JPS61107553A - Optomagnetic reproducing device - Google Patents

Abstract

PURPOSE:To reproduce information recorded on each optomagnetic recording layer individually by splitting a laser beam having a wavelength corresponding to the optomagnetic recording layer and detecting individually a Kerr rotation angle difference. CONSTITUTION:The thickness of the 1st magnetic recording layer 16 is selected preferably between 100Angstrom -120Angstrom , a Kerr rotation angle difference deltathetak of >=0.3 deg. corresponds to, e.g., information [1] and the difference of <=0.3 deg. corresponds to, e.g., information [0], then the information of the 1st magnetic recording layer 16 is reproduced with a laser ray of wavelength 8,300Angstrom and the information of the 2nd magnetic recording layer 20 is reproduced by a laser ray of wavelength 7,800Angstrom . Thus, the Kerr rotation angle difference corresponding to the vertical magnetizing direction stored in the 1st magnetic recording layer 16 is obtained surely by the reflected light of wavelength lambda1 from the optomagnetic disc 10. Thus, a signal corresponding to a data stored in the 1st magnetic recording layer 16 is obtained surely. Similarly, a signal corresponding to the data stored in advance in the 2nd magnetic recording layer 20 is obtained surely even in a reflected light of wavelength lambda2 from the optomagnetic disc 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for recording information written in each magneto-optical recording layer from a magneto-optical recording medium consisting of a plurality of magneto-optical recording layers laminated with a non-magnetic layer interposed therebetween. The present invention relates to a magneto-optical reproducing device.

Prior Art A magneto-optical reproducing device is known in which information written by locally magnetizing a magneto-optical material in the perpendicular direction, which has spontaneous magnetization and allows light to pass therethrough, is read out using the magneto-optic effect. ing. Generally, in such a device,
The use of the Kerr effect or Faraday effect, in which when linearly polarized light is incident parallel to the magnetization direction of a magneto-optical material, the plane of vibration (polarization plane) of the reflected or transmitted light rotates in relation to the direction of magnetization. The information written on the magneto-optical material is read out. Such magneto-optical reproducing devices use magneto-optical recording media to which a thin layer of magneto-optical material is fixed. It is desirable to prepare a magneto-optical recording medium in which a plurality of magneto-optical recording materials are laminated with a non-magnetic intermediate layer interposed therebetween, and to read out information written in each of the magneto-optical recording layers made of each magneto-optical material for each layer.

Problems to be Solved by the Invention However, as mentioned above, when attempting to read information based on the Kerr rotation angle of light transmitted through a magneto-optical material using the Kerr effect or Faraday effect, it is difficult to read information based on the Kerr rotation angle of light transmitted through a magneto-optical material. It was unclear whether the Kerr rotation angle occurred, and it was difficult to read out information for each 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 magneto-optical recording medium, which is made up of a plurality of magneto-optical recording layers laminated via a non-magnetic layer, is irradiated with laser beams of different wavelengths. The reason is that each piece of recorded information is played back separately.

By doing this, a stable Kerr rotation angle difference can be obtained regardless of the magnetization direction of one magneto-optical recording layer and the magnetization direction of other magnetic recording layers for each laser beam having a different wavelength. Therefore, by separating the laser beams with wavelengths corresponding to the magneto-optical recording layers and individually detecting the Kerr rotation angle difference, it is possible to reproduce the information recorded on each magneto-optical recording layer separately.

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 2°, and is made of a transparent nonmagnetic material, such as aluminum nitride (A7!N),
Silicon oxide (S i O), silicon dioxide (Si
O□), metal silicon (Si), or the like is used.

The nonmagnetic layer 14.22 prevents the first magnetic recording layer 16 and the second magnetic recording layer 20 from chemical changes (oxidation, etc.).
A thickness of about 0 per person is adopted for each. However, the first
It may be omitted if chemical changes in the magnetic recording layer 16 and the second magnetic recording layer 20 are difficult to predict. 1f! with the nonmagnetic intermediate layer 1B sandwiched between the nonmagnetic layers 14 and 22! ! The optical recording layer 16 and the 2'M1 optical recording layer 20 are interposed, and in this embodiment, the first WL optical recording layer 16 is 110
The upper right second magnetic recording layer 20 has a thickness of about 800 layers, and the upper right nonmagnetic intermediate layer 18 has a thickness of about 17,830 layers. 1st
Magnetic recording [16 and the second magnetic recording layer 20 are made of a magneto-optical material with a remarkable magneto-optical effect, such as amorphous GdTbFe,
Materials such as TbFe, TbFeCo, GdCo, GdDyFe, polycrystalline MnCuBi, single crystal 'l'bFeos, rare earth iron garnet, etc. may be used. In this embodiment, G d T b Fe is adopted. Further, the non-magnetic intermediate layer 1i18 may 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, S i Oz, S iO.

It is preferable to sequentially stack SiO□. 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 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 1o. In this way, the objective lens 38 and the like are moved in parallel in the horizontal direction. The readout laser light sources 26 and 28 emit linearly polarized laser beams of different wavelengths toward the chromic mirror 34 through collimator lenses 30 and 32, respectively. In this embodiment, the wavelength λ 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 gicroic mirror 40, where the wavelength λ
1 laser beam passes through.

On the other hand, the laser beam of wavelength λ2 is reflected and separated. The laser beam with wavelength λ1 and the laser beam with wavelength λ2 are received by first detection device 42 and second detection device 44, respectively.

The first detection device 42 and the second detection device 44 are
It detects the Kerr rotation angles of the laser beam with wavelength C and the laser beam with wavelength λ2, respectively, and based on the Kerr rotation angle difference, the first magnetic recording layer 16 and the second magnetic recording layer 20 are preliminarily magnetized by perpendicular magnetization. The recorded information 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. The planes of polarization of analyzers 48 and 50 are orthogonal to each other and each inclined by 45'' to the plane of polarization 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 the photodiodes 52 and 54 are supplied to a differential amplifier 56, and the differential amplifier 56 outputs a signal corresponding to the information stored in the first magnetic recording layer 16. This cancels out the noise. Here, the laser light source 2
6 and 28 use a semiconductor laser light source or external resonant laser light source that outputs a linearly polarized laser beam, but when using an internal resonant laser light source that outputs a circularly polarized laser beam, it is necessary to pass the laser beam through a polarizer. It is sufficient if the laser beam is emitted.

The regeneration effect of this embodiment will be explained below. According to the magneto-optical reproducing device 11, the first magnetic recording layer 1°6 and the second magnetic recording layer N2 are laminated with each other with the non-magnetic intermediate layer 18 in between.
Each 0 is 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(al) and (bl), when the second magnetic recording layer 20 is magnetized in the N direction and the S direction, the second magnetic recording layer 16 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 layer 20 must be detected.

After various studies, the present inventor found that the Kerr rotation angle of the reflected light is the difference in the Kerr rotation angle of the reflected light related to four types of combinations of the magnetization directions of the first magnetic recording layer 16 and the second magnetic recording layer 20. changes with different characteristics as the thickness of one magnetic recording layer changes, and when the thickness of one magnetic recording layer is set to a specific thickness during such Kerr rotation angle difference change characteristics, the magnetic recording of the other It was discovered that the Kerr rotation angle difference is determined only in relation to the magnetization direction of one magnetic recording layer, regardless of the magnetization direction of the layers, and the present example was constructed based on this knowledge. .

That is, according to the inventor's simulation, for a laser beam of wavelength λ1 (8300 people), as shown in FIG. 5, when the thickness of the first magnetic recording layer 16 is around 100 people, the second magnetic recording layer 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 magnetic recording layer 1
If the magnetization direction of 6 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, 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.
Each case is shown below. 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. Regarding the laser beam of wavelength λ2 (7,800 people), as shown in FIG. 6, when the thickness of the first magnetic recording layer 16 is around 120 people, the second A stable Kerr rotation angle difference corresponding to the magnetization direction of the magnetic recording layer 20 can be obtained.

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 correspond to the information "l" when the Kerr rotation angle difference δθ is 0.3' or more, and the information rOJ when δθ1 is 0.3° or less, 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.

In this way, according to this embodiment, data stored in advance in the first magnetic recording layer 16 and the second magnetic recording layer 20 are respectively retrieved. In addition, this dramatically increases the information recording density per unit area and the information storage amount per disk compared to conventional magneto-optical disks, which have only one magnetic recording layer. There is.

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. A component E3F of the electric field of this reflected light that has the same polarization plane as the incident light
The Kerr rotation angle ψ is obtained as shown in equation (1) based on the component Ex having a plane of polarization 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), Here, b and bat are the following equation (5), (
If it is expressed as a complex representation like 61, then bll"bll"+j l)t+"...(5
) bz+= bit ' + j t)z+ ”
(6) The electric field magnitudes 1Exl and 1Eyl are as shown in the following equations.

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

bZl” (a41aff! a43a31)
"'αψHowever, D""a++aiz al
:1a21...'α1). (9), Q
Each aiμ used in OI, Ql) can be expressed as each component of a 4×4 matrix as shown in the following equation.

(atJ) = (MAL) - (MA21) ・(
MA31] ・(MA41)・(MA51)・(MA6
1) ....θ≧Each matrix in equation (12) is expressed as shown in equations (to)) to (18) under the following conditions.

no: refractive index of the transparent substrate 12 nl and dl: refractive index and film thickness of the nonmagnetic layer 14 n2 and d2: refractive index and film thickness of the first magnetic recording layer 16 Hn3 and d3: refractive index of the nonmagnetic intermediate layer 18 and film thicknesses n4 and d4: refractive index and film thickness n5 and d of the second magnetic recording layer 20,: refractive index and film thickness nh of the nonmagnetic layer 22: refractive index δ 0 of the reflective layer 24,
工 i＾− １−） へ＜:１ −くΣ Σ ド F−１１１〕 １１＜ , −3Σ 9 − prefecture − ゛ ° + ΣII
j II=1 kube2
ΣIt should be noted that the characteristics shown in FIGS.
d T b Fe Since this is the characteristic when 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, so the first magnetic The thickness of the recording layer 16 is also set to an optimum value according to the change characteristics of the Kerr rotation angle difference. On the contrary, the second
The thickness of the 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 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, for example, a pair of 2TbF layers on a pair of GdFe layers 62.
It can be composed of an e-layer 64. TbFe layer 64
Since the Curie temperature is low, information can be written even with low power. Furthermore, since the GdFe layer 62 magnetically couples with the TbFe layer 64 and has excellent optical characteristics, 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, Information can be reproduced using one laser light source or a number less 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. 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 10 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 designed to be driven between two positions: a position close to the magnetic disk 10 and a position remote from the magnetic disk 10. 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 70 (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 the 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 δr of the objective lens 70 is made smaller than the thickness (17,830) of the non-magnetic intermediate N18 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 09), δf=±4/π・λ (1/2NA)''...(1
9) However, λ: Wavelength of the light beam NA: Numerical aperture of the objective lens 70 For example, the wavelength λ of the 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 20
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 information in the first magnetic recording layer 16 reaches the second magnetic recording layer 20, but the focal depth δ of the objective lens 70
Since f is smaller than the thickness of the non-magnetic intermediate layer 18, the laser light 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, so the information recorded on the second magnetic recording layer 20 is not erased. In the present embodiment, the objective lens 70 is configured to be moved toward and away from the magneto-optical disk 10, but conversely, it is configured such that the magneto-optical disk 10 is moved toward and away from the objective lens 70. There is no problem even if it is done. 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 magneto-optical 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 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 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 focused on the second magnetic recording layer 20''. 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. According to this embodiment, the first magnetic recording layer 16 and the second magnetic recording layer 20 have a common data erasing/writing location, and a drive for driving the objective lens 70, etc. This has the advantage that no equipment is 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 and 82 and a pair of collimator lenses 84 and 86 are provided. , one laser light source 80
The laser beam outputted from the laser beam source 82 is focused on one magnetic recording layer, for example, the first TIfI magnetic recording layer 16, through the collimator lens 84 and the half mirror 88, and the laser beam emitted from the other laser 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 positions of the laser light sources 80 and 82 and the collimator lenses 84 and 86 are adjusted in advance so that the laser beams output from the laser light sources 80 and 82 are focused on the first magnetic recording layer 16 and the second M1 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 point 70 may be selectively located on the first magnetic recording layer 1.6 and the second magnetic recording layer 20. That is, a screw shaft 96 rotated by a drive motor 94 whose position is fixed.
is screwed together with a slider 98 that is movable in a direction parallel to the screw shaft 96, and a laser light source 92 fixed to the slider 98 is rotated by the rotation of a drive motor 94, and the light from the objective lens 70 and the collimator lens 90 is It is moved in the axial direction. 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 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
The magnetic recording layer 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 has a Curie temperature of 120°C.
GdDyFe with a Curie temperature of about 150° C. is used for the second magnetic recording layer 20.
e is used. 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. The focal depth δf of this objective lens 104 is the same as that of a conventional magneto-optical writing device, and the first magnetic recording layer 16 and the second magnetic recording layer 2
0 can be heated at the same time. for example,
When the wavelength of the laser beam 106 irradiated onto the magneto-optical disk 100 through the objective lens 104 is 0.83 μm, the numerical aperture NA of the objective lens 104 is 0.45. Depth of focus δf
is set to be ±1.3 μm from the above equation θ9).

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 Example 7. Yo, □830 eh, ah
... ;ru.

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 enter the magneto-optical disk 100 while doing so, the first!
The FF recording layer 16 and the second TJi recording layer 20 are heated to, for example, 150° C. or higher. 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 information is stored by being perpendicularly magnetized in the direction along the magnetic field M. be done. 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 17th
A laser beam 106 is made incident on the magneto-optical disk 100 at a desired position shown in the figure. At this time, the output of the laser light source is reduced so that the condensing portion of the laser beam 106 becomes 120
A desired recording location on the first magnetic recording layer 16 is heated to a temperature of 150° C. or higher. 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 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 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 to be described 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 an embodiment of the present invention, and is a schematic diagram showing the configuration of a magneto-optical reproducing 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 FIG. 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 into each of the magnetic recording layers laminated on the magneto-optical disk shown in FIG. 1, respectively. 15th
17 and 17 are diagrams illustrating another example of the structure of the magneto-optical disk in FIG. 1 and the operation of recording information on each of the magnetic recording layers laminated therein, respectively.
18 and 18 are diagrams showing locations written as a result of the information writing operations shown in FIGS. 15 and 17. 10: Magneto-optical disk (magneto-optical recording medium) 11: Magneto-optical reproducing device (Fig. 1, Fig. 5, Fig. 6, Fig. 9, Fig. 10, Fig. 15, Fig. 16, Fig. 17)

Claims (1)

[Claims] A magneto-optical recording medium consisting of a plurality of magneto-optical recording layers laminated with non-magnetic layers interposed therebetween is irradiated with laser beams of different wavelengths to separately record the information recorded in each of the magneto-optical recording layers. A magneto-optical reproducing device characterized by being adapted to perform reproduction.