JPH1083588A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize high recording density by forming grooves or lands in such a manner that the difference Δd in depth between adjacent grooves or the difference Dd in height between adjacent lands satisfies the relation of 0.20<=Δd×n/λ<=0.30, wherein λ is the wavelength and n is the refractive index. SOLUTION: On one surface of a transparent substrate 1, grooves G1 , G2 to guide (for tracking) a light beam 5 and lands L1 , L2 between grooves are formed, and a reading layer 2, magneto-optical recording layer 3, and protective layer to prevent oxidation are formed thereon. As for the transparent substrate 1, a glass substrate or plastic substrate such as polycarbonate, polystyrene, polybiphenol chloride epoxy or acryl resin is preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical device for recording and reproducing information by irradiating a light beam from a semiconductor laser or the like and utilizing the fact that the polarization plane of light is changed by a magneto-optical effect (such as the Kerr effect). The present invention relates to a magneto-optical recording medium such as a disk.

[0002]

2. Description of the Related Art Conventionally, a magneto-optical disk, which is a kind of magneto-optical recording medium, has a multilayer perpendicular magnetization film comprising at least two layers of a recording layer and a recording auxiliary layer formed on a disk-shaped transparent substrate. A bit having an upward magnetization and a bit having a downward magnetization are spirally recorded on the recording layer, and the bit is irradiated with a light beam such as a semiconductor laser, and the rotation angle (Kerr rotation angle) of the polarization plane of the reflected light is upward. Utilizing the opposite of the downward magnetization, it is reproduced as binarized digital data.

[0003] Further, it comprises a magneto-optical recording layer composed of a perpendicular magnetic film and a read layer laminated thereon and composed of an in-plane magnetic film at room temperature. When information is recorded, the read layer is irradiated with a light beam and heated. In the case where a perpendicular magnetization portion is formed at an irradiated portion and information is read out, a type utilizing the Kerr effect by the perpendicular magnetization portion of the readout layer has been proposed (Japanese Patent Laid-Open No. 8-55).
375). In this case, the in-plane magnetized portion of the readout layer does not show the Kerr effect, and the polarization plane of the incident light beam does not rotate. However, in the perpendicular magnetization portion of the readout layer, the polarization plane of the light beam is rotated and reflected by the Kerr effect. Is done. The change / non-change of the polarization plane of the reflected light is detected and recorded and reproduced as binarized digital data.

In the above-described example in which recording is performed using an in-plane magnetic film, a groove and a land for guiding (tracking) a light beam are formed on at least one surface of a transparent substrate made of glass, plastic, or the like, and the depth of the groove is set to d. Where λ is the wavelength of the light beam and n is the refractive index of the transparent substrate,
By setting 0.13 × λ / n ≦ d ≦ 0.18 × λ / n, even if the track density is increased, that is, the width of the groove and the width of the land are reduced, Thus, a high recording density was obtained by reducing the amount of crosstalk from the recording medium.

In such a magneto-optical disk, the recording layer or the readout layer can be initialized as many times as possible by providing an initialization layer or applying a strong initialization magnetic field from the outside. Is expected as a recording medium.

[0006]

However, in the above-mentioned conventional example, the light intensity showing a substantially Gaussian distribution is 1 / e ² (e is the natural logarithm base and e ≒ 2) of the light intensity at the center of the light beam. .72) is D.
When the track pitch p is 0.6 ≦ D / p ≦ 1.
It is said that it is better to set to 2, that is, the light beam diameter D cannot be made larger than 1.2 times the track pitch p. That is, if the recording density is increased by reducing the track pitch, the diameter of the light beam must be reduced to the same extent.

Conventionally, generally, the spot of a light beam is
The light is narrowed down to the diffraction limit by the condenser lens and is minimized. To further reduce the spot of the light beam, it is necessary to shorten the light wavelength or increase the aperture ratio of the condenser lens. However, semiconductor lasers with short wavelengths such as green and blue are currently under development, and if the aperture ratio of the condenser lens is increased, the condenser lens becomes too close to the magneto-optical recording medium, making it difficult to design a peripheral mechanism. Further, since the depth of focus becomes shallow, very high focusing accuracy is required. Therefore, it has been difficult to reduce the light beam diameter.

Accordingly, the present invention has been completed in view of the above circumstances, and an object of the present invention is to reduce the amount of crosstalk from an adjacent groove or land without reducing the diameter of a light beam, thereby achieving a high recording density. It is to realize.

[0009]

The magneto-optical recording medium according to the present invention comprises a groove provided on a transparent substrate for guiding a light beam and a magneto-optical recording layer laminated on a land between the grooves. In a magneto-optical recording medium for recording and reproducing information on lands, a difference Δd is provided between the depth of adjacent grooves and / or the height of adjacent lands, the wavelength of the light beam is λ, the refractive index of the transparent substrate Where n is
It is characterized in that 0.20 ≦ Δd × n / λ ≦ 0.30.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIG. 3A is a partial cross-sectional view of the optical disc, and FIG. 3B is a side view in which grooves and lands of the optical disc are partially enlarged.

In FIG. 1, grooves G ₁ , G ₂ for guiding (tracking) a light beam 5 and lands L ₁ , L ₂ between the grooves are formed on one substrate surface of a transparent substrate 1. A readout layer 2, a magneto-optical recording layer 3, and a protective layer 4 for preventing oxidation are formed thereon. The tracking of the light beam 5 is performed by a known three-beam method (far-field method) or the like. The present invention relates to a focusing beam for detecting information, but may be applied to a tracking beam.

In the present invention, when the difference in height between adjacent lands is Δd ₁ , and the difference in depth between adjacent grooves is Δd ₂ , Δd ₁ × n / λ, Δd ₂ × n / λ
Are set to be 0.20 or more and 0.30 or less. At this time, if only Δd ₁ exists, Δd = Δ
When only d ₁ and Δd ₂ are present, Δd = Δd _{2. When} both are present, Δd means Δd ₁ and Δd ₂ , in which case Δd ₁ and Δd ₂ may be different values, and Δd = Δd ₁ = Δd ₂ . Note that the above λ
Is the wavelength of the light beam 5, and n is the refractive index of the transparent substrate 1.

When, for example, as shown in FIG. 1B, the readout layer 2 on the land is irradiated with the light beam 5 whose light beam diameter D of the spot 6 at the irradiation site is larger than the width of the land, the groove is formed. As a result, reflected beams (crosstalk) 5A and 5B are generated. The reflected beams 5A and 5B interfere with each other, and are strengthened or weakened depending on the manner of interference. At this time, the reflected beam 5
When the phase difference between A and 5B is about 1/2 of the wavelength, they are mutually weakened and the reflected light intensity is minimized, so that the optical path length difference (twice the depth difference between grooves) 2Δd ₂ is calculated. , 0.
It is set to be 40 × λ / n or more and 0.60 × λ / n or less. Therefore, Δd _{2 is set} to 0.20 × λ / n or more and 0.30 × λ / n.
That is, Δd ₂ × n / λ is set to 0.20 or more and 0.30 or less. This is the same when irradiating the groove, and Δd ₁ λ / n is set in the above range.

In the present invention, when the track pitch is p and the light beam diameter at a position where the light intensity of the light beam is 1 / e ² of the light intensity at the beam center is D, 0.6 ≦ D / p
It is preferable to set ≦ 1.5. If it is less than 0.6, information reading will be insufficient, and if it exceeds 1.5, crosstalk will increase.

At least one of Δd ₁ and Δd ₂ as Δd only needs to be present, and when both exist, Δd ₁ and Δd ₂ are made substantially equal in the groove and the land. This is preferable because the effect of attenuating the reflected beam is obtained. Further, it is preferable that the width of the groove and the width of the land are substantially the same because the same effect can be obtained in the groove and the land. It is preferable to form a bit (recording magnetic domain) in both the land and the groove, that is, so-called land / groove recording in order to increase the recording capacity. However, it is preferable to form the bit in either the land or the groove. You may. At least Δd ₂ if there is a bit only in the land
Is provided, and when there is a bit only in the groove, it is necessary that at least Δd ₁ be provided.

Thus, the present invention has the effect of reducing crosstalk from adjacent grooves or lands and reducing the light beam diameter to achieve high recording density.

Further, in the present invention, the transparent substrate 1 is preferably a glass substrate, a plastic substrate made of polycarbonate, polystyrene, polychlorinated biphenyl, epoxy, acrylic resin or the like. The readout layer 2 exhibits in-plane magnetization at room temperature and has a temperature of 100 to 1 higher than room temperature.
A material that can change to perpendicular magnetization at about 25 ° C. and has a Curie temperature of about 200 ° C.
dFeCo, GdCo, GdFe, TbFeCo, Dy
FeCo, HoFeCo and the like are suitable. The magneto-optical recording layer 3 may be made of a material having a perpendicular magnetization from room temperature to the Curie temperature and having a Curie temperature of about 150 to 250 ° C. and having a predetermined atomic ratio of DyFeCo, TbFeC.
o, GdTbFe, NdDyFeCo, GdDyFeC
o, GdTbFeCo and the like are preferable. As the protective layer 4, an ultraviolet curable resin such as polyurethane acrylate,
A thermosetting resin is preferable, and can be cured after forming a flat surface after application.

A functioning as a protective layer, an antireflection layer or a Kerr rotation angle enhancing layer between the transparent substrate 1 and the readout layer 2 and between the magneto-optical recording layer 3 and the protective layer 4.
A transparent dielectric layer made of 1N or the like may be laminated, and further, between the magneto-optical recording layer 3 and the protective layer 4 in order to increase the reflectivity of the light beam 5 and increase the light use efficiency. Al, A
A reflective layer made of u or the like may be provided.

The groove and the land, the readout layer 2, the magneto-optical recording layer 3, and the protective layer 4 are provided on one substrate surface of the transparent substrate 1, but may be provided on both (front and back) substrate surfaces. Different information can be recorded and reproduced on both sides.

Further, the present invention can be applied to a magneto-optical recording medium having grooves and lands formed thereon. For example, the present invention relates to a magneto-optical recording medium having a multi-layered perpendicular magnetic film, which comprises a recording layer and a recording auxiliary layer. The present invention can be applied to an overwritable type including a recording layer, a writing layer, an intermediate layer (control layer), and an initialization layer.

It should be noted that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the present invention.

[0022]

Embodiments of the present invention will be described below. An optical disk having a configuration as shown in FIG. 1 is manufactured, and Δd = Δd ₁ = Δd ₂
And the values are 70 nm (0.16λ / n), 90 nm
(0.21λ / n), 110 nm (0.25λ / n),
130 nm (0.30λ / n), 150 nm (0.35
λ / n), and the crosstalk amount when D / p was changed from 0.75 to 1.50 is shown in Table 1. Note that λ
A transparent substrate 1 is a polycarbonate substrate with n = 1.58, the readout layer 2 is made of GdFeCo having a predetermined atomic ratio, and the magneto-optical recording layer 3 is made of TbFeCo having a predetermined atomic ratio. The protective layer 4 is made of polyurethane acrylate.

[0023]

[Table 1]

As shown in Table 1, even when D / p is increased to 1.50, that is, when the light beam diameter is set to about 1.5 times the track pitch p, the crosstalk amount is -27 at the maximum.
It could be reduced to dB. D / p is 1.50
If smaller, the amount of crosstalk was further reduced.

As another embodiment, it is assumed that there is only a depth difference Δd = Δd ₂ between adjacent grooves.
It is shown in Table 2. Other configurations were the same as those in Table 1.

[0026]

[Table 2]

As shown in Table 2, even if D / p was increased to 1.50, the amount of crosstalk could be reduced to a maximum of -26 dB. When D / p was smaller than 1.50, the crosstalk amount was further reduced.

[0028]

According to the present invention, 0.20 ≦ Δd × n / λ ≦
By setting it to 0.30, even if the light beam diameter is as large as 1.5 times the track pitch, that is, even if the light beam diameter is kept as it is and the track pitch is reduced, the adjacent groove or land may be used. The recording density can be reduced and the high recording density can be realized.

The present invention can be applied to any medium that reads information using a magneto-optical effect (such as the Faraday effect and the Kerr effect), such as a magneto-optical disk, a magneto-optical tape, and a magneto-optical card.

[Brief description of the drawings]

FIG. 1A is a partial cross-sectional view of a magneto-optical disk of the present invention, and FIG. 1B is a partially enlarged side view of a groove and a land of FIG.

[Explanation of symbols]

 1: transparent substrate 2: readout layer 3: magneto-optical recording layer 5: light beam 5A, 5B: reflected beam (crosstalk) 6: spot

Claims (1)

[Claims] 1. A magneto-optical recording medium comprising: a groove provided on a transparent substrate for guiding a light beam; and a magneto-optical recording layer laminated on a land between the grooves, and recording and reproducing information on the groove and / or the land. In the above, when a difference Δd is provided between the depth of adjacent grooves and / or the height of adjacent lands, the wavelength of the light beam is λ, and the refractive index of the transparent substrate is n, 0.20 ≦ Δd × n /Λ≦0.30, a magneto-optical recording medium.