JPH04255939A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To constitute a magneto-optical recording medium to be stable in recording and reproducing properties even when it is repeatedly used. CONSTITUTION:In a magneto-optical recording medium having at least a recording layer and a reproducing layer and reading out a recording signal while changing magnetization of the reproducing layer, the above reproducing layer is formed as an artificial lattice structure which is built up by repeatedly laminating rare earth metallic layer 40RE with transition metallic layer 40TM alternately.

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] The present invention relates to a magneto-optical recording medium. [0002] When using a magneto-optical recording and reproducing method in which information recording pits, that is, bubble magnetic domains are formed by local heating by laser beam irradiation, and this recorded information is read out by magneto-optical interaction, that is, Kerr effect or Faraday effect. In order to increase the recording density of magneto-optical recording, it is necessary to make the recording pits smaller, but in this case, the resolution during reproduction becomes a problem. This resolution is determined by the wavelength of the laser during reproduction, the numerical aperture of the objective lens, and the numerical aperture of the objective lens. A. determined by A general magneto-optical recording and reproducing system will be explained with reference to FIG. FIG. 4A shows a schematic top view of a recording pattern. For example, recording pits 4 are shown with diagonal lines on land portions 2 sandwiched by grooves 1 on both sides.
A method for reproducing a magneto-optical recording medium 3, such as a magneto-optical disk, recorded in accordance with binary information "1" and "0" will be explained. Let us now consider the case where the beam spot of the readout laser beam on the magneto-optical recording medium 3 is a circular spot indicated by reference numeral 5. At this time, if the pit interval is selected so that only one recording pit 4 can exist in one beam spot 5 as shown in FIG. 4A, , there are two modes: whether there is a recording pit 4 in the spot 5 or not. Therefore, when the recording pits 4 are arranged at equal intervals, the output waveform becomes, for example, a sine wave whose positive and negative sides are inverted with respect to the reference level 0, as shown in FIG. 4D, for example. However, as shown in a schematic diagram of a recording pattern in FIG.
comes in. For example, if we look at three adjacent recording pits 4a, 4b, and 4c, FIGS. 5B and 5C.
As shown in the figure, there is no change in the playback output when adjacent recording pits 4a and 4b enter one beam spot 5, and when recording pits 4b and 4c enter into the same beam spot, so the playback output As shown in FIG. 5D, the waveform becomes, for example, a straight line, making it impossible to distinguish between the two. As described above, in the conventional general magneto-optical recording and reproducing system, the recording pits 4 recorded on the magneto-optical recording medium 3
Even if high-density recording, that is, the formation of high-density recording pits, is possible because the data is read out in its original state, problems with S/N (C/N) arise due to resolution constraints during playback. Sufficient high-density recording and playback is not possible. Problem to be Solved by the Invention: Such S/N (C
/N), it is necessary to improve the resolution during reproduction, but there is a problem that this resolution is limited by the laser wavelength, the numerical aperture of the lens, etc. In order to solve these problems, the present applicant has previously proposed a super-resolution (super-resolution) magneto-optical recording and reproducing system (hereinafter referred to as MSR) (for example, in Japanese Patent Application No. 1-225685, "Optical ``Magnetic recording and reproducing method''). [0007] To explain this MSR, this MS
In R, the recording pits 4 of the magneto-optical recording medium are generated only in a predetermined temperature range during reproduction by utilizing the temperature distribution caused by the relative movement between the magneto-optical recording medium and the beam spot 5 for reproduction. This results in higher resolution playback. [0008] Examples of this MSR system include a so-called embossed type reproduction system and a so-called annihilation type reproduction system. The raised type MSR method will be explained with reference to FIG. FIG. 6A is a schematic top view showing a recording pattern of the magneto-optical recording medium 10, and FIG. 6B is a schematic cross-sectional view showing its magnetization mode. In this case, as shown in FIG. 6A, the magneto-optical recording medium 10 is moved relative to the beam spot 5 of the laser beam in the direction shown by arrow D. In this case, for example, as shown in FIG. 6B,
A reproducing layer 11 made of at least a perpendicular magnetization film and a recording layer 13
A magneto-optical recording medium 10, for example, a magneto-optical disk, further comprising an intermediate layer 12 which is interposed between both layers 11 and 13 and whose perpendicular anisotropy is smaller than that of these layers 11 and 13. is used. Each layer 11, 12, 13 in the figure
The line arrows in the middle schematically show the direction of the magnetic moment; in the illustrated example, the downward direction is the initialized state, and the upward direction in the figure indicates the magnetic domain due to magnetization, which creates information recording pits in at least the recording layer 13. 4 is formed. [0010] In such a magneto-optical recording medium 10,
To explain the reproduction mode, first, the initializing magnetic field H is applied from outside.
i is applied to initialize the reproduction layer 11 by magnetizing it downward in FIG. 6B. That is, in the reproducing layer 11, the recording pits 4 disappear, but at this time, in the portion having the recording pits 4, the directions of magnetization of the reproducing layer 11 and the recording layer 13 are maintained in opposite directions by the magnetic domain walls generated in the intermediate layer 12. The recording pits 4 are latent image recording pits 4.
It remains as 1. On the other hand, an initializing magnetic field H is applied to the magneto-optical recording medium 10.
A reproducing magnetic field Hr in the opposite direction to i is applied at least to the reproducing section. In this state, as the medium 10 moves, the area with the initialized latent image recording pits 41 comes under the beam spot 5, and the area heated by the beam irradiation is located on the leading end side under the beam spot 5, as shown in FIG. As you move to the left, on the tip side of spot 5, as shown surrounded by a broken line a,
Substantially, a high temperature region 14 is generated, and in this region 14 the domain wall of the intermediate layer 12 disappears, and the magnetization of the recording layer 13 is transferred to the reproduction layer 11 by exchange force, and the latent image recording pits that existed in the recording layer 13 are 41 are highlighted as recording pits 4 that can be reproduced on the reproduction layer 11. Therefore, if the rotation of the deflection plane of the beam spot 5 due to the Kerr effect or Faraday effect due to the direction of magnetization in the reproducing layer 11 is detected, this recording pit 4 can be detected.
can be read out. At this time, in the low temperature region 15 other than the high temperature region 14 within the beam spot 5,
The latent image recording pits 41 are not embossed on the reproducing layer 11, and as a result, within the beam spot 5, there are recording pits 4 that can be read only in the narrow high temperature area 14 shown with diagonal lines. Even when the recording density is such that a plurality of recording pits 4 enter the beam spot 5, that is, even in a magneto-optical recording medium 10 with high density recording, only a single recording pit 4 can be read out. High resolution playback is possible. In order to perform such reproduction, the initialization magnetic field Hi, the reproduction magnetic field Hr, the coercive force, thickness, magnetization,
The domain wall energy, etc. is generated in the high temperature region 1 within the beam spot 5.
4 and the temperature of the low temperature region 15. That is,
The coercive forces of the reproducing layer 11 and recording layer 13 are HC1 and HC3.
, the thicknesses are h1 and h3, and the saturation magnetizations MS are MS1 and MS3, then the condition for initializing only the reproduction layer 11 is the following equation 1. [Equation 1] Hi>hC1+σW2/2MS1h1 00
15] Here, σW2 represents the interfacial domain wall energy between the reproducing layer 11 and the recording layer 13. Further, the condition for maintaining the information in the recording layer 13 by the magnetic field is expressed by Equation 2. [Math. 2] Hi<HC3−σW2/2MS3h3 00
17] Also, even after passing under the initializing magnetic field Hi, the reproducing layer 11
In order to maintain the domain wall created by the intermediate layer 12 between the recording layer 13 and the recording layer 13, the following condition 3 is required. [Math. 3] HC1>σW2/2MS1h1 0018
At the temperature TH selected within the high temperature region 14, the following condition 4 is required. [Formula 4] HC1−σW2/2MS1h1<Hr
<HC1+σW2/2MS1h1 By applying the reproducing magnetic field Hr that satisfies the equation 4, the magnetization of the latent image recording pits 41 of the recording layer 13 is applied to the reproducing layer 11 only in the portion where the domain wall formed by the intermediate layer 12 exists. It can be made to stand out as a transfer or recording pit 4. The magnetic recording medium 10 used in the above-mentioned MSR method has been described as having a three-layer structure consisting of the reproducing layer 11, the intermediate layer 12, and the recording layer 13, but as shown in FIG. A four-layer structure in which the reproduction auxiliary layer 31 is provided on the intermediate layer 12 side of the reproduction layer 11 may also be used. The reproduction auxiliary layer 31 is for assisting the characteristics of the reproduction layer 11.
The magnetization of the reproducing layer 11 aligned by the initializing magnetic field Hi remains stable even with the presence of the domain wall, and the coercive force rapidly decreases near the reproducing temperature. Then, the magnetic domain wall confined in the intermediate layer 12 spreads to the reproduction auxiliary layer 31, and finally the reproduction layer 11 is reversed and the magnetic domain wall disappears, so that recording pits can be raised well. When a four-layer structure including the reproduction auxiliary layer 31 is adopted as described above, the coercive force HC1 of the reproduction layer 11 is replaced by HCA according to the following equation 5, and σW2/MS
1h1 is replaced by σW2/(MS1h1+MS1ShS). [Equation 5] HCA=(MS1h1HC1+MS1
Sh1SHC1S)/(MS1h1+MS1Sh1S)
(However, the above-mentioned embossed MSR
Then, HC1<HCA<HC1S) Here, MS1S,
HC1S and h1S are the magnetization of the reproduction auxiliary layer 31, respectively;
Represents coercive force and thickness. However, in the case of such a raised type MSR, various problems such as retention and reversal of the magnetization of each magnetic layer occur during the initialization process, recording process, and reproduction process including the initialization process. It is necessary to satisfy the conditions, especially in the case of the three-layer structure shown in FIG.
1 and the four-layer structure shown in FIG. 7, strict conditions are imposed on the reproduction auxiliary layer 31, so the composition range selected for these is narrow. Therefore, even if a magneto-optical recording medium initially has characteristics selected to satisfy the above-mentioned operation, when the above-mentioned process is repeated due to repeated use of recording and reproduction, its reproduction C/ N is deteriorating. Such deterioration of characteristics such as C/N is caused by crystallization and interlayer atomic diffusion in the magnetic layer due to repeated temperature rises due to recording, erasing, and reproduction, and this is particularly important when stability of characteristics is required. It is thought that a problem will arise in the reproducing layer 11 or the reproducing auxiliary layer 31. [0027] The present invention is directed to the instability, aging, and
In other words, it aims to solve the reliability problem. [Means for Solving the Problems] As shown in a schematic cross-sectional view of an example of the present invention in FIG. In the magneto-optical recording medium 10 in which recorded signals are read out while changing the magnetization state, the reproduction auxiliary layer 31 is composed of a rare earth metal layer 40RE and a transition metal layer 40TM, as schematically shown in cross section in FIG.
An artificial lattice film structure is created by repeatedly laminating films. Further, the present invention provides a magneto-optical recording medium which has a reproducing layer and a recording layer and reads recorded signals while changing the magnetization state of the reproducing layer, in which the reproducing layer is a rare earth metal layer as shown in FIG. An artificial lattice structure is formed by repeatedly laminating 40RE and a transition metal layer 40TM. Here, the rare earth metal layer 40RE is selected to have a thickness of about 1 to 2 atomic layers, and the transition metal layer 40TM is selected to have a thickness of about 2 atomic layers or more depending on the intended composition. [Operation] According to the above-described structure of the present invention, the magnetic properties such as coercive force, magnetization, etc. have a great influence on the reproducing operation, and under various conditions of external magnetic fields such as temperature conditions and reproducing magnetic fields. The reproduction auxiliary layer 41 or the reproduction layer 11, which is required to be set strictly, has an artificial lattice structure formed by repeatedly laminating the rare earth metal layer 40RE and the transition metal layer 40TM, so that the reproduction characteristics can be maintained even with repeated use. As a result, we were able to avoid fluctuations in the temperature, improve reliability, and extend lifespan. [0032] This is because the rare earth metal and the transition metal are each formed into a laminated structure of their own layers, so compared to the case where the rare earth metal and the transition metal are formed as an integrated alloy layer, for example, the rare earth metal It is possible to maintain a stable state by bonding a plurality of adjacent transition metal atoms, for example two atoms, to one atom of
Furthermore, by forming unique layers of rare earth metals and transition metals, crystallization is less likely to occur even when the temperature rises, and the properties of the amorphous layer can be stably maintained. [Example] Referring to FIG. 1, a magneto-optical recording medium has a magneto-optical recording layer 21 mainly consisting of four layers: a reproducing layer 11, a reproducing auxiliary layer 31, an intermediate layer 12, and a recording layer 13. An example of configuring 10 will be described. In this case, a dielectric layer 23 made of a transparent SiN film with a thickness of 800 Å, for example, is formed as a protective film or an interference film on a light-transmissive substrate 20 made of glass, acrylic, polycarbonate, etc. Reproduction layer 11 on top
, the reproduction auxiliary layer 31, the intermediate layer 12, and the recording layer 13 are sequentially laminated by continuous sputtering. Furthermore, a non-magnetic metal film or dielectric film, such as Si with a thickness of 800 Å, is applied on top of this.
A protective film 25 made of N film is deposited. [0035] At least the reproduction auxiliary layer 31, furthermore, for example, the reproduction layer 11, the intermediate layer 12, and the recording layer 13, are each formed by repeating a rare earth metal 40RE and a transition metal layer 40TM, as schematically shown in FIG. It has a laminated artificial lattice structure. The reproducing layer 11 includes, for example, a rare earth metal layer 40RE made of Gd with a thickness TRE=3.4 Å corresponding to about one atomic layer, and a rare earth metal layer 40RE made of Fe85Co15 with a thickness TTM=4.9 Å corresponding to several atomic layers. The magnetic layer is selected such that the overall composition thereof is, for example, Gd23(Fe85Co15)77, and the thickness is, for example, 300 Å. The reproduction auxiliary layer 31 has a thickness of Tb. 3.
It has a repeated stacked structure of a rare earth metal layer 40RE with a thickness of 4 Å and a transition metal layer 40TM with a thickness of 4.7 Å made of Fe95Co5, and the composition as a whole is Tb12 (Fe95C).
o5) 88, so that the magnetic layer has a thickness of 100 Å. The intermediate layer 12 has a thickness of 3.4 Å due to Gd.
The rare earth metal layer 40RE and the transition metal layer 40TM of Fe95Co5 with a thickness of 4.7 Å are repeatedly laminated, and the composition as a whole is Gd20(Fe95Co5
) 80 and the thickness of the magnetic layer is 100 Å. The recording layer 13 has a thickness of 3.4 Å due to Tb.
It has a repeated laminated structure of a rare earth metal layer 40RE of Tb25(Fe85Co1) and a transition metal layer 40TM of 4.7 Å thick made of Fe85Co15, and its composition as a whole is Tb25(Fe85Co1
5) 75, so that the magnetic layer has a thickness of 400 Å. The formation of the reproducing layer 11, the reproducing auxiliary layer 31, the intermediate layer 12, and the recording layer 13 is performed using a sputtering apparatus having a plurality of sputtering sources, a schematic plan view of which is shown in FIG. Can be done. In the illustrated example, the structure is such that targets 61, 62, 63, and 64, which serve as four sputtering sources, are provided in the same chamber, and the target 61 is Fe85Co.
The target 62 is made of Tb, the target 63 is made of Gd, and the target 64 is made of Fe95C.
Consists of o5. The substrate 20 is rotated on its own axis as shown by the arrow A, and is also relatively revolved as shown by the arrow B so as to sequentially pass the sputtering positions of the targets 61, 62, 63, and 64. [0043] In the formation of the reproducing layer 11, F
Only the e85Co15 target 61 and the Gd target 63 are operated, and sputtering is performed by relative rotation and revolution as indicated by arrows A and B. In this way, Fe85
The GdFeCo regeneration layer 11 can be formed with a repeating structure of a transition metal layer 40TE made of Co15 and a rare earth metal layer 40RE made of Gd. Next, Tb target 61 and Fe95Co
5. The same sputtering is performed by operating only the target 64 to form the reproduction assisting layer 31 of TbFeCo. Next, target 63 and Fe95Co
5 The same sputtering was performed by operating only the target 64, and the rare earths were separated by Gd into 40RE and Fe95.
The intermediate layer 12 is formed by a repeated laminated structure of transition metal layers 40TM made of Co5. [0046] Next, Fe85Co15 target 16
By operating only the Tb target 62 and the transition metal layer 40TM, the recording layer 13 having a repeated laminated structure of the transition metal layer 40TM and the rare earth metal layer 40RE is formed. Magneto-optical disk 10 with such a configuration
On the other hand, recording is performed using an optical modulation method or a magnetic field modulation method, and reading of the recorded pits is performed using the raised MSR method described with reference to FIGS. 6 and 7. The example shown in FIG. 1 is a case where the magneto-optical recording layer 21 has a basic four-layer structure of the reproducing layer 11, the reproducing auxiliary layer 31, the intermediate layer 12, and the recording layer 13. The present invention can also be applied to a configuration in which the basic structure is a three-layer structure of the reproducing layer 11, intermediate layer 12, and recording layer 13 as described above. In this case, at least the reproducing layer 11 preferably has a repeated laminated structure of the rare earth metal layer 40RE and the transition metal layer 40TM described in FIG. 2 for the reproducing layer 11, intermediate layer 12, and recording layer 13. In this case, for example, the reproducing layer 11 is made entirely of GdFeCo, and the intermediate layer 12 is made entirely of TbFe.
In general, the recording layer 13 can be made entirely of TbFeCo. Note that the constituent layers of the magneto-optical recording layer 21 and the composition of each constituent layer are not limited to the above-mentioned example, but may be selected to have various compositions and compositions. As described above, according to the present invention, in a magneto-optical recording medium applied to an embossed type MSR, the best reproduction characteristics, that is, embossment of information pits on the reproduction layer 11, The reproduction layer 11 itself, which affects initialization, inversion, etc., or the reproduction auxiliary layer 41, which has a characteristic of high coercive force at room temperature and serves to compensate for the characteristics of the reproduction layer, is a rare earth metal layer 4.
By creating an artificial lattice structure by repeatedly stacking 0RE and transition metal layer 40TM, we have stabilized the composition and the state, resulting in a long-life and highly reliable magneto-optical recording medium. be.

[Brief explanation of the drawing]

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

FIG. 2 is a schematic cross-sectional view of a laminated film of a rare earth metal layer and a transition metal layer of a magneto-optical recording layer according to the present invention.

FIG. 3 is a plan view of an example of a sputtering apparatus for producing a magneto-optical recording medium according to the present invention.

FIG. 4 is an explanatory diagram of a conventional magneto-optical recording and reproduction mode.

FIG. 5 is an explanatory diagram of a conventional magneto-optical recording and reproduction mode.

FIG. 6 is an explanatory diagram of an embossed MSR.

FIG. 7 is a schematic cross-sectional view of a magneto-optical recording medium.

[Explanation of symbols]

11 Reproduction layer 12 Middle class 13 Recording layer 21 Magneto-optical recording layer 22 Good thermal conductive material layer

Claims (2)

[Claims] 1. A magneto-optical recording medium comprising at least a reproducing layer, a reproducing auxiliary layer, and a recording layer, in which recorded signals are read out while changing the magnetization state of the reproducing layer, wherein at least the reproducing auxiliary layer is made of a rare earth metal. 1. A magneto-optical recording medium characterized by having a repeatedly laminated film of a layer and a transition metal layer. 2. A magneto-optical recording medium comprising at least a reproducing layer and a recording layer, in which recorded signals are read out while changing the magnetization state of the reproducing layer, wherein at least the reproducing layer comprises a rare earth metal layer and a transition metal layer. What is claimed is: 1. A magneto-optical recording medium characterized by having a repeatedly laminated film.