JPH0380445A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve the coercive force of the magneto-optical recording medium by parting the artificial lattice films alternately laminated with Co layers and Pt layers and/or Pd layers to crystal grain lumps of <=500Angstrom diameter at <=10Angstrom spacing, thereby forming a recording layer. CONSTITUTION:The artificial lattice films which can be utilized as the recording layer are formed of any of a Co-Pd system and Co-Pt-Pd system (the former two may be formed as a Pt-Pd alloy layer and may be in arbitrary order) similar to the Co-Pt system alternately laminated with the Co and Pt and the total film thickness is preferably 50 to 1,000Angstrom for practicability. The lattice films are parted by having the <=10Angstrom spacing as opposed to the continuous structure, by which the good magneto-optical characteristics are obtd. at <=500Angstrom diameter of the respective crystal grain lumps. The crystal grain lumps are isolated in the form of islands and good characteristics are not obtainable in the spacings larger than the above-mentioned range. Magnetic domains increase and the increase in the coercive force is not expected if the grain lumps are larger than the above-mentioned range.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magneto-optical recording medium that uses magneto-optic effects to record and reproduce information using laser beams, etc. It relates to magneto-optical/recording media with corners.

[Summary of the invention]

In the present invention, when forming an artificial lattice film in which Co layers, Pt layers, and/or Pd layers are alternately laminated as a bottom film as a recording layer of a magneto-optical recording medium, the above artificial lattice film is separated by a gap of 10 Å or less to a diameter of 50 Å. By creating a structure divided into the following crystal grain clusters, the coercive force is particularly improved.

[Conventional technology]

In recent years, magneto-optical recording has attracted attention as a rewritable, high-density recording method in which information is recorded by writing magnetic domains in a magnetic thin film using thermal energy such as semiconductor laser light, and this information is read out using the magneto-optic effect. ing.

The recording material used in this magneto-optical recording method is G
Rare earth elements such as d, Tb, and Dy, and Fe.

Conventionally, a typical example has been an amorphous alloy in combination with a transition element such as Co. However, the rare earth elements and Fe that constitute these amorphous alloys are very easily oxidized and have the property of easily combining with O2 in the air to form oxides. As such oxidation progresses, it leads to corrosion and pitting, leading to loss of signals. In particular, when rare earth elements undergo selective oxidation, the C/N ratio decreases as coercive force and residual magnetic Kerr rotation angle decrease. The problem arises of deterioration. Such problems cannot be avoided as long as rare earth elements are used.

On the other hand, as an alternative recording material, the present inventors previously proposed in Japanese Patent Application No. 63-178135 that an artificial lattice film in which CoN and Pt layers and/or Pd layers were alternately laminated was used as a recording layer. , proposes a magneto-optical recording medium in which the total thickness of the recording layer is 50 to 800 mm, and a metal underlayer is formed if necessary.

This magneto-optical recording medium has excellent corrosion resistance because it does not contain rare earth elements, and also has a high magnetic Kerr rotation angle.

[Problem to be solved by the invention]

However, in order to promote higher speed, higher density, and higher reliability in the magneto-optical recording method for future practical use, further improvement in coercive force is desired.

Therefore, an object of the present invention is to provide a magneto-optical recording medium that can achieve a high coercive force and a high magnetic Kerr rotation angle.

[Means for Solving the Problems] As a result of intensive studies to achieve the above object, the present inventors found that the recording layer is composed of CON, Pt layer and/or Pd layer.
The inventors have discovered that excellent magneto-optical properties can be achieved by constructing an artificial lattice film consisting of alternately laminated layers and by specifying the fine structure of the artificial lattice film, leading to the completion of the present invention. .

The magneto-optical recording medium of the present invention is proposed based on such knowledge, and has an artificial lattice film in which CoJi, Pt layers and/or PdN are alternately laminated as a recording layer,
The above artificial lattice film has a diameter of 50 Å due to gaps of 10 Å or less.
It is characterized by being divided into the following crystal grain agglomerates.

First, the artificial lattice film that can be used as a recording layer in the magneto-optical recording medium of the present invention is a Co--Pt based artificial lattice film in which 00 layers and Pt layers are alternately laminated, a Co-Pt-based artificial lattice film in which 00 layers and Pd layers are alternately laminated, and A Pd-based superlattice film, and a Co-Pt-Pd-based superlattice film in which a Co layer, a Pt layer, and a Pd layer (however, the latter two may be Pt-Pd alloy layers) are laminated in any order. Either.

In either case, the total thickness of the superlattice film is desirably 50 to 1000 thick from the viewpoint of achieving practically necessary and sufficient magneto-optical properties.

Furthermore, in the Co-Pt superlattice film, the thickness of the 00 layer is 2 to 8 people, the thickness of the Pt layer is 3 to 40 people, and the Co-
In the Pd-based superlattice film, the layer thickness of the 00 layer is 1 to 9 people,
It is desirable to choose the layer thickness of the Pd layer from 2 to 40 layers. These layer thickness ranges are set from the viewpoint of optimizing the magneto-optical properties, and in any case, satisfactory properties cannot be obtained outside the above ranges.

Ideally, each of the superlattice films mentioned above should have a so-called superlattice structure, in which the interfaces of each metal layer are formed flat without interfering with each other, but even if the interfaces are slightly disordered, the overall Alternatively, it may have a composition modulation structure in which the composition changes while maintaining a constant period. For example, looking at the range of layer thicknesses of the metal layers mentioned above, the metal bond radius of each metal (Co = 1.25, Pd layer 1.38, Pt
In some cases, the lower limit is less than one atom, considering the layer thickness (1.39 people), but this is also a result of taking into consideration the compositional modulation structure.

The present inventors used a transmission electron microscope to observe the fine structure of artificial lattice films that exhibit good magneto-optical properties among artificial lattice films in which Co layers, Pt layers, and/or Pd layers are alternately laminated. It has been found that when the grating film has a structure divided by minute gaps, significantly better magneto-optical properties appear than when the grating film has a continuous structure.

The above-mentioned gap is 10 Å or less, and the diameter of crystal grain agglomerates produced as a result of division by the gap is 500 Å or less. If the gap is larger than 10, individual crystal grain clusters become isolated in the form of islands, making it impossible to obtain good properties. In addition, the diameter of the crystal grain agglomerate is 5
If it is larger than 00, the magnetic domain becomes large and an increase in coercive force cannot be expected. The crystal grain agglomerate may be composed of a single crystal grain or may be composed of an agglomeration of a plurality of fine particles.

The above-mentioned superlattice film is most commonly created by sputtering, but the present inventors found that when the argon gas pressure during film formation was selected to be in a relatively high range of 15 mTorr or more, the above-mentioned fine structure was created. It was also found that it can be easily obtained.

The evaporation source during sputtering is Co-Pt based.

When creating a binary superlattice film such as a Co--Pd system, it is necessary to prepare each metal component independently. In addition, when creating a ternary superlattice film such as the Co-Pt-Pd system, in addition to preparing evaporation sources independently for each component metal, it is also possible to use a combination of these for Pd and Pt in particular. Possible methods include using an alloy evaporation source, or using a composite evaporation source in which a chip with a smaller component is placed on a target with a larger component.

In addition to the above-mentioned sputtering, methods for forming the artificial lattice film include vacuum evaporation and molecular beam epitaxy (MBE).
) etc. can be applied.

Furthermore, before forming the artificial lattice film on the substrate,
If necessary, a metal base film may be formed to control the film quality of the artificial lattice film. In this case, it is particularly preferable that the metal base film has a face-centered cubic structure and a lattice constant similar to that of the metal layer constituting the artificial lattice film.

[Effect]

In the magneto-optical recording medium of the present invention, the recording layer is composed of an artificial lattice film in which a Co layer, a Pt layer, and/or a Pd layer are alternately laminated, and furthermore, the artificial lattice film has crystal grains with a diameter of 500 Å or less with gaps of 10 Å or less. It has a structure divided into blocks.

In such an artificial lattice film, a single magnetic domain structure is easily achieved by first forming crystal grain agglomerates to a certain size or less. Generally, the size and direction of magnetic domains change during the magnetization process, but in the present invention, the effect of forcibly fixing the magnetic domain wall of the magnetic domain formed in the crystal grain agglomeration by minute gaps (so-called domain wall pinning effect) can be improved. Demonstrate. therefore,
In addition to the above-mentioned original property of the superlattice film of having large perpendicular magnetic anisotropy, we believe that the above-mentioned miniaturization of magnetic domains and suppression of domain wall motion will result in a significant increase in coercive force. It will be done.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on experimental results.

In this example, a Co-Pt based artificial lattice film is used as a recording layer of a magneto-optical recording medium on a glass substrate.
This is an example in which the film was formed by sputtering.

As a sputtering target, C with a diameter of 100 mm is used.
Using O disk and Pt disk, input power is 0.2
~LA, 300V.

First, we investigated changes in coercive force and magnetic Kerr rotation angle due to argon gas pressure in the sputtering atmosphere. That is, the argon gas pressure was 4 mTorr.

10 mTorr, 15 mTorr+20 mT
orr + 25 tsTorr, and under each argon gas pressure, CoN with a thickness of 4 and Pt layers with a thickness of 9 were alternately laminated on a water-cooled glass substrate to obtain a Co-P with a total thickness of 120.
A t-based superlattice film was formed.

FIG. 1 shows the coercive force and magnetic Kerr rotation angle of these Co--Pt superlattice films obtained from magnetic Kerr curves obtained using a polar Kerr measuring device. In the figure, the vertical axis is coercive force (Oe) and magnetic Kerr rotation angle (@), and the horizontal axis is argon gas pressure (mTorr) in the sputtering atmosphere.
), the plot of black circles (・) represents coercive force, and the plot of white circles (○)
The plots represent the magnetic Kerr rotation angle, respectively. From this figure, it can be seen that the coercive force increases significantly in the region where the argon gas pressure exceeds 10 mTorr. However, the magnetic Kerr rotation angle decreased slightly in this region.

Figure 2 shows the magnetic Kerr curve of the above-mentioned Co-Pt superlattice film when the argon gas pressure is 20 mTorr. The ratio of the residual magnetic Kerr rotation angle θ) was almost the ideal value of 1.

By the way, the present inventors previously filed a patent application No. 63-178135.
In the specification of the issue, the effect of a metal underlayer in a magneto-optical recording medium having a Co-Pt superlattice film as a recording layer is mentioned, but the metal underlayer according to the present invention is also applied and its effects are studied. did.

That is, after forming a Pt base film with a thickness of 1000 on a glass substrate, a Co-Pt base film with a total thickness of 120 as described above was formed.
A superlattice film was formed and the coercive force was measured.

The results are shown in Figure 3. In the figure, the vertical axis represents coercive force (Oe), and the horizontal axis represents argon gas pressure (mTorr). Than this,
The tendency for the coercive force to change significantly around the argon gas pressure IQ mTorr is similar to that shown in Figure 1, but its absolute value increases significantly due to the presence of the metal base film, and when the argon gas pressure is 20 mTorr 300 in the above areas
A high coercive force of 0 to 50,000 e was achieved.

Therefore, next, we fixed the argon gas pressure at 20 mTorr and the total thickness of the superlattice film at 120 mTorr, and created superlattice films 1 to 1 with various combinations of Co layer and Ptl layer thickness shown in Table 1 below. Film 6 was formed and the change in coercive force was examined. The results are shown in Table 1.

Table 1 As is clear from this table, under a relatively high argon gas pressure of 20 mTorr, a high coercive force of 500 to 7000e was achieved in all the superlattice films.

Next, the argon gas pressure was fixed at 20 mTorr, the Co layer thickness was fixed at 4 layers, the Pt layer thickness was fixed at 9 layers, and the total thickness was 8 mm.
We investigated changes in coercive force and magnetic Kerr rotation angle when changing the number of people in the range of 0 to 900 people. The results are shown in Figure 4. In the figure, the vertical axis is coercive force (Oe) and squareness ratio, and the horizontal axis is C
The black circle (・) represents the total thickness (in) of the o-Pt superlattice film.
The plots with ◯ represent the coercive force, and the plots with white circles (○) represent the squareness ratio.

From this figure, the coercive force showed a tendency to increase as the total thickness increased, and in particular, it showed a remarkable increasing tendency up to a total thickness of around 220 people, and a gradual increasing tendency after that. The - side squareness ratio maintained the ideal value of 1 until the total thickness of 220 people, and showed a tendency to gradually decrease at the total thickness thereafter.

In other words, in this artificial lattice film, after satisfying the squareness ratio of 1,
This means that a high coercive force of up to 12,000 e can be achieved with a total thickness of 220. Even when the total thickness was as large as 900 Å, a sufficiently large squareness ratio of 0.65 was achieved.

Next, we investigated the influence of the background vacuum degree on the magneto-optical properties during the deposition of the artificial lattice film. That is, when forming a Go-Pt superlattice film with a total thickness of 120 layers by alternately laminating Co layers with a thickness of 4 layers and Pt layers with a thickness of 9 layers at an argon gas pressure of 1Q t*Torr. ,
The background vacuum level is lX 10-' ~ 5 X 1
The coercive force and magnetic Kerr rotation angle of the obtained superlattice film were measured by varying the coercive force within a range of 0-' Torr. The results are shown in Figure 5. In the figure, the vertical axis is coercive force (Oe) and magnetic Kerr rotation angle (°), and the horizontal axis is background vacuum degree (Torr
), the plot of black circles (・) represents coercive force, and the plot of white circles (○)
The plots represent the magnetic Kerr rotation angle, respectively. From this figure, it can be seen that the coercive force and the magnetic Kerr rotation angle increase as the background vacuum level increases (this is due to the amount of spraying. This is due to the fact that the chamber is evacuated more thoroughly before sputtering. This is because the chance for the superlattice film to undergo oxygen oxidation is reduced.There have been cases where high coercive force was achieved accidentally even under low vacuum conditions.
Most of them had low squareness ratios, and it could not be said that excellent magneto-optical properties were stably achieved. Therefore, when sputtering is performed under relatively high argon gas pressure, it is desirable to set the background vacuum degree high.

Finally, in order to explore the correlation between the excellent magneto-optical properties of the Co-Pt superlattice film and its fine structure, the present inventors examined a cross section of a typical Co-Pt superlattice film using a transmission electron microscope. Observed. The observed sample was the Co shown in Figure 1 above.
- Among Pt-based superlattice films, argon gas pressure 4IITO
rr and 25 mTorr, respectively. The photographs are shown in Fig. 6(A) and Fig. 6(B). Fig. 6(A) shows that the argon gas pressure during film formation was 4 m
In the case of Torr, Figure 6 (B) is the same < 25 mTo
This corresponds to the case of rr. When the argon gas pressure during film formation is as low as 4 mTorr, the artificial lattice film has a seemingly continuous structure densely packed with crystal grain aggregates with a diameter of several 10 to 80 particles. On the other hand, when the argon gas pressure is as high as 25 mTorr, it is clear that gaps of about 10 degrees have developed between these crystal grain agglomerates.
It is suggested that this contributes to miniaturization of magnetic domains and suppression of demagnetization.

Although all of the above explanations were made for Co--Pt based superlattice films, almost the same results were obtained with Co--Pd based super lattice films using Pd instead of Pt.

〔Effect of the invention〕

As is clear from the above description, the magneto-optical recording medium according to the present invention is a co-Pt superlattice film or a Co-Pt superlattice film formed under relatively high argon gas pressure and having gaps between crystal grain aggregates. - This utilizes the excellent magneto-optical effect of the Pd-based superlattice film. The magneto-optical recording medium has a high coercive force and a high magnetic Kerr rotation angle, and therefore enables high-density recording and reproduction with excellent frequency characteristics, reproduction output, sensitivity, C/N ratio, etc. In particular, since a high coercive force of 10,000 e or more is achieved, stable recording is possible that is not affected by stray external magnetic fields, and the bias magnetic field during writing can be controlled over a wide range, making it easier to reduce noise. Other advantages also arise.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing how the coercive force and magnetic Kerr rotation angle of a Co--Pt based superlattice film depend on the argon gas pressure during sputtering film formation. FIG. 2 is a characteristic diagram showing how the coercive force and squareness ratio of an example of a Co--Pt-based super lattice film depend on the total thickness. FIG. 5 is a characteristic diagram showing how the coercive force and magnetic Kerr rotation angle of a Co--Pt superlattice film depend on the degree of background vacuum during sputtering film formation. Figure 6(A):j-3 and Figure 6(B) are transmission electron micrographs showing the dependence of the fine structure of the Co-Pt superlattice film on argon gas pressure; When the argon gas pressure is 4 mTorr, Fig. 6 (B) is 25 mT.
This corresponds to the case of orr, respectively.

Claims (1)

[Claims] The recording layer is an artificial lattice film in which Co layers, Pt layers, and/or Pd layers are alternately laminated, and the artificial lattice film has a diameter of 50 Å with a gap of 10 Å or less.
A magneto-optical recording medium characterized by being divided into the following crystal grain agglomerates.