JPH06187681A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a high C/N in even in a small magnetic field by forming a TbDyFeCo film expressed by a specified formula as the magneto-optical recording layer having axis of easy magnetization perpendicular to the film plane and specifying the coercive force of the layer at room temp. a magneto- optical disk for recording, reproducing and erasing of information by using laser light. CONSTITUTION:An interference layer 2, recording layer 3, protective layer 4 and reflecting layer 5 are successively formed on a transparent substrate 1 having grooves consisting of polycarbonate, epoxyacrylate, etc. In this constitution, the magneto-optical recording layer 3 consists of a TbDyFeCo film expressed by the formula and has the axis of easy magnetization perpendicular to the film plane and 2-8 KOe coercive force. Since TbDyFeCo shows a large Kerr rotation angle as 0.25-0.35 degree and low Curie temp. as 140-150 deg.C, the obtd. medium has a high C/N and high sensitivity. In this way, the proportion of TbDy is made lower while the proportion of FeCo is made higher to obtain 2-8 KOe coercive force. In the formula, x, y, and z satisfy 0<x<=0.5, 0.8<=y<1.0 and 0.19<=z<0.21.

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 such as a magneto-optical disk for recording / reproducing / erasing information by using a laser beam, and particularly to increase C / N in a low magnetic field. And a magneto-optical recording medium.

[0002]

2. Description of the Related Art Since a magneto-optical disk records / reproduces / erases information by using a laser beam, it has a large storage capacity like a conventional optical disk and a magnetic recording layer. Rewriting is possible because the body is used. Moreover, recording and reproducing can be performed in a non-contact manner, and since it is not affected by dust, it has excellent reliability. Therefore, research and development are actively carried out at present, and since it was commercialized several years ago, it has been rapidly expanding to optical file systems and external storage devices of personal computers.

Materials for this magneto-optical recording layer (hereinafter referred to as recording layer) are TbFeCo, NdDyFeCo, Tb.
A rare earth-transition metal (RE-TM) amorphous alloy such as DyFeCo is currently most often used because it has no grain boundary noise and a perpendicular magnetization film can be easily obtained by using sputtering.

The principle of erasing / recording of a magneto-optical recording medium will be described first with respect to an optical modulation method which is currently generally adopted. Data is erased by continuously irradiating and heating a laser beam with a magnetic field applied from the outside to align the magnetization of the recording layer in the same direction as the external magnetic field. For data recording, the external magnetic field is reversed from that at the time of erasing, the output of the laser beam is increased only where the data mark is recorded, the recording layer is heated, and the magnetization of the recording layer is reversed.

On the other hand, the magnetic field modulation method is the opposite of the light modulation method, and is a method of applying a magnetic field in the recording direction to a position where a data mark is recorded while continuously irradiating laser light at the time of recording. Differently, since direct overwriting is possible, it is being actively developed as a future recording method. If these external magnetic fields are too large, the magnetic field generating section (electromagnet) in the magneto-optical recording / reproducing apparatus may become large, or power consumption may increase. Especially in the case of the magnetic field modulation method, this problem is important. Therefore, the external magnetic field should be as small as possible. However, current magneto-optical recording media cannot obtain sufficient C / N unless a magnetic field of at least 300 (Oe) is applied.

The present invention has been made to solve the above-mentioned drawbacks of the conventional magneto-optical recording medium, and it is an object of the present invention to provide a magneto-optical recording medium capable of excellent recording / erasing even when the external magnetic field is small. To aim.

[0007]

Therefore, as a result of intensive studies to overcome the above-mentioned drawbacks, the present inventors have found that the magneto-optical recording layer is a TbDyFeCo film having a specific composition and By adopting a film having an easy axis of magnetization in the perpendicular direction and a coercive force at room temperature of 2 to 8 KOe,
In particular, they have found that good recording and erasing can be performed in a low magnetic field, and have completed the present invention.

That is, according to the present invention, in a magneto-optical recording medium having a structure in which at least a magneto-optical recording layer is formed on a transparent substrate, the magneto-optical recording layer is a TbDyFeCo film represented by the following general formula 1. And has an axis of easy magnetization perpendicular to the film surface and a coercive force at room temperature of 2 to 8 (KO
There is provided a magneto-optical recording medium characterized by being e).

[Chemical 1] (However, 0 <x ≦ 0.5, 0.8 ≦ y <1.0 and 0.
19 ≦ z <0.21) Further, according to the present invention, in the above structure, the magneto-optical recording layer contains 1 to 5 atomic% of at least one of Al, Ti, Cr, Pd, Ta and Pt. A magneto-optical recording medium is provided. Further, according to the present invention, in the above structure, at least the interference layer, the magneto-optical recording layer, the protective layer and the reflective layer are sequentially formed on the transparent substrate,
There is provided a magneto-optical recording medium, wherein the magneto-optical recording layer has a film thickness of 150 to 300 Å. Furthermore, according to the present invention, in the above structure, the reflective layer is Si,
There is provided a magneto-optical recording medium characterized by being an Al alloy containing 1 to 4 atomic% of one or more of Ti, Cr, Zr, Mo, Pd, Ta and Pt.

The magneto-optical recording medium of the present invention will be described with reference to FIG. 1 based on a specific configuration example. The configuration example of FIG. 1 has a configuration in which an interference layer 2, a recording layer 3, a protective layer 4, and a reflective layer 5 are sequentially formed on a transparent substrate 1 with pregrooves. Each element will be described in detail below.

(Substrate) As the transparent substrate 1 used in the present invention, polycarbonate (PC), polymethylmethacrylate (PMMA), amorphous polyolefin (AP)
Examples thereof include a grooved molded substrate made of a resin such as O) or a substrate having a grooved UV-curable resin (epoxy acrylate etc.) layer formed on the surface of a glass such as aluminosilicate or barium borosilicate. These substrates are disk-shaped and have a thickness of about 0.6 to 1.2 mm. 1A of FIG.
Shows a glass substrate and 1B shows an ultraviolet curable resin layer.

(Interference Layer) In the present invention, the substrate 1 is used.
The interference layer 2 is provided between the recording layer 3 and the recording layer 3. A transparent film having a high refractive index (1.8 or more) is used for the interference layer 2, and the apparent Kerr rotation angle (θk) is increased by utilizing the multiple reflection of the reproduction light in this layer, and thereby C ( The purpose is to raise the carrier level and decrease the reflectance to lower the N (noise) level, and improve the total C / N. Further, since the recording layer 3 is made of a material such as RE-TM amorphous alloy which is likely to be corroded by oxidation, the interference layer 2 also serves as a protective film for preventing the recording layer 3 from being corroded. You must have both. For that purpose, it is necessary to prevent water and oxygen from entering from the substrate 1, have high corrosion resistance of themselves, and have low reactivity with the recording layer 3. As a specific material, SiO,
Metal oxides such as SiO ₂ , Al ₂ O ₃ and Ta ₂ O ₅ , S
Examples thereof include metal nitrides such as i, Al, Zr, and Ge, and metal sulfides such as ZnS. Particularly, compounds containing at least Si and N among Si, B, O, and N (SiN, SiON,
SiBN, SiBON) is suitable. It should be noted that these may be multi-layered films, and the film thickness varies depending on the refractive index, but is generally 500 to 2000 Å in total, preferably 8
It is 00 to 1200Å.

(Recording Layer) This recording layer 3 is characterized by this structural example.
It is in. The recording layer 3 is a TbDyFeCo film represented by the following general formula 1, has an easy axis of magnetization in the direction perpendicular to the film surface, and has a coercive force at room temperature of 2 to 8 (KOe).

[Chemical 1] (However, 0 <x ≦ 0.5, 0.8 ≦ y <1.0 and 0.
19 ≦ z <0.21) TbDyFeCo generally has a large θk (Kerr rotation angle) (0.25 to 0.35 deg) and Tc (Curie temperature).
Since it is low (140 to 180 ° C.), it can be said that it is a magneto-optical recording material capable of realizing a medium having high C / N and high sensitivity (JP-A-59-61011). However, in order to obtain a high C / N in a low magnetic field as described above, the composition is rich in RE (TbDy) and has a smaller TM (FeCo) than the compensation composition, and the Hc (coercive force) at room temperature is 2 to 8 (KOe ) Must be.

The recording layer 3 may contain a small amount (1 to 5 atomic%) of Al, Cr, Ti, Pt and Pd in order to improve the corrosion resistance. The film thickness is 150 to 300 Å in the case of the medium structure having the reflective layer 5 as shown in FIG.
Is suitable. The structure provided with the reflective layer 5 can use both the Kerr effect and the Faraday effect of the recording layer 3 so that the C / N ratio is improved.
Excellent (signal-to-noise ratio) and jitter characteristics.

(Protective Layer) Normally, a protective layer 4 is formed on the recording layer 3.
To provide. However, the effect of the present invention is not impaired even if it is not provided. This protective layer 4 prevents entry of harmful substances such as moisture, oxygen, or halogen elements from the air (for one-sided specifications) or adhesive (for both-sided specifications) into the recording layer 3,
Since it is provided for the purpose of protecting the recording layer 3, it must have high corrosion resistance of itself as well as the interference layer 2 and low reactivity with the recording layer 3. Specific materials are the same as those listed for the interference layer 2. The film thickness of the protective layer 4 has a great influence on C / N and recording sensitivity, but it is usually 0 to 600 Å
Is preferred.

(Reflective Layer) The reflective layer 5 may be provided directly on the recording layer 3 or via the protective layer 4. High C of recording medium
/ N, in order to increase the sensitivity, it is preferable that the reflective layer 5 has high reflectance with respect to reproduction light and low thermal conductivity. It must also have corrosion resistance. As a specific material, S
An Al alloy containing 1 to 4 atomic% of one or more of i, Ti, Cr, Zr, Mo, Pd, Pt, and Ta is preferable. If the film thickness is too thin, the C / N decreases, and if it is too thick, the recording sensitivity deteriorates, so 300 to 600 Å is suitable.

(Manufacturing method, etc.) As means for forming the interference layer 2, the recording layer 3, the protective layer 4 and the reflective layer 5 on the substrate 1, a physical vapor deposition method such as sputtering or ion plating,
A chemical vapor deposition method such as plasma CVD is used.

In addition to the layer structure shown in FIG. 1, an organic protective layer (cover layer) having a thickness of 5 to 10 μm is further provided on the protective layer 4 or the reflective layer 5, or the layers thereof are bonded to each other. The effect of the present invention is not impaired even with a constitution in which the components are bonded together.

[0018]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

Examples 1 to 3 A substrate having a diameter of 130 mm, a thickness of 1.2 mm, and a pregroove made of an ultraviolet (UV) curing resin formed on glass was set in a vacuum chamber of a sputtering apparatus, and 5 × 10 ^{− was formed. 7} To
It was evacuated to rr or less. Next, a mixed gas of Ar and N ₂ was introduced into the vacuum chamber, and the pressure was 3 × 10 ⁻³ Tor.
Adjust to r and discharge power 2KW with Si as the target
High frequency magnetron sputtering was performed at (4 W / cm ² ) to deposit an SiN film of 1000 liters as an interference layer.
Then, a TbDyFeCo alloy was used as a target to form a TbD recording layer by DC magnetron sputtering.
A 200 Fe layer of yFeCo film was formed (see Table 1 for composition and coercive force at room temperature). Further, as a protective layer, a SiN film is formed by 300Å by the same method as that of the interference layer, and a reflective layer is formed of AlT.
An i film was sequentially formed by 500Å to obtain a magneto-optical recording medium as an example of the present invention. In addition, Hc in Table 1 was determined from the θk-H curve measured from the substrate (glass) surface.

[0020]

[Table 1]

Comparative Examples 1 to 3 An interference layer, a recording layer, a protective layer, and
A reflective layer was formed, but a recording layer using a TbDyFeCo film (see Table 1 for composition and coercive force at room temperature) outside the range of the characteristics limited by the present invention was prepared as a comparative example.

2 and 3 show the relationship between the external magnetic field (Hex) and C / N at the time of recording / erasing in the magneto-optical recording media of Examples and Comparative Examples. The measurement conditions are as follows. -Recording radius 30 mm-Laser wavelength 780 nm-Recording frequency 4.9 MHz-Disk rotation speed 2400 rpm (CA
V) ・ Recording laser power 6mW ・ Reproducing laser power 1mW

2 and 3, the C / C in the low magnetic field of 300 (Oe) or less is higher in all the examples of the present invention than in the comparative example.
N is high.

In the above description, a medium for the optical modulation system has been described as a specific embodiment, but the effect is also sufficiently exerted as a magneto-optical recording medium for direct overwrite using the magnetic field modulation system.

[0025]

As described above, according to the present invention, a magneto-optical recording medium having a high C / N even in a low magnetic field can be realized by using a TbDyFeCo film having a specific composition range and specific characteristics for the recording layer. .

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a specific configuration example of a magneto-optical recording medium of the present invention.

FIG. 2 is a diagram showing a relationship between an external magnetic field (Hex) and C / N at the time of recording / erasing in the magneto-optical recording media of Examples 1 to 3.

FIG. 3 is a diagram showing a relationship between an external magnetic field (Hex) and C / N during recording / erasing of the magneto-optical recording media of Comparative Examples 1 to 3.

[Explanation of symbols]

 1 transparent substrate 2 interference layer 3 recording layer 4 protective layer 5 reflective layer

Claims (4)

[Claims] 1. In a magneto-optical recording medium having a structure in which at least a magneto-optical recording layer is formed on a transparent substrate, the magneto-optical recording layer is TbDyF represented by the following general formula 1.
A magneto-optical recording medium, which is an eCo film, has an easy axis of magnetization in a direction perpendicular to the film surface, and has a coercive force of 2 to 8 (KOe) at room temperature. [Chemical 1] (However, 0 <x ≦ 0.5, 0.8 ≦ y <1.0 and 0.
19 ≦ z <0.21) 2. The magneto-optical recording layer comprises Al, Ti, Cr,
The magneto-optical recording medium according to claim 1, wherein at least one of Pd, Ta and Pt is contained in an amount of 1 to 5 atom%. 3. A transparent substrate, on which at least an interference layer, a magneto-optical recording layer, a protective layer and a reflective layer are sequentially formed, and the magneto-optical recording layer has a thickness of 150 to 300 Å. Item 3. The magneto-optical recording medium according to Item 1 or 2. 4. The reflective layer comprises Si, Ti, Cr, Zr,
The magneto-optical recording medium according to claim 3, wherein the magneto-optical recording medium is an Al alloy containing 1 to 4 atomic% of at least one of Mo, Pd, Ta and Pt.