JPH0528454A - Perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the reproduced output of long wavelengths by forming the perpendicular magnetic recording medium of a Co-O system as a two-layered structure and specifying the magnetic characteristics of the lower layer film to a prescribed value. CONSTITUTION:A-1st perpendicularly magnetized film 102 of the Co-o system and a 2nd perpendicularly magnetized film 103 of the Co-O system are successively laminated on a nonmagnetic base 101. The perpendicular magnetic anisotropy energy Kv obtd. after the shape magnetic anisotropy 2Es of the perpendicularly magnetized film 102 to serve as a substrate layer is removed is 1.4X10<6=kv<=3.2X10<6> erg/cc and the ratio 2piMs<2/k>VM of the shape magnetic anisotropy 2piMs<2> and the perpendicular magnetic anisotropy energy kv is specified to 1.5<2piMs<2>/kv<3.0. Further, the film thickness of the perpendicularly magnetized film 103 is 1500 to 200OAngstrom and the direction of the perpendicular magnetic anisotropy excluding the shape magnetic anisotropy is inclined by 10 to 40 deg. with the normal direction of the film plane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a perpendicular magnetic recording medium suitable for recording digital signals in a digital VTR or the like.

[0002]

2. Description of the Related Art In the field of magnetic recording, there is a demand for higher density year by year, and in addition, the signal form is changing from an analog signal to a digital signal, and it is necessary to design a medium suitable for the signal form as the density increases. Has become. Up to now, the magnetic recording method has mainly been a so-called in-plane magnetic recording method which uses a magnetic recording medium having an easy axis of magnetization in the surface, but in this method, the higher the recording density, the higher the magnetic recording. Since the magnetization directions of the medium are arranged so as to repel each other, the densification is naturally limited, and it is difficult to achieve the required densification.

Further, in the in-plane magnetic recording method, in a pattern in which the magnetization reversal is repeated twice, the closer the intervals of the respective magnetization reversals become (the higher the density is), the more the magnetic repulsion and the peak shift due to the waveform interference occur. However, there are drawbacks such as occurrence of an error rate and deterioration of the error rate. Therefore, in recent years, a perpendicular magnetic recording method using a magnetic recording medium having an easy axis of magnetization in the direction perpendicular to the film surface has been developed as a new method of magnetic recording, and its practical application is expected. In the perpendicular magnetic recording method, the demagnetization effect is extremely small as compared with the in-plane magnetic recording method, and the recording density can be dramatically increased.

[0004]

By the way, as a perpendicular magnetic recording medium for recording and reproducing a digital signal by the perpendicular magnetic recording method, C having a large perpendicular magnetic anisotropy is used.
The OO perpendicular magnetic recording medium has been attracting attention.
In the OO perpendicular magnetic recording medium, the magnetization is reversed by a relatively small magnetic field when the magnetic field is substantially perpendicular to the magnetic film, whereas the magnetization is reversed in the hard axis direction, that is, the longitudinal direction. It has the feature of requiring a large magnetic field. In a perpendicular magnetic recording system aiming at practical use, it is considered to use a ring type magnetic head. However, this ring type magnetic head has a relatively large perpendicular magnetic field component in the vicinity of the head (near the interface between the upper layers of the medium). However, in other portions, the horizontal component is mainly large, and thus it cannot be said that it is necessarily suitable for recording on the Co—O type perpendicular magnetic recording medium.

One means for improving this is to increase the saturation magnetic flux density Bs of the head material to increase the generated magnetic field, but to increase the saturation magnetic flux density Bs which is a material constant while maintaining a high magnetic permeability. Is not easy.
Therefore, in a Co—O based perpendicular magnetic recording medium, a second magnetic layer is provided between the main recording magnetic layer and the base film for the purpose of assisting the recording and reproducing process.
It has been attempted to improve the weak points in the perpendicular magnetic recording process by the ring type magnetic head by forming the layered structure.

In this case, since the auxiliary magnetic layer serving as the underlayer is located farthest from the head, the head magnetic field is small, and the horizontal component is the main component, the horizontal direction (parallel to the film surface). It must be easily magnetized with a relatively small magnetic field. However, this auxiliary second
When a soft magnetic thin film such as a permalloy thin film or a Fe-Si thin film is used as the magnetic layer of, the magnetization becomes unstable because the magnetic anisotropy is too small. There is an inconvenience that

Therefore, the present invention has been proposed in view of such a conventional situation, and it is possible to improve the electromagnetic conversion characteristics, particularly the reproduction output in the long wavelength region, without causing an increase in noise. It is an object of the present invention to provide a perpendicular magnetic recording medium suitable for recording digital image signals and the like.

[0008]

Means for Solving the Problems As a result of earnest studies over a long period of time, the inventors of the present invention have achieved the above-mentioned object, and as a result,
By using a Co—O based perpendicularly magnetized film having a lower oxygen concentration than the main magnetic layer as the lower auxiliary magnetic layer,
It was found that it can be magnetized with a relatively small magnetic field, and its perpendicular magnetic anisotropy stabilizes the magnetization and does not cause noise.

The perpendicular magnetic recording medium of the present invention has been completed on the basis of such findings, and a first Co—O based perpendicular magnetization film and a second Co—O film are formed on a non-magnetic support. First C which is a base layer formed by sequentially laminating a series perpendicular magnetization film
Shape of OO perpendicular magnetization film Magnetic anisotropy energy 2πM
The perpendicular magnetic anisotropy energy K _V obtained by removing s ² is 1.
4 is a _{^{× 10 6 ≦ K V ≦ 3.2}} × 10 6 erg / cc, and the shape magnetic anisotropy energy 2PaiMs ² the ratio 2πMs ² / K _V of the perpendicular magnetic anisotropy energy K _V 1.5 <2
πMs ² / K _V <3.0, and the second C
The film thickness of the OO-based perpendicular magnetization film is 1500 to 2000Å, and the direction of the perpendicular magnetic anisotropy excluding the shape magnetic anisotropy is inclined by 10 ° to 40 ° with respect to the normal direction of the film surface. It is characterized by that.

The perpendicular magnetic recording medium of the present invention is a Co-O type perpendicular magnetic recording medium formed mainly by a vacuum vapor deposition method, and is assumed to have a tape width of 8 mm or less and a total thickness of 10 μm or less. As shown in FIG. 1, the basic structure is such that a first Co—O based perpendicular magnetic film 102 as a lower layer and a second Co—O based perpendicular magnetic film 103 as a main magnetic layer are sequentially formed on a base film 101. It is made by stacking.

Here, the first Co—O system perpendicularly magnetized film 10 is formed.
2 is the perpendicular magnetic anisotropy energy K _V obtained by removing the shape magnetic anisotropy energy 2πMs ² of 1.4 × 10 ⁶ ≦ K.
_V ≦ 3.2 × 10 ⁶ erg / cc, ratio of shape magnetic anisotropy energy 2πMs ² to perpendicular magnetic anisotropy energy K _V 2πM
It is necessary to set s ² / K _V to 1.5 <2πMs ² / K _V <3.0.

In order to satisfy the above-mentioned characteristics, the oxygen concentration contained in the first Co—O-based perpendicular magnetic film 102 may be reduced. Therefore, the first Co—O-based perpendicular magnetic film 102 has _{Co w Ni y Fe z) 1} -n O n ··· (1) [provided that, 0 ≦ y ≦ 0.10,0 ≦ z ≦ 0.10, w +
y + z = 1 and 0.02 ≦ n ≦ 0.08. ] The composition may be

The first Co--O system perpendicularly magnetized film 1 is also provided.
02 is the angle θ _E formed by the so-called intrinsic perpendicular magnetic anisotropy direction (direction of the easy axis of magnetization) from which the shape magnetic anisotropy is removed and the normal direction of the film surface is −4.
It is preferable that 0 ° ≦ θ _E ≦ 40 °, and the film thickness t ₁ is preferably 100 Å ≦ t ₁ ≦ 500 Å. In addition, in the angle θ _E , a plus sign indicates a case inclining along the traveling direction of the magnetic head, and a minus sign indicates a case inclining against the traveling direction of the magnetic head.

On the other hand, the second Co--O which is the main magnetic layer is used.
The system perpendicular magnetization film 103 may have a normal composition, but in particular, the metal component may contain a small amount of Ni instead of 100% Co in order to improve the contact characteristics with the magnetic head. The addition of Ni affects so-called cupping,
Helps improve cupping. In particular, the amount of Ni added is 3 to
When it is 10 atomic%, the interface between the medium heads is improved due to the effect of improving the cupping, and the magnetic recording system using the rotating drum exhibits excellent electromagnetic conversion characteristics.

Therefore, the second Co—O system perpendicularly magnetized film 103 is formed of (Co _1-x Ni _x ) _1-m O _m (2) [where 0.03 ≦ x ≦ 0.10 , 0.1 ≦ m ≦ 0.
3] is preferable.

The film thickness t ₂ of the second Co—O system perpendicularly magnetized film 103 must be 1500Å ≦ t ₂ ≦ 2000Å. This thickness t ₂ of the thickness t ₂ of the second Co-O-based perpendicular magnetic layer 103 becomes impossible to normally record is less than 1500Å is the main magnetic layer, 2000 Å conversely
First Co—O based perpendicular magnetization film 10 which is a lower layer
2 is insufficient, and the first Co—O-based perpendicular magnetization film 102
This is because the effect due to the provision of can hardly be expected. In addition, the second Co—O-based perpendicularly magnetized film 10
The magnetic properties of No. 3, especially the coercive force Hc _{V in the} vertical direction are
It is preferable that (Oe) ≦ Hc _V ≦ 1450 (Oe).

Further, in the second Co--O system perpendicularly magnetized film 103, the direction of the easy axis of magnetization is not made completely perpendicular to the film surface, but as shown in FIG. The so-called intrinsic easy axis E from which the directionality is removed is 10 ° to 40 with respect to the normal line Y of the magnetic layer 101.
It is preferable to set it so that it is inclined. That is, the angle θ _E formed by the easy axis E and the normal line Y is 10 ° ≦ θ _E ≦ 40 °
It is preferable to set in the range of. This means that θ _E is 10
If it is less than 0 °, the die pulse ratio becomes large, and conversely, if θ _E exceeds 40 °, the advantage of perpendicular magnetic recording is lost. As described above, the direction E of easy axis of magnetization of the Co—O-based vapor deposition film is
Can be tilted with respect to the normal direction Y by adjusting the range of the incident angle of the vapor flow by an incident angle limiting mask or the like when depositing the Co—O based vapor deposition film, for example.

As a magnetic head used for recording / reproducing on / from the perpendicular magnetic recording medium, a ring type magnetic head having a magnetic gap length Lg of 0.18 μm or less is preferable. The saturation magnetic flux density Bs of the ring type magnetic head is preferably 13 kG or more. Therefore, a soft magnetic metal thin film having a high saturation magnetic flux density is arranged on the magnetic gap forming surface, and a magnetic gap is formed between the soft magnetic metal thin films. A composite type magnetic head formed is suitable.

Further, the recording density of this recording system is set to 8
The track width of the magnetic gap of the ring type magnetic head must be 7 μm or less in order to achieve × 10 ⁵ bits / mm ² or more. At the time of recording / reproducing, as shown in FIG. 2, with respect to the perpendicular magnetic recording medium running along the surface of the rotating drum, the ring-shaped magnetic head H is moved along the inclination direction of the easy axis of the magnetic layer 101, that is, The vehicle travels in the direction of arrow X in the figure.

[0020]

In the Co-O type perpendicular magnetic recording medium, the lower auxiliary magnetic layer has a lower oxygen concentration than the main magnetic layer and has a proper ratio of perpendicular magnetic anisotropy energy to shape magnetic anisotropy energy. By using the Co—O system perpendicularly magnetized film set to the value, it is possible to magnetize with a relatively small magnetic field, and the magnetization is stabilized by the perpendicular anisotropy. Therefore, by selecting the film thickness of the main magnetic layer to an appropriate value, the electromagnetic conversion characteristics, particularly the reproduction output in the long wavelength region, is secured, and noise is also suppressed.

[0021]

Embodiments to which the present invention is applied will be described below in detail with reference to the drawings and experimental results.

A. Structure of recording / reproducing apparatus As a digital VTR for digitizing a color video signal and recording it on a recording medium such as a magnetic tape, a component type digital VT of a D1 format for a broadcasting station is used.
R and D2 format composite type digital V
TR has been put to practical use.

The former D1 format digital VTR
Is 1 for the luminance signal and the first and second color difference signals.
After A / D conversion at a sampling frequency of 3.5 MHz and 6.75 MHz, a predetermined signal processing is performed and recording is performed on a magnetic tape. Since the sampling frequency of these component components is 4: 2: 2. 4: 2:
It is also called two methods. On the other hand, in the latter D2 format digital VTR, a composite color video signal is sampled with a signal having a frequency four times as high as the frequency of a color subcarrier signal, A / D-converted, and subjected to predetermined signal processing, and then a magnetic tape. I am trying to record it.

In any case, these digital VTs are
Since R is designed on the assumption that both are used for broadcasting stations, image quality is given the highest priority, and a digital color video signal in which one sample is A / D converted into, for example, 8 bits is substantially compressed. It is designed to record without doing anything. Therefore, for example, a D1 format digital VTR can obtain a reproduction time of at most about 1.5 hours even if a large cassette tape is used, which is unsuitable for use as a general domestic VTR.

Therefore, in this embodiment, for example, 5 μm
The signal having the shortest wavelength of 0.5 μm is recorded with respect to the track width of, and the recording density is 4 × 10 ⁵ bit / mm ² or more,
Alternatively, by using a method of realizing 8 × 10 ⁵ bit / mm ² or more and compressing recorded information in such a form that reproduction distortion is small, a magnetic tape with a tape width of 8 mm or less is used. Even if you record for a long time
It shall be applied to a reproducible digital VTR.
The configuration of this digital VTR will be described below.

A. Signal Processing Unit First, the signal processing unit of the digital VTR used in this embodiment will be described. FIG. 3 shows the entire configuration on the recording side. The input terminals indicated by 1Y, 1U, and 1V are provided with three primary color signals R from a color video camera,
A digital luminance signal Y formed from G and B and digital color difference signals U and V are supplied. In this case, the clock rate of each signal is the same as the frequency of each component signal of the D1 format. That is, the respective sampling frequencies are 13.5 MHz and 6.75 MHz, and the number of bits per sample is 8 bits. Therefore, the input terminals 1Y, 1U, 1
The data amount of the signal supplied to V is about 216 Mb
ps. The data amount of the blanking time is removed from this signal, and the data amount is compressed to about 167 Mbps by the effective information extraction circuit 2 that extracts only the information of the effective area.

Then, the luminance signal Y of the output of the effective information extraction circuit 2 is supplied to the frequency conversion circuit 3 and the sampling frequency is converted from 13.5 MHz to 3/4 thereof. As the frequency conversion circuit 3, for example, a thinning filter is used so that aliasing distortion does not occur. The output signal of the frequency conversion circuit 3 is supplied to the blocking circuit 5, and the order of the luminance data is converted into the order of blocks. The block forming circuit 5 is provided for the block encoding circuit 8 provided in the subsequent stage.

FIG. 5 shows the structure of a block as an encoding unit. This example is a three-dimensional block, and for example, by dividing a screen across two frames, a large number of unit blocks of (4 lines × 4 pixels × 2 frames) are formed as shown in FIG. Note that, in FIG. 5, solid lines indicate odd field lines, and broken lines indicate even field lines.

Of the outputs of the effective information extraction circuit 2,
The two color difference signals U and V are supplied to the sub-sampling and sub-line circuit 4, and after the sampling frequencies are respectively converted from 6.75 MHz to half thereof, the two digital color difference signals are selected line by line from each other, Combined with the data. Therefore, a line-sequential digital color difference signal is obtained from the sub-sampling and sub-line circuit 4. FIG. 6 shows a pixel configuration of a signal subsampled and sublined by the subsampling and subline circuit 4. 6 in FIG.
Indicates a sub-sampling pixel of the first color difference signal U, and Δ
Indicates the sampling pixel of the second dye signal V, and x indicates the position of the pixel thinned by the sub-sample.

The line-sequential output signal from the sub-sampling and sub-line circuit 4 is supplied to the blocking circuit 6. In the blocking circuit 6, one blocking circuit 5
Similarly, the color difference data in the scanning order of the television signal is converted into the data in the block order. Like the one blocking circuit 5, the blocking circuit 6 converts the color difference data into a block structure of (4 lines × 4 pixels × 2 frames). The output signals of the blocking circuit 5 and the blocking circuit 6 are supplied to the synthesizing circuit 7.

In the synthesizing circuit 7, the luminance signal and chrominance signal converted in the order of blocks are converted into 1-channel data, and the output signal of the synthesizing circuit 7 is supplied to the block coding circuit 8. As the block encoding circuit 8, an encoding circuit (referred to as ADRC) adapted to the dynamic range of each block and a DCT (Dis) will be described later.
A create cosine transform circuit or the like can be applied. The output signal from the block encoding circuit 8 is further supplied to the framing circuit 9 and converted into frame structure data. In the framing circuit 9, the pixel system clock and the recording system clock are changed.

Next, the output signal of the framing circuit 9 is supplied to the error correction code parity generation circuit 10 to generate the error correction code parity. The output signal of the parity generation circuit 10 is supplied to the channel encoder 11, and channel coding is performed so as to reduce the low frequency part of the recording data. Channel encoder 11
Output signal of the pair of magnetic heads 13 via recording amplifiers 12A and 12B and a rotary transformer (not shown).
It is supplied to A and 13B and recorded on the magnetic tape. The audio signal and the video signal are separately compression-coded and supplied to the channel encoder 11.

By the above-mentioned signal processing, the input data amount of 216 Mbps is reduced to about 167 Mbps by extracting only the effective scanning period, and further it is reduced to 84 Mbps by the frequency conversion, the sub-sample and the sub-line. This data is compressed and encoded by the block encoding circuit 8 to be compressed to about 25 Mbps,
By adding additional information such as parity and audio signal after that, the recording data amount becomes 31.56 Mbps.

Next, the structure on the reproducing side will be described with reference to FIG. At the time of reproduction, as shown in FIG. 4, the reproduction data from the magnetic heads 13A and 13B is first supplied to the channel decoder 15 via the rotary transformer and the reproduction amplifiers 14A and 14B. Channel decoder 15
At, the channel coding is demodulated, and the output signal of the channel decoder 15 is supplied to the TBC circuit (time base correction circuit) 16. In this TBC circuit 16, the time-axis fluctuation component of the reproduction signal is removed. The reproduction data from the TBC circuit 16 is supplied to the ECC circuit 17,
Error correction using the error correction code and error correction are performed. The output signal of the ECC circuit 17 is supplied to the frame decomposition circuit 18.

The frame decomposing circuit 18 separates each component of the block coded data from each other, and
The clock of the recording system is changed to the clock of the pixel system. The respective data separated by the frame decomposing circuit 18 are supplied to the block decoding circuit 19, the restored data corresponding to the original data is decoded in each block, and the decoding data is supplied to the distribution circuit 20. The distribution circuit 20 separates the decoded data into a luminance signal and a color difference signal. The luminance signal and the color difference signal are supplied to the block decomposition circuits 21 and 22, respectively. The block decomposing circuits 21 and 22 convert the decoding data in the order of blocks into the order of raster scanning, contrary to the blocking circuits 5 and 6 on the transmission side.

The decoded luminance signal from the block decomposition circuit 21 is supplied to the interpolation filter 23. In the interpolation filter 23, the sampling rate of the luminance signal is 3 fs to 4 fs.
(4fs = 13.5 MHz). The digital luminance signal Y from the interpolation filter 23 is taken out to the output terminal 26Y.

On the other hand, the digital color difference signal from the block decomposition circuit 22 is supplied to the distribution circuit 24, and the line-sequential digital color difference signals U and V are separated into the digital color difference signals U and V, respectively. The digital color difference signals U and V from the distribution circuit 24 are supplied to the interpolation circuit 25 and are interpolated. The interpolation circuit 25 interpolates the data of the thinned lines and pixels by using the restored pixel data, and the sampling rate from the interpolation circuit 25 is 2f.
s digital color difference signals U and V are obtained and output terminal 2
6U and 26V are taken out respectively.

B. Block Coding As the block coding circuit 8 in FIG.
(Adaptive Dynamic Range Co
ding) encoder is used. The ADRC encoder detects the maximum value MAX and the minimum value MIN of a plurality of pixel data included in each block, and detects the maximum value MA.
The dynamic range DR of the block is detected from X and the minimum value MIN, the coding adapted to this dynamic range DR is performed, and the requantization is performed with the number of bits smaller than the number of bits of the original pixel data. As another example of the block encoding circuit 8, pixel data of each block is converted into DCT (Discrete Cosine Tran).
After sform), the coefficient data obtained by this DCT may be quantized, and the quantized data may be run-length Huffman encoded and compression-encoded.

Here, an example of an encoder that uses an ADRC encoder and in which image quality does not deteriorate even when multi-dubbing is performed will be described with reference to FIG. 7, a digital video signal (or a digital color difference signal) in which one sample is quantized into 8 bits is input to the input terminal 27 from the synthesizing circuit 7 in FIG. Input terminal 2
Blocked data from 7 is maximum and minimum value detection circuit 2
9 and the delay circuit 30. The maximum value / minimum value detection circuit 29 determines the minimum value MIN and the maximum value MAX for each block.
To detect. From the delay circuit 30, the input data is delayed for the time required to detect the maximum value and the minimum value.
The pixel data from the delay circuit 30 is supplied to the comparison circuit 31 and the comparison circuit 32.

The maximum value MAX from the maximum / minimum value detection circuit 29 is supplied to the subtraction circuit 33, and the minimum value MIN is supplied to the addition circuit 34. The subtractor circuit 33 and the adder circuit 34 are supplied from the bit shift circuit 35 with a value of one quantization step width (Δ = 1 / 16DR) when non-edge matching quantization is performed with a fixed length of 4 bits. The bit shift circuit 35 is configured to shift the dynamic range DR by 4 bits so as to perform division by (1/16). The subtraction circuit 33 obtains a threshold value of (MAX-Δ), and the addition circuit 34 obtains a threshold value of (MIN + Δ). The threshold values from the subtraction circuit 33 and the addition circuit 34 are supplied to the comparison circuits 31 and 32, respectively. The value Δ defining this threshold is not limited to the quantization step width and may be a fixed value corresponding to the noise level.

The output signal of the comparison circuit 31 is the AND gate 3
6 and the output signal of the comparison circuit 32 is supplied to the AND gate 37. The input data from the delay circuit 30 is supplied to the AND gate 36 and the AND gate 37. The output signal of the comparison circuit 31 becomes high level when the input data is larger than the threshold value, and therefore the output terminal of the AND gate 36 has the pixel data of the input data included in the maximum level range of (MAX to MAX-Δ). Is extracted. On the other hand, the output signal of the comparison circuit 32 becomes high level when the input data is smaller than the threshold value. Therefore, the output terminal of the AND gate 37 is (MIN to MIN).
The pixel data of the input data included in the minimum level range of + Δ) is extracted.

The output signal of the AND gate 36 is supplied to the averaging circuit 38, and the output signal of the AND gate 37 is supplied to the averaging circuit 39. These averaging circuits 38, 39
Calculates the average value for each block, and the reset signal of the block period from the terminal 40 is averaged by the averaging circuits 38, 39.
Is being supplied to. From the averaging circuit 38, (MAX ~
The average value MAX ′ of the pixel data belonging to the maximum level range of (MAX−Δ) is obtained, and the averaging circuit 39 outputs (MIN).
The average value MIN ′ of the pixel data belonging to the minimum level range of ˜MIN + Δ) is obtained. The subtraction circuit 41 subtracts the average value MIN ′ from the average value MAX ′.
From the dynamic range DR '.

Further, the average value MIN 'is supplied to the subtraction circuit 42, and the average value MIN' is subtracted from the input data passed through the delay circuit 43 in the subtraction circuit 42 to form the data PDI after removal of the minimum value. .. The data PDI and the modified dynamic range DR ′ are used by the quantization circuit 44.
Is supplied to. In this embodiment, the number of bits n assigned to quantization is 0 bit (code signal is not transferred),
It is a variable length ADRC that is any one of 1 bit, 2 bits, 3 bits, and 4 bits, and is subjected to edge matching quantization. The allocated bit number n is determined for each block in the bit number determination circuit 45, and the data of the bit number n is supplied to the quantization circuit 44.

The variable length ADRC has a dynamic range D
Efficient encoding can be performed by reducing the number of allocated bits n in a block having a small R ′ and increasing the number of allocated bits n in a block having a large dynamic range DR ′. That is, the threshold values for determining the number of bits n are set to T1 to T4 (T1 <T2 <T3 <
T4), the code signal is not transferred to the block of (DR ′ <T1), only the information of the dynamic range DR ′ is transferred, and the block of (T1 ≦ DR ′ <T2) is (n = 1). The block of (T2 ≦ DR ′ <T3) is (n = 2), the block of (T3 ≦ DR ′ <T4) is (n = 3), and the block of (DR ′ ≧ T4) is The block is (n = 4).

In such variable length ADRC, the threshold values T1.about.
By changing T4, the generated information amount can be controlled (so-called buffering). Therefore, the variable length ADRC can be applied to a transmission line such as the digital video tape recorder of the present invention which requires that the amount of generated information per field or frame be a predetermined value.

In the buffering circuit 46 for determining the threshold values T1 to T4 for making the generated information amount a predetermined value, a plurality of threshold value groups (T1, T2, T3, T4), for example, 3 are set.
Two sets are prepared, and these sets of thresholds are distinguished by the parameter code Pi (i = 0, 1, 2, ... 31). The generated information amount is set to monotonically decrease as the number i of the parameter code Pi increases. However, the quality of the restored image deteriorates as the amount of generated information decreases.

Threshold value T from buffering circuit 46
1 to T4 are supplied to the comparison circuit 47, and the dynamic range DR ′ through the delay circuit 48 is supplied to the comparison circuit 47. The delay circuit 48 delays DR ′ by the time required for the buffering circuit 46 to determine the threshold set. In the comparison circuit 47, the dynamic range DR ′ of the block is compared with each threshold value, the comparison output is supplied to the bit number determination circuit 45, and the allocated bit number n of the block is determined. In the quantizing circuit 44, the data PDI after the minimum value removal via the delay circuit 49 is converted into the code signal DT by the edge matching quantization using the dynamic range DR ′ and the allocated bit number n. The quantization circuit 44 is composed of, for example, a ROM.

The modified dynamic range DR 'and average value MIN' are output via the delay circuits 48 and 50, respectively, and the parameter code Pi indicating the set of the code signal DT and the threshold value is output. In this example, the signal that has been non-edge-match quantized is edge-match quantized newly based on the dynamic range information, so that image deterioration when dubbing is small.

C. Channel Encoder and Channel Decoder Next, the channel encoder 11 and the channel decoder 15 of FIG. 3 will be described. In the channel encoder 11, as shown in FIG. 8, it is an adaptive scramble circuit to which the output of the parity generation circuit 10 is supplied, and a plurality of M-sequence scramble circuits 51 are prepared. The M-sequence is selected so that an output having a small number of components and DC components can be obtained. The precoder 52 for the partial response class 4 detection method performs arithmetic processing of 1 / 1-D ² (D is a unit delay circuit). The output of the precoder 52 is passed through the recording amplifiers 12A and 13A to the magnetic head 1
Recording and reproduction are performed by 3A and 13B, and reproduction output is amplified by reproduction amplifiers 14A and 14B.

On the other hand, in the channel decoder 15, as shown in FIG. 9, the arithmetic processing circuit 53 on the reproducing side of the partial response class 4 performs 1 + D arithmetic on the outputs of the reproducing amplifiers 14A and 14B. Also,
In the so-called Viterbi decoding circuit 54, decoding of data resistant to noise is performed by an operation using the correlation and the likelihood of the data with respect to the output of the operation processing circuit 53. The output of the Viterbi decoding circuit 54 is supplied to the descrambling circuit 55, the data rearranged by the scrambling process on the recording side is returned to the original series, and the original data is restored. With the Viterbi decoding circuit 54 used in this embodiment, the reproduction C / N conversion is improved by 3 dB as compared with the case of performing the decoding for each bit.

D. As shown in FIG. 10, the traveling magnetic heads 13A and 13B are attached to the drum 76 in an integrated structure. A magnetic tape (not shown) is obliquely wound around the peripheral surface of the drum 76 at a winding angle slightly larger than 180 ° or slightly smaller than 180 °.
A and the magnetic head 13B are configured to scan the magnetic tape at the same time.

Further, the directions of the gaps of the magnetic head 13A and the magnetic head 13B are tilted in the opposite directions (for example, the magnetic head 13A is tilted + 20 ° with respect to the track width direction, and the magnetic head 13B is tilted -20 °. Are set so that the amount of crosstalk between adjacent tracks is reduced by so-called azimuth loss during reproduction.

11 and 12 show the magnetic head 13A,
This shows a more specific structure when 13B is an integral structure (so-called double azimuth head). For example, the magnetic head 13 integral with the upper drum 76 rotated at a high speed.
A and 13B are attached, and the lower drum 77 is fixed. Here, the winding angle θ of the magnetic tape 78 is 16
The drum diameter is 6 ° and the drum diameter φ is 16.5 mm. Therefore, on the magnetic tape 78, one field of data is divided into five tracks and recorded. With this segment system, the length of the track can be shortened, and the error due to the linearity of the track can be reduced.

As described above, by performing the simultaneous recording with the double azimuth head, the error amount due to the linearity can be reduced as compared with the case where the pair of magnetic heads are arranged at the facing angle of 180 °. In addition, since the head-to-head distance is small, the pairing adjustment can be performed more accurately. Therefore, with such a traveling system, recording / reproducing can be performed on a narrow track.

B. Examination of Recording / Reproducing Characteristics Next, a Co—O system perpendicular magnetic recording medium having various underlayers was manufactured, and the recording / reproducing characteristics were examined using a ring type magnetic head.

First, a Co-O type perpendicular magnetic recording medium was manufactured by a manufacturing method described later using the vacuum vapor deposition apparatus shown in FIG. This vacuum vapor deposition apparatus is a continuous roll-up type vapor deposition machine which has two vapor deposition sections and is capable of vapor depositing a lower layer film and an upper layer film at the same time, and is provided in one vacuum chamber 82 which is kept at a high vacuum by an exhaust system 81. A pair of cooling cans 83 in the substantially central portion
a and 83b are arranged, and the cooling can 83
An unwinding roll 84, a winding roll 85, and a guide roll 86 are arranged above the a and 83b. Therefore, the base film B is sent out from the unwinding roll 84 to the cooling can 83a, and while traveling along the cooling can 83a, the first Co—O-based perpendicularly magnetized film is formed, and then the guide roll 86 is moved. This is sent to the cooling can 83b through the cooling can 8
While traveling along 3b, a second Co—O-based perpendicularly magnetized film is formed and wound on the winding roll 85.

On the other hand, evaporation sources 87a and 87b made of Co or Co-Ni alloy or the like are arranged opposite to each other below the cooling cans 83a and 83b, and these evaporation sources 87a and 87b are obliquely above the evaporation sources 87a and 87b. Source 87
Electron gun 88 for irradiating an electron beam toward a and 87b
a and 88b are provided, and the evaporation sources 87a and 87b are configured to be heated and evaporated by the irradiation of electron beams from the electron guns 88a and 88b. Further, oxygen introducing pipes 89a, 89b for introducing oxygen into the film and introducing oxygen into the film are arranged between the evaporation sources 87a, 87b and the cooling cans 83a, 83b, and optionally. The amount of oxygen-introduced gas is controlled and jetted onto the base film B, and the oxygen concentration in the vapor-deposited Co—O-based perpendicularly magnetized film can be individually controlled.

Incident angle limiting masks 90a and 90b and incident angle limiting masks 90c and 90d for regulating the incident angle of the vapor streams coming from the evaporation sources 87a and 87b are installed near the cooling cans 83a and 83b. .. Therefore, the maximum incident angle θ ₁ and the minimum incident angle θ _{2 at} the time of forming each Co—O-based perpendicular magnetic film are determined by the incident angle limiting mask 9
0a, 90b or incident angle limiting masks 90c, 90
It depends on the opening position between d.

Using the above continuous winding type vapor deposition apparatus, a predetermined Co-based alloy is vaporized from an electromagnetic gun heating vaporization source, and oxygen gas is continuously introduced into the vacuum chamber during vapor deposition to continuously elongate the high-altitude gas. Partially oxidized C on the molecular film
An o-based alloy film was formed to produce a metal thin film type magnetic tape having a two-layer structure. As the long polymer film, here, a polyamide film having a film thickness of 9.0 μm and Young's modulus of 1200 kg / mm ² is used, and the running speed thereof is set to 16 m / min, and the long polymer film is supported. The cooling can was cooled with a refrigerant and controlled so that the surface temperature of the can was 0 ° C. or lower.

The lower layer film in each of the examples and comparative examples (first
Table 1 shows the production conditions of the Co-O perpendicular magnetic film) and the oxygen concentration of the lower layer film formed, the direction of the easy axis of magnetization θ _E , the saturation magnetic flux density Bs, and the intrinsic magnetic anisotropy without magnetic anisotropy. Table 2 shows the ratio 2πMs ² / K _V of the perpendicular perpendicular magnetic anisotropy energy K _V and the shape magnetic anisotropy energy 2πMs ² to the intrinsic perpendicular magnetic anisotropy energy K _V. The oxygen concentration in each of the above characteristics was measured using an Auger electron spectrometer (AES). Saturation magnetic flux density B
s was measured using a vibrating sample magnetometer (VSM).

In addition, intrinsic perpendicular magnetic anisotropy
Energy K_VAnd its direction (direction of easy axis of magnetization) θ_EIs a magnet
It was measured using a pneumatic torque meter. The measurement method is as follows.
It is Ri. That is, as shown in FIG.
Samples S and T are prepared, and the film surfaces are orthogonal to each other.
And is fixed to the rotary shaft W. At this time,
The orientations of the film surfaces of the samples S and T are
Set to exist in the same quadrant. Then the applied magnetic field
To the in-plane direction of the sample S or sample T
In this state, change the magnitude of the applied magnetic field and
Occurred on the whole of these two samples S and T fixed to W
To obtain the dependence of the applied torque on the applied magnetic field.
Data analysis method [J. Appl. Phys. 47, 4669, (1976)]
To obtain the magnetic anisotropy constant. That is, the
Luc L and (L / H)²Plot the relationship between
Extrapolate the applied magnetic field to infinity and
Qi anisotropy constant K _NTo decide.

Magnetic anisotropy energy K obtained here
_N is the synthesized apparent magnetic anisotropy energy of two orthogonal samples S and T. On the other hand, sample S,
The following relationship is established between the true magnetic anisotropy energy K _V of T and the apparent magnetic anisotropy energy K _N. K _V = K _N / sin 2θ _E (3) Therefore, by substituting the apparent magnetic anisotropy energy constant K _N obtained above into the relational expression (3), the true magnetic anisotropy is obtained. The energy K _V can be calculated.

[0063]

[Table 1]

[0064]

[Table 2]

In each of the examples and comparative examples, the upper layer film which is the main magnetic layer (second Co—O based perpendicular magnetization film)
Was formed under the same conditions, but the upper layer film was formed under the following conditions: alloy composition Co _0.95 Ni _0.05 , deposition incident angle 15 ° to 4 °
5 °, oxygen introduced amount 380 cc / min, film thickness 1900Å, oxygen concentration of the upper layer film formed is 17 atomic%, saturation magnetic flux density Bs8250G, coercive force Hc _V 1250 in the vertical direction.
(Oe), effective anisotropic magnetic field Hk (eff) 4.90 kOe, easy magnetization axis direction θ _E 25 °, intrinsic perpendicular magnetic anisotropy energy K _V 2.70 × 10 ⁶ erg / cc.

The long medium thus produced is
After applying a fluorine-based lubricant to the surface of the magnetic layer, apply 8 mm
The sample was tape-shaped by slitting it in the width. In addition, a sample in which only the upper layer film was deposited without the lower blocking film was Comparative Example 5
And Recording and reproduction were performed on each of the above-described samples using a composite type magnetic head having a basic structure as shown in FIG. 15, and the characteristics were evaluated. In this composite type magnetic head, the abutting surfaces of the pair of ferrite cores 91A and 91B are cut obliquely to form soft magnetic metal thin films 92A and 92B made of Fe-Ga-Si-Ru alloy (saturation magnetic flux density Bs = 14 kG), respectively. Along with the film formation, a gap material is sandwiched between the end faces of these soft magnetic metal thin films 92A and 92B to form a magnetic gap g. Nonmagnetic glass 93 is filled on both sides of the magnetic gap g so as to secure contact with the magnetic tape, and a winding groove 94 is provided on one ferrite core 91B.

What was evaluated was the reproduction output (recording wavelength λ =
0.5 μm, λ = 5.0 μm) and noise (wavelength λ =
0.5 μm, λ = 38 μm), and the measurement results are shown in Table 3. Table 4 shows the measurement results of D _{50 and} error rate as indexes of the recording / reproducing characteristics of digital signals.

[0068]

[Table 3]

[0069]

[Table 4]

From the above, the following can be understood. First, under the vapor deposition conditions of the lower layer film, if the oxygen concentration is too low (Comparative Example 1), the reproduction output at long wavelength is significantly improved, but at the same time, the noise at long wavelength is significantly deteriorated. On the other hand, when the oxygen concentration is too high (Comparative Example 2), the noise does not increase but the reproduction output is not improved. Further, if the film thickness is too thick (Comparative Example 3) or too thin (Comparative Example 4), the effect does not appear. On the other hand, in each of the embodiments to which the present invention is applied, the noise is small, the reproduction output is large, high density recording is possible when recording a digital signal, and the error rate is also small.

Thus, the conditions for the lower layer film of the two-layer medium are as follows:
It is defined by the oxygen concentration and the film thickness. This is a condition that balances the easiness of magnetization and the stability from the viewpoint of magnetic properties, and this is the shape magnetic anisotropy energy of the film 2π.
It is defined by the ratio of Ms ² and perpendicular magnetic anisotropy energy K _V.

The specific embodiment of the present invention has been described above. However, the present invention is not limited to this embodiment, and various modifications can be made without departing from the gist of the present invention. Needless to say.

[0073]

As is apparent from the above description, in the present invention, the Co--O type perpendicular magnetic recording medium is used.
Adopting a layered structure, the magnetic properties of the lower layer film, especially the shape magnetic anisotropy energy 2πMs ² and the perpendicular magnetic anisotropy energy K
_{Since the V} ratio is set to an appropriate value, the electromagnetic conversion characteristics, especially the reproduction output at long wavelengths can be significantly improved without increasing noise.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of essential parts showing a configuration example of a perpendicular magnetic recording medium to which the present invention is applied.

FIG. 2 is a schematic diagram for explaining an easy axis direction θ _E of a magnetic layer and a traveling direction of a magnetic head.

FIG. 3 is a block diagram showing a configuration on a recording side of a signal processing unit of a digital VTR which compresses and records a digital image signal in a form such that reproduction distortion is small.

FIG. 4 is a block diagram showing a configuration on a reproduction side of a signal processing unit.

FIG. 5 is a schematic diagram showing an example of a block for block coding.

FIG. 6 is a schematic diagram for explaining subsampling and sublines.

FIG. 7 is a block diagram showing an example of a block encoding circuit.

FIG. 8 is a block diagram showing an outline of an example of a channel encoder.

FIG. 9 is a block diagram showing an outline of an example of a channel decoder.

FIG. 10 is a plan view schematically showing an example of the arrangement of magnetic heads.

FIG. 11 is a plan view showing a configuration example of a rotating drum and a winding state of a magnetic tape.

FIG. 12 is a front view showing a configuration example of a rotating drum and a winding state of a magnetic tape.

FIG. 13 is a schematic diagram showing a configuration example of a vacuum vapor deposition device.

FIG. 14 is a schematic diagram for explaining a method for measuring a magnetic anisotropy constant with a magnetic torque meter.

FIG. 15 is a schematic perspective view showing the structure of a magnetic head used for evaluation.

[Explanation of symbols]

 1Y, 1U, 1V ... Component signal input terminals 5, 6 ... Blocking circuit 8 ... Block coding circuit 11 ... Channel encoders 13A, 13B ... Magnetic head 22 ... Channel decoder 26 ... Block decoding circuit 28, 29 ... Block decomposition circuit 101 ... Base film 102 ... First Co-O system perpendicular magnetization film 103 ... -Second Co-O system perpendicularly magnetized film

Claims (1)

Claim: What is claimed is: 1. A first Co—O-based perpendicular magnetization film and a second Co—O-based perpendicular magnetization film are sequentially laminated on a non-magnetic support to form a base layer. 1. The shape of the Co—O system perpendicularly magnetized film of No. ¹ has a perpendicular magnetic anisotropy energy K _V of 1.4 × 10 ⁶ ≦ K _V ≦ 3.2 × 10 excluding the magnetic anisotropy energy of 2πMs ^2.
6 erg / cc, and the shape magnetic anisotropy energy is 2
Ratio of πMs ² to perpendicular magnetic anisotropy energy K _V 2πMs
² / K _V is 1.5 <2πMs ² / K _V <3.0, and the thickness of the second Co—O-based perpendicular magnetization film is 1500 to 2
000Å, and the direction of perpendicular magnetic anisotropy with the shape magnetic anisotropy removed is 10 ° to 40 ° with respect to the normal direction of the film surface.
A perpendicular magnetic recording medium characterized by being inclined.