JPH04351734A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To increase the margin of laser beam powers without entailing an increase in the laser beam power at the time of recording by providing laminated films, a dielectric layer and a metallic layer on a substrate and adequately selecting the film thicknesses thereof. CONSTITUTION:The dielectric layer 2, a memory layer 3, an intermediate layer 4, the recording layer 5, the dielectric layer 6, the metallic layer 7, and a protective layer 8 are successively laminated on the light transparent substrate 1. The total thickness of the laminated films 9 of the memory layer 3, the intermediate layer 4 and the recording layer 5 is specified to 1000 to 1500Angstrom , the thickness of the dielectric layer 6 to 500Angstrom and the thickness of the metallic layer to 250 to 1500Angstrom . The power margins of the high level laser power PH and low level laser power PL can be increased in this way without increasing the respective output values of the powers PH, PL according to, for example, binary recording at the time of the magneto-optical recording.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical (thermal) recording medium, and more particularly to a magneto-optical recording medium comprising a three-layered magnetic layer.

0002

2. Description of the Related Art A thermal (optical) magnetic recording method for a recording medium in which information bits (magnetic domains) are read by magneto-optical interaction is based on a recording medium having a magnetic thin film made of a perpendicularly magnetized film. By performing so-called initialization in which the direction of magnetization is aligned in advance in one direction perpendicular to the film surface, and by forming a magnetic domain with perpendicular magnetization opposite to this magnetization direction by local heating such as laser beam irradiation. Information is recorded as digitized information bits.

In the thermomagnetic recording method, prior to rewriting information, a process of erasing recorded information corresponding to the above-mentioned initialization, that is, time is required for erasing, and recording at a high transfer rate is realized. Can not. In response to this, various recording methods have been proposed using the so-called overwrite method, which eliminates the need for such independent erasing process time. Among the overwrite type thermomagnetic recording methods, methods that are considered promising include, for example, an external magnetic field modulation method for the medium, and a two-head method in which an erasing head is provided in addition to a recording head. ing.

[0004] The external magnetic field modulation method is, for example,
As disclosed in Japanese Patent No. 48806, an amorphous ferrimagnetic thin film recording medium having an easy axis of magnetization perpendicular to the film surface is irradiated with a heating beam, and an input digital signal current is applied to the irradiated area. Recording is performed by applying a magnetic field with a polarity corresponding to the state.

[0005] Such magneto-optical recording media generally consist of a magnetic layer laminated on a light-transmissive substrate such as polycarbonate via a dielectric layer, and a protective layer etc. is further coated on top of this to prevent light transmission. In this method, readout light is irradiated from the magnetic substrate side and the magnetization in the magnetic domain of the irradiated area is read out using the Kerr effect. An Al layer may be provided between the magnetic layer and the protective layer.

However, in magneto-optical recording media in which the magnetic layer for magneto-optical recording is a perpendicularly magnetized film and readout is performed using the Kerr effect by reflection from the film itself, or in recording media for optical intensity modulation overwriting, the optical In magneto-optical recording media where the magnetic layer for magnetic recording has a large thickness, disposing such an Al layer causes a decrease in recording sensitivity due to the heat dissipation effect. placement tends to be eliminated. However, in such a magneto-optical recording medium in which the Al layer is not included, the problem of corrosion (pitting) of the magnetic layer may occur due to corrosion from the protective layer side.

[0007] In order to solve such a problem, the present applicant previously proposed in Japanese Patent Application Laid-Open No. 3-86947 a film with a thickness of 25 Å on a protective film on a magnetic layer for magneto-optical recording, that is, a magneto-optical recording film. We have proposed a magneto-optical recording medium in which a resin protective film is deposited through a ~200 Å thin aluminum film. As shown in FIG. 5, which is an example of a schematic enlarged cross-sectional view, this magneto-optical recording medium is made of S
A dielectric layer 2 such as i3N4, a magneto-optical recording film 13 corresponding to the above-mentioned laminated film made of TbFeCo etc., and a protective film 16 made of a dielectric layer such as Si3N4,
The Al thin film 17 and a resin protective film 18 made of, for example, an ultraviolet curing resin are laminated.

In this way, the protective film 16 and the resin protective film 18
By providing an Al thin film 17 with a thickness of 25 Å to 200 Å between the resin protective film 18 and the resin protective film 18, corrosion from the resin protective film 18 is avoided, a decrease in S/N is prevented, and reliability is improved.

By the way, when attempting to perform high-speed recording with a high information transfer rate using the external magnetic field modulation method as described above, an electromagnet that operates on the order of MHz is required, and it is difficult to create such an electromagnet. Even so, there is a problem that power consumption and heat generation are large, making it impractical.

Furthermore, the two-head method requires an extra head and must be installed at a distance, placing a large burden on the drive system and being uneconomical, making it unsuitable for mass production. have.

[0011] In order to solve such problems, the present applicant has developed a light (thermal) light (heat) system that can easily perform overwriting by simply switching and controlling the heating temperature of the medium using a laser beam or the like. For example, the magnetic recording method was
-52354 and JP-A-63-52355. The optical (thermal) magnetic recording method proposed in these applications uses a thermal (optical) magnetic recording medium having a laminated structure of first and second rare earth-transition metal magnetic thin films, and applies a required first external magnetic field. The first magnetic thin film is heated to a first temperature T1 which is approximately equal to or higher than the Curie temperature Tc1 of the first magnetic thin film and at which reversal of the sublattice magnetization of the second magnetic thin film does not occur.
The information to be recorded, for example, "0 ”, “1”, and during the cooling process, the direction of the sublattice magnetization of the first magnetic thin film due to the exchange coupling force of the first and second magnetic thin films is changed to that of the sublattice magnetization of the second magnetic thin film. For example, recording bits (magnetic domains) of "0" and "1" are formed in the first magnetic thin film in the same direction, and a second external magnetic field or the composition of the second magnetic thin film is
By selecting the compensation temperature to exist between room temperature and the second temperature T2, overwriting is possible by inverting the sublattice magnetization of the second magnetic thin film only by the first external magnetic field at room temperature. This is to ensure that a state is obtained.

[0012] In this case, a special process (time) for erasing is not required, a high transfer rate can be achieved, and the problems of the above-mentioned two-head system or external magnetic field modulation system can be solved. .

[0013] On the other hand, the present applicant had previously
No. 1 and JP-A-2-121103, in such a thermomagnetic recording method, in order to control the domain wall energy density σw at room temperature of the domain wall generated between each magnetic thin film, proposed a magneto-optical recording medium that stabilizes the state in which interfacial domain walls exist by providing an intermediate layer having in-plane magnetic anisotropy or small perpendicular magnetic anisotropy.

The magneto-optical recording medium proposed in the above-mentioned Japanese Patent Application Laid-open No. 2-24801 has a dielectric film on a light-transmitting substrate 1 made of polycarbonate or the like, as shown in FIG. body layer 2 and a first magnetic thin film or memory layer 3
, the intermediate layer 4 and the second magnetic thin film, that is, the recording layer 5, and a protective layer 6 made of, for example, a dielectric layer, which are successively deposited.

A recording/reproducing method for this recording medium 10 will be explained. In this case, the above-mentioned Japanese Patent Application Laid-Open No. 63-523
Similar to the thermal (optical) magnetic recording method according to Application No. 54, the first
and information recording by heating to second temperatures T1 and T2. That is, in this recording method, each magnetization state in the memory layer 3 and the recording layer 5 described above corresponding to the temperature T is schematically shown in FIG. For example, at room temperature TR, information such as "0" and "1" is recorded in two states: state A in which the directions of magnetization of the memory layer 3 and recording layer 2 are the same, and state B in which the directions of magnetization are opposite to each other. It is what you do.

To explain this method, first, for example, a part in state A is irradiated with a laser beam, and the intensity or irradiation time of this laser beam is modulated and controlled in accordance with a recording signal to control the heating temperature T. , approximately equal to or higher than the Curie temperature Tc1 of the memory layer 3 and the required recording magnetic field (external magnetic field) He
x to a first heating temperature T1 at which no magnetization reversal occurs in the recording layer 5. When such heating is performed, the memory layer 3 exhibits a state C in which it loses its magnetization, but when this heating is completed and the laminated film 9 falls below the temperature Tc1, magnetization occurs in the memory layer 3. At this time, the exchange coupling force with the recording layer 5 is made to be dominant, so that the direction of magnetization of the memory layer 3 is the same as that of the recording layer 5. In other words, state A is generated and, for example, information of "0" is recorded.

On the other hand, the heating temperature T is set higher than the above-mentioned temperature T1, and the magnetization of the recording layer 5 is controlled by the recording magnetic field (external magnetic field) He.
A second heating temperature T2 that can be reversed by x
Heat to. When such heating is performed, the memory layer 3 loses its magnetization, and on the other hand, state D occurs in which the magnetization of the recording layer 5 is reversed by the recording magnetic field Hex, but when this heating ends, the laminated film 9 falls to the temperature Tc1. State E, that is, a state in which the direction of magnetization is opposite to the original initial state, is formed in the memory layer 3 by the exchange coupling force caused by the recording layer 5. At this time, an external auxiliary magnetic field Hsub serving as an initialization magnetic field, that is, an auxiliary magnetic field, is applied to the recording layer 5 to reverse the magnetization direction of only the recording layer 5, which has been selected to have a relatively low coercive force near the room temperature TR. Magnetization state B in which a domain wall is generated between the layer 3 and the recording layer 5, that is, magnetization state A, is different from state B in which only the direction of magnetization of the memory layer 3 is reversed, for example, "1".
Record information.

In the magneto-optical recording medium having the above-described structure, information "0" and "1" are recorded in states A and B, and the direction of magnetization in the memory layer 3 is read out and the laser beam irradiation curve is read out. It can be detected by rotation.

In this case, light intensity modulation overwriting is possible in both states A and B. In other words, the temperature T1 from both state A and state B
and T2, by going through the process of state C, the information "0" and “1” causes state A and state B
can be overwritten.

In this method, information is recorded depending on the magnetization state of the memory layer 3. In this method, the memory layer 3 and the recording layer 5 have in-plane magnetic anisotropy or small perpendicular magnetic anisotropy. The memory layer 3 is magnetically coupled via the oriented intermediate layer 4.
The domain wall energy σw between the recording layer 5 and the recording layer 5 is reduced, and the external auxiliary magnetic field Hsub for the transition from the state E to B, that is, the initialization of the recording layer 5, can be reduced, and the entire laminated film 9 can be reduced. The thickness can be reduced.

When performing binary recording as described above, the first temperature T1 and the second temperature T1 are set in accordance with the information to be recorded.
2. It is necessary to raise the temperature for both. Therefore, in the light intensity modulation method, it is necessary to appropriately control the temperature distribution in these heated portions, but conventionally this has been controlled only by the irradiation laser power. However, in this magneto-optical recording medium, there are two levels of power PH and PL, a high output level and a low output level, for performing binary recording independently.
There was a problem in setting the margin, that is, the margin was relatively small.

On the other hand, in such a light modulation type magneto-optical recording medium, on the dielectric protective film on the side opposite to the substrate of the magneto-optical recording film, a dielectric layer and an ultraviolet ray are further applied via a metal layer. A structure formed by laminating a cured resin film was proposed (A.O.
Kamuro, et al. , MORIS (MO Re
coding International Sym
posium), 18-T-13, 1991). As shown in FIG. 8, a schematic enlarged cross-sectional view of this magneto-optical recording medium, a dielectric layer 2, a magneto-optical recording film 13, a dielectric layer 6A, a metal layer 7, a dielectric The body layer 6B and the protective layer 8 are sequentially applied.

In this magneto-optical recording medium, the magneto-optical recording film 1
By depositing the metal layer 7 on the magneto-optical recording film 13 through the dielectric layer 6A, thermal radiation can moderate the temperature change of the magneto-optical recording film 13 caused by laser beam irradiation, thereby increasing the margin of the laser beam irradiation power. It is something that I know. In this case, the thickness of the magneto-optical recording film 13 is 1000 Å, the thickness of the metal layer 7 is 200 Å, and the thickness t1 of the dielectric layers 6A and 6B is
and t2 are set to 100 Å, respectively, so that the heat generated by the laser beam irradiation of the magneto-optical recording film 13 is efficiently transmitted to this metal layer 7, but as a result, the required temperature T1 for performing binary recording is set to 100 Å. Alternatively, there is a possibility that the power of the laser beam to raise the temperature to T2 becomes large.

[0024]

[Problems to be Solved by the Invention] The problem to be solved by the present invention is that in a magneto-optical recording medium used for the above-mentioned light intensity modulation overwriting method, an increase in laser light power occurs during recording. Instead, the reliability is improved by increasing the margin of this laser light power.

[0025]

[Means for Solving the Problems] FIG. 1 shows an enlarged schematic cross-sectional view of an example of the magneto-optical recording medium of the present invention. The magneto-optical recording medium of the present invention sequentially comprises a dielectric layer 2, a memory layer 3 having perpendicular magnetic anisotropy, and a perpendicular magnetic anisotropy having in-plane magnetic anisotropy or a small perpendicular magnetic anisotropy, on a light-transmitting substrate 1. intermediate layer 4 having
, a recording layer 5 having perpendicular magnetic anisotropy, a dielectric layer 6, a metal layer 7, and a protective layer 8 are laminated.
a first heating state of heating to a temperature T1 at which no reversal of the magnetic moment of the recording layer 5 occurs, and a temperature T that is higher than the Curie temperature Tc1 and sufficient to reverse the magnetic moment of the recording layer 5;
2. In a magneto-optical recording medium that performs recording magnetization by modulating a second heating state in accordance with an information signal to be recorded and cooling from each heating state,
The total thickness of the laminated film 9 consisting of the memory layer 3, the intermediate layer 4, and the recording layer 5 is set to 1000 Å or more and 1500 Å or less, the dielectric layer 6 has a thickness of 500 Å or more and 1500 Å or less, and the metal layer 7
The thickness of the layer is 250 Å or more and 1500 Å or less.

[0026]

[Operation] As described above, in the magneto-optical recording medium of the present invention, the total thickness of the laminated film 9 is set to 1000 Å or more and 1500 Å or less, the dielectric layer 6 has a thickness of 500 Å or more and 1500 Å or less, and the metal layer 7 has a thickness of This configuration makes it possible to increase the power margin of the laser light power for performing binary recording of "0" and "1", for example, as described above. It is possible to make changes.

In the conventional optical intensity modulation type recording method,
In order to reliably control the temperature setting according to the binary information generated by laser beam irradiation as described above, when providing a metal layer with high thermal conductivity, this thickness was kept relatively small. As a result of intensive research by the present inventors, it was found that by appropriately selecting the total thickness of the magnetic laminated film for magneto-optical recording and the thickness of the dielectric layer provided between this and the metal layer, the metal layer It has been found that even if the thickness of the laser beam is made relatively large, an increase in laser power can be avoided.

Therefore, according to the magneto-optical recording medium of the present invention,
Two levels of power P, high output and low output, necessary to perform binary recording independently without increasing laser power.
It is possible to increase the power margin of each of the H and PL laser light powers.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the magneto-optical recording medium of the present invention will be explained in detail below. In this example, the magneto-optical recording medium performs the light intensity modulation type overwrite magnetic recording described in FIG. 7, and as shown in FIG. , a dielectric layer 2 made of SiN etc., a memory layer 3 made of TbFeCoCr etc., an intermediate layer 4 made of GdFeCoCr etc., GdTb
A recording layer 5 made of FeCoCr or the like, a dielectric layer 6 made of SiN or the like, and a metal layer 7 made of Al or the like are sequentially deposited by, for example, sputtering, and then a protective layer 8 made of ultraviolet curable resin or the like is deposited. Configure. In this case, the thickness of the dielectric layer 2 is 800 Å, the thickness of the memory layer 3 is 300 Å,
The thickness of the intermediate layer 4 is 300 Å, and the thickness of the recording layer 5 is 700 Å.
, the thickness of the dielectric layer 6 is 800 Å, and the thickness of the metal layer 7 is 30 Å.
It was set to 0 Å.

FIG. 2 shows the range in which the power can be set during recording of the optical intensity modulation magneto-optical recording medium, that is, the power margin. In this case, the power margin means that the error rate is 1×1
0-4 or less indicates an area where direct overwriting is possible. As mentioned above, in the optical intensity modulation recording method, different temperatures T1 and T are used to record binary information.
The laser power that can raise the temperature to 2 is set, and the high level laser power is shown as PH, and the low level laser power is shown as PL.

In FIG. 2, the area surrounded by a solid line a shows the power margin in the magneto-optical recording medium of the present invention with the above-described structure, and the area surrounded by the broken line b shows the power margin in the magneto-optical recording medium with the above-described structure as a comparative example. , shows the power margin when the protective layer 8 is provided directly on the dielectric layer 6 without providing a metal layer. In this case, the recording method is (2.7) RLL (Run L) according to the ISO standard in each example.
When recording a random data pattern using the so-called 2.7 modulation method, the recording magnetic field Hex is 400 [Oe], and the external auxiliary magnetic field Hsub
Recording was performed at a linear velocity of 7.5 m/s on a track with a distance of 30 mm from the innermost periphery or center of the disk-shaped magneto-optical recording medium.

As can be seen from FIG. 2, compared to the comparative example surrounded by line b, the example surrounded by line a has a wider allowable range of low level power PL, and therefore the power margin can be made to the same level as high level power PH. Although it can be relatively large, in the comparative example in which the metal layer 7 is not provided, the low level power PL
The tolerance range is narrow and the margin cannot be increased.

FIG. 3 shows the film thickness dependence of the margin of this low level power PL. In FIG. 3, the margin of low-level power PL was measured when the film thickness of the metal layer 7 of the magneto-optical recording medium shown in FIG. 1 was changed and recording was performed using the same recording method as explained in FIG. show the results,
The area surrounded by lines c and d shows the PL power margin. As can be seen from FIG. 3, when the metal layer 7 is not provided, PL=3.8 mW to 6.3 mW, and the PL power margin is about 2 mW. On the other hand, the Al metal layer 7 is
When 00 Å is deposited, PL=4.3 mW to 8.2 mW, and the PL power margin is about 5 mW, and the power margin gradually increases in proportion to the thickness of the metal layer 7.

FIG. 4 shows the results of calculating the average value of this PL power margin and determining how much margin the low level power PL has above and below it. As can be seen from FIG. 4, when no metal layer is provided, a power margin of only about 20% is obtained. In addition, in order to obtain the practically required power margin of about 30%,
The thickness of the metal layer 7 is required to be approximately 250 Å or more.

On the other hand, if the thickness of the metal layer 7 exceeds 1500 Å, the linear velocity at the outermost periphery of the disk-shaped magneto-optical recording medium will be high when recording is performed, for example. There is a risk that the temperature cannot be raised, leading to a decrease in sensitivity. Therefore, the thickness of the metal layer needs to be about 250 Å or more and 1500 Å or less.

By the way, in the case of the above-mentioned Japanese Patent Application Laid-Open No. 3-86947, it was difficult to increase the power margin in this way, and it was not possible to obtain a power margin of about 30% or more, which is practically required. .

In the above example, the thickness of the dielectric layer 6 was set to 800 Å, but if this thickness is less than 500 Å, the layered film 9 consisting of the memory layer 3, intermediate layer 4, and recording layer 5 will be formed. Since the distance between the metal layer 7 and the metal layer 7 becomes small, the sensitivity decreases due to heat dissipation of the metal layer 7, and the laminated film 9
may cause oxidation. Further, if the thickness exceeds 1500 Å, there is a possibility that the above-mentioned effect of increasing the power margin by the metal layer 7 cannot be obtained. Therefore, this dielectric layer 6
The thickness is selected to be 500 Å or more and 1500 Å or less.

Furthermore, in the above embodiment, the laminated film 9
Although the film thickness is set to 1300 Å, this film thickness may be about 1000 Å or more and 1500 Å or less.

In the above example, GdFeCoCr was used as the material for the intermediate layer 4, but by appropriately selecting the material for the intermediate layer 4, the domain wall energy can be kept low at room temperature and high near the Curie point. When setting the saturation magnetization Ms at room temperature to 0≦Ms
≦450 emu/cm3, in particular, the perpendicular magnetic anisotropy is 1×106 erg/cm3 or less, and the temperature characteristic curve of the effective magnetic anisotropy constant K exhibits an upwardly convex characteristic or a linear characteristic. Using a metal material, for example, Gd
In the case of FeCo-based materials, Gdx (Fe1-y C
oy)1-x, 0.25≦x≦0.40, and 0≦y≦1.0 (x, y atomic ratio). When using GdFeCo material here, other Dy, T
Various other elements such as b, Nd, etc. may be added. When the material of the intermediate layer 4 is limited in this way, when performing the magneto-optical recording method explained in FIG. Overwriting can be performed more reliably.

In the above example, a case was explained in which Al was deposited as the metal layer 7, but other materials with relatively high thermal conductivity such as Au, Pt, Cu, etc. may be used as the metal layer 7. Can be used.

In addition to the above-mentioned SiN, materials for the dielectric layer 6 include SiO, SiO2, TiO2, and TiO2.
, CeO, HfO2 , BeO, ThO2 , Si3
Various materials such as N4, ITO, etc. can be used.

[0042]

As described above, the magneto-optical recording medium of the present invention has a structure in which a laminated film 9, a dielectric layer 6, and a metal layer 7 for magneto-optical recording are provided, and the thickness of each of these layers is appropriately selected. By doing so, when performing magneto-optical recording, for example, without increasing the respective output values of high-level laser power PH and low-level laser power PL corresponding to binary recording,
The power margin of each power PH and PL can be increased.

[Brief explanation of drawings]

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

FIG. 2 is a diagram showing a margin of recording laser power in a magneto-optical recording medium.

FIG. 3 is a diagram showing a change in low-level laser power due to a change in the thickness of a metal layer.

FIG. 4 is a diagram showing a change in low-level laser power margin due to a change in the thickness of a metal layer.

FIG. 5 is a schematic enlarged cross-sectional view of a conventional magneto-optical recording medium.

FIG. 6 is a schematic enlarged cross-sectional view of a conventional magneto-optical recording medium.

FIG. 7 is an explanatory diagram of the magnetization state of the laminated film of the magneto-optical recording medium.

FIG. 8 is a schematic enlarged cross-sectional view of a conventional magneto-optical recording medium.

[Explanation of symbols]

1. Light-transparent substrate 2 Dielectric layer 3 Memory layer 4 Middle class 5 Recording layer 6 Dielectric layer 7 Metal layer 8 Protective layer 9 Laminated film

Claims (1)

[Claims] Claim 1: A dielectric layer sequentially formed on a light-transmissive substrate;
A memory layer having perpendicular magnetic anisotropy, an intermediate layer having in-plane magnetic anisotropy or small perpendicular magnetic anisotropy, a recording layer having perpendicular magnetic anisotropy, a dielectric layer, and a metal layer. and a protective layer, and is heated to a temperature T1 which is approximately equal to or higher than the Curie temperature Tc1 of the memory layer and at which no reversal of the magnetic moment of the recording layer occurs.
and a temperature T which is equal to or higher than the Curie temperature Tc1 and is sufficient to reverse the magnetic moment of the recording layer.
2. In the magneto-optical recording medium, the memory layer and the intermediate layer are modulated in accordance with the information signal to be recorded, and recording magnetization is performed by cooling the respective heating states. and the recording layer have a total thickness of 1000 Å or more and 1500 Å or less, the dielectric layer has a thickness of 500 Å or more and 1500 Å or less, and the metal layer has a thickness of 250 Å or more and 1500 Å or less. A magneto-optical recording medium characterized by: