JP2857008B2 - Reproduction method of magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing method of a magneto-optical recording medium for reading information recorded on a magneto-optical recording medium such as a magneto-optical disk, a magneto-optical tape, and a magneto-optical card.

[0002]

2. Description of the Related Art As a rewritable optical disk memory, a magneto-optical disk memory has been put to practical use. However, a drawback of the conventional magneto-optical disk memory is that a recording bit diameter is smaller than a focused semiconductor laser beam diameter. In addition, when the recording bit interval is small, there is a problem that the reproduction characteristics are deteriorated. This is because adjacent recording bits enter into the focused laser beam, so that individual recording bits cannot be separated and reproduced.

In order to solve such a defect, magneto-optical recording of a two-layer structure having in-plane magnetization at room temperature and having a readout layer which becomes a perpendicular magnetization film as the temperature rises and a recording layer which becomes a perpendicular magnetization film. A method has been proposed in which a recording medium can be used to separate and reproduce individual recording bits even if the recording bits are smaller than the laser beam diameter.

[0004] A method of separating and reproducing a recording bit smaller than a beam spot diameter by using the above-described magneto-optical recording medium having a two-layer structure will be described with reference to FIGS. 9A and 9B. .

The magneto-optical recording medium has a recording layer 42 having a Curie temperature of about 150 ° C. and a read layer 41 which is an in-plane magnetic film at room temperature and becomes a perpendicular magnetic film at a read temperature of about 50 ° C. or higher. doing. When recording information on the magneto-optical recording medium, the temperature of the recording layer 42 is raised to a temperature near the Curie temperature by irradiating a high-power light beam, and the recording layer 42 is irradiated with the information to be recorded.
This is performed by reversing the direction of magnetization. On the other hand, at the time of reproduction, a light beam having a lower power than at the time of recording is irradiated.

At this time, since the light spot 44 moves in the direction of arrow E in FIG.
The range where the above temperature is reached is a range 45 shifted backward with respect to the light spot 44. In only this range 45, the readout layer 41 becomes a perpendicular magnetization film and the recording layer 42
, The magnetization direction of the readout layer 41 becomes the same as the magnetization direction of the recording layer 42. here,
Since the position of the light spot 44 is shifted from the range 45 of the readout layer 41 at which the temperature is equal to or higher than 50 ° C., the recording bit 46 existing in the area where the light spot 44 and the above range 45 intersect.
Only the recorded bits 47 existing outside the light spot 44 are not reproduced.

By providing the readout layer 41 in this manner, even when a plurality of recording bits (recording bits 46 and 48) exist in the light spot 44, the readout layer 4
The portion corresponding to the recording bit 48 in No. 1 is an in-plane magnetized film that has not been heated to 50 ° C. or more.
It is possible to reproduce only 6 separately.

[0008]

However, in the above-mentioned magneto-optical recording medium, the readout layer 41 in an in-plane magnetization state is used.
If the magnetization direction is inappropriate, there is a problem that the noise level during reproduction increases. That is, the magnetization direction of the portion in the in-plane magnetization state in the readout layer 41 is determined by the direction of the stray magnetic field 49 generated from the recording layer 42. Therefore, the direction of magnetization of the readout layer 41 in the in-plane magnetization state is in the direction indicated by arrows b and c in the figure. Then, the above-mentioned arrow b ′ existing in the light spot 44
The upward and downward magnetization indicated by c ′ acts as noise on the recording bit 46 to be read, causing an increase in the noise level.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to provide a readout layer that becomes an in-plane magnetic film at room temperature and becomes a perpendicular magnetic film when the temperature rises, and a recording layer made of the perpendicular magnetic film. When reproducing a recording bit smaller than a laser beam diameter recorded on a magneto-optical recording medium having a low noise level, the object of the present invention is to provide a reproducing method of a magneto-optical recording medium capable of obtaining a high-quality reproduction signal. I have.

[0010]

According to the present invention, there is provided a reproducing method for a magneto-optical recording medium, comprising: a recording layer comprising a perpendicular magnetic film capable of magneto-optically recording information; When reading recorded information using a magneto-optical recording medium having a readout layer in which the magnetic anisotropy is in an in-plane magnetization state in which the perpendicular magnetic anisotropy is superior and the perpendicular magnetic anisotropy becomes superior in temperature when heated, The method is characterized in that a light beam is applied to the magneto-optical recording medium and a magnetic field having an in-plane direction component is applied.

[0011]

According to the method described above, when a light beam is irradiated during reproduction to raise the temperature of the readout layer to a predetermined temperature or more, the readout layer becomes perpendicularly magnetized, and receives the exchange coupling force from the recording layer. Since the magnetization direction of the heated read layer matches the magnetization direction of the recording layer, it is possible to read information recorded with a recording bit smaller than the laser beam diameter. By applying a magnetic field having a temperature that does not rise above a predetermined temperature,
That is, the direction of magnetization of the readout layer, which indicates an in-plane magnetization state that is in an inappropriate state due to the influence of the stray magnetic field of the recording layer, can be aligned in one direction, so that the noise level during reproduction is reduced. Thus, a high-quality reproduced signal can be obtained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 2, a magneto-optical disk (magneto-optical recording medium) from which information is read by the reproducing method of this embodiment is provided on a substrate 3 made of, for example, polycarbonate, a transparent dielectric layer 4 and a room temperature. And the readout layer 1 in which the in-plane magnetic anisotropy is superior and the perpendicular magnetic anisotropy is superior at a read temperature of about 50 ° C. or more, and the Curie temperature of about 150 ° C. Recording layer 2, transparent dielectric layer 5, and overcoat film 6
They are stacked in this order.

A method for manufacturing a magneto-optical disk having such a configuration will be described below. First, Al, Gd,
A polycarbonate disk substrate having pregrooves and prepits is placed in a sputtering apparatus provided with a quinary target composed of Dy, Fe, and Co to face the target, and the inside of the sputtering apparatus is 1 × 10 ^−6. Tor
After evacuation to r, a mixed gas of Ar and N ₂ was introduced, power was supplied to the Al target, and a gas pressure of 4 × 1
0 ^-3 Torr, sputtering speed 12 nm / min, Al
A transparent dielectric layer 4 made of N is formed.

The thickness of the transparent dielectric layer 4 is set to a value obtained by dividing 1/4 of the wavelength of the reproduction light by its refractive index in order to improve the reproduction characteristics.
In this case, the thickness may be about 10 nm to 80 nm, and in this embodiment, the thickness of the transparent dielectric layer 4 is set to 60 nm.

Next, after the inside of the sputtering apparatus is evacuated again to 1 × 10 ⁻⁶ Torr, Ar gas is introduced and Gd,
Power is supplied to the Fe and Co targets and the gas pressure is 4 ×
G at 10 ⁻³ Torr and a sputtering rate of 15 nm / min.
A readout layer 1 made of dFeCo is formed. The readout layer 1 needs to be in an in-plane magnetization state at room temperature and to have a perpendicular magnetization state at a high temperature, so that it needs to be rich in RE (rare earth element). In this embodiment, the readout layer 1 did not have a compensation temperature, and its Curie temperature was 350 ° C. The composition of the prepared readout layer 1 is G
In _{d 0.26 (Fe 0. 8 Co 0.2} ) 0.74, film thickness was 50nm.

Subsequently, the power supplied to Gd is stopped, and power is supplied to the target of Dy.
The recording layer 2 made of eCo is formed. The recording layer 2 may be RE-rich or TM (transition metal) -rich at room temperature, but at least in the vicinity of the Curie temperature.
M must be rich. Recording layer 2 produced in this example is a TM rich at room temperature, the coercive force H _C2 is 800k
A / m, no compensation temperature exists, Curie temperature is 150 ° C. The composition is Dy _0.23 (Fe
_0.82 Co _0.18 ) _0.77 , and the film thickness was 50 nm.

Next, a mixed gas of Ar and N ₂ is introduced into the sputtering apparatus, and power is supplied to the Al target.
Gas pressure 4 × 10 ^-3 Torr, sputtering speed 12 nm / m
In, a transparent dielectric layer 5 made of AlN is formed. Here, the film thickness of the transparent dielectric layer 5 may be any value as long as the recording layer 2 can be protected from corrosion such as oxidation, and is 50 nm in this embodiment.

Thereafter, an overcoat film 6 was formed by applying, for example, an ultraviolet-curing resin or a thermosetting resin by a spin coating method and irradiating or heating with ultraviolet rays.

In order to record information on the magneto-optical disk formed as described above, as shown in FIG. 3, a laser beam 8 is condensed and irradiated from the substrate 3 side by an objective lens 7, and A magnetic field having a vertical component is applied by a magnet 9 provided opposite to the objective lens 7 with the interposition therebetween to invert the magnetization in the recording layer 2 according to information.

In order to reproduce the recorded information, FIG.
As shown in (1), a lower power laser beam 8 is applied during recording, and the magnet 9 is rotated by 90 degrees from the state at the time of recording, and a magnetic field having an in-plane direction component is applied to the readout layer 1.

That is, as shown in FIGS. 1 (a) and 1 (b), when the light spot 10 is irradiated during reproduction, two recording bits 13 and 15 are present therein. Since the light spot 10 moves in the direction of arrow B in the figure, the portion of the readout layer 1 where the temperature rises to 50 ° C. or higher is a range 11 shifted backward from the light spot 10. In this range 11, the readout layer 1 becomes a perpendicular magnetization film and receives exchange coupling force from the recording layer 2 so that only the magnetization direction of this portion is the magnetization direction of the recording layer 2 corresponding to the recording bits 13 and 14. In the same direction as Here, as described above, since the position of the light spot 10 is shifted from the position of the range 11, only the recording bits 13 existing in the portion where the light spot 10 and the range 11 overlap are reproduced.

The direction of magnetization of the readout layer 1 in the in-plane magnetization state is determined by the stray magnetic field generated from the recording layer 2, and the magnetization affected by the stray magnetic field of the recording layer 2 changes the light spot 10. When it exists in the inside, there was a problem that a noise level would rise. Therefore, in the reproducing method of this embodiment, the magnetization direction of the readout layer 1 in the in-plane magnetization state is aligned in one direction (the direction indicated by the arrow a in the drawing) by applying a magnetic field having an in-plane direction component. The generation of noise due to the influence of the stray magnetic field of the recording layer 2 is suppressed, and an increase in the noise level is prevented. Note that this magneto-optical
In a magnetic disk, the in-plane magnetization state is low in the low temperature region.
And the perpendicular magnetization state becomes stable in the high temperature region.
Characteristics. Therefore, the read at the time of the above-mentioned reproduction
In the high temperature region (50 ° C. or higher), the perpendicular magnetization
The state is stable, and the above-mentioned appropriate in-plane magnetic field is applied.
However, it does not affect the reproduced signal.

Therefore, by applying such a reproducing method, even when a plurality of recording bits exist in the light spot 10, it is possible to separate and reproduce the individual recording bits, and to reduce the noise level. A low and high quality reproduced signal can be obtained.

Next, in order to confirm by experiment the reduction in noise level due to the application of a magnetic field having an in-plane direction component at the time of reproduction, the following experiment was performed using the magneto-optical disk manufactured as described above. went.

First, as shown in FIG. 3, the magneto-optical disk is rotated at a rotational speed of 1800 rpm (linear velocity 5 m / s).
16.5mm radius from the center of the magneto-optical disk
The recording layer 2 was irradiated with a laser beam 8 of 0 mW and a magnetic field was applied from a magnet 9 to align the magnetization direction of the recording layer 2 in one direction, thereby setting an erased state. Next, after rotating the magnet 9 by 180 degrees to invert the polarity of the generated magnetic field, a laser beam of 8 mW is applied at about 7 MHz.
To record a single frequency recording bit having a length of 0.35 μm at a period of about 0.7 μm.

Next, as shown in FIG.
The laser beam 8 of 2 mW was irradiated while applying a magnetic field having an in-plane direction component, and reproduction was performed. Here, by changing the position of the magnet 9 with respect to the magneto-optical disk, the in-plane magnetic field intensity on the magneto-optical disk was changed, and the change in the noise level was measured. Table 1 shows the results. Note that, as a reference value of the noise level, the noise level when the reproduction was performed in the arrangement state of the magnet 9 during recording (the state of FIG. 3) was set to 0 dB.

[0028]

[Table 1]

As is clear from the above results, the readout layer 1 which is an in-plane magnetic film at room temperature and becomes a perpendicular magnetic film at high temperature
When reproducing information recorded with recording bits smaller than the beam spot diameter using a magneto-optical disk having a recording layer 2 composed of a perpendicular magnetization film and applying a magnetic field having an in-plane direction component, Irradiation makes it possible to obtain a high-quality reproduction signal with a low noise level.

The method of applying a magnetic field having an in-plane direction component during reproduction is not limited to the method of rotating a magnet according to recording and reproduction as described above. A configuration in which the electromagnet is rotated may be used.

Further, as shown in FIG. 5, for example, a configuration in which an electromagnet 17 for generating a reproducing magnetic field is arranged adjacent to an electromagnet 16 for generating a recording magnetic field may be applied. In this case, while driving only the electromagnet 16 during recording, driving only the electromagnet 17 during reproduction applies a magnetic field having a vertical component during recording and applying a magnetic field having an in-plane direction component during reproduction. It becomes possible to do.

Further, as shown in FIG. 6, the electromagnet 17 for generating the reproducing magnetic field is connected to the electromagnet 1 for generating the recording magnetic field with respect to the magneto-optical disk so as not to hinder the irradiation of the laser beam 8.
6 may be provided on the opposite side. When the methods shown in FIGS. 5 and 6 are used, magnets can be used instead of the electromagnets 16 and 17.

As shown in FIG. 7, it is also possible to obtain both a recording magnetic field and a reproducing magnetic field from one electromagnet 16 by shifting the center position of the electromagnet 16 and the laser beam irradiation point. That is, as shown in FIG. 8, the intensity of the magnetic field generated by the electromagnet 16 is such that the vertical component _Hw becomes maximum at the electromagnet center position, and as the distance from the center position increases,
The vertical component H _w is small. On the other hand, the horizontal (in-plane) component H _r of the magnetic field intensity is almost zero at the electromagnet center position, gradually increases with increasing distance from the center.

Therefore, in the conventional magneto-optical recording / reproducing method, since a recording magnetic field having only a vertical component is required, the laser beam irradiation position is made coincident with the electromagnet center position (the position indicated by X in the figure). By setting the laser beam irradiation position to a position deviated from the center position of the electromagnet (the position indicated by Y in the figure), it is possible to obtain both the recording magnetic field _Hw and the reproducing magnetic field _Hr .

In this case, the recording magnetic field _Hw is applied to the magneto-optical disk also at the time of reproduction. However, since the laser light at the time of reproduction uses a weaker power than at the time of recording, It will not span affect the recording layer 2 by the recording magnetic field H _w.

[0036]

The method of reproducing a magneto-optical recording medium according to the present invention comprises:
As described above, the recording layer consisting of a perpendicular magnetization film capable of magneto-optical recording of information and the in-plane magnetization state where the in-plane magnetic anisotropy is superior at room temperature, and the perpendicular magnetic anisotropy is superior when the temperature is increased. When reading recorded information using a magneto-optical recording medium having a readout layer that is in a perpendicular magnetization state, the magnetic recording medium is irradiated with a light beam and a magnetic field having an in-plane direction component is applied. is there.

Therefore, the direction of the in-plane magnetization existing in the light spot can be aligned in one direction, so that even when information recorded with recording bits smaller than the laser beam diameter is reproduced, the noise level is reduced. There is an effect that a low-quality reproduction signal can be obtained.

[Brief description of the drawings]

FIG. 1A is a schematic diagram showing a surface state of a reading layer of a magneto-optical disk to which a reproducing method according to an embodiment of the present invention is applied, and FIG. 1B is a schematic diagram showing a magnetization state of a reading layer and a recording layer. FIG.

FIG. 2 is a sectional view of the magneto-optical disk.

FIG. 3 is a schematic diagram showing a state where information is recorded on the magneto-optical disk using a magnet.

FIG. 4 is a schematic diagram showing a state in which the magneto-optical disk is reproduced while applying a magnetic field having an in-plane component using a magnet.

FIG. 5 is a schematic view showing a method for applying a magnetic field having an in-plane direction component using an electromagnet in another embodiment of the present invention.

FIG. 6 is a schematic view showing a method of applying a magnetic field having an in-plane direction component using an electromagnet in still another embodiment of the present invention.

FIG. 7 is a schematic diagram showing a method for generating both a recording magnetic field and a reproducing magnetic field by using one electromagnet in still another embodiment of the present invention.

8 is a graph showing a relationship between a magnetic field intensity generated when the electromagnet shown in FIG. 6 is used and a position on a medium.

9A and 9B are schematic diagrams illustrating a surface state of a readout layer of a magneto-optical disk to which a conventional reproducing method is applied, and FIG. 9B is a schematic diagram illustrating magnetization states of a readout layer and a recording layer.

[Explanation of symbols]

 1 readout layer 2 recording layer

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Akira Takahashi 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-5-12746 (JP, A) JP-A-5-112 12732 (JP, A) JP-A-2-78042 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 11/10

Claims (1)

(57) [Claims] 1. A recording layer comprising a perpendicular magnetic film capable of magneto-optical recording of information and an in-plane magnetization state in which the in-plane magnetic anisotropy is superior at room temperature. When reading recorded information using a magneto-optical recording medium having a readout layer that is in a perpendicular magnetization state, it is necessary to irradiate the magneto-optical recording medium with a light beam and to apply a magnetic field having an in-plane direction component. A method for reproducing a magneto-optical recording medium.