JPH04337544A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To meet the requirements for higher densities and larger capacities by providing the magneto-optical recording medium having a high magneto- optical effect and high recording sensitivity even in a short wavelength region. CONSTITUTION:After 1st and 2nd recording layers 3, 4 are provided via an interference layer 2 on a transparent substrate 1, a protective layer 5 is provided thereon. The 1st recording layer 3 is constituted of an alloy film contg. one or more of Co and Fe. At least one or over among Pt, Pd, Rh, Ga, Si, Cr, Al, and Ge, are incorporated into this alloy film. The 2nd recording layer 4 is constituted of an amorphous alloy film consisting of a rare earth metal and a transition metal. A substrate layer 6 for improving the crystal orientability of the 1st recording layer 3 is provided between the interference layer 2 and the 1st recording layer 3. The higher C/N is easily obtd. even with the short wavelength laser by adopting such layer constitution.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for recording, reproducing and erasing information using laser light.

0002

[Prior Art and Problems to be Solved by the Invention] Magneto-optical disks use laser light to record, reproduce, and erase information, so they have a large storage capacity, and since they use a magnetic film for the recording layer, they cannot be rewritten. It is possible. In addition, it has excellent reliability because it can record and reproduce without contact and is not affected by dust. This magneto-optical recording layer (hereinafter referred to as recording layer)
Materials used include TbFeCo, NdDyF
Rare earth-transition metals (RE
-TM) Amorphous alloys are known, and are actively being developed because they have no grain boundary noise and can easily produce perpendicularly magnetized films using sputtering, and are currently being commercialized. .

On the other hand, in order to meet future demands for high density and mass production, short wavelength lasers (wavelength: currently 8
30 nm→670, 470 nm), and it is necessary to increase the areal density by reducing the recording bit size. However, currently commonly used RE-TM amorphous alloys such as TbFeCo have the problem that the Kerr rotation angle decreases as the wavelength becomes shorter, resulting in a lower C/N ratio. As a means to solve this problem, NdDyFeCo was added to the reproducing layer of the two-layer film using magnetic exchange coupling.
It has been proposed to use a material with a large Kerr rotation angle even in a short wavelength range, such as , or to use an artificial lattice film in which Co and Pt or Co and Pd are alternately laminated as a recording layer.

However, NdDyFeCo films and Co
None of the methods using superlattice films such as /Pt are easy to manufacture or have extremely high noise levels, and have not yet achieved characteristics superior to those of conventional magneto-optical recording media.

Therefore, an object of the present invention is to have a large magneto-optical effect such as the Kerr rotation angle even in a short wavelength range, and to improve the recording sensitivity in order to cope with the shortening of the wavelength of lasers, which is essential for high density and large capacity. The object of the present invention is to provide a magneto-optical recording medium with high performance.

[0006]

[Means for Solving the Problems] As a result of extensive research, the inventors of the present invention have developed an alloy (with a film thickness of 100 Å or less) in which a specific element is added to Co or Fe, and an alloy with an easy magnetization axis perpendicular to the film surface. We proposed a magneto-optical recording medium in which the C/N does not decrease even for short wavelength lasers of 670 nm or less by using a double-layer film with an RE-TM amorphous alloy film having a -18449).

However, since a Co or Fe alloy film is usually a non-oriented polycrystalline film, it is an in-plane magnetized film with an axis of easy magnetization parallel to the film surface, and it is easy to magnetize it in the perpendicular direction. Not. However, as a result of further investigation, the present inventors discovered that by providing a specific underlayer, the crystal planes of these alloy films are oriented in a certain direction, and that a two-layer film using this oriented alloy is possible. discovered that it is more suitable for short wavelength recording than those that are not oriented, and completed the present invention.

That is, according to the present invention, in a magneto-optical recording medium in which at least an interference layer, a first recording layer, a second recording layer and a protective layer are sequentially formed on a transparent substrate, the first recording layer has the following structure. 1 of Co and Fe represented by the general formula 1
The second recording layer is made of a rare earth-transition metal amorphous alloy film having an axis of easy magnetization perpendicular to the film surface, and the interference layer and the first recording layer are There is provided a magneto-optical recording medium characterized in that an underlayer is provided between the first and second recording layers for the purpose of improving the crystal orientation of the first recording layer.

[Chemical formula 1]

The configuration of the present invention will be explained in detail below with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of the configuration of a magneto-optical recording medium according to the present invention, in which an interference layer 2, a first recording layer 3, a second recording layer 4, and a protective layer 5 are sequentially laminated on a transparent substrate 1. In this structure, the first recording layer 3 is made of an alloy film containing one or more of Co or Fe, and the second recording layer 4 is an RE-TM amorphous film having an axis of easy magnetization in a direction perpendicular to the film surface. Made of quality alloy membrane,
and a first recording layer 3 between the interference layer 2 and the first recording layer 3.
The feature is that a base layer 6 is provided to improve the crystal orientation of the Fe or Co alloy film.

(Substrate) As the transparent substrate 1 used in the present invention, polycarbonate (PC), polymethyl methacrylate (PMMA), amorphous polyolefin (AP
Examples include a grooved molded substrate made of a resin such as O), or a substrate formed with a grooved ultraviolet curing resin (epoxy acrylate or the like) layer on a glass surface of aluminosilicate, barium borosilicate, or the like. These substrates are disk-shaped and have a thickness of about 1.2 mm. 1A in FIG. 1 shows a glass substrate, and 1B shows an ultraviolet curing resin layer.

(Interference layer) In the present invention, the above substrate 1
An interference layer 2 is provided between the two. A transparent film with a high refractive index (1.8 or more) is used for this interference layer 2, and the apparent Kerr rotation angle is increased by utilizing multiple reflections of the reproduced light in this layer, thereby increasing the C (carrier) level. By increasing the reflectance and decreasing the reflectance, the N (noise) level can be lowered.
The purpose is to improve the total C/N. Furthermore, since a material that is prone to corrosion such as oxidation, such as RE-TM amorphous alloy film, is used for the second recording layer 4, this interference layer 2 is used as a protective film to prevent oxidation of the recording layer. They must also fulfill their roles. For that, board 1
It is necessary to prevent water and oxygen from penetrating, have high corrosion resistance, and have low reactivity with the recording layer. Specific materials include SiO, SiO2, Al2O3, Ta
Examples include metal oxides such as 2O5, metal nitrides with Si, Al, Zr, Ge, etc., inorganic carbides such as B4C, SiC, and metal sulfides such as ZnS, and these may be composites (e.g., SiAlON, SiZrN) or a multilayer film. The optimal value of the film thickness varies depending on the refractive index, but is usually 500 to 2000 Å, preferably 800 to 1200 Å.

(Recording layer) One of the features of the present invention is the recording layer. This recording layer has a Co or Fe alloy film (first recording layer 3) and an RE-
It is composed of two layers: a TM amorphous alloy film (second recording layer 4), and the first recording layer 3 is provided on the side of the substrate 1 where the recording/reproducing light is incident. Information is recorded in the second recording layer 4, but when the first recording layer 3 is as thin as 100 Å or less, it is magnetized in the perpendicular direction due to magnetic exchange coupling with the second recording layer 4, and Co Signals can be read using both the magneto-optic effect (Kerr rotation, Faraday rotation) of the alloy or Fe alloy and the magneto-optic effect of the second recording layer 4. The compositions of both layers are as shown below.

[Table 1]

[0013] The second recording layer 4 contains Cr, Ti, and Pt.
, Pd may be contained in a small amount (1 to 5 atomic %). 1st
The recording layer 3 is located on the incident side of the reproduction light, and is preferably made of a material with as large a magneto-optic effect as possible. Co and Fe films inherently have a large magneto-optic effect and do not deteriorate even in the short wavelength range of 670 nm or less, but since the axis of easy magnetization is in the in-plane direction, a perpendicular magnetization film is required for a single layer in the recording layer of a magneto-optical recording medium. It is inappropriate as such. Furthermore, even if a two-layer film using magnetic exchange coupling is used, it is not easily magnetized in the perpendicular direction. Therefore, in the present invention, at least one element of Pt, Pd, Rh, Ga, Si, Cr, Al, and Ge is added so as not to reduce the magneto-optic effect of Co and Fe and to facilitate magnetization in the perpendicular direction. .

FIG. 2 shows (A) a Co80Pt20 film (subscripts represent atomic %) and (B) a Co film as a first recording layer 3 on a glass substrate, and a Tb12 film as a second recording layer 4.
Dy12Fe68Co8 (800 Å) was sequentially formed, and the relationship between the residual Kerr rotation angle (θkr) measured from the glass substrate side and the film thickness of the first recording layer 3 is shown. first recording layer 3
Compared to the sample (B) using a Co film, the sample (A) with Pt added has (θkr) approximately twice as large. The film thickness when θkr is maximum is 70 to 80 (Å)
, and it decreases rapidly when it exceeds 150 Å. This is because magnetic exchange coupling does not work if the film is too thick, and in the case of a Co alloy, the film thickness of the first recording layer 3 is preferably 50 to 100 Å, although it varies depending on the composition. The same can be said of Fe alloys.

The second recording layer 4 is a layer provided for the purpose of recording, and must be a perpendicularly magnetized film with a large coercive force (Hc) in order for recorded bits to exist stably. Therefore, RE-TM amorphous alloys, which are generally known as magneto-optical recording materials, such as TbFeCo and NdD
Suitable materials include yFeCo and TbDyFeCo. Naturally, it is better for this second recording layer 4 to be able to record with a small laser power, so the Curie point (Tc) is 160 to 20.
Among them, those represented by the following general formula 2, which are as low as 0°C, are preferable. Further, the film thickness is preferably 400 to 1200 Å.

[Chemical formula 3]

(Underlayer) Another feature of the present invention is that
It is in the underlayer 6 provided between the interference layer and the first recording layer. This underlayer 6 improves the crystallinity of the Co or Fe alloy film, which is the first recording layer 3, and orients specific crystal planes in a certain direction, thereby making it easier to magnetize in the direction perpendicular to the film surface. The purpose is to In addition, since the underlayer 6 is located on the recording and reproducing light incident side with respect to the recording layer, it needs to be a film that is highly transparent to the recording and reproducing light. Specific materials include ZnO, AlN, MgO, BeO
Examples include. Since the first recording layer 3 must be grown epitaxially, the underlying layer 6 itself must naturally be a crystal film with a certain degree of orientation in a specific plane. On the other hand, if the crystal film is thick, the crystal grains will become large and cause media noise, so it is better to make it as thin as possible. Therefore, the thickness is preferably about 50 to 500 Å. however,
The optimum value is determined by the thickness of the interference layer 2, etc., taking into account multiple reflections of the reproduction light. Further, the base layer 6 and the interference layer 2 may be used together.

(Protective layer) In the present invention, a protective film 5 is usually provided on the recording layer. This protective layer 5 is exposed to air (in the case of a single-sided disc) or an adhesive layer (in the case of a double-sided disc).
It is provided for the purpose of protecting the recording layer by preventing harmful substances such as water, oxygen, or halogen elements from entering the recording layer.Like the interference layer 2, it has high corrosion resistance and is highly resistant to corrosion with the recording layer. It is also necessary that the reactivity is low. In addition to the materials mentioned for the interference layer 2, specific materials include Al, Cr, and N.
Metals such as i, Mo, and Pt, or alloys made of these metals can also be used.

Means for forming the interference layer 2, underlayer 6, first and second recording layers 3, 4, and protective layer 5 on the substrate 1 include physical vapor deposition methods such as sputtering and ion plating, and plasma A chemical vapor deposition method such as CVD is used. In addition to the layer configuration shown in FIG. 1, the present invention also includes a structure in which an organic protective film (cover layer) of 5 to 10 μm is further provided on the protective layer 5, or in which the film surfaces are bonded together with an adhesive. The effect of the invention will not be impaired.

[0019]

EXAMPLES Next, the present invention will be explained in more detail with reference to examples. Examples 1 to 16 A pregrooved glass substrate made of ultraviolet curable resin with a diameter of 130 mm and a thickness of 1.2 mm was set in a vacuum chamber of a sputtering device, and evacuated to a temperature of 5 x 10-7 (Torr) or less. . First, a mixed gas of Ar and N2 is introduced into a vacuum chamber, the pressure is adjusted to 5 x 10-3 (Torr), and the discharge power is 2KW (4W/cm) using Si as a target.
In step 2), high-frequency sputtering is performed to form an interference layer of Si.
An Nx film (see Table 2 for film thickness) was formed. Next, an underlayer film (see Table 2 for film composition and film thickness) was successively deposited by the same method, and then a two-layer recording layer (film composition: and film thickness (see Table 2). Furthermore, as a protective layer, SiNx is formed by the same method as the interference layer.
A film of 800 Å was deposited to form a disk, each of which was used in Example 1.
-3, 5-7, 9-11, and 13-15 magneto-optical disks. The magneto-optical disks of Examples 4, 8, 12, and 16 had a configuration in which the interference layer and the underlayer were combined. still,
The subscripts in the compositions in Table 2 represent atomic %.

[0020]

[Table 2]

Comparative Example 1 In Example 1, the thickness of the interference layer (SiN film) was 1000
Å, no underlayer is provided, and a Co film (50
A magneto-optical disk was obtained in the same manner except that Å) was used.

Comparative Example 2 A magneto-optical disk was obtained in the same manner as in Example 2 except that neither the underlayer nor the first recording layer was provided.

The θkr and reflectance (R) of the magneto-optical disks of Examples 1 to 16 and Comparative Examples 1 and 2 were measured from the substrate side, and the performance index √R·θkr of each was determined. This is also shown in Table 2. Note that the wavelength of light used at this time was 670 nm. Further, FIG. 3 shows the wavelength dependence of √R·θkr of the magneto-optical disks of Example 1 and Comparative Examples 1 and 2.

From Table 2, it can be seen that √R·θkr is higher in Examples 1 to 16 of the present invention than in the two comparative examples at a wavelength of 670 nm. or,
As shown in FIG. 3, in Example 1, √R·θkr did not decrease much even in the shorter wavelength range, and similar results were obtained for other Examples 2 to 16.

[0025]

Effects of the Invention As explained in detail above, according to the present invention, since a Co or Fe alloy film crystal-oriented by an underlayer is used as one layer of the recording layer of a two-layer film structure, even short wavelength lasers can achieve high performance. The output can be obtained, and a high-density, large-capacity magneto-optical recording medium can be realized. Furthermore, if a TbDyFeCo film with a low Curie point is used as the other side of the recording layer, a medium with even higher sensitivity can be obtained. Furthermore, production becomes easier.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a magneto-optical recording medium of one configuration example according to the present invention.

FIG. 2 is a diagram showing the relationship between the magnetic Kerr rotation angle and the first recording layer thickness.

FIG. 3 is a diagram showing the wavelength dependence of θkr in Example 1 and Comparative Examples 1 and 2.

[Explanation of symbols]

1 Transparent substrate 2 Interference layer 3 First recording layer 4 Second recording layer 5 Protective layer 6 Base layer

Claims (4)

[Claims] 1. At least an interference layer, a first
In a magneto-optical recording medium in which a recording layer, a second recording layer and a protective layer are sequentially formed, the first recording layer has the following general formula 1.
The second recording layer is made of a rare earth-transition metal amorphous alloy film having an axis of easy magnetization perpendicular to the film surface, and has an interference film. 1. A magneto-optical recording medium characterized in that an underlayer is provided between the first recording layer and the first recording layer for the purpose of improving the crystal orientation of the first recording layer. [Chemical formula 1] Claim 2: The thickness of the first recording layer is 50 to 100 Å.
The magneto-optical recording medium according to claim 1, characterized in that: 3. The magneto-optical recording medium according to claim 1, wherein the second recording layer is made of an alloy represented by the following general formula 2. [Chemical 3] 4. The magneto-optical recording medium according to claim 1, wherein the underlayer is made of one of ZnO, AlN, MgO and BeO.