JPH0447548A - magneto-optical recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention records information by forming bits of reversed magnetic domains using a laser beam and an external magnetic field. The present invention relates to a magneto-optical recording medium that uses magneto-optic effects to read information.

[Conventional technology]

Magneto-optical memory is known as an erasable optical memory. Compared to magnetic recording media using conventional magnetic heads, magneto-optical memory has the advantage of being capable of high-density recording and non-contact recording and playback, but on the other hand, the recorded area must be erased before recording. It has the disadvantage that it cannot be magnetized in one direction (it must be magnetized in one direction). In order to compensate for this shortcoming,
A method of providing separate recording/reproducing heads and erasing heads,
Alternatively, a laser power modulation override method using a special exchange-coupled double-layer film and an initializing magnetic field has been proposed.

However, these methods have the disadvantages that the apparatus is large-scale and expensive, that a high-output semiconductor laser is required, and that bit edge recording is difficult.

Therefore, a magnetic field modulation override method has been proposed in which recording is performed while simultaneously modulating the applied magnetic field while irradiating a continuous laser beam.

[Problems to be Solved by the Invention] The magnetic field modulation override method cannot modulate a large magnetic field at high speed. Therefore, a medium that can be overridden even with a small magnetic field is desired.

An exchange-coupled bilayer film consisting of a high coercive force layer with a low Curie temperature and a low coercive force layer with a high Curie temperature is an excellent medium that has both high sensitivity and a high CN (carrier-to-noise) ratio. A high coercive force layer of a rare earth-iron group amorphous alloy with dominant rare earth sublattice magnetization and a low coercive force layer of a rare earth-iron group amorphous alloy with dominant iron group sublattice magnetization have a compensation temperature between room temperature and the Curie temperature. A normal exchange-coupled two-layer film consisting of a magnetic layer has a large override magnetic field and is not suitable as a medium for a magnetic field modulation override system.

An object of the present invention is to solve the problems of the prior art described above and to provide a magneto-optical recording medium suitable for use in the magnetic field modulation override method.

[Means for solving problems]

The above object of the present invention is to provide a first magnetic layer capable of perpendicular magnetization;
a second magnetic layer having a higher Curie temperature and a lower coercive force than the first magnetic layer, and a magneto-optical recording medium in which the first magnetic layer and the second magnetic layer are exchange-coupled. wherein the first magnetic layer is formed from a rare earth iron group amorphous alloy in which rare earth sublattice magnetization is dominant and does not have a compensation temperature between room temperature and its Curie temperature; This is achieved by forming the layer from a rare earth-iron group amorphous alloy with dominant iron group sublattice magnetization.

The first magnetic layer is preferably formed from an alloy having the following composition.

((Tb,..-Dy,) (Fe100-Coy)) 100-t Cr.

O≦X≦100.0≦y≦40, 0≦2≦10 When such a material is used as the first magnetic layer, particularly excellent recording characteristics and stability of recorded information are obtained.

Further, the second magnetic layer is preferably formed from an alloy having the following composition.

(Gd (F'e,,.-,-Co,-)) t
oo-t・cr.

However, 0≦y゛≦50, 0≦2°≦10 If such a material is used as the second magnetic layer, the readout characteristics will be particularly high.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing one embodiment of the magneto-optical recording medium of the present invention. In FIG. 1, reference numeral 1 denotes a transparent substrate made of glass, plastic, or the like. On this substrate 1, a first protective layer 2, a second magnetic layer 3, a first magnetic layer 4, and a second protective layer 5 are sequentially formed by sputtering or the like. Furthermore, on the second protective layer 5,
A backing dummy substrate 7 is bonded together with an adhesive 6. This dummy substrate 7 is made of the same material as the substrate 1. Further, as the adhesive, a pot melt adhesive is suitable.

The first magnetic layer (hereinafter referred to as high coercive force layer) 4 is perpendicularly magnetizable and has a relatively low Curie temperature and a relatively high coercive force at room temperature. This high coercive force layer 4 is formed from a rare earth-iron group amorphous alloy in which rare earth sublattice magnetization is dominant, and which has no compensation temperature between room temperature and its Curie temperature.

The second magnetic layer (hereinafter referred to as a low coercive force layer) 3 has a higher Curie temperature and a lower coercive force at room temperature than the high coercive force layer 4. As the material for this low coercive force layer 3, a rare earth-iron group amorphous alloy in which iron group sublattice magnetization is dominant is used. Further, the low coercive force layer 3 and the high coercive force layer 4 are exchange-coupled with each other.

The protective layers 2 and 5 are for preventing oxygen and moisture from entering the first and second magnetic layers and for preventing oxidation of the magnetic layers. Such a protective layer is made of Six N4, Si
It is formed from derivatives such as O2 and SiC.

In the recording medium configured as described above, information is recorded and reproduced by irradiating the magnetic layer with a laser beam from the substrate 1 side. At this time, the protective layer 2 also functions as an antireflection layer for the beam.

Next, the material of the magnetic layer will be explained in more detail.

As a material for the above-mentioned high coercive force layer 4, TbDy-FeCo-Cr using Tb or Dy, which is a non-S state element, as a rare earth element is preferable in order to increase the coercive force. As for the composition, the atomic ratio is ((Tb,...-, Dy,) (Fe 100-y Co, )) +6
6-1 When expressed as Cf @, 0≦x≦100, O
The range of ≦y≦40°0≦2≦10 is preferable. The film thickness is about 100 to 2000, more preferably 400 to 1.
000 people is good. Curie temperature T of this high coercive force layer
There is approximately Tc=1.3 (100-x) between c and the atomic ratio of Dy xSCo and 2 of SCr.
The following relationship was obtained.

Therefore, the values of x, y, and z may be appropriately selected so that the Curie temperature of the high coercive force layer becomes a desired value.

In a magneto-optical memory, information is recorded using the thermal effect of laser light, so the lower the Curie temperature of the magnetic film, the higher the recording sensitivity. What determines the recording sensitivity in an exchange-coupled two-layer magnetic film is the Curie temperature of the high coercive force layer, so lowering the Curie temperature of the high coercive force layer will increase the recording sensitivity.However, considering the stability of recorded information, The Curie temperature of the high coercive force layer cannot be lowered that much.
When considering the stability of recorded information, it is necessary to consider not only the stability at room temperature but also the stability at temperatures slightly higher than room temperature. That is, inside the magneto-optical memory drive device,
There are various sources of heat, some of which are 50 to 60.
Temperatures can rise to around 30 degrees Fahrenheit.Furthermore, when reading information, the medium is irradiated with a weak laser beam that does not record information, but it is still unavoidable that the temperature of the medium rises to some extent. It is. Also,
This is because, due to the operation of the drive device, it may be necessary to read data while a bias magnetic field for recording/erasing is applied.

Therefore, in a drive device at about 50 to 60 degrees Celsius,
Under the application of a bias magnetic field, the recorded information needs to be stable even if the temperature of the medium further increases due to the readout light. Considering all these, the Curie temperature of the high coercive force layer is 150~')Q(1'fTL"iuf+<t
s#1. A good material for the low coercive force layer 3 is Gd-FeCo-Cr, in which Gd, which is an S-state element, is used as the rare earth element in order to lower the coercive force. However, as for the composition, the atomic ratio is (Gd (Fe+++o-y Coy)) r
oo-tCr.

When represented as It is desirable that the ratio is greater than the Cr composition ratio of the low coercive force layer. The film thickness is preferably about 100 to 2000 people, more preferably about 200 to 600 people.

The magneto-optic effect of rare earth-iron amorphous alloy thin films in the visible wavelength range is mainly due to the magneto-optic effect of iron group elements, and the iron group magnetic moment near room temperature is Fe y
. Cos. The iron group magnetic moment reaches its maximum at a composition of about 100%, and when the Co content is less than that, the iron group magnetic moment decreases considerably, and when the Co content is more than that, the iron group magnetic moment decreases slightly. Therefore, C.

It is preferable that the amount of -Fe in the cod should be around 30 atomic % or more.

In the above description, alloys containing Co and Cr were mentioned as materials suitable for the high coercive force layer and the low coercive force layer. below,
The effects of the additional elements Co and Cr will be explained.

Magneto-optical recording media using thin films of rare earth-iron amorphous alloys have poor durability, and suffer from problems such as selective oxidation of rare earth elements, surface oxidation of magnetic films, and pitting corrosion. Improvement methods have been proposed. One of these is the addition of elements for the purpose of improving the durability of the magnetic film itself (for example, Journal of the Japan Society of Applied Magnetics 9 (1985
)93).

Examples of additive elements are Cr, AI, Ti, and Ni.

Examples include Co and Pt.

When considering the addition of elements to improve durability, Cr is the best in terms of its effect alone, but it has the drawbacks of lowering the Curie temperature and lowering the magneto-optic effect. As the Curie temperature decreases, the recording sensitivity increases, but the stability of recorded information against temperature rises deteriorates, so unnecessary decreases in the Curie temperature are undesirable.Also, a decrease in the magneto-optical effect impairs the readout characteristics. It's bad, so it's not good.

Although CO is another element for improving durability, its effect on improving durability is inferior to that of Cr. Furthermore, although the magneto-optic effect increases, this is accompanied by an increase in the Curie temperature, resulting in a decrease in recording sensitivity.

Considering the addition of both elements Cr and Co, the decrease in the Curie temperature caused by the addition of Cr can be prevented by adding Co, but even if the Curie temperature is kept unchanged,
The magneto-optic effect is also reduced.

In an exchange-coupled bilayer film, the high coercive force layer only records and retains information, so the Curie temperature of the high coercive force layer must be appropriately low, but since it has no bearing on readout, its magneto-optical effect is It doesn't matter how low it is. On the other hand, since the low coercive force layer only performs reading of information, the low coercive force layer needs to have a large magneto-optical effect, but since it is not related to recording, it does not matter how high its Curie temperature is.

Focusing on this point, in the high coercive force layer, a small amount of Co and Cr
It is desirable to add a large amount of so as to reduce the magneto-optical effect, but to avoid changing the Curie temperature and obtain a large effect on durability. This reduction in magneto-optic effect does not affect read characteristics.

On the other hand, in the low coercive force layer, by adding a large amount of CO and a small amount of Cr, or by not adding Cr, the Curie temperature increases, but the magneto-optic effect is not reduced, and a large durability effect is achieved. It is desirable to obtain

This increase in Curie temperature does not affect recording sensitivity.

Therefore, the Co composition ratio of the high coercive force layer is lower than the Co composition ratio of the low coercive force layer, and the Cr composition ratio of the high coercive force layer is
It is desirable that the composition ratio of Cr is greater than the composition ratio of Cr in the low coercive force layer.

However, as manufacturing processes become cleaner, rot4>f-
i'! lj and ↓ Kozutotosu kariru J, <Nu work today 1A 7μ, 2, t-φ-1^, it is not necessary to add Cr.

"Jitsu"L-den" - A magneto-optical recording medium of the present invention having the structure shown in FIG. 1 was produced using a normal magnetron sputtering method. As the substrate 1 and the dummy substrate 7, disk-shaped polycarbonate (PC) substrates with a diameter of 130 mm were used. Also, adhesive 6
A hot melt (HM) adhesive was used.

The protective layers 2 and 5 were made of SiN with a refractive index of about 2.2 to 2.3. The thickness of the protective layer 2 is approximately 500 mm, the thickness of the protective layer 5 is approximately 700 mm, and the film stress is approximately 10 to 30 kg/mrr.
The compressive stress was set to r. These protective layers were formed using RF radiation using a Si3N4 target and a mixed gas of Ar and N2.
It was formed by sputtering. The refractive index is Ar and N,
It is controlled by changing the gas mixture ratio, and the film stress is controlled by changing the gas mixture ratio.
It was controlled by changing the gas pressure of 10 N2 gas. In order to obtain the above refractive index and film stress, approximately 1% N2 is added, and A r +N! Gas pressure is approximately 0.1, refractive index is 2.2
If it is smaller, the light interference effect will be small and the reflectance will not decrease, resulting in poor sensitivity and poor CN ratio. 2.3
If it is larger, absorption will appear in SiN, resulting in a poor CN ratio. Membrane stress is 10 to 30 kg/mtr? If it is smaller, the structural relaxation of the magnetic layer will be greater and therefore the reliability will be worse. 10~30kg/mrr? If it is larger, the force applied to the PC board will be greater, which will cause the disc to warp. The effect of film stress on the structural relaxation of the magnetic layer is greater in the protective layer 2 than in the protective layer 5. In other words, when the film stress of the protective layer 2 is small, the structural relaxation is large;
Even if the film stress of the protective layer 5 is small, the structural relaxation is not so large. Therefore, in order to reduce structural relaxation and disk warpage, it is desirable to make the film stress of the protective layer 2 relatively large and the film stress of the protective layer 5 relatively small.

The low coercive force layer 3 has (G d (F e 70CO31
1)) Consists of 98Cr, with a saturation magnetization of approximately 50 to 150
The iron group sublattice magnetization of emu/cg is dominant. The film thickness is about 400 people, and the film stress is about 10-30 Kg/m.
rr? is the compressive stress. This low coercive force layer was formed by RF co-sputtering using Ar gas and targets of Gd and (F e 76 COso) *tCr s. The composition, that is, the saturation magnetization, is Gd and (F
The film stress was controlled by changing the RF power applied to the target, and the film stress was controlled by changing the gas pressure of Ar gas. In order to obtain the above film stress, the Ar gas pressure must be set to approximately 0.15 Pa.
And so.

Membrane stress is 10 to 30 kg/mrr? If it is smaller, the structural relaxation of the magnetic layer will be greater and therefore the reliability will be worse. If it is larger than 10 to 30 kg/mrr+', the force applied to the PC board becomes large, which causes the disk to warp.

The high coercive force layer 4 is (Tb − (Fes2cOa))
It consists of isCr 4, and the saturation magnetization is about 200 = m
The rare earth sublattice magnetization of u/crd is dominant. The film thickness is approximately 400 mm, and the film stress is a compressive stress of approximately 10 to 30 Kg/mrrI'. This high coercive force layer consists of Tb and (Fe*2Co
g) Formed by RF co-sputtering using an OACRS target and Ar gas. The composition, that is, the saturation magnetization is Tb and (FeezCOs) 95C
The rs was controlled by changing the RF power applied to the target, and the film stress was controlled by changing the gas pressure of Ar gas. In order to obtain the above film stress, the Ar gas pressure was set to about 0.15 Pa.

The membrane stress is 10-30 kg/mrr? If it is smaller, the structural relaxation of the magnetic layer will be thicker, resulting in poor reliability. If it is larger than 10 to 30 kg/mrr+', the force applied to the PC board will be large, causing the disk to warp.

Pasting the dummy substrate 7 together using the adhesive 6 is as follows:
This is to maintain the flatness of the substrate 1 and to prevent mechanical scratches on the protective layer and magnetic layer. Generally, the amount of moisture absorbed by a PC board immediately after film formation is very small, and the amount of moisture absorbed by a PC board left indoors is quite large. Therefore, if a dummy PC board left indoors is bonded together immediately after film formation, an imbalance will occur in the amount of moisture absorbed by the disk PC board and the dummy PC board. And after that, disk P
Moisture absorption occurs only in the C substrate, causing the disc to warp. For this purpose, the disk PC board after film formation is left indoors for about 24 hours or more to absorb sufficient moisture, and then the dummy PC board is
It is desirable to attach it to the substrate.

For comparison, as a high coercive force layer, the saturation magnetization is approximately 100 e.
The rare earth sublattice magnetization of mu/crd is dominant (
A magneto-optical recording medium having the same structure as the above example was manufactured except that the rb(F"e,,Coa)) sac ra film was used.

The reflectance of the magneto-optical recording medium produced here was about 25% in the flat portion. Before explaining the experiment of override magnetic field of magneto-optical recording medium, Tb-Fe
The relationship between the Curie temperature and the compensation temperature with respect to the saturation magnetization of Co--Cr will be explained.

Figure 2 shows the RF radiation applied to Tb and FeCo-Cr targets when forming the high coercive force layer of the magneto-optical recording medium.
The relationship between Curie temperature and compensation temperature for saturation magnetization is shown for samples made with different power. The saturation magnetization was measured by a vibrating sample magnetometer, and the Curie temperature and compensation temperature were measured by a variable temperature magneto-optical Kerr effect measuring device.

The Curie temperature is the temperature at which spontaneous sublattice magnetization disappears, and the compensation temperature is the temperature at which spontaneous sublattice magnetization exists, but the rare earth sublattice magnetization and iron group sublattice magnetization have the same magnitude but different signs, and the apparent This is the temperature at which the upper white magnetization disappears. Since saturation magnetization is defined at room temperature, a composition with saturation magnetization of O can be said to have a compensation temperature at room temperature.

Beyond the compensation temperature, at temperatures higher than that, iron group sublattice magnetization becomes dominant. Therefore, if the iron group sublattice magnetization is dominant at room temperature, the iron group sublattice magnetization is dominant up to the Curie temperature. Furthermore, what is rare earth sublattice magnetization dominant at room temperature remains rare earth sublattice magnetization dominant up to the compensation temperature.
From the compensation temperature to the Curie temperature, the iron group sublattice magnetization becomes dominant. If the magnetization is dominant in the rare earth sublattice at room temperature and there is no compensation temperature between room temperature and the Curie temperature, the magnetization is dominant in the rare earth sublattice from room temperature to the Curie temperature.

From Figure 2, the saturation magnetization is approximately 15 with dominant rare earth sublattice magnetization.
For those below 0 emu/rd, there is a compensation temperature between room temperature and Curie temperature, and about 150 emu/rd.
crr? In the above cases, there is no compensation temperature.

The saturation magnetization at the boundary between the presence and absence of compensation temperature is approximately 150 emu/crri in this case, which is
It changes depending on the concentration of o and Cr.

From the above, the saturation magnetization of the medium prepared as a comparative example is approximately 1
0100e/crrr rare earth sublattice magnetization dominant Tb-
Although the FeCo-Cr high coercive force layer has a compensation temperature, the saturation magnetization of the medium according to the embodiment of the present invention is 200 emυ/c.
nf rare earth sublattice magnetization dominant Tb-Fe Co-
The Cr high coercive force layer has no compensation temperature.

The magnitude of the magnetic field required for override was measured for the examples and comparative examples produced as described above. The override magnetic field was measured at a disk rotation speed of 1.800 rpm and a radius of 45 mm using an evaluation machine having a semiconductor laser with a wavelength of 830 nm and an objective lens with a numerical aperture of 0.52.

The evaluation method is to first perform erasing by irradiating continuous light while applying a bias magnetic field of -1,0000e to align the magnetization in one direction. Next, recording is performed by irradiating pulsed light while applying a certain device magnetic field. Then, read out that part and measure the carrier and noise. More than -6
The results obtained for bias magnetic fields from 000e to 6000e are shown in FIGS. 3 and 4. FIG. 3 shows the results for the medium of the present invention having a Tb--FeCo--Cr high coercive force layer with no compensation temperature and dominated by rare earth sublattice magnetization with a saturation magnetization of 200 e mu/c g. On the other hand, FIG. 4 shows a Tb-FeC with compensation temperature dominated by rare earth sublattice magnetization with saturation magnetization of about 10100e/crTI'.
This is a comparative example having an o-Cr high coercive force layer. In the figure, C indicates a carrier and N indicates noise.

In FIG. 4, carriers rise from about -4000e and are saturated at about 2000e. This indicates that a magnetic field of ±4000e or more is required for override. On the other hand, in Figure 3, -30
The carriers rise from about 00e and are saturated at about 2000e. This indicates that a magnetic field of ±3000e or more is sufficient for override. That is, it can be seen that the use of the exchange-coupled double-layer film of the present invention has the effect of reducing the override magnetic field.

As the high coercive force layer of the tributary, rare earth sublattice magnetization with a saturation magnetization of 200 emu/cg ((T b aoD V 6°) -
(FesyCo+5)) A magneto-optical recording medium having the same structure as Example 1 was produced except that e6cr< was used.

In addition, as a comparative example, only the high coercive force layer was used, and the saturation magnetization was approximately 1.
00 e mu / crd rare earth sublattice magnetization dominant ((T b −, D v , −) − (Fρ − C00
)) *A medium was prepared in which the aCrn film was changed. These media include T bioD yao and (FestCO1
3)) esc r! target was used.

Next, for this example and comparative example, the magnitude of the magnetic field required for override was measured using the same method as in Example 1.

In the comparative example, carriers start up when the bias magnetic field is about -3500e, and are saturated at about 1500e.

Therefore, a magnetic field of ±3500e or more is required for override.

On the other hand, in the example, carriers rise from about -1500e and are saturated at about 1500e. Therefore, a magnetic field of ±1500e or more is sufficient for override. That is, it can be seen that the use of the exchange-coupled double-layer film of the present invention has the effect of reducing the override magnetic field.

As the high coercive force layer of the support 55, rare earth sublattice magnetization dominant (D y (Fe s□COz
)) A magneto-optical recording medium having exactly the same structure as in Example 1 was prepared except that 9ec ra was used. In addition, as a comparative example, only the high coercive force layer has a saturation magnetization of about 100 e
Rare earth sublattice magnetization dominant (
A medium was prepared in which the Dy-(Fe82CO18))sec r4 film was used. Dy and (F e B2CO+s) sac r 5 targets were used to prepare these media.

Next, for this example and comparative example, the magnitude of the magnetic field required for override was measured using the same method as in Example 1.

In the comparative example, carriers start up when the bias magnetic field is about -4000e, and are saturated at about 1500e.

Therefore, a magnetic field of ±4000e or more is required for override.

On the other hand, in the example, carriers rise from about -2000e and are saturated at about 1500e. Therefore, a magnetic field of ±2000e or more is sufficient for override. That is, it can be seen that the use of the exchange-coupled double-layer film of the present invention has the effect of reducing the override magnetic field.

〔Effect of the invention〕

As explained above, the present invention provides a high coercive force layer made of a rare earth-iron group amorphous alloy in which rare earth sublattice magnetization is dominant, and which has no compensation temperature between room temperature and its Curie temperature; By constructing a magneto-optical recording medium with a low coercive force layer made of a rare earth iron group amorphous alloy with dominant lattice magnetization, it is possible to reduce the bias magnetic field when recording on this medium using the magnetic field modulation override method. This is what was obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of an embodiment of the magneto-optical recording medium of the present invention, FIG. 2 is a diagram showing changes in Curie temperature and compensation temperature with respect to saturation magnetization in a Tb-FeCo-Cr film, and FIG. FIG. 4 is a diagram showing changes in carriers and noise with respect to a bias magnetic field in an example of the present invention, and FIG. 4 is a diagram showing changes in carriers and noise with respect to a bias magnetic field in a comparative example. 1...Substrate 2.5...Protective layer 3...Second magnetic layer 4...First magnetic layer 6...Adhesive 7...Dummy substrate Figure 2 Temperature (C) - Iron group sublattice magnetization dominant Rare earth sublattice magnetization dominant 111

Claims (3)

[Claims] (1) It has a first magnetic layer that is perpendicularly magnetizable and a second magnetic layer that has a higher Curie temperature and lower coercive force than the first magnetic layer; In a magneto-optical recording medium formed by exchange coupling with a magnetic layer, the first magnetic layer is made of a rare earth material having a dominant rare earth sublattice magnetization and which has no compensation temperature between room temperature and its Curie temperature.
the second magnetic layer is made of an iron group amorphous alloy, and
A magneto-optical recording medium comprising a rare earth-iron group amorphous alloy in which iron group sublattice magnetization is dominant. (2) The first magnetic layer has the following composition ((Tb_1_0_0_-_xDy_x) -(Fe_1_0_0_-_yCo_y))_1_0_
0_-_zCr_z However, 0≦x≦100) 0≦y≦
40, 0≦z≦10, the magneto-optical recording medium according to claim 1. (3) The second magnetic layer has the following composition (Gd-(Fe_1_0_0_-_y_'Co_y_'
))_1_0_0_-_z_'Cr_z_'However, 0
The magneto-optical recording medium according to claim 1, wherein y'≦50, 0≦z'≦10.