JP3163788B2 - 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 for recording and reproducing information using a laser beam. In recent years, magneto-optical disks have been in the spotlight as external recording media for electronic computers. Magneto-optical disks use a laser beam to form recording bits on the order of submicron on a magneto-optical recording medium, thereby significantly increasing the storage capacity compared to conventional external recording media such as floppy disks and hard disks. It is possible to increase it, and future development is expected.

[0002]

2. Description of the Related Art An optical disk has a storage capacity of 128 megabytes (MB) on one side of 3.5 inches. The storage capacity of one 3.5-inch floppy disk is about 1 MB, and one optical disk can have the storage capacity of 128 floppy disks. Thus, the optical disk is a replaceable recording medium having a very high recording density.

[0003] However, when compared with a hard disk, the storage capacity is by far the most advantageous, but in terms of data transfer speed, the hard disk is approximately 3 MB / sec, while the magneto-optical disk is approximately 640 KB / sec. This is because the magneto-optical disk is not currently overwritten and when recording,
It is necessary to delete the information recorded on the medium in advance, and the transfer speed is reduced accordingly.

[0004] As a magneto-optical recording medium capable of overwriting, a magneto-optical recording medium in which the medium has a two-layer film structure, and overwrite is enabled by erasing information by using an initialization magnet is disclosed in Japanese Patent Application Laid-Open No. H11-163,873. It is proposed in 1987-175948.

Further, a magneto-optical recording medium having a multi-layered structure and eliminating the need for an initialization magnet than the above-described magneto-optical recording medium is described in "13th Annual Conference of the Japan Society of Applied Magnetics, 23aC-4". It is proposed in.

The overwriting method using these magneto-optical recording media is a method in which overwriting is enabled by modulating the intensity of laser light, and is called a light modulation type overwriting method.

[0007]

In the light modulation type overwrite method described above, when high power (a laser beam having a high light intensity) is applied to a magneto-optical recording medium, writing is performed, and low power (a laser light having a low light intensity) is applied. Irradiation (laser light) erases information.

FIG. 4 shows a pulse waveform diagram of a laser beam used for such recording, reproduction, and erasing. The high power (P
_H ) indicates the write power, low power (P _L ) indicates the erase power, and read power (P _R ) indicates the read power.

Mark (bit) pitch as a unit of information
When writing is narrowed, that is, a high power (P _H ) pulse
If you write with a shorter interval , the next mark
In the case of
ing. Therefore, between the previous mark and the next mark
Low power irradiated to the space portion (P _L) is the thermal interference
It is necessary to lower it in consideration of the remaining heat.

For example, when writing is performed with the pulse interval of the high power (P _H ) widened, the next mark can be written.
In this case, the influence of the thermal interference of the preceding mark is reduced. did
Thus, the space between the previous mark and the next mark
The low power (P _L ) applied to the minute
Since the influence is small, a large value of low power (P _L ) is required as compared with the case where the mark pitch becomes narrow .

Therefore, even if the mark pitch fluctuates, if overwriting is always performed with the same value of low power and high power, the C / N value after overwriting fluctuates,
In the worst case, the value of C / N may deviate from the standard value.

The present invention eliminates the above-mentioned problems and eliminates the effects of thermal interference even when the mark pitch (bit pitch) changes, that is, when the pitch between high-power (P _H ) pulses for writing changes. Less. It is another object of the present invention to provide a magneto-optical recording medium capable of obtaining a recording signal having a good C / N value after overwriting even when overwriting is always performed with the same low power and high power.

[0013]

Means for Solving the Problems] magneto-optical recording medium of the present invention, as shown in claim 1, the rare earth - consists transition metal amorphous ferrimagnetic alloy, the recording of information, first used in reproducing
, A second magnetic layer for assisting recording and erasing on the first magnetic layer, a fourth magnetic layer which is always magnetized in one direction, and a magnetization of the fourth magnetic layer Is transferred to the second magnetic layer by magnetic interaction at a temperature not higher than the Curie temperature of the layer, with the first, second, third and fourth magnetic layers .
In a magneto-optical recording medium for performing overwriting by modulating the light intensity of laser light used for recording and reproducing information, the second magnetic layer, the third magnetic layer An element having a higher thermal conductivity than any one of the magnetic layer and the fourth magnetic layer is added to the third magnetic layer and the fourth magnetic layer.
It is characterized by being added to at least one of them.

According to a second aspect of the present invention, the element added to the magneto-optical recording medium is copper, aluminum, gold, or
It is one of silver metal elements .

[0015]

[0016]

According to the method of the present invention, the magnetization of the initialization layer of the fourth magnetic layer is adjacent to the second magnetic layer for assisting recording and erasing on the first magnetic layer, and the magnetization of the fourth magnetic layer is equal to or lower than the Curie temperature of the layer. In the switch layer of the third magnetic layer which transmits to the second magnetic layer or the initialization layer, a metal having a higher thermal conductivity than the second magnetic layer, the third magnetic layer, and the fourth magnetic layer. Add elements.

Alternatively, the switch layer of the third magnetic layer,
A metal element having a higher thermal conductivity than the second magnetic layer, the third magnetic layer, and the fourth magnetic layer is added to both magnetic layers of the initialization layer of the magnetic layer. In each of these first to fourth magnetic layers, the direction of magnetization of the rare earth element and the transition metal element is
They are formed of different rare earth-transition metal amorphous ferrimagnetic alloy films.

By doing so, the heat of the laser beam applied to the first magnetic layer and the second magnetic layer can be more effectively transferred to the first and second magnetic layers than to move in the in-plane directions of the first and second magnetic layers. Since the third and fourth magnetic layers have high thermal conductivity, the third and fourth magnetic layers can easily move in the vertical direction.

As a result, heat is easily dissipated from the first magnetic layer and the second magnetic layer. Therefore, even when the mark pitch is narrowed, that is, when the pulse interval of the writing laser pulse is narrowed, heat interference is prevented. The influence is reduced, and even when overwriting is always performed with the same value of low power and high power, a good value of C / N after overwriting can be obtained.

[0020]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
This will be described in detail. FIG. 1 is a sectional view of a magneto-optical recording medium according to the present invention. As shown in FIG. 1, a first protective layer 2-1, Tb ₁₈ Fe ₇₇ Co ₅ made of Tb—SiO ₂ is formed on a substrate 1 made of transparent glass. A first magnetic layer 3 for recording and reproducing information,
The second magnetic layer 4 made of ₅ Dy ₂₃ Fe ₃₂ Co ₄₀ and assisting recording and erasing on the first magnetic layer 3 is formed by magnetron sputtering.

Further, a fourth magnetic layer 6 to be described later
Due to magnetic interaction below the Curie temperature of the layer
Tb to the second magnetic layer 4_{twenty one}Fe₇₉Consisting of
A third magnetic layer 5, which is always magnetized in one direction,
Tb called the initialization layer₃₀Co ₇₀Fourth magnetic layer comprising
6, Tb-SiO_TwoThe second protective layer 2-2 consisting of
The film is formed by the tron sputtering method.

As another embodiment, an intermediate layer of Tb ₂₁ Fe ₄₉ Co ₃₀ is provided between the first magnetic layer 3 and the second magnetic layer 4 in order to facilitate exchange coupling between the two magnetic layers. May be inserted.

Then, 30 atomic% of copper was added to the third magnetic layer 5 made of Tb ₂₁ Fe ₇₉ and the fourth magnetic layer 6 made of Tb ₃₀ Co ₇₀ to form a magneto-optical recording medium. As a comparative example, a magneto-optical recording medium in which copper was not added was formed in the third magnetic layer 5 made of Tb ₂₁ Fe ₇₉ and the fourth magnetic layer 6 made of Tb ₃₀ Co ₇₀ .

Using both such magneto-optical recording media,
Overwriting was performed at a linear velocity of 9 m / sec and a pulse width of 57 ns.
FIG. 2 shows a case where the magneto-optical recording medium of the present invention to which copper is added is used. In FIG. 2, the area shaded by a solid line within the curve a in FIG. Low power (m
W), and shows an area where the signal quality (C / N) after overwriting is 45 dB or more when overwriting is performed from the longest mark pitch (4.16 μm) to the shortest mark pitch (1.56 μm).

In the area of the curve b in FIG. 2 which is shaded by a dotted line, the vertical axis indicates high power (mW), the horizontal axis indicates low power (mW), and the shortest mark pitch (1.56 μm ) Indicates an area where the C / N after overwriting is 45 dB or more when overwriting to the longest mark pitch (4.16 μm) is performed.

As is apparent from FIG. 2, there is an overlapped area where the C / N is 45 dB or more, and this area is an overwritable area. For example, the low power is 4 mW and the high power is 9 mW. Indicates that overwriting is possible even if the mark pitch fluctuates.

As a comparative example, a conventional magneto-optical recording medium to which no copper was added was formed in a third magnetic layer made of Tb ₂₁ Fe ₇₉ and a fourth magnetic layer made of Tb ₃₀ Co ₇₀ , and this was used. FIG. 3 shows the result of overwriting performed at a linear velocity of 9 m / sec and a pulse width of 57 ns.

The area surrounded by the curve a in FIG. 3 and shaded by a solid line has high power (mW) on the vertical axis, low power (mW) on the horizontal axis, and has the longest mark pitch (4.16 μm). This shows the area where the C / N after overwriting is 45 dB or more when overwriting to the shorter mark pitch (1.56 μm).

The area surrounded by the curve b in FIG. 3 and shaded by a dotted line has high power (mW) on the vertical axis, low power (mW) on the horizontal axis, and has the shortest mark pitch (1.56 μm ) Indicates an area where the C / N after overwriting is 45 dB or more when overwriting to the longest mark pitch (4.16 μm) is performed.

As is apparent from FIG. 3, the regions where the C / N is 45 dB or more do not overlap, which means that in the conventional magneto-optical recording medium, the value of C / N after overwriting is 45 dB or more. This indicates that in order to obtain a recording signal, it is necessary to change the laser power at the time of writing according to the change in the mark pitch.

[0031]

As described above, according to the magneto-optical recording medium of the present invention, even when the mark pitch fluctuates, the influence of thermal interference can be reduced, and the high power and the low power have the same power. Thus, there is an effect that a magneto-optical recording medium capable of obtaining a recording signal having a good C / N value can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing the relationship between high power, low power, and C / N after overwriting when overwriting is performed using the magneto-optical recording medium of the present invention.

FIG. 3 is a diagram showing the relationship between high power, low power, and C / N after overwriting when overwriting is performed using a magneto-optical recording medium of a comparative example.

FIG. 4 is a pulse waveform diagram of laser light used for overwriting.

[Explanation of symbols]

 1 Substrate 2-1 First Protective Layer 2-2 Second Protective Layer 3 First Magnetic Layer 4 Second Magnetic Layer 5 Third Magnetic Layer 6 Fourth Magnetic Layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 11/105

Claims (2)

(57) [Claims] 1. A rare earth - consists transition metal amorphous ferrimagnetic alloy, the recording of information, first performs a first magnetic layer used in the reproduction, recording to the first magnetic layer, an auxiliary erasing A second magnetic layer, a fourth magnetic layer that is always magnetized in one direction, and transfer the magnetization of the fourth magnetic layer to the second magnetic layer by magnetic interaction below the Curie temperature of the layer. And the third magnetic layer to be used is the first, second, third, and fourth magnetic layers.
The second magnetic layer, the third magnetic layer, and the second magnetic layer are overlaid on each other by modulating the light intensity of a laser beam used for recording and reproducing information to perform overwriting. The element having a higher thermal conductivity than any of the magnetic layers of the fourth magnetic layer is referred to as the third magnetic layer.
Magneto-optical recording medium, characterized in that added to at least one of the magnetic layer and the fourth magnetic layer. 2. The magnetic recording medium according to claim 1, which is added to the magneto-optical recording medium.
Element is copper, aluminum, gold or silver metal element
A magneto-optical recording medium characterized by any one of the above .