JPH08221825A - Magneto-optical recording medium and device - Google Patents

Abstract

PURPOSE: To obtain a magneto-optical recording medium having a high recording density with which a high C/N value is obtainable when recording and reproducing light of a prescribed wavelength is used to obtain the sufficient recording density. CONSTITUTION: Glass which is patterned thereon with UV curing resins is used as a substrate. A first dielectric layer consisting of nitride, a reproducing layer consisting of a GdFeCo alloy, a recording layer consisting of a TbFeCo alloy, a second dielectric layer consisting of nitride and a reflection layer consisting of an Al alloy are laminated thereon in this order by a sputtering method. The thicknesses of the respective layers are specified to 40nm, 10nm, 15nm, 15nm, 50nm in order of lamination. This magneto-optical recording medium is so formed that the magnitude of the temp. change Hc/T of the coercive force near the temp. at which the coercive force of the magnetic layer to be recorded with information attains 500Oe attains the value expressed by the equation when the medium is irradiated with a light of <=450 to 650nm wavelength to execute the recording or reproducing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium and a device for realizing a high recording density in magneto-optical recording. Among them, especially wavelengths of 450 nm or more and 650
The present invention relates to a recording medium having a reflective film structure for performing recording or reproduction by irradiating light having a shorter wavelength than that of a current product of nm or less, and a recording / reproducing apparatus using the same.

Here, the reflection film structure means a medium structure having a non-magnetic film having a high reflectance, in which a magnetic film is arranged so as to be sandwiched between a substrate and the substrate. With this reflective film structure, it is possible to obtain a strong signal strength by making use of the light interference effect. Since the reproduction light is incident from the substrate side, it is desirable to make the total thickness of the magnetic film as thin as 30 nm or less in order to obtain an increase in signal intensity due to the reflection film. In addition, this structure usually has two layers of a recording layer and a reproducing layer as a magnetic film, and
The first dielectric layer / reproducing layer / recording layer / second dielectric layer / reflection film are laminated in this order.

[0003]

2. Description of the Related Art Conventionally, for example, the Journal of Japan Applied Magnetics 18
As described in Vol. 189, page 192 to page 192 (1994), a structure of a reflective film structure magneto-optical recording medium using an exchange-coupling two-layer film aiming at realization of high recording density is being studied. However, the wavelength used for recording and reproduction is 68
It was 0 nm or 830 nm.

As is well known, the diameter of the recording spot focused on the recording medium is proportional to the wavelength of the irradiation light. Therefore, for example, in order to realize a high recording density of 1 Gbit / cm ² or more, the recording / reproducing light is 650 nm.
It is appropriate to use the following shorter wavelengths. However, a recording medium having a reflective film structure capable of obtaining a sufficient signal intensity at such a short wavelength has not been known until now.

[0005]

In the present invention, in order to obtain a sufficient recording density, the wavelength is 450 nm or more and the wavelength is 650 nm.
It is an object of the present invention to provide a magneto-optical recording medium and a device thereof that can obtain a high C / N value when the following recording / reproducing light is used.

[0006]

As is well known, in magneto-optical recording, a recording medium is heated by a laser beam and recording is performed at a place where the coercive force is lowered. At this time, the recording medium is
For example, it is heated to about 200 ° C and its coercive force is 500O.
e or lower. If the temperature gradient of the coercive force of the medium at the time of recording is small, the size and shape of the recording domain will vary due to the influence from the surroundings, and the noise will increase. Therefore, a certain temperature gradient ∂Hc / ∂T of the coercive force Hc is required during recording. From the experiment, ∂Hc
If the size of / ∂T is smaller than 10 Oe / deg, noise generated by recording becomes large. Also ∂Hc / ∂
When T is larger than 80 Oe / deg, Hc at the recording temperature is too large and the magnetic domain cannot be written well. Therefore, the value of | ∂Hc / ∂T | is 10 Oe / deg ≦ | ∂Hc / ∂T | ≦ 80 Oe / de
It has been found that the means for g is suitable.

Further, in order to realize such a temperature characteristic of coercive force, in the composition of the recording layer containing TbFeCo as a main component, the composition of terbium is set to 25 atomic% or more and the compensation temperature is set to 100 ° C. or more. I had to raise it.

In order to obtain a sufficient signal strength, a reproducing layer containing GdFeCo as a main component is arranged on the recording layer in the reflective film structure so as to be in close contact with the recording film and arranged on the substrate side to form an exchange coupling film. Was convenient. Since the reproducing layer has a smaller coercive force than the recording layer, if the film thickness is made too large, the effect of the reproducing layer appears to be large and the magnetic domains are disturbed, causing noise. In order to prevent this, a means of making the thickness of the reproducing layer less than 1.0 times the thickness of the recording layer was suitable. However, in order to obtain a sufficient reproduction signal, the film thickness had to be 0.5 times or more.

By using a means of forming a transparent dielectric layer made of nitride or the like in close contact with the substrate with an appropriate thickness, it was possible to make good use of the optical interference condition to increase the signal strength. Wavelength 450nm or more 650nm
When the following light is used, the thickness of this dielectric film should be 30
Setting in the range of 60 nm to 60 nm was effective for utilizing the optical interference condition. The signal intensity obtained was smaller or thinner than this.

Further, in order to quickly dissipate the heat generated by the light collection to form a small domain, it was effective to thicken a layer made of, for example, an aluminum alloy as the reflective layer. If the film thickness is less than 40 nm,
The light passes through and the function as a reflective film structure is lowered, and the effect of releasing heat during reproduction light irradiation is also reduced. On the other hand, it takes time to form a reflective layer having a thickness of 200 nm or more, and the manufacturing cost also increases. Therefore, it is effective to set the thickness of the reflective layer to 40 nm or more and 200 nm or less. It was found that the C / N of the disk manufactured by using such means reached 50 dB, and it was practically usable. The figure of merit (square root of (reflectance) x (Kerr rotation angle)) of this disk was measured and found to be 0.42d.
It became eg. In other words, if the figure of merit is at least this value, it is possible to provide a disk that can be used practically.

[0011]

The recording medium has a coercive force of about 500 Oe or less during recording. The change of coercive force with temperature ∂Hc / ∂T is 10 Oe / deg or more, 80
By setting it to Oe / deg or less, the shape of the recording domain is less likely to change due to the influence from the surroundings. As a result, noise during recording could be reduced.

By changing the composition ratio of terbium to 25 atomic% or more, the above-mentioned temperature change of coercive force could be realized.

Further, a reproducing layer containing gadolinium is arranged on the substrate side so as to be in close contact with the recording film, and the thickness thereof is set to 0.5 times or more and less than 1.0 times the film thickness of the recording layer.
It was possible to obtain a recording signal of an appropriate size without increasing noise.

Furthermore, when a transparent dielectric layer made of a nitride having a thickness of 30 nm to 60 nm is closely attached to the substrate, when a light having a wavelength of 450 nm to 650 nm is used as the recording / reproducing light, the performance index ((reflectance is It was possible to obtain a sufficient signal level by maximizing the square root of () × (Kerr rotation angle)).

In addition to this, a thickness of 40 nm or more and 200
By attaching an alloy film having a thickness of nm or less as a reflective layer, it is possible to improve the dispersion of heat applied during reproduction, prevent the temperature of the recording medium from rising when irradiated with strong light, and obtain a high signal output. It was

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1] FIG. 1 shows a sectional shape of a disk used in this embodiment. What was patterned on the glass with an ultraviolet curable resin was used as a substrate. A first dielectric layer made of a nitride, a reproducing layer made of a GdFeCo alloy, a recording layer made of a TbFeCo alloy, a second dielectric layer made of a nitride, and a reflective layer made of an aluminum alloy are stacked thereon in this order by a sputtering method. did. The thickness of each layer is 40 nm, 10 nm, 15 nm, 15 n in the order of lamination.
m and 50 nm.

The change in the coercive force of this disk with temperature was as shown in FIG. In the figure, the dotted line shows
The temperature change of the coercive force when the coercive force reaches 500 Oe is ∂Hc / ∂T. In this case, the magnitude is 38O.
e / deg. The terbium composition of the recording film of this disc was 32 atomic%.

This disc was irradiated with laser light having a wavelength of 530 nm for recording, and noise was evaluated. As a result, the noise generated during recording was approximately -67 dB. At this time, the carrier level was measured to be -17 dB, so a value of 50 dB was obtained as C / N. At this time, the figure of merit (square root of (reflectance) x (Kerr rotation angle)) of this disk was measured to be 0.42 deg.

Next, the noise during recording was measured by changing the fraction of terbium in the recording film of this disc. The result is shown in FIG. When the terbium fraction is less than 0.25,
It can be seen that the temperature variation ∂Hc / ∂T of the coercive force in the vicinity of the compensation temperature approaching room temperature and the coercive force of 500 Oe decreases, and the noise during recording increases.

This change is represented by | ∂Hc / ∂ of recording noise.
FIG. 4 shows the T | dependence. ｜ ∂Hc /
∂T ｜ is less than 10 Oe / deg and ｜ ∂Hc / ∂T ｜
In the range of 80 Oe / deg or more, the noise is increased. It is considered that in the region of 10 Oe / deg or less, the size and shape of the recording domain varied due to the influence from the surroundings. In the region of 80 Oe / deg or more, it is considered that the noise was increased because Hc became large and a region in the domain that was not inverted by the magnetic field of the coil was formed. From this result, | ∂Hc / ∂T | is 10 Oe / deg ≦ | ∂Hc / ∂T | ≦ 80 Oe / de
It can be seen that when g is set, a medium with less noise during recording can be obtained.

[Example 2] The same recording medium as in Example 1 was used. However, not only the reproducing layer film thickness of 10 nm but also 7 kinds of disks were prepared by changing the thickness from 0.2 nm to 20 nm by the sputtering method. Since the film thickness of the recording layer is 15 nm, the film thickness ratio (reproducing layer film thickness / recording layer film thickness) is changed from 0.2 to 1.3. When the C / N of each disk was measured, the result was as shown in FIG. When the film thickness ratio is 0.5 or less and 1.0 or more, the C / N ratio decreases. It is considered that when the film thickness ratio is 0.5 or less, the reproducing layer does not play a sufficient role. On the other hand, it is considered that when the film thickness ratio is 1.0 or more, the shape of the magnetic domain formed in the reproducing layer is disturbed, which directly leads to an increase in noise. Therefore, it is understood that a region having a thickness ratio of 0.5 times or more and less than 1.0 times is appropriate.

Example 3 The same recording medium as in Example 1 was used. However, the film thickness of the transparent dielectric (first dielectric layer) is 4
Not only 0 nm but also 6 types from 25 nm to 70 nm were produced by the sputtering method. Figure of Merit (square root of (reflectance) ×
(Kerr rotation angle)) is shown in FIG. Wavelength 4
It can be seen that when the light of 50 nm to 650 nm is irradiated, a high figure of merit is obtained in the film thickness range of 30 nm to 60 nm. It is considered that this is because, in this range, the reflective film structure disk of the present example is under the condition that the figure of merit is increased by the interference of light.

Example 4 Next, a recording medium similar to that of Example 1 was prepared, but the reflection film thickness was 30 nm to 200 nm.
C / N was measured by changing to FIG. 7 shows the result. When the reflective film thickness is less than 40 nm, the heat generated by the irradiation of the reproducing light does not escape well, so the recording medium is warmed, the Kerr rotation angle decreases, and the C / N also decreases.
On the other hand, at 40 nm or more, up to around 200 nm, the C / N value can be maintained without a decrease in the Kerr rotation angle even if the reproducing light intensity is increased by allowing heat to escape. In the region of 200 nm or more, it takes time to manufacture and the manufacturing cost increases.
Therefore, the reflection film thickness is 40 nm or more and 200 nm.
It has been found that the following is appropriate.

[0025]

The coercive force Hc is 500 Oe near the recording temperature.
Since the size of the change in coercive force with temperature ∂Hc / ∂T was set to an appropriate value, variations in the size and shape of the recording pits were reduced, and noise during recording was reduced. Such a recording film was formed as an exchange-coupling film with a rare earth-transition metal alloy layer having a terbium composition of 25 atomic% or more and a reproducing layer containing gadolinium with appropriate thicknesses.
Further, a transparent dielectric layer having a proper thickness was attached in close contact with the substrate, and in addition, an alloy thick film was attached as a reflective layer, whereby a recording medium having a high C / N could be manufactured.

[0026]

[Brief description of drawings]

FIG. 1 is a sectional view of a reflective structure disk.

FIG. 2 is a diagram showing temperature dependence ∂Hc / ∂T of Hc.

FIG. 3 is a diagram showing Tb fraction dependency of recording noise.

FIG. 4 is a diagram showing | ∂Hc / ∂T | dependence of recording noise.

FIG. 5 is a diagram showing C / N vs. reproducing layer film thickness / recording layer film thickness.

FIG. 6 is a diagram showing the dependence of a figure of merit (square root of (reflectance) × (Kerr rotation angle)) on the film thickness of a transparent dielectric (first nitride layer).

FIG. 7 is a diagram showing the dependency of recording noise on the thickness of a reflective layer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G11B 11/10 586 9296-5D G11B 11/10 586Z

Claims (7)

[Claims] 1. A temperature change of coercive force ∂Hc / ∂ near a temperature at which the coercive force of a magnetic layer for recording information is 500 Oe when recording or reproducing is performed by irradiating light having a wavelength of 450 nm or more and 650 nm or less. The size of T is 10 Oe / deg ≦ | ∂Hc / ∂T | ≦ 80 Oe / de
A magneto-optical recording medium having g. 2. The magneto-optical recording medium according to claim 1, wherein a recording medium having a rare earth-transition metal alloy layer having a composition of terbium of 25 atomic% or more is used. 3. A reproducing layer containing gadolinium is provided, and the reproducing layer is arranged in close contact with the recording film and is arranged on the substrate side, and the film thickness thereof is 0.5 times or more the film thickness of the recording layer. 1.0
3. The magneto-optical recording medium according to claim 2, which is less than double. 4. A magneto-optical recording medium according to claim 1, wherein a transparent dielectric layer having a thickness of 30 nm or more and 60 nm or less is closely attached to the substrate. 5. An alloy film having a thickness of 40 nm or more and 200 nm or less is provided as a reflective layer.
A magneto-optical recording medium according to claim 1. 6. The value of (square root of (reflectance) × (Kerr rotation angle)) measured from the substrate surface is 0.42 deg or more, according to any one of claims 1 to 5. Magneto-optical recording medium. 7. A recording / reproducing apparatus using the recording medium according to claim 1.