JPH05342655A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To prevent interference between patterns due to thermal interference corresponding to a data pattern to be recorded and to enable ultrahigh density recording. CONSTITUTION:An inorg. dielectric layer 2, a magneto-optical recording layer 3 having perpendicular magnetic anisotropy, an inorg. dielectric layer 4 and heat circulation controlling layers 5, 6 are successively laminated on a glass or plastic substrate 1 to obtain a magneto-optical recording medium. The heat circulation controlling layers 5, 6 are two layers different from each other in heat conductivity, the heat conductivity of the lower layer 5 closer to the magneto-optical recording layer 3 is not higher than that of the recording layer 3 and the upper layer 6 farther from the recording layer 3 has higher heat conductivity than the recording layer 3 and the lower layer 5. The shape of recording magnetic domains can be controlled and fine magnetic recording domains can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording for recording, reproducing or erasing using a laser beam and an externally applied magnetic field, and more particularly to a structure of a magneto-optical recording medium suitable for ultra high density optical recording. ..

[0002]

2. Description of the Related Art With the progress of advanced information society in recent years, there is an increasing need for a high-density and large-capacity file memory. Under such circumstances, optical recording is drawing attention as a memory that meets these needs. Optical recording can be roughly classified into three types: a read-only type represented by a CD, a write-once type widely used as an archiver file for a document file, and a rewritable type widely used for a document file and an image file. .. Of these, rewritable optical recording using magneto-optical recording has been put to practical use. In recent years, many research institutions are conducting research and development aiming at higher density of the magneto-optical recording. By the way, as a method of improving the recording density, the track pitch is reduced, the recording bits are reduced, or recording is performed by adding information to the edge portion of the recording bit (pit edge recording) (increasing the linear density), and Techniques such as reducing the size of recording bits have been proposed. It is effective to record by combining these methods. In this case, it is important to control the size and shape of the recording magnetic domain formed. Known examples of these techniques include JP-A-59-178641.

[0003]

In the above-mentioned prior art, no consideration is given to the technology relating to the control of the shape and size of the recording magnetic domain, which is an important technology for high density recording, and it is difficult to realize high density recording. There was a case.

An object of the present invention is to provide a technique for controlling the shape and size of a recording magnetic domain by controlling the heat flow flowing in a recording medium during recording or erasing in magneto-optical recording.

[0005]

In order to achieve the above object, a heat flow control layer is provided in a magneto-optical recording medium. That is, an inorganic compound film typified by silicon nitride, a magneto-optical recording film having perpendicular magnetic anisotropy, an inorganic compound film again, and finally a heat flow control film were sequentially laminated on a disk substrate having uneven guide grooves. It can be realized by using a magneto-optical recording medium having a multilayer structure.

Here, the heat flow control film is composed of two layers.
The first layer formed on the side closer to the magneto-optical recording film is a material layer having a thermal conductivity equal to or smaller than that of the magneto-optical recording film. And formed on the side farther from the magneto-optical recording layer 2
The layer is composed of a magneto-optical recording film and a material layer having a higher thermal conductivity than the heat flow control layer of the first layer. The third layer of the inorganic compound film in the magneto-optical recording medium may also serve as the first layer formed on the side closer to the previous magneto-optical recording film.

As a result, since minute recording magnetic domains can be easily formed, recording can be performed with a high bit line density, and the length of recording magnetic domains can be easily controlled, which is also suitable for pit edge recording. There was no change in the minimum recordable recording power value due to the provision of this heat flow control layer. Here, in the control of the heat flow in the magneto-optical recording medium by the heat flow control layer, the action of absorbing the heat given to the magneto-optical recording layer at the time of recording or erasing in the layer whose thermal conductivity is equal to or smaller than that of the magneto-optical recording layer. A layer having a higher thermal conductivity than the magneto-optical recording layer and a layer close to the magneto-optical recording layer by suppressing the diffusion of heat to the periphery of the layer having the same or smaller thermal conductivity as the magneto-optical recording layer. Has a function of dissipating heat absorbed by a layer having a thermal conductivity equal to or smaller than that of the magneto-optical recording layer. As a result, recording control can be easily performed.

Further, by forming this heat flow control layer, the heat flow in the magneto-optical recording medium at the time of recording or erasing can be controlled so that the maximum attainable temperature of the magneto-optical recording film becomes 300 ° C. or less. Thereby, structural relaxation due to heat of the magneto-optical recording film can be suppressed. As a result, it is possible to suppress a decrease in the reproduction signal output due to repeated recording and erasing. Of course, if the heat resistance of the magneto-optical recording film is improved, the maximum temperature reached by the magneto-optical recording film is not limited to 300 ° C. and can be set higher. However, in this case, it is necessary to consider the heat resistant temperature of the substrate.

Further, by making this heat flow control layer act as a light reflection layer, multiple interference occurs in the recording medium as a side effect, resulting in a Kerr rotation angle and a Faraday.
Since the magneto-optical effect such as the rotation angle can be increased, the reproduction signal output can be increased.

By controlling the thermal conductivity of the heat flow control layer composed of these two layers, the magnetization reversal region of the magneto-optical recording film can be arbitrarily selected, so that the size of the recording magnetic domain that can be formed can be arbitrarily selected. Further, since the shape of the magnetic domains formed can be controlled, a magneto-optical recording medium suitable for pit edge recording can be obtained. At the same time, it is possible to suppress interference between patterns due to heat according to the data pattern to be recorded. Of course, it is needless to say that the effect can be greatly increased by using it together with the control of the recording waveform.

In addition to the two layers shown above as a method for controlling the thermal conductivity of the heat flow control layer, the thermal conductivity may be continuously changed. What is important here is not the method of changing the thermal conductivity but the value of the thermal conductivity of each layer and the film thickness of the heat flow control layer on the side closer to the magneto-optical recording film. The effect of the present invention does not depend on the structure of the magneto-optical recording film used. That is, in addition to a normal single layer film, a magnetically coupled two-layer film or three-layer film may be used as the magneto-optical recording film.

From the above, super high density optical recording was realized.

[0013]

By providing the heat flow control layer in the magneto-optical recording medium, the heat flow in the magneto-optical recording medium can be controlled, so that the shape of the recording magnetic domain can be controlled and the minute recording magnetic domain can be formed. Here, the first heat flow control layer absorbs the heat applied to the recording film, and the second heat flow control layer allows the heat to radiate without being diffused to the surroundings, so that the maximum attainable temperature of the recording film is 300. It can be kept at or below ° C. As a result, the structural relaxation of the recording film can be suppressed, so that the reproduction output is not lowered with the repeated rewriting. Further, since there is no interference between patterns due to thermal interference depending on the data pattern to be recorded, ultra-high density optical recording can be realized. Further, since it is possible to control the shape of the recording magnetic domain to be formed, particularly to make the magnetic domain width constant and control the magnetic domain length, pit edge recording becomes possible. In addition, since the magneto-optical effect can be increased by providing the heat flow control layer with a light reflecting effect, the reproduction signal output can be increased.

[0014]

【Example】

Example 1 The sectional structure of the magneto-optical disk produced in this example is shown in FIG. First, a silicon nitride layer 2 having a film thickness of 750 nm was formed by a sputtering method on a substrate 1 made of plastic such as polycarbonate or glass having uneven guide grooves. The manufacturing conditions at that time were Ar gas and discharge gas.
/ N ₂ , pure Si was used as the target, and the sputtering was performed at a discharge gas pressure of 10 mTorr and an input RF power density of 6.6 W / cm ² .

Subsequently, a magneto-optical recording film 3 made of a TbFeCoNb alloy was formed by the sputtering method. The manufacturing conditions were such that Ar was used as the discharge gas and TbFeCoNb alloy was used as the target, the discharge gas pressure was 5 mTorr, and the input RF was applied.
Sputtering was performed at a power density of 4.4 W / cm ² . Next, the silicon nitride film 4 is again sputtered to 250 n
It was formed to a film thickness of m. The manufacturing conditions at that time are the same as those of the silicon nitride film 2 described above.

Next, a Ni film 3 is formed as the first heat flow control layer 5.
It was formed by a sputtering method to have a film thickness of 5 nm. The production conditions were such that Ar was used as the discharge gas and pure Ni was used as the target, and the sputtering was performed at a discharge gas pressure of 15 mTorr and an input RF power density of 3.3 W / cm ² . An Al film having a thickness of 40 nm was formed as the second heat flow control layer 6 by the sputtering method. The manufacturing conditions were such that Ar was used as the discharge gas and pure Al was used as the target, the discharge gas pressure was 15 mTorr, and the input RF power density was 3.3 W / cm ² .

The recording / erasing characteristics were examined using the magneto-optical disk manufactured as described above. First, the dependence of the reproduction signal output on the recording laser power was examined. As a result, recording was performed at the innermost peripheral position (r = 30 mm) with a frequency of 12 MHz, a pulse width of 80 ns, and a laser power of 5.5 mW. The carrier-to-noise ratio at that time was C / N = 62 dB. A pattern shown in FIG. 2A was recorded on this disc, and the signal was reproduced. The results of observing the reproduced signal waveform c and the recorded magnetic domain b with a polarization microscope are shown. According to this, it was found from the waveform and magnetic domain observation results that fine magnetic domains were well formed without thermal interference.

When a change in reproduction signal output when recording / reproducing / erasing was repeated using this disc, it was found to be 10
^There was no change in the value after ⁷ repetitions.

When the highest temperature reached in the structure of this example was examined, it was found to be 300 ° C. at the highest. From this,
Since the temperature of the recording film does not exceed 300 ° C., structural relaxation of the amorphous recording film does not occur, which is effective in improving heat resistance. In this way, the temperature of the recording film can be controlled arbitrarily,
As schematically shown in FIG. 3, the first heat flow control layer absorbs the heat given to the magneto-optical recording film, and the heat is not accumulated to heat the magneto-optical recording film. This is because the second heat flow control layer was formed as a layer having higher thermal conductivity than this layer. The minimum recordable power and the recording / erasing repeatability by using this structure did not show a big difference from the conventional disc. However, the shape of the recording magnetic domain formed is good, a magnetic domain length having a desired length can be obtained, and a recording magnetic domain having a desired magnetic domain width and having a constant magnetic domain width can be obtained. It was In particular, 0.
It was effective for forming minute recording magnetic domains of 7 μm or less.

The effect of the present invention does not depend on each material and composition used, but on the thermal structure of the disk. Although Ni is used for the first heat flow control layer in this embodiment, the same effect can be obtained by using stainless steel, Monel, Nb, and Cr. The same effect can be obtained by using Pb, Cu, Ag, or Au in addition to Al as the second heat flow control layer. In addition to the TbFeCoNb film, the recording film may be formed by using an alternately laminated multilayer film in which Pt and Co are alternately laminated, a garnet-based recording film, a Heusler alloy, and the like, and the thermal conductivity of each recording film is Considered. The thermal conductivity of the first heat flow control layer and the second heat flow control layer, and further the material may be selected.

<Embodiment 2> The sectional structure of the magneto-optical disk manufactured in this embodiment is shown in FIG. First, a silicon nitride layer 2 having a film thickness of 750 nm was formed by a sputtering method on a substrate 1 made of plastic such as polycarbonate or glass having uneven guide grooves. The manufacturing conditions at that time were such that Ar / N ₂ was used as a discharge gas and pure Si was used as a target, and the sputtering was performed at a discharge gas pressure of 10 mTorr and an input RF power density of 6.6 W / cm ² .

Subsequently, a magneto-optical recording film 3-1 made of a TbFeCoNb alloy was formed by the sputtering method. The manufacturing conditions are Ar for the discharge gas and TbFeCoN for the target.
Sputtering was performed at a discharge gas pressure of 5 mTorr and an input RF power density of 4.4 W / cm ² using each of the b alloys.
Next, the magneto-optical recording film 3 made of TbDyFeCoCr 3-
2 was formed by the sputtering method. The manufacturing conditions were such that Ar was used as the discharge gas and TbDyFeCoCr alloy was used as the target, and the sputtering was performed at a discharge gas pressure of 5 mTorr and an input RF power density of 4.4 W / cm ² . Next, the silicon nitride film 4 was again formed to a thickness of 250 nm by the sputtering method. The manufacturing conditions at that time are the same as those of the silicon nitride film 2 described above.
Is the same as.

Next, a Ni film 3 is formed as the first heat flow control layer 5.
It was formed by a sputtering method to have a film thickness of 5 nm. The production conditions were such that Ar was used as the discharge gas and pure Ni was used as the target, and the sputtering was performed at a discharge gas pressure of 15 mTorr and an input RF power density of 3.3 W / cm ² . An Al film having a thickness of 40 nm was formed as the second heat flow control layer 6 by the sputtering method. The manufacturing conditions were such that Ar was used as the discharge gas and pure Al was used as the target, the discharge gas pressure was 15 mTorr, and the input RF power density was 3.3 W / cm ² .

The recording / erasing characteristics were examined using the magneto-optical disk thus manufactured. First, the dependence of the reproduction signal output on the recording laser power was examined. As a result, recording was performed at the innermost peripheral position (r = 30 mm) with a frequency of 12 MHz, a pulse width of 80 ns and a laser power of 7.5 mW. The carrier-to-noise ratio at that time was C / N = 61 dB. This disc was overwritten by modulating the light intensity using the waveform shown in FIG. As a result, 1
Change in the reproduction signal output even after repeated 0 ⁷ times of overwriting was not observed. In addition, the controllability of the magnetic domain shape and the size of the magnetic domain was also particularly effective for minute magnetic domains of 0.7 μm or less.

If a material having a small thermal conductivity is used for the first heat flow control layer, the diffusion of heat to the surroundings can be suppressed. As a result, the size of the magnetic domain formed can be controlled and the range of the erased area formed around the recording area can be narrowed, so that interference between tracks (thermal crosstalk) can be greatly suppressed. Moreover, since the material having a large thermal conductivity is used for the second heat flow control layer, the heat stored in the first heat flow control layer can be diffused to the surroundings without increasing the temperature of the recording film. Therefore, since the highest temperature reached by the recording film can be set to 300 ° C. or less, structural relaxation of the recording film can be suppressed,
It was possible to suppress a change in recording sensitivity and a decrease in reproduced signal output due to rewriting.

[0026]

According to the present invention, since the heat flow in the magneto-optical recording medium can be controlled by providing the heat flow control layer in the magneto-optical recording medium, the shape of the recording magnetic domain can be controlled and the minute recording magnetic domain can be formed. Will be possible. Further, since there is no interference between patterns due to thermal interference depending on the data pattern to be recorded, ultra-high density optical recording can be realized. Further, since it is possible to control the shape of the recording magnetic domain to be formed, particularly to make the magnetic domain width constant and control the magnetic domain length, pit edge recording becomes possible. In addition, the maximum temperature of the magneto-optical recording film is set to 300
Since the temperature can be set to not more than 0 ° C., it is possible to suppress the reduction of the reproduction signal output, and it is possible to greatly improve the rewriting characteristics. Further, by providing the heat flow control layer with a light reflecting effect, the magneto-optical effect can be increased, and thus the reproduction signal output can be increased.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium.

FIG. 2 is a timing chart of a recording signal pattern and a reproduction signal.

FIG. 3 is an explanatory diagram showing a heat flow flowing in a recording medium.

FIG. 4 is a sectional view of a magneto-optical recording medium.

FIG. 5 is a characteristic diagram showing a pattern of a recording signal.

[Explanation of symbols]

1 ... Substrate, 2 ... Silicon nitride film, 3 ... Magneto-optical recording film, 4
... Silicon nitride film, 5 ... First heat flow control layer, 6 ... Second heat flow control layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Ide 1-280, Higashi Koigokubo, Kokubunji, Tokyo Metropolitan Research Center, Hitachi, Ltd.

Claims (9)

[Claims] 1. In magneto-optical recording for recording, erasing or reproducing by using a laser beam and an externally applied magnetic field, an inorganic dielectric layer and a perpendicular magnetic anisotropy are formed on a glass or plastic substrate as a magneto-optical recording medium. A magneto-optical recording layer, an inorganic dielectric layer, and a heat flow control layer, which are at least one layer,
The heat flow control layer is composed of two layers having different thermal conductivities, and a layer close to the magneto-optical recording layer has a thermal conductivity equal to or smaller than that of the magneto-optical recording layer and is separated from the magneto-optical recording layer. A magneto-optical recording medium, wherein the layer is composed of the magneto-optical recording layer and a layer having a thermal conductivity higher than that of the layer close to the magneto-optical recording layer. 2. The magneto-optical device according to claim 1, wherein the heat flow in the magneto-optical recording medium at the time of recording or erasing is controlled, and more preferably, the maximum temperature of the magneto-optical recording film is controlled to 300 ° C. or less. recoding media. 3. The magneto-optical recording layer according to claim 1, wherein the layer having thermal conductivity equal to or smaller than that of the magneto-optical recording layer absorbs heat applied to the magneto-optical recording layer during recording or erasing. The layer having the thermal conductivity equal to or smaller than that of the magneto-optical recording layer and the layer closer to the magneto-optical recording layer has the effect of suppressing the diffusion of heat to the periphery of the layer, A magneto-optical recording medium having a function of releasing heat absorbed by a layer having a thermal conductivity equal to or smaller than that of the magnetic recording layer. 4. The heat flow control layer according to claim 1 has a function as a light reflection layer, and more advantageously, this causes multiple interference in a recording medium, and a Kerr rotation angle or /
And a Faraday magneto-optical recording medium with an increased rotation angle. 5. A magneto-optical recording medium in which the magnetization reversal region of the magneto-optical recording film is controlled by controlling the thermal conductivity of the two-layer heat flow control layer according to claim 1. 6. A magneto-optical recording medium according to claim 1, wherein the magneto-optical recording film having the perpendicular magnetic anisotropy comprises at least two kinds of magnetic films having different magnetic characteristics. 7. A magneto-optical recording medium in which the shape of magnetic domains to be formed is controlled by controlling the thermal conductivity of the heat flow control layer consisting of the two layers according to claim 1. 8. A magneto-optical recording medium in which the thermal conductivity of the heat flow control layer according to claim 1 is continuously changed in the film thickness direction. 9. The shift of recording bits due to thermal interference between patterns depending on the data pattern to be recorded is suppressed by controlling the thermal conductivity of the two-layer heat flow control layer according to claim 1. Magneto-optical recording medium.