JPH0636385A - Magneto-optical recording method - Google Patents

Abstract

(57) [Abstract] [Purpose] A temperature gradient or a cooling rate of the recording layer of a recording medium by irradiating two or more kinds of laser pulses by an optical modulation method on a magneto-optical recording medium having a single-layered perpendicular magnetization film as the recording layer. When creating a difference in overwriting and making a difference in temperature gradient or cooling speed, it is easy to increase the margin of recording conditions, improve the certainty of overwrite, improve the reproduction signal,
Provided is a magneto-optical recording method capable of reducing the error rate. [Structure] Overwriting is performed using a laser pulse in which one of two types of laser pulses has one falling edge and the other has a plurality of falling edges. As a result, the difference in the temperature gradient or the cooling rate becomes large, and the intended purpose can be achieved.

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 method for irradiating a magneto-optical recording medium having a single-layered perpendicular magnetization film as a recording layer with two or more kinds of laser pulses for overwriting.

[0002]

2. Description of the Related Art In recent years,
As a rewritable optical recording medium, a magneto-optical recording medium utilizing the magneto-optical effect has been energetically researched and developed, and some have come to practical use. This magneto-optical recording medium has the advantages of large-capacity and high-density recording, non-contact recording / playback, ease of access, and rewriting, and can be used for document information files, video / still image files, computer memory, etc. Are seen as promising. In order to make a magneto-optical recording medium a recording medium having a performance equal to or higher than that of a magnetic disk, there are some technical problems, and one of the main ones is an overwrite technique.

In the magneto-optical recording media currently on the market, it is necessary to erase the original information in advance to rewrite the information and then write new information.
This erasing operation is a time loss. Overwriting technology eliminates this drawback. The overwrite technology proposed so far is roughly classified into a magnetic field modulation method and an optical modulation method (multi-beam method, two-layer film method, etc.) depending on the recording method.

The magnetic field modulation system is a system in which the intensity of light is kept constant and the polarity of the applied magnetic field is reversed in accordance with the recorded information for recording. In this method, in order to perform the reversal of the magnetic field at a high speed, a countermeasure such as using a flying type magnetic head has been studied, but there is a problem that medium replacement becomes difficult. Only the surface can be used,
There is a problem that the storage capacity is halved.

On the other hand, the optical modulation system is a system in which the applied magnetic field is kept constant and the irradiation laser is turned on / off or intensity-modulated according to the recorded information to perform recording. Among the optical modulation methods, the multi-beam method is a pseudo-overwrite method that uses 2-3 lasers and reverses the direction of the magnetic field each time the magneto-optical recording medium makes one revolution to perform recording / erasing. It has drawbacks such as a complicated structure and increased cost. The two-layer film system is a system in which the recording layer of the magneto-optical recording medium is a two-layer film to achieve overwriting, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-175948.
The system described in the publication uses a magneto-optical recording medium having a recording layer made of TbFe and an auxiliary layer made of TbFeCo, for example, and after initialization, a magnetic field is applied and a laser having a different power is applied. Is intended to realize overwriting. That is, in this method, the magnetization of the auxiliary layer is aligned in one direction with an initializing magnetic field of about 4 KOe in advance before recording, and a high-power laser is irradiated to change the medium temperature T to T> Tc ₂ (Tc ₂ is the auxiliary layer Curie temperature), and a recording magnetic field (direction opposite to the initialization magnetic field) is applied to reverse the magnetization of the auxiliary layer,
Recording is performed by transferring the magnetization to the recording layer when the medium is cooled, and the medium temperature is Tc ₁ <T <Tc ₂ (Tc ₁ is the Curie temperature of the recording layer) by irradiating a low-power laser. Erasure is performed by raising the temperature to a certain temperature and transferring the magnetization direction of the auxiliary layer to the recording layer. However, although this method is advantageous in terms of high speed, it has a problem that the laser power at the time of writing is high and that a very large magnetic field must be applied during the initialization process performed before overwriting. .

As described above, several methods have been proposed as an overwrite method for magneto-optical recording, but each of them has not only advantages but also disadvantages. It is said that breakthroughs must be repeated.

On the other hand, a method of performing optical modulation overwrite using a magneto-optical recording medium having a single-layered perpendicular magnetization film as a recording layer has also been proposed [Han-Ping; Appl. Phys. Lett.,
49, p8 (1986) etc.]. When overwriting is performed using a single-layer magneto-optical recording medium whose recording layer (magnetic film) is not an exchange-coupling multilayer film as described above, whether or not a reversed magnetic domain is formed depends on the temperature gradient after the light pulse irradiation. And the cooling rate, in particular the temperature gradient. However, this method has the following problems. That is, in this method, until now, the pulse width or the power of the laser pulse was changed to make the difference between the temperature gradient and the cooling rate, but the above difference can be obtained only by changing the pulse width and the power. It was difficult to attach and the margin of recording conditions was very small. Therefore, there are problems such as low certainty of overwriting, a small reproduction signal, and a high error rate, and the fact is that it has not been put to practical use.

According to the present invention, a magneto-optical recording medium having a single-layered perpendicularly magnetized film as a recording layer as described above is irradiated with two or more kinds of laser pulses by an optical modulation method to obtain a temperature gradient in the recording layer of the recording medium. Alternatively, when creating a difference in cooling rate and performing overwriting, it is easy to make a difference in temperature gradient or cooling rate, thereby expanding the margin of recording conditions, improving the certainty of overwriting, and improving the reproduction signal (S / N It is an object of the present invention to provide a magneto-optical recording method capable of reducing the error rate.

[0009]

In order to achieve the above object, according to the present invention, a magneto-optical recording medium having a single-layered perpendicular magnetization film as a recording layer is irradiated with two or more kinds of laser pulses to overwrite. In the magneto-optical recording method for carrying out the method, there is provided a magneto-optical recording method characterized by using a laser pulse having a change in a falling portion. Further, according to the present invention, there is provided a magneto-optical recording method characterized in that, in the above, a laser pulse falling in one step and a laser pulse falling in a plurality of steps are used. Further, according to the present invention, there is provided a magneto-optical recording method characterized by using a laser pulse having a short pulse width falling in one step and a laser pulse having a long pulse width falling in a plurality of steps. Further, according to the present invention, there is provided a magneto-optical recording method characterized by using a laser pulse in which the speed at which the power decreases at the trailing edge of the pulse is changed. Further, according to the present invention, in the above, a laser pulse having a short pulse width in which the speed of power decrease at the pulse trailing edge is increased, and a laser pulse having a long pulse width in which the power decrease rate at the pulse falling edge is slowed down. A magneto-optical recording method is provided, which uses a pulse. Further, according to the present invention, light for performing overwriting by further irradiating two or more kinds of laser pulses while constantly irradiating the magneto-optical recording medium having a single-layered perpendicularly magnetized film as a recording layer with a laser having a predetermined power. In the magnetic recording method, there is provided a magneto-optical recording method characterized in that laser irradiation is performed with a value smaller than the predetermined power only immediately after irradiation with one type of laser pulse. Further, according to the present invention, there is provided a magneto-optical recording method characterized by using a laser pulse falling in a plurality of steps as the other type of laser pulse. Further, according to the present invention, in a magneto-optical recording method for performing overwriting by irradiating a magneto-optical recording medium having a single-layered perpendicular magnetization film as a recording layer with two or more kinds of laser pulses, one of the lasers is used. There is provided a magneto-optical recording method characterized in that a subpulse having a pulse width shorter or a power smaller than that of the main pulse is added immediately after the main pulse is used as the pulse.

[0010]

According to the present invention, in a magneto-optical recording method in which a magneto-optical recording medium having a single-layered perpendicularly magnetized film as a recording layer is irradiated with two or more kinds of laser pulses to perform overwriting, directly or substantially at the falling portion. By using the laser pulse that has been changed, the difference between the temperature gradient and the cooling rate can be made large. Therefore, it is possible to increase the margin of recording conditions, improve the certainty of overwriting, improve the reproduction signal (improve S / N), and reduce the error rate.

[0011]

EXAMPLES The present invention will be described in detail below based on examples. The present invention is directed to a magneto-optical recording method in which a magneto-optical recording medium having a single-layered perpendicular magnetization film as a recording layer is irradiated with two or more types of laser pulses to perform overwriting. The laser pulse is used to directly or substantially change the trailing edge of the laser.

The magneto-optical recording method which is the object of the present invention uses a magneto-optical recording medium having a single layer of perpendicularly magnetized film which is not an exchange coupling multilayer film as a recording layer, and two or more kinds having different pulse widths and / or powers are used. In order to perform overwriting by irradiating the laser pulse of
There is a method proposed in the specification of No. 73191, but the method is not limited to this.

In the method proposed in the above specification, a laser pulse having a power Pw ₁ and a pulse width τ ₁ is continuously formed several times until a magnetic domain having a desired length is formed on a magneto-optical recording medium when forming a magnetic domain. When irradiating and erasing magnetic domains, power Pw ₀ ,
A laser pulse having a pulse width τ ₀ is continuously irradiated several times until the erasing magnetic domain has a desired length, and the laser irradiation is Pw ₁ , Pw ₀ and τ ₁ , τ ₀ is τ ₁ ≧ τ _0.
And Pw ₁ · τ ₁ > Pw ₀ · τ ₀ . This method is proposed based on the findings obtained by conducting the following overwrite experiment. That is, first, the magneto-optical recording medium is irradiated with a laser pulse having a power Pw ₁ and a pulse width τ ₁ in a stationary state under a constant magnetic field Hex, so that a magnetic domain is formed (a).
I called the condition). Next, using the condition a, the magneto-optical recording medium is finely moved with respect to the laser and continuously irradiated while oscillating a laser pulse to obtain a stripe-shaped magnetic domain. A laser pulse was applied to obtain a condition for cutting the magnetic domain (referred to as a'condition). Then, under these conditions, overwriting experiments were carried out by changing irradiation time and power variously. As a result, as shown in FIG. 14, a magnetic domain is formed in the region corresponding to the a condition, and no magnetic domain is formed in the portion corresponding to the a'condition, or the magnetic domain is completely erased if it existed before. It was Such magnetic domain formation and erasure do not depend on previously written magnetic domain information, and are determined only by two conditions a and a '.

The present invention is directed to the above-described light modulation type overwriting method, and a specific example will be described below with reference to the drawings. FIG. 1 is a diagram showing a pulse waveform when overwriting is performed using two types of laser pulses so far, and in the methods of FIGS. 2 to 5, A and B are different.

FIG. 2 is a diagram showing a pulse waveform when overwriting is performed using a laser pulse in which one of two types of laser pulses falls in one step and the other falls in a plurality of steps. When the number of steps is plural, the number of steps may be any number, but 2 to 5 is suitable. FIG. 3 shows a case in which two types of laser pulses having different pulse widths are used, the trailing edge of a laser pulse having a short pulse width is one step, and the trailing edge of a laser pulse having a long pulse width is a plurality of steps.

FIG. 4 shows the case where the power reduction rate (dP / dt) at the falling edge of two types of laser pulses is changed. The fall time is preferably as short as possible with respect to the pulse width for the faster power reduction rate, and the fall time is suitably 20% or more of the pulse width for the slower one. In Figure 5, two types of laser pulses with different pulse widths are used, and the power reduction rate of the shorter pulse width is increased,
This is the case where the power reduction rate of the longer pulse width is slowed.

As shown in FIGS. 2 to 5, the difference in the temperature gradient or cooling rate of the recording medium can be increased by directly changing the trailing edge of the pulse.

In ordinary magneto-optical recording, it is usual that the recording medium is always irradiated with DC light having a power sufficiently smaller than the recording power. FIG. 6 shows that DC light is constantly irradiated to such an extent that the recording magnetic domain does not change, two kinds of laser pulses are added to this, and after one kind of laser pulse is irradiated, the laser irradiation power is set to the DC light power. It is smaller than. It is desirable that the power of the DC light be a value above the power at the time of reading so that the recording magnetic domain does not change.
The power when the power is made smaller than the power of the DC light after the laser pulse irradiation is "0", which is more effective, but it is not always necessary. The time when the power becomes smaller than that of the DC light is preferably about 20 to 200% of the pulse width before that. FIG. 7 shows the same irradiation method as in FIG.
This is a case where two types of laser pulses having different pulse widths are used and the power is made smaller than that of the DC light after irradiation with the laser pulse having the short pulse width. FIG. 8 shows FIG. 2 and FIG.
The cases are combined, and the conditions are the same as in the case of FIG. 2 and the case of FIG. In FIG. 9, two laser pulses having different pulse widths are used in the case of FIG. 8, the power is made smaller than that of the DC light after the irradiation of the laser pulse having the short pulse width, and the trailing edge of the laser pulse having the long pulse width is plural. It is a step.

In the cases shown in FIGS. 6 to 9, the power is made smaller than that of the DC light for a certain period after the irradiation of one kind of laser pulse, but in this case as well, the trailing portion of the pulse is substantially changed. Therefore, as in the above case, the difference in the temperature gradient or the cooling rate of the recording medium can be increased.

FIG. 10 and FIG. 11 show a case where a subpulse having a pulse width shorter than the main pulse or a power smaller than that of the main pulse is added immediately after irradiation of one type of laser pulse (main pulse). The pulse width of the sub-pulse irradiated immediately after is appropriate to be about 20 to 100% of the main pulse,
A power of about 20 to 100% is suitable. The interval between the main pulse and the sub-pulse should be less than the pulse width of the previous laser pulse. In FIG. 12, two types of laser pulses having different pulse widths are used in FIG. 11, and a subpulse having a short pulse width or a small power is irradiated immediately after a laser pulse having a long pulse width is irradiated.

In the cases shown in FIGS. 10 to 12, the sub-pulse is added immediately after the laser pulse of one kind for irradiation, and in this case as well, the trailing edge of the pulse is substantially changed. As described above, the difference in the temperature gradient or the cooling rate of the recording medium can be increased.

FIG. 13 shows changes not only in the falling edge of the pulse but also in the rising edge. By doing so, a further effect can be expected.

[0023]

According to the method of the first aspect, there is an effect of increasing the difference in temperature gradient or cooling rate, the margin of recording conditions is expanded, the certainty of overwrite is improved, and the reproduction signal is improved (S / N) and the error rate can be reduced. According to the method of claim 2, since one type of laser pulse falls in a plurality of steps, the temperature gradient immediately after the pulse irradiation becomes gentle and the cooling rate thereafter becomes slow. According to the method of claim 3, laser pulse irradiation with a long pulse width has the same effect as the method of claim 2,
By combining this with the fall of a plurality of steps, the effect becomes large. According to the method of claim 4, when the power reduction rate is slow, the same effect as that of the method of claim 2 is obtained, and when the power reduction rate is fast, the opposite effect is obtained. According to the method of claim 5, the laser pulse irradiation of the long pulse width has the same effect as the method of the claim 2, and the laser pulse irradiation of the short pulse width has the opposite effect.
The effects are increased by combining the same effects. According to the invention of claim 6, by making the power immediately after the laser pulse irradiation smaller than the steady DC power, there is an effect that the temperature gradient becomes steep and the subsequent cooling speed becomes faster. According to the invention of claim 7, the combined effect of the method of claim 2 and the method of claim 6 is expected. According to the invention of claim 8, there is the same effect as the method of claim 2.

[Brief description of drawings]

FIG. 1 is a diagram showing a pulse waveform when overwriting is performed using two types of laser pulses.

FIG. 2 is a diagram showing an example of a waveform of a laser pulse used in the method of the present invention.

FIG. 3 is a diagram showing another example of the waveform of a laser pulse used in the method of the present invention.

FIG. 4 is a diagram showing still another example of the waveform of a laser pulse used in the method of the present invention.

FIG. 5 is a diagram showing still another example of the waveform of a laser pulse used in the method of the present invention.

FIG. 6 is a diagram showing still another example of the waveform of a laser pulse used in the method of the present invention.

FIG. 7 is a diagram showing still another example of the waveform of a laser pulse used in the method of the present invention.

FIG. 8 is a diagram showing still another example of the waveform of a laser pulse used in the method of the present invention.

FIG. 9 is a diagram showing still another example of the waveform of a laser pulse used in the method of the present invention.

FIG. 10 is a diagram showing still another example of the waveform of a laser pulse used in the method of the present invention.

FIG. 11 is a diagram showing still another example of the waveform of a laser pulse used in the method of the present invention.

FIG. 12 is a diagram showing still another example of the waveform of a laser pulse used in the method of the present invention.

FIG. 13 is a diagram showing still another example of the waveform of a laser pulse used in the method of the present invention.

FIG. 14 is an explanatory diagram of a range of recording conditions and erasing conditions of the method proposed previously.

Front Page Continuation (72) Inventor Osamu Nonoyama 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd. (72) Inventor Masaetsu Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd. (72) Inventor Koji 1-3-6 Nakamagome Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Genji Tanaka 1-3-3 Nakamagome Nakatamagome, Tokyo Inside Ricoh Co., Ltd.

Claims (8)

[Claims] 1. A magneto-optical recording method in which a magneto-optical recording medium having a single-layered perpendicularly magnetized film as a recording layer is irradiated with two or more types of laser pulses to perform overwriting, and a laser having a trailing portion changed. A magneto-optical recording method using a pulse. 2. The magneto-optical recording method according to claim 1, wherein a laser pulse falling in one step and a laser pulse falling in a plurality of steps are used. 3. A laser pulse having a short pulse width that falls in one step and a laser pulse having a long pulse width that falls in a plurality of steps are used.
The magneto-optical recording method described in. 4. The magneto-optical recording method according to claim 1, wherein a laser pulse in which the speed at which the power falls at the trailing edge of the pulse is changed is used. 5. A laser pulse having a short pulse width in which the speed of power decrease at the falling edge of the pulse is fast, and a laser pulse having a long pulse width in which the speed of power decrease at the falling edge of the pulse is slow are used. The magneto-optical recording method according to claim 4. 6. A magneto-optical recording method in which a magneto-optical recording medium having a single-layered perpendicularly magnetized film as a recording layer is always irradiated with laser light of a predetermined power, and at the same time, two or more kinds of laser pulses are irradiated to overwrite. 2. In the magneto-optical recording method, laser irradiation is performed with a value smaller than the predetermined power only immediately after irradiation with one type of laser pulse. 7. The magneto-optical recording method according to claim 6, wherein a laser pulse falling in a plurality of steps is used as the other type of laser pulse. 8. A magneto-optical recording method for performing overwriting by irradiating a magneto-optical recording medium having a single-layered perpendicular magnetization film as a recording layer with two or more kinds of laser pulses.
A magneto-optical recording method, characterized in that, as the kind of laser pulse, a sub-pulse having a pulse width shorter or a power smaller than that of the main pulse is added immediately after the main pulse.