JP2003162851A - Magneto-optical recording method, magneto-optical data- storage medium and production method of magneto- optical data-storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magneto-optical recording method that prevents data corruption caused by cross writing, realizes a narrower track pitch and performs high density in the direction of the radius of a disk while extending a recording power margin in the DWDD (Domain Wall Displacement Detection) method which is advantageous to high line density, and also provide a magneto-optical data-storage medium and production method thereof. <P>SOLUTION: In the magneto-optical data-storage medium in which a recording track and a non-recording track are alternately arranged adjacent to each other, in order to record information, a recordable magnetic field strength distribution is formed at the recording track, and a recording-impossible magnetic field strength distribution is formed at a track except the recording track. For this purpose, when the width of the recording track is defied as W<SB>a</SB>and that of non-recording track is defined as W<SB>b</SB>, a magnetic head having a core with its width satisfying the equation W<W<SB>a</SB>+2W<SB>b</SB>is employed, and the recording magnetic field is sensitively detected at a magnetic field-detecting region and then the center of the recording track in the direction of its radius coincides with the center of the magnetic field strength distribution. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ultra-high density magneto-optical recording.

[0002]

2. Description of the Related Art As one of large-capacity rewritable memories, attention is paid to a magneto-optical recording medium for reproducing and recording by using a laser beam. Laser wavelength λ of reproduction optical system
And the numerical aperture NA of the objective lens, the beam waist diameter is 2 Wo
Since (2Wo = K · λ / NA, K is a constant) is determined, the magneto-optical recording medium can detect a spatial frequency up to about 2NA / λ during signal reproduction. However, there is an ever-increasing demand for larger capacity of magneto-optical recording media. In order to meet this requirement, that is, 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 structure and reading method are devised to improve the recording density. Improved techniques have been 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.

In JP-A-3-93058 and JP-A-6-124500, signal recording is performed on a recording layer of a multilayer film having a reproducing layer and a recording layer which are magnetically coupled, and magnetization of the reproducing layer is performed. After aligning the orientations (the direction of magnetization in JP-A-6-124500 is in-plane), the signal is read by irradiating with laser light and heating to transfer the signal recorded in the recording layer to the temperature rising region of the reproducing layer. Playback methods have been proposed.

According to this method, the area (aperture) where the laser is heated by the laser to reach the transfer temperature and the signal is detected with respect to the spot diameter of the reproducing laser can be limited to a smaller area. Intersymbol interference at the time is reduced, and signals with a pit period less than the optical detection limit K · λ / NA can be reproduced. The above reproduction method is MSR (Magnet
It is called the ically-induced Superresolution Readout method.

As another example, Japanese Patent Laid-Open No. 6-290496 proposes a magneto-optical recording medium, a reproducing method, and a reproducing apparatus which make up for the drawbacks of the MSR reproducing method.

In the MSR reproducing method, since the signal detection area that is effectively used is small with respect to the spot diameter of the reproducing laser, the reproducing signal amplitude is significantly reduced, and a sufficient reproducing output cannot be obtained. It has drawbacks.

On the other hand, in Japanese Patent Laid-Open No. 6-290496, a magneto-optical recording medium composed of an exchange-coupling multilayer film makes it possible to reproduce a signal with a period below an optical detection limit at high speed without lowering the reproduction signal amplitude. There has been proposed a magneto-optical recording medium, a reproducing method, and a reproducing apparatus capable of greatly improving the recording density and the transfer speed. There, a temperature distribution is given to the reproducing / recording mark by an attached laser heating device, and the pressure that moves into the reproducing light spot is induced on the domain wall by this temperature distribution and the temperature dependence of the domain wall energy in the reproducing / recording mark. . When the reproducing / recording mark is heated to near the Curie temperature of the second magnetic layer, the first magnetic layer (reproducing layer)
The exchange coupling between the first magnetic layer and the third magnetic layer (recording layer) is broken, and the domain wall of the first magnetic layer instantaneously moves into the reproduction light spot due to the presence of the magnetic coupling disconnection regions on both sides of the recording track. As a result, the directions of atomic spins in the reproduction light spot are all aligned in one direction, and the reproduction recording mark is enlarged. Therefore, the reproduction signal amplitude is always constant and the maximum amplitude regardless of the recorded domain wall spacing (that is, the recording mark length), and is completely free from problems such as waveform interference due to the optical diffraction limit. It is. The above playback method is based on DWDD (DomainWall Displacement Detectio).
n) It is called the playback method.

As described above, the MSR reproduction system, D
The WDD reproducing method greatly contributes to high density in the track direction, that is, high linear density. However, in order to further increase the capacity, it is necessary to increase the density in the radial direction of the magneto-optical disk.

Higher density in the radial direction can be achieved by narrowing the track pitch. However, the narrowing of the track pitch also narrows the recording area that affects the reproduction signal, the reproduction signal amplitude decreases, and the signal quality deteriorates.

Regarding the problem of the deterioration of the signal quality, D
In the WDD reproducing method, recording marks must be formed over the recording track width to maximize the use of the recording area for high-quality signal reproduction. Therefore, even if the track pitch is narrowed, the signal amplitude is relatively easy to obtain. In the conventional optical system (λ = 650 to 680 nm, NA = 0.55 to 0.60), good signal quality can be maintained even when the recording track width is 0.3 to 0.4 μm.

[0012]

However, the narrowing of the track pitch also causes a problem of reduction of the recording power margin. This is because the laser power threshold of so-called cross write, in which a signal is mistakenly recorded on an adjacent track other than the track to be recorded due to the narrowing of the track pitch, becomes low, and cross write The problem is that the usable recording power range up to the laser power on the verge of being narrowed.

In the DWDD reproducing system, the reduction of the recording power margin due to the narrowing of the track pitch is
It becomes a more serious problem. As described above, in the DWDD reproducing method, in order to perform the reproducing operation satisfactorily by the movement of the domain wall, the recording mark must be formed over the recording track width during recording. Therefore, in principle, a larger recording laser power is required as compared with other methods such as the MSR reproducing method which does not require such a method. In addition to that, the recording marks of the adjacent recording tracks are also recorded in the full track width, so that the power for committing the cross write is low compared to other methods. Therefore, the recording power margin defined in the range from the recordable laser power to the laser power on the verge of cross write becomes narrower. Therefore, in the DWDD playback system,
The effect of narrowing the track pitch on the recording power margin can be said to be a serious problem compared to other methods.

The object of the present invention is to provide a DW which is advantageous for increasing the linear density.
In the DD reproducing method, a magneto-optical recording method capable of preventing data destruction due to cross-write and increasing the recording power margin, realizing a further narrowing of the track pitch, and achieving high density in the disk radial direction, An object of the present invention is to provide a magneto-optical recording medium and a method for manufacturing the magneto-optical recording medium.

[0015]

SUMMARY OF THE INVENTION The above-mentioned problem is a magneto-optical recording of information on a magneto-optical recording medium provided with recording tracks and unrecorded tracks alternately adjacent to each other by irradiating a laser beam and applying a magnetic field. In the recording method, this can be overcome by forming a recordable magnetic field strength distribution on the recording track and forming a non-recordable magnetic field strength distribution on a track other than the recording track to record information.
As described above, by sufficiently reducing the magnetic field intensity leaking to the tracks other than the recording track, the recording laser power that causes the data destruction due to the cross write can be increased.

For that purpose, first, the width of the recording track is set to W.
_a , W <W _a +2, where W _b is the width of the unrecorded track
A magnetic head having a core with a width of W _b is used for recording.
As a result, it is possible to suppress the magnetic field for tracks other than the recording track, which is a prerequisite for forming the magnetic field strength distribution, to a minute magnetic field that cannot be recorded.

Furthermore, by converting the magnetization of the magnetic field detection area, which is modulated by the recording magnetic field generated from the magnetic head, into a magneto-optical signal and using it for accurate positioning of the magnetic head with respect to the magneto-optical recording medium, Match the center of the recording track with the center of the magnetic field strength distribution. Actually, the Kerr rotation angle in the magnetic field detection region is measured to find the position of the magnetic head that maximizes the Kerr rotation angle. As described above, the magnetic field strength distribution of the present invention can be easily formed.

Further, it is necessary to manufacture a magneto-optical recording medium in which at least one magnetic field detection region capable of detecting the recording magnetic field generated from the magnetic head with high sensitivity is formed in each recording track. In the embodiment of the present invention, the magneto-optical recording medium in which the magnetic field detection region exhibits in-plane magnetic anisotropy is used. However, if the recording magnetic field generated from the magnetic head can be detected with high sensitivity, this It is not limited.

The magnetic field detection region can be easily formed by an annealing process by irradiation with a laser beam having a higher output than the recording power. The irradiation of the laser beam changes the magnetic properties of the irradiation area (that is, the magnetic field detection area). In the embodiment of the present invention, the perpendicular magnetic anisotropy changes to the in-plane magnetic anisotropy. Needless to say, the object of the present invention can be achieved if the magnetization changes so that the recording magnetic field generated from the magnetic head can be detected with high sensitivity.

[0020]

1 is a conceptual diagram for forming a magnetic field strength distribution in the present invention. In the magneto-optical recording medium 20 in which the recording tracks 21 and the unrecorded tracks 22 are alternately provided, a recordable magnetic field strength distribution is formed in the recording tracks 21, and a magnetic field that cannot be recorded in the tracks other than the recording tracks. The information is recorded by forming an intensity distribution. In this embodiment, as will be described later, the groove is a recorded track and the land is an unrecorded track. In the embodiment of the present invention, in order to form the magnetic field strength distribution, first, the width of the recording track 21 is set to W _a ,
When the width of the unrecorded track 22 is W _b , W <W _a +2
By using the magnetic head 10 having the core 11 of W _b , a minute magnetic field is generated on tracks other than the recording tracks on which the magnetic field distribution is formed, and the magnetic head 10 is applied to the magneto-optical recording medium 20. On the other hand, it must be arranged at an appropriate position, that is, at a position where the center of the recording track 21 and the center of the magnetic field strength distribution coincide with each other.

FIG. 2 shows a typical structure of the single magnetic pole type magnetic head 10 used in this embodiment. A core 11 (main magnetic pole) made of an amorphous magnetic thin film of CoNbZr is sandwiched by sliders 12. The coil 14 winds around the auxiliary core 13 and excites it. Film thickness (W = 0.7μm)
The magnetic head 10 is mounted so that the direction is the radial direction of the disk, that is, the track width direction. This magnetic head 10 enables generation of a minute magnetic field.

The magneto-optical recording medium 20 according to the present embodiment.
FIG. 3 shows a configuration diagram of the above. The substrate 24 used was manufactured by injection molding using polycarbonate (PC). Track pitch (W _a + W _b ) is 0.65 μm, groove width (W
_a ) is a groove recording substrate having 0.40 μm and a groove depth of 0.06 μm. The groove width is defined by the half width of the groove depth. Here, the relationship of W <W _a + 2W _b is satisfied. Although polycarbonate (PC) is used for the injection molded substrate in the present embodiment, polymethylmethacrylate (PM) is used.
MA), amorphous polyolefin (APO) or the like may be used as the molding material. It is also possible to use a so-called 2P molded substrate made of an ultraviolet curable resin. Although the groove recording substrate is used, naturally, a land recording substrate or a land / groove recording substrate can also be used. Even a sample servo substrate without grooves can be used if an unrecorded track is formed.

A recording film was formed by sputtering on the substrate 24 manufactured as described above. The first dielectric layer 25 (SiN) and the first magnetic layer 26 (reproducing layer) (G) are formed on the substrate 24.
dFeCo, film thickness 40 nm, second magnetic layer 27 (TbF)
e, film thickness 15 nm), the third magnetic layer 28 (recording layer) (Tb
FeCo, film thickness 80 nm), second dielectric layer 29 (Si
N) are sequentially stacked, which is a magneto-optical recording medium for DWDD reproduction system. As each dielectric layer (25, 29),
In addition to the above dielectric materials, for example, AlN, SiO ₂ , Si
Transparent dielectric materials such as O, ZnS, MgF ₂ can be used. Further, as the second magnetic layer 27 and the third magnetic layer 28,
It may be composed of various magnetic materials including the above-mentioned magnetic material. For example, Pr, Nd, Sm, Gd,
One or more rare earth metal elements such as Tb, Dy, and Ho are 10 to 40 atomic%, and Fe, Co, and Ni.
60 to 9 of one kind or two or more kinds of transition metals such as
It may be composed of a rare earth / transition metal amorphous alloy composed of 0 atomic%. Also, in order to improve corrosion resistance, etc., C
A small amount of elements such as r, Mn, Cu, Ti, Al, Si, Pt and In may be added.

Further, the land 22 of the manufactured magneto-optical recording medium 20 was annealed with a laser beam having a disk rotation speed of 3.0 m / s and a laser power of 12 mW (λ = 650 nm, NA = 0.65). By this process, the magnetic anisotropy is changed from the perpendicular magnetic anisotropy to the in-plane magnetic anisotropy in each land 22, and due to the existence of such a land 22, excellent DWDD reproduction is achieved in the groove 21 between them. Is possible.

In order to obtain the magnetic field strength distribution of the present invention, the positional relationship between the magnetic head 10 and the magneto-optical recording medium 20 must be as shown in FIG. Therefore, the center of the magnetic field strength distribution must be accurately arranged at the center of the groove 21 (recording track). Therefore, it is necessary to detect the recording magnetic field generated from the magnetic head 10 with high sensitivity. In the present invention, as shown in FIG. 4, the magnetic modulation by the recording magnetic field in the magnetic field detection area 23 is converted into a magneto-optical (MO) signal to position the magnetic head 10.

The magnetic field detection area 23, as shown in FIG.
Disk rotation speed 3.0m / s, laser power 13mW
A laser beam of (λ = 650 nm, NA = 0.65) is condensed by the objective lens 30 and is intermittently applied to the groove 21,
It was formed at 20 locations on one circumference at equal intervals. The spacing at this time was set to πr / 1000 (mm) when the radial position of the track forming the magnetic field detection area 23 was r (mm). In this case, r ≧ 24 mm. However, these numerical values do not limit the present invention.

The magnetic field detection region 23 has an in-plane magnetic anisotropy in its magnetic property due to irradiation with a high-power laser, and when a recording magnetic field is applied from the magnetic head 10, it is magnetized in accordance with the direction of the magnetic field. Is reversed. When the laser light (probe light) enters and is reflected by the magnetic field detection region 23, the plane of polarization of the reflected light has a magnetic Kerr rotation angle determined by the magnetization modulated by the recording magnetic field from the magnetic head 10. It's spinning. Therefore, if the magnetic Kerr rotation angle can be detected, the recording magnetic field applied to the magnetic field detection area 23 can be detected with high sensitivity.

Here, the magneto-optical recording medium 20 is manufactured so that the magnetic field detection region 23 exhibits in-plane magnetic anisotropy, but at least the magnetization of the first magnetic layer 26 is modulated by the recording magnetic field of the magnetic head 10. If it is manufactured so that it can be detected with high sensitivity, the effect of the present invention can be obtained.

FIG. 5 shows a block diagram of a magnetic field detecting device of the present invention using the magnetic field detecting region 23. Semiconductor laser 3
The light radiated from 1 is collimated by the collimator lens 32 into a parallel light flux, and is condensed on the magneto-optical recording medium 20 by the objective lens 34 via the polarization beam splitter 33. When recording information, in the magnetic field detection area 23 on the magneto-optical recording medium 20, the magnetization is modulated by the recording magnetic field from the magnetic head 10 so that the recording magnetic field is oriented. The information on the modulation magnetization is included in the reflected light from the magneto-optical recording medium 20 as magneto-optical (MO) information such as the magnetic Kerr rotation angle. As a result, information on the recording magnetic field from the magnetic head 10 is obtained. The reflected light is condensed by the objective lens 34, reflected by the polarization beam splitter 33, and converted into λ / 2.
The polarization direction is rotated by approximately 45 degrees by the wave plate 35, and the birefringent prism 36 separates the light flux into two light beams having polarization directions orthogonal to each other.
The light is focused on the sensors 38a and 38b. Then, the differential amplifier 39 takes a differential between the output of the RF sensor 38a and the output of the RF sensor 38b to obtain the MO signal output as the magnetization information of the magnetic field detection area 23. This MO signal output is taken into the amplitude detection control circuit 40, and a control signal that maximizes the amplitude of the MO signal output is generated.
0 is input to the tracking driver 41, and the tracking actuator 42 is operated. By operating in this way, the magnetic field strength applied to the magnetic field detection area 23 is maximized, that is, the center of the magnetic field strength distribution generated from the magnetic head 10 is aligned with the center of the recording track 21. , The magnetic head position is controlled.
In this way, it becomes possible to always maintain the magnetic field strength distribution as shown in FIG.

Here, in consideration of the eccentricity of the magneto-optical recording medium 20 and the like, the magnetic field detector was used to maximize the effects of the present invention. Is not limited to this as long as it can be as shown in FIG. Further, in the present embodiment, the single-pole magnetic head 10 and the optical pickup are mounted so as to face each other via the magneto-optical recording medium 20. In addition to this embodiment, even when the magnetic head and the optical pickup are on the same side of the medium as in the case of the head in which the magnetic head and the optical pickup are integrated, the magnetic field strength distribution is as shown in FIG. If it can be set, the effect of the present invention can be obtained.

[0031]

EXAMPLES The cross write characteristics of the magneto-optical recording medium 20 were measured using the magneto-optical recording apparatus having the magnetic field detecting apparatus as described above. Wavelength λ, NA used for recording and reproduction
Is λ = 650 nm and NA = 0.65. The cross write characteristics are measured by recording on N tracks while applying a constant recording magnetic field (500 Oe) using the recording laser power as a parameter, then recording on N ± 1 tracks, and then reproducing the signals on N tracks. The procedure was to measure the jitter of the reproduced signal. The recording information is a disc rotation speed of 3.0 m / sec, a recording frequency of a recording magnetic field of 5 M.
The carrier signal was written in Hz. For information reproduction, disk rotation speed is 3.0 m / s, laser power (reproduction power)
It was performed at 2.1 mW.

FIG. 6A shows the measurement result of the cross light characteristics obtained as described above. Jitter σ <4.0n
20% as the recording power margin when specified by s
was gotten. Here, the recording power margin is ΔP / P
_Center x 100 (%) is required. Here, P is the recording power, where P _{low is} the recording power on the low side and σ is 4.0 ns, and P _high is the recording power on the high side.
P _center is P _center = (P _high + P _low ) / 2,
ΔP is ΔP = (P _high −P _low ) / 2.

(Comparative Example) The same measurement was performed on the same magneto-optical recording medium 20 as in this example except that the magnetic head was a conventional type. The conventional magnetic head core 50 used here is as shown in FIG. 7, and the size is 400 μm in the radial direction of the disk. Further, the magnetic field strength distribution has a very large core size with respect to the track pitch (0.65 μm) of the magneto-optical recording medium 20, so that a uniform magnetic field of 500 Oe was applied over some tracks.
The magnetic field strength immediately above the recording track was the same as 500 Oe, but the magnetic field power consumption at this time was overwhelmingly smaller when the core size was smaller.

The result of the cross write characteristics measured by recording with the above magnetic head core 50 is shown in FIG. 6B, and 10% was obtained as the recording power margin when the jitter σ <4.0 ns was specified. .

[0035]

According to the magneto-optical recording method and the magneto-optical recording medium of the present invention, the recording power margin is greatly expanded. As a result, a recording power margin can be secured even if the track pitch is narrowed, and as a result, it is possible to improve the recording density in the radial direction due to the narrowed track pitch and achieve a further increase in capacity.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of magnetic field strength distribution of the present invention.

FIG. 2 is a configuration diagram of a single magnetic pole type magnetic head having a fine core used in the present invention.

FIG. 3 is a configuration diagram of a DWDD reproducing system magneto-optical recording medium used in the present invention.

FIG. 4 is a conceptual diagram of forming a magnetic field detection area and detecting a recording magnetic field according to the present invention.

FIG. 5 is a configuration diagram of a magnetic field detection system according to the present invention.

FIG. 6 is experimental data of (a) cross write characteristics measured by the magneto-optical recording apparatus used in the present invention, and (b) cross write characteristics measured by a conventional magneto-optical recording apparatus.

FIG. 7 is a conceptual diagram of a magnetic field strength distribution when a conventional magnetic head core is used.

[Explanation of symbols]

10 magnetic head 11 cores 12 sliders 13 Auxiliary core 14 coils 20 magneto-optical recording medium 21 groove (recording track) 22 land (unrecorded track) 23 Magnetic field detection area 24 Groove recording substrate 25 First Dielectric Layer 26 First magnetic layer (reproducing layer) 27 Second magnetic layer 28 Third magnetic layer (recording layer) 29 Second dielectric layer 30 objective lens 31 Semiconductor laser 32 Collimating lens 33 Polarizing beam splitter 34 Objective lens 35 λ / 2 wave plate 36 Birefringent prism 37 Condensing lens 38a, 38b RF sensor 39 Differential amplifier 40 Amplitude detection control circuit 41 Tracking driver 42 Tracking actuator 50 Conventional magnetic head core

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G11B 11/105 G11B 11/105 561P

Claims (6)

[Claims] 1. A magneto-optical recording method for recording information by irradiating a laser beam and applying a magnetic field to a magneto-optical recording medium in which recording tracks and unrecorded tracks are alternately adjacent to each other. A magneto-optical recording method characterized in that a magnetic field intensity distribution is formed, and a magnetic field intensity distribution that cannot be recorded on a track other than the recording track is formed to record information. Wherein the width of the recording track W _a, when the width of the unrecorded tracks and _{W b, W <W a +} 2W b is recorded by a magnetic head comprising a core width, the light according to claim 1 Magnetic recording method. 3. Recording by converting the magnetization of a magnetic field detection region, which is modulated by a recording magnetic field generated from a magnetic head, into a magneto-optical signal and utilizing it for accurate positioning of the magnetic head with respect to a magneto-optical recording medium. The magneto-optical recording method according to claim 2, wherein the center of the track and the center of the magnetic field strength distribution are made to coincide with each other. 4. A magneto-optical recording medium in which at least one magnetic field detection region capable of detecting a recording magnetic field generated from a magnetic head with high sensitivity is formed in each recording track. 5. The magneto-optical recording medium according to claim 4, wherein the magnetic field detection region capable of detecting the recording magnetic field generated from the magnetic head with high sensitivity has in-plane magnetic anisotropy. 6. The method for producing a magneto-optical recording medium according to claim 4, wherein the magnetic field detection region is formed by irradiation with a laser beam having a higher output than the recording laser power.