JPH10241218A - Magneto-optical recording medium - Google Patents

Abstract

(57) [Problem] To provide a medium that satisfies all of a reduction in crosstalk, an improvement in super-resolution effect, and a reproduction signal intensity in a CAD system. A reproducing layer, an intermediate layer, and a recording layer made of an alloy magnetic material containing a rare earth metal and a transition metal are provided on a substrate, and the reproducing layer is magnetized at room temperature substantially parallel to the film surface. A magneto-optical recording medium characterized by using an alloy represented by the following formula (1) as an intermediate layer. (RE _N Gd _100-N ) _M TM _100-M RE: One or more elements selected from Tb and Dy TM: One or more elements selected from Fe and Co 10 ≦ N ≦ 100, 26 ≦ M ≦ 35

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 medium.

[0002]

2. Description of the Related Art A magneto-optical recording medium has been put to practical use as a high-density, low-cost rewritable information recording medium. In particular, a medium using a recording layer of an amorphous alloy of a rare earth metal and a transition metal shows very excellent characteristics.

[0003] Magneto-optical disks are extremely large-capacity recording media, but with the increase in the amount of information in society, a further increase in capacity is desired. The recording density of an optical disc is usually
It is determined by the size of the spot of the reproduction light. Since the spot size can be reduced as the laser wavelength becomes shorter, studies have been made to shorten the laser wavelength, but this is very difficult.

On the other hand, in recent years, so-called super-resolution techniques which attempt to obtain a resolution higher than that determined by the wavelength of the laser by various means have been attempted. One of them is using a magneto-optical disk and using magnetically induced super resolution using the exchange coupling force between multilayer films.
solution or MSR).

As one form of MSR, CAD (Cent
er aperture detection). CAD
The medium has two magnetic layers, a recording layer and a reproducing layer. In the reproducing layer, the magnetization becomes in-plane magnetization parallel to the film surface near room temperature, and forms a "mask region" in which no signal is reproduced.

On the other hand, when the temperature rises, the magnetization of the reproducing layer decreases and becomes perpendicular magnetization, and becomes an "aperture region" for transferring the magnetization of the recording layer by the exchange coupling force. At the time of reproduction, since a temperature distribution is formed in the reproduction spot, the signal is reproduced only from the high temperature part (aperture area). By limiting the signal reproduction area, the reproduction spot is effectively reduced, and the resolution of the signal is improved.

As a result, high-density recording becomes possible. Further, since the adjacent track at room temperature also becomes a mask area, almost no signal leakage (crosstalk) from the adjacent track occurs. Therefore, the interval between the recording tracks can be reduced.

[0008]

In order to accurately transfer the magnetic domains of the recording layer to the reproducing layer at the reproducing temperature, the exchange coupling force in the aperture region and the perpendicular magnetic anisotropy of the reproducing layer are sufficiently large. There is a need. On the other hand, in the mask region, the reproducing layer preferably has a low exchange coupling force and low perpendicular magnetic anisotropy, and is in a state where magnetic domains are not transferred.

Conventionally, in order to sufficiently rotate the magnetization from the perpendicular direction to the in-plane direction inside the reproducing layer at room temperature, it was necessary to increase the thickness of the reproducing layer to about 100 nm. In this case, since the reproducing layer is too thick, there is a problem that the magnetization of the reproducing layer is not sufficiently perpendicular at the reproducing temperature, and the reproducing signal is reduced. Further, there is a problem that the recording sensitivity is lowered and the film formation cost is increased due to the large film thickness.

When the thickness of the reproducing layer is reduced to avoid this, the magnetization does not sufficiently turn in the in-plane direction at room temperature, and a sufficient super-resolution effect cannot be obtained. "Proceeding of MORIS'94,
p417 ”describes that by inserting a GdFe intermediate layer in a CAD medium, magnetization rotation occurs in the intermediate layer, and the thickness of a reproducing layer for generating a mask region can be reduced. However, even in this method, since the perpendicular magnetic anisotropy of the intermediate layer was low, the magnetization was not sufficiently perpendicular in the aperture region, and the reproduction signal level was insufficient.

[0011]

SUMMARY OF THE INVENTION The present invention provides a medium that satisfies all of the requirements of the cross-talk reduction, the super-resolution effect, and the reproduction signal strength in the CAD system. The gist of the present invention is that a reproducing layer, an intermediate layer, and a recording layer made of an alloy magnetic material containing a rare earth metal and a transition metal are provided on a substrate, and are magnetized substantially parallel to a film surface at room temperature as a reproducing layer. And a magneto-optical recording medium characterized by using an alloy represented by the following formula (1) as an intermediate layer.

[0012]

(RE _N Gd _100-N ) _M TM _100-M RE: One or more elements selected from Tb and Dy TM: One or more elements selected from Fe and Co 10 ≦ N ≦ 100, 26 ≦ M ≤35

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the contents of the present invention will be described in detail. The magneto-optical recording medium of the present invention has at least three magnetic layers of a reproducing layer, an intermediate layer, and a recording layer. In a normal CAD medium, a reproducing layer is provided directly on a recording layer.

However, in the case of the present invention, an intermediate layer having a predominant composition of a rare earth metal at room temperature is provided. This intermediate layer contains one or more elements selected from Tb and Dy in an amount of 10% or more of the entire rare earth element, and has a composition in which rare earth metal magnetization is dominant at room temperature. In such an intermediate layer, since the magnetization is large at room temperature, the perpendicular magnetic anisotropy is relatively low in the mask region at the time of reproduction, and the magnetization decreases at room temperature or higher, and is sufficiently high in the aperture region at the time of reproduction. Perpendicular magnetic anisotropy is obtained.

Since the intermediate layer is predominantly of a rare earth metal and has low perpendicular magnetic anisotropy at room temperature, the rotation of the magnetization from the recording layer to the reproducing layer tends to occur. As a result, the reproducing layer can direct magnetization in a plane with a smaller film thickness. On the other hand, at the reproducing temperature, the magnetization of the intermediate layer decreases, and a sufficiently high perpendicular magnetic anisotropy is generated to transfer the magnetization of the recording layer to the reproducing layer.

At this time, since the thickness of the reproducing layer is smaller than the conventional one, the magnetization of the reproducing layer can be directed sufficiently in the direction perpendicular to the film surface, and a high reproduction signal level can be obtained. This can be considered that at room temperature (mask region), a part of the magnetization rotation in the reproducing layer is replaced by the intermediate layer. Therefore, the thickness of the reproducing layer can be reduced. Perpendicular magnetic anisotropy K⊥
Is the uniaxial anisotropy Ku and the demagnetizing field energy 2πMs ² (M
s is the saturation volume susceptibility)

[0017]

K⊥ = Ku−2πMs ² (2)

## EQU1 ## Since the intermediate layer contains Tb or Dy, the original anisotropic Ku is considerably large. However, since Ms is large in the mask region, K⊥ becomes small due to the demagnetizing field energy, and the magnetization rotates in the in-plane direction. On the other hand, in the aperture region, Ms decreases,

[0019]

[Expression 4] K⊥ ≒ Ku (3)

The magnetization is perpendicular to the film surface due to the inherently high anisotropy of the intermediate layer. Therefore, as the thickness of the reproducing layer becomes thinner, the magnetization of the reproducing layer surface becomes more perpendicular,
It is possible to obtain a high reproduction signal level.

Compared with the case where the intermediate layer using GdFe is used, the intermediate layer has a higher perpendicular magnetic anisotropy in the aperture portion, so that the magnetization of the reproducing layer becomes more perpendicular, and A high reproduction signal level can be obtained. In the conventional CAD medium, only the temperature change of the magnetization in the reproducing layer is used, but in the present invention, the temperature change of the two layers of the reproducing layer and the recording layer is used.

Therefore, a change in magnetization is obtained more steeply with respect to temperature, and the super-resolution characteristic is improved. Hereinafter, preferable characteristics of each layer will be described in order. Materials used for the regeneration layer include:
GdFeCo, GdCo, GdFe, GdDyFe, G
dDyCo, GdDyFeCo and the like are preferably used. Among them, GdFeCo having small perpendicular magnetic anisotropy and high Curie temperature is preferably used.

[0023]

## EQU00005 ## Gdx (FeyCo _100- y) _100- x (all in atomic%)

In this case, it is preferable that 26 ≦ x ≦ 34 and 0 ≦ y ≦ 90. More preferably 27 ≦ x ≦ 32 and 5 ≦
y ≦ 85. Particularly preferably, 28 ≦ x ≦ 31 and 30 ≦ y ≦ 70
It is. However, additives such as Ti, Cr, Pt, and Mo may be added in an amount of about 5 atomic% or less. A preferable volume magnetic susceptibility Ms1 of the reproducing layer at room temperature (the temperature of the environment in which the medium is used, which is 25 ° C. in the present invention) is 100 emu / cc or more, and more preferably 150 emu / cc or less.

If Ms1 is too small, the magnetization in the mask region does not become sufficiently in-plane, and the effect of super-resolution is reduced. However, if Ms1 is too large, the magnetization is not sufficiently perpendicular in the aperture region, so that it is preferably 400 emu / cc or more, more preferably 350 emu / cc or more.

Preferred coercive force Hc of the reproducing layer at room temperature
1 is 500 (Oe) or less, and more preferably 30 (Oe).
0 (Oe) or less. As described above, if the thickness of the reproducing layer is too large, the magnetization does not stand sufficiently perpendicular in the aperture region. Therefore, the thickness of the reproducing layer is preferably 90 nm or less. More preferably, it is 80 nm or less. Particularly preferably, it is 70 nm or less.

If the thickness of the reproducing layer is too small, the magnetization in the mask region is not sufficiently directed in the plane, and the super-resolution capability is reduced. Therefore, the thickness of the reproducing layer is preferably 20 nm or more. More preferably, it is 30 nm or more. The intermediate layer has a rare earth metal dominant magnetization at room temperature, such that the magnetization decreases with increasing temperature and the perpendicular magnetic anisotropy improves. A substance satisfying the following formula is used as the material of the intermediate layer.

[0028]

(RE _N Gd _100-N ) _M TM _100-M

RE: one or more elements selected from Tb and Dy TM: one or more elements selected from Fe and Co 10 ≦ N ≦ 100, 26 ≦ M ≦ 35 More preferably, 20 ≦ N ≦ 100, particularly preferably Preferably, 30 ≦ N ≦ 90.

Specifically, TbFe, TbFeCo, Dy
FeCo, TbDyFeCo, GdDyFe, GdDy
FeCo, GdTbDyFeCo and the like are preferably used. Among them, an alloy mainly composed of TbFeCo having high perpendicular magnetic anisotropy is preferably used. In order to sufficiently reduce the exchange coupling force between the reproducing layer and the recording layer, at room temperature, 15
It preferably has a volume susceptibility of 0 emu / cc or more.

In order to sufficiently improve the perpendicular magnetic anisotropy when the temperature rises, it is preferable that the temperature at which the volume susceptibility becomes 100 emu / cc or less exists between 50 ° C. and 200 ° C. However, in order to sufficiently exhibit the effect of lowering the perpendicular magnetic anisotropy at room temperature, the magnetization at room temperature is preferably larger than the magnetization of the recording layer.

In general, the higher the Co ratio in the transition metal, the greater the magnetization at the same transition metal content. As a result, the perpendicular magnetic anisotropy at room temperature can be reduced. Therefore, the ratio of Co to the entire transition metal in the intermediate layer is preferably higher than that of the recording metal. In order to increase the magnetization at room temperature, the ratio of Co in the transition metal is preferably 20% or more. More preferably, it is 30% or more.

However, additives such as Ti, Cr, Pt and Mo may be added in an amount of about 5 atomic% or less. The thickness of the intermediate layer is preferably 3 nm or more and 50 nm or less. More preferably, 5 nm or more and 40 nm or less, particularly preferably 8 nm or more.
nm or more and 30 nm or less. If the intermediate layer is too thin, the effect of the present invention is lost, and if it is too thick, magnetic domain transfer from the recording layer hardly occurs.

The coercive force of the intermediate layer at room temperature is preferably 3 kOe or less. More preferably, it is 2 kOe or less. Since the recording layer is a layer in which recording is stably stored, it is necessary that the recording layer has a Curie temperature that does not deteriorate with a reproduction beam. Curie temperature is 25
About 0 to 350 ° C. is preferable. If the Curie temperature is too high, the laser power required for recording will be too high.

The recording layer also needs to have high perpendicular magnetic anisotropy in order to give a strong force to the magnetization of the reproducing layer.
The material of the recording layer is made of RE _x (FeCo) _100-x , and preferably 16 ≦ x ≦ 26. Where R
E is one or more elements selected from Tb and Dy.

Specifically, TbFeCo, TbCo, Dy
FeCo, TbDyFeCo and DyCo are preferably used. As the recording layer, T having particularly large perpendicular magnetic anisotropy is used.
An alloy mainly composed of bFeCo is preferably used. Among them,

[0037]

## EQU00007 ## Tbx (FeyCo _100- y) _100- x (all in atomic%)

In this case, it is preferable that 16 ≦ x ≦ 26 and 60 ≦ y ≦ 90. More preferably, 18 ≦ x ≦ 24, 70
≤ y ≤ 85. In the present invention, the intermediate layer has a composition in which rare earth metal magnetization is dominant at room temperature. For this reason, the leakage magnetic flux from the intermediate layer around the recording area at the time of recording influences at the time of recording, and there is a possibility that the recording magnetic field dependency is deteriorated.

Therefore, it is preferable that the recording layer has a composition in which the transition metal magnetization is dominant at room temperature, so as to cancel the leakage magnetic field of the intermediate layer. However, additives such as Ti, Cr, Pt, and Mo may be added in an amount of about 5 atomic% or less. The thickness of the recording layer is preferably 20 nm or more and 70 nm or less. It is preferable that the film thickness of the recording layer is sufficient to cancel the leakage magnetic field of the intermediate layer and improve the recording magnetic field dependency.

In order to stably store the information recorded on the recording layer, it is preferable that the coercive force of the recording layer is larger than that of the reproducing layer. The coercive force of the recording layer is preferably 3 kOe or more. More preferably, it is 5 kOe or more. Between the intermediate layer and the reproducing layer, there may be a case where a cutting layer which cuts exchange coupling at a high temperature portion during reproduction is inserted between the intermediate layer and the reproducing layer because of its non-magnetic or Curie temperature lower than that of either layer.

In this case, the transfer of the magnetization direction from the recording layer to the reproduction layer is performed by a magnetostatic coupling force. Even when using transfer by magnetostatic coupling, due to the presence of the intermediate layer, the magnetization of the surface of the intermediate layer is inclined at low temperatures, so that the coupling between the reproducing layer and the recording layer is reduced. By raising, the coupling becomes stronger and a high super-resolution effect can be obtained. In this case, it is preferable that each of the reproducing layer and the recording layer has sufficient magnetization to obtain a sufficiently strong magnetostatic coupling force in the aperture region.

Since an alloy of a rare earth metal and a transition metal is very easily oxidized, it is preferable to adopt a mode in which protective films are provided on both sides of the magnetic layer. As the protective film, Si oxide, A oxide
1, Ta oxide, Ti oxide, Si nitride, Al nitride, Carbide S
A simple substance such as i or a mixture thereof is preferably used. The thickness of the protective film is preferably about 50 nm to 150 nm. After forming the protective film on the substrate side, the magnetic anisotropy of the magnetic layer can be improved by plasma etching the surface.

The provision of a high thermal conductive material made of Al, Cu, Au, Ag, or the like alone or an alloy mainly composed of Al, Cu, Au, or Ag as a heat radiation layer directly or through a protective layer on the recording layer side of the magnetic layer is not possible. This is a desirable configuration for stabilizing the heat distribution at the time. The thickness of the heat radiation layer is 10 nm to 100
About nm is preferable. In the method of the present invention, since the crosstalk can be suppressed to a very low level, it is possible to perform recording on both lands and grooves in addition to ordinary land recording or groove recording.

[0044]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the invention.

[0045]

Example 1 A polycarbonate substrate having a guide groove with a track pitch of 1.0 μm was introduced into a sputtering apparatus, and the vacuum was exhausted to a degree of vacuum of 5 × 10 ⁻⁵ Pa or less.
Thereafter, 80 nm of Ta oxide was formed on the substrate as a protective layer by using reactive sputtering.

Next, Gd ₂₈ (Fe ₅₀ Co ₅₀ ) is formed on Ta oxide.
50nm of the reproducing layer made of _{72, (Tb N Gd 100-} N)
_M (Fe ₇₀ Co ₃₀ ) _100-M 20 nm intermediate layer, T
A 50 nm recording layer made of b ₂₁ (Fe ₇₅ Co ₂₅ ) ₇₉ was provided. Finally, a 50 nm protective layer made of SiN was provided.
The value of N was varied from 0 to 100. The value of M was varied from 18 to 38.

The Curie temperatures of the reproducing layer, the intermediate layer and the recording layer were all found to be 300 ° C. or higher. Further, in the reproducing layer, the magnetization of the rare earth metal was dominant at room temperature (25 ° C.), and the volume susceptibility was 260 emu / cc. The compensation temperature was 190 ° C. The temperature at which the volume susceptibility reached 150 emu / cc was 120 ° C. The reproducing layer was an in-plane magnetized film at room temperature. The recording layer had a transition metal magnetization dominance at room temperature and a coercive force of 12 kOe.

The disk manufactured in this manner was set at wavelength 6
The CNR (narrow band signal-to-noise ratio) was evaluated by optical modulation recording using an evaluator having a numerical aperture of 80 nm and a numerical aperture of 0.55. The recording conditions were a linear velocity of 7 m / s, a frequency of 9 MHz, a reproduction power of 3.0 mW, a recording power of 9 mW, a recording duty of 30%,
The recording magnetic field is 300 Oe. The results are summarized in FIG.

FIG. 4 also shows crosstalk measured on adjacent tracks when recording was performed at 2 MHz. Crosstalk is defined as 20log10 (I2 / I1) using the signal intensity I1 on the recording track and the signal intensity I2 on the adjacent track.

[0050]

EXAMPLE 2 The intermediate layer _{(Dy N Gd 100-N)} M (Fe 70 C
o ₃₀ ) A disc was prepared in the same manner as in Example 1 except that a 20 nm layer of _100-M was used. The value of x was varied from 0 to 100. The value of y varied from 18 to 38. The CNR and crosstalk of the disk thus manufactured were measured in the same manner as in Example 1. The results are shown in FIG. 5 and FIG.

[0051]

Embodiment 3 The intermediate layer is made of (Tb ₈₀ Gd ₂₀ ) ₂₈ (Fe ₇₀ Co
₃₀ ) A disk was prepared in the same manner as in Example 1 except that the film thickness was changed to ₇₂ . The value of DI was varied from 0 to 100 nm. The CNR of the disc thus produced was measured in the same manner as in Example 1. The results are shown in FIG.

[0052]

Embodiment 4 The intermediate layer is made of (Tb ₈₀ Dy ₂₀ ) ₂₈ (Fe ₇₀ Co
₃₀ ) A disc was prepared in the same manner as in Example 1 except that the layer was made of ₇₂ and had a thickness of 20 nm, and the thickness DR of the reproducing layer was changed. The value of DR was varied from 30 to 150 nm as shown in Table 1. The CNR of the disc thus produced was measured in the same manner as in Example 1. The results are shown in FIG.

[0053]

Embodiment 5 The intermediate layer was made of 20 nm (Tb ₈₀ Gd ₂₀ ).
₂₈ (Fe ₇₀ Co ₃₀ ) ₇₂ , and the recording layer is made of Tbx (Fe ₇₅ C
o ₂₅ ) Example 1 except that a 50 nm layer of _100- x was used.
A disc was created in the same way as. The value of x was varied from 14 to 32. Using the disc manufactured in this manner, the recording magnetic field dependence of CNR (narrow band signal-to-noise ratio) was evaluated by optical modulation recording using an evaluator having a wavelength of 680 nm and a numerical aperture of 0.55. The recording conditions were a linear velocity of 7 m / s, a frequency of 9 MHz, a reproduction power of 3.0 mW, a recording power of 9 mW,
The recording duty is 30%. The results are shown in FIG.

[0054]

Embodiment 6 The intermediate layer is made of 20 nm (Tb ₈₀ Gd ₂₀ ).
₂₈ (Fe ₇₀ Co ₃₀ ) ₇₂ , and the recording layer is Dyx (Fe ₇₅ C
o ₂₅ ) Example 1 except that a 50 nm layer of _100- x was used.
A disc was created in the same way as. The value of x was varied from 14 to 32. Using the disc manufactured in this manner, the recording magnetic field dependence of CNR (narrow band signal-to-noise ratio) was evaluated by optical modulation recording using an evaluator having a wavelength of 680 nm and a numerical aperture of 0.55. The recording conditions were a linear velocity of 7 m / s, a frequency of 9 MHz, a reproduction power of 3.0 mW, a recording power of 9 mW,
The recording duty is 30%. The results are shown in FIG.

[0055]

Embodiment 7 The intermediate layer is made of (Tb ₈₀ Gd ₂₀ ) ₂₈ (Fe _y Co
_1-y ) A disc was prepared in the same manner as in Example 1 except that the layer was made of ₇₂ and had a thickness of 20 nm. The value of y was varied from 0 to 100. The disk manufactured in this manner was used in Example 1
The CNR was measured in the same manner as in. The results are shown in FIG.

[0056]

By using the magneto-optical recording medium of the present invention, it is possible to obtain a CAD super-resolution medium having both high reproduction signal level, low crosstalk and high resolution.

[Brief description of the drawings]

FIG. 1 is an explanatory longitudinal sectional view of a CAD magneto-optical recording medium of the present invention.

FIG. 2 is an explanatory longitudinal sectional view of a conventional CAD magneto-optical recording medium.

FIG. 3 is a graph showing the relationship between the composition of a GdTbFeCo intermediate layer and CNR.

FIG. 4 is a graph showing the relationship between the composition of a GdTbFeCo intermediate layer and crosstalk.

FIG. 5 is a graph showing the relationship between the composition of the GdDyFeCo intermediate layer and the CNR.

FIG. 6 is a graph showing the relationship between the composition of a GdDyFeCo intermediate layer and crosstalk.

FIG. 7 is a graph showing the relationship between the thickness of the intermediate layer and the CNR.

FIG. 8 is a graph showing the relationship between the thickness of the reproducing layer and the CNR.

FIG. 9 is a graph showing the relationship between the composition of the TbFeCo recording layer and the recording magnetic field dependence.

FIG. 10 is a graph showing the relationship between the composition of a DyFeCo recording layer and the recording magnetic field dependence.

FIG. 11 is a graph showing the relationship between Co composition and CNR of an intermediate layer.

Claims (3)

[Claims] 1. A reproducing layer, an intermediate layer, and a recording layer comprising an alloy magnetic material containing a rare earth metal and a transition metal are provided on a substrate, and the reproducing layer is magnetized substantially parallel to the film surface at room temperature. A magneto-optical recording medium characterized by using an alloy represented by the following formula (1) as an intermediate layer. (RE _N Gd _100-N ) _M TM _100-M (1) RE: one or more elements selected from Tb and Dy TM: one or more elements selected from Fe and Co 10 ≦ N ≦ 100, 26 ≦ M ≦ 35 2. The magneto-optical recording medium according to claim 1, wherein the reproducing layer is made of GdFeCo. 3. The magneto-optical recording medium according to claim 1, wherein the recording layer is made of RE _x (FeCo) _100-x and 16 ≦ x ≦ 26.