JPS61107503A - Photomagnetic recording device - Google Patents

Abstract

PURPOSE:To record information by collecting a laser beam outputted from a recording laser device only to one layer selected from photomagnetic layers. CONSTITUTION:The 1st magnetic recording layer 16 and the 2nd magnetic recording layer 20 are heated to a temperature, e.g., >= 150 deg.C by making a laser ray 106 incident on an photomagnetic disc 100 while forming a magnetic field in the direction M through the excitation of a ring coil 102. As a result, the magnetization stored so far is erased and locations 108, 110 in a direction along the magnetic field M are magnetized vertically and the information is stored. In recording the information to the 1st magnetic recording layer 16 only, the laser ray 106 is made incident on the photomagnetic disc 100. In this case, the temperature of the spot of laser ray 106 is between 120-150 deg.C by decreasing the output of the laser ray source so as to heat the desired recording location on the 1st magnetic recording layer 16.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a magneto-optical recording medium comprising a plurality of magneto-optical recording layers laminated with a non-magnetic layer interposed therebetween, in which information is recorded in each magneto-optical recording layer. The present invention relates to a magneto-optical recording device.

Prior Art and Problems Magneto-optical reproduction uses the magneto-optic effect to read out information written by locally magnetizing a magneto-optical material that has spontaneous magnetization and a large coercive force in the perpendicular direction. Devices are known. Generally, in such devices, when linearly polarized light is incident on a magneto-optical material parallel to the direction of magnetization, the plane of vibration of the reflected or transmitted light rotates in relation to the direction of magnetization. The information written on the magneto-optical material is read by using the Faraday effect.In such devices, a magneto-optical recording medium to which a layer of magneto-optical material formed in the form of a thin film is fixed. However, in order to improve the information recording density per unit area, a magneto-optical recording medium is prepared in which magneto-optical materials are laminated with a non-magnetic intermediate layer interposed between them. It is desirable to write information separately to each magneto-optical recording layer.

Means for Solving the Problems The present invention has been made against the background of the above circumstances.
The gist of this is that a recording laser is applied to only one of the magneto-optical recording layers of the magneto-optical recording medium, which is composed of a plurality of magneto-optical recording layers laminated via non-magnetic layers. The reason is that information is recorded by condensing a laser beam output from a laser beam.

In this way, the laser beam is focused on only one of the plurality of magneto-optical recording layers to selectively heat and record, thereby dramatically increasing the recording density. Information can be recorded on each magneto-optical recording layer of the magneto-optical recording medium. Since the laser beam focused on only one layer is dispersed in the other magneto-optical recording layers, no information is erased or recorded in the other layers.

It is desirable that the depth of focus of the objective lens that focuses the laser beam is smaller than the thickness of the nonmagnetic layer sandwiched between the magneto-optical recording layers. This is to prevent other magneto-optical recording layers from being heated when the light is focused on one magneto-optical recording layer and heated.

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 N16. 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 14.22.1 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 (
A I N), silicon oxide (S i O), silicon dioxide (Sio2), metallic silicon (Si), or the like is used. The nonmagnetic layers 14 and 22 prevent the first magnetic recording layer 16 and the second magnetic recording layer 20 from chemical changes (oxidation, etc.), and in this embodiment, thicknesses of about 1421 and about 1336 are respectively adopted. has been done. However, the first magnetic recording layer 16 and the second magnetic recording layer 2
It may be omitted if a chemical change of 0 is difficult to predict.

A first magnetic recording layer 16 and a second magnetic recording layer 20 sandwiching a nonmagnetic intermediate layer 18 are interposed between the nonmagnetic layers 14 and 22. In this embodiment, the first magnetic recording layer 16 is
The second magnetic recording layer 20 has a thickness of about 10 layers, the thickness of the second magnetic recording layer 20 has a thickness of about 800 layers, and the non-magnetic intermediate layer 18 has a thickness of about 17,830 layers.

The first magnetic recording layer 16 and the second TJ11 magnetic recording layer 20 are made of a magneto-optical material having a remarkable magneto-optical effect, such as amorphous Gd.
TbFe, TbFe, TbFeCo, GclCo, Gd
DyFe, polycrystalline MnCuB1. Single crystal TbFeO
Materials such as S, rare earth iron garnet, etc. may be used. In this embodiment, GdTbFe is used. Further, the non-magnetic intermediate layer 18 only needs to be made of a light-transmitting non-magnetic material, and the same material as the non-magnetic layer 14 may 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 laminate the layers. 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 nonmagnetic layer 22 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 an IT retention 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 IO. 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 gicroic mirror 34 through collimator lenses 30 and 32, respectively. In this example, the wavelength λ1 of the laser light source 26 is 8300 people, and the wavelength λ2 of the laser light source 28 is 7800 people. The guichroic mirror 3-4 allows the laser beam of wavelength λ1 to pass through, while
By reflecting the laser beam of wavelength λ2, a combined laser beam of wavelengths λ1 and λ2 is made incident on the magneto-optical disk 10 through the half mirror 36 and the objective lens 38. The combined laser beam reflected from the magneto-optical disk 10 passes through an objective lens 38 and a half mirror 36.
The light reaches the guichroic mirror 40, where the laser beam with wavelength λ1 is passed through, while the laser beam with wavelength λ2 is reflected and separated. The laser beam with a wavelength λ1 and the laser beam with a wavelength λ2 are transmitted to a first detection device 42 and a second detection device 44, respectively.
can be accepted.

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 zero polarization planes are orthogonal to each other and 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, as the laser light sources 26 and 28, a semiconductor laser light source or an external resonant laser light source that outputs a linearly polarized laser beam is used, but when an internal resonant laser light source that outputs a circularly polarized laser beam is used. For this purpose, the laser beam may be emitted through a polarizer.

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

In order to read information independently from each magnetic recording layer 16 and 20, as shown in FIGS.
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,
Furthermore, as shown in FIGS. 4(a) and (bl), when the second magnetic recording layer 20 is magnetized in the N direction and the S direction, the second magnetic recording layer 20 is magnetized regardless of the magnetization direction in the first magnetic recording layer 16. The Kerr rotation angle difference corresponding to the magnetization direction of the recording layer 20 must be detected.

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 T61 magnetic recording layer 20 is S and N, respectively. Also, S/N
and S/S indicate that the magnetization direction of the first magnetic recording layer 16 is the S direction, and the magnetization directions of the second magnetic recording layer 20 are the N direction and the S direction. Also, the wavelength λ2 (7
Regarding the laser beam of 800 people), as shown in FIG. 6, the first T! When the thickness of the magnetic recording layer 16 is around 120 mm, the Kerr rotation angle difference corresponding to the magnetization direction of the second magnetic recording layer 20 can be stably obtained regardless of the magnetization direction of the first magnetic recording layer 16.

As a result, the thickness of the first magnetic recording layer 16 is adjusted to be around 100 and 120 people, preferably 100 to 120 people.
If you choose among 20 people, and if the Kerr rotation angle difference δθ is 0.36 or more corresponds to the information "■", and if δθ3 is 0.3' or less corresponds to the information "0", the wavelength is 83.
The information in the first magnetic recording layer 16 is reproduced by a laser beam with a wavelength of 7800, and the information in the second magnetic recording layer 2 is reproduced with a laser beam having a wavelength of 7800.
0 information is played.

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,
The Kerr rotation angle difference corresponding to the perpendicular magnetization direction stored in the first magnetic 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 Maxwell'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. The Kerr rotation angle ψ is determined by equation (1) based on the component Ey of the electric field of this reflected light, which has the same polarization plane as the incident light, and the component Ex, which has 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=tan 2αcoo (φ−θ)...
(1) However, in equation (1), if the complex is expressed as
z+=t)z+'+j bz+"...16
1 The magnitude of the electric field lEx! , 1Eyl is as shown in the following equation.

The above b11 and b21 are defined as in the following formula.

b++= (az+azz az3a:u)
・ ・ ・(91D bZI= (a41a33 a41a31)
” 'α [However, D=alla33 a+ia
i+ ”・(+1).(9), α(It
, each aij used in (o) is 4×4 as shown in the following equation
It can be represented as each element of a matrix.

(atJ) = (MAI) ・(M^21), ・
(MA31) ・(MA41)・[Gate A51]・(MA
61) ...(12) Each matrix in the equation (1) is expressed as shown in the equations (13) to θB) under the following conditions.

no: refractive index nl and d of the transparent substrate 12;: refractive index and film thickness n2 and d2 of the nonmagnetic layer 14: refractive index and film thickness n and d3 of the first magnetic recording layer 16; refractive index,
and film thickness n4 and d4
: refractive index and film thickness n and d5 of the second magnetic recording layer 20 : refractive index and film thickness n6 of the non-magnetic layer 22 : refractive index of the reflective layer 24 : dielectric constant tensor of the first magnetic recording layer 16 : second Dielectric constant tensor demand of magnetic recording layer 20
3-
] To, l j
Σ ni-morning-kuΣ ro Ri II
j II-Yo
- Please note that the characteristics shown in Figures 5 and 6 are only for the first magnetic recording layer 1.
6 is GdTbFe, and if other magneto-optical materials are used, the obtained Kerr rotation angle difference and the change characteristics with respect to the thickness of the first magnetic recording layer 16 will be different. The thickness of 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 that is about three times that of a conventional magneto-optical disk that does not have an INL or 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, for example, a pair of GdFe layers 62 and 2TbFe layers.
It can be comprised of layer 64. Since the T b Fe layer 64 has a low Curie temperature, information can be written even with low power.

Further, GdFe layer 64 is magnetically coupled to this TbFe layer 64.
Since the layer 62 has excellent 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 λ1 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 λ of 8,300 people and a wavelength λ2 of 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 1
6 and the second magnetic recording layer 20 are made to correspond to laser beams with wavelengths λ1 and λ2, and the respective wavelengths λ1 and λ
The first magnetic recording layer 1 is
6 and the second magnetic recording layer 20, for example, the sum signal of the first magnetic recording layer 16 and the second magnetic recording layer 20 is reproduced with a laser beam of wavelength λ1. At the same time, the first magnetic recording layer 16 and the second magnetic recording layer 2 are detected using a laser beam of wavelength λ2.
The difference signal of 0 may be detected and the information stored in the first magnetic recording layer 16 and the second magnetic recording layer 20 may be reproduced through subsequent signal processing.

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 20 of the magneto-optical disk IO 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 10 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 driven between two positions, a position close to the magnetic disk 10 and a position away from the magnetic disk 10.
1 Sea urchins are turning. 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). An annular permanent magnet 75 and yoke members 77 and 79 are fixed to the main body 67, 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 magnitude 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 IO.

It is known that the depth of focus δf of the objective lens 70 is given by the following equation (19), δf = + 4 / π, λ (1/2NA)"
...Q9) However, λ: Wavelength of light NA: Numerical aperture of objective lens 70 For example, wavelength λ of laser light source 66 in this embodiment is 0.8
3 μm, the numerical aperture NA of the objective lens 70 is 0.6, and the depth of focus δf in that case is 50.7 μm.
It is said that Therefore, when the objective lens 70 is positioned at a position away from the magneto-optical disk 10 by the drive coil 71, the laser beam emitted from the laser light source 66 is focused on the second magnetic recording layer 20, and the second magnetic recording layer The magneto-optical material constituting layer 20 is heated 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 down to below the Curie temperature, the magnetic field will be perpendicular to the direction of the magnetic field formed by the electromagnet 74. Become magnetized. As a result, the second magnetic recording layer 2o
The desired information is written to the desired location. The laser beam for erasing information in the second magnetic recording layer 20 passes through the first magnetic recording layer 16, 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 70 is positioned close to the magneto-optical disk 10 by driving the drive coil 71, the laser beam emitted from the laser light source 66 is directed to the first magnetic recording layer. The light is focused at 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 the information in the first VA recording layer 16 reaches the second magnetic recording layer 20, but the depth of focus δr of the objective lens 70 is smaller than the thickness dimension of the non-magnetic intermediate layer 18. Therefore, the laser beam reaching the second magnetic recording layer 20 is diffused. As a result, the temperature of the second magnetic recording layer 20 does not reach the Curie temperature.
The information recorded in will not be deleted. In this embodiment, the objective lens 70 is configured to approach and be separated from the magneto-optical disk 10;
10 may be configured to be moved closer to and further away from the objective lens 70. 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. 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 beam 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 1° 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 shorter wavelength is provided, and after reflecting the laser beam emitted from the new laser light source 78 at the half mirror 76, it passes through the objective lens 70 and hits the first magnetic recording layer 16. It is also possible to condense the light. According to this embodiment, the first magnetic recording layer 1
6 and the second magnetic recording layer 20 are common, and there is an advantage that a drive device for driving the objective lens 70 and the like is not required.

Further, as shown in FIG. 13, an objective lens 70 is provided at a fixed position relative to the magneto-optical disk 10 in the height direction, and a pair of laser light sources 80.82 and a pair of collimator lenses 84.86 are 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, the light may be incident on the magneto-optical disk 10 through the objective lens 70, and may be focused on the second magnetic recording layer 20. The laser light sources 80.82 and the collimator lens 8 are arranged so that the laser beams output from the laser light sources 80.82 are focused on the first magnetic recording layer 16 and the second magnetic recording layer 20, respectively.
The position of 4°86 has been adjusted in advance. In the case of this embodiment, the wavelengths of the laser beams emitted from the laser beams ago and s2 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 laminated, 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 10 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
As the focal depth δf of 04, a large focal depth δf similar to that of the conventional magneto-optical writing device is used, 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 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 non-magnetic intermediate layer 18' is 2.5 μm or less.6.
．． 7 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. By exciting the laser beam 102, a magnetic field is formed in the direction indicated by M in the figure, and the laser beam bi 10
By making s incident on the magneto-optical disk 100, the first magnetic recording layer 16 and the second magnetic recording layer 20 are
Heat to 50°C or higher. As a result, the first magnetic recording layer 16
In the heated portion of the second magnetic recording layer 20, the previously stored magnetization is canceled and information is stored by being perpendicularly magnetized in the direction along the magnetic field M. 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, a laser beam 106 is made incident on the magneto-optical disk 100 at a desired position shown in FIG. At this time, the output of the laser light source is lowered so that the condensed part of the laser beam 106 is at a temperature of 120° C. or more and 150" C or less, thereby heating the desired recording location on the first magnetic recording layer 16. The output 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. The previously perpendicular magnetization is canceled and the perpendicular magnetization occurs in the direction along the magnetic field M. Recording location 112 in FIG. 18 indicates a location where information is stored according to this method. If 102 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 memory 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 the magnetic recording layers are stacked on a three-layer plate, information can be recorded on 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 dichroic mirrors or polarizing prisms, and the dichroic mirrors 34 and 40 may be replaced with half mirrors or a combination of these and filters, provided that some reduction in efficiency is tolerated.

Further, in the above embodiment, for convenience of explanation, the recording device and the reproducing device were separated, but in reality, recording and reproducing are normally performed by a common device. In the embodiment of the present invention, by using a laser with a large output, the reproducing laser can also be used as a recording laser, so that the reproducing laser can also be used as a recording laser, and the optical system can also be used for reproducing as it is for recording. It can also be used for personal purposes.

Therefore, in this embodiment, only the portions related to recording of the magneto-optical recording/reproducing apparatus 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. 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 magnetic 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 a writing device according to an embodiment of the present invention, which writes information to 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 other embodiments of the present invention, and are schematic diagrams showing a writing device for writing information to each of the magnetic recording layers laminated on the magneto-optical disk shown in FIG. 1. . Figures 15 and 17 are
16 and 18 are diagrams illustrating another configuration example of the magneto-optical disk shown in the figure and the operation of recording information on each of the magnetic recording layers laminated therein; FIGS.
18 is a diagram showing locations written as a result of the information writing operations of FIGS. 5 and 17; FIG. 10: Magneto-optical disk (magneto-optical recording medium) 18: Non-magnetic intermediate layer (non-magnetic layer) 66.78, 80.82, 92: Laser light source (recording laser device) Applicant Brother Industries, Ltd. Figure 1 Figure 5 Figure 6 Figure 9 Figure 10 Figure 15 Figure 16 Figure 17 Procedural master's letter (spontaneous) November 28, 1980 To Mr. Manabu Shiga, Commissioner of the Patent Office 1. Indication of the case 1988 Patent side No. 228742 2, Name of the invention Magneto-optical recording device 3, Person making the amendment Relationship to the case Name of patent applicant (526) Brother Industries, Ltd. 4, Agent ■450 Detailed explanation of the invention in the specification Column B, Contents of Amendment (1) "Magnetic optic material" in lines 6 and 7 of page 2 of the specification is corrected to "magnetic optic material". (2) Correct "magnetic disk" in line 17 of page 4 to "magneto-optical disk." (3) Correct "by" to "wa" in line 4 of page 5. (4) “cooJ to rcosJ” on page 14, line 2.
Correct. (5) The contents of page 17, formula 04) and the proviso will be corrected as shown in the attached sheet. (6) In (7) on the bottom line of page 18, (8) on the bottom line of page 20, and in the second line of page 26, "separate from" should be corrected to "approach". (9) In the third line of page 27, ``approaching'' is corrected to ``separating from''. α0 Add the following sentence without a line break next to "Moyoi." on page 29, line 5 of the same page. ``In other words, the chromatic aberration of the objective lens 70 is used to change the focal length depending on the wavelength.''

Claims (2)

[Claims] (1) Among the magneto-optical recording layers of a magneto-optical recording medium formed by laminating a plurality of magneto-optical recording layers via a non-magnetic layer,
1. A magneto-optical recording device characterized in that information is recorded by focusing a laser beam output from a recording laser device only on a selected layer. (2) The magneto-optical recording device according to claim 1, wherein the thickness of the nonmagnetic layer is set to be larger than the depth of focus of the objective lens of the recording laser device.