JPH0447545A - Structure of magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a large magneto-optical effect by utilizing the multiple interference of light and to allow ultra-high-density optical recording by using films formed with distributions of optical complex indices of refraction in a thin film direction. CONSTITUTION:The multilayered film layers 2 alternately laminated with Pt and Co are formed on a substrate 1 and a Tb27Fe58Co12Nb3 film is formed as a rare earth/transition metal element film 3. The multilayered films 2 alter nately laminated with the Pt and Co of the same constitution as the constitution of the 1st layer are again formed thereon to constitute the magneto-optical recording film. The apparent refractive index is changed by the film thicknesses of the respective layers of the Pt and the Co in this case. The thickness of the Pt near both boundaries of the recording films is increased and the thickness of the Co in the intermediate position is increased. The magneto-optical effect is improved by the multiple interference effect of light within the recording films in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magneto-optical recording medium that is particularly suitable for performing ultra-high density recording in magneto-optical recording in which recording, reproduction, and erasing are performed using laser light. Regarding the structure of

[Conventional technology]

With the recent development of an advanced information society, the need for large-capacity, high-density file memory is increasing. Under these circumstances, optical recording is attracting attention as a memory that can meet this demand. Following the write-once type, which allowed information to be recorded only once, rewritable plastic type magneto-optical disks were commercialized. Currently, improvements in its performance are being considered.

One of these is an improvement in recording density. One method for this purpose is to perform recording using short wavelength laser light to form minute recording points.

In particular, in magneto-optical recording, when the wavelength of light used in conventional materials such as TbFeCo becomes shorter, Kerr (Ker)
r) The rotation angle became small and a sufficient reproduction signal output could not be obtained. As a known method to solve this problem, EPO
304873A1 can be mentioned.

[Problem to be solved by the invention]

However, the above-mentioned conventional technology does not have a magneto-optical recording film structure that achieves a sufficiently large magneto-optic effect, and therefore does not allow for high-density recording.
The large signal output required for playback could not be obtained.

An object of the present invention is to provide a structure of a magneto-optical recording medium that can obtain a large magneto-optical effect by utilizing multiple interference of light, and to realize ultra-high density optical recording.

[Means to solve the problem]

As a method for increasing the recording density, attempts are being made to increase the recording density by forming minute recording magnetic domains using light with a short wavelength.

In that case, T b Fe , which is currently widely used in magneto-optical recording that uses the Kerr effect for reproduction.
As the wavelength of light becomes shorter, Co-based recording materials become more
Rotation angle Rotation angle 2 The emissivity decreased. Therefore, the figure of merit 5
・Since θ1 decreases, it may cause errors and noise. In order to solve this problem, searches are being made for materials that can provide a sufficiently large Kerr rotation angle even with short wavelength light. However, it has not been possible to find a material that is error-free and provides a sufficient reproduced signal output.

Therefore, we considered improving the structure of the magneto-optical recording film and the entire structure of the magneto-optical medium in order to increase the magneto-optic effect. For this purpose, a distribution of optical complex refractive index is provided so that the magneto-optic effect increases in the film thickness direction of the magneto-optical recording film or magneto-optical recording medium.

By providing this refractive index distribution in the film thickness direction, multiple interference of light occurs in the magneto-optical recording film, increasing the magneto-optic effect. Furthermore, by forming a dielectric layer with high optical transparency, such as silicon nitride, and controlling the film thickness and refractive index of the film, the aforementioned increase in the magneto-optic effect can be further improved.

As a specific structure, in a multilayer film in which pt and Co are alternately laminated, the apparent refractive index can be changed by changing the thickness of each layer of pt and Go. By increasing the thickness of PT near both interfaces of the recording film and increasing the thickness of Co in the middle, it was possible to increase the magneto-optic effect due to the multiple interference effect of light within the recording film. Also, P t
A similar effect was obtained with a structure in which a TbFeCo film was sandwiched between a TbFeCo film and a TbFeCo film. In particular, this structure is Pt/
The Co layer not only has an effect as a reflective film, but also this layer itself exhibits the Kerr effect, and the magneto-optical effect, which is increased by multiple interference, is even greater.

Further, in addition to this structure, it is also possible to simply provide an alternate laminated film of Pt/CO on either one. In addition, Pd, Rh, Au, or an alloy thereof may be used in place of the above-mentioned pt. Further, instead of Co, Fe, Ni, or an alloy thereof, or an alloy with the above-mentioned noble metal element may be used.

The above method is a case where an optical complex refractive index distribution is provided within the recording film, but it is also possible to provide an optical complex refractive index distribution throughout the recording medium. As a specific example, the magneto-optic effect can be increased by sandwiching the recording medium with an inorganic dielectric compound represented by silicon nitride, or by providing it on one side.

Furthermore, by controlling the film thickness and complex refractive index of the recording medium, light can pass through the recording medium.

By forming a disk with a layer of Pd, Ag, Au, Al, Cr, Pb, etc. formed as the uppermost layer, it was possible to further increase the complex refractive index.

In this way, by providing an optical complex refractive index distribution within the magneto-optical film and further within the magneto-optical recording medium, it has been possible to increase the magneto-optic effect and further improve the performance of the optical disk.

[Effect]

By providing a distribution of the optical complex refractive index in the film thickness direction of a magneto-optical recording film or magneto-optical recording medium and controlling its value, multiple interference of light occurs within the film or medium, increasing the magneto-optic effect. It is measured. Furthermore, by providing a distribution of optically complex refractive index and controlling the film thickness of the recording film and each layer of the recording medium, multiple interference can be further increased, and the magneto-optic effect can be further increased.

〔Example〕

The details of the present invention will be explained below using Examples 1 and 2.

[Example 1] FIG. 1 is a schematic diagram showing the cross-sectional structure of the magneto-optical recording film produced in this example. First, a multilayer film layer 2 in which PT and CO were laminated alternately was formed on a glass or plastic substrate 1 to a thickness of 100 mm using the vine method.
The thickness per layer is 12 and the Co is 5. This film thickness varies depending on the manufacturing conditions, the sputtering method, the thin film forming method used, and the thin film forming method, and must be examined each time. Tb27Fe, , Co as the rare earth-transition metal element film 3 without breaking the vacuum.
,, Nb.

A film was formed to a thickness of 150 by sputtering.

Then, a P t /Co alternately laminated multilayer film 2 having the same structure as the first layer was again formed to a thickness of 100 mm by sputtering to form a magneto-optical recording film.

When we measured the optical complex refractive index of each layer of this medium, we found that
The complex refractive index n0 of the Pt/Co alternately laminated film is 2
．． 20-4.60i, and that of TbFeCoNb was 3.5-3.60i.

FIG. 2 shows the results of measuring the magneto-optic effect of a magneto-optical recording film in which the optical complex refractive index has a gradient as described above. In addition, Fig. 3 shows the Ke measured at λ”400 nm.
It showed rr hysteresis.

As a result, the Kerr rotation angle of this recording film increased as the wavelength of the light used to measure the Kerr effect became shorter, and reached 0.7° at λ=4QQnm. K at that time
The err hysteresis loop has good squareness and coercive force of 3
kOe, which was large enough to perform magneto-optical recording.

Next, a magneto-optical disk was formed using this recording film.

In this case as well, a distribution of optical complex refractive index was provided in the film thickness direction. Its structure is as shown in FIG. A silicon nitride film (optical complex refractive index n
+k,=2.10+○l) was formed to a film thickness of 500 people. Then, a magneto-optical recording film 5 having the same structure as before was formed. The film thickness and refractive index are as described above. A silicon nitride film was formed thereon again as a dielectric film 4 to a thickness of 100 mm. The optical constants at this time are the same as those for the first layer.

Finally, as the metal layer 6, a film of Al, Ti, etc. was formed to a thickness of 500 mm. The optical complex refractive index at that time is 1.5
-7.2i. All films were formed using a sputtering method.

Recording, reproduction, or erasing was performed on the thus manufactured disk using a laser beam having a wavelength of 480 nm. First, data was recorded on this disc using an optical modulation recording method at a laser power of 6.3 mW, a recording frequency of 25 MHz, and a pulse width of 40 nS. As a result, it was possible to form minute recording magnetic domains of 0.3 μmφ as shown in FIG. 5(a).

Furthermore, when recording was performed using the magnetic field modulation method, a crescent-shaped magnetic domain as shown in FIG. 5(b) was obtained.

Even with high-density recording using either method, the carrier-to-noise ratio (C/N) was 50 dB.

By using this recording medium, narrowing the pitch of the guide grooves, and also using the bit edge recording method, it was possible to realize ultra-high density optical recording.

In particular, in order to improve edge controllability when performing bit edge recording, it is important to control the flow of heat in the magneto-optical recording film. It is effective to control the

This effect is obtained by controlling the optical complex refractive index rather than depending on the magnetic properties of the material. In other words, the material used for the dielectric layer is not limited to silicon nitride, but may be any material that does not react with the recording film material, such as aluminum nitride, silicon oxide, tantalum oxide, zirconia, or alumina. The purpose is to use a material whose coefficient is small at the wavelength of the light used and whose optical complex refractive index can be easily controlled.

Furthermore, in the Pt/Co alternately laminated film of the magneto-optical recording layer, Pd, Rh, and Au may be used instead of pt, or an alloy thereof may be used. Fe or N instead of CO
A similar effect can be obtained by using i.

The same effect can be obtained by using alloys such as FeCo, CoNi, and FeNi, and among them, the effect of increasing the Kerr rotation angle was significantly large when FeCo alloy was used. Also TbFeC.

The same effect can be obtained by using Dy, Ho, or Gd in addition to Tb in the layer, and also in this system, an alloy of two or more elements may be used as the rare earth element. For example, GdTbFeCo is one example.

As the metal layer, in addition to A+2-Ti, Au, Cr+Ag
+ pb, Cu, Rh, Pd, Pt may be used, and Ti, Nb,
Ta, Cr, W, Mo and furthermore Au, Cr, Ag,
Pb, Cu, Rh, Pd.

Elements other than the parent element such as pt may be added.

Furthermore, as disk structure control, the 4
It is important to control the film thickness and thermal conductivity of each layer in the layered structure. In addition, the third dielectric layer may be omitted, or the thickness of the third dielectric layer may be 1000 to 2000.
The fourth metal layer may be omitted. Alternatively, the metal layer may be formed after directly forming the magneto-optical recording film on the substrate, or the metal layer may be formed via a dielectric layer. In designing the disk structure, it is important to reach a consensus on both optical and thermal design.

[Example 2] FIG. 6 is a schematic diagram showing the cross-sectional structure of a magneto-optical recording film produced according to the present invention. CO is deposited as an iron group element layer 7 on a plastic or glass substrate 1 by a dual simultaneous sputtering method.
PLs were alternately laminated as the noble metal element layer 8. The film thickness is 12 pt per layer up to the initial 130 people.
There were 5 humans and 5 COs, and then 9 Pts and 5 COs, making a total of 150 people. The optical complex refractive index of the film is 2.0-5.13i in the initial stage and 2.43-4.351 in the latter half.
and a distribution of refractive index. This is Pt/C.

It is the apparent optical complex refractive index of the film. This alternately laminated multilayer film can be formed by vacuum evaporation method or CVD method in addition to sputtering method.
Any method such as the law may be used.

In that case, the bulk density (deviation from the theoretical density) of the film differs depending on the manufacturing method and device, so the film thickness per layer of each layer differs.

FIG. 7 shows the results of measuring the magneto-optical properties of the magneto-optical recording film thus produced. As a result, 600-7
The Kerr rotation angle is minimum in the wavelength range of 00 nm,
In regions where the wavelength is longer and shorter than this, the Kerr rotation angle becomes larger. And λ = 4, which is advantageous for ultra-high density optical recording.
At 00 nm, the Kerr rotation angle θ was 0.80°. Also, the Kerr hysteresis loop at that time is
As shown in Figure 8, it has good squareness and coercive force of 1.
, it was large at 5 koe.

If the optical complex refractive index is set to a constant value as in the past, λ=
The Kerr rotation angle at 400 nm is pt/Co =
0.68° for 12 and 15 people, P t / C.

= 0.55° for 9 people and 75 people, so it was found that having a distribution in the refractive index is effective in increasing the Kerr rotation angle.

Next, a disk was manufactured using this recording film. Its structure is as shown in FIG. That is, on a glass or plastic substrate 1 having uneven guide grooves,
After forming the magneto-optical recording V115 with the above structure, A(+
,oTi,. It has a simple structure in which only the metal layer 6 is fabricated. Recording was performed on this disk using the magnetic field modulation recording method.

As a result, a recording magnetic domain having the shape shown in FIG. 5(b) was obtained. The C/N was also 50 dB, which was sufficient for recording code data. It can also be used as a rewritable compact disc.

In this example, alternately laminated films of pt and Go were used, but pt
In addition to CO, Pd, Rh, Au or alloys thereof may be used, and in addition to CO, Fe, Ni or alloys thereof,
Furthermore, similar effects can be obtained by using alloys with metal group elements such as CoPt and CoPd. This is effective in increasing the perpendicular magnetic anisotropy and increasing the Kerr rotation angle.

〔Effect of the invention〕

According to the present invention, the magneto-optic effect can be increased by providing a complex refractive index distribution in the film thickness direction in the magneto-optical recording film or magneto-optical recording medium.

As a result, a sufficiently large reproduction output can be obtained even when a minute recorded magnetic domain is reproduced with short wavelength light, so that the recording capacity can be increased. That is, it is effective for ultra-high density optical recording.

[Brief explanation of drawings]

1 and 6 are cross-sectional views of magneto-optical recording films according to examples of the present invention, and FIGS. 2 and 7 show wavelength dependence of the Kerr rotation angle of magneto-optical recording films according to examples of the present invention. Characteristic diagrams, FIGS. 3 and 8 are diagrams showing the Kerr hysteresis loop of a magneto-optical recording film according to an embodiment of the present invention, and FIGS. 4 and 9 are diagrams showing the structure of a magneto-optical disk according to an embodiment of the present invention. The cross-sectional view and FIG. 5 are schematic diagrams showing the shape of recording magnetic domains on a magneto-optical recording medium according to an embodiment of the present invention. 1...Substrate, 2...Pt/Co alternate laminated film,
3... Rare earth transition gold layer element film, 4... Dielectric layer, 5
... magneto-optical recording film, 6... metal layer, 7... iron group element layer, 8... noble metal diagram) - 11 Kikei 2-7fKi for pregnancy ■ 3- Snoring - Transition... 嘱Entrance (1m) Unfigure 6-M Bentozu optical survey (lI To Mr. Jki Kinsho I anti (a-) oooooooo---- 3-1 Pickled I ■ Figure l)! NZ; In (nm) ■ Diagram

Claims (1)

[Claims] 1. An optical recording medium for recording, reproducing, or erasing information using laser light, characterized by using a film having a distribution of optical complex refractive index in the film thickness direction. Structure of magneto-optical recording medium. 2. Magneto-optical recording characterized in that at least one element among the material, composition, or structure of the recording film used is controlled to form the optical complex refractive index distribution according to claim 1. Structure of the medium. 3. The recording medium according to claims 1 and 2 includes at least one element selected from Pt, Pb, Rh, or Au and at least one element selected from Fe, Co, and Ni. A structure of a magneto-optical recording medium characterized by using a film in which elements are alternately laminated, and by controlling the film thickness, a distribution of optical complex refractive index is provided in the film thickness direction. 4. As a recording medium according to claims 1 and 2, the first layer contains at least one element selected from Pt, Pd, Rh, or Au, and Fe, Co, and N.
Form an alloy or alternately laminated film with at least one element selected from i, and on top of that, at least one element selected from Tb, Dy, Ho, and Gd as a second layer. By forming a film that is alloyed or alternately laminated with at least one element selected from Fe, Co, and Ni, and then forming a film similar to the first layer as the third layer, the film can be formed. A structure of a magneto-optical recording medium characterized by having a distribution of optical complex refractive index in the thickness direction. 5. As a recording medium according to claims 1 and 2, first, a silicon nitride layer is formed to a thickness that causes multiple interference at the wavelength of the laser beam used, and then the recording medium is prepared as described in claim 4. A recording medium is formed, and a silicon nitride layer is formed on the silicon nitride layer to a thickness that causes multiple interference at the wavelength of the laser beam used, thereby giving a distribution of optical complex refractive index in the film thickness direction. Structure of magneto-optical recording medium. 6. As a recording medium according to claims 1 and 2, first, a silicon nitride layer is formed as the first layer to a thickness that causes multiple interference at the wavelength of the laser beam used,
On top of that, a second layer containing at least one element selected from Tb, Dy, Ho, and Gd and Fe, Co, and Ni.
After forming an alloy or alternately laminated layers consisting of at least one element selected from Pt, Rh, Pd, and Au and at least one element selected from Pt, Rh, Pd, and Au as the third layer, It is characterized by having a distribution of optical complex refractive index in the film thickness direction by forming an alloy or alternately laminated film consisting of at least one element selected from Co and Ni. Structure of magneto-optical recording medium. 7. As a recording medium according to claims 1 and 2, the first layer is made of at least one element selected from Pt, Pd, Rh, and Au and Fi, Co, and N.
After forming an alloy or an alternately laminated film consisting of at least one element selected from i, at least one element selected from Tb, Dy, Ho, and Gd and Fe as the second layer. , Co, and Ni are alternately stacked or alloyed, and silicon nitride is used as the third layer to form a film with a thickness that causes multiple interference at the wavelength of the laser beam. A structure of a magneto-optical recording medium characterized by forming an optical complex refractive index distribution in a direction. 8. As a recording medium according to claims 1 and 2, first, a silicon nitride layer is formed to a thickness that causes multiple interference at the wavelength of the laser beam used as the first layer,
As the second layer, at least one element selected from Tb, Dy, Ho, and Gd and at least one element selected from Fe, Co, and Ni were alternately laminated or an alloy layer was formed. Later, by forming a silicon nitride film as the third layer to a thickness that causes multiple interference at the wavelength of laser light, a magneto-optical film was developed in which a distribution of optical complex refractive index was formed in the film thickness direction. Structure of recording medium. 9. In a magneto-optical recording medium having the structure according to claims 3 to 5 and 7 to 8, Pt, Au, Al, Ag, Cu, Rh, Pd, Cr,
A structure of a magneto-optical recording medium characterized by providing a metal layer mainly composed of Pb. 10. In a magneto-optical recording medium having the structure according to claims 3 to 5 and 7 to 8, at least one selected from Pt, Pd, Rh, and Au is provided on the medium. 1. A structure of a magneto-optical recording medium, characterized in that a film or an alloy film is provided in which various elements and at least one element selected from Fe, Co, and Ni are alternately laminated. 11. In the metal layer according to claim 9, the recording-erasing characteristics of the optical disk can be controlled by controlling the thermal conductivity of the film, and more preferably Nb is used to control the thermal conductivity. , Ti, Ta, Cr, W, and Mo. 12. T described in claims 4 and 6 to 8
At least one element selected from Nd, Pr, and Sm is a part of one element selected from b, Dy, Ho, and Gd.
A structure of a magneto-optical recording medium characterized by using a material substituted with different elements. 13. A structure of a magneto-optical recording medium, characterized in that the alternately laminated film or alloy film formed on the recording medium according to claim 10 has perpendicular magnetic anisotropy.