JP3823696B2 - Magnetic recording / reproducing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording / reproducing apparatus having means for recording a signal as light information using light and further reproducing information using a magnetic head, and has high resolution and excellent signal-to-output ratio even in high-density recording. The present invention relates to a magnetic recording / reproducing apparatus having (S / N).
[0002]
[Prior art]
There has been a remarkable increase in the amount of information in recent years, and the storage capacity of magnetic disks, floppy disks, magnetic tapes, and optical storage devices used as file media has undergone dramatic development. Particularly in the magnetic disk device, the recording density is improved at an annual rate of 40 to 60%, and a device having a surface recording density of 4 Gb / in ² has already been put into practical use. Such a high density of the magnetic recording apparatus has been achieved by technological innovations such as high resolution of the magnetic disk, high S / N, and high sensitivity of the magnetic head. However, when looking at a magnetic disk, high resolution and high S / N have been achieved by miniaturization of magnetic thin film particles constituting the magnetic disk, but this has the physical limitation of thermal fluctuation. To do. That is, it is necessary to make the magnetic particles finer in order to reduce the noise of the magnetic recording medium magnetic thin film. However, if the magnetic particles are made too fine, the recorded information disappears due to thermal disturbance. That is, there is a trade-off between high S / N ratio and thermal stability. As a technique for avoiding this, a perpendicular magnetic recording technique and a thermomagnetic recording have been proposed as candidates. The former is one reason that the magnetic recording medium thin film can be made thicker than a conventional in-plane recording thin film, so that the volume of the magnetic particles can be increased accordingly. In thermomagnetic recording, the use of a magnetic film having a very large coercive force at room temperature for the recording film as compared with the magnetic film for magnetic recording is the reason why the resistance to thermal fluctuation is increased.
[0003]
By the way, in the latter thermomagnetic recording system, recording of information is usually performed by irradiating the recording layer with laser light so that the magnetization of the recording film is directed vertically in the direction perpendicular to the film surface. The reproduction of the recorded information is performed by reading the recorded magnetization direction directly from the recording film or from the transfer layer formed thereon using the Kerr effect.
[0004]
In this optical recording method, a recording bit smaller than the spot diameter of the light beam can be formed, but it is difficult to read a bit smaller than the spot diameter of the light beam in the reproduction process, and the resolution is inferior at a high linear recording density. There is a problem. As one of the solutions, Japanese Patent Laid-Open No. 10-21598 discloses that a magnetic head used in a magnetic recording / reproducing apparatus is used without using an optical head in a reproducing process. Generally, in a reproducing magnetic head, the resolution is determined by the gap length (gap length) of the magnetic head, but in a magnetoresistive head that has recently been put to practical use, the gap length is limited to 0.2 μm. This corresponds to a resolution capable of reproducing a recording bit of 0.1 μm. Therefore, if this is used, the surface recording density can be improved by a factor of 5 at a time, considering that the resolution of the current optical disk using a light source having a wavelength of 660 nm is about 0.5 μm. However, in reality, it is difficult to realize such a large resolution improvement. The first reason is due to the shape of the recorded light spot. When recording is performed using a normal optical recording apparatus and the shape of the recording spot is observed with a magnetic polarization microscope, a crescent shape as shown in FIG. 4 is obtained. This is because the cross-sectional shape of the light beam used for recording is circular. On the other hand, in the magnetic reproducing head, the shape of the gap portion that absorbs the leakage magnetic flux generated from the medium is a rectangle that is long in the track width direction. Therefore, the magnetic flux generated from the crescent-shaped recording spot cannot be efficiently reproduced, and the effect becomes larger as the recording bit length becomes shorter. This is the reason why a sufficiently high resolution cannot be obtained even if a magnetic reproducing head is used.
[0005]
[Problems to be solved by the invention]
In the optical recording / magnetic head reproducing system, there is a problem that when the recording bit length is shortened, the reproduction output is greatly reduced and the ability of the reproducing magnetic head cannot be fully utilized.
[0006]
[Means for Solving the Problems]
The above-mentioned problem can be solved by making the curvature of the adjacent bit boundary line as large as possible and making the shape of the recorded magnetic domain almost rectangular when performing magneto-optical recording on the recording medium.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
<Example 1>
FIG. 2 shows an outline of the magnetic recording / reproducing apparatus of the present invention. Reference numeral 21 denotes a laser diode for optical recording. Reference numeral 22 denotes an objective lens for condensing the laser beam on the recording layer 24, and a diaphragm 23 is provided on the light outflow side through a spherical lens. 27 is a magnetic field modulation coil for modulating the magnetization direction of the recording film in accordance with the signal current, and 28 is a circuit for driving the optical laser and the magnetic head. By these elements, information is recorded on the recording film of the medium as magnetization directed upward or downward. Reading of information is performed by magnetically transferring the magnetization of the recording layer to the reproducing layer 25 and reproducing the leakage magnetic field generated therefrom by the magnetic head 29.
[0008]
The signal read by the magnetic head is demodulated to the original information by the signal processing circuit 210. The structure of the recording medium used in this example is shown in FIG. After forming SiN as a protective layer 32 on the polycarbonate substrate 31, a 40 nm thick recording layer 33 having a composition of Tb ₂₁ Fe ₇₀ Co ₉ , a 70 nm reproducing layer 34 made of Tb ₃₅ Fe ₅₆ Co ₉ , and a further thickness A 20 nm thick SiN protective layer 32 is sequentially formed. As the magnetic reproducing head, a GMR head having a track width of 1.0 μm using a giant magnetoresistive effect and a shield interval Gs of 0.2 μm was used. The distance between the head and the medium surface was 0.04 μm. A laser diode having a wavelength of 660 nm was used as a recording light source. The spot diameter was 1.0 μm.
[0009]
Using the magnetic storage device having the above-described configuration, the influence on the recording spot shape, reproduction output, and resolution was investigated by providing a diaphragm on the laser beam outflow side. First, all “1” recording was performed by changing the recording bit length B using a rectangular aperture of 0.6 μm in the track direction and 1.0 μm in the track width direction. As a comparative example, recording was performed without using a diaphragm, and the same measurement was performed. FIG. 1 shows the relationship between the linear recording density and the reproduction output. As is apparent from the figure, when the aperture is used (11), a high reproduction output is maintained up to a bit length of about 0.10 μm (record mark period 0.2 μm), whereas when no aperture is used (12). When the bit length becomes 0.5 μm or less (record mark cycle 1.0 μm), the reproduction output rapidly decreases.
[0010]
FIG. 4 schematically shows the result of observation of the recording spot shape in each case with a polarizing microscope. When no diaphragm was used, the recording spot (41) had a crescent shape with a track width Tw = 0.8 μm. The radius of curvature R of the curved arc portion is 0.4 μm, and the bit gap B = 0.5 μm at which the reproduction output starts to drop sharply, the shield gap portion (42; indicated by a bold line in the figure) of the GMR head immediately above the bit. ), The magnetic flux from the non-recorded area having the opposite polarity is picked up in addition to the magnetic flux from the recording bit, and it can be understood that the output sharply decreases. On the other hand, when the aperture is used, the recording spot (43) has a track width Tw = 0.8 μm and the bit boundary line has a slightly arc shape, but its curvature radius R is 3.6 μm, which reflects the shape of the aperture. It was almost rectangular. Compared with the case where the bit length is 0.5 μm and no diaphragm is used, almost the entire shield gap of the GMR head is placed in the recording bit. That is, it can be seen that since a reverse magnetic flux generated from an unrecorded area is not read, a high reproduction output can be obtained, and the resolution is significantly improved as compared with the case where no diaphragm is used. In this case, however, the bit length is shortened, and the distance (BA) obtained by subtracting the length A in the track direction of the arc portion from the bit length B is 2/2 of the effective gap length (Gs / 2). When the length is shorter than about 3 (B = 0.1 μm in the embodiment), the output is lowered due to the gap loss characteristic of the GMR head, although it is not arranged to pick up the magnetic flux from the unrecorded area. Where Gs is the shield interval.
[0011]
From the above results, it can be confirmed that the following two requirements are necessary to obtain high reproduction output and resolution characteristics in the optical recording and magnetic head reproducing system. The first requirement is to increase the curvature of the bit boundary line of the recording spot as much as possible to obtain a spot shape close to a rectangle. The second requirement is that the gap loss of the GMR head is small, that is, the distance obtained by subtracting the length in the track direction of the arc portion from the bit length is about 2/3 of the shield interval Gs. Summarizing these conditions, the conditional expression of the present invention, B−A = B− (R− (R ² − (Tw / 2) ² ) ^0.5 ) ≧ 2/3 · Gs / 2 is derived. Alternatively, when a higher reproduction output is required, it is desirable that a relationship of B− (R− (R ² − (Tw / 2) ² ) ^0.5 ) ≧ Gs / 2 holds.
[0012]
【The invention's effect】
As described above, according to the present invention, since the spot shape when thermomagnetic recording is performed on a medium using an optical head can be made substantially rectangular, the reproduction efficiency when magnetic reproduction is performed using a GMR head is improved. Therefore, the reproduction resolution characteristic of the GMR head can be utilized. As a result, it is possible to achieve high output and high S / N reproduction characteristics at a high linear recording density.
[Brief description of the drawings]
FIG. 1 is a diagram showing the dependence of reproduction output on a recording mark period when a diaphragm is provided and when an aperture is not provided.
FIG. 2 is a schematic diagram of a magnetic recording / reproducing apparatus of the present invention.
FIG. 3 is a diagram showing a medium structure for optical recording and magnetic reproduction.
FIG. 4 is a diagram showing the shape of a spot written on a recording layer.
[Explanation of symbols]
11... Recording mark cycle dependency of reproduction output when an aperture is provided 12... Recording mark cycle dependency of reproduction output when no aperture is provided 21... Laser diode 22. ... reproducing layer 26 ... substrate 27 ... magnetic field modulation coil 28 ... optical laser, magnetic head drive circuit 29 ... reproducing magnetic head 210 ... signal processing circuit 31 ... substrate 32 ... protective layer 33 ... recording layer 34 ... reproducing layer 41 ... stop Recording spot shape 42 when no aperture is provided ... GMR head magnetic shield gap shape 43 ... recording spot shape when a diaphragm is provided.

Claims (3)

A magnetic recording medium having a magnetic recording layer, a thermomagnetic recording head for writing information to the magnetic recording medium, and a magnetoresistive reproducing head or a giant magnetoresistive reproducing head for reading recorded information from the magnetic recording medium; In an apparatus having a drive device for relatively moving the magnetic recording medium and the head,
The thermomagnetic recording head has a diaphragm having a rectangular shape on the light outflow side,
The shape of the aperture is reflected on the boundary line of the recording bits recorded using the aperture,
The radius of curvature R of the magnetic domain shape recorded on the magnetic recording layer, the recording track width T _W , the recording bit length B, and the shield interval Gs of the (giant) magnetoresistive head are B− (R− (R ² − ( Tw / 2) ² ) ^0.5 ) ≥ k · Gs / 2 The relationship is satisfied, and k is 2/3. A magnetic recording medium having a magnetic recording layer, a thermomagnetic recording head for writing information to the magnetic recording medium, and a magnetoresistive reproducing head or a giant magnetoresistive reproducing head for reading recorded information from the magnetic recording medium; In an apparatus having a drive device for relatively moving the magnetic recording medium and the head,
The thermomagnetic recording head has a diaphragm having a rectangular shape on the light outflow side,
The shape of the aperture is reflected on the boundary line of the recording bits recorded using the aperture,
The radius of curvature R of the magnetic domain shape recorded on the magnetic recording layer, the recording track width T _W , the recording bit length B, and the shield interval Gs of the (giant) magnetoresistive head are B− (R− (R ² − ( Tw / 2) ² ) ^0.5 ) ≥ k · Gs / 2 The relationship is satisfied, and k is 1.   3. The magnetic recording / reproducing apparatus according to claim 1, wherein an effective gap length of the (giant) magnetoresistive read head is Gs / 2.

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