JPS61107552A - Optical recording medium - Google Patents

Abstract

PURPOSE:To increase rapidly the information storage density in response to the number of layers of an optomagnetic recording layer by laminating plural optomagnetic recording layers via a nonmagnetic layer and recording respectively information on the optomagnetic recording layer. CONSTITUTION:The nonmagnetic layer 14, the 1st magnetic recording layer 16, a nonmagnetic intermediate layer 18, the 2nd magnetic recording layer 20, and a reflecting layer 24 are laminated sequentially on one face of a transparent base 12 of an optomagnetic disc 10. The wavelength lambda1 of a laser light source 26 is 8,300Angstrom and the wavelength lambda2 of the laser light source 28 is 7,800Angstrom . A dichroic mirror 34 transmits a laser ray of wavelength lambda1 and reflects a laser ray of wavelength lambda2 to make a combined laser ray with wavelengths lambda1, lambda2 incident in the optomagnetic disc 10 through a half mirror 36 and an objective lens 38.

Description

Detailed Description of the Invention Technical Field The present invention relates to a magneto-optical recording medium used in a magneto-optical recording/reproducing device, and in particular to a technology for dramatically improving the recording density per unit area. It's about me.

PRIOR TECHNOLOGY Optical magnetism that locally magnetizes a material that has spontaneous magnetization and allows light to pass through it in the perpendicular direction, thereby writing information and reading out the written information using the magneto-optic effect. There are known devices for reproducing the distribution t.

Optical Ea gas for recording information is generally constructed by fixing a thin layer of magneto-optical material onto a substrate made of acrylic resin or glass. A disk-shaped magneto-optical recording medium is known as a magneto-optical disk.

Problems to be Solved by the Invention However, the size of the recording bit in such conventional magneto-optical recording media is determined by the size of the beam spot of the light used for writing or reading information, and the size of the beam spot is determined by the size of the beam spot of the light used for writing or reading information. Since there is a close relationship with the wavelength of light, there is a limit to the size of recording bits per unit area due to the wavelength of the light used, which limits the information recording density. Further, the size of the magneto-optical recording medium is limited due to deformation of the material used for the substrate of the magneto-optical recording medium, manufacturing tolerances of the magneto-optical recording medium, and the like. For example, in the case of a magneto-optical disk, the limit is 30 cmφ. Therefore, for example, the amount of information stored per magneto-optical disk is naturally limited.

Means for Solving the Problem The present invention has been made against the background of the above circumstances.
The gist is that a plurality of magneto-optical recording layers are laminated with a non-magnetic layer interposed therebetween, and information can be recorded and reproduced separately in each of the magneto-optical recording layers.

In this way, a plurality of magneto-optical recording layers are laminated with a non-magnetic layer interposed therebetween, and information is recorded in each of the magneto-optical recording layers, so that the amount per unit area of the magneto-optical recording medium is The amount of information recorded or the amount of information stored per magneto-optical recording medium increases dramatically depending on the number of stacked magneto-optical recording layers.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 shows a magneto-optical reproducing device 11 which is an example of a device for reading information from a disc-shaped magneto-optical disk 10 as a magneto-optical recording medium. In the figure, a magneto-optical disk 10 has a non-magnetic layer 14 on one side of a transparent substrate 12. First magnetic recording layer 16. Nonmagnetic intermediate layer 18. Second magnetic recording layer 20
．． The nonmagnetic layer 22 and the reflective layer 24 are sequentially laminated by known fixing means such as vapor deposition and sputtering. The transparent base 12 is made of a transparent material such as glass or transparent resin, but in this embodiment, acrylic resin, such as polymethyl methacrylate (PMMA), is used. This is because when acrylic resin is used, manufacturing and handling of the magnetic disk 10 becomes easier. The nonmagnetic layer 14.22 protects the magnetic thin films of the first magnetic recording layer 16 and the second magnetic recording layer 20, and is made of a transparent nonmagnetic material such as aluminum nitride (ANN), silicon oxide (SIO), Silicon dioxide (StO□), metal silicon (Si), or the like is used. Nonmagnetic layer 1
4.22 prevents the first magnetic recording layer 16 and the second magnetic recording layer 20 from chemical changes (oxidation, etc.),
In this embodiment, the upper right thickness of about 1421 people and the zero thickness of about 1336 people are respectively adopted. However, it may be omitted if chemical changes in the first magnetic recording layer 16 and the second magnetic recording layer 20 are difficult to predict. Nonmagnetic layer 14
And between 22 and 22! - The first magnetic recording layer 16 and the second magnetic recording layer 20 sandwiching the magnetic intermediate layer 18 are interposed, and in this embodiment, the first magnetic recording layer 16 has 110 people, and the upper right second magnetic recording layer 20 has 800 people. The upper right non-magnetic intermediate layer 18 has a thickness of approximately 17,830 people. The first magnetic recording layer 16 and the second magnetic recording layer 20 are made of a magneto-optical material having a remarkable magneto-optical effect, such as amorphous GdTbFe, Tb
Materials such as Fe, TbFeCo, 'C, dCo, GdDyFe, polycrystalline MnCuBi, single crystal TbFeOz, and rare earth iron garnet may be used. In this example, G
dTbFe is used. In addition, the nonmagnetic intermediate layer 18
may be any transparent non-magnetic material, and the non-magnetic layer 1
Materials similar to 4 can be used.

This non-magnetic intermediate layer 18 may be formed by laminating multiple layers of light-transmitting non-magnetic material, which is convenient for increasing the film thickness. For example, SiO□, Sin.

It is preferable to sequentially stack 5in2. In addition, the reflective layer 24
Various materials capable of reflecting light, such as aluminum vapor-deposited films, are used for this purpose. However, instead of the non-magnetic N22 and the reflective layer 24, a thick plastic layer may be provided. This is because such a plastic layer can sufficiently reflect light at its interface and also provide a protective function for preventing oxidation of the second magnetic recording layer 20.

The magneto-optical disk 10 is rotated, for example, around a vertical axis by a drive device (not shown), and a reading light beam emitted from the magneto-optical reproducing device 11 is scanned in the radial direction of the magneto-optical disk 10. In this way, the objective lens 38 and the like are moved in parallel in the horizontal direction. The reading laser light sources 26 and 28 emit linearly polarized laser beams of different wavelengths toward the dichroic ink mirror 34 through collimator lenses 30 and 32, respectively. In this embodiment, the wavelength λ1 of the laser light source 26 is 8,300 people, and the wavelength λ2 of the laser light source 28 is 7,800 people. The guichroic mirror 34 allows the laser beam with the wavelength λ1 to pass through, while reflecting the laser beam with the wavelength λ2, so that the composite laser beam consisting of the wavelengths λ1 and λ2 is incident on the magneto-optical disk 10 through the half mirror 36 and the objective lens 38. let The combined laser beam reflected from the magneto-optical disk 10 passes through the objective lens 38 and the half mirror 36, and reaches the dichroic ink mirror 40, where the wavelength λ
, are passed through, while the laser beam of wavelength λ2 is reflected and separated. Wavelength λ1
The laser beam of wavelength λ2 and the laser beam of wavelength λ2 are received by a first detection device 42 and a second detection device 44, respectively.

The first detection device 42 and the second detection device 44 detect Kerr rotation angles of a laser beam with a wavelength λ and a laser beam with a wavelength λ2, respectively, and detect the Kerr rotation angle of the first magnetic recording layer 16 based on the Kerr rotation angle difference. Information recorded in advance by perpendicular magnetization in the second magnetic recording layer 20 is read out. The first detection device 42 and the second detection device 44 are configured in exactly the same way, and for example, the first detection device 42 is configured as shown in FIG. In the figure, a laser beam of wavelength λ1 reflected by a magneto-optical disk 10 is separated into two directions by a half mirror 46, one laser beam is received by a photodiode 52 via an analyzer 48, and the other laser beam is received by a photodiode 52. 50 and is received by a photodiode 54. Analyzer 48 and 5
The polarization planes of o are perpendicular to each other and are each inclined by 45° to the polarization plane of the laser beam. therefore,
When the polarization plane of the laser beam is rotated, for example, the amount of light received by one photodiode 52 decreases, while the amount of light received by the other photodiode 54 increases. The outputs of photodiodes 52 and 54 are connected to a differential amplifier 56.
The differential amplifier 56 outputs a signal corresponding to the information stored in the first magnetic recording layer 16, and noise caused by fluctuations in the amount of light is canceled. Here, the laser light sources 26 and 28 are semiconductor lasers that output linearly polarized laser beams.
゛□; A laser light source or an external resonant laser light source is used, but when using an internal resonant laser light source that outputs a circularly polarized laser beam, the laser beam should be emitted through a polarizer. good.

The regeneration effect of this embodiment will be explained below. According to the magneto-optical reproducing device 11, the first TIIL recording layer 16 and the second magnetic recording layer 20, which are stacked on each other with the non-magnetic intermediate layer 18 in between, are independently reproduced.

In order to read information independently from each magnetic recording layer 1G and 20, as shown in FIGS. 3(a) and (bl),
When the first magnetic recording layer 16 is magnetized in the N direction and the S direction, Kerr rotation corresponding to the magnetization directions N and S in the first magnetic recording layer 16 regardless of the magnetization direction in the second magnetic recording layer 20. An angular difference must be obtained,
Moreover, as shown in FIG. 4(a) and (bl), the second v
When the A magnetic recording layer 20 is magnetized in the N direction and the S direction, a Kerr rotation angle difference corresponding to the magnetization direction of the second magnetic recording layer 20 is detected regardless of the magnetization direction in the first magnetic recording layer 16. Must be.

After various studies, the inventor discovered that the first magnetic recording layer 1
The difference in the Kerr rotation angle of the reflected light associated with four types of combinations of magnetization directions between the magnetic recording layer 6 and the second magnetic recording layer 20 changes with different characteristics as the thickness of one of the magnetic recording layers changes. If the thickness of one magnetic recording layer is set to a specific thickness in the Kerr rotation angle difference change characteristic, the Kerr rotation angle will change only in relation to the magnetization direction of one magnetic recording layer, regardless of the magnetization direction of the other magnetic recording layer. It was discovered that the difference was determined, and this embodiment was constructed based on this finding. That is, according to the inventor's simulation, for a laser beam of wavelength λ1 (8,300 people), as shown in FIG. Regardless of the magnetization direction of the first magnetic recording layer 16, the Kerr rotation angle difference corresponding to the magnetization direction of the first magnetic recording layer 16 can be stably obtained. For example, the first
When the magnetization direction of the magnetic recording layer 16 changes from S to N, the Kerr rotation angle difference changes from 0 degrees to about 0.6 degrees. In the figure, N/S and N/'N indicate the case where the magnetization direction of the first magnetic recording layer 16 is the N direction, and the magnetization direction of the second magnetic recording layer 20 is S and N, respectively. Moreover, S/N and S/S indicate the case where the magnetization direction of the first magnetic recording layer 16 is the S direction, and the magnetization direction of the second magnetic recording layer 20 is the N direction and the S direction. Also, the wavelength λ2 (78
Regarding the laser beam of 00 persons, as shown in FIG. 6, when the thickness of the first magnetic recording layer 16 is around 120 persons,
Regardless of the magnetization direction of the first magnetic recording layer 16, the Kerr rotation angle difference corresponding to the magnetization direction of the second magnetic recording layer 20 can be stably obtained.As a result, the thickness of the first magnetic recording layer 16 can be reduced to 100
person and a neighborhood centered on 120 people, preferably 100
Select between 120 people and the Kerr rotation angle difference δθ is 0.
．． 3' or more, for example, the information is "1", and δθ is 0.
For example, if the angle is 3° or less, it corresponds to information "0".
Information in the first magnetic recording layer 16 is reproduced with a laser beam having a wavelength of 8300 mm, and information in the second magnetic recording layer 20 is reproduced with a laser beam having a wavelength of 7800 mm.

Therefore, as mentioned above, since the thickness of the first magnetic recording layer 16 of the magneto-optical disk 10 is selected to be 110,
A Kerr rotation angle difference corresponding to the perpendicular magnetization direction stored in the first optical recording layer 16 can be reliably obtained in the reflected light from the magneto-optical disk 10 having the wavelength λ1. Therefore, the first detection device 42 of the magneto-optical reproducing device 11 can reliably obtain a signal corresponding to the data stored in the first magnetic recording layer 16. Further, similarly, the Kerr rotation angle difference corresponding to the perpendicular magnetization direction of the second magnetic recording layer 20 is reliably obtained in the reflected light from the magneto-optical disk 10 of the laser beam with the wavelength λ2, and the second detection device 44 2 magnetic recording layer 2
A signal corresponding to the data stored in advance at 0 can be reliably obtained.

As described above, according to this embodiment, the data stored in advance in the first magnetic recording layer 16 and the second magnetic recording layer 20 is retrieved, so that the conventional magneto-optical disk having only one magnetic recording layer is used. The information recording density per unit area and the amount of information stored per sheet have been dramatically increased compared to the previous one.

Here, in the simulations of Figures 5 and 6,
For example, equation (1) is preferably used. By solving Manxwell's electromagnetic equation for each layer of the magneto-optical disk 10 and applying boundary conditions, the relationship between incident light and reflected light when linearly polarized light is incident is derived. Of the electric field of this reflected light, the Kerr rotation angle ψ is determined based on the component Ey having the same polarization plane as the incident light and the component Ex having the polarization plane perpendicular to the incident light.

The Kerr rotation angle difference δθ shown in FIG. 5 was determined by taking the difference from the minimum value since the Kerr rotation angle ψ changes depending on the direction of magnetization.

tan 2ψ-tan2αcoo (φ-θ)...(
1) However, (in formula 11, IEyl bl+' b21゛.Here, bll and bZ+ are expressed as the following formula (51, (
If it is expressed in complex form as in 6), bll"bll"+j bll"...(5)
bz1= 1)z+ ' +j bz+ "...
(6) The electric field magnitudes 1Exl and IEyl are as shown in the following equations.

The above bl+ and b21 are defined as in the following equation.

■ 1) ++= (az+azs az:+ai+)
・・191bz+= (a41al:l a4
3affl) ...'α0) However, D=aza3
3 a13a31 '' (11).(9
), α0), and (n) can be expressed as each component of a 4×4 matrix as shown in the following equation.

(a=J) = (MAL) −(MA21) ・(
MA31) -(MA41)・(MA51)・(MA6
1) ...(12) Each matrix in equation (12) is expressed as shown in equations (+3) to 08) under the following conditions.

no=refractive index n and dl of transparent substrate 12 : refractive index and film thickness n2 and d2 of nonmagnetic layer 14 : refractive index and film thickness n and d of first magnetic recording layer 16 : nonmagnetic intermediate layer 18 refractive index and film thickness n4 and d, : refractive index and film thickness n, and ds of second magnetic recording layer 2D: refractive index and film thickness n of non-magnetic layer 22, refractive index of second reflective layer 24: first Permittivity tensor of magnetic recording layer 16: Permittivity tensor of second magnetic recording layer 20:
δ11
Engineering 1
'Ct+%
Ya j to (01!I
< Σ Σ9
F−−−−−−1−−−−11< , j Σ
Ro Rol -kuΣ 0
(〉II J
I+ol! l cry
U) Kuni<11 Σ F,
J-Giant 8 S
- Note that the characteristics shown in FIGS. 5 and 6 are only the characteristics when the first magnetic recording layer 16 is made of GdTbFe, so the Kerr rotation angle difference obtained when other magneto-optical materials are used. Since the change characteristics with respect to the thickness of the first magnetic recording layer 16 are different, the thickness of the first magnetic recording layer 16 is also set to an optimum value according to the change characteristics of the Kerr rotation angle difference. Conversely, the thickness of the second magnetic recording layer 20 may be set to a value that provides a sufficient Kerr rotation angle difference.

Further, as shown in FIG. 7, the magneto-optical disk 10 may have a structure of three or more layers. For example, in the magneto-optical disk 10, the second non-magnetic intermediate layer 58 and the third magnetic recording layer 60 are interposed between the second magnetic recording layer 20 and the non-magnetic layer 22.

In such a case, in order to reproduce the information written in the first magnetic recording layer 16, the second magnetic recording layer 20, and the third magnetic recording layer 60, laser light sources with three different wavelengths are required. However, it is possible to obtain an information recording density approximately three times that of a conventional magneto-optical disk, which has only one magnetic recording layer.

Further, as shown in FIG. 8, each of the first magnetic recording layer 16 and the second magnetic recording layer 20 is a multilayer magnetic layer without a nonmagnetic layer intervening therebetween, such as a pair of GdFe layers 62 and Tb
It can be composed of an Fe layer 64. TbFe layer 6
4 has a low Curie temperature, so information can be written even with low power. Further, it is magnetically coupled to this TbFe layer 64. Since the G d Fe layer 62 has excellent magneto-optical properties, it has the advantage that data can be written and read more easily.

Furthermore, the magneto-optical recording medium is not limited to the disc-shaped magneto-optical disk 10 as described above, but may also be tape-shaped or drum-shaped.

In addition, in the above embodiment, two laser light sources 26 and 28 are used to obtain laser beams of wavelengths λ and λ2.
However, if you use a device that oscillates at multiple wavelengths, such as a semiconductor laser array that oscillates at two different wavelengths, an argon laser device, etc., or a wavelength-tunable dye laser light source, it is possible to Alternatively, information can be reproduced using fewer laser light sources than the number of magnetic recording layers.

Furthermore, in the embodiments described above, the laser light sources 26 and 2
8 outputs laser beams with a wavelength λ1 for 8,300 people and a wavelength λ2 for 7,800 people, respectively, but these wavelengths λ1. λ2 is the wavelength of an easily available commercially available semiconductor laser element, and it goes without saying that the wavelengths of the laser beams from the laser light sources 26 and 28 are not limited thereto.

Further, in the above embodiment, the first magnetic recording layer 16 and the second magnetic recording layer 20 are made to correspond to the laser beams of wavelengths λ1 and λ2, and the changes in the Kerr rotation angle difference between the respective wavelengths λ and λ2 are For example, the information written in the first magnetic recording layer 16 and the second magnetic recording layer 20 is reproduced based on the wavelength λ1.
The sum signal of the first magnetic recording layer 16 and the second magnetic recording layer 20 is detected with a laser beam of wavelength λ2, and the difference signal of the first magnetic recording layer 16 and the second magnetic recording layer 20 is detected with a laser beam of wavelength λ2. , by subsequent signal processing, the first T11
The information stored in the magnetic recording layer 16 and the second magnetic recording layer 20 may be reproduced.

Next, an example of a magneto-optical recording device (writing device) for writing information into the first magnetic recording layer 16 and the second magnetic recording layer 2o of the magneto-optical disk 1o will be described. In the following description, parts common to those in the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

In FIG. 9, a laser beam output from a writing laser light source 66 including a collimator lens is made incident on the magneto-optical disk 1o through an objective lens 70 held by an objective lens barrel 68. The objective lens barrel 68 is attached to the main body 67 via an objective lens positioning mechanism 69, and the objective lens 70 is driven by an electromagnetic driving force generated in a cylindrical drive coil 71 fixed to the objective lens barrel 68. It is designed to be driven between two positions, a position close to the magnetic disk 1o and a position away from the magnetic disk 1o. That is, the objective lens barrel 68 is supported by the main body 67 via a leaf spring 73 so as to be relatively movable in the optical axis direction of the objective lens 7o (vertical direction in FIG. 9). Main body 6
An annular permanent magnet 75 and yoke members 77 and 79 are fixed to 7, and the drive coil 71 is positioned in a magnetic field formed between these yoke members 77 and 79. Therefore, when a drive current is supplied to the drive coil 71, the objective lens 70 is driven to a desired position according to the thickness of this drive current. Here, the depth of focus δf of the objective lens 70 is made smaller than the thickness (17,830 layers) of the nonmagnetic intermediate layer 18 in the magneto-optical disk 10.

It is known that the depth of focus δf of the objective lens 70 is given by the following formula α, δf=±4/π・λ (1/2NA)2 ・・α However, λ: Wavelength of light NA: Objective For example, the numerical aperture of the lens 70 is the wavelength λ of the laser light source 66 of this embodiment. , 8
3. , mr, oh, yo, yo, yo, 7o7゜0ka
□・; Number of mouths NA is 0.6, depth of focus δ in that case
Therefore, when the objective lens 70 is positioned at a position apart from the magneto-optical disk 10 by the drive coil 71, the laser beam emitted from the laser light source 66 is magnetic recording layer 20
The light is focused on the magneto-optical material constituting the second magnetic recording layer 20 and heated to above its Curie temperature to eliminate the perpendicular magnetization already stored. At this time, if a magnetic field is formed perpendicularly by the electromagnet 74, when the part corresponding to the beam spot heated by the laser beam cools below the cue temperature, the magnetic field will be perpendicular to the direction of the magnetic field formed by the electromagnet 74. Become magnetized. As a result, desired information is written at a desired location on the second magnetic recording layer 20. The laser beam for erasing information in the second magnetic recording layer 20 passes through the first magnetic recording layer I6, but the focal depth δf of the objective lens 70 is made sufficiently smaller than the thickness of the non-magnetic intermediate layer 18. Therefore, the first magnetic recording layer 16 can be sufficiently heated, and the information recorded on the first magnetic recording layer 16 will not be erased.

Next, as shown in FIG. 10, when the objective lens 7° is positioned close to the magneto-optical disk 10 by the driving of the drive coil 71, the laser beam emitted from the laser light source 66 is directed toward the first magnetic recording medium. The light is focused in layer 16,
As in the case described above, information is erased and new information is recorded at a desired location. At this time as well, the laser beam for erasing information in the first magnetic recording layer 16 reaches the second magnetic recording layer 20, but the focal depth δ of the objective lens 7o
Since f is smaller than the thickness of the nonmagnetic intermediate layer 18, the laser beam reaching the second magnetic recording layer 2o is diffused. As a result, the temperature of the second magnetic recording layer 20 does not reach the Curie temperature, so the information recorded on the second magnetic recording layer 2o is not erased. Note that in this embodiment, the objective lens 70 is configured to be moved toward and away from the magneto-optical disk 1o, but conversely, the objective lens 70 is configured to be moved toward and away from the objective lens 70. There is no problem. Further, since the laser beam emitted from the writing laser light source 66 used in the magneto-optical recording device is for locally heating the magnetic recording layer 16 or 20, a circularly polarized laser beam may also be used. Furthermore, monochromatic light other than laser beams may be used.

Various aspects of the magneto-optical writing device using the objective lens 70 as described above will be described below.

For example, as shown in FIG.
6 and a pair of objective lenses 70 that focus the laser light emitted from the laser light source 66 onto the first magnetic recording layer 16 and the second magnetic recording layer 20, respectively, in the height direction with respect to the magneto-optical disk 10. The relative positions of may be fixed. This has the advantage that a drive device for changing the relative distance between the objective lens 70 and the magneto-optical disk 10 is not required.

Further, as shown in FIG. 12, while the laser beam emitted from the laser light source 66 is focused on the second magnetic recording layer 20 through the half mirror 76 and the objective lens 70, the laser beam emitted from the laser light source 66 is A new laser light source 78 that emits a laser beam with a short wavelength is also provided,
The laser beam emitted from the new laser light source 78 may be reflected by the half mirror 76 and then focused on the first magnetic recording layer 16 through the objective lens 7o. According to this embodiment, the first magnetic recording layer 16 and the second
There is an advantage that the data erasing/writing location of the magnetic recording layer 20 becomes common, and a drive device for driving the objective lens 70 and the like is not required.

Further, as shown in FIG. 13, the objective lens 7° is provided at a fixed relative position in the height direction with respect to the magneto-optical disk 10, while a pair of laser light sources 80, 82 and a pair of collimator lenses 84, 86 are provided. provided, one laser light source 80
The laser beam outputted from the laser beam is focused on one magnetic recording layer, for example, the first magnetic recording layer 16, through the collimator lens 84 and the half mirror 88, and the laser beam emitted from the other laser light source 82 via the collimator lens 86 is focused on the half mirror. -88 and reflect it, □
The light may be made incident on the magneto-optical disk 10 through the objective lens 70 and focused on the second magnetic recording layer 20.

The positions of the laser light source 80.82 and the collimator lens 84° & 6 are adjusted in advance so that the laser beams output from the laser light source 80.82 are focused on the first magnetic recording layer 16 and the second magnetic recording layer 20, respectively. It is being done. In the case of this embodiment, the wavelengths of the laser beams emitted from the laser light sources 80 and 82 may be the same or different.

Further, as shown in FIG. 14, while the collimator lens 90 and the objective lens 70 are fixed at relative positions in the height direction with respect to the magneto-optical disk 10, the objective lens 70 can be fixed by moving the laser light source 92 in the optical axis direction. The focal position 70 may be selectively located on the first magnetic recording layer 16 and the second magnetic recording layer 20. That is, a screw shaft 96 rotated by a fixed drive motor 94 is screwed into a slider 98 that is movable in a direction parallel to the screw shaft 96, and is fixed to the slider 98 by rotation of the drive motor 94. The laser light source 92 is moved in the optical axis direction of the objective lens 70 and the collimator lens 90. Note that the slider 98 may be driven by a positioning device similar to the objective lens positioning mechanism 69 described above, or may be driven by an electrostrictive or magnetostrictive element.

However, in order to write information to each magnetic recording layer of a magneto-optical disk in which multiple magnetic recording layers are stacked, it is possible to write information by selecting the material of the magnetic recording layer without using the magneto-optical writing device as described above. Information can be written using a conventional magneto-optical writing device using an objective lens with a long depth of focus.

As shown in FIG. 15, the magneto-optical disk 100 has a non-magnetic intermediate layer 18 similar to the magneto-optical disk 1o described above.
The first magnetic recording layer 16 and the second magnetic recording layer 20 are sandwiched between
are laminated on the transparent substrate 12. First magnetic recording layer 1
6 and the second magnetic recording layer 20 are made of magneto-optical materials having different Curie temperatures. For example, the first magnetic recording layer 16 contains GdDy having a Curie temperature of about 120°C.
Fe is used, and the second magnetic recording layer 20 is made of GdTbFe, which has a Curie temperature of about 150°C. Above the magneto-optical disk 100, an annular coil 102 and an objective lens 104 are provided with fixed relative positions in the height direction with respect to the magneto-optical disk 100. This objective lens 1
The depth of focus δr of 04 is a large depth of focus δr similar to that of the conventional magneto-optical recirculation device, so that the first magnetic recording layer 16 and the second magnetic recording layer 20 can be heated at the same time. For example, if the wavelength of the laser beam 106 irradiated onto the magneto-optical disk 100 through the objective lens 104 is 0.83 μm, the objective lens 104
The numerical aperture NA of the objective lens 104 is set to 0.45, and the depth of focus δf of the objective lens 104 in this case is ±1 from the above equation (19).
．． It is said to be 3 μm.

That is, the total length of the depth of focus δf is 2.6 μm, and the thickness of the nonmagnetic intermediate layer 18 is 2.5 μm or less.
This is desirable. In this example, there are 17,830 people.

Therefore, when writing information to the first magnetic recording layer 16 and the second magnetic recording layer 20 at the same time, as shown in FIG. 15, a magnetic field is formed in the direction indicated by M in the figure by exciting the annular coil 102. By making the laser beam 106 incident on the magneto-optical disk lOO while
Heat to above temperature. As a result, in the heated portions of the first magnetic recording layer 16 and the second magnetic recording layer 20, the previously stored magnetization is canceled and the magnetization is perpendicularly magnetized in the direction along the magnetic field M, thereby providing information. is memorized. Reference numerals 108 and 110 in FIG. 16 respectively indicate locations that are perpendicularly magnetized by this write operation. When recording information only on the first magnetic recording layer 16, the laser beam 106 is directed onto the magneto-optical disk 10 at a desired position shown in FIG.
0. At this time, the output of the laser light source is lowered so that the condensed part of the laser beam 106 is heated to a temperature of 120° C. or higher and 150° C.
A desired recording location on the first magnetic recording layer 16 is heated so that the temperature is below .degree. The output of the laser light source can be adjusted, for example, by changing the drive current or duty ratio of the drive pulse supplied to the laser light source, or by switching the filter through which the output light passes. As a result, the perpendicular magnetization recorded up to that point is canceled and the perpendicular magnetization is performed in the direction along the magnetic field M. Recording location 112 in FIG. 18 indicates the location where information was stored according to this method. In addition, the first
If the toroidal coil 102 of FIG. 7 is energized in the opposite direction, it will be perpendicularly magnetized in the opposite direction, as shown at memory location 114. Similar operations are repeated to reverse the magnetization direction of storage location 108.

Further, in the magneto-optical disk 100, the first magnetic recording layer 1
Even if the Curie temperature of No. 6 is higher than the Curie temperature of the second magnetic recording layer 20, information is recorded in the same way. Further, even if three or more magnetic recording layers are laminated, information can be recorded in each magnetic recording layer according to the same operation as described above if the Curie temperature of each layer is different.

Although one embodiment of the present invention has been described above based on the drawings, each drawing is a schematic diagram for explaining the gist and should not be interpreted as being limited thereto. For example, although the magneto-optical disk 10 or 100 in each figure is shown in cross-section of its main part, the thickness of each layer shown in this cross-section is shown for ease of understanding and does not reflect the actual thickness. It does not indicate the ratio of thickness. In addition, in the optical systems shown in FIGS. 1, 2, 9 to 15, and 17, only important optical elements are shown symbolically, and in reality, the same functions are shown. replaced with other elements,
Other optical elements may be inserted as appropriate, or each lens, half mirror, etc. may be configured in a composite manner. In particular, the half mirrors 76 and 88 may be replaced with a guichroic mirror or a polarizing prism, and if a slight decrease in efficiency is tolerated, the guichroic mirrors 34 and 40 can be replaced with a half mirror or a combination of these and a filter. can.

Further, in the above-mentioned embodiment, for convenience of explanation, the recording device and the reproducing device are separated, but in reality, recording and reproducing are normally performed by a common device. In the embodiments of the present invention, by using a laser with a large output, the reproducing laser can also be used as a recording laser, and the optical system for reproducing can also be used as it is for recording. therefore,
In this embodiment, only the portions related to recording of the magneto-optical recording/reproducing device are taken out as a recording device, and only the portions related to reproduction are taken out and explained as a reproducing device.

The above-mentioned embodiment is merely one embodiment of the present invention, and various modifications may be made to the present invention without departing from the spirit thereof.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of an apparatus for reading information from a magneto-optical disk according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing in detail the configuration of a detection device included in the device of FIG. 1. 3 and 4 are diagrams showing combinations of magnetization directions of the magneto-optical disk of FIG. 1 for each magnetic recording layer, respectively. FIGS. 5 and 6 are diagrams showing the change characteristics of the Kerr rotation angle difference with respect to the thickness of the first T11 recording layer for each read wavelength in the combinations of magnetization directions shown in FIGS. 3 and 4, respectively. 7 and 8 are sectional views of main parts showing other embodiments of the magneto-optical disk of FIG. 1, respectively. FIG. 9 is a schematic diagram showing the configuration of a writing device for writing information into each of the magnetic recording layers laminated in the magneto-optical disk shown in FIG. 1. FIG. 10 shows another operating position of the device of FIG. 9; 11 to 14 are schematic diagrams showing other configurations of the writing device for writing information to each of the magnetic recording layers stacked on the magneto-optical disk shown in FIG. 1. 15 and 17 are diagrams illustrating other configuration examples of the magneto-optical disk of FIG. 1 and the operation of recording information on each of the magnetic recording layers laminated therein, and FIGS. FIG. 18 is a diagram showing locations written as a result of the information writing operations of FIGS. 15 and 17. 10: Magneto-optical disk (magneto-optical recording medium) 18: Non-magnetic intermediate layer (non-magnetic layer) Fig. 1 Fig. 5 Fig. 6 Fig. 10) Fig. 8 Fig. 9 Fig. 10 Fig. 15 @16 Fig. 17 November 28, 1982 1. Display of the case 1988 Patent Application No. 228743 2. Name of the invention Magneto-optical recording medium 3. Person making the amendment Relationship with the case Patent application Person Name (526) Brother Industries, Ltd. 4, Agent ■450 Detailed Description of the Invention in the Specification Column 6, Contents of Amendment (1) "
"Magneto-optical medium" is corrected to "magneto-optical recording medium." (2) On page 4, line 8, "magnetic disk" is corrected to "magneto-optical disk." (3) On page 4, line 15, "by" is corrected to "wa". (4) rcooJ on page 13, line 13
Correct to J. (5) The contents of formula (14) and the proviso on page 16 of the same are corrected as shown in the attached sheet. (6) In the bottom line of page 17, (7) in the bottom line of page 19, and (8) in the second line of page 25, ``separate from'' is corrected to ``approach.'' (9) On page 26, line 3 of the same page, change “approaching” to “separating from 1 force”
Correct to. α0) On page 28, line 5, add the following sentence after "Mora 1, 1°" without changing the G or gusset. ``In other words, the chromatic aberration of the objective lens 70 is used to change the focal length depending on the wavelength.''
Top・ ・ ・ ・ ・ ・ ・(14) λ)n, (λ: Wavelength)

Claims (1)

[Claims] 1. A magneto-optical recording medium, characterized in that a plurality of magneto-optical recording layers are laminated via non-magnetic layers, and information can be recorded and reproduced separately in each of the magneto-optical recording layers.