JPH06333277A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve recording and reproducing characteristics and to improve stability of bits in a magneto-optical recording medium having a magnetic film on a substrate by constituting the magnetic film of specified two kinds of layers. CONSTITUTION:The magnetic film of this magneto-optical recording medium consists of two kinds of layers. One of the layers consists of Nd and 3d transition metals or an alloy containing at least one element selected from 3d transition metals. The other layer consists of 3d transition metals or rare earth elements containing at least one of 3d transition metals. The total film thickness of the two layers is <=13nm. By this method, the obtd. medium can be used for high-density recording and reproducing and has excellent bit stability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a magneto-optical recording medium, in particular, a magnetic film comprising two alloy layers containing a rare earth element, which enables high-density recording / reproducing characteristics and pit stability. The present invention relates to an excellent magneto-optical recording medium.

[0002]

2. Description of the Related Art A magneto-optical recording medium has attracted attention as a recording medium because it has a large capacity, a medium replaceable, and a rewritable characteristic. For this, further increase in capacity and density are required. Therefore, shortening the wavelength of the laser beam can be mentioned as one of the means, and the shorter the wavelength, the smaller the pit diameter at the time of reproduction, so that higher density recording / reproduction becomes possible.

However, a heavy rare earth-3d transition metal amorphous film such as TbFeCo currently used as a recording medium has a low Kerr rotation angle at a short wavelength, and thus the characteristics of the medium are not sufficient in this wavelength range. There is a disadvantage that. On the other hand, when Nd is used as the rare earth element, conversely at the short wavelength, θ
It is known that k becomes large [see Suzuki et al., Journal of Japan Society for Applied Magnetics, 11 (1987), 193], Nd-3d.
Since the transition metal film is ferromagnetic, it has a large saturation magnetization, and has a problem that a means such as substrate heating is required for perpendicular magnetization.

[0004]

Therefore, this Nd-
Several attempts have been made to perpendicularly magnetize a 3d transition metal film (hereinafter abbreviated as Nd-containing film), which are roughly classified into 1) addition of heavy rare earth elements, 2) utilization of exchange coupling force by a multilayer film, Gd, of which,
The addition of heavy rare earth elements such as Tb and Dy (see Japanese Patent Laid-Open No. 61-165847) is effective for increasing the perpendicular magnetic anisotropy of the film and decreasing Ms, but this method provides sufficient protection. When trying to obtain a perpendicular magnetic film having magnetic force, the composition ratio of heavy rare earths becomes an amount that does not change much as in conventional TbFeCo and the like, which is a disadvantage that the characteristic of Nd type that θk is large at a short wavelength is halved. There is.

[0005] As for this, as in 2), there has been proposed a method of laminating an Nd-containing film with a perpendicularly magnetized film of heavy rare earth-3d transition metal (Japanese Patent Laid-Open No. 1-130344).
Iiyori et al., J. Magn. Soc. Jap., 15, Suppl. No.S
1 (1991), 189), but these have a total magnetic film thickness of 1
It is thicker than 00 nm, the recording sensitivity is lower than that of TbFeCo which is currently in practical use, and since laser light does not pass through the magnetic film, enhancement using a reflective film cannot be used, and in terms of disk productivity. It has the drawback of not being practical.

For this magneto-optical recording medium, in addition to the above, a method of alternately laminating two layers or more (Japanese Patent Laid-Open No.
No. 130344, Japanese Patent Laid-Open No. 1-237945) and Nd-3
Method for adding heavy rare earth element to d-transition metal film (Patent Document 2)
No. 267754 and Japanese Patent Laid-Open No. 3-248350) are also proposed, but the former has a difficulty in mass production, and the latter has a small effect of increasing θk at a short wavelength as described above. In addition to this, a perpendicularly magnetized film of NdFe2 element alloy has also been proposed (Japanese Patent Laid-Open No. 61-16584).
However, this method has a problem that it is not suitable for practical use because the method of heating the substrate is adopted.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a magneto-optical recording medium which solves the above disadvantages, drawbacks and problems, in a magneto-optical recording medium comprising a magnetic film provided on a substrate. The magnetic film is composed of two types of layers, one of which is a layer composed of 3d transition metal or an alloy containing at least one element selected from them and Nd, and the other is a layer of 3d transition metal or selected from them. Alloy containing at least one element, Gd, Tb, D
a layer composed of a rare earth element containing at least one element selected from y, and the total film thickness of the two layers is 13 nm.
It is characterized by the following.

That is, the inventors of the present invention have made various studies on a conventionally known method for modifying a magneto-optical recording medium having two magnetic layers, and as a result, the magnetic layer has a layer made of 3d transition metal or its alloy and Nd. 3d transition metal or its alloy and two layers of at least one rare earth element selected from Gd, Tb, and Dy, it is possible to increase the film thickness ratio of the layer containing Nd. The wavelength θk can be increased, and if the amount of the rare earth element in the layer containing at least one rare earth element of Gd, Tb, and Dy is larger than the amount of the rare earth element of the compensating composition, the coercive force becomes large and the bit stability is improved. That a good medium can be obtained, and this 2
If the total film thickness of the two layers is 13 nm or less, the magnetization of the layer including the Nd layer is oriented in the direction perpendicular to the film surface, the square shape in the hysteresis loop is good, and the recording sensitivity is good and the disc productivity is excellent. The present invention has been completed by confirming that it is possible to obtain a medium which has excellent recording / reproducing characteristics and bit stability and can be obtained with high productivity. This will be described in more detail below.

[0009]

The present invention relates to a magneto-optical recording medium,
This is a magneto-optical recording medium in which a magnetic film is provided on a substrate as described above, and the magnetic film is composed of two types of layers, one of which is a 3d transition metal or at least one element selected from them. And a layer containing Nd and an alloy containing 3d transition metal or an alloy containing at least one element selected from them, and Gd,
According to this, the layer is composed of a rare earth element containing at least one element selected from Tb and Dy, and the total thickness of the two layers is 13 nm or less. This provides an advantage that a magneto-optical recording medium having good recording / reproducing characteristics and bit stability can be obtained with high productivity.

As shown in FIG. 1, the magneto-optical medium of the present invention comprises a substrate on which a first dielectric layer, a first magnetic layer, a second magnetic layer, a second dielectric layer and a reflective layer are sequentially formed. The first magnetic film and the second magnetic film may be laminated in reverse order. The substrate, the dielectric film, and the reflective layer constituting this magneto-optical recording medium may be the same as known ones. Therefore, this substrate is made of glass or polycarbonate, polyolefin, polymethylmethacrylate, or other transparent resin. The dielectric layer may be made of ceramics such as SiN, AlN, or SiC in consideration of the durability of the magnetic film and the car-enhancement effect, and the reflective layer has high reflectance and thermal conductivity. Al, Cu, Au, A
It suffices to use g, Pt or the like or an alloy containing these.

The magnetic film constituting the magneto-optical recording medium of the present invention is made of an amorphous alloy of rare earth element-transition metal. The first magnetic layer is a layer formed of a 3d transition metal such as Fe, Co, or Ni or an alloy containing at least one element selected from these and a rare earth element composed of Nd. In order to improve the corrosion resistance, elements such as Cr, Nb and Pt may be added. When Nd is less than 10% in this composition, Ms is too large and it is difficult to obtain the effect of making the magnetization perpendicular, and when the content is more than 40%, Ms is too small. Since it is not possible to obtain a sufficient θk, it is necessary to set this to 10 to 40%, which means that this composition is N _dx M _1-x (M is a 3d transition metal or at least one of them). Alloy)), the x value may be 0.1 ≦ x ≦ 0.4.

The second magnetic film is made of the above-mentioned 3d transition metal or its alloy and at least one rare earth element selected from Gd, Tb and Dy, which is compensated. It is necessary to use a composition that contains more rare earth elements than the composition (hereinafter referred to as RE-rich composition). FIG. 2 shows that the second magnetic layer has a composition containing less rare earth elements than the compensating composition (hereinafter referred to as TM-rich composition) and the RE-rich composition described above.
FIG. 3 is a graph showing the relationship between the coercive force of the layer film and the ratio of the thickness of the first magnetic layer. When the RE-rich composition layer is laminated on the first magnetic layer, the coercive force of the entire magnetic layer is shown. Can be increased, a large coercive force can be obtained in the magnetic two-layer film of the present invention, and the stability of the bit is also improved.
On the other hand, in the case of the TM-rich composition, if this is laminated on the magnetic layer, the coercive force rapidly deteriorates, and the bit becomes unstable, making it difficult to retain information.

In the magneto-optical recording medium of the present invention, the total film thickness of the first magnetic film and the second magnetic film is 13 nm or less, and the first magnetic film and the second magnetic film each have a film thickness of 13 nm or less. Although the thickness is 3 nm or more, the film thickness of the second magnetic film needs to be thicker than the film thickness of the primary film formation. This is because it is advantageous that the thickness of the first magnetic layer is thin in order to make the magnetization of the first magnetic film, which is a single layer and exhibits the in-plane direction, perpendicular by the exchange coupling force acting between the two layers. This is because the film thickness of the second magnetic layer required to make the layer magnetization perpendicular is 3 to 6 nm, and even if the thickness is further increased, the effect on the direction of the first layer magnetization is not changed.

Further, regarding the Kerr rotation angle θk, when the total of the first and second magnetic layers is equal to or less than the film thickness that transmits the laser light, the first relative to the total is obtained.
Since θk at a short wavelength can be increased as the ratio of the magnetic film thickness increases, the total film thickness of the first and second magnetic films is set to 13 nm or less in the present invention, and the film thickness of the second magnetic film is set to 13 nm or less. The thickness is preferably thicker than the thickness of the first magnetic film.

When the magnetic film in the magneto-optical recording medium of the present invention is set in this manner, the heavy rare earth element of the present invention has such a heavy rare earth element as compared with the conventional method in which the heavy rare earth element is added to the layer containing Nd. Since no element is added, θk at short wavelength
It is possible to obtain a good medium having a rectangular shape capable of increasing the magnetic field. However, if the first magnetic film and the second magnetic film are too thin, it is difficult to obtain the effect of forming them into two layers. Both must be 3 nm or more.

Further, in the magneto-optical recording medium of the present invention, since the thickness of this magnetic layer is thinned to 13 nm or less, the recording sensitivity does not decrease and the mass productivity of the disk becomes excellent. The decrease in θk due to the reduction in film thickness can be eliminated by using the enhancement effect of the dielectric layer and the reflection layer, and this is because the upper and lower dielectric layers are sandwiched by the dielectric layers, and there is no practical problem in terms of durability. become.

[0017]

EXAMPLES Next, examples and comparative examples of the present invention will be described. Example 1 SiN as a first dielectric layer on a slide glass substrate
Layer, an NdFe layer as a first magnetic layer, a TbFe layer as a second magnetic layer, a SiN layer as a second dielectric layer, and an Al as a reflective layer were sequentially formed to form a magneto-optical recording medium. The NdFe layer is formed by a sputtering method using a composite target in which Nd is placed on Fe as a target, and the TbFe layer is formed by a sputtering method using a composite target in which Tb is placed on Fe as a target.
When measured by PMA, this was Nd 35% -Fe, TbFe had a Re-rich composition, and the thickness of the first magnetic film was 5 nm and the thickness of the second magnetic film was 4 nm.

Next, as characteristic values for comparing the rectangular shapes of these, θk (residual θk) when the external magnetic field H = 0 and H
Using the ratio of saturated θk (saturated θk) to the sample, the residual θk / saturated θk ratio and the coercive force of this sample were measured from the substrate side, and the saturated θk at wavelengths of 780 nm and 450 nm were measured. When the SiN film thickness was adjusted so that the reflectance R was 20%, the results shown in Table 1 below were obtained.

Example 2 The composition of the magnetic film was the same as in Example 1, except that the thickness of the first magnetic film was 5 nm and the thickness of the second magnetic film was 3 nm. A magneto-optical recording medium was prepared in 1. and its physical properties were measured by the same methods as in Example 1, and the results shown in Table 1 below were obtained.

Example 3 The first magnetic film was made of Nd 33%, Fe 40%, Co 7% and had a thickness of 5 nm, and the second magnetic film was Tb 36%, Fe 43%,
A magneto-optical recording medium was prepared in the same manner as in Example 1 except that the film thickness was 3 nm consisting of Co7%.
When measured by the same method as described above, the results shown in Table 1 described later were obtained.

Comparative Example 1 The compositions of the first and second magnetic films were the same as in Example 1, but the same method as in Example 1 except that the total film thickness was 30 nm with the film thicknesses of these films being 15 nm. A magneto-optical recording medium was prepared by using the above method, and its physical properties were measured by the same method as in Example 1.
The results shown in Table 1 below were obtained.

The composition of the first magnetic film is the same as that of the first embodiment, the second magnetic film has Tb 19% -Fe and TM-rich composition, and the film thicknesses of the first and second magnetic films are both. 5
A magneto-optical recording medium was prepared by the same method as in Example 1 except that the thickness was nm, and the physical properties were measured by the same method as in Example 1. As a result, the results shown in Table 1 below were obtained. .

Comparative Example 3 The magnetic film was a single layer made of NdTbFe, and the film thickness was 15
A magneto-optical recording medium was prepared in the same manner as in Example 1 except that the value was set to nm, and its physical properties were measured in the same manner as in Example 1. As a result, the results shown in Table 1 below were obtained. .

Comparative Example 4 The magnetic film was a single layer made of TbFeCo, and the film thickness was 20.
A magneto-optical recording medium was prepared in the same manner as in Example 1 except that the value was set to nm, and its physical properties were measured by the same methods as in Example 1. The results shown in Table 1 below were obtained.

[0025]

[Table 1]

[0026]

The present invention relates to a magneto-optical recording medium, which is a magneto-optical recording medium in which a magnetic film is provided on a substrate as described above, and the magnetic film is composed of two layers. One of them is a 3d transition metal or an alloy containing at least one element selected from them and Nd.
The other is a layer consisting of 3d transition metal or an alloy containing at least one element selected from them,
It is a layer formed of a rare earth element containing at least one element selected from Gd, Tb and Dy, and the total thickness of the two layers is 13 nm or less. It is said that the magnetic film consists of two alloy layers containing rare earth elements, and since the film thickness is also specified, high-density recording / reproducing can be specified and bit stability is also excellent. The advantage is that the productivity is also good.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing the structure of a magneto-optical recording medium according to the present invention.

FIG. 2 is a graph showing the relationship between the coercive force Hc and the film thickness ratio of the first magnetic film and the first and second magnetic films of the magneto-optical recording medium according to the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Tawara 3-2-1 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa Shin-Etsu Chemical Co., Ltd. Corporate Research Center (72) Kazuhiko Nakayama Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa 3-2-1, Shin-Etsu Chemical Co., Ltd. Corporate Research Center

Claims (5)

[Claims] 1. A magneto-optical recording medium having a magnetic film provided on a substrate, wherein the magnetic film is composed of two types of layers, one of which is a 3d transition metal or at least one element selected from them. The other layer is a layer containing an alloy containing Nd, and the other is a 3d transition metal or an alloy containing at least one element selected from them, and Gd, Tb, and D.
a layer composed of a rare earth element containing at least one element selected from y, and the total film thickness of the two layers is 13 nm.
A magneto-optical recording medium characterized by the following: 2. A magnetic layer comprising 3d transition metal and Nd, of two types of layers constituting the magnetic film, having a thickness larger than that of the other layer, and the thickness of each layer is 3 nm or more. Claim 1
The magneto-optical recording medium described in 1. 3. The magnetic layer comprising a 3d transition metal and at least one rare earth element selected from Gd, Tb and Dy has a composition containing more rare earth elements than the compensating composition. Magneto-optical recording medium. 4. The composition of 3d transition metal and Nd is Nd _x
When expressed by M _1-x , this x value is 0.1 ≦ x ≦ 0.4 (M
Is a 3d transition metal or an alloy containing at least one element thereof). 5. A magneto-optical recording medium according to claim 1, wherein a first dielectric layer, a magnetic layer composed of two kinds of layers, a second dielectric layer and a reflective layer are sequentially formed on a substrate. .