JPH04216339A - Magneto-optical recording medium and production thereof - Google Patents

Abstract

PURPOSE:To provide the magneto-optical recording medium having a high sensitivity by forming the magneto-optical recording medium having an overwritable multilayered structure on the magneto-optical recording medium on which particularly information is already recorded. CONSTITUTION:This magneto-optical recording medium is provided with the 1st layer 3 of memory layers for recording/reproducing, the 2nd layer 4 which is an auxiliary layer to assist writing, the 3rd layer 5 which is a coupling layer to control the coupling of the 2nd layer and the 4th layer, and the 4th layer 6 which is an initialization layer to initialize the 2nd layer as the multilayered films coupled to each other by the exchange interactions on each other on a substrate 1 and is constituted by lowering the thermal conductivity of at least one layer of the above-mentioned 3rd layer and 4th layer 6 lower than the thermal conductivity of either of the above-mentioned 1st layer or 2nd layer.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a magneto-optical recording medium.
In particular, the present invention relates to a highly sensitive magneto-optical recording medium, which is a multilayer structured magneto-optical recording medium that can be overwritten on the surface of the magneto-optical recording medium on which information has already been recorded, and a method for manufacturing the same. Optical disks include read-only compact disks, writeable and readable magneto-optical disks, and overwritable magneto-optical disks that allow easy recording and playback of information are attracting attention.

[Prior Art] Previously, the present applicant has published Japanese Patent Application Laid-Open No. 1-24105
In No. 1, magneto-optical recording media that are coupled to each other by exchange interaction are stacked in a four-layer structure, the first layer being a memory layer for recording/reproducing, the second layer being an auxiliary layer for assisting writing,
providing an initialization layer for initializing the auxiliary layer on the auxiliary layer;
A coupling layer with a Curie temperature lower than that of the auxiliary layer is provided between the auxiliary layer and the initialization layer, and a magneto-optical recording medium is proposed that can be overwritten only by the strength of the writing light without using an external auxiliary magnetic field.

[Problems to be Solved by the Invention] However, in the magneto-optical recording medium of the conventional structure, as the number of laminated layers of the medium increases, the film thickness of the entire medium becomes thicker, and it becomes difficult to use the laser beam for writing information. Since heat is dissipated from the memory layer through other layers stacked in a multilayer structure, there is a problem that writing sensitivity decreases. The present invention aims to eliminate the above-mentioned drawbacks and provide a highly sensitive magneto-optical recording medium in which the writing sensitivity does not decrease even when the medium is stacked in a multilayer structure so that writing can be performed without using an external auxiliary magnetic field. shall be.

[Means for Solving the Problems] The magneto-optical recording medium of the present invention which achieves the above object and its manufacturing method have a first layer of a memory layer for recording/reproduction and a second layer of an auxiliary layer for assisting writing. , a third bonding layer that controls the bonding between the second layer and the fourth layer.
In a magneto-optical recording medium provided on a substrate as a multilayer film in which a fourth layer of an initialization layer for initializing a second layer is bonded to each other by exchange interaction, the third layer and a fourth layer are bonded to each other by exchange interaction. It is characterized in that the thermal conductivity of at least one of the layers is lower than the thermal conductivity of either the first layer or the second layer. Further, the thermal conductivity of at least one of the third layer and the fourth layer is 0.08 W/cm·K or less. In addition, the third layer or the fourth layer is
It is characterized by forming layers.

[Operation] By lowering the thermal conductivity of the third bonding layer and the fourth initialization layer, the heat of the writing laser beam irradiated from the substrate side to the first memory layer is The third layer above,
And the amount of heat escaping to the vicinity of the heating spot through the fourth layer is reduced. By doing so, writing can be performed with lower laser power, that is, writing sensitivity is improved. A method for lowering the thermal conductivity is to increase the sputtering gas pressure during film formation. When the sputtering gas pressure increases, the amount of gas taken into the film increases, making it easier to form gaps in the formed film, resulting in a decrease in thermal conductivity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, the magneto-optical recording medium of the present invention has terbium-silicon dioxide (Tb-SiO2) on a transparent glass or polycarbonate substrate 1.
) is formed by a sputtering method,
On top of that is terbium-iron-cobalt (Tb-Fe-C).
o) The first layer 3 of the transition metal-rich memory layer has a coercive force of 15 KOe or more, a Curie temperature of 200° C.
is formed to a thickness of 50 nm by magnetron sputtering. Further, on top of that, there is a second layer 4 of a rare earth-rich auxiliary layer made of gadolinium-dysprosium-iron-cobalt (Gd-Dy-Fe-Co) with a coercive force of 3 KOe and a Curie temperature of 260°C, with a thickness of 120 nm. It is formed by magnetron sputtering method. Note that the sputtering gas pressure during film formation of the first layer and the second layer was 0.2 Pa. Furthermore, it is made of terbium-iron (Tb-Fe) with a coercive force of 3KOe and a Curie temperature of 120°C.
transition metal rich (the magnetization strength of the transition metal component is
A third layer 5 of a coupling layer with a magnetization strength higher than that of the rare earth metal component is formed with a thickness of 20 nm by magnetron sputtering, and on top of this, terbium-cobalt (Tb-Co) is formed.
) with a coercive force of 8 KOe and a Curie temperature of 30
The fourth layer 6 of the initialization layer, which is rare earth rich (the magnetization strength of the rare earth metal component is greater than the magnetization strength of the transition metal component) at 0° C. or higher, is formed to a thickness of 40 nm by magnetron sputtering. There is. And on top of that is Tb-SiO2
A protective layer 2-2 is formed. Table 1 shows the physical constants of the magneto-optical recording medium of the present invention thus formed. Further, the first, second and third embodiments will be explained using Table 2. However, in Table 2, (high) means high thermal conductivity, and (low) means low thermal conductivity.

[Table 1] The linear speed of writing was set at
m/sec, write magnetic field of 300 Oe, low level write power of 5 mW, mark length of 1.5 μm.
Figure 2 shows the relationship curves for each example when the vertical axis is the laser power that minimizes the second harmonic and the horizontal axis is the film-forming gas pressure. . Point A in FIG. 2 is a conventional magneto-optical recording medium, where the first, second,
For both the third and fourth layers, the Ar gas sputtering gas pressure was set to 0.
2Pa, the characteristics of a conventional magneto-optical recording medium made into a film are shown.

[Table 2] As shown in curves 11, 12, and 13 in FIG. 2, as the sputtering gas pressure increases in Examples 1, 2, and 3, the value of the laser power at which the second harmonic becomes the minimum decreases. This indicates that the writing laser power is reduced. FIG. 3 shows a modulation level diagram of the writing laser power. In addition, Figure 4 shows the relationship curve between Ar gas sputtering gas pressure and thermal conductivity when forming the third layer, and the relationship curve between sputtering gas pressure and thermal conductivity when forming the fourth layer. show. As shown in Figure 2, PSHM exhibits the effects of this embodiment.
Consider the case where (high level laser power) becomes 11.8 mW or less. When considering the case where only the third layer is formed at high gas pressure as in Example 1 and the case where only the fourth layer is formed at high gas pressure as in Example 2, in Example 1, the pressure is 0.7 Pa or more, In Example 2, when the film is formed at a pressure of 0.4 Pa or more, the effect of reducing the writing laser power appears. When the film was formed under these conditions, the thermal conductivity of the third layer in Example 1 was 0.08W, as shown in curves 21 and 22 of FIG.
/cm・K Below, the thermal conductivity of the fourth layer of Example 2 is 0.
It becomes 11W/cm・K. Therefore, considering the margin, the thermal conductivity of the third layer and/or the fourth layer is 0.08 W/cm・K.
It is good to say. Furthermore, if the sputtering gas pressure is increased too much, the formed film will become porous, so it is preferable to set the sputtering gas pressure to a value of about 2 Pa or less. Furthermore, if the thermal conductivity of the first layer and the second layer is lowered, the sensitivity tends to further improve. If the sputtering gas pressure is increased, the magnetic properties of the formed film will deteriorate.In particular, if the sputtering gas pressure is increased when forming the first and second layer films, the recording properties will deteriorate. There is a risk of adverse effects. On the other hand, in the case of the third and fourth layers,
Since it only has the function of initializing the second layer, even if the magnetic properties deteriorate somewhat, the recording properties will not be affected. Therefore, it is practically effective to apply the method of decreasing the thermal conductivity by increasing the sputtering gas pressure only to the third and fourth layers as in the present invention.

[Effects of the Invention] As described above, according to the present invention, in an overwrite type medium in which writing is performed by changing the intensity of optical modulation without using an external magnetic field, the thickness of the medium can be increased. Also, it is possible to obtain a magneto-optical recording medium with no decrease in sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a magneto-optical recording medium of the present invention.

FIG. 2 is a diagram showing the relationship between the film forming gas pressure of the third layer and/or the fourth layer and the writing laser power.

FIG. 3 is an explanatory diagram of the modulation level of writing laser power.

FIG. 4 is a diagram showing the relationship between sputtering gas pressure for film formation and thermal conductivity.

[Explanation of symbols]

1 Substrate 2-1, 2-2 Protective layer 3 1st layer (memory layer) 4 2nd layer (auxiliary layer) 5 3rd layer (bonding layer) 6 4th layer (initialization layer) 11, 12, 13 pieces Relationship curve between film forming gas pressure and laser power in Example

Claims (3)

[Claims] [Claim 1] First layer (3) of recording/playback memory layer
and a second layer (4) of an auxiliary layer that assists writing.
Third layer (5) of the bonding layer that controls the bonding between the second layer and the fourth layer
In a magneto-optical recording medium provided on a substrate (1) as a multilayer film in which a fourth layer (6) of an initialization layer that initializes a second layer are bonded to each other by exchange interaction, The thermal conductivity of at least one of the third layer (5) and the fourth layer (6) is lower than the thermal conductivity of either the first layer (3) or the second layer (4). Features of magneto-optical recording media. [Claim 2] The third layer (5) and the fourth layer (6)
The thermal conductivity of at least one of the layers is 0.08 W/c
2. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium has a particle diameter of m·K or less. 3. A method for manufacturing a magneto-optical recording medium according to claim 1 or 2, wherein the sputtering gas pressure is higher than the sputtering gas pressure used when forming the first layer (3) and the second layer (4). A method for manufacturing a magneto-optical recording medium, characterized in that the third layer (5) or the fourth layer (6) is formed using gas pressure.