JPH0620313A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To enable the control of exchange coupling force between 1st and 2nd magnetic layers by regulating the pressure of a sputtering gas at the time of forming a magnetic layer interposed between the 1st and 2nd magnetic layers and regulating the thickness of the middle layer. CONSTITUTION:A 1st protective layer 21, a 1st magnetic layer 3, a middle layer 4 having a formed columnar structure, a 2nd magnetic layer 5 and a 2nd protective layer 22 are successively formed by sputtering in a prescribed thickness each on a glass substrate 1 with a laser beam guide groove to obtain a magneto-optical recording medium. The magnetic layer 4 consists of crystals each having a fine columnar structure with an axis in a direction perpendicular to the film forming surface for growth. This middle layer 4 tends to reduce the interfacial magnetic wall energy in accordance with the increase of the pressure of a sputtering gas and tends to reduce the energy in accordance with the increase of the thickness of the layer 4. When the thickness of the layer 4 exceeds a prescribed value, exchange coupling of the layers 3, 5 is lost.

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 for recording / reproducing information using laser light. In recent years, a magneto-optical disk has attracted attention as an external recording medium for electronic computers. A magneto-optical disk has a recording capacity significantly higher than that of a conventional external recording medium such as a floppy disk or a hard disk by creating recording bits on the sub-micron order on a magneto-optical recording medium by using laser light. It is possible to increase the number, and future development is expected more and more.

[0002]

2. Description of the Related Art An optical disk is a 3.5-inch disk with one side having a storage capacity of about 128 megabytes. 3.5
The storage capacity of one inch floppy disk is about 1 megabyte, and one floppy disk 12
It can have a storage capacity of 8 sheets.

As described above, the optical disk is an exchangeable recording medium having a very high recording density. However, compared with the hard disk, the storage capacity is advantageous, but the data transfer rate is about 3 megabytes / sec for the hard disk and about 640 megabytes / sec for the magneto-optical disk.

This is because the magneto-optical disk is not currently overwritten, and when recording is performed, it must be erased in advance, and the transfer speed is reduced by the amount required for the erase.

As an example of a magneto-optical recording medium that can be overwritten, there is JP-A-62-175948 as an example in which the medium structure is made into two layers and an initialization magnet is used so that overwriting can be performed.

According to this method, the Curie temperature and the coercive force have a relationship as shown by the curve a in FIG.
The relationship between the Curie temperature and the coercive force is the same as that of the auxiliary layer shown by the curve b in FIG. 4, and the Curie point and the coercive force have different curves with respect to temperature. To use.

As shown by the curve a, the coercive force H _c1 of the recording layer at room temperature T _R is the coercive force H _{c2 of the} auxiliary layer shown by the curve b.
The magneto-optical recording medium having a higher Curie temperature T _c1 than the Curie temperature T _c2 of the auxiliary layer is used.

Prior to recording, the directions of the magnetic moments of the auxiliary layer are aligned in one direction, the Curie temperature T _c1 of the recording layer or higher corresponding to the signal to be recorded, and the magnetization reversal of the auxiliary layer occurs. A first heating state in which the recording layer and the auxiliary layer are heated to a non-existing temperature, and a second heating state in which the heating temperature is higher than the first heating state and is sufficient to reverse the magnetization of the auxiliary layer. Binary information is recorded by heating the magneto-optical recording medium by irradiating it with laser light and then cooling it from each heating state. Further, in this method, in addition to the recording magnet used for recording, an initialization magnet for aligning the magnetic moments of the auxiliary layer in one direction is installed.

By the way, such a method requires a large initialization magnet in addition to the recording magnet, which has a drawback that the magneto-optical recording apparatus becomes large in scale. Is a major obstacle.

Further, the magneto-optical recording medium is layered as a multi-layered structure having a two-layered structure or more, and an initializing magnet is not required.
Have been disclosed in.

A magneto-optical recording medium in which the above-mentioned two-layer film or a multilayer film of two or more layers is laminated is overwritten by utilizing the exchange coupling force acting between the magneto-optical recording media. The control of the exchange coupling force is very important for accurate overwriting.

Usually, when a first magnetic layer having perpendicular magnetic anisotropy and a second magnetic layer having perpendicular magnetic anisotropy are continuously formed by a direct sputtering method, the adjacent magnetic layers are adjacent to each other. In many cases, the exchange coupling force acting between them is too strong to make overwriting impossible.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above matters, and it is possible to control the exchange coupling force acting between magneto-optical recording media laminated in a multilayer structure. For the purpose of providing.

[0014]

A magneto-optical recording medium according to the present invention has a first aspect having a perpendicular magnetic anisotropy as described in claim 1.
In a magneto-optical recording medium in which the magnetic layer and the second magnetic layer are laminated and the magnetic layers are exchange-coupled to each other, a columnar structure is formed between the first magnetic layer and the second magnetic layer. It is characterized in that it is provided as an intermediate layer with the magnetic layer thus formed interposed.

According to a second aspect of the present invention, the thickness of the intermediate layer is equal to or smaller than the thickness of the magnetic layer on the thin side. According to a third aspect of the present invention, at the boundary surface between the first magnetic layer and the second magnetic layer adjacent to each other, the layer structure of the boundary surface of at least one of the magnetic layers has a columnar structure. It is characterized by

According to a fourth aspect of the present invention, the layer structure of at least one of the first magnetic layer and the second magnetic layer to be laminated has a columnar structure. is there.

[0017]

In order to allow overwriting, an intermediate layer composed of a magnetic layer having a columnar structure is provided between magnetic layers having perpendicular magnetic anisotropy, or adjacent magnetic layers are laminated. Of the surfaces, at least one surface has a columnar structure,
Alternatively, at least one of the adjacent magnetic layers has a columnar structure.

As described in Japanese Patent Application No. 2-150293, the above-mentioned columnar structured magnetic layer has a fine columnar structure having an axis in the direction perpendicular to the growing film-forming surface. The presented crystals are aggregated to form a gap where the columnar structures are not in contact with each other, and the columnar film is observed by a scanning electron microscope.

This Japanese Patent Application No. 2-150293 discloses a structure of a magneto-optical recording medium in which a columnar structure film is sandwiched between non-columnar structure films. In this case, the above-mentioned columnar structure film is thermally conductive. Therefore, the purpose of the present invention is to prevent the heat transfer of the magnetic layer irradiated with the laser beam and to improve the sensitivity of the formed magneto-optical recording medium. And does not mention the thickness of the columnar structure film.

When the degree of columnarization of the magnetic layer becomes large, the interface domain wall energy of the magnetic layer becomes small and the exchange coupling force becomes weak, and when the thickness of the intermediate layer having the columnar structure increases, The interfacial domain wall energy of the magnetic layer of the intermediate layer is lowered and the exchange coupling force is weakened.

Therefore, the exchange coupling force between the magnetic layers sandwiching the intermediate layer can be controlled by controlling the degree of columnarization of the intermediate layer or by controlling the thickness of the intermediate layer having the columnar structure. Is possible.

The degree of columnarization of the magnetic layer varies depending on the sputtering gas pressure of the argon gas. The higher the sputtering gas pressure, the more the columnarization progresses, so that the magnetic domain wall energy of the formed magnetic layer is small. Therefore, when forming the intermediate layer by the sputtering method, the sputtering gas pressure is controlled to control the degree of columnarization of the magnetic layer.

For example, the case of inserting an intermediate layer between adjacent magnetic layers will be described. As the film structure changes from the non-columnar structure film to the columnar structure film, the squareness ratio of the hysteresis loop of the magnetic layer deteriorates and an in-plane magnetization component appears.

Further, the perpendicular magnetic anisotropy constant Ku also decreases, and the exchange coupling force is weakened. Therefore, the greater the degree of columnarization and the thicker the columnar film thickness, the weaker the exchange coupling force. It should be noted that when a columnar structure film is used as an intermediate layer for controlling the exchange coupling force, the recording sensitivity may be deteriorated. However, the columnar structure film will be presented at the 38th Applied Physics Association Conference Lecture No. 31pR-13. As described above, the density is smaller than that of the non-columnar structure film, it is not densely crystallized, and the thermal conductivity is small. The recording sensitivity is not affected even if the thickness of the entire layer is increased.

[0025]

FIG. 1 shows a first embodiment of the magneto-optical recording medium of the present invention.
Shown in (a). As shown in FIG. 1 (a), a first protective layer 2-1 made of Tb-SiO ₂ having a thickness of 90 nm and a terbium layer having a thickness of 60 nm are sequentially formed on a glass substrate 1 having a laser light guide groove. The first magnetic layer 3 made of dysprosium-iron-cobalt (Tb ₅ Dy ₂₃ Fe ₃₂ Co ₄₀ ) and the columnar structured terbium-iron-cobalt (Tb ₂₁ Fe ₄₉ Co ₃₀ ) having a thickness of 10 nm. Middle layer 4
And 30 nm thick terbium-iron-cobalt (Tb ₁₃ Fe ₇₇ C
The second magnetic layer 5 made of O ₅ ), and the second protective layer 2-2 made of 90 nm Tb-SiO ₂ are formed by magnetron sputtering.

Table 1 shows film forming conditions for the respective protective layers, the first and second magnetic layers, and the intermediate layer.

[0027]

[Table 1]

As described in Japanese Patent Application No. 2-150293, the above-mentioned magnetic layer having a columnar structure has a fine columnar structure having an axis in the direction perpendicular to the growing film-forming surface. The presented crystals are aggregated to form a gap where the columnar structures are not in contact with each other, and the columnar film is observed by a scanning electron microscope.

FIG. 2 shows the relationship between the magnitude of the interfacial domain wall energy of this intermediate layer and the gas pressure of the argon gas used as the sputtering gas. As shown in FIG. 2, the interface domain wall energy tends to decrease as the pressure of the argon gas of the sputtering gas increases. This means that the degree of columnar structure progresses as the pressure of the sputtering gas increases. Then
Therefore, it is understood that the interface domain wall energy is reduced.

The relationship between the thickness of the intermediate layer of the present invention having a columnar structure and the domain wall energy is shown in FIG. As shown in FIG. 3, the interface domain wall energy tends to decrease as the thickness of the intermediate layer increases. When the thickness of the columnar structured intermediate layer becomes 40 nm or more, the interface domain wall energy becomes almost zero. Therefore, exchange coupling between the first magnetic layer and the second magnetic layer cannot be performed.

Therefore, as shown in the first embodiment, the thickness of the columnar structured film used as the intermediate layer is preferably about 10 nm.
It is desirable to keep the thickness smaller than the thickness of the thinner magnetic layer among the plurality of magnetic layers that are exchange-coupled.

As described above, the exchange coupling force varies depending on the thickness of the intermediate layer and the layering conditions of the intermediate layer. Therefore, the thickness of the intermediate layer is controlled to a predetermined thickness to obtain the optimum exchange coupling force. Then, when the gas pressure of the Ar gas of the sputtering gas when forming the intermediate layer is adjusted to an appropriate value and sputtering is performed, an overwritable magneto-optical recording medium whose exchange coupling force is controlled to a predetermined value is obtained. can get.

For example, in the configuration of FIG. 1 (a) described above,
Using the magneto-optical recording medium formed under the conditions shown in Table 1, the magneto-optical recording medium was rotated at a speed of 9 m / sec, and the overwriting condition was the old information writing frequency of 2.2 MHz and the overwriting writing frequency. 5.8MHz, high level laser power 8mW, low level laser power 2mW
When the C / N value after overwriting was measured under the condition
A value of 47 dB was obtained.

As another embodiment of the present invention, as shown in FIG. 1 (b), the first magnetic layer 3 is formed on the adjacent film surface 11 between the first magnetic layer 3 and the second magnetic layer 5. Either the film surface on the side of the layer 3 or the film surface 11 on the side of the second magnetic layer 5 is formed by continuously sputtering the first magnetic layer 3 and the second magnetic layer 5. In this case, the columnar structure film may be formed by adjusting the gas pressure of Ar gas as the sputtering gas and performing sputtering.

Each of the protective layers of this embodiment, the first
Table 2 shows the film forming conditions for the second magnetic layer and the intermediate layer.

[0036]

[Table 2]

As shown in Table 2, when forming the second magnetic layer, the gas pressure of Ar gas of the sputtering gas for forming the film is set to 1.0 Pa at the start of film formation, and the film formation time is set. The film thickness is reduced to 0.2 Pa with the lapse of time.

Alternatively, as another embodiment of the present invention, as shown in FIG. 1 (c), the sputtering gas pressure of Ar gas is changed in either the first magnetic layer 3 or the second magnetic layer 5. Then, the second magnetic layer 5 may be used as the columnar structured film 12 by sputtering.

The protective layer of each of the present embodiments, the first
Table 3 shows the film forming conditions for the second magnetic layer and the intermediate layer.

[0040]

[Table 3]

[0041]

As described above, according to the present invention, the first
Of the magnetic layer provided between the first magnetic layer and the second magnetic layer
By adjusting the sputtering gas pressure of Ar gas and adjusting the thickness of the intermediate layer, it becomes possible to control the exchange coupling force between the first magnetic layer and the second magnetic layer. There is an effect that an overwritable magneto-optical recording medium can be obtained in which the exchange coupling force is controlled to a predetermined value.

[Brief description of drawings]

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

FIG. 2 is a diagram showing the relationship between sputtering gas pressure and interface wall energy.

FIG. 3 is a relationship diagram between the film thickness of a columnar structure intermediate layer and the interfacial domain wall energy.

FIG. 4 is a characteristic diagram of a conventional overwritable magneto-optical recording medium.

[Explanation of symbols]

 1 glass substrate 2-1 first protective layer 3 first magnetic layer 4 intermediate layer 5 second magnetic layer 11 film surface 12 columnar structured film

Claims (4)

[Claims] 1. A first magnetic layer having perpendicular magnetic anisotropy.
In a magneto-optical recording medium in which (3) and a second magnetic layer (5) are laminated and the magnetic layers are exchange-coupled to each other, the first magnetic layer (3) and the second magnetic layer ( A magneto-optical recording medium characterized in that a magnetic layer having a columnar structure is interposed between (5) to provide an intermediate layer (4). 2. A magneto-optical recording medium, characterized in that the thickness of the intermediate layer (4) according to claim 1 is equal to or smaller than the thickness of the magnetic layer having the smaller thickness. 3. A first magnetic layer having perpendicular magnetic anisotropy.
In a magneto-optical recording medium in which (3) and a second magnetic layer (5) are laminated and the magnetic layers are exchange-coupled to each other, the first magnetic layer (3) and the first magnetic layer (3) adjacent to each other are laminated. 2 magnetic layers
A magneto-optical recording medium characterized in that, in the film surface (11) of (5), at least one film surface (11) has a columnar structure. 4. A first magnetic layer having perpendicular magnetic anisotropy.
A magneto-optical recording medium in which (3) and a second magnetic layer (5) are laminated and the magnetic layers are exchange-coupled to each other, wherein the first magnetic layer (3) or the second magnetic layer A magneto-optical recording medium, wherein the film structure of at least one of the magnetic layers of (5) is columnar.