JP2000207791A - Magnetic storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic storage medium that can improve the quality of a reproduction signal, especially, jitter characteristics, in a reproduction method that can reproduce a high-density recording signal exceeding an optical diffraction limit by detecting a magnetic domain wall movement. SOLUTION: First and second magnetic layers 11 and 12 consist of a magnetic film with relatively smaller magnetic domain wall coercive force than third and forth magnetic layers 13 and 14, the second and third magnetic layers 12 and 13 consist of a magnetic film where Curie temperature is higher than room temperature and is lower that of the first and fourth magnetic layers 11 and 14, the difference in the Curie temperature between the second and third magnetic layers 12 and 13 should be within 10 deg.C, and the film thickness of the second magnetic layer 12 is 1-20 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium for recording information according to the arrangement of magnetization of a magnetic material. In particular, the present invention relates to a recording medium capable of improving the recording density in a magneto-optical recording system in which information is reproduced by a light beam.

[0002]

2. Description of the Related Art Various magnetic recording media have been put into practical use as rewritable recording media. In particular, a magneto-optical recording medium, in which magnetic domains are written on a magnetic thin film using the heat energy of a semiconductor laser to record information, and this information is read out using a magneto-optical effect, is a large-capacity interchangeable medium capable of high-density recording. Expected. In recent years, along with the trend of digitizing moving images, there has been an increasing demand for increasing the recording density of these magnetic recording media to produce larger-capacity recording media.

Generally, the linear recording density of an optical recording medium greatly depends on the laser wavelength of a reproducing optical system and the numerical aperture NA of an objective lens. That is, when the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens are determined, the beam waist diameter is determined, so that the spatial frequency of a recording pit from which a signal can be reproduced is limited to about 2 NA / λ. Therefore, in order to realize a higher density in a conventional optical disk, it is necessary to shorten the laser wavelength of the reproducing optical system or increase the numerical aperture of the objective lens. However, it is not easy to shorten the laser wavelength due to problems such as device efficiency and heat generation.
In addition, when the numerical aperture of the objective lens is increased, there arises a problem that the demand for mechanical accuracy becomes severe, for example, the depth of focus becomes shallow.

For this reason, various so-called super-resolution techniques have been developed for improving the recording density by devising the structure of the recording medium and the reproducing method without changing the laser wavelength or the numerical aperture of the objective lens.

For example, in JP-A-3-93058, signal recording is performed on a recording holding layer of a multilayer film having a reproducing layer and a recording holding layer that are magnetically coupled.
A signal reproducing method has been proposed in which the magnetization direction of the reproducing layer is aligned, heated by irradiating a laser beam, and the signal recorded on the recording holding layer is read while being transferred to a temperature rising region of the reproducing layer. According to this method, the area where the laser is heated by the laser to reach the transfer temperature and the signal is detected can be limited to a smaller area with respect to the spot diameter of the laser for reproduction, so that the interference between codes during reproduction can be reduced. 2NA / λ
It is possible to reproduce signals of the above spatial frequencies.

However, according to this reproducing method, the signal detection area to be used effectively becomes smaller with respect to the spot diameter of the reproducing laser, so that the amplitude of the reproduced signal is reduced and a sufficient reproduced output cannot be obtained. Has disadvantages. For this reason, the effective signal detection area cannot be made too small with respect to the spot diameter, and eventually, it is not possible to achieve a large increase in the recording density determined by the diffraction limit of the optical system.

In view of such a problem, the present inventor has already disclosed in Japanese Patent Application Laid-Open No. Hei 6-290496 that a domain wall existing at a boundary portion of a recording mark is moved to a high temperature side by a temperature gradient.
A magnetic recording medium and a reproducing method capable of reproducing a signal having a recording density exceeding the resolution of the optical system by detecting the domain wall movement without reducing the reproduction signal amplitude have been proposed.

[0008]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. 6-29049
The contents described in No. 6 will be briefly described below, and the problems to be solved by the present invention will be described.

The recording medium comprises a first magnetic layer having a small domain wall coercive force, a second magnetic layer having a low Curie temperature, and a third magnetic layer having a large domain wall coercive force. Reference J. Magn. Soc. Jpn.,
22, suppl. No. S2, pp. 47-50 (1998)
The first magnetic layer is a moving layer (displac
ement layer), the second magnetic layer functions as a switching layer that controls the start position of domain wall movement, and the third magnetic layer functions as a memory layer that holds information.
er).

When a temperature distribution is formed on the surface of the magnetic film, a distribution of the domain wall energy density is formed along with the temperature distribution, and a domain wall driving force for moving the domain wall to a high temperature side having low energy is generated.

In a place where the temperature is lower than the Curie temperature of the blocking layer, the respective magnetic layers are exchange-coupled to each other. Therefore, even if the above-mentioned domain wall driving force acts, the domain wall is hindered by the large domain wall coercive force of the memory layer. No movement occurs.

However, since the exchange coupling force is weakened at a temperature Ts near the Curie temperature of the blocking layer, only the domain wall in the moving layer having a small domain wall coercive force moves independently to the high temperature side.

When the medium is moved relatively to the temperature distribution, the domain wall movement occurs at a time interval corresponding to the spatial interval of the domain wall. Therefore, by detecting the occurrence of the domain wall motion, it becomes possible to reproduce a signal regardless of the resolution of the optical system.

Here, the domain wall moving start temperature Ts is
The frictional force that hinders the movement of the domain wall is determined as a threshold temperature at which the frictional force becomes smaller than the domain wall driving force.

If the magnitude relationship between the two is reversed as rapidly as possible before and after the threshold temperature Ts, the domain wall movement start position does not fluctuate and jitter can be suppressed. For this reason, the blocking layer is made of a material having as large anisotropy as possible and a large domain wall energy density so that the exchange coupling force between the moving layer and the memory layer rapidly decreases toward the Curie temperature of the blocking layer. It is better to do.

However, even when the temperature exceeds the Curie temperature of the barrier layer, the magnetic atoms on the barrier layer side receive a large molecular magnetic field from the barrier layer at the interface between the barrier layer and the barrier layer. Causes spin ordering. Since the blocking layer is essentially made of a material having a large anisotropy, if spin ordering occurs under the influence of a molecular magnetic field, the anisotropy becomes considerably large, and a large domain wall coercive force is induced.

Considering the diffusion of atoms, it is considered that the anisotropy of the blocking layer near the interface is further increased.

Therefore, even if the exchange coupling force with the memory layer suddenly decreases, the domain wall coercive force of the blocking layer near this interface remains, and the frictional force that hinders the movement of the domain wall does not decrease sharply. The start position fluctuates, and the jitter increases. These are the problems of the prior invention.

The present invention has been made in order to solve the problems of the above-mentioned prior application, and has been described in detail.
Before and after, the magnitude relationship between the frictional force that hinders the movement of the domain wall and the domain wall driving force reverses sharply, the magnetic domain wall movement start position does not fluctuate, and a magnetic recording medium that can perform signal reproduction with suppressed jitter is used. The purpose is to provide.

[0020]

The above object is achieved by the following magnetic recording medium.

At least the first, second, third, and fourth
At room temperature, the first and second magnetic layers are formed from a magnetic film having a relatively small domain wall coercive force as compared with the third and fourth magnetic layers at room temperature. Wherein the second and third magnetic layers are magnetic films having a Curie temperature higher than room temperature and lower than the Curie temperature of the first and fourth magnetic layers, and the second magnetic layer and the third magnetic layer A magnetic recording medium, wherein the difference in Curie temperature is within 10 ° C. and the thickness of the second magnetic layer is 1 nm or more and 20 nm or less.

In the above-mentioned magnetic recording medium, the first magnetic layer may be formed in a stepwise or continuous manner in the film thickness direction.
A magnetic recording medium characterized by having a structure in which the Curie temperature decreases as approaching the magnetic layer.

Further, each of the recording tracks has a recording track, and at both sides of the recording track, the coupling due to the exchange interaction in the film surface direction of the first magnetic layer is cut or reduced. It is a magnetic recording medium.

A magnetic layer having a Curie temperature close to the Curie temperature of the barrier layer and having a small domain wall coercive force and a small intrinsic anisotropy is inserted between the moving layer and the barrier layer as a barrier auxiliary layer. Therefore, at a temperature near the Curie temperature of the barrier layer,
No domain wall coercive force is induced at the interface of the blocking layer on the side of the blocking auxiliary layer.

At the interface on the moving layer side of the blocking auxiliary layer, a large molecular magnetic field from the moving layer receives a large molecular magnetic field, so that the ordering of spin occurs in the blocking layer near the interface. Is small and the domain wall coercive force is small, so that even if spin ordering occurs, a very large domain wall coercive force is not induced.

As a result, if the exchange coupling force with the memory layer suddenly decreases, the frictional force which hinders the movement of the domain wall also sharply decreases, and the magnitude relationship with the domain wall driving force is suddenly reversed. The movement start position does not fluctuate, and signal reproduction with suppressed jitter can be performed.

However, when the thickness of the auxiliary shielding layer is increased,
Since the exchange coupling force between the moving layer and the memory layer is weakened, and the characteristic that the exchange coupling force sharply decreases with an increase in temperature is impaired, the thickness of the cut-off auxiliary layer is set to 20 nm or less, preferably 10 nm or less. There is a need. Further, since the range of the molecular magnetic field is about 1 nm, it is necessary to make the thickness of the blocking auxiliary layer at least 1 nm or more.

When the Curie temperature of the auxiliary blocking layer is higher than the Curie temperature of the blocking layer by 10 ° C. or more, at the breaking temperature,
A large magnetic domain wall coercive force is induced in the blocking layer by the molecular magnetic field from the blocking auxiliary layer. On the other hand, if the temperature is lower by 10 ° C. or more, the exchange coupling force gradually decreases toward a temperature near the Curie temperature of the blocking auxiliary layer. Therefore, the difference between the Curie temperatures of the blocking auxiliary layer and the blocking layer needs to be within 10 ° C.

In the above magnetic recording medium, the first magnetic layer has a structure such that the Curie temperature decreases stepwise or continuously in the film thickness direction as it approaches the second magnetic layer. By using a magnetic recording medium, a domain wall driving force relatively large as compared with the domain wall coercive force can be applied to the domain wall in the first magnetic layer. Is improved.

Further, a magnetic recording medium having a recording track, in which the coupling due to exchange interaction in the direction of the film surface of the first magnetic layer is cut or reduced on both sides of the recording track, is improved. In addition, information can be recorded as an unclosed domain wall array pattern without substantially forming domain walls on both sides of the magnetic domain.

When the recording pattern in such a state is read out while moving the domain wall, the domain wall can be moved without generating / disappearing the side domain wall, so that the domain wall movement is stabilized and the reproduction signal characteristics are further improved. I do.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of the layer structure of a magnetic recording medium used in the reproducing method of the present invention. In this embodiment, an underlayer 16,
The first magnetic layer 11, the second magnetic layer 12, the third magnetic layer 13, the fourth magnetic layer 14, and the upper layer 17 are sequentially laminated.

As the substrate 15, for example, polycarbonate, acrylic, glass or the like can be used. As the underlayer 16 or the upper layer 17, for example, SiN, Ai
Dielectric materials such as N, SiO, ZnS, MgF, and TaO can be used. The material is not necessarily required to be a translucent material unless the movement of the domain wall is optically detected.

Layers other than the magnetic layer are not essential. The order of lamination of the magnetic layers may be reversed. Also, in this configuration,
Further, Al, AlTa, AlTi, AlCr, Cu, P
A thermal property may be adjusted by adding a metal layer made of t, Au, or the like. Further, a protective coat made of a polymer resin may be provided. Alternatively, a substrate after film formation may be attached.

Each of these layers can be formed by, for example, continuous sputtering with a magnetron sputtering apparatus or continuous vapor deposition. In particular, the respective magnetic layers are exchange-coupled to each other by being continuously formed without breaking the vacuum.

In the above medium, each of the magnetic layers 11 to 14
May be made of various magnetic materials such as a magnetic bubble material and an antiferromagnetic material in addition to the materials generally used for magnetic recording media and magneto-optical recording media.

For example, Pr, Nd, Sm, Eu, Gd,
One or more rare earth metal elements such as Tb, Dy, Ho, Er and the like, 10 to 40 atomic%, Fe, Co,
90% or more of one or more of iron group elements such as Ni
It can be constituted by a rare earth-iron group amorphous alloy composed of 60 atomic%.

In order to improve corrosion resistance and the like, these alloys are made of Cr, Mn, Cu, Ti, Al, Si, Pt, In.
May be added in small amounts.

Also, a platinum group-iron group periodic structure film such as Pt / Co, Pd / Co, a platinum group-iron group alloy film, Co-Ni
Antiferromagnetic materials such as -O and Fe-Rh alloys, and materials such as magnetic garnets can also be used.

In the case of a heavy rare earth-iron group amorphous alloy, the saturation magnetization can be controlled by the composition ratio between the rare earth element and the iron group element. With a compensating composition, the saturation magnetization at room temperature can be reduced to 0 emμ / cc.

The Curie temperature can also be controlled by the composition ratio. To control independently of saturation magnetization,
As the iron group element, a method in which a material in which part of Fe is replaced by Co and the amount of replacement is controlled can be more preferably used. That is, by replacing 1 atomic% of Fe with Co, a Curie temperature rise of about 6 ° C. can be expected. Therefore, the amount of Co to be added is adjusted by using this relationship so as to obtain a desired Curie temperature.

Conversely, the Curie temperature can be lowered by adding a small amount of a nonmagnetic element such as Cr, Ti, or Al.

The Curie temperature can also be controlled by adjusting the composition ratio of two or more rare earth elements.

Specifically, the Curie temperatures of the first magnetic layer are 150 to 300 ° C., the second magnetic layer is 100 to 200 ° C., the third magnetic layer is 100 to 200 ° C., and the fourth magnetic layer is 150 to 300 ° C.
It is preferable to adjust the temperature to the range of 50 ° C.

Although the domain wall coercive force and the domain wall energy density are controlled mainly by selecting the material elements, they can also be adjusted by the conditions of the underlayer and the film forming conditions such as the sputtering gas pressure. Tb and Dy-based materials have large anisotropy and large domain wall coercive force and domain wall energy density, and Gd-based materials are small.
These physical properties can be controlled by adding impurities or the like.

The film thickness can be controlled by the film forming speed and the film forming time.

The recording of a data signal on the magnetic recording medium of the present invention is performed by making the magnetization orientation of the fourth magnetic layer correspond to the data signal by magnetic recording or thermomagnetic recording. In thermomagnetic recording, the fourth
There are a method of modulating the external magnetic field while irradiating a laser beam having a power such that the magnetic layer has a Curie temperature or higher, and a method of modulating the laser power while applying a magnetic field in a certain direction.

In the latter case, if the intensity of the laser beam is adjusted so that only a predetermined area in the light spot becomes higher than the Curie temperature of the fourth magnetic layer, a recording magnetic domain smaller than the diameter of the light spot can be formed. A high-density recording pattern having a resolution higher than or equal to the resolution can be formed.

Hereinafter, the present invention will be described in detail with reference to specific examples, but the present invention is not limited to the following examples unless departing from the gist of the present invention.

[0051]

(Example 1) DC magnetron sputtering
B-doped Si and Gd, Dy, Tb,
Attach each target of Fe, Co, and Al, and
Polycarbonate substrate with guide groove for locking
After fixing to the substrate holder, 1 × 10 ^-FiveHigh below Pa
Evacuate the chamber with a cryopump until vacuum
I noticed. Ar gas becomes 0.5 Pa while evacuating
Into the chamber and rotate the substrate,
Each layer was formed by sputtering the target.

When forming the SiN layer, N ₂ gas is added in addition to Ar gas.
A gas was introduced and a film was formed by DC reactive sputtering.

First, a 90 nm SiN layer is used as an underlayer.
A film was formed. Subsequently, a GdFe layer having a thickness (h1) of 30 nm as the first magnetic layer, a GdFeAl layer having a thickness (h2) of 10 nm as the second magnetic layer, a TbFe layer having a thickness (h3) of 10 nm as the third magnetic layer, and a fourth magnetic layer were formed. TbFeC as layer
The o-layer was sequentially formed to a thickness (h4) of 80 nm.

Finally, a 50 nm thick SiN layer was formed as a protective layer.
A film was formed.

Each magnetic layer is composed of Gd, Tb, Fe, Co, A
The composition ratio was controlled by the ratio of the power supplied to each target of l.

The composition ratio was adjusted so that each magnetic layer had a composition near the compensation composition. (Strictly, the rare-earth element and the iron-group element were compensated at a temperature near the Curie temperature of the third magnetic layer, which is the reproduction temperature, and the rare-earth element was adjusted to be slightly dominant at room temperature.) The Curie temperature (Tc1) of the first magnetic layer is adjusted to be about 230 ° C.,
The Curie temperature (Tc2) of the second magnetic layer and the Curie temperature (Tc3) of the third magnetic layer were adjusted to 160 ° C., and the Curie temperature (Tc3) of the fourth magnetic layer was adjusted to about 310 ° C.

(Comparative Example 1) As a comparative example, a sample similar to that of Example 1 except that the second magnetic layer was not inserted was produced.

The dynamic characteristics of the samples of Example 1 and Comparative Example 1 were evaluated using a magneto-optical disk evaluation apparatus equipped with a magnetic head for magnetic field modulation recording which has been generally used conventionally. . The sample has a linear velocity of 1.5m /
The rotation was performed so as to be sec.

At the time of recording, the recording / reproducing laser was set to 4 mW.
By modulating the magnetic field at ± 200 Oe while applying direct current, a pattern of an upward magnetization region and a downward magnetization region corresponding to the modulation of the magnetic field is formed in a cooling process after heating the fourth magnetic layer to the Curie temperature or higher. did.

The power Pr of the reproducing laser is set to 1.8 mW.
When the jitter in a tone pattern having a mark length of 0.1 μm was measured, the sample of Comparative Example 1 had a jitter of 8.5 nsec, whereas the sample of Example 1 had a jitter of 6 nsec.

(Example 2) Samples were prepared by changing the thickness of the second magnetic layer of the sample of Example 1 in various ways, and the dynamic characteristics were similarly evaluated. , 8.5 nsec or less, and the effect of inserting the second magnetic layer was recognized.

(Example 3) Samples of Example 1 were prepared by changing the Curie temperature of the second magnetic layer in various ways, and the dynamic characteristics were similarly evaluated.
A jitter of 8.5 nsec or less was obtained in the range of not more than ℃, and the effect of inserting the second magnetic layer was recognized.

Example 4 The first magnetic layer was formed as follows:
The layers were sequentially formed. First, as a twelfth constituent layer, GdFeCoAl having a Curie temperature (Tc12) of 260 ° C.
GdFeCoA having a Curie temperature (Tc11) of 210.degree.
One layer was sequentially formed to a thickness (h11) of 10 nm. Next, as the second magnetic layer, GdFeCoA having a Curie temperature of 160 ° C.
One layer was formed to a thickness of 10 nm.

Subsequently, the third and fourth magnetic layers were formed in Example 1.
A film was formed with the same material and the same thickness. The composition ratio was adjusted so that each magnetic layer had a composition near the compensation composition.

The recording / reproducing characteristics of the magnetic recording medium of the present embodiment were measured by the same method as in Embodiment 1, and the result was 5.5 ns.
The ec jitter was obtained.

(Embodiment 5) A tracking servo was applied to the guide groove of the magnetic recording medium of Embodiment 4 to obtain a linear velocity of 1.5 m / m.
While driving the medium in sec, a focused laser beam for recording / reproduction was continuously irradiated at 10 mW, and only the magnetic film on the guide groove was locally annealed. With this process,
The magnetism of the magnetic film on the guide groove was degraded, and the domain wall energy was not accumulated in this portion.

On the lands of this sample, magnetic domains were recorded over the entire land width to form unclosed domain walls. As a result of performing reproduction in the same manner as in Example 1, noise during reproduction was reduced, and a jitter of 5 nsec was obtained.

In addition to the examples described above, the magnetic recording medium of the present invention is not limited to the change in the polarization plane due to the magneto-optical effect, and may detect and reproduce another change caused by the movement of the domain wall.

The recording film of the magnetic recording medium of the present invention may not be a perpendicular magnetization film as long as it is a magnetic material.

The interface between the magnetic layers does not necessarily have to be sharp and sharp, and may have a configuration in which the characteristics gradually change in the film thickness direction.

[0071]

As described above in detail, the effect of the present invention is to provide a reproducing method capable of reproducing a high-density recording signal exceeding an optical diffraction limit by detecting domain wall movement. In particular, it is to provide a magnetic recording medium capable of improving jitter characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of a layer configuration of a magnetic recording medium of the present invention.

[Explanation of symbols]

 11 First magnetic layer 12 Second magnetic layer 13 Third magnetic layer 14 Fourth magnetic layer 15 Substrate 16 Underlayer 17 Upper ground layer

Claims (3)

[Claims] At least first, second, third, and fourth magnetic layers are exchange-coupled at room temperature and sequentially laminated, and at room temperature, the first and second magnetic layers are And the second and third magnetic layers have a Curie temperature higher than room temperature and lower than the Curie temperatures of the first and fourth magnetic layers. Wherein the difference between the Curie temperatures of the second magnetic layer and the third magnetic layer is 10 ° C. or less, and the thickness of the second magnetic layer is 1 nm or more and 20 nm or less. Magnetic recording medium. 2. The magnetic material according to claim 1, wherein the first magnetic layer has a structure such that the Curie temperature decreases stepwise or continuously in the film thickness direction as it approaches the second magnetic layer. recoding media. 3. The magnetic recording according to claim 1, further comprising a recording track, wherein the coupling due to exchange interaction in the film surface direction of the first magnetic layer is cut or reduced at both sides of the recording track. Medium.