JPH11126381A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical recording medium with which the higher density of the recording density accompanying the microminiaturization of recording magnetic domains is realized and an improvement in regenerative signal quality are made possible. SOLUTION: The magneto-optical recording medium which is formed with the recording magnetic domains and is recorded with information by utilizing the temp. distribution by irradiation with a laser beam and the externally impressed magnetic fields by a magnetic field generator is subjected to recording of information by the recording magnetic domains of d/L×100<20(%) when the distance from the start position of the arbitrary recording magnetic domain to the position where the magnetic domain width of this recording magnetic domain exhibits the max. value or begins to exhibit the max. value is defined as (d) and the length of the max. width of the recording magnetic domains width as L.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a magneto-optical recording medium for recording / reproducing with a laser beam, and more particularly to a magneto-optical recording medium capable of high-density recording of the medium.

[0002]

2. Description of the Related Art As one of large-capacity memories in which information can be rewritten, a magneto-optical recording medium that performs reproduction and recording using a laser beam has attracted attention. Since the beam waist diameter is determined by the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens, the magneto-optical recording medium can detect a spatial frequency of up to about 2 NA / λ during signal reproduction. However,
There is a growing demand for a further increase in the capacity of magneto-optical recording media. For the purpose of satisfying this requirement, that is, in order to increase the recording density of the magneto-optical recording medium to a density exceeding the diffraction limit determined by the wavelength λ and the numerical aperture NA, the recording medium configuration and reading method are devised to reduce the recording density. Improved techniques are being developed.

The following is an example of a magneto-optical recording medium in which the recording density is increased to a minute recording magnetic domain length exceeding the optical diffraction limit.

For example, in JP-A-3-93058 and JP-A-6-124500, signal recording is performed on a recording holding layer of a multilayer film having a magnetically coupled reproducing layer and a recording holding layer. At the same time, a signal reproducing method has been proposed in which a signal recorded on the recording holding layer is read while transferring the signal recorded on the recording holding layer to a heated region of the reproducing layer by heating by irradiating a laser beam (see FIG. 3).

According to this method, an area (aperture) where the spot diameter of the reproduction laser is heated by the laser to reach the transfer temperature and a signal is detected.
Can be limited to a smaller area, so that intersymbol interference during reproduction can be reduced, and a signal having a bit period equal to or less than the optical detection limit λ / 2NA can be reproduced.

As another example, JP-A-6-290496 has been proposed as a magneto-optical recording medium, a reproducing method, and a reproducing apparatus which compensate for the disadvantages of the super-resolution magneto-optical recording / reproducing method.

In JP-A-6-290496, a magneto-optical recording medium composed of a multilayer film composed of at least three layers utilizing magnetic exchange coupling is used to reduce the reproduction signal amplitude to below the optical detection limit. A magneto-optical recording medium, a reproducing method, and a reproducing apparatus capable of reproducing a signal having a period of at a high speed and greatly improving the recording density and the transfer speed have been proposed.

That is, a temperature distribution is given to the read / write mark by an attached heating device, and the temperature distribution and the temperature dependency of the magnetic energy in the read / write mark induce a pressure on the domain wall to move into the read light spot. (See FIG. 4). As a result, the domain wall instantaneously moves into the reproducing light spot, the directions of the atomic spins in the reproducing light spot are reversed, and all are aligned in one direction, and the reproduction signal amplitude is the interval between the recorded magnetic domain walls (that is, the recording mark). Regardless of the length, the amplitude is always constant and maximum, and the problem of waveform interference and the like due to the optical diffraction limit is completely eliminated. The above-mentioned reproducing method will be referred to as a domain wall moving magnetic domain expansion reproducing method.

[0009]

The super-resolution magneto-optical recording / reproducing system and the domain wall moving magnetic domain enlarging / reproducing system are both reproducing systems which exceed the optical diffraction limit. Is based on the premise that minute recording magnetic domains exceeding the diffraction limit are formed. The recording of microdomains beyond this diffraction limit can be broadly divided into
There are two methods, an optical modulation recording method and a magnetic field modulation recording method.

In the case of the light modulation recording method, the tip of the Gaussian intensity distribution of the laser light is used. A recording is performed by generating a temperature distribution region exceeding the diffraction limit and exceeding the minute recording temperature on the recording medium and modulating the intensity of the laser beam with a constant applied magnetic field.

On the other hand, in the magnetic field modulation recording system, a laser beam is irradiated so that the temperature distribution formed by the laser beam formed on the recording medium always has the same distribution (for example, continuous irradiation of the laser beam at a recording power). Recording is performed by modulating an external magnetic field. At this time, by setting the modulation speed of the magnetic field to be high, recording of a minute magnetic domain is enabled.

In the light modulation recording method and the magnetic field modulation recording method as described above, a recording magnetic domain having a shape reflecting a temperature distribution by a laser beam having a Gaussian intensity distribution is formed. That is, in the light modulation recording method, recording magnetic domains are formed in a circular or elliptical shape, and in the magnetic field modulation recording method,
Arrow-shaped recording magnetic domains are formed.

Such a recording magnetic domain having an arc shape is particularly useful in a super-resolution magneto-optical recording / reproducing method for realizing a reproducing method that exceeds the optical diffraction limit and a domain wall moving magnetic domain enlarging / reproducing method. At the time of reproduction, it adversely affects reproduction signal quality. In the following, with reference to the drawings, an explanation will be given of the influence of the arrow-shaped recording magnetic domain on the reproduction signal quality. FIGS. 5 and 6 are schematic diagrams for explaining the effect of the arc-shaped recording magnetic domain on the reproduction signal quality in the super-resolution magneto-optical recording / reproducing system, and FIGS. 7 and 8 in the domain wall moving magnetic domain enlarging / reproducing system.

In the super-resolution magneto-optical recording / reproducing method,
For example, when a small magnetic domain is recorded by a magnetic field modulation recording method as shown in FIG. 5, since the magnetic domain shape is an arrow feather shape, a plurality of recording magnetic domains are provided in an aperture area which plays a role of reproducing recorded magnetic domain information. And adversely affect the reproduced signal.

On the other hand, in the domain wall moving domain expansion / reproduction system shown in FIG. 7, since the recording magnetic domain is in an arc shape, the domain wall movement and the magnetic domain expansion phenomenon are less likely to occur, and the rising and falling edges of the reproduction signal. The decline slows down. In this reproducing method, when the isotherm of the temperature at which the domain wall can be moved (domain wall moving temperature) covers the entire domain wall forming the recording domain shape by heating the medium, the domain wall moves and expands the domain. To play the information. Therefore, when the arcuate shape of the domain wall of the recording magnetic domain intersects with the shape of the isotherm of the domain wall moving temperature as shown in FIG. 7, the stage at which the isotherm starts to contact the recording magnetic domain (the isotherm indicated by a solid line in the drawing) In), domain wall movement and domain expansion increase domain wall energy,
It will be difficult. When the isotherm moves to the position indicated by the broken line in the figure, the entire domain wall moves. Such a phenomenon can be said not only when recording is performed by the magnetic field modulation recording method but also when recording is performed by the light modulation recording method. Then, in the reproduction of the recording magnetic domain by the magnetic field modulation recording method as shown in FIG. 7, before a sufficient reproduction signal by an arbitrary recording magnetic domain is obtained, a reproduction spot or an isotherm of a domain wall moving temperature is formed in the next recording magnetic domain. Ingress,
The information of the latter recorded magnetic domain is also reproduced, which affects reproduction characteristics.

In view of the above problems, an object of the present invention is to provide a reproducing signal quality in a magneto-optical recording medium which realizes a high recording density particularly in accordance with the miniaturization of the recording magnetic domain, from the viewpoint of the recording magnetic domain shape. Is achieved.

[0017]

The above object is achieved by the following means.

That is, according to the present invention, a recording magnetic domain is formed by utilizing a temperature distribution by laser beam irradiation and an externally applied magnetic field by a magnetic field generator, and in a magneto-optical recording medium for recording information, the start of an arbitrary recording magnetic domain is started. When the distance from the position to the position where the magnetic domain width of the recording magnetic domain shows the maximum value or starts to show the maximum value is d, and the length of the maximum width of the recording magnetic domain width is L, d / L × 100 <20 The present invention proposes a magneto-optical recording medium characterized in that information is recorded by a recording magnetic domain of (%), and in a direction in which magnetic properties are lost in an unrecorded area between recorded areas before information is recorded. That the alteration process has been performed, the process before recording is heated to a temperature that causes the magnetic properties of the unrecorded areas between the recording areas to lose magnetic properties, and the process before recording is performed using a laser. Heating It is carried out by at least a first,
A magneto-optical recording medium in which second and third magnetic layers are sequentially laminated, wherein a perpendicular magnetic field has a smaller domain wall coercive force and a larger domain wall mobility than the third magnetic layer at a temperature near an ambient temperature. A first magnetic layer comprising a magnetic film; a second magnetic layer comprising a magnetic layer having a lower Curie temperature than the first magnetic layer and the third magnetic layer; and a perpendicular magnetic film. A magneto-optical recording medium comprising the third magnetic layer, wherein at least a first and a second magnetic layer are sequentially laminated, wherein information is recorded on at least the second magnetic layer; Reading while changing the magnetization state of the first magnetic layer.

The present invention is characterized in that a recording magnetic domain shape in which d / L × 100 indicating the degree of arc shape as shown in FIG. 1 is less than 20 (%) is formed. By forming such a recording magnetic domain shape, in the case of reproducing a recording magnetic domain, in the case of the super-resolution magneto-optical recording / reproducing method, the influence of signal reproduction by a plurality of recording magnetic domains can be suppressed as shown in FIG. The area of the recording magnetic domain to be reproduced in the aperture becomes larger than that of the conventional example, and the signal quality can be improved as the signal amplitude increases. In the case of the domain wall displacement magnetic domain expansion reproduction method, as shown in FIG. 8, the influence of signal reproduction by a plurality of recording magnetic domains can be suppressed, and the rise and fall of the reproduction signal should be steeper than in the conventional example. And improve the signal quality. The effect that the rising and falling of the reproduction signal of the present invention obtained by the domain wall displacement magnetic domain expansion reproduction method becomes steeper also exerts the same effect in the normal reproduction method, and improves the signal quality by improving the jitter. .

In the formation of the recording magnetic domain of the present invention, for example, as shown in FIG. 2, an unrecorded area (for example, a groove in this embodiment) located on both sides of a recording area (for example, a land in this embodiment). This can be realized by performing a pretreatment (heat treatment by laser irradiation in the present embodiment) for changing the magnetic properties of the part (1) in a direction in which the magnetic properties are lost.

[0021]

Embodiments of the present invention will be described below.

[0022]

【Example】

<Example 1> The substrate used in this example was manufactured by injection molding using polycarbonate (PC). The track pitch is 1.1 μm and the groove depth is 0.3 μm. When a magnetic film is formed on this substrate, magnetic coupling can be separated between adjacent tracks by grooves. . In this embodiment, polycarbonate (PC) is used for the injection molded substrate, but polymethyl methacrylate (PMMA), amorphous polyolefin (APO)
Etc. may be used as a molding material. Also, a so-called 2P molded substrate made of an ultraviolet curable resin can be used.

A recording film as proposed in JP-A-6-290496 was formed on the substrate prepared as described above by sputtering. As the recording film, the first
Dielectric layer (SiN), first magnetic layer (GdFe), second magnetic layer (TbFe), third magnetic layer (TbFeC)
o), a second dielectric layer (SiN) is sequentially laminated. As each dielectric layer, for example, a transparent dielectric material such as AlN, SiO ₂ , SiO, ZnS, MgF ₂ or the like can be used in addition to the above-mentioned dielectric layer. Also, as each magnetic layer,
Various magnetic materials including the above-described magnetic materials may be used. For example, Pr, Nd, Sm, Gd,
One or more rare earth metal elements such as Tb, Dy and Ho are 10 to 40 at%, and one or more transition metals such as Fe, Co and Ni are 60 to 90 a%.
% of a rare earth-transition metal amorphous alloy. In addition, to improve corrosion resistance, etc.
Elements such as r, Mn, Cu, Ti, Al, Si, Pt, and In may be added in small amounts.

The magneto-optical recording medium manufactured as described above is subjected to tracking control as a process before recording measurement so that a laser spot is positioned in a groove portion.
Disk rotation speed 2m / sec, laser power 10m
DC light irradiation was performed with W (λ = 680 nm, NA = 0.55), and a pretreatment was performed to alter the magnetic properties of the magnetic layer on the groove in such a direction as to lose the magnetic properties.

Information is recorded on the magneto-optical recording medium after the above pre-processing, and the C / N ratio (carrier level versus nozzle-nozzle ratio) is measured using a measuring device having a heating laser added to the optical system of the magneto-optical disk recording / reproducing device. Ratio) was measured. The recorded information was laser power 3.5 mW (λ = 680 nm, NA = 0.5
The external magnetic field 200 Oe was modulated while irradiating the laser light of 5), and a carrier signal was written at a disk rotation speed of 2 m / sec, a recording frequency of 5 MHz, and a recording mark length of 0.2 μm. Information reproduction is performed at λ = 680 nm, NA = 0.
When the laser power was set to 55 and the laser power was set to 2 mW, a C / N ratio of 51 dB was obtained.

The recording medium recorded with the 0.2 μm mark was observed for its magnetic domain shape by MFM (magnetic force microscope). The MFM observation image at this time is shown in FIG. At this time, d / L × 100 = 0 (%).

<Example 2> Preparation and measurement were performed in the same manner as in Example 1 except that the pretreatment step of changing the magnetic properties of the magnetic layer on the groove in a direction to lose the magnetic properties was performed at a laser power of 9 mW. Was done. At this time, C of 49 dB
/ N ratio and d / L × 100 = 6 (%).

<Example 3> Preparation and measurement were performed in the same manner as in Example 1 except that the pretreatment step of changing the magnetic properties of the magnetic layer on the groove in a direction to lose the magnetic properties was performed at a laser power of 8 mW. Was done. At this time, 47 dB C
/ N ratio and d / L × 100 = 13 (%).

<Example 4> Preparation and measurement were performed in the same manner as in Example 1 except that the pretreatment step of changing the magnetic properties of the magnetic layer on the groove in a direction to lose the magnetic properties was performed at a laser power of 7 mW. Was done. At this time, 45 dB C
/ N ratio and d / L × 100 = 20 (%).

<Comparative Example 1> Preparation and measurement were performed in the same manner as in Example 1 except that the pretreatment step of changing the magnetic properties of the magnetic layer on the groove so as to lose the magnetic properties was omitted. At this time, the C / N ratio of 42 dB and FIG.
An MFM observation image as shown by was obtained. d / L × 1
00 was 31 (%).

<Comparative Example 2> Production and measurement were performed in the same manner as in Example 1 except that the pretreatment step of changing the magnetic properties of the magnetic layer on the groove in a direction to lose the magnetic properties was performed at a laser power of 6 mW. went. At this time, C /
N ratio and d / L × 100 = 25 (%).

<Embodiment 5> Track pitch is 0.9 μm
Production and measurement were performed in the same manner as in Comparative Example 2 except that a polycarbonate substrate was used. At this time,
C / N ratio of 46 dB, and d / L × 100 = 18
(%)Met.

As described above, Examples 1 to 5 and Comparative Example 1
In the case where the dependence of the C / N ratio on (d / L × 100) is plotted from the result of FIG. 2, the result as shown in FIG. 11 is obtained. From FIG. 11, when d / L × 100 ≦ 20 (%), a C / N ratio of at least 45 dB or more is obtained.

<Embodiment 6> The substrate used in this embodiment is:
It was produced by injection molding using polycarbonate (PC). The track pitch is 1.1 μm. In this embodiment, polycarbonate (PC) is used for the injection molded substrate, but polymethyl methacrylate (PMMA), amorphous polyolefin (APO), or the like may be used as a molding material. Also, a so-called 2P made of an ultraviolet curable resin.
Molded substrates can also be used.

A recording film as proposed in JP-A-6-124500 was formed on the substrate thus prepared by sputtering. As the recording film, the first
Dielectric layer (SiN), first magnetic layer (GdFeC)
o), a second magnetic layer (TbFeCo), and a second dielectric layer (SiN) are sequentially stacked. As each dielectric layer, for example, AlN, SiO ₂ ,
A transparent dielectric material such as SiO, ZnS, MgF ₂ or the like can be used. Each magnetic layer may be made of various magnetic materials including the above-mentioned magnetic materials. For example, one kind of rare earth metal element such as Pr, Nd, Sm, Gd, Tb, Dy, Ho or the like may be used. 2 or more types are 10 to 40
It can be constituted by a rare earth-transition metal amorphous alloy composed of at.% and 90 to 60 at. In addition, Cr, Mn, Cu, T
Elements such as i, Al, Si, Pt, and In may be added in small amounts.

The magneto-optical recording medium manufactured as described above is subjected to tracking control as a process before recording measurement so that a laser spot is positioned in a groove portion.
Disk rotation speed 2m / sec, laser power 10m
With W (λ = 680 nm, NA = 0.55), a pretreatment for changing the magnetic properties of the magnetic layer on the groove in a direction to lose the magnetic properties was performed.

Information was recorded on the magneto-optical recording medium after the above pretreatment, and the C / N ratio (ratio of carrier level to nozzle) was measured. Recorded information is a laser power of 3.5 mW (λ
(680 nm, NA = 0.55) while modulating an external magnetic field of 200 Oe to write a carrier signal at a disk rotation speed of 2 m / sec, a recording frequency of 2.5 MHz, and a recording mark length of 0.4 μm. When reproduction of information was performed with λ = 680 nm, NA = 0.55, and laser power of 2 mW, a C / N ratio of 49 dB was obtained.

With respect to the recording medium recorded with the 0.4 μm mark, the recording magnetic domain shape was observed by MFM. At this time, d / L × 100 = 0 (%).

<Example 7> Preparation and measurement were performed in the same manner as in Example 5 except that the pretreatment step of changing the magnetic properties of the magnetic layer on the groove in a direction to lose the magnetic properties was performed at a laser power of 9 mW. Was done. At this time, 48 dB C
/ N ratio and d / L × 100 = 7 (%).

Example 8 Preparation and measurement were performed in the same manner as in Example 5 except that the pretreatment step of changing the magnetic properties of the magnetic layer on the groove in a direction to lose the magnetic properties was performed at a laser power of 8 mW. Was done. At this time, 47 dB C
/ N ratio and d / L × 100 = 13 (%).

<Example 9> Preparation and measurement were performed in the same manner as in Example 5 except that the pretreatment step of changing the magnetic properties of the magnetic layer on the groove in such a direction as to lose the magnetic properties was performed at a laser power of 7 mW. Was done. At this time, C of 46 dB
/ N ratio and d / L × 100 = 20 (%).

<Comparative Example 3> Preparation and measurement were performed in the same manner as in Example 5 except that the pretreatment step of changing the magnetic properties of the magnetic layer on the groove so as to lose the magnetic properties was omitted. At this time, a C / N ratio of 43 dB and d / L
× 100 = 29 (%).

<Comparative Example 4> Preparation and measurement were performed in the same manner as in Example 5 except that the pretreatment step for changing the magnetic properties of the magnetic layer on the groove in a direction to lose the magnetic properties was performed at a laser power of 6 mW. Was done. At this time, C of 44 dB
/ N ratio and d / L × 100 = 25 (%).

<Embodiment 10> Track pitch is 0.9 μm
m, except that a polycarbonate substrate was used.
Production and measurement were performed in the same manner as in Comparative Example 4. At this time, a C / N ratio of 46 dB and d / L × 100 =
18 (%).

From the results of Examples 6 to 10 and Comparative Examples 3 and 4, the C / N ratio for (d / L × 100) was determined.
When the dependence of the ratio is graphed, a result as shown in FIG. 12 is obtained. From FIG. 12, when d / L × 100 ≦ 20 (%), a C / N ratio of at least 45 dB or more is obtained.

[0046]

According to the magneto-optical recording medium of the present invention, in the case of the super-resolution magneto-optical recording / reproducing method, the influence of signal reproduction by a plurality of recording magnetic domains can be suppressed. The area is larger than that of the conventional example, and the signal quality can be improved as the signal amplitude increases. In the case of the domain wall displacement magnetic domain expansion reproduction method, the effect of signal reproduction by a plurality of recording magnetic domains can be suppressed, and the rise and fall of the reproduction signal can be made steeper than in the conventional example. Enable improvements.

[Brief description of the drawings]

FIG. 1 is a schematic view of a magneto-optical recording medium showing one example of the present invention.

FIG. 2 is a schematic view of a magneto-optical recording medium showing another example of the present invention.

FIG. 3 is a principle diagram of a super-resolution magneto-optical recording / reproducing method.

FIGS. 4 (a) to 4 (c) are principle diagrams of a domain wall moving magnetic domain expansion reproduction method.

FIG. 5 is an explanatory diagram of a super resolution magneto-optical recording / reproducing phenomenon of a conventional arrow feather-shaped magnetic domain.

FIG. 6 is an explanatory diagram of a super-resolution magneto-optical recording / reproducing phenomenon of a recording magnetic domain according to the present invention.

FIG. 7 is an explanatory view of a domain wall moving magnetic domain expansion reproduction phenomenon of a conventional arrow blade-shaped magnetic domain.

FIG. 8 is an explanatory diagram of a domain wall displacement magnetic domain expansion reproduction phenomenon of a recording magnetic domain according to the present invention.

FIG. 9 is an MFM image of a recording magnetic domain formed on the magneto-optical recording medium of Example 1.

FIG. 10 is an MFM image of a recording magnetic domain formed on the magneto-optical recording medium of Comparative Example 1.

FIG. 11 shows the shape (d / L × 10) of signal quality (C / N).
0) It is a graph which shows dependence (domain wall moving magnetic domain expansion reproduction method).

FIG. 12 shows the shape (d / L × 10) of signal quality (C / N).
0) Graph showing dependence (super-resolution magneto-optical recording / reproducing method).

Claims (6)

[Claims] In a magneto-optical recording medium for recording information by forming a recording magnetic domain by using a temperature distribution by laser beam irradiation and an externally applied magnetic field by a magnetic field generator, the recording magnetic domain starts from an arbitrary recording magnetic domain starting position. When the distance to the position where the magnetic domain width of the recording magnetic domain indicates the maximum value or starts to show the maximum value is d, and the maximum width of the recording magnetic domain width is L, d / L
A magneto-optical recording medium for recording information in a recording magnetic domain in which × 100 <20 (%). 2. The magneto-optical recording medium according to claim 1, wherein before the recording of the information, a process of changing the magnetic properties in a direction in which the magnetic properties are lost in an unrecorded area between the recording areas is performed. 3. The magneto-optical recording medium according to claim 1, wherein the pre-recording processing according to claim 2 is heated to a temperature at which the magnetic properties of the unrecorded areas between the recording areas are changed in a direction in which the magnetic properties are lost. 4. The magneto-optical recording medium according to claim 1, wherein the processing before recording according to claim 3 is performed by heating using a laser. 5. A magneto-optical recording medium in which at least a first, a second and a third magnetic layer are sequentially laminated, wherein at a temperature near an ambient temperature, a domain wall resistance is relatively higher than that of the third magnetic layer. A first magnetic layer composed of a perpendicular magnetization film having a small magnetic force and a large domain wall mobility, and a magnetic layer having a lower Curie temperature than the first magnetic layer and the third magnetic layer;
2. The magneto-optical recording medium according to claim 1, comprising the second magnetic layer and the third magnetic layer, which is a perpendicular magnetization film. 6. A magneto-optical recording medium in which at least first and second magnetic layers are sequentially laminated, wherein information is recorded on at least the second magnetic layer, and the recorded information is transferred to the first magnetic layer. 2. The magneto-optical recording medium according to claim 1, wherein the reading is performed while changing the magnetization state of the recording medium.