JP3332107B2 - Magneto-optical recording medium - Google Patents

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 medium which can be directly overwritten (hereinafter referred to as "overwrite").

[0002]

2. Description of the Related Art A magneto-optical recording medium has been put to practical use as a large-capacity rewritable memory medium. The current magneto-optical recording medium has a problem that the data transfer speed at the time of recording is slow because the old information needs to be erased collectively when data is rewritten. This problem is solved by an overwrite technique, which eliminates the need for a batch erasing operation of old information, so that the time required for recording can be reduced by more than half.

[0003] The overwrite technique includes a magnetic field modulation method of irradiating a laser beam of a constant intensity to rapidly modulate the polarity of an external magnetic field according to an information signal, and modulating a laser beam intensity according to an information signal by applying an external magnetic field of a constant intensity. Light intensity modulation method. The former is suitable when the recording frequency is relatively low, for example, for recording an audio signal, but when high-frequency recording is required, for example, application to computer files is likely to cause an increase in power consumption, which is not preferable. On the other hand, the light intensity modulation method has advantages in that high-frequency recording is easy even with low power consumption, and compatibility with existing magneto-optical recording media is easily obtained.

The inventors of the present application have already proposed a light intensity modulation overwrite method using a leakage magnetic field generated by a bias magnetic layer (Japanese Patent Laid-Open No. Hei 4-212743).
In this method, using a medium in which a bias magnetic layer is laminated on a recording layer, a spatial change in magnetization is formed in the bias magnetic layer by light beam heating to generate a leakage magnetic field (Hl) toward the recording layer. Thereby, overwriting is realized. This leakage magnetic field can be set so as to be large in a portion of the bias magnetic layer that is heated above its Curie temperature (Tcb) and small in a portion that is heated below Tcb. When an appropriate temperature difference is provided between the recording layer and the bias magnetic layer by providing a thermal control layer between the recording layer and the bias magnetic layer, the direction of magnetization of the recording layer is determined when the recording power (Pw) is irradiated with a light beam. The portion heated above the temperature (which is approximately equal to the Curie temperature of the recording layer: Tcs) is applied by the bias magnetic layer to the Tc.
b, and when irradiating the light beam with the erasing power (Pe), the portion of the recording layer that is heated to Tcs or more is set to the bias magnetic layer by Tcb. It can be arranged to correspond to the part that is heated below. Therefore, if an external magnetic field (Hex) having an appropriate constant strength is applied from the outside, the direction of the effective magnetic field (Heff) applied to the recording layer during recording and erasing can be reversed.
As a result, light intensity modulation overwriting becomes possible. In this method, it is important how to efficiently supply the leakage magnetic field generated by the bias magnetic layer to the recording layer.

On the other hand, it is necessary to set the leakage magnetic field (Hl) generated by the bias magnetic layer to be large in a portion heated above Tcb and small in a portion heated below Tcb in the recording layer. As described above, it is important to increase the difference in the value of H1 supplied to the heated portion between the irradiation of Pw light and the irradiation of Pe light, that is, to improve the overwrite performance. For this purpose, it is desirable that the spatial distribution of the magnetization (Msb) of the bias magnetic layer has a shape that changes rapidly only near the Tcb heating part. Here, since the spatial distribution of Msb is determined by the temperature characteristics of Msb in the bias magnetic layer and the temperature distribution formed in the bias magnetic layer at the time of light beam irradiation, Msb changes rapidly only near Tcb. It is important to select a bias magnetic layer having a temperature characteristic and to select a thermal response characteristic of a medium so that the temperature distribution changes as rapidly as possible near Tcb.

[0006] However, the above-mentioned Japanese Patent Application Laid-Open No. Hei 4-21274 has been disclosed.
In No. 3, the temperature difference in the thickness direction of the bias magnetic layer is not sufficiently considered with respect to the spatial distribution of Msb, and the difference between Hl during Pw light irradiation and Hl during Pe light irradiation is not always sufficient.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to improve the efficiency of supplying a leakage magnetic field to the recording layer or to reduce the Ts of the Msb distribution.
An object of the present invention is to provide a magneto-optical recording medium having high overwrite performance by improving the agility in the vicinity of the cb heating portion to increase the difference between Hl during Pw light irradiation and Hl during Pe light irradiation. .

[0008]

According to the present invention, first, a recording layer and a bias magnetic layer for supplying a leakage magnetic field to the recording layer are provided, and a recording track is formed on the main surface thereof. Wherein the distance between the recording layer between the recording tracks and the bias magnetic layer between the recording tracks is larger than the distance between the recording layer between the recording tracks and the bias magnetic layer between the recording tracks. A magneto-optical recording medium characterized by being short.

Second, a magneto-optical recording medium comprising a recording layer and a bias magnetic layer for supplying a leakage magnetic field to the recording layer, wherein the Curie temperature of the bias magnetic layer is:
There is provided a magneto-optical recording medium characterized in that the bias magnetic layer changes along the film thickness direction so that a portion close to the recording layer is higher than a portion away from the recording layer.

Hereinafter, the present invention will be described in detail.
In the first aspect of the present invention, as a means for improving the efficiency of supplying the leakage magnetic field (Hl) generated by the bias magnetic layer to the recording layer, the bias magnetic field between the recording layer and the recording track in the recording track as described above is used. The distance between the layers was set shorter than the distance between the recording layers between the recording tracks and the bias magnetic layer on the recording tracks.

Here, the recording track is a medium circumferential line in which a recording magnetic domain array is formed, and the space between the recording tracks is
This is a circumferential line between adjacent recording tracks. Also,
The distance between the layers is determined by the surface of the recording layer closer to the bias magnetic layer (S plane) and the surface of the bias magnetic layer closer to the recording layer (B surface).
Surface), which is measured along the thickness direction of the medium. Incidentally, the magneto-optical recording medium of the present invention,
Usually, a recording layer, a thermal control layer, and a bias magnetic layer are sequentially formed and laminated on a predetermined substrate. For example, the surface B on a recording track is located on the substrate surface more than the surface S between recording tracks. When the distances are close, the distance between the S plane and the B plane is represented by a negative value, and the magnitude of the distance is determined in consideration of the sign.

FIG. 1 is a partial longitudinal sectional view showing an example of a magneto-optical recording medium according to this embodiment. In FIG. 1, 1 is a recording layer, 2 is a thermal control layer, 3 is a bias magnetic layer, 4 is a substrate, L _N and L _{N + 1} are Nth and N + 1th recording track portions, and G _N is Nth recording track interval, S
L is the S surface on the recording track, SG is the S surface on the recording track, BL is the B surface on the recording track, and BG is the B surface on the recording track.

Here, according to the first embodiment of the present invention, S
The distance between L and BG is set shorter than the distance between SG and BL. This setting is easy if a groove for tracking guide provided on the surface of the substrate 4 is used.
G, assuming that the thickness of the heat control layer 2 is DT, in FIG. 1, the distance between SL and BG is represented by DT-DG, and the distance between SG and BL is represented by DT + DG. With such a configuration, the leakage magnetic field can be efficiently supplied from the bias magnetic layer 3 to the recording track portion of the recording layer 1.

Providing a groove for a tracking guide in a substrate is widely known in the art.
It is also known that a recording magnetic domain array is formed on a so-called land portion as a recording track as described above, but in this embodiment, an overwrite method using a leakage magnetic field is applied using such a technique. The magnetic recording medium is characterized in that it is designed to improve the supply efficiency of the leakage magnetic field, and provides a unique operation and effect that cannot be obtained by the conventional technology.

Even in the case of groove recording in which a so-called groove portion is used as a recording track, if the medium is designed so as to satisfy the above relationship, the leakage magnetic field can be efficiently supplied to the recording track portion of the recording layer. it can.

Next, a second embodiment of the present invention will be described. In this embodiment, as described above, the Curie temperature (Tcb) of the bias magnetic layer changes along the film thickness direction such that a portion close to the recording layer is higher than a portion away from the recording layer. I have.

That is, in a medium in which a recording layer and a bias magnetic layer are laminated, a light beam is irradiated from the recording layer side. It is higher than the part away from the recording layer. Therefore, by changing Tcb along the thickness direction of the bias magnetic layer as described above, the position at which the bias magnetic layer is heated to Tcb can be aligned with the thickness direction of the bias magnetic layer. Is the spatial distribution of magnetization (Msb) of the
In the vicinity of b, it can be steeper than the conventional medium.

In a preferred embodiment, the temperature distribution in the thickness direction formed in the bias magnetic layer at the time of light beam irradiation and T
This is because the distribution of cb in the film thickness direction is substantially the same, so that the Tcb heating portions can be aligned in the film thickness direction, and the spatial distribution of Hl becomes steep.

The temperature difference in the thickness direction of the bias magnetic layer changes with time during light beam irradiation, and the difference is large in the temperature rising process and small in the temperature falling process due to thermal diffusion in the film thickness direction. Therefore, in order to exhibit the above effect more remarkably, it is preferable that the temperature difference in the film thickness direction is maintained to a significant degree even in the temperature decreasing process. Accordingly, as a more preferred embodiment, a film structure in which a layer having a thermal conductivity substantially equal to or higher than that of the bias magnetic layer on the surface of the bias magnetic layer opposite to the recording layer can be mentioned. In this embodiment, as such a layer, it is preferable to use a magnetic thin film made of the same material as that of the bias magnetic layer, and particularly to use an initialization magnetic layer having a function of preventing the magnetization reversal of the bias magnetic layer. Is most preferred.

The initialization magnetic layer is provided to prevent reversal of the magnetization of the bias magnetic layer and to facilitate overwriting repeatedly. Even if only the initialization magnetic layer is provided, the temperature difference in the thickness direction of the bias magnetic layer is maintained even during the temperature decreasing process, and the effect of the present invention can be more expected. However, a thermal diffusion layer is further provided on the initialization magnetic layer. By doing so, a desired temperature difference in the thickness direction of the bias magnetic layer can be formed more clearly, and the above-mentioned effect becomes more remarkable.

When a magnet for initializing the bias magnetic layer is provided in the magneto-optical drive device, it is not necessary to form the initialization magnetic layer. The diffusion layer can be provided directly on the bias magnetic layer. In this case, a significant temperature difference in the thickness direction of the bias magnetic layer can be secured with a simpler medium structure.

[0022]

Embodiments of the present invention will be described below. (Embodiment 1) FIG. 1 is a partial longitudinal sectional view showing an embodiment of a magneto-optical medium according to the first aspect of the present invention. As described above, a recording layer 1 and a heat control layer 2 are formed on a substrate 4. And a bias magnetic layer 3 are formed in this order. The substrate 4 is provided with a groove for tracking guide, where L _N and L _{N + 1} are the Nth and N + 1th recording track portions, G _N is the Nth recording track portion, and SL is the recording track. S surface on truck, SG
Is the S surface on the recording track, and BL is B on the recording track.
The surface BG is the surface B between the recording tracks.

The medium shown in FIG. 1 can be formed, for example, by the following procedure. That is, first, according to a usual technique, for example, a photosensitive resin is applied onto a glass plate, developed by laser exposure, and then developed to form a master. After forming a metal film on the master, a stamper is formed by electroforming. Next, the substrate 4 is formed by injection molding a polycarbonate resin using the stamper. Here, the depth DG of the groove for tracking guide can be changed according to the conditions for forming the master, but is usually set to an optimum depth determined by the wavelength of the light beam used for recording and reproduction and the refractive index of the substrate. 70n
DG is set to about m.

Next, the recording layer 1, the heat control layer 2,
The bias magnetic layer 3 is formed by a thin film forming technique, for example, a sputtering method. In this case, the heat control layer 2 is not essential and does not have to be provided. However, even when there is no thermal control layer (DT = 0), the magnetic interaction between the recording layer 1 and the bias magnetic layer 3 is mainly magnetostatic and the exchange interaction is small due to the gist of this mode. And

Although not shown in FIG. 1, the substrate 4
It is permissible to provide an optical interference layer between the magnetic layer and the recording layer 1, or to provide a protective layer on the bias magnetic layer 3.
A more preferable aspect for overwriting is a medium provided with an initialization layer on the bias magnetic layer 3 for preventing the magnetization reversal of the bias magnetic layer.

In the medium having the structure shown in FIG. 1, for example, a TbFeCo film having a thickness of 25 nm
As the bias magnetic layer 3, a 200 nm thick TbFeCo film can be used.

Recording (overwriting) of information on the medium created as described above is performed, for example, in the following procedure. First, a disk-shaped medium is mounted on a magneto-optical drive device, rotated at a linear velocity of 9 m / s, and moved upward by 100 m / s.
An external magnetic field Hex of Oe is applied, the light beam intensity is set to a recording power Pw: 12 mW, the erasing power Pe: 8 mW, the reproduction power: 1.5 mW, the recording pulse width is set to 100 ns, the recording frequency is set to 5 MHz, and the light beam is recorded. Track L _N
Focus on top.

At the time of irradiation with Pw light, the portion where the recording layer is heated above the Curie temperature (Tcs) (magnetization direction determining portion) corresponds to the portion where the bias magnetic layer is heated above Tcb, and the recording layer faces downward. Large leakage magnetic field (Hl)
And the direction of the effective magnetic field Heff formed by the superposition of Hl and Hex becomes downward, and the magnetization of the recording layer becomes downward. Further, at the time of Pe light irradiation, the Tcs heating part of the recording layer corresponds to the heating part of the bias magnetic layer below Tcb, and
Is small, Heff is upward, and the magnetization of the recording layer is upward. At the reproduction level (1.5 mW), a magneto-optical signal corresponding to the direction of magnetization of the recording layer is read.

Here, the portion where the recording layer is heated to Tcs or higher and the portion where the bias magnetic layer is heated to Tcb move from the end of _LN to the center with time, but Hl is the bias magnetic layer. since generated due to the magnetization of the magnetization and G _N portions and G _N-1 parts of a portion which is heated to less than Tcb of L _N of the layer (i.e. inter-track section), the recording track of the bias magnetic layer Not only the corresponding part but also the part between the recording tracks is important.
This is important when the heating position is at the _LN end.

FIG. 2 is a characteristic diagram showing the relationship between the magnitude of Hl based on the calculation result and the distance (Z) between the bias magnetic layer and the recording layer. Here, the step of the groove for tracking guide is taken into consideration. However, it can be seen that Hl increases as Z decreases. Further, when there is a step, Hl greatly depends on the distance between SL and BG due to the importance of the magnetization of the bias magnetic layer in the inter-track portion as described above,
The degree of this is further increased as compared with FIG. 2, and the slope of the curve in FIG. 2 becomes steeper.

For comparison, G _N in FIG. 1 was selected as a recording track, and a similar recording test was performed.
_The overwrite performance was lower than when _N was selected as the recording track.

From the above, the distance between SL and BG is represented by S
It was confirmed that by setting the distance shorter than the G-BL distance, Hl can be more efficiently supplied to the recording track.

(Embodiment 2) FIG. 3 is a partial longitudinal sectional view showing an embodiment of a magneto-optical medium according to the second aspect of the present invention.
11 is a recording layer, 12 is a thermal control layer, 13 is a bias magnetic layer, 14 is an initialization magnetic layer, 15 is an interference layer, 16 is a protective layer, and 17 is a substrate (optical disk substrate). These functions are the same as those in the first embodiment, and the heat control layer 12, the initialized magnetic layer 14, the interference layer 15, and the protective layer 16 are not essential layers but are provided as necessary.

The medium shown in FIG. 3 can be obtained by, for example, forming each layer by sputtering on a preformatted resin substrate 17. In the medium having the structure shown in FIG. 3, for example, a 25 nm-thick TbF
eCo film, 15 nm thick Si—N as heat control layer 12
200 nm thick TbFe as the film and bias magnetic layer 13
Co film, 200 nm thick TbC as the initialization magnetic layer 14
As the o film and the protective film 16, a 50-nm-thick Si—N film can be used.

The Curie temperature (Tcs) of the recording layer 11 and the Curie temperature (Tcb) of the bias magnetic layer 13 are:
By changing the composition of each film, Tcs can be set at, for example, 200 ° C. by keeping the composition of the recording layer 11 constant, and the composition of the bias magnetic layer 13 can be changed in the film thickness direction. By doing, Tcb
Can be set, for example, to 200 ° C. in a portion near the recording layer 11 and 180 ° C. in a portion away from the recording layer 11. In order to change Tcb along the thickness direction of the bias magnetic layer 13 as described above, for example, the Co composition ratio in the bias magnetic layer 13 may be gradually reduced along the film growth direction. As a specific method, the bias magnetic layer 13 is formed by multiple simultaneous sputtering using a single target of Tb, Fe, and Co, and the input ratio between the Fe target and the Co target is determined in the initial stage of the formation of the bias magnetic layer 13. Should be large, and should be gradually reduced with growth.

FIG. 4 is a diagram schematically showing a temperature (T) distribution, a Tcb distribution, and a Tcb heating portion (rcb) distribution of the bias magnetic layer at the time of light beam irradiation in the thickness direction (Z) of the bias magnetic layer. (A) is an example of a bias magnetic layer in which Tcb is changed along the film thickness direction according to the present invention, and (b) is an example of a bias magnetic layer having a uniform Tcb in the film thickness direction. FIG. 4A shows a case where the T distribution and the Tcb distribution in the Z direction at the time of reaching the maximum temperature by light beam irradiation are adjusted.

As shown in FIG. 4 (a), Tcb is changed along the thickness direction of the bias magnetic layer so that a portion closer to the recording layer has a higher Tcb than a portion farther from the recording layer. As a result, the position of rcb is aligned in the film thickness direction, and the spatial distribution of Hl becomes very sharp near rcb,
It clearly presents a small shape outside the rcb and a large shape inside the rcb.

On the other hand, in the bias magnetic layer having a uniform Tcb in the film thickness direction as shown in FIG. 4B, the rcb distribution reflects the T distribution in the film thickness direction.
The agility of Hl near b is inferior to the slower rcb distribution.

Next, in order to clarify the effect of forming a gradient in Tcb along the thickness direction of the bias magnetic layer, a bias magnetic layer having the characteristics shown in FIGS. An overwrite test was attempted using a medium with.

FIG. 4A shows the structure shown in FIG.
The two types of media having the bias magnetic layers having the characteristics shown in (b) are installed in a magneto-optical drive, and the linear velocity is 9 m / s, P
w: 12 mW, Pe: 8 mW, reproduction power: 1.5 m
W, external magnetic field (Hex): -100 Oe, recording frequency:
Recording (overwriting) was performed under the conditions of 2 to 5 MHz and a recording pulse width: 100 ns.

As a result, the magneto-optical recording medium provided with the bias magnetic layer of FIG. 4A having a gradient of Tcb along the film thickness direction has a bias of FIG. 4B without the gradient of Tcb. A higher reproduction signal amplitude was obtained than in a magneto-optical medium having a magnetic layer, and the effect of forming a Tcb gradient in the film thickness direction was demonstrated.

As another example, instead of the initialization magnetic layer in the medium shown in FIG. 3, a medium in which an Al alloy film having higher thermal conductivity is formed is prepared, and thermal analysis is performed on the medium to perform bias magnetic layer formation. The temperature distribution at the time when the maximum temperature in the film thickness direction was reached was derived, and the gradient of Tcb in the film thickness direction was set so as to substantially match this temperature distribution. Since this medium does not have an initialization magnetic layer, the magnetization reversal threshold of the bias magnetic layer is lower than that of the medium having the initialization magnetic layer.
The magnetization of the bias magnetic layer was reversed by the irradiation of w light. Then, after the magnetic field applying means for initializing the bias magnetic layer was installed in the magneto-optical driving device, the device was operated under the same conditions as in the above-described example.

As a result, the amplitude of the overwrite signal of the magneto-optical recording medium of this embodiment is higher than that of the medium having the bias magnetic layer having the characteristics shown in FIG. It has been confirmed that the effect of the present invention is more remarkably exhibited when a temperature gradient is provided.

[0044]

According to the present invention, firstly, it is possible to improve the utilization efficiency of the leakage magnetic field supplied from the bias magnetic layer to the recording layer, and secondly, the bias magnetic layer is heated to the Curie temperature. The steepness of the magnetization distribution in the portion where the recording layer is heated can be improved to increase the change in the stray magnetic field supplied to the portion heated to the temperature for determining the magnetization of the recording layer due to the light intensity. A high magneto-optical recording medium can be provided.

[Brief description of the drawings]

FIG. 1 is a partial longitudinal sectional view showing an example of a magneto-optical recording medium according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a distance between a recording layer and a bias magnetic layer and a value of Hl.

FIG. 3 is a partial longitudinal sectional view showing an example of a magneto-optical recording medium according to a second embodiment of the present invention.

FIG. 4 is a diagram schematically showing a temperature (T) distribution, a Tcb distribution, and a distribution of a Curie temperature heated portion (rcb) of the bias magnetic layer at the time of light beam irradiation in the bias magnetic layer thickness direction (Z).

[Explanation of symbols]

1, 11 recording layer, 2, 12 thermal control layer, 3, 13
... bias magnetic layer, 4, 17 ... substrate, 14 ... initialized magnetic layer, 15 ... interference layer, 16 ... protective layer

Claims (2)

(57) [Claims] A land and a groove are formed in a circumferential direction.
Substrate, recording layer formed on the substrate, and recording layer
A via formed thereon to supply a leakage magnetic field to the recording layer
A magnetic layer, and the land as a recording track.
Magneto-optical recording medium that performs magneto-optical recording by irradiating light from the substrate side
The recording layer in the land, which is the body and forms the recording track
Magnetic layer in the groove between the track and the recording track
The distance between the recording tracks in the groove between the recording tracks
Magnetic layer in the land that forms the recording track with the layer
Characterized by being shorter than the distance between
body. 2. A magneto-optical recording medium comprising a recording layer and a bias magnetic layer for supplying a leakage magnetic field to the recording layer, wherein the Curie temperature of the bias magnetic layer is close to the recording layer of the bias magnetic layer. A magneto-optical recording medium characterized in that the thickness of the magneto-optical recording medium changes along the film thickness direction so that a portion to be formed is higher than a portion away from the recording layer.