JPH0666095B2 - Magneto-optical recording device - Google Patents

Description

Description: TECHNICAL FIELD The present invention is a magneto-optical recording medium formed by laminating a plurality of magneto-optical recording layers with a non-magnetic layer in between, and records information in each magneto-optical recording layer. The present invention relates to a magneto-optical recording device.

2. Description of the Related Art Magneto-optical reproducing apparatus adapted to read information written by locally magnetizing a magneto-optical material having spontaneous magnetization and large coercive force in a vertical direction by utilizing a magneto-optical effect. It has been known. Generally, in such a device, the Kerr effect or the Faraday effect is used, in which when the linearly polarized light is incident parallel to the magnetization direction of the magneto-optical material, the vibrating surface of the reflected light or the transmitted light rotates in relation to the direction of the magnetization. By doing so, the information written on the magneto-optical material is read out. In such an apparatus, a magneto-optical recording medium to which a layered magneto-optical material formed in a thin film is fixed is used. In order to improve the information recording density per unit area, the magneto-optical material is made non-magnetic. It is desired to prepare a magneto-optical recording medium formed by stacking via an intermediate layer and write information individually into each magneto-optical recording layer composed of each magneto-optical recording material.

Means for Solving Problems The present invention has been made against the above circumstances.
The gist thereof is a magneto-optical recording device for recording information by irradiating a laser beam on a magneto-optical recording medium in which at least two magneto-optical recording layers are laminated via a non-magnetic layer, A laser light source for outputting the laser beam, a focusing means for focusing and irradiating the laser beam output from the laser light source on the magneto-optical recording layer, and only one selected layer of the magneto-optical recording layer Focus position control means for controlling the focus position so as to be held within the depth of focus of the light collecting means.

With this configuration, the laser beam output from the laser light source is focused and irradiated onto the magneto-optical recording layer by the focusing means, and only one layer selected by the focus position control means is focused. Since the focus position is controlled so as to be maintained within the depth of focus of each of the magneto-optical recording layers of the magneto-optical recording medium, only the one layer is selectively heated and recorded to dramatically increase the recording density. Information can be recorded in. Since the laser beam is dispersed in the other magneto-optical recording layer which is not located within the depth of focus, information is not erased and recorded in other layers.

It is desirable that the depth of focus of the focusing means for focusing the laser beam is smaller than the thickness of the non-magnetic layer sandwiched by the magneto-optical recording layers. By doing so, since two or more magneto-optical recording layers cannot be held within the depth of focus at the same time, for example, when recording information on a magneto-optical recording medium composed of three or more magneto-optical recording layers. Also, even if the focal position is slightly deviated, it is possible to reliably focus the light on one magneto-optical recording layer and heat it, and the other magneto-optical recording layers are not heated.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a magneto-optical reproducing device 11 which is an example of a device for reading information from a disk-shaped magneto-optical disk 10 as a magneto-optical recording medium. In the figure, magneto-optical disk
10 is a non-magnetic layer 14, a first magnetic recording layer 16,
Non-magnetic intermediate layer 18, second magnetic recording layer 20, non-magnetic layer 22, reflective layer 2
4 are sequentially laminated by a known fixing means such as vapor deposition and sputtering. Transparent base 12
Is made of transparent material such as glass or transparent resin,
In this embodiment, an acrylic resin such as polymethylmethacrylate (PMMA) is used. This is because when the acrylic resin is used, the magneto-optical disk 10 can be easily manufactured and handled. The nonmagnetic layers 14 and 22 protect the magnetic thin films of the first magnetic recording layer 16 and the second magnetic recording layer 20, and are made of a transparent nonmagnetic material such as aluminum nitride (Al
N), silicon oxide (SiO), silicon dioxide (SiO ₂ ),
Alternatively, metallic silicon (Si) or the like is used. Non-magnetic layer 1
Numerals 4 and 22 prevent the first magnetic recording layer 16 and the second magnetic recording layer 20 from being chemically changed (oxidized, etc.).
Thicknesses of around 21Å and 1336Å are used respectively. However, the first magnetic recording layer 16 and the second magnetic recording layer
It may be omitted if 20 chemical changes are difficult to predict.
A first non-magnetic intermediate layer 18 is sandwiched between the non-magnetic layers 14 and 22.
The magnetic recording layer 16 and the second magnetic recording layer 20 are interposed, and in this embodiment, the first magnetic recording layer 16 is about 110Å, the second magnetic recording layer 20 is about 800Å, and the nonmagnetic intermediate layer 18 is 17830Å.
It has a certain thickness. First magnetic recording layer 16 and second
The magnetic recording layer 20 is a magneto-optical material having a remarkable magneto-optical effect, such as amorphous GdTbFe, TbFe, TbFeCo, GdCo, GdDyFe, and polycrystalline M.
Materials such as nCuBi, single crystal TbFeO ₃ and rare earth iron garnet may be used. In this embodiment, GdTbFe is adopted.
Further, the non-magnetic intermediate layer 18 may be made of a translucent non-magnetic substance, and the same substance as the non-magnetic layer 14 may be used.
The non-magnetic intermediate layer 18 may be formed by laminating a light-transmitting non-magnetic material in multiple layers, which is convenient because the film thickness is increased. For example, it is preferable to sequentially stack SiO ₂ , SiO, and SiO ₂ . Further, for the reflective layer 24, various substances such as an aluminum vapor deposition film that can reflect light are used. However, instead of the nonmagnetic layer 22 and the reflective layer 24, a plastic layer having a large film thickness may be provided. According to such a plastic layer,
This is because light can be sufficiently reflected at the interface, and a protective function for preventing oxidation of the second magnetic recording layer 20 can be obtained.

The magneto-optical disk 10 is rotatably driven, for example, about a vertical axis by a driving device (not shown), and the reading light beam emitted from the magneto-optical reproducing device 11 is scanned in the radial direction of the magneto-optical disk 10. Thus, the objective lens 38 and the like are moved in parallel in the horizontal direction. The laser light sources 26 and 28 for reading are linearly polarized laser beams having different wavelengths from each other and collimator lenses.
Firing towards dichroic mirror 34 through 30 and 32 respectively. In this embodiment, the wavelength λ ₁ of the laser light source 26 is 8300 Å and the wavelength λ ₂ of the laser light source 28 is 7800 Å.
Is. The dichroic mirror 34 allows the laser beam having the wavelength λ ₁ to pass through, while reflecting the laser beam having the wavelength λ ₂ to generate a combined laser beam having the wavelengths λ ₁ and λ ₂ through the half mirror 36 and the objective lens 38. Incident on. The synthetic laser beam reflected from the magneto-optical disk 10 is an objective lens 38 and a half mirror 36.
After reaching the dichroic mirror 40, the laser beam of wavelength λ ₁ is passed there while the wavelength of λ ₂
Are separated by being reflected.
The laser beam having the wavelength λ _{1 and} the laser beam having the wavelength λ ₂ are received by the first detecting device 42 and the second detecting device 44, respectively. The first detection device 42 and the second detection device 44 detect the Kerr rotation angles of the laser beam of wavelength λ _{1 and} the laser beam of wavelength λ ₂ , respectively, and the first magnetic recording layer is based on the Kerr rotation angle difference. The information previously recorded by perpendicular magnetization in the 16 and second magnetic recording layers 20 is read out. First detection device 42 and second detection device 44
Are configured in exactly the same way, for example, the first detection device
42 is constructed as shown in FIG. In the figure, the laser beam of wavelength λ ₁ reflected by the magneto-optical disk 10 is split into two directions by the half mirror 46, and one laser beam is received by the photodiode 52 via the analyzer 48,
The other laser beam passes through the analyzer 50 and is received by the photodiode 54. The planes of polarization of the analyzer and 50 are orthogonal to each other and are each inclined by 45 ° with respect to the plane of polarization of the laser beam. Therefore, when the plane of polarization of the laser beam rotates, 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
The signal is supplied to the differential amplifier 56, and the differential amplifier 56 outputs a signal corresponding to the information stored in the first magnetic recording layer 16 and cancels noise due to the fluctuation of the light amount. Here, the laser light source 26 and
28 is a semiconductor laser light source or an external resonance type laser light source that outputs a linearly polarized laser beam, but when using an internal resonance type laser light source that outputs a circularly polarized laser beam, the laser beam is passed through a polarizer. Should be emitted.

The reproducing operation of this embodiment will be described below. According to the magneto-optical reproducing device 11, the first magnetic recording layer 16 and the second magnetic recording layer 20 which are laminated on each other with the non-magnetic intermediate layer 18 interposed therebetween are reproduced independently.

In order to read information independently from each magnetic recording layer 16 and 20, as shown in FIGS. 3 (a) and 3 (b), the first
When the magnetic recording layer 16 is magnetized in the N direction and the S direction, respectively, regardless of the magnetization direction in the second magnetic recording layer 20, the Kerr rotation angle difference corresponding to the magnetization directions N and S in the first magnetic recording layer 16. In the case where the second magnetic recording layer 20 is magnetized in the N direction and the S direction, respectively, as shown in FIGS. 4 (a) and 4 (b),
The Kerr rotation angle difference corresponding to the magnetization direction of the second magnetic recording layer 20 must be detected regardless of the magnetization direction of the magnetic recording layer 16.

The present inventor has made various investigations, and the first magnetic recording layer 16
The Kerr rotation angle difference of the reflected light relating to four kinds of combinations of the magnetization directions of the first magnetic recording layer and the second magnetic recording layer 20 changes with different characteristics according to the change of the thickness of one magnetic recording layer, and When 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 difference is related only to the magnetization direction of one magnetic recording layer regardless of the magnetization direction of the other magnetic recording layer. Therefore, the present embodiment is constructed based on this finding. That is, according to the simulation by the present inventor, regarding the laser beam (8300Å) having the wavelength λ ₁ , as shown in FIG. 5, when the thickness of the first magnetic recording layer 16 is around 100Å, the second magnetic recording layer 20 The Kerr rotation angle difference corresponding to the magnetization direction of the first magnetic recording layer 16 can be stably obtained regardless of the magnetization direction. For example, if the magnetization direction of the first magnetic recording layer 16 changes from S to N, the Kerr rotation angle difference changes from 0 degree to about 0.6 degree. In the figure, N / S and N
/ N is the magnetization direction of the first magnetic recording layer 16 is the N direction,
The case where the magnetization directions of the second magnetic recording layer 20 are S and N are shown respectively. S / N and S / S are the first magnetic recording layer
The magnetization direction of 16 is the S direction, and the magnetization directions of the second magnetic recording layer 20 are the N direction and the S direction.
As for the laser beam having the wavelength λ ₂ (7800Å), as shown in FIG. 6, when the thickness of the first magnetic recording layer 16 is around 120Å, the second magnetic recording layer 16 is magnetized regardless of the magnetization direction of the second magnetic recording layer 16. A Kerr rotation angle difference corresponding to the magnetization direction of the recording layer 20 can be stably obtained.

As a result, the thickness of the first magnetic recording layer 16 is 100Å and 120Å
Is selected around the center, preferably between 100Å and 120Å, when the car rotation angle difference δθ _K is 0.3 ° or more, for example, information “1”, and when δθ _K is 0.3 ° or less, for example, information “0”. Correspondingly, the information of the first magnetic recording layer 16 is reproduced by the laser beam of wavelength 8300Å, and the information of the second magnetic recording layer 20 is reproduced by the laser beam of wavelength 7800Å.

Therefore, as described above, the film thickness of the first magnetic recording layer 16 of the magneto-optical disk 10 is selected to be 110Å, so that the wavelength λ
_In the reflected light from the first magneto-optical disk 10, the Kerr rotation angle difference corresponding to the perpendicular magnetization direction stored in the first magnetic recording layer 16 can be surely obtained. Therefore, in the first detection device 42 of the magneto-optical reproduction device 11, a signal corresponding to the data stored in the first magnetic recording layer 16 can be reliably obtained. Similarly, also in the reflected light of the laser beam of wavelength λ ₂ from the magneto-optical disk 10, the Kerr rotation angle difference corresponding to the perpendicular magnetization direction of the second magnetic recording layer 20 can be surely obtained, and the second detection device 44 can A signal corresponding to the data previously stored in the second magnetic recording layer 20 can be surely obtained.

As described above, according to this embodiment, since the data stored in advance in the first magnetic recording layer 16 and the second magnetic recording layer 20 are respectively taken out, the conventional magneto-optical disk having only one magnetic recording layer. In comparison with the above, the information recording density per unit area and the information storage amount per sheet have been dramatically increased to about twice.

Here, in the simulations of FIGS. 5 and 6,
For example, the expression (1) is preferably used. Solving Maxwell's electromagnetic equation for each layer of magneto-optical disk 10,
Further, by applying the boundary condition, the relationship between the incident light and the reflected light when linearly polarized light is incident can be derived. 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 in the electric field of the reflected light, the Kerr rotation angle ψ is obtained as shown in the equation (1).

The Kerr rotation angle difference δθk shown in FIG. 5 was obtained by taking the difference from the minimum value because the Kerr rotation angle ψ changes depending on the magnetization direction.

tan2ψ = tan2α cos (φ−θ) (1) However, in equation (1), Is. Here, if b ₁₁ and b ₂₁ are expressed in complex as in the following equations (5) and (6), then b ₁₁ = b ₁₁ ′ + jb ₁₁ ″ (5) b ₂₁ = b ₂₁ ′ + jb ₂₁ ″ (6) The magnitudes of the electric fields | Ex | and | Ey | are given by the following equations.

The above b ₁₁ and b ₂₁ are defined as follows.

However, D = a ₁₁ a ₃₃ −a ₁₃ a ₃₁ (11). Ai used in (9), (10), and (11)
j can be represented as each element of a 4 × 4 matrix as follows:

(Aij) = [MA1], [MA21], [MA31], [MA41], [MA51], [MA61] (12) Each matrix in Eq. (12) is (13) under the following conditions:
It is expressed as shown in equations (18) to (18).

n ₀ : Refractive index n ₁ and d _{1 of the} transparent substrate 12: Refractive index and film thickness n ₂ and d _{2 of the} non-magnetic layer 14: Refractive index and film thickness n ₃ and d _{3 of} the first magnetic recording layer 16: Non Refractive index and film thickness n ₄ and d _{4 of the} magnetic intermediate layer 18: Refractive index and film thickness n ₅ and d _{5 of} the second magnetic recording layer 20: Refractive index and film thickness n _{6 of the} non-magnetic layer 22: Reflective layer 24 Refractive index of : Dielectric constant tensor of the first magnetic recording layer 16 : Dielectric constant tensor of the second magnetic recording layer 20 However, n ₁₀ = n ₁ / n ₀ However, N ₂₁ = n ₂ / n ₁ , k _1Z = (2π / λ) n ₁ (λ: wavelength) However, However, n ₄₃ = n ₄ / n ₃ , k _3Z = (2π / λ) n ₃ However, Since the characteristics shown in FIGS. 5 and 6 are only characteristics when the first magnetic recording layer 16 is GdTbFe, the Kerr rotation angle difference and the difference obtained when other magneto-optical materials are used. Since the change characteristic with respect to the thickness of the first magnetic recording layer 16 is different, the thickness of the first magnetic recording layer 16 is also set to an optimum value according to the change characteristic of the Kerr rotation angle difference. On the contrary, the thickness of the second magnetic recording layer 20 may be set to a value at which a sufficient Kerr rotation angle difference can be obtained.

Further, as shown in FIG. 7, the magneto-optical disk 10 may have a structure of at least two layers, that is, three or more layers. For example, in the magneto-optical disk 10, the second non-magnetic intermediate layer
The 58 and the third magnetic recording layer 60 are interposed between the second magnetic recording layer 20 and the nonmagnetic layer 22. In such a case, the first magnetic recording layer 16, the second magnetic recording layer 20, the third magnetic recording layer 60
In order to reproduce the information written on the disk, laser light sources of three kinds of wavelengths are required, but the information recording is about three times as large as that of the conventional magneto-optical disk having only one magnetic recording layer. The density can be obtained.

Further, as shown in FIG. 8, each of the first magnetic recording layer 16 and the second magnetic recording layer 20 is composed of a plurality of magnetic layers, for example, a pair of GdFe layers 62 and TbFe layers 64 without a nonmagnetic layer therebetween. You can Since the TbFe layer 64 has a low Curie temperature, information can be written even at low power. Further, since the GdFe layer 62 that is magnetically coupled to the TbFe layer 64 has excellent magneto-optical characteristics, there is an advantage that writing and reading of data becomes easier.

Further, the magneto-optical recording medium may be not only the disc-shaped magneto-optical disk 10 as described above, but also a tape-shaped or drum-shaped one.

Further, in order to obtain the laser beams having the wavelengths λ ₁ and λ ₂ in the above-mentioned embodiment, two laser light sources 26 and 28 are prepared. For example, a semiconductor laser array or an argon laser which oscillates at two different wavelengths. If a device such as a device that oscillates at a plurality of wavelengths or a wavelength tunable dye laser light source is used, it is possible to reproduce information with one laser light source or a number of laser light sources smaller than the number of magnetic recording layers.

Further, although in the foregoing embodiments, the laser light source 26 and 28 are those laser beam having a wavelength lambda ₂ wavelength lambda ₁ and 7800Å respectively 8300Å is output, these wavelengths lambda _1,
Needless to say, λ ₂ is the wavelength of a commercially available semiconductor laser device that is easily available, and the wavelengths of the laser beams of the laser light sources 26 and 28 are not limited to this.

In the illustrated embodiment, the first magnetic recording layer 16 and the second magnetic recording layer 20 in correspondence to the laser beam of wavelength lambda ₁ and lambda _2, and the Kerr rotation angle difference of the wavelengths lambda ₁ and lambda ₂ The information written in the first magnetic recording layer 16 and the information written in the second magnetic recording layer 20 are respectively reproduced on the basis of the change of the above. For example, the first magnetic recording layer 16 is irradiated with a laser beam of wavelength λ _1. And a sum signal of the second magnetic recording layer 20 is detected, and a difference signal of the first magnetic recording layer 16 and the second magnetic recording layer 20 is detected with a laser beam having a wavelength λ ₂ .
By the subsequent signal processing, the first magnetic recording layer 16 and the second magnetic recording layer 16
The information stored in the magnetic recording layer 20 may be reproduced.

Next, an example of a magneto-optical recording device (writing device) for writing information on 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, the same parts as those in the above-described embodiment will be designated by the same reference numerals and the description thereof will be omitted.

In FIG. 9, the laser beam emitted from the writing laser light source 66 including the collimator lens is the objective lens barrel.
It is incident on the magneto-optical disk 10 through the objective lens 70 held by 68. The objective lens barrel 68 is attached to the main body 67 via an objective lens positioning mechanism 69,
The objective lens 70 is driven between two positions, a position close to the magneto-optical disk 10 and a position separated from it, by an electromagnetic driving force generated in a cylindrical drive coil 71 fixed to the objective lens barrel 68. It has become. That is, the objective lens barrel 68 is supported by the main body 67 via the 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 body 67, and the drive coil 71
Are located in the magnetic field formed between them and the yoke members 77, 79. Therefore, when the drive current is supplied to the drive coil 71, the objective lens 70 is driven to a desired position according to the magnitude of the drive current. Here, the depth of focus δf of the objective lens 70 is made smaller than the thickness (17830Å) of the non-magnetic 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 equation (19): δf = ± 4 / π · λ (1 / 2NA) ² (19) where λ: wavelength NA of light beam : Numerical aperture of the objective lens 70 For example, the wavelength λ of the laser light source 66 of this embodiment is 0.83 μm.
Then, the numerical aperture NA of the objective lens 70 is set to 0.6, and the depth of focus δf in that case is set to ≦ 0.7 μm. Therefore, when the objective lens 70 is positioned at a position close to the magneto-optical disc 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 is performed. The magneto-optical material comprising layer 20 is heated above its Curie temperature to eliminate the already stored perpendicular magnetization. At this time, if a magnetic field is formed in the vertical direction by the electromagnet 74, when the portion corresponding to the beam spot heated by the laser beam is cooled to the Curie temperature or lower, it is magnetized perpendicularly to the direction of the magnetic field formed by the electromagnet 74. To be done. As a result, desired information is written in a desired location on the second magnetic recording layer 20. The laser beam for erasing the information in the second magnetic recording layer 20 passes through the first magnetic recording layer 16, but the depth of focus δf of the objective lens 70 is made sufficiently smaller than the thickness dimension of the nonmagnetic intermediate layer 18. Therefore, the first magnetic recording layer 16
In the first magnetic recording layer 16 cannot be sufficiently heated.
The information recorded in is not erased.

Next, as shown in FIG. 10, the objective lens 70 is driven by the drive coil.
When it is positioned at a position separated from the magneto-optical disk 10 by driving 71, the laser beam emitted from the laser light source 66 is focused on the first magnetic recording layer 16 and, in the same manner as the above case, information is output in a desired case. Are erased and new information is recorded. At this time as well, the laser beam for erasing the information in the first magnetic recording layer 16 reaches the second magnetic recording layer 20, but the depth of focus δf of the objective lens 70 has a non-magnetic intermediate layer.
Since the thickness is smaller than the thickness dimension of 18, 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, so that the information recorded in the second magnetic recording layer 20 is not erased. That is, the focus position is changed by moving the objective lens 70 close to and away from the magneto-optical disk 10, and one of the first magnetic recording layer 16 and the second magnetic recording layer 20 held within the depth of focus is changed. Information is recorded on only one side. As is clear from the above description, in this embodiment, the objective lens 70 corresponds to the condensing means, and the objective lens positioning mechanism 69 corresponds to the focus position control means. In the present embodiment, the objective lens 70 is configured to be moved closer to and separated from the magneto-optical disk 10, but conversely, the magneto-optical disk 10 is configured to be moved closer to and separated from the objective lens 70. But it doesn't matter. 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 be used, and Monochromatic light other than laser light may be used.

In order to write information on the magneto-optical disk 10 composed of at least two layers, that is, three or more magneto-optical recording layers as shown in FIG. It suffices that it can be positioned at three or more positions corresponding to the magnetic recording layer.

Hereinafter, various aspects of the magneto-optical writing device using the objective lens 70 as described above will be described.

For example, as shown in FIG. 11, a pair of laser light sources 66
And a pair of objective lenses 70 that focus laser beams emitted from the laser light sources 66 on the first magnetic recording layer 16 and the second magnetic recording layer 20, respectively, in the height direction of the magneto-optical disk 10. The relative position may be fixed and the laser beam may be emitted from one of the pair of laser light sources 66 as needed. By doing this, the objective lens
There is an advantage that a drive device for changing the relative distance between the 70 and the magneto-optical disk 10 is unnecessary. In this case, the pair of laser light sources 66 and the pair of objective lenses 70 correspond to the focus position control means.

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 light source 66
A new laser light source 78 that emits a laser beam having a wavelength shorter than that of the laser beam emitted from is provided, and after the laser beam emitted from the new laser light source 78 is reflected by the half mirror 76, the first laser beam is passed through the objective lens 70. 1 magnetic recording layer
You may make it condense on 16. That is, the chromatic aberration of the objective lens 70 is used to change the focal length depending on the wavelength. According to this embodiment, there are advantages that the first magnetic recording layer 16 and the second magnetic recording layer 20 have the same data erasing / writing location, and the driving device for driving the objective lens 70 and the like is unnecessary. In this embodiment, the laser light sources 66 and 78 and the half mirror 76 correspond to the focus position control means.

Further, as shown in FIG. 13, while the objective lens 70 is provided at a fixed position relative to the magneto-optical disk 10 in the height direction,
A pair of laser light sources 80 and 82, and a pair of collimator lenses
84 and 86 are provided, a laser beam output from one laser light source 80 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 other laser light source 82 collimates. The laser beam emitted through the lens 86 may be reflected by the half mirror 88 and may be incident on the magneto-optical disk 10 through the objective lens 70 to be condensed on the second magnetic recording layer 20. The laser light sources 80 and 82 and the collimator lens 8 are arranged so that the laser beams respectively output from the laser light sources 80 and 82 are focused on the first magnetic recording layer 16 and the second magnetic recording layer 20.
The positions of 4,86 are adjusted in advance. 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. In the present embodiment, the laser light source 80, 82, the collimator lens 84,
The 86 and the half mirror 88 correspond to the focus position control means.

Further, as shown in FIG. 14, while the collimator lens 90 and the objective lens 70 are provided in a fixed position relative to the magneto-optical disk 10 in the height direction, the objective lens is moved by moving the laser light source 92 in the optical axis direction. The focal position of 70 may be alternatively positioned on the first magnetic recording layer 16 and the second magnetic recording layer 20. That is, the screw shaft 96 rotated by the position-fixed drive motor 94 is screwed with the slider 98 provided so as to be movable in the direction parallel to the screw shaft 96, and is fixed to the slider 98 by the rotation of the drive motor 94. The laser light source 92 that has been selected is the objective lens 70 and the collimator lens.
It can be moved along the 90 optical axis. In this embodiment, the drive motor 94, the screw shaft 96 and the slider 98 correspond to the focus position control means. 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.

Although one embodiment of the present invention has been described above with reference to the drawings, each drawing is a schematic diagram for explaining the gist and should not be construed as being limited thereto. For example, the magneto-optical disk 10 in each figure is shown for the cross section of its main part, but the thickness of each layer shown in this cross section is shown for ease of understanding, and the actual thickness It does not indicate the ratio of. Further, in the optical system shown in FIGS. 1, 2, and 9 to 1, only important optical elements are symbolically shown, and in fact, other optical elements having the same function may be used. It may be replaced, another optical element may be appropriately inserted, 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 if the reduction in efficiency is tolerated, the dichroic mirrors 34 and 40 may be replaced with half mirrors or a combination of these and filters.

Further, in the above-mentioned embodiment, the recording device and the reproducing device are separated for the sake of convenience of description, but in reality, the common device is used for recording and reproduction. Also in the embodiment of the present invention, the reproducing laser can be used also as the recording laser by using the high output laser, and it is also possible to use the reproducing optical system as it is for recording. Therefore, in the present embodiment, only the portion of the magneto-optical recording / reproducing apparatus related to recording is handled as the recording apparatus, and only the portion related to the reproducing is taken out as the reproducing apparatus.

The above description is merely one embodiment of the present invention, and the present invention can be variously modified without departing from the spirit thereof.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the structure of an apparatus for reading information from a magneto-optical disk. FIG. 2 is a schematic diagram showing in detail the structure of the detection device included in the device of FIG. FIGS. 3 and 4 are views showing combinations of magnetization directions of the magneto-optical disk of FIG. 1 for each magnetic recording layer. FIGS. 5 and 6 are views showing the change characteristics of the Kerr rotation angle difference with respect to the thickness of the first magnetic recording layer in the combination of the magnetization directions shown in FIGS. 3 and 4 for each read wavelength. FIG. 7 and FIG. 8 are cross-sectional views of essential parts showing other embodiments of the magneto-optical disk of FIG. 1, respectively. FIG. 9 is a schematic diagram showing a writing apparatus for writing information on each of the magnetic recording layers stacked in the magneto-optical disk shown in FIG. 1 as an apparatus according to an embodiment of the present invention. FIG. 10 is a view showing another operating position of the apparatus shown in FIG. FIGS. 11 to 14 are other embodiments of the present invention, and are schematic diagrams respectively showing a writing device for writing information in each of the magnetic recording layers laminated on the magneto-optical disk shown in FIG. . 10: Magneto-optical disk (magneto-optical recording medium) 16: First magnetic recording layer (magneto-optical recording layer) 20: Second magnetic recording layer (magneto-optical recording layer) 18: Non-magnetic intermediate layer (non-magnetic layer) 66, 78,80,82,92: Laser light source 69: Objective lens positioning mechanism (focus position control means) 70: Objective lens (focusing means)

Claims (2)

[Claims] 1. A magneto-optical recording apparatus for recording information by irradiating a laser beam on a magneto-optical recording medium in which at least two magneto-optical recording layers are laminated via a non-magnetic layer, wherein the laser A laser light source for outputting a light beam; a condensing unit for converging and irradiating the laser beam output from the laser light source onto the magneto-optical recording layer; and only one selected layer of the magneto-optical recording layer A focus position control means for controlling the focus position so that the focus position is maintained within the depth of focus of the means. 2. The magneto-optical recording apparatus according to claim 1, wherein the thickness of the non-magnetic layer is set to be larger than the depth of focus of the condensing means.