JPH0817080A - Magneto-optical recording / reproducing method and magneto-optical recording medium used therefor - Google Patents

Abstract

(57) [Abstract] [Purpose] A recording / reproducing method for a magneto-optical disk which has a high linear recording density and can be applied to magneto-optical recording and multi-valued recording using a short wavelength laser, and a medium can be easily formed. The purpose is to provide a magneto-optical disk. According to the method and medium of the present invention, a medium having a noise level difference ΔN of 6 dB or less after erasure and after thermal demagnetization is used, and recording / reproduction of a mark row having a mark length of 0.2 μm or less is performed. Method to do. A magneto-optical recording layer is formed on a substrate directly or via an under layer, and the center line average surface roughness Ra of the substrate or the under layer in contact with the magneto-optical recording layer is 0.
A range of 3 nm or more and 3 nm or less, and the magneto-optical recording layer has a film thickness of 3 nm or more and 50 nm or less,
A medium having a specific composition. Tb with a film thickness of 50 to 300 nm
A medium having a magneto-optical recording layer made of an Fe-based or TbFeCo-based thin film, characterized in that the magnetization Ms at room temperature, the coercive force Hc at room temperature, and the Curie temperature Tc are in specific ranges.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording / reproducing method and a magneto-optical recording medium, and more particularly to a magneto-optical recording / reproducing method and a magneto-optical recording medium suitable for high density recording.

[0002]

2. Description of the Related Art A magneto-optical recording medium (hereinafter sometimes abbreviated as a recording medium or a medium) is normally recorded / reproduced by a light beam and an external magnetic field. Recording is performed by heat from a light beam and an external magnetic field. That is, the coercive force (hereinafter sometimes referred to as Hc) of the medium is reduced by locally raising the temperature of the medium by the light beam, and the magnetization direction is recorded by the external magnetic field.

The reproduction is performed by detecting a change in polarization (magneto-optical effect) of the light beam transmitted or reflected by the magneto-optical recording layer. The information is stored in the medium as a mark string whose magnetization direction is changed by the modulation of the light intensity or the magnetic field intensity. The shortest mark length recorded on the magneto-optical recording medium is usually limited by the spot diameter of the reproducing light beam.

8 commonly used in magneto-optical disks
In the case of a wavelength of 25 nm, the spot diameter is about 1.4 μm, so the shortest mark length is about 0.8 μm. The storage capacity of the magneto-optical recording medium is 128 even in the case of a magneto-optical disk having a diameter of 90 mm which is normally used at present.
Although it is as large as about megabytes, higher capacity is desired as a storage medium for moving image information and the like. To increase the capacity, it is necessary to shorten the mark length and write a large number of marks in a short area.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention conducted a study on high density recording and high capacity of a magneto-optical recording medium by a magnetic field modulation method. The magnetic field modulation method is said to be excellent as a means for recording a mark having a light beam spot size (usually about 1.4 μm) or less (for example, 13th Annual Meeting of the Applied Magnetics Society of Japan, p198).

As a result of examination, it was found that recording / reproduction was difficult when the mark length was 0.2 μm or less. This value is relatively larger than the generally known minimum magnetic domain size of the magneto-optical recording medium (for example, D. RUGAR, e.
t. al. , IEEE Trans. Magn. , M
AG-23, 1987).

This is because the wavelength of the semiconductor laser is shortened and the super-resolution technology (for example, O plus E, No154 19) is used.
September 1992 P81-83), multi-valued recording (for example, Japanese Patent Laid-Open No. 2-33750), partial response, etc. are possible, and there is no suitable recording medium when recording marks of 0.2 μm or less. That is a serious problem. The present invention was devised in view of these points,
An object of the present invention is to provide a magneto-optical recording / reproducing method suitable for high-density recording and a magneto-optical recording medium used therefor.

[0008]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, the gist of the present invention is a method for recording / reproducing a mark train having a mark length of 0.2 μm or less on a magneto-optical recording medium, which has a noise level when thermally demagnetized by a light beam in a non-magnetic field. , Similarly, noise level difference ΔN when magnetized in one direction using an external magnetic field
Relates to a magneto-optical recording / reproducing method characterized by using a magneto-optical recording medium having a value of 6 dB or less.

The present inventors measured the minimum recordable mark length Wmin of various magneto-optical recording media by making various magneto-optical disks and performing recording / reproducing. Mark recording was performed by a magnetic field modulation method, and an arbitrary mark length was recorded by modulating a magnetic field at a specific single frequency. The disk rotation speed was made as small as possible in order to reduce the influence of the magnetic field change speed.

In some cases, the evaluation of the mark may have a recording mark length smaller than the light beam spot, and it may not be possible by the usual CNR measurement. Therefore, the present inventors have devised a special evaluation method, that is, an evaluation method by measuring the change in noise of a specific frequency component of the reproduction signal. When a single mark having a length sufficiently smaller than the beam spot is correctly recorded, the total magneto-optical effect of the marks in the beam spot is always constant, and the noise component is small.

When the mark cannot be recorded correctly, in other words, when the mark length W to be recorded is smaller than the minimum recordable mark length Wmin of the magneto-optical recording layer,
Correct recording is impossible, and the total magneto-optical effect of the marks in the laser spot is not constant. for that reason,
The noise component becomes large. This evaluation method is an application of the AC erase method that is usually performed on magnetic disks and the like.

As a result of this evaluation, it was difficult to record to 0.2 μm or less in many magneto-optical recording media. This value is considerably larger than what is generally said. The values so far described are for the case where the magnetization was recorded at room temperature, and it is considered that it does not reflect the original characteristics of the magneto-optical recording that records at high temperature. Therefore, the present inventors wondered whether this problem could be overcome by using a specific medium.

The specific medium is a medium in which the magnetic domain width Wdem in a state of being thermally demagnetized in the absence of a magnetic field by the heat of the light beam is sufficiently smaller than the minimum mark length W to be recorded. The inside of the magnetic body is divided into many magnetic domains, and the magnetization is constant inside the magnetic domain (for example,
Chikaku, "Physics of Ferromagnetic Materials", Sokabo Co., Ltd.).

Since the magneto-optical recording layer uses a perpendicularly magnetized film having an easy axis of magnetization perpendicular to the substrate surface, the demagnetization state is a state where the magnetization is zero, but in a detailed view, a state in which upward and downward magnetic domains are separated. Has become. The magnetic domains in the demagnetized state can be observed by a magnetic force microscope MFM or the like, but their shapes are various, and they are stripe-shaped, bubble-shaped, labyrinth-shaped, or a mixture thereof.

The definition of Wdem is possible for stripes, bubbles, and mazes, but difficult for complicated shapes. The magnetic domain pattern can be indirectly measured by image processing, for example, by the value of (perimeter) ² / (area), but the value changes depending on the processing conditions and the reliability is poor. in this way,
Since the measurement of Wdem is difficult, the present inventors have devised a method for evaluating a physical quantity corresponding to Wdem by a simple measurement.

First, the thermally demagnetized medium was reproduced by a magneto-optical recording / reproducing apparatus, the noise level at a specific frequency was measured by a spectrum analyzer, and the magnetization of the medium was aligned in one direction, and the measurement was performed under the same measurement conditions. By measuring the noise level, the noise difference ΔN that does not depend on the fluctuation of the reflectance of the measuring machine and the medium is obtained. Playback conditions are ISO / IE
Complies with C10090.

The resolution bandwidth of the spectrum analyzer is 3
It is set to 0 kHz. The measurement frequency is 5 MHz when the medium moving speed (disk rotation speed) is 5.65 m / sec, the light wavelength is 825 nm, and the lens numerical aperture is 0.53. Linear velocity v m
/ Sec, wavelength λ μm, lens numerical aperture NA frequency
f MHz is given by equation (4).

[0018]

(4) f = 0.57vλ / NA (4)

The magnetization of the medium which has been thermally demagnetized is zero as a whole, but is not zero locally and is divided into magnetic domains. When Wdem is sufficiently smaller than the beam spot diameter, the total sum of magneto-optical effects in the beam spot becomes almost zero.

Therefore, even if the beam spot moves, there is almost no change in the sum of magneto-optical effects, and noise is hardly observed. When Wdem is large, that is, when the beam spot diameter cannot be ignored, the total magneto-optical effect in the beam is not zero, and when the beam spot moves, the total magneto-optical effect changes discontinuously according to the magnetic domain. To do.

Therefore, the noise becomes large, and Wdem can be evaluated by ΔN. The reason for evaluating the state after thermal demagnetization in a magnetic field is to stabilize the medium.
Magneto-optical recording media are often formed by sputtering, etc., but since they often have unstable magnetic domain widths in a non-equilibrium state immediately after formation, thermal demagnetization is required to measure the magnetic domain width. .

A magneto-optical recording / reproducing apparatus is used for thermal demagnetization. Conditions for thermal demagnetization such as irradiation beam power are ISO / IEC10
The erase conditions specified in 090 are complied with. However,
The applied magnetic field is zero. The use of the magneto-optical recording / reproducing apparatus has an advantage that the thermal demagnetization can be easily performed and the magnetic demagnetization can be performed under the condition that the influence of the leakage magnetic field of the medium itself is omitted.

The minimum recording magnetic domain width Wmin correlates with this noise level difference (ΔN).
It is difficult when N is 6 dB or more. In the region where ΔN is 6 dB or less, Wmin has a substantially proportional relationship with ΔN. That is, it is preferable that the recording amount of 0.2 μm or less is as small as ΔN, and is preferably 3 dB or less.

The magneto-optical recording medium used in the magneto-optical recording method of the present invention is a medium having a ΔN smaller than 6 dB, a magnetic domain width Wdem of 0.2 μm and a minimum mark length W to be recorded or less. , Recordable minimum mark length Wm
The medium in is W or less. These media will be described below. First, general items common to these media will be described, and then each of them will be described.

In the present invention, the substrate is usually a resin substrate such as a polycarbonate resin, an acrylic resin or a polyolefin resin provided with irregularities for tracking servo,
A ceramic substrate such as glass, a metal substrate such as an aluminum alloy, or a laminated substrate of these can be used. The substrate generally has a thickness of 0.5 to 1.5 mm.

A magneto-optical recording layer is provided on these substrates. A magnetic thin film having perpendicular magnetic anisotropy is used as the magneto-optical recording layer. For example, DyFeCo, TbFe
Magnetic alloy films of rare earth-transition metals such as Co, GdFeCo, NdFeCo, magnetic artificial lattice films of noble metals / transition metals such as Pt / Co, magnetic oxide films such as garnet, and laminated films of these magnetic thin films Is used.

The magneto-optical recording layer is usually formed by sputtering or vapor deposition, and the film thickness is preferably about 3 nm to 50 nm. An underlayer may be provided between the substrate and the magneto-optical recording layer. The underlayer is usually SiO ₂ ,
Such as _{Al 2 O 3, Ta 2 O} 5, Si 3 N 4, nitrides, and mixtures thereof, it is preferably used comprising a composite compound such as Al-Ta-O.

The base film is usually provided for the purpose of preventing the permeation of oxygen or moisture, the optical interference effect, the heat insulating effect and the like. Normally, light is incident through the substrate, but it may be incident from the opposite direction to the substrate. In this case, the base film (the film between the substrate and the recording layer) is a metal film such as Al, Au, Ag or an alloy thereof for the purpose of reflecting light, or an alloy such as an alloy of AlTa using these. May be used.

The film thickness is preferably about 2 nm to 200 nm. When light is incident from the substrate side, it is preferable to further provide a reflective layer on the recording layer for the purpose of adjusting reflectance, recording sensitivity, signal intensity and the like. Al, Au, A as the reflective layer
g or alloys thereof, or AlT using these
A metal film such as an alloy such as a is used.

These reflective layers are used for the purpose of improving the recording sensitivity of the magneto-optical recording medium, the stability against repeated reproduction, etc., in addition to the reflection of light. Other layers may be provided between the substrate, the underlayer, the magneto-optical recording layer, and the reflective layer in order to improve the characteristics. In particular, it is often practiced to provide a heat insulating layer between the magneto-optical recording layer and the reflective layer.

The magneto-optical recording medium used in the present invention is preferably realized by the following medium. That is, in a magneto-optical recording medium in which a magneto-optical recording layer is formed directly on a substrate or via an under layer, the center line average surface roughness Ra of the substrate or the under layer in contact with the magneto-optical recording layer is 0.3 nm or more. From 3 nm
2. The following range, the magneto-optical recording layer has a film thickness of 3 nm or more and 50 nm or less, and has a composition (atomic%) shown in the following formula (1). It is a magneto-optical recording medium used in a recording / reproducing method.

[0032]

In TbxFeyCoz, (1) 10 ≦ x ≦ 25 55 ≦ y ≦ 90 0 ≦ z ≦ 20

Further, it is particularly preferable that a magneto-optical recording layer is formed on a substrate via an underlayer, and the underlayer has a substrate temperature of 100 ° C. or less and a pressure of 0.4 Pa or more and 1.0 Pa or less. A magneto-optical recording medium made of a sputtered Ta oxide, wherein a magneto-optical recording layer is formed on a substrate via an underlayer, and the underlayer has a Ta oxide density of 9 g / cm ³ or a simple substance. The magneto-optical recording medium is made of an oxide of the following substances.

Ra is preferably 0.5 nm or more and 2.5 n
m or less, the film thickness is 10 nm or more and 30 nm or less, the Tb content is 15% or more and 20% or less, and the Co content is 15% or less. The magneto-optical recording layer can be easily formed into a perpendicularly magnetized film by sputtering, and a TbFeCo-based thin film that is normally used at present is preferable in practice.

When the Tb content is less than 10%, TbF
The remanent magnetization in the perpendicular direction at the zero applied magnetic field is extremely reduced due to the effect of the magnetization of eCo itself. ΔN increases as the Tb content increases. If the Co composition is more than 20%, the magnetization and the Curie temperature increase, and the magnetic field sensitivity and the light beam sensitivity are extremely lowered.

The larger the Ra of the substrate or the underlayer, the more ΔN
However, when it is larger than 3 nm, the reflectance fluctuation becomes large. The composition of the TbFeCo-based thin film is determined by chemical analysis using an inductively coupled plasma emission spectrometer (ICP), fluorescent X-rays, etc.
A gas such as r, oxygen, or nitrogen, or an element intentionally added to prevent a change over time may be included as long as the magnetic characteristics of the medium are not significantly changed.

The definition of Ra complies with JIS0601.
The measurement is made with an atomic force microscope AFM, and the cutoff value is 1
μm. As a method of controlling Ra of the substrate, for example, in the case of an aluminum substrate or a glass substrate, there are chemical etching, etching by sputtering or the like, or tape polishing.

In the case of a plastic substrate, Ra of the molded substrate can be changed by a method of changing Ra according to the stamper manufacturing conditions (for example, resist type, developing condition, plating condition, etc.). Ra can also be changed by adding a filler such as alumina powder to the resin.

Ra of the resin substrate can also be changed by performing etching such as sputtering.
As a practically preferable method of controlling Ra, a specific underlayer is provided on the substrate. That is, a desired Ra can be obtained by providing an underlayer made of a specific substance or a specific preparation condition.

As described above, the underlying layer usually has optical interference effect, heat insulating effect, anti-oxidation effect on the magneto-optical recording layer, etc., but the oxide of Ta satisfies the above conditions and is used as the material of the underlying layer. It is suitable. Ra of the oxide of Ta can be easily controlled to a desired value depending on the film forming conditions. That is,
The underlayer has a substrate temperature of 100 ° C. or lower and 0.4 Pa or higher.
Oxide of Ta sputtered at pressures below 0 Pa provides a desirable underlayer.

When the substrate temperature for forming the underlayer by sputtering is higher than 100 ° C., it becomes difficult to use the plastic substrate, and Ra may have different values. Therefore, the temperature is preferably 80 ° C. or lower. A film having Ra of 0.3 nm or more at a sputtering pressure of 0.4 Pa or more can be easily obtained, but a sputtering pressure of more than 1.0 Pa results in a thin film with many voids, which causes a problem with stability over time.

Therefore, the sputtering pressure is preferably 0.4 Pa or more and 1.0 Pa or less, particularly preferably 0.5 Pa or more and 0.8 Pa or less. Ra can also be changed by adding an additive to the oxide of Ta.
That is, the underlayer has a density of Ta oxide and simple substance of 9 g / c.
It is also preferable to use a combination of oxides of substances of m ³ or less.

As oxides used in combination, Al, Si, Z
Examples thereof include oxides of r, Y, Mg, Ti, Ce, Li, Fe, Co and the like. The underlayer can be obtained by reactive sputtering with an alloy target of these and Ta, or by sputtering a sintered body composed of a mixture of these oxides.

From the characteristics of sputtering in which target particles are scattered by collision of sputtering gas particles, the additive is preferably an oxide of an element having a Ta density of about 16.6 g / cm ³ of about 1/2. In particular, the addition of an Al oxide having a density of 2.7 g / cm ³ is particularly preferable for practical use because Ra is easily controlled and the effect of preventing oxidation of the magneto-optical recording layer is improved.

The magneto-optical recording medium used in the present invention is
In a TbFeCo-based thin film to which a specific element is added,
It can be obtained as long as it satisfies a certain physical property value. That is,
This medium is a magneto-optical recording medium in which a magneto-optical recording layer is formed on a substrate directly or via an underlayer, and the magneto-optical recording layer is B, N, O, Al, Si, Ti, Cr, Ge, P
It is composed of a TbFeCo-based thin film having a film thickness of 3 to 50 nm containing one or more elements selected from r, Nd, Sm, Gd and Dy, and has a magnetization Ms at room temperature, a coercive force Hc at room temperature, and a Curie temperature Tc. The magneto-optical recording medium used in the recording / reproducing method according to claim 1, which satisfies the following expressions (2) and (3).

[0046]

[Equation 6] 1.0 × 10 ⁶ ≦ Ms × Hc ≦ 2.0 × 10 ⁶ erg / cm ³ (2) 100 ≦ Tc ≦ 300 ° C. (3)

By adding a specific element to TbFeCo,
ΔN decreases. Although this principle is not clear, impurities as an additive element hinder the domain wall movement of the TbFeCo-based thin film, so that fine magnetic domains can exist, and Wde
It is considered that m and ΔN are decreased.

B, N, O, Al and S are added elements.
i, Ti, Cr, Ge, Pr, Nd, Sm, Gd, Dy
Is valid. From the standpoint of preventing oxidation of the magneto-optical recording layer, Al, Ti, and Cr are particularly preferable from the practical point of view of producing by including a trace amount of Al, Ti, and Cr in the sputtering gas.

By making the magnetic domains finer by the additional element, ΔN can be obtained in a relatively wide composition satisfying the above formulas (2) and (3).
Is confirmed to be 6 dB or less. Further, the magneto-optical recording medium used in the present invention is TbF having a specific film thickness.
It can be obtained as long as a certain physical property value is satisfied in the e-based or TbFeCo-based thin film. That is, this medium
A magneto-optical recording medium in which a magneto-optical recording layer is formed directly on a substrate or via an underlayer, wherein the magneto-optical recording layer has a film thickness of 50.
.About.300 nm of a TbFe-based or TbFeCo-based thin film, and the magnetization Ms at room temperature, the coercive force Hc at room temperature, and the Curie temperature Tc satisfy the following formulas (4) and (5). Do

(7) 0.5 × 10 ⁶ ≦ Ms × Hc ≦ 2.0 × 10 ⁶ erg / cm ³ (4) 100 ≦ Tc ≦ 300 ° C. (5)

Further, the magneto-optical recording medium used in the present invention is a TbFe system or TbFeCo having a specific film thickness.
It can be obtained as long as a certain physical property value is satisfied in the system thin film. That is, this medium is a magneto-optical recording medium in which a magneto-optical recording layer is formed directly on a substrate or via an underlayer, and the magneto-optical recording layer has a film thickness of 50 to 300 nm of TbFe.
And a TbFeCo-based thin film, and is characterized in that the magnetization Ms at room temperature, the coercive force Hc at room temperature, and the Curie temperature Tc satisfy the following formulas (4) and (5). The magneto-optical recording medium used is TbFe-based or TbFeCo having a specific film thickness.
It can be obtained as long as a certain physical property value is satisfied in the system thin film.

That is, this medium is a magneto-optical recording medium in which a magneto-optical recording layer is formed directly on a substrate or via an underlayer, and the magneto-optical recording layer has a thickness of 50 to 300 nm.
2. A bFe-based or TbFeCo-based thin film, wherein the magnetization Ms at room temperature, the coercive force Hc at room temperature, and the Curie temperature Tc satisfy the following formulas (4) and (5). This is a magneto-optical recording medium used in the recording / reproducing method.

[0052]

[Formula 8] 0.5 × 10 ⁶ ≦ Ms × Hc ≦ 2.0 × 10 ⁶ erg / cm ³ (4) 100 ≦ Tc ≦ 300 ° C. (5)

The magnetic energy stored in the recording layer mainly includes domain wall energy in addition to magnetostatic energy. Generally, the magnetic domain size and shape are determined mainly by the balance between the magnetic energy represented by these two and the coercive force of the recording layer. Analytical handling is extremely difficult because the actual magnetic domain shape is complicated and temperature changes must be taken into consideration in the case of magneto-optical recording, but the general tendency is that magnetic domains are subdivided. For example, magnetostatic energy is said to decrease and domain wall energy to increase.

A film thickness of 50 to 300 nm (preferably 50)
Although it is not clear why ΔN is 6 dB or less at a film thickness larger than nm, it is considered that the magnetic domains are subdivided and noise is reduced. It is considered that when the magnetic domains are subdivided, the magnetic energy stored in the recording layer is reduced and a stable state is achieved. The magneto-optical recording layer has a film thickness of 50 to 300.
It was confirmed that in the case of a TbFe-based or TbFeCo-based thin film having a thickness of nm, ΔN is 6 dB or less even if the above formulas (4) and (5) are in a relatively wide range. If the film thickness is too large, the recording sensitivity will decrease, so it is more preferable that the film thickness be 200 nm or less. When the film thickness is less than 50 nm, it becomes difficult to subdivide the magnetic domains, and it is considered that the conditions described in claims 2 to 5 are necessary.

[0055]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. Example 1 An underlayer made of Ta oxide was formed on a polycarbonate resin substrate by a reactive sputtering method of Ar and oxygen with Ta as a target at a pressure of 0.7 Pa to a thickness of 90 nm.

The substrate temperature measured by the heat label is 35-35.
It was 40 ° C. Also, the same as the underlayer formed on the glass substrate is the same as Na manufactured by US Digital Instrumental Corporation.
Ra measured by noscope III at a cutoff value of 1 μm was 1.0 nm. On top of this, Tb ₂₂ Fe
_The magneto-optical recording layer made of ₇₀ Co ₈ (atomic%) is 20 nm,
A heat insulating layer made of silicon nitride has a thickness of 30 nm and is made of Al ₉₇ Ta ₃
And a protective layer made of a cured product of an ultraviolet curable resin was formed in a thickness of 4 μm to form a magneto-optical disk having a diameter of 90 mm.

This magneto-optical disk was subjected to thermal demagnetization at a disk rotation speed of 5.65 m / sec and laser power of 9 mW using a magneto-optical recording / reproducing apparatus using a laser having a wavelength of 825 nm and a magnetic head, and ΔN was measured. 0.2
It was dB. This disc was measured with the same magneto-optical recording / reproducing apparatus for a magnetic field of 120 Oersted, a laser power of 4 mW, and a disc rotation speed of 1 m / sec to measure Wmin.
It was 0.06 μm, and it was confirmed that a mark of 0.2 μm or less could be recorded.

Example 2 A magneto-optical disk having a diameter of 90 mm was prepared in the same manner as in Example 1 except that the underlayer was formed to have a thickness of 90 nm by a reactive sputtering method using Ar ₈₀ Ta ₂₀ as a target and Ar and oxygen. ΔN, Wmin, and Ra of this magneto-optical disk were measured in the same manner as in Example 1, and the results were 1.3 dB, 0.10 μm, and 1.4 nm, respectively.
It was confirmed that recording of marks of 0.2 μm or less was possible.

Example 3 An underlayer made of Ta oxide was formed to a thickness of 90 nm at a pressure of 0.59 Pa, and a magneto-optical recording layer made of Tb ₁₈ Fe ₇₄ Co ₈ was formed to a thickness of 20 nm thereon. A magneto-optical disk having a diameter of 90 mm was prepared in the same manner as in Example 1 except for the above. For this magneto-optical disk, Δ as in Example 1.
As a result of measuring N, Wmin, and Ra, each is 2.3d.
B, 0.10 μm, 0.8 nm, and it was confirmed that recording of marks of 0.2 μm or less was possible. Also, Nanoscope made by US Digital Instrument
As a result of observing the magnetic domain image by the magnetic force microscope mode of III, a magnetic domain of 0.1 μm was confirmed.

Example 4 Example 3 was repeated except that a magneto-optical recording layer made of Tb ₂₁ Fe ₆₉ Co ₈ O ₂ made of an argon / oxygen mixed gas having an oxygen concentration of 0.05% by volume was formed to a thickness of 22 nm. A magneto-optical disk having a diameter of 90 mm was created under the same conditions. As a result of measuring ΔN, Wmin, MsHc product and Tc at room temperature of this magneto-optical disk, they were 4.1 dB and 0.12, respectively.
μm, 1.6 × 10 ⁶ erg / cm ³ 180 ° C.

Example 5 An underlayer made of Ta oxide was formed on a polycarbonate resin substrate to a thickness of 60 nm by a reactive sputtering method of Ar and oxygen with Ta as a target. On this Tb ₁₈
A magneto-optical recording layer made of Fe ₇₄ Co _{8 having a} thickness of 163 nm, a heat insulating layer made of silicon nitride having a thickness of 30 nm, and a reflective layer made of Al ₉₇ Ta ₃ having a thickness of 50 nm were formed in this order, and a protective film made of a cured product of an ultraviolet curable resin was formed. A magneto-optical disk having a diameter of 90 mm and having a thickness of 4 μm was prepared.

This magneto-optical disk was subjected to thermal demagnetization at a disk rotation speed of 5.65 m / sec and laser power of 9 mW using a magneto-optical recording / reproducing apparatus using a laser having a wavelength of 825 nm and a magnetic head, and ΔN was measured. 3.0
It was dB. This disc was recorded by the same magneto-optical recording / reproducing apparatus with a magnetic field of 150 oersted and a laser power of 4.5 m.
As a result of measuring Wmin at W and a disk rotation speed of 2 m / sec, it was confirmed that a mark of 0.12 μm, which is 0.2 μm or less, can be recorded. Furthermore, NanoscopeI
As a result of observing the magnetic domain image by II, a recorded magnetic domain array image having a mark length of 0.15 μm was clearly observed. The MsHc product and Tc of the recording layer of this magneto-optical disk at room temperature are
The values were 1.0 × 10 ⁶ erg / cm ³ and 220 ° C., respectively.

Comparative Example 1 A magneto-optical disk having a diameter of 90 mm was prepared in the same manner as in Example 1 except that the underlayer made of Ta oxide was formed by sputtering at a pressure of 0.32 Pa to a thickness of 90 nm. As a result of measuring ΔN, Wmin, and Ra of this magneto-optical disk in the same manner as in Example 1, the results were 8.1.
dB, 0.26 μm, 0.2 nm, and it was difficult to record a mark of 0.2 μm or less.

Comparative Example 2 Tb ₂₄ Fe ₅₃ Co ₂₃ as a magneto-optical recording layer having a thickness of 20 nm
A magneto-optical disk having a diameter of 90 mm was prepared in the same manner as in Comparative Example 1 except that the magneto-optical disk was formed. As a result of measuring ΔN and Wmin of this magneto-optical disk in the same manner as in Example 1, it was 14.2 dB and 0.38 μm, respectively, and it was difficult to record marks of 0.2 μm or less.

[0065]

In the magneto-optical recording system and medium according to the present invention, the difference ΔN in noise level after erasing and after thermal demagnetization is 6 dB.
A method of recording / reproducing a mark row having a mark length of 0.2 μm or less using the following medium, and a medium used therefor. The linear recording density is remarkably improved, and it can be applied to magneto-optical recording using a short wavelength laser and multilevel recording. Further, the medium formation becomes easy, and high density recording becomes practical.

Claims (6)

[Claims] 1. A method for recording / reproducing a mark train having a mark length of 0.2 μm or less on a magneto-optical recording medium, the noise level when thermally demagnetized by a light beam in a non-magnetic field, and the same external level. A magneto-optical recording / reproducing method characterized by using a magneto-optical recording medium having a noise level difference ΔN of 6 dB or less when magnetized in one direction using a magnetic field. 2. A magneto-optical recording medium in which a magneto-optical recording layer is formed on a substrate directly or via an under layer, the center line average surface roughness R of the substrate or the under layer being in contact with the magneto-optical recording layer.
a is in the range of 0.3 nm or more and 3 nm or less, the magneto-optical recording layer has a film thickness of 3 nm or more and 50 nm or less, and has the composition (atomic%) shown in the following formula (1). A magneto-optical recording medium used in the recording / reproducing method according to claim 1. In TbxFeyCoz, (1) 10 ≦ x ≦ 25 55 ≦ y ≦ 90 0 ≦ z ≦ 20 3. A magneto-optical recording layer is formed on a substrate via an underlayer, and the underlayer has a substrate temperature of 100.degree.
The magneto-optical recording medium according to claim 2, which is made of an oxide of Ta sputtered at a pressure of Pa or more and 1.0 Pa or less. 4. A magneto-optical recording layer is formed on a substrate via an underlayer, and the underlayer has a density of Ta oxide and simple substance of 9 g /
The magneto-optical recording medium according to claim 2, wherein the magneto-optical recording medium is made of an oxide of a substance having a cm3 or less. 5. A magneto-optical recording medium having a magneto-optical recording layer formed on a substrate directly or via an underlayer, wherein the magneto-optical recording layer is B, N, O, Al, Si, Ti, Cr, Ge. , P
TbFe system or Tb having a film thickness of 3 to 50 nm containing one or more elements selected from r, Nd, Sm, Gd and Dy
Magnetization M consisting of FeCo thin film and at room temperature
The magneto-optical recording medium used in the recording / reproducing method according to claim 1, wherein s, coercive force Hc at room temperature, and Curie temperature Tc satisfy the following equations (2) and (3). [Formula 2] 1.0 × 10 ⁶ ≦ Ms × Hc ≦ 2.0 × 10 ⁶ erg / cm ³ (2) 100 ≦ Tc ≦ 300 ° C. (3) 6. A magneto-optical recording medium in which a magneto-optical recording layer is formed on a substrate directly or via an underlayer, wherein the magneto-optical recording layer is TbFe-based or TbFeC having a thickness of 50 to 300 nm.
It is composed of an o-based thin film and has a magnetization Ms at room temperature, a coercive force Hc at room temperature, and a Curie temperature Tc represented by the following formula (4).
And the following formula (5) is satisfied:
A magneto-optical recording medium used in the recording and reproducing method described. [Expression 3] 0.5 × 10 ⁶ ≦ Ms × Hc ≦ 2.0 × 10 ⁶ erg / cm ³ (4) 100 ≦ Tc ≦ 300 ° C. (5)