upper layer is composed of a plurality of ferromagnetic metal thin films, the average growth directions of the ferromagnetic metal thin films belonging to the same layer do not need to coincide with each other. Accordingly, the angle θ in each thin film may be different.

The angle θ between the average growth direction of the columnar crystal grains and the main surface of the substrate is determined as follows. First, the medium is cut on a plane including the growth direction of the columnar crystal grains and perpendicular to the main surface of the base. In the cross section, the cross section of the columnar crystal particles constituting each ferromagnetic metal thin film appears in an arc shape. The angle formed between the side surface of the columnar crystal grains appearing in this cross section (the boundary line between adjacent columnar crystal grains) and the main surface of the substrate was measured for at least 100 columnar crystal grains for each ferromagnetic metal thin film. The average value of those in the metal thin film is determined. These average values are defined as an angle θ between the average growth direction of the columnar crystal grains in each ferromagnetic metal thin film and the main surface of the base. The measurement position of θ is an intermediate point in the thickness direction of the ferromagnetic metal thin film.

The angle θ depends on the incident direction of the ferromagnetic metal in the oblique vapor deposition method, and particularly depends on the minimum incident angle θmin.

The ferromagnetic metal thin film constituting the magnetic layer is preferably a Co-based alloy containing Co as a main component, and the Co content in the ferromagnetic metal thin film is preferably at least 60 atomic%. As the Co-based alloy, Co and Ni are mainly used, or Co, Ni and Cr
Is preferred. The content of each element other than Co may be appropriately selected according to the required magnetic properties and corrosion resistance.

The magnetic properties of the magnetic layer are not particularly limited, and the desired magnetic properties may be obtained by appropriately selecting the composition of the magnetic layer, the average growth direction of the columnar crystal grains, and the like. To achieve this, the coercive force Hc in the plane of the magnetic layer should be 800 Oe or more, and the residual magnetic flux density Br should be 2500G.
As described above, it is preferable that the maximum magnetic flux density Bm be 3000 G or more. Normally, Hc is about 1700 Oe or less,
Br is about 5000G or less and Bm is about 7000G or less.

Each ferromagnetic metal thin film is formed by an oblique evaporation method. There is no particular limitation on the oblique vapor deposition apparatus and method, and a normal one may be used.

In the oblique vapor deposition method, for example, oblique vapor deposition is performed from one or more stationary metal sources while feeding a long film-shaped non-magnetic substrate fed from a supply roll along the surface of a rotating cooling drum. It is to be taken up on a take-up roll. In this case, the incident angle is the maximum incident angle θma at the beginning of vapor deposition.
It changes continuously from x to the final minimum incident angle θmin, and columnar crystal grains grow in an arc on the substrate surface. When forming the upper layer on the lower layer, the winding roll at the time of forming the lower layer may be used as a supply roll to perform vapor deposition with the running direction of the substrate reversed.

The values of θmax and θmin may be appropriately determined according to the desired magnetic properties and the like.
It is preferable that the angle θmin be about 0 to 90 ° and the θmin be about 10 to 60 °.

It is preferable that oxygen gas be introduced into the atmosphere during the oblique deposition to improve coercive force and stability against oxidation.

The material of the substrate used in the present invention is not particularly limited as long as it is non-magnetic, and various films that can withstand heat during the deposition of the ferromagnetic metal thin film, for example, polyethylene terephthalate can be used. Also, JP-A-63-1031
Various materials described in No. 5 can be used.

It is preferable that fine projections are provided on the surface of the substrate used in the present invention. Since the magnetic layer is a vapor-deposited film and is extremely thin, the properties of the substrate surface appear directly on the surface of the magnetic layer. Therefore, if minute projections are provided on the surface of the base, minute projections can appear on the surface of the magnetic layer.
The protrusions on the surface of the magnetic layer reduce the friction of the magnetic layer to improve the runnability when taped, and also enhance the durability of the medium.

The nature and formation method of the minute projections on the surface of the substrate are not particularly limited, but the arrangement pattern of the projections and the surface roughness of the substrate after the formation of the projections affect the magnetic properties of the magnetic layer, particularly the coercive force. In the present invention, it is preferable that the protrusions are provided by disposing fine particles on the surface of the substrate.

The fine particles to be used are preferably in the form of particles, in particular, substantially spherical. For example, SiO ₂ , Al ₂
O ₃ , MgO, ZnO, MgCO ₃ , CaCO ₃ , Ca
Inorganic containing at least one of oxides such as SO ₄ , BaSO ₄ and TiO ₂ , sulfates and carbonates, and oxides or acid salts of metals such as Si, Al, Mg, Ca, Ba, Zn and Mn. Particles or spherical particles of one or more organic compounds such as polystyrene, polyester, polyamide, and polyethylene are preferred. These fine particles may or may not have magnetism.

The average particle size of the fine particles is 100 to 1000
A, particularly preferably 300 to 600A. If the average particle size is less than the above range, the friction reducing effect is small,
The effect of improving durability is also insufficient. On the other hand, if the average particle size exceeds the above range, the surface roughness of the magnetic layer becomes large, making it difficult to obtain the center line average roughness Ra described later, which lowers the coercive force and makes the high frequency characteristics insufficient. .

The arrangement density of the fine particles is 10 per 1 mm ^2.
It is preferable that the number is 10,000 to 100 million, especially 1 to 70 million. If the arrangement density is too low, the effect of providing fine particles becomes insufficient. Further, even if the arrangement density is too high, the effect is not improved, and it is difficult to set the chain ratio described later.

It is preferable that the fine particles are arranged as uniformly as possible. If the particles are aggregated or extremely close to each other, they behave as apparently large particles (secondary particles), which is not preferable. The degree of proximity between fine particles is defined herein as a chain ratio. That is, assuming that the average diameter of the particles disposed on the surface of the substrate is R and the distance between adjacent particles is d, the chain ratio = (number of particles per unit area satisfying d <R) × 100 / (Number of particles per unit area) (unit is%). In addition, the distance d between particles and the number of particles are measured by an electron micrograph.

In the present invention, such a chain ratio is 70%
Hereinafter, it is particularly preferably 0 to 60%. When the chain ratio exceeds the above range, the fine particles behave as secondary particles, so that the growth directions of the columnar crystal particles are difficult to be uniform, and the coercive force is reduced. In addition, after the formation of the magnetic layer, the diameter and height of the protrusions appearing on the surface of the magnetic layer become extremely large, the surface properties of the magnetic layer are reduced, and the electromagnetic conversion characteristics are reduced due to spacing loss.

Center line average roughness R of the substrate after disposing fine particles
a is preferably 40 A or less, particularly preferably 30 A or less. If Ra exceeds the above range, the growth directions of the columnar crystal grains are difficult to be uniform, and the coercive force tends to decrease. If Ra is too low, the effect of reducing friction is insufficient and durability is lowered, so Ra is preferably 10 A or more.

The method for disposing the fine particles on the surface of the substrate is not particularly limited. For example, a method in which the fine particles are dispersed in a thin binder in which a synthetic resin is dissolved in a solvent is applied to the substrate, or such a binder is used. A method in which fine particles are adhered after coating is preferably used.

It is preferable that 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. Further, in order to ensure the running property when the tape is formed, it is preferable to provide various known backcoat layers on the side of the substrate opposite to the magnetic layer.

The method of digital recording / reproducing performed on the magnetic recording medium of the present invention is not particularly limited. For example, digital recording / reproducing may be performed in various formats according to the above-mentioned various reports, etc. 50-500ns
ec, digital recording is performed at a recording wavelength of about 0.35 to 0.80 μm.

The magnetic recording medium for digital recording of the present invention is usually taped and used for various purposes.

[0052]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention.

Example 1 As fine particles, SiO ₂ (average particle diameter 300 A) 0.1
5% by weight, 0.2% by weight of methylcellulose as a binder, and a silane coupling agent [N-β (aminoethyl) -γaminopropylmethyldimethoxysilane]
02% by weight was thoroughly mixed and dispersed with a formulation containing water as a residual solvent, and the resulting suspension was applied to a 7 μm-thick polyethylene terephthalate (PET) substrate surface,
Dried.

The arrangement density of the fine particles after drying is 10 million particles /
mm ² , the chain ratio was 50%, and Ra on the substrate surface was 30A.

Next, a ferromagnetic metal thin film was deposited on the surface of the substrate.

The substrate is unwound from the supply roll, moved along the peripheral surface of the rotating cylindrical cooling drum, and a ferromagnetic metal thin film is formed by obliquely depositing a ferromagnetic metal to form a lower layer. Wound up.

Next, the take-up roll is used as a supply roll, and a ferromagnetic metal is obliquely vapor-deposited in an incident direction that intersects the incident direction during the oblique vapor deposition with the normal direction of the substrate surface interposed therebetween. Was formed as an upper layer to obtain a magnetic recording medium sample.

In forming the upper layer and the lower layer, a mixed gas of Ar gas and O ₂ gas was flowed into the vacuum chamber, and the pressure in the vacuum chamber was maintained at 10 ^-4 Torr. In addition, the mixed gas was caused to flow so as to be sprayed on a portion of the substrate to be deposited near the minimum incident angle. The maximum incident angle θmax at the time of forming each layer was 90 °, and the minimum incident angle θmin was 35 °.

For forming the upper layer and the lower layer of each sample, a ferromagnetic metal having a composition of 80 atomic% of Co and 20 atomic% of Ni was used.

A plurality of samples were prepared by changing the ratio of the lower layer thickness to the upper layer thickness. The angle θ between the average growth direction of the columnar crystal grains in the lower layer and the upper layer of each sample and the main surface of the substrate was 55 °. The angle θ was measured by the method described above. The number of columnar crystal particles measured was 100. The total thickness of the lower and upper layers of each sample was 2000A.

Each sample was cut into a width of 8 mm with a slitter to form a tape, and the sample was mounted on a video cassette such that the relative movement direction of the magnetic head with respect to the tape was on the growth direction of the columnar crystal grains in the upper layer. Next, each cassette is
VCR equipped with a head (S90 manufactured by Sony Corporation)
Was charged to 0), and records the sign isolated rectangular wave of 1 MHz, the zero-crossing of isolated reproduction wave - and the zero crossing time T _R measured - peak time T _L, the peak. FIG. 2 shows the relationship between the recording current and T _L / T _R.

Further, a sine wave of 10 MHz was recorded on each sample, and the reproduced output was measured. FIG. 3 shows the relationship between the recording current and the reproduction output.

From the results shown in FIGS. 2 and 3, the effect of the present invention is clear. That is, for the lower layer thickness and the upper layer thickness are equal comparative sample, a sample of the present invention the thickness of the lower layer is in the range of 1.2 to 5.0 times the upper thickness, T _L / T _R Is closer to 1 and the T _L / T _R is about 1 to 1.2 at the optimum recording current (−10 dBm), indicating that the isolated reproduction waveform has good symmetry.
Since the recording current range in which T _L / T _R falls within the range of 0.8 to 1.5 is as wide as −20 to −7 dBm, the degree of freedom in circuit design is high, and it is very advantageous in terms of compatibility. You can see that there is. Note that dBm represents a power level, and 1 mW of power is 0 dBm. In addition, the sample of the present invention has almost the same reproduction output as the comparative sample.

In each sample, the coercive force Hc in the in-plane direction of the magnetic layer was about 1200 Oe, and the residual magnetic flux density Br was about 450 Oe.
0G and the squareness ratio were about 0.78.

When the error rate of each of the above samples was measured with a modified digital audio tape recorder (DAT), the sample of the present invention had an error rate lower by two digits or more than the comparative sample.

[0066]

According to the magnetic recording medium for digital recording of the present invention, the symmetry of the reproduced waveform is good and a sufficient output can be obtained, so that the error rate is low. Further, since a window margin per unit waveform can be narrowed and short-wavelength recording can be performed, high-density recording can be performed and high S / N can be obtained. In addition, since equalization is not easy or equalization is not required, compatibility with a coating type metal tape or the like is high.

[Brief description of the drawings]

FIG. 1 is a sectional view partially showing a preferred embodiment of a magnetic recording medium for digital recording according to the present invention.

FIG. 2 is a graph showing a relationship between a recording current and T _L (zero cross-peak time of an isolated reproduction wave) / T _R (peak-zero cross time).

FIG. 3 is a graph showing a relationship between a recording current and a reproduction output.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic recording medium for digital recording 2 Base 3 Magnetic layer 31 Lower layer 311 Columnar crystal particle 32 Upper layer 321 Columnar crystal particle 10 Magnetic head

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 5/66 G11B 5/02

Claims (4)

(57) [Claims] 1. A magnetic layer having a ferromagnetic metal thin film composed of columnar crystal grains formed by an oblique vapor deposition method is formed on a substrate surface, and the magnetic layer is a lower layer composed of at least one ferromagnetic metal thin film. And an upper layer made of at least one ferromagnetic metal thin film, wherein an average growth direction of the columnar crystal particles in the lower layer and an average growth direction of the columnar crystal particles in the upper layer intersect with a normal line of the base interposed therebetween. The thickness of the lower layer is 1.2 to 5.0 of the thickness of the upper layer.
A magnetic recording medium for digital recording, characterized in that digital recording is performed by a magnetic head which is doubled and relatively moves in the growth direction of columnar crystal grains in the upper layer. 2. When the positive and negative solitary wave signals are recorded and reproduced at an optimum recording current, the time from the zero cross point to the peak point of the reproduced signal is 0.5% of the time from the peak point to the zero cross point. 2. The magnetic recording medium for digital recording according to claim 1, wherein the ratio is 1.5 to 1.5 times. 3. A half width of 50 to 500 nsec and a wavelength of 0.35.
3. The magnetic recording medium for digital recording according to claim 1, wherein digital recording is performed with a signal of .about.0.80 .mu.m. 4. The coercive force in the plane of the magnetic layer is 800.
4. The magnetic recording medium for digital recording according to claim 1, wherein the magnetic recording medium has a magnetic flux density of not less than Oe and a residual magnetic flux density of not less than 2500 G.