JPH0513339B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to a magneto-optical recording medium configured by laminating a plurality of magneto-optical recording layers with non-magnetic layers interposed therebetween. The present invention relates to a magneto-optical reproducing device.

Prior Art A magneto-optical reproducing device is known that utilizes the magneto-optic effect to read out information written by locally magnetizing a magneto-optical material that has spontaneous magnetization and can transmit light in the perpendicular direction. There is. Generally, in such devices, when linearly polarized light is incident parallel to the magnetization direction of a magneto-optical material, the Kerr effect occurs, in which the plane of vibration (polarization plane) of the reflected or transmitted light rotates in relation to the direction of magnetization. Alternatively, information written on the magneto-optical material can be read by using the Faraday effect. 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 Fraaday effect, the magnetization of any layer Therefore, 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, and its gist consists of at least two
A magneto-optical reproducing device for reproducing information separately recorded on each magneto-optical recording layer of a magneto-optical recording medium in which magneto-optical recording layers are laminated with a non-magnetic layer interposed therebetween, comprising: (a) (b) a first laser light source and a second laser light source that respectively output at least two first and second laser lights having different wavelengths;
(c) beam combining means for combining the first laser beam and the second laser beam into one beam; and (c) the single beam combined by the beam combining means is focused and made to enter the magneto-optical recording medium. a single light focusing means; (d) a separating means for separating one beam emitted from the magneto-optical recording medium into laser beams of the first wavelength and a second wavelength; and (e) the separating means. The present invention includes a first detection means and a second detection means for receiving the separated laser beams of the first wavelength and the second wavelength and detecting the respective Kerr rotation angles.

By doing so, when the first laser beam and the second laser beam having different wavelengths are combined into one beam by the beam combining means and are made to enter the magneto-optical recording medium through the condensing means, the One beam emitted from the magneto-optical recording medium is separated by the separating means into laser beams of the first wavelength and the second wavelength, and the Kerr rotation angle of each of the first wavelength and the second wavelength is set to the first wavelength. detection means and a second
Detected by a detection means.

Effects of the Invention A stable Kerr rotation angle difference can be obtained from the magnetization direction of one magneto-optical recording layer for each of the first laser beam and the second laser beam having different wavelengths, regardless of the magnetization direction of other magnetic recording layers. Therefore, the first wavelength and the second wavelength separated by the separation means are
By individually detecting the Kerr rotation angle differences of the laser beams of different wavelengths, the information recorded in each magneto-optical recording layer can be particularly reproduced.

Embodiment Hereinafter, an embodiment 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 includes a non-magnetic layer 14, a first magnetic recording layer 16, a non-magnetic intermediate layer 18, a second magnetic recording layer 20 and a non-magnetic layer 2 on one side of a transparent substrate 12.
2. The reflective layer 24 is constructed by sequentially laminating layers by known fixing means such as vapor deposition or 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, the magneto-optical disk 10 is easier to manufacture and handle. Nonmagnetic layers 14, 22
are the first magnetic recording layer 16 and the second magnetic recording layer 20
A transparent non-magnetic material such as aluminum nitride (AlN), silicon oxide (SiO), silicon dioxide (SiO ₂ ), or metallic silicon (Si) is used to protect the magnetic thin film of the magnetic thin film. The nonmagnetic layers 14 and 22 protect the first magnetic recording layer 16 and the second magnetic recording layer 20 from chemical changes (oxidation, etc.), and in this embodiment, the nonmagnetic layers 14 and 22 have a thickness of approximately 1421 Å and 1336 Å.
Different thicknesses are used. but,
It may be omitted if chemical changes in the first magnetic recording layer 16 and the second magnetic recording layer 20 are difficult to predict. 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, and in this embodiment, the first magnetic recording layer 16 has a thickness of about 110 Å. , the second magnetic recording layer 20 has a thickness of about 800 Å, and the non-magnetic intermediate layer 18 has a thickness of 17830 Å.
It has a certain thickness. The first magnetic recording layer 16 and the second magnetic recording layer 20 are made of a magneto-optical material having a remarkable magneto-optical effect, such as amorphous GdTbFe, TbFe,
TbFeCo, GdCo, GdDyFe, polycrystalline MnCuBi,
Materials such as single crystal TbFeO ₃ and rare earth iron garnet can be used. In this example, 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 can be used. This nonmagnetic intermediate layer 18
may be formed by laminating multiple layers of translucent non-magnetic material,
This is more convenient for increasing the film thickness.
For example, it is preferable to sequentially stack SiO ₂ , SiO, and SiO ₂ . In addition, various materials capable of reflecting light, such as an aluminum vapor-deposited film, are used for the reflective layer 24 . However, instead of the nonmagnetic layer 22 and the reflective layer 24, a thick plastic layer may be provided. According to such a plastic layer, light can be sufficiently reflected at the interface thereof, and the second magnetic recording layer 2
This is because a protective function for preventing 0 oxidation can also be obtained.

The magneto-optical disk 10 is driven to rotate, for example, around a vertical axis by a drive device (not shown), and the continuous light beam emitted from the magneto-optical reproducing device 11 is directed in the radial direction of the magneto-optical disk 10. As the vehicle travels, the objective lens 38 and the like are moved in parallel in the horizontal direction. The successive laser light sources 26 and 28 emit linearly polarized laser beams of different wavelengths toward a dichroic mirror 34 through collimator lenses 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. The dichroic mirror 34 passes the laser beam with the wavelength λ ₁ and reflects the laser beam with the wavelength λ ₂ so that the combined laser beam consisting of the wavelengths λ ₁ and λ ₂ is transmitted to the magneto-optical disk through the half mirror 36 and the objective lens 38. 10. The combined laser beam reflected from the magneto-optical disk 10 passes through the objective lens 38 and the half mirror 36 and reaches the dichroic mirror 40, where the laser beam with wavelength λ ₁ is passed, while the laser beam with wavelength λ ₂ is passed through. They are separated by being reflected. The laser beam of wavelength λ ₁ and the laser beam of wavelength λ ₂ are received by a first detection device 42 and a second detection device 44, respectively. The first detection device 42 and the second detection device 44 detect Kerr rotation angles of a laser beam with a wavelength λ ₁ and a laser beam with a wavelength λ ₂ , respectively.
Information previously recorded in the magnetic recording layer 16 and the second magnetic recording layer 20 by perpendicular magnetization is read out. The first detection device 42 and the second detection device 44 are configured in exactly the same way,
For example, the first detection device 42 is configured as shown in FIG. In the figure, a laser beam of wavelength λ ₁ reflected by a magneto-optical disk 10 is separated into two directions by a half mirror 46, one laser beam passes through an analyzer 48 and is received by a photodiode 52, and the other laser beam is The light passes through a probe 50 and is received by a photodiode 54. The planes of polarization of analyzers 48 and 50 are perpendicular to each other and each inclined at 45° 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 decreases.
The amount of light received increases. Photodiode 5
The outputs of 2 and 54 are supplied to a differential amplifier 56, and from the differential amplifier 56 the outputs of the first magnetic recording layer 1
A signal corresponding to the information stored in 6 is output, 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,
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, which are stacked on each other with the nonmagnetic intermediate layer 18 in between, are independently reproduced.

In order to read information independently from each magnetic recording layer 16 and 20, as shown in FIGS. 3a and 3b, when the first magnetic recording layer 16 is magnetized in the N direction and the S direction, the second magnetic recording layer 20
Regardless of the magnetization direction in the first magnetic recording layer 1
A Kerr rotation angle difference corresponding to the magnetization directions N and S in the second magnetic recording layer 20 must be obtained, and as shown in FIGS. In case the first
Regardless of the magnetization direction in the magnetic recording layer 16, the second
The Kerr rotation angle difference corresponding to the magnetization direction of the magnetic recording 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,
In addition, when the thickness of one magnetic recording layer is set to a specific thickness under such Kerr rotation angle difference change characteristics, the relationship between the magnetization direction of one magnetic recording layer only and regardless of the magnetization direction of the other magnetic recording layer is It was discovered that the Kerr rotation angle difference is determined, and the present embodiment is constructed based on this knowledge. That is, according to the inventor's simulation, for a laser beam of wavelength λ ₁ (8300 Å), as shown in FIG. Regardless of the magnetization direction, the Kerr rotation angle difference corresponding to the magnetization direction of the first magnetic recording layer 16 can be stably obtained. 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 degrees to about 0.6 degrees. In the figure, N/S and N/N indicate that the magnetization direction of the magnetic recording layer 16 is N at the first time.
The magnetization directions of the second magnetic recording layer 20 are 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 direction of the second magnetic recording layer 20 is the N direction and the S direction.
Regarding the laser beam with wavelength λ ₂ (7800Å),
As shown in FIG. 6, when the thickness of the first magnetic recording layer 16 is around 120 Å, the Kerr rotation angle difference corresponding to the magnetization direction of the second magnetic recording layer 20 is independent of the magnetization direction of the first magnetic recording layer 16. Obtained stably.

As a result, the thickness of the first magnetic recording layer 16 was reduced to 100 Å.
and a neighborhood centered at 120 Å, preferably 100 Å
and 120Å, and the Kerr rotation angle difference δθ _K is 0.3°.
If the above case corresponds to information "1" and the time when δθ _K is 0.3° or less corresponds to information "0", the information in the first magnetic recording layer 16 is reproduced with a laser beam with a wavelength of 8300 Å, and the information with a wavelength of 7800 Å The information in the second magnetic recording layer 20 is reproduced by the laser beam.

Therefore, as mentioned above, the magneto-optical disk 10
Since the film thickness of the first magnetic recording layer 16 is selected to be 110 Å, the Kerr rotation corresponding to the perpendicular magnetization direction stored in the first magnetic recording layer 16 occurs in the reflected light from the magneto-optical disk ₁₀ with wavelength λ 1. Angle difference can be obtained reliably. Therefore, the first
In the detection device 42, a signal corresponding to the data stored in the first magnetic recording layer 16 can be reliably obtained. Similarly, the Kerr rotation angle difference corresponding to the perpendicular magnetization direction of the second magnetic recording layer ₂₀ can be reliably obtained even in the reflected light from the magneto-optical disk 10 of the laser beam with the wavelength λ 2 . A signal corresponding to the data stored in advance in the second magnetic recording layer 20 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 amount of information stored per disk compared to conventional magneto-optical disks, which have only one magnetic recording layer. There is.

Here, for example, equation (1) is suitably used for the simulations in FIGS. 5 and 6. 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 can be 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.

Note that the Kerr rotation angle difference δθk shown in FIG.
Since the Kerr rotation angle ψ changes depending on the direction of magnetization, it was determined by taking the difference from its minimum value.

tan2ψ＝tan2αcos(φ−θ) ……(1) However, in equation (1), tanα＝｜Ex｜／｜Ey｜ ……(2) θ＝tan ^-1 b ₁₁ ″／b ₁₁ ′ ……( 3) φ=tan ^-1 b ₂₁ ″/b ₂₁ ′ ……(4). Here, assuming that b ₁₁ and b ₂₁ are expressed in complex terms as shown in the following equations (5) and (6), b ₁₁ = b ₁₁ ′+ jb ₁₁ ″...(5) b ₂₁ = b ₂₁ ′+ jb ₂₁ ″...(6) The magnitude of the electric field |Ex|, |Ey| is as shown in the following equation.

｜Ey｜=√ ₁₁ ′ ² + ₁₁ ″ ² …(7) ｜Ex｜=√ ₂₁ ′ ² + ₂₁ ″ ² ……(8) The above b ₁₁ and b ₂₁ are defined as the following formula .

b ₁₁ = 1/D (a ₂₁ a ₃₃ − a ₃₂ a ₃₁ ) ……(9) b ₂₁ = 1/D (a ₄₁ a ₃₃ − a ₄₂ a ₃₁ ) ……(10) However, D = a ₁₁ a ₃₃ − ₁₃ a ₃₁ ……(11). Each a _ij used in (9), (10), and (11) can be expressed as each component of a 4×4 matrix as shown below.

(a _ij ) = [MA1] / [MA21] / [MA31] / [MA41] / [
MA51]・[MA61]...(12) Each matrix in equation (12) becomes (13) under the following conditions.
It is expressed as shown in equations (18).

no: refractive index of transparent substrate 12 n ₁ and d ₁ : refractive index and film thickness of nonmagnetic layer 14 n ₂ and d ₂ : refractive index and film thickness of first magnetic recording layer 16 n ₃ and d ₃ : nonmagnetic intermediate Refractive index and thickness n ₄ and d ₄ of layer 18 : Refractive index and thickness n ₅ and d ₅ of second magnetic recording layer 20 : Refractive index and thickness n ₆ of nonmagnetic layer 22 : Refraction of reflective layer 24 Rate n ₂ ² 1 jg ₂ 0 - jg ₂ 1 0 0 0 1 : Dielectric constant tensor of the first magnetic recording layer 16 n ₄ ² 1 jg ₄ 0 - jg ₄ 1 0 0 0 1 : Dielectric constant tensor of the second magnetic recording layer 20 permittivity tensor However, n ₂₁ = n ₂ / n ₁ , k ₁₂ = (2π/λ) n ₁
(λ: wavelength) [MA31] = e ^jk2zz1d2 0 0 0 0 e ^-jk2z2d2 0 0 0 0 e ^jk2z2d2 0 0 0 0 e ^-jk2z1d2・[MA3] ^-1 ...(15) However, However, n ₄₃ = n ₄ / n ₃ , k ₃₂ = (2π/λ) n ₃ [MA51] = e ^jk4zld4 0 0 0 0 e ^-jk4z2d4 0 0 0 0 e ^jk4z2d4 0 0 0 0 e ^-jk4z1d4・[MA5 〕 ^-1 ……(17) Note that the characteristics shown in FIGS. 5 and 6 are only the characteristics when the first magnetic recording layer 16 is made of GdTbFe, so the Kerr rotation angle difference and the Since the change characteristics with respect to the thickness of the first magnetic recording layer 16 are different, the thickness of the first magnetic recording layer 16 is also set to an optimum value according to the change characteristics of the Kerr rotation angle difference. Conversely, the thickness of the second magnetic recording layer 20 may be set to a value that provides a sufficient Kerr rotation angle difference.

Further, as shown in FIG. 7, the magneto-optical disk 1
0 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, the first magnetic recording layer 16,
In order to reproduce the information written in the second magnetic recording layer 20 and the third magnetic recording layer 60, laser light sources with three different wavelengths are required, but in the past, only one magnetic recording layer was provided. It is possible to obtain information recording density approximately three times that of a magneto-optical disk.

Further, as shown in FIG. 8, the first magnetic recording layer 1
6 and the second magnetic recording layer 20 are each made of a multilayer magnetic layer without a nonmagnetic layer, for example, a pair of GdFe layers.
It can be comprised of layer 62 and TbFe layer 64. Since the TbFe layer 64 has a low Curie temperature, information can be written even with low power. In addition, GdFe magnetically coupled with this TbFe layer 64
Layer 62 has excellent magneto-optical properties, which has the advantage of making it easier to write and read data.

In addition, as a magneto-optical recording medium, not only the disk-shaped magneto-optical disk 10 as described above but also a tape-shaped,
It may be drum-shaped.

In addition, in the above embodiment, two laser light sources 26 are used to obtain laser beams with wavelengths λ ₁ and λ ₂ .
and 28 are available, but 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, etc. Information can be reproduced using one laser light source or a number less than the number of magnetic recording layers.

Further, in the above embodiment, the laser light source 26
and 28 are wavelengths λ ₁ and 7800 of 8300 Å, respectively
A laser beam with a wavelength λ ₂ of 1.5 Å is output, but these wavelengths λ ₁ and λ ₂ are the wavelengths of easily available commercially available semiconductor laser elements, and the laser light source 26
It goes without saying that the wavelengths of the laser beams 28 and 28 are not limited to these.

That is, the magneto-optical disk 10 has a non-magnetic layer (first protective layer) 14 substantially similar to the above embodiment.
A wavelength of 8300 Å when the nonmagnetic layer (intermediate layer) 18 has a thickness of 17860 Å, the nonmagnetic layer (second protective layer) 22 has a thickness of 1164.4 Å, and the second magnetic recording layer 20 has a thickness of 800 Å. Regarding the laser beam with λ ₁ , as shown in FIG. 19, when the thickness of the first magnetic recording layer 16 is around 90 Å, the magnetization of the first magnetic recording layer 16 is constant regardless of the magnetization direction of the second magnetic recording layer 20. A stable Kerr rotation angle difference corresponding to the direction can be obtained. Regarding the laser beam with a wavelength λ ₂ of 6800 Å, as shown in FIG. 20, when the thickness of the first magnetic recording layer 16 is around 100 Å, the second magnetic Recording layer 2
A Kerr rotation angle difference corresponding to the zero magnetization direction can be stably obtained. Therefore, for a magneto-optical disk 10 in which the first magnetic recording layer 16 has a thickness of around 90 Å to 100 Å, a laser light source 26 that outputs a laser beam with a wavelength λ ₁ of 8300 Å and a wavelength λ ₂ of 6800 Å are used. By using the laser light source 28 that outputs a laser beam of , the information recorded in the first magnetic recording layer 16 and the second magnetic recording layer 20 can be particularly read out.

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 λ ₁ and λ ₂ , and the Kerr rotation angle difference between the wavelengths λ ₁ and λ ₂ is For example, the information written in the first magnetic recording layer 16 and the second magnetic recording layer 20 is reproduced based on the change in the first magnetic recording layer 16 and the second magnetic recording layer ₂₀ , respectively. and the second magnetic recording layer 20, a difference signal between the first magnetic recording layer 16 and the second magnetic recording layer 20 is detected with a laser beam of wavelength λ ₂ , and by subsequent signal processing, the first
Information stored in the magnetic recording layer 16 and the second magnetic recording layer 20 may be reproduced.

Next, 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, respectively.
An example will be explained. 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 moved by an electromagnetic driving force generated in a cylindrical drive coil 71 fixed to the objective lens barrel 68. is driven between two positions, a position close to the magneto-optical disk 10 and a position away from the magneto-optical disk 10. That is, the objective lens barrel 6
8 connects the objective lens 7 to the main body 67 via a leaf spring 73.
It is supported so as to be relatively movable in the optical axis direction of 0 (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, the drive coil 7
When a driving current is supplied to the lens 1, the objective lens 70 is driven to a desired position according to the magnitude of this driving current. Here, the depth of focus δf of the objective lens 70 is made smaller than the thickness (17830 Å) of the nonmagnetic intermediate layer 18 in the magneto-optical disk 10. It is known that the depth of focus δf of the objective lens 70 is given by the following equation (19), δf = ±4/π・λ (1/2NA) ² ...(19) where λ is the wavelength of the light beam NA : Numerical aperture of the objective lens 70 For example, if the wavelength λ of the laser light source 66 of this embodiment is
Assuming that it is 0.83 μm, the numerical aperture NA of the objective lens 70 is 0.6, and the depth of focus δf in that case is ≦
It is said to be 0.7 μm. Therefore, when the objective lens 70 is positioned close to 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 The magneto-optical material constituting the magnetic recording layer 20 is heated above its Curie temperature to eliminate the perpendicular magnetization already stored. At this time, if a magnetic field is formed in the vertical direction by the electromagnet 76, when the portion corresponding to the beam spot heated by the laser beam cools below the Curie temperature, the magnetic field formed by the electromagnet 74 magnetized perpendicular to the direction of As a result, desired information is written at a desired location on the second magnetic recording layer 20. The laser beam for erasing information in the second magnetic recording layer 20 passes through the first magnetic recording layer 16, but the depth of focus 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
, the information recorded in the first magnetic recording layer 16 is not erased because sufficient heating cannot be performed.

Next, as shown in FIG.
is positioned at a position away from the magneto-optical disk 10 by driving the drive coil 71, the laser beam emitted from the laser light source 66 is focused on the first magnetic recording layer 16, and as in the case described above. Information is erased and new information is recorded at the desired location. 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 focal depth δf of the objective lens 70 is smaller than the thickness dimension of the non-magnetic intermediate layer 18. Therefore, 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. Note that in this embodiment, the objective lens 70
are arranged to be close to and separated from the magneto-optical disk 10, but conversely, the magneto-optical disk 10
There is no problem even if the lens is configured to be moved closer to and further away from the objective lens 70. Also, a laser light source 66 for writing used in the magneto-optical recording device
Since the laser beam emitted from the laser beam is for locally heating the magneto-optical recording layer 16 or 20, it may be a circularly polarized laser beam, or it may be monochromatic light other than a laser beam.

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.
A pair of objective lenses 70 that respectively focus light on the magnetic recording layer 20 may be provided at fixed positions relative to the magneto-optical disk 10 in the height direction. In this way, the objective lens 70 and the magneto-optical disk 10
There is an advantage that a drive device for changing the relative distance between the two is not required.

Further, as shown in FIG. 12, a laser light source 66
The laser beam emitted from the second magnetic recording layer 20 passes through the half mirror 76 and the objective lens 70.
At the same time, a new laser light source 78 that emits a laser beam with a shorter wavelength than the laser beam emitted from the laser light source 66 is provided, and the laser beam emitted from the new laser light source 78 is reflected at the half mirror 76. After that, the light may be focused on the first magnetic recording layer 16 through the objective lens 70. 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 is an advantage that the first magnetic recording layer 16 and the second magnetic recording layer 20 have a common data erasing/writing location, and a driving 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 relative position in the height direction with respect to the magneto-optical disk 10, while a pair of laser light sources 80, 8
2, and a pair of collimator lenses 84 and 86 are provided, and the 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, The laser beam emitted from the other laser light source 82 via the collimator lens 86 is reflected by the half mirror 88, and is reflected by the magneto-optical disk 10 through the objective lens 70.
Alternatively, the light may be incident on the second magnetic recording layer 20 and focused on the second magnetic recording layer 20. Laser beams output from the laser light sources 80 and 82 respectively reach the first magnetic recording layer 16.
and to be focused on the second magnetic recording layer 20,
Laser light sources 80, 82 and collimator lens 8
The positions of 4 and 86 have been 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.

Further, as shown in FIG. 14, the collimator lens 90 and the objective lens 70 are connected to the magneto-optical disk 1.
The focal position of the objective lens 70 can be selected between the first magnetic recording layer 16 and the second magnetic recording layer 20 by moving the laser light source 92 in the optical axis direction. It is also possible to position them all at once. That is, a screw shaft 96 rotated by a drive motor 94 whose position is fixed.
is screwed together with a slider 98 provided movably in a direction parallel to the screw shaft 96, and a laser light source 92 fixed to the slider 98 is connected to the objective lens 70 and the collimator lens 90 by rotation of the drive motor 94. It is moved in the direction of the optical axis. 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, a magneto-optical disk 100
As in the magneto-optical disk 10 described above, a first magnetic recording layer 16 and a second magnetic recording layer 20 are laminated on a transparent substrate 12 with a non-magnetic intermediate layer 18 in between. The first magnetic recording layer 16 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 uses GdDyFe with a Curie temperature of about 120° C., and the second magnetic recording layer 20 uses GdTbFe with 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. The focal depth δf of this objective lens 104 is a lens with a large focal depth δf similar to that of a conventional magneto-optical writing device, so that the first magnetic recording layer 16 and the second magnetic recording layer 20 can be heated simultaneously. There is. For example, a laser beam 106 is irradiated onto the magneto-optical disk 100 through an objective lens 104.
When the wavelength of is 0.83μm, objective lens 1
The numerical aperture NA of 04 is set to 0.45, and the depth of focus δf of the objective lens 104 in this case is set to ±1.3 μm from the above equation (19). That is, the total length of the focal depth δf is 2.6 μm, and the thickness of the nonmagnetic intermediate layer 18 is
It is desirable that the thickness be 2.5 μm or less. In this example, it is 17830 Å.

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 laser beam 106 is directed toward the magneto-optical disk 100 while forming a magnetic field in the direction indicated by M in the figure by exciting the annular coil 102.
The first magnetic recording layer 16 and the second magnetic 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 indicate locations that are perpendicularly magnetized by this writing 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 becomes higher than 120°C.
The first magnetic recording layer 16
Heat the desired recording location on top. 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 perpendicular magnetization occurs in the direction along the magnetic field M. Recording location 112 in FIG. 18 indicates where information is 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. Furthermore, even if the Curie temperature of the first magnetic recording layer 16 is higher than the Curie temperature of the second magnetic recording layer 20 in the magneto-optical disk 100, information is recorded in the same way. Further, even if three or more magnetic storage layers are laminated, information can be recorded in each magnetic recording layer according to the same operation as described above, as long as each layer has a different Curie temperature.

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 to this. For example, although the magneto-optical disk 10 or 100 in each figure is shown as a 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. Other elements may be substituted, other optical elements 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 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.

In addition, in the above-mentioned embodiment, for convenience of explanation,
Although the system is divided into a recording device and a reproducing device, in reality, recording and reproducing are normally performed using 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 form a recording device, and only the portions related to reproduction are taken out to be used 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 variation 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 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. 10th
The figure 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 stacked on the magneto-optical disk shown in FIG. 1. Figures 15 and 17 are
16 and 18 are diagrams illustrating other configuration examples of the magneto-optical disk shown in the figure and the operation of recording information on each of the magnetic recording layers laminated therein; FIG. 3 is a diagram showing a location written as a result of an information writing operation. Figures 19 and 20 show a wavelength λ ₁ of 8300 Å.
FIG. 6 is a diagram corresponding to FIGS. 5 and 6 for a laser beam having a wavelength λ ₂ of 6800 Å. 10: Magneto-optical disk (magneto-optical recording medium), 1
1: magneto-optical reproducing device, {16: first magnetic recording layer,
20: Second magnetic recording layer} (magneto-optical recording layer).

Claims (1)

[Scope of Claims] 1. A magneto-optical recording medium for reproducing information separately recorded in the magneto-optical recording layers in which at least two magneto-optical recording layers are laminated with a non-magnetic layer interposed therebetween. The reproducing device includes a first laser beam that outputs at least two first laser beams and a second laser beam that have different wavelengths from each other.
a laser light source and a second laser light source; a beam combining means for combining the first laser beam and the second laser beam into one beam; and condensing the single beam combined by the beam combining means to a single beam focusing means for making the light incident on the magneto-optical recording medium; a separating means for separating one beam emitted from the magneto-optical recording medium into laser beams of the first wavelength and the second wavelength; and the separating means. 1. A magneto-optical reproducing device comprising: first detection means and second detection means for receiving laser beams of a first wavelength and a second wavelength separated by a laser beam and detecting respective Kerr rotation angles.