JPH0242664A - Thermo-magneto-optical recording medium, recording device thereof and thermomagneto-optical recording system using them - Google Patents

Abstract

PURPOSE:To allow simultaneous erasing and recording by the thermomagneto- optical recording medium consisting of two layers of magnetic layers, a light beam for recording and a magnetic field imparting means for applying adequate magnetic fields. CONSTITUTION:The magneto-optical disk is formed with a substrate 11, a dielectric film 12, a 1st magnetic layer 13, and a 2nd magnetic layer 14 successively from a light projecting surface side. The recording and reproducing device is constituted of the 1st magnetic field imparting means 23 provided to the position different from an optical head 22 in common use for recording and reproducing to the magneto-optical disk 21 and the 2nd magnetic field imparting means 24 provided in the position opposite to the optical head 22 with the disk in-between. Namely, the recording is executed by switching of the two different powers which increase the temp. of the magnetic film to the Curie point or above. The overwriting is allowed in this way without erasing the previously recorded information.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a photothermal magnetic recording medium used for recording information, a recording device thereof, and a photothermal magnetic recording method using these.

2. Description of the Related Art Magneto-optical disks are being put into practical use as rewritable, large-capacity optical disks.

By the way, the recording method for magneto-optical disks involves applying a bias magnetic field using a permanent magnet or electromagnet to a magneto-optical film that has been magnetized in one direction in advance, and modulating the intensity of light focused on the magneto-optical film in accordance with a signal. It's a method.

In this method, before recording, it is necessary to perform an erasing operation in which the disk is magnetized in one direction, and when re-recording is performed using a single optical head, two operations, erasing and recording, are required. Furthermore, it is necessary to switch the direction of the magnetic field for recording and erasing, and there is a problem in that the direction of the magnetic field cannot be changed instantaneously, whether using permanent magnets or electromagnets.

Several methods have already been proposed to solve these problems. They can be roughly divided into magnetic field modulation type and light modulation type. In particular, the latter is attracting attention due to its excellent high-speed response and applicability to double-sided disks.

The light modulation type that has been proposed so far includes a method that utilizes magnetization reversal at a compensation point (Japanese Patent Laid-Open No. 154347/1983, U.S. Patent No. 4,649,519), and a method that uses magnetization by heating a permanent magnet layer. Method of utilizing characteristic changes
9203), a method using exchange coupling between two layers (
JP-A-62-175948), etc.

Problems to be Solved by the Invention The present invention performs simultaneous erasure by using optical modulation recording using a method different from these conventionally proposed methods. In other words, the problem to be solved by the present invention is to enable simultaneous erasure that can be applied to double-sided discs.

Means for Solving the Problem In order to solve this problem, the present invention provides a photothermal magnetic recording medium consisting of two magnetic layers, a light beam for recording, and a magnetic field applying means for applying an appropriate magnetic field. configured.

In particular, in the photothermal magnetic recording medium having two magnetic layers, when the first magnetic layer and the second magnetic layer are arranged in order from the light input surface side, the relationship between the first magnetic layer and the second magnetic layer is as follows. The following conditions are satisfied.

The first is that the coercive force of the first magnetic layer at room temperature is greater than the coercive force of the second magnetic layer at room temperature. Here, normal temperature means the temperature of the medium at a portion that is not affected by heating due to light beam irradiation, and is considered to be within the operating temperature range of a normal recording/reproducing device, approximately 0°C to 50°C. That is reasonable. In this temperature range, the coercive force of the second magnetic layer is smaller than the magnetic field applied by the first magnetic field applying means disposed outside the light beam irradiation part, and the coercive force of the first magnetic layer is larger. It is necessary. Furthermore, in order for the first magnetic field applying means to be easily realized by a small permanent magnet, a 5 koe
Therefore, it is desirable that the coercive force of the second magnetic layer be 5 koe or less in the above temperature range. On the other hand, the coercive force of the first magnetic layer needs to be 5 koe or more in order to be unaffected by the magnetic field applying means, but it is also not affected by heating due to light beam irradiation during reproduction. In order to achieve this, it is desirable that the coercive force of the first magnetic layer is 10 koe or more.

The second is a structure in which the Curie point of the first magnetic layer is greater than or equal to that of the second magnetic layer, and this is a known example (Japanese Patent Laid-Open No. 62175948).
This is a different point. This Curie point is determined by the balance point between signal amplitude and recording sensitivity, and is 150"C.
It is desirable that the temperature is above 250°C or below.

The third reason is that the magnitude of the demagnetizing field induced by the first magnetic layer is larger than the magnitude of the demagnetizing field induced by the first magnetic layer during laser irradiation during recording. This can be achieved by selecting a composition that makes the residual magnetization in the vicinity of the Curie point larger than that of the first magnetic layer in the temperature range from room temperature to the Curie point. It can be realized. In addition, as another method, the thickness of the second magnetic layer may be
This can also be achieved by increasing the thickness of the magnetic layer.

The fourth point is that the compensation temperature of the second magnetic layer does not exist in the temperature range from room temperature to the Curie point, which is a known example (Japanese Patent Laid-Open No. 62-15434
No. 7, U.S. Pat. No. 4,649,519).

A combination that satisfies these conditions is, for example, in the rare earth-transition metal amorphous ferrimagnetic film used for photothermal magnetic recording, for example, Gd Tb FeCo is used, and the first
The magnetic layer contains more Cd and less Co than the second magnetic layer, and also has a compensation temperature of the first magnetic layer near room temperature and a compensation temperature of the second magnetic layer lower than room temperature. This can be achieved by doing this.

The light beam for recording is modulated into high power and low power during recording, and at either power, both the first magnetic layer and the second magnetic layer are heated above the Curie point. This is the above-mentioned known example (Japanese Unexamined Patent Publication No. 62-154
No. 347, U.S. Patent No. 4,649,519, JP-A-62-219203, JP-A-62-1759
Publication No. 48) This is different from all others.

The first magnetic field applying means for recording is constituted by a magnetic field applying means for applying a magnetic field to a portion other than the light beam irradiation part during recording.

This first magnetic field applying means always applies a magnetic field in a fixed direction regardless of the time of recording and reproduction.
No. 2-154347, U.S. Patent No. 4.649,519
In this respect, the present invention is different from those of Japanese Patent Laid-Open No. 62-219203). In addition, it is desirable that the first magnetic field applying means be constituted by a permanent magnet from the viewpoint of power consumption and downsizing. Due to the need to provide a magnetic field of 1 koe~
A range of 5 koe is desirable.

Further, in addition to the first magnetic field applying means, a second magnetic field applying means for the beam irradiation area during recording may be auxiliary provided. However, the second magnetic field applying means is always
It is configured to apply a magnetic field in the same direction as the magnetic field applying means. Therefore, the same magnetic field applying means can serve as the first magnetic field applying means and the second magnetic field applying means. Further, the strength thereof is much smaller than the magnetic field applied by the first magnetic field applying means, and is preferably in the range of 0 to 1 koe.

Operation A method of recording using the configuration described above will be explained using a magneto-optical disk as an example of a photothermal magnetic recording medium.

First, after producing a magneto-optical disk, the first magnetic layer is magnetized.

This magnetization direction is opposite to the direction of the magnetic field applied by the first magnetic field applying means during recording.

Further, the first magnetic layer may be magnetized with a magnetic field larger than the coercive force of the first magnetic layer, or it may be magnetized with a smaller magnetic field by performing optical heating. . When the magnetized state at this time is viewed from a plane perpendicular to the traveling direction of the beam, it becomes state 1. Here, the magnetization direction is set to ↑.

Next, when the magneto-optical disk is mounted on a recording device having a first magnetic field applying means and rotated, the second magnetic layer is magnetized in the opposite direction by the first magnetic field applying means, and is in state 2. Become.

However, at this time, the demagnetizing field from the surroundings is much larger in the second magnetic layer than in the first magnetic layer. As the beam moves away from the beam irradiation and is cooled, both magnetic layers are magnetized along the direction of the demagnetizing field of the second magnetic layer.

(State 4) Next, there are cases where the laser beam for recording has a high power and a case where the laser beam has a low power, which will be explained separately.

(2) In the case of low power, low power is irradiated to both the first magnetic layer and the second magnetic layer so that the temperature exceeds the Curie point in a narrow range.

At that time, magnetization disappears in areas above the Curie point, and a demagnetizing field from the surroundings is generated there. (State 3) Furthermore, while the disk rotates once, the second magnetic layer is magnetized by the first magnetic field applying means, resulting in state 5, which corresponds to state 2.

2) In the case of high power: By irradiating with a high power even higher than the above-mentioned low power, both the first magnetic layer and the second magnetic layer become at or above the Curie point over a wide range. At that time, magnetization disappears in areas above the Curie point, and a demagnetizing field from the surroundings is generated there. (State 6) However, at this time, the demagnetizing field from the surroundings is much larger in the second magnetic layer than in the first magnetic layer. When moving away from the beam irradiation and being cooled, the lower temperature peripheral portion is cooled first and magnetization occurs along the demagnetizing field of the second magnetic layer. (state 7
) At this time, a new demagnetizing field in the opposite direction is generated from the part newly magnetized by cooling to the part above the Curie point. As cooling progresses further, the center, which had previously been above the Curie point, becomes magnetized in a direction aligned with a new, oppositely directed demagnetizing field. (State 8) Furthermore, while the disk rotates once, the second magnetic layer is magnetized by the first magnetic field applying means, resulting in state 9.

Next time, if the same track is irradiated with low power, state 3
If irradiation is performed with high power, the state moves to state 6.

Therefore, when reproducing a domain recorded with light modulated with high power and low power, the pattern in which states 5 and 9 repeat depending on the recorded information.

Note that in state 7, the strength of the newly generated demagnetizing field may be insufficient to fix the magnetization in the center. At that time, it is also effective to provide a second magnetic field applying means for applying an auxiliary magnetic field in a direction that helps the newly generated demagnetizing field, that is, in the same direction as the first magnetic field applying means.

However, the magnetic field applied thereby must be smaller than the strength of the demagnetizing field in state 3. Further, the second magnetic field applying means can also utilize the leakage magnetic field of the optical head pickup.

Note that if the Curie point of the first magnetic layer is smaller than the Curie point of the second magnetic layer, the peripheral area heated above the Curie point will be magnetized in the opposite direction during both low power recording and high power recording. An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a magneto-optical disk of the present invention. From the light input side, board 1
1. Dielectric film 12. First magnetic layer 13. second magnetic layer 1
It is configured in the order of 4. As the substrate 11, a glass substrate with track guide grooves formed by a photopolymer method was used. Note that the track pitch is 2.5 μm.

The dielectric film 12 is made of 760 ZnS. The first magnetic layer 13 is made of CdTbFeCo,
The film thickness is 400 mm, the coercive force is 15 koe or more, and the Curie point is 240°C. Further, the second magnetic layer 14 has T
It is made of bFeCo, has a film thickness of 800 mm, a coercive force of 2 to 3 koe, and a Curie point of 250°C, and is rich in transition metals from room temperature to the Curie point.

Embodiment 2 An embodiment of the magneto-optical disk recording and reproducing apparatus shown in Embodiment 1 is shown in FIG. A first magnetic field applying means 23 is provided on the magneto-optical disk 21 at a location different from the optical head 22 for both recording and reproduction, and a second magnetic field applying means 24 is provided at a position facing the optical head 22 with the disk interposed therebetween. It is made up of.

The first magnetic field applying means 23 is made of a Sa+Co permanent magnet and applies a magnetic field of 3 koe to the magnetic thin film.

Further, the second magnetic field applying means 24 is similar to the first magnetic field applying means 2.
A magnetic field of 400 koe is applied in the same direction to the magnetic thin film.

Example 3 The magneto-optical disk shown in Example 1 was magnetized in advance by strobe irradiation from the substrate side in a magnetic field of 5 koe, so that the first magnetic layer was magnetized so that the substrate side was the north pole. Thereafter, the disc was heated to 90 Orpm using the recording and reproducing apparatus shown in the example.
The signal frequency IMHz was recorded at a high power of 10 mW and a low power of 5 mW.

After that, as a result of reproduction with a reproduction power of 3.0 mW, C/
N 45dB was obtained.

Example 4 After carrying out Example 3, the signal frequency was changed to 1.2 MHz without subsequently going through the so-called erasure process.
Recording was performed in the same manner as in Example 4. Thereafter, as a result of similar reproduction, C/845 dB was obtained. Also IM
No trace of Hz was observed.

Example 5 The same recording and reproducing apparatus as in Example 2 and the same magneto-optical disk as in Example 1 were used, except that the second magnetic field applying means was not provided, and the same recording and reproducing as in Example 3 was carried out. As a result, a C/N of 35 dB was obtained.

Furthermore, as a result of recording in the same manner as in Example 4, it was found that C/
While obtaining an N of 35 dB, no residual IMHz signal was observed.

In this embodiment, a permanent magnet is attached to the recording and reproducing apparatus as the magnetic field applying means, but a method of attaching it to the cartridge case of the disk is also possible.

Effects of the Invention As described above, by using a photothermal magnetic recording medium according to the structure of the present invention and a recording/reproducing device for recording and reproducing the same, two different powers can be switched to bring the temperature of the magnetic film to the Curie point or higher. By recording with , it becomes possible to overwrite previously recorded information without erasing it. Furthermore, the present invention can be applied to a laminated disk, and if the second magnetic field is omitted or the leakage magnetic field from the optical head is used, the side opposite to the optical head with the photothermal magnetic recording medium in between can be used. There is also the advantage that there is no need to arrange anything at the same time, and the recording/reproducing device can be made thinner.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a photothermal magnetic recording medium in the present invention,
FIG. 2 is a block diagram of a recording apparatus for the photothermal magnetic recording medium. 11...Substrate, 12...Dielectric film, 1
3...First magnetic layer, 14...Second magnetic layer, 21...Magneto-optical disk, 22...
...Optical head, 23...First magnetic field applying means, 24...Second magnetic field applying means.

Claims (6)

[Claims] (1) Consisting of two magnetic layers each having a perpendicular easy axis of magnetization, a first magnetic layer and a second magnetic layer are formed in order from the light incident surface, [1] Storage of the first magnetic layer at room temperature The magnetic force is larger than the coercive force of the second magnetic layer at room temperature [2] The Curie point of the first magnetic layer is equal to or larger than the Curie point of the second magnetic layer. The magnetization direction of the magnetic layer does not change in the temperature range from room temperature to the Curie point [4] When irradiating the recording light beam, the recording region of the first magnetic layer
The magnitude of the demagnetizing field induced by the second magnetic layer is
A photothermal magnetic recording medium characterized in that the magnitude of the demagnetizing field induced by the magnetic layer is larger than that of the magnetic layer. (2) The photothermal magnetic recording medium according to claim 1, further comprising means for applying a first magnetic field to a portion other than the laser irradiated portion during recording, and the means for applying the first magnetic field causes the photothermal The magnetic field applied to the magnetic recording medium is [1] smaller than the coercive force at room temperature of the first magnetic layer described in item 1, and [2] larger than the coercive force at room temperature of the second magnetic layer described in item 1. A recording device for a photothermal magnetic recording medium, characterized in that: (3) In addition to the means for applying the first magnetic field according to claim 2, the method further comprises means for applying a second magnetic field to the laser irradiated area during recording, and the means for applying the second magnetic field as claimed in claim 2. The magnetic field applied to the photothermal magnetic recording medium according to claim 1 is [1] in the same direction as the magnetic field applied to the photothermal magnetic recording medium by means for applying a first magnetic field, and [2] according to claim 1. A recording device for a photothermal magnetic recording medium, characterized in that the coercive force of the second magnetic layer is smaller than that at room temperature. (4) The photothermal magnetic recording according to item 1, wherein the first magnetic layer is initially magnetized in a direction opposite to the magnetic field applied by the means for applying the first magnetic field described in item 2. Medium. (5) By using the photothermal magnetic recording medium described in item 1 and the recording device described in item 2, by switching two different powers to make both the first magnetic layer and the second magnetic layer equal to or higher than the Curie point. , a photothermal magnetic recording method characterized by recording. (6) By using the photothermal magnetic recording medium described in item 1 and the recording device described in item 3, by switching two different powers to make both the first magnetic layer and the second magnetic layer equal to or higher than the Curie point. , a photothermal magnetic recording method characterized by recording.