JPH03252940A - Structure of magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain enough reproducing output by providing a magneto-optical recording film of specified multilayer structure. CONSTITUTION:The recording film is formed by alternately depositing a FeCo, CoNi, or FeNi binary alloy to which at least one element selected from Au, Ag, Pt, Rh, and Pd is added by 1-20 atm.%. and one element selected from Pt, Pd, and Rh, to <=50 Angstrom film thickness. Thereby, perpendicular magnetic anisotropic energy can be increased and the effect of perpendicular magnetic anisotropy is increased by alternate deposition of platinum group elements and iron group elements. Thus, reproducing output can be greatly improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to magneto-optical recording in which recording, reproduction or erasing is performed using laser light, and in particular to a method for increasing the perpendicular magnetic anisotropy energy of a recording film, This invention relates to the structure of a magneto-optical recording film that is effective in stably retaining recorded information.

[Conventional technology]

With the recent development of an advanced information society, concerns about high-density and large-capacity file memories are increasing. Optical memory is attracting attention as one type of memory that can meet this demand. In recent years, many companies have commercialized rewritable magneto-optical recording devices. Furthermore, research is currently being actively conducted to improve the performance of the next generation of magneto-optical disks. One of these is the improvement of recording density, and it is known that recording and reproducing using short wavelength light is effective. In that case, the problem is
The point is that as the wavelength of light becomes shorter, the magneto-optic effect of the recording film becomes smaller. It is known that it is effective to use an alloy of light rare earth elements and iron group elements as a magneto-optical recording material to solve this problem. A known example thereof is USP-46955]4.

[Problem to be solved by the invention]

The magneto-optical recording materials in the prior art described above easily react with water and oxygen in the atmosphere to form oxides, resulting in a decrease in reliability. Therefore, there was a problem in that a high vacuum was required for film formation. As an alternative material,
It has been effective to use a recording film with a multilayer structure in which platinum group elements such as pt and Pd and iron group elements such as Fe and CO are alternately laminated, but the perpendicular magnetic anisotropy energy is 10
Since it is as low as 5 J/m, which is the lower limit at which it can stably exist as a perpendicularly magnetized film, there were cases in which recorded information could not be saved.

The present invention aims to obtain a structure of a magneto-optical recording film having sufficiently large perpendicular magnetic anisotropy energy in an alternately laminated film of platinum group elements and iron group elements. The purpose is to provide magnetic disks.

[Means to solve the problem]

As the wavelength of light used for recording and reproducing on magneto-optical disks becomes shorter, magneto-optic effects, especially Kerr (Kerr)
) The rotation angle becomes small, and sufficient reproduction cannot be obtained, which may cause errors.

To solve this problem, we investigated magneto-optical materials that exhibit a sufficiently large magneto-optic effect even for short-wavelength light. As a result, platinum group elements such as Pt, Rh and Pd and Fe,
When a film in which iron group elements such as Co and Ni were alternately laminated was used as a recording film, a large magneto-optical effect was exhibited for light with a short wavelength.

However, the perpendicular magnetic anisotropy energy of this recording film is 105 J/m 2 , which is the lower limit value that exists stably as a perpendicularly magnetized film, and there have been cases where recorded information cannot be stored.

To solve this problem, Au is used as a magneto-optical recording film.

An alloy with at least one element of Fe, Co, or Ni added with at least one element of Ag, Pt, Pd, or Rh, and at least one element selected from Pt, Pd, or Rh are alternately laminated. By doing so, it was possible to increase the perpendicular magnetic anisotropy energy to 4×10 SJ/rri or more. Furthermore, Fe Co, C as iron group elements
Au and A are added to the two-element yarn of oN i and FeNi.
1 to 20a of one of the following elements: g, Pt, Rh, or Pd
By alternately stacking an alloy to which Pt% is added and at least one element selected from Pt, Pd, or Rh, and selecting an appropriate Co concentration or Fe concentration, the magneto-optical effect, especially the Kerr rotation angle, can be improved. There was an optimal concentration that increased the Here, adding more than 20 at % of the noble metal element conversely decreases the perpendicular magnetic anisotropy energy and has little effect, and the optimum value is around 8 to 15%.

In addition, the thinner the noble metal element and iron group element alloy layer is, the more the perpendicular magnetic anisotropy energy increases.
This is noticeable below Å, and by combining this with a white metal layer, the anisotropy can be further increased.

When this material was used as a magneto-optical recording film, the optimal disk structure was the one described below. After forming a first dielectric film layer of silicon nitride, aluminum nitride, or silicon oxide on a glass or plastic disk substrate having uneven guide grooves, the above-mentioned magneto-optical recording film was formed. Next, after forming a second dielectric film using the same material as the first dielectric film, A Q + A u v is applied to control the reflection of light and the temperature distribution of the magneto-optical recording film.
It has a four-layer structure including a metal layer mainly containing one of A g +Pt, Pd, Cu, Cr, and Pb.

Here, N was added to the fourth metal layer to control thermal conductivity.
b, Ti, Ta, W, Mo, or an element other than the base material of the metal material mentioned above may be added.

On the other hand, it is effective to use multiple interference of light in order to increase the Kerr rotation angle, and to provide the above-mentioned interference effect to either or both of the first dielectric film and the second dielectric film.

In addition to the four-layer structure shown above, the disk structure only needs to have at least a magneto-optical recording film and a metal layer, and either one of the first dielectric layer or the second dielectric layer or You can omit both.

When the disk structure is simplified in this way, the price becomes low, the range of applications is expanded, and it becomes easy to use it for consumer use.

When providing a multiple interference effect to either the first dielectric film or the second dielectric film, the thickness of the dielectric layer that does not have the multiple interference effect is increased to improve the protective effect of the magneto-optical recording film. This has the effect of increasing reliability. In addition,
By using a recording film composed of two types of parts with different magnetic properties (for example, Curie temperature, compensation temperature, or coercive force) of the magneto-optical recording film and using an external auxiliary magnetic field, so-called override is possible, and the recording density can be increased. In addition to improving the performance of the disk, it is possible to further improve the performance of the disk.

[Effect]

When a thin alloy film of a noble metal element and an iron group element is made thinner, from several hundred to several large, the perpendicular magnetic anisotropy energy increases in inverse proportion to the film thickness. Alternatively, even when platinum group elements and iron group elements are alternately laminated, the perpendicular magnetic anisotropy energy can be arbitrarily selected by controlling the film thickness of each layer. However, in either case, it is 105 J/tri, and this value is the lower limit that can stably exist as a perpendicularly magnetized film. We considered using these properties of both to increase the perpendicular magnetic anisotropy energy. In other words, when platinum group elements and alloys of iron group elements containing noble metal elements are alternately laminated, 4X
A magneto-optical recording film having a large perpendicular magnetic anisotropy energy of 105 J/m or more was obtained.

This is achieved by increasing the perpendicular magnetic anisotropy energy by forming a thin alloy film of noble metal elements and iron group elements, and by alternately stacking platinum group elements and iron group elements. This is based on the fact that the expression effect of

〔Example〕

The present invention will be explained in detail below.

[Example 1] First, FIG. 1 shows a schematic diagram of the cross-sectional structure of the magneto-optical recording film produced in this example. On the cleaned glass substrate 1, 8 large amounts of Pt, Co, 3 were formed as the first recording layer 2, and a second recording layer 3 was formed.
12 pts were stacked alternately. The film is formed by sputtering, and the total film thickness is 400 mm. The sputtering conditions at that time were: Ar was used as the discharge gas, pt and PtCo alloys were used as targets, discharge gas pressure = 5 x 10-3 Torr, input RF power density: 6
．． Sputtering was performed at 3 W/d. During sputtering, hold the substrate at 12
It was rotated at .degree. rpm, and formation was performed by two-dimensional simultaneous sputtering. Finally, as the metal layer 4, A[,. A Ti1° alloy film was formed to a thickness of 500 mm by sputtering.

At this time, Ar is used for the discharge gas, and AQTi is used for the target.
Ti-containing gases were used, and the discharge gas pressure was I x 10-2.
Sputtering was performed at Torr and input RF power of 3.2 W/-.

The perpendicular magnetic anisotropy energy of the magneto-optical recording film near the metal layer prepared in this way was measured using a vibrating sample magnetometer (VSM).
) and a magnetic torque meter, it was found to be 8X105J.
/rri and perpendicular magnetization film of pt and Co or ptl
. Co. Compared to that of a film in which alloy thin films and SiN X are alternately laminated, the strength is 8 times higher than that of 1×105 J/m 2 , and the stability as a perpendicularly magnetized film is increased.

Next, FIG. 2 shows the results of investigating the dependence of the Kerr rotation angle of this film on the wavelength of light. In this way, as the wavelength of the light used is shortened, the Kerr rotation angle obtained increases. In particular, a sharp increase in the Kerr rotation angle was observed in the wavelength region shorter than the wavelength λ" of 550 nm, and at λ" of 400 nm,
θ = 0.56°.

This is a conventional Pt/Co alternate laminated film or PtC.

The value of θ was larger than that of the alloy thin film.

A disk using this magneto-optical recording film was manufactured.

A schematic diagram showing the cross-sectional structure is shown in FIG. A silicon nitride film was formed to a thickness of 50 OA by sputtering on a glass or plastic substrate 1 having uneven guide grooves. The conditions at that time were: Ar was used as the discharge gas, and Si3N
4 as a target, discharge gas pressure crab I
Sputtering was performed at −2 Torr and input RF @ power of 4.2 W/a&. Next, the magneto-optical recording film 6 is coated with the method 2 described in the previous section.
A multilayer structure was formed under certain conditions. The total film thickness is 400A. Next, a second dielectric film 7 was formed to a thickness of 100A. The method and conditions at that time were the same as those for the first dielectric film 5. Finally, as the metal layer 4, AQ, 5Ta1. A film was formed. The method and conditions were the same as in the previous section for forming the AQ, Ti film, except that an AQTa alloy was used as the target.

Recording, reproduction, and erasing were performed on the disk thus produced using a laser beam of λ=470 nm. Recording was performed at a disk rotation speed of 2400 rpm, a recording frequency of 18 MHz, a laser output of 6 mW, and a period of 1.5 T. When the reproduced signal output at that time was measured, it was 48 dB, and code data recording was possible. Furthermore, when recording/reproducing/erasing was repeated, it was possible to repeat it 10' times or more. The disk manufactured in this example has Kerr enhancement in both the first and second dielectric films, but the second dielectric film has Kerr enhancement.
If the refractive index of the dielectric film is made larger than 2.0 in this example, enhancement is achieved with only this film, and the thickness of the first dielectric film is doubled, water and oxygen that enter from the substrate side can be prevented. The reliability of the disc is improved because it can be protected by this film.

In this embodiment, PT is used as the additive noble metal material, but the material is not limited to this, and similar effects can be obtained by using Ag, Au, Pd, Rh, or the like. Further, similar effects can be obtained by using Ni or Fe in addition to CO as the iron group element of the base material. Furthermore, similar effects can be obtained by using Rh or Pd in addition to pt as the platinum group element which is alternately laminated with this alloy material.

Furthermore, similar effects can be obtained by using silicon oxide or aluminum nitride in place of nitrogen silicon as the first and second dielectric materials in the disk. In this case, what must be taken into consideration is the refractive index and thermal conductivity of the film, and these points should be taken into consideration when designing the disk, especially when designing the optical design and thermal design.

Further, in accordance with this, the thermal conductivity of the metal layer 4 may be considered and adjusted by adjusting the overall film thickness and additive element concentration (for example, Ti concentration in the case of AQ-Ti system). In addition, Pt and Rh are used as metal layer materials.

Pd, Cr, Cu, Au, and Pb may be used, and in addition to these, an element other than the parent element or Nb or T may be used.

Thermal conductivity may be adjusted by adding elements such as Ta, Cr, W, and Mo. Especially Au, Cu, Rh.

Since the Pd and Pt systems have high reflectance, further improvement in reproduction output has been achieved.

[Example 2 The cross-sectional structure of the magneto-optical recording film produced in this example is as in Example 1.
The schematic diagram showing the structure is as shown in FIG. As the first recording layer 2, P t 1o (F e
l-X CO'')s to a film thickness of 7A, and 12 PT layers were alternately laminated as the second recording layer 3.Here, the target used for forming the first recording layer 2 was: P
Chip-shaped C on tFe alloy.

It is a composite target with uniformly arranged. Then, the Co concentration was varied by changing the number of CO chips placed.

Except for this purpose, the conditions are the same as in the first embodiment.

Figure 4 shows the Co concentration and the obtained Kerr rotation angle (λ=40
0 nm). In this way, P of the first record N2
As the Co concentration increases in the t-Fe-Co system, the Kerr rotation angle increases, reaching a maximum of 0.65° at x=0.4 to 0.6. The perpendicular magnetic anisotropy energy at this time also increased and was 1 x 106 J/rn'. This effect is the same even when noble metal materials such as Pd, Rh, Au, and Ag are used, and Fe-Co is the iron group element.
Similar results were also obtained by changing Fe in the FeNi system and Co in the Co--Ni system. Further, even when Pd or Rh was used instead of PT for the second recording layer 3, no difference in magnetic properties was observed.

A disk using this magneto-optical recording film was manufactured.

Its structure is the same as that produced in Example 1, and the schematic diagram of the cross-sectional structure is as shown in FIG. Here, the composition of the first recording layer 2 is P tl, (F e, , C
oo,,),. Closed. A disk was manufactured under the same conditions as in Example 1 except for the above, and its characteristics were measured.

As a result, the C/N when recording with the closest pattern on the innermost circumference
was 49.5 dB. Even after repeating recording, reproducing, and erasing 107 times, no change was observed in the reproduction output. This effect is not limited to this system, but other noble metal elements or platinum group elements may be used, and the first
The noble metal element added in the recording layer 2 and the platinum group element used in the second recording layer 3 do not need to be the same, and may be any material. Further, the same is true for iron group elements, and a similar effect is observed for Fe--Ni and Co--Ni, and this change follows the Slater-Pauling law.

〔Effect of the invention〕

According to the present invention, in a platinum group element/iron group element multilayer magneto-optical material, a multilayer structure thin film in which an alloy material in which a metal group element is added to an iron group element and a platinum group element are alternately laminated has a perpendicular magnetic field. The anisotropy energy is 4~8X10J/rn', which is 10SJ/rn' compared to that of the system without added noble metal elements.
It was able to increase significantly compared to . Thereby, this film can exist stably as a perpendicular magnetization film, and recorded information can be stably stored. Furthermore, since these materials contain a large amount of noble metal elements, they have high corrosion resistance and are effective in improving reliability. Furthermore, FeCo, CoNi.

Since the FeNi system follows the Slater-Pauling law, the Kerr rotation angle can be increased without deteriorating the magnetic properties and reflectance. As a result, high-density optical recording was realized because the reproduction output could be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the cross-sectional structure of a magneto-optical recording film according to an embodiment of the present invention, FIG. 2 is a wavelength dependence characteristic diagram of the Kerr rotation angle in the recording film according to an embodiment of the present invention, and FIG. FIG. 4 is a schematic diagram showing the cross-sectional structure of a magneto-optical disk according to an embodiment of the invention.
The figure shows Ker of a (Pt/Pjxo(Fel+, Co,),.) system multilayer film.
It is a CO concentration dependence diagram of r rotation angle. DESCRIPTION OF SYMBOLS 1... Substrate, 2... First recording layer, 3... Second recording layer, 4... Metal layer, 5... First dielectric film, 6...
- Magneto-optical recording film, 7... second dielectric film. X-no whisper map whisper (2) evil C, concentration, zu (β)

Claims (1)

[Claims] 1. In magneto-optical recording in which recording, reproduction, or erasing is performed using laser light, the recording materials include Pt, Pd,
At least one element layer selected from Rh, and P
Contains 1 to 20 at% of at least one element selected from t, Pd, Rh, Au, Ag, Fe, Co, Ni
Magneto-optical recording characterized by using a magneto-optical recording film with a multilayer structure in which alloy layers with at least one element selected from the following are laminated alternately and each layer has a film thickness of 50 Å or less. Structure of the medium. 2. In magneto-optical recording in which recording, reproduction, or erasing is performed using laser light, the structure of the magneto-optical disk is as follows:
On a glass or plastic substrate having uneven guide grooves on its surface, at least the magneto-optical recording material layer according to claim 1, Pt for controlling the temperature distribution of the magneto-optical recording material layer, Al, Au, Ag, Cu, R
A magneto-optical device characterized by having a metal layer mainly composed of at least one element selected from h, Pd, Cr, and Pb, and further preferably having a multiple interference layer for increasing the optical effect. Structure of recording medium. 3. In the metal layer according to claim 2, for controlling the temperature distribution of the magneto-optical recording material layer, Nb, Cr,
A structure of a magneto-optical recording medium characterized by using a metal layer to which Ti, Ta, W, Mo, or an element constituting the metal layer according to claim 2 other than the main element is added. 4. In the magneto-optical recording medium with a multilayer structure according to claim 1, the magneto-optic effect is increased by providing a dielectric layer made of an inorganic compound in the middle of the recording film and selecting the film thickness. A structure of a magneto-optical recording medium characterized by controlling the wavelength of light at which the magneto-optic effect is maximized. 5. At least one compound selected from silicon nitride, aluminum nitride, or silicon oxide or a composite thereof is used as the material for the dielectric layer made of an inorganic compound as described in claim 4. A structure of a magneto-optical recording medium characterized by: 6. In the formation of a magneto-optical recording material with a multilayer structure according to claim 1, distribution of magnetic properties in the film thickness direction,
Furthermore, the structure of the magneto-optical recording medium is characterized by using a magneto-optical recording film having a distribution of Curie temperature, coercive force or compensation temperature.