JPH0245248B2 - - Google Patents

Description

[Detailed Description of the Invention] The purpose of the present invention is to read out information recorded at high density on a magnetic material such as a magnetic tape or a magnetic disk by a method such as magneto-optical recording, using a simple method and with high precision. shall be.

Conventionally, magnetic heads have been used as a method for recording information on magnetic tapes and magnetic disks.

In order to increase the recording density using a magnetic head recording method, it is necessary to narrow the head gap, narrow the track width, and bring the head and magnetic material closer together.

However, narrowing the head gap or narrowing the track width will reduce the output and make tracking during playback difficult, and in order to bring the head and magnetic material closer together, it is necessary to protect the surface of the magnetic material. Due to the thickness of the membrane, it is not possible to get very close to it. Therefore, there was a limit to increasing the recording density using a recording method using a magnetic head.

Therefore, a magneto-optical recording method has been proposed as a method for recording information in a magnetic material at high density.
(NHK Giken Monthly Report June 1973, May 1974) The magneto-optical recording method raises the temperature of a magnetic material to around the Curie temperature in a weak magnetic field, then lowers the temperature. Recording is performed using an effect called thermoremanent magnetization, in which the magnet becomes more and more strongly magnetized as the magnetic field decreases, and the strength of magnetization increases to the extent that it can be magnetized by a strong magnetic field at room temperature. It is something.

An example of the above-mentioned proposed magneto-optical recording system is shown in FIG.

In Figure 1, 1 is a magnetic tape, 2 is a magnetic material layer, 3 is a base layer, 4 is a magnetic head, 5 is a laser beam, 6 is a converging lens, 7 is a spot where the laser beam hits the magnetic material, and 8 is a recording The arrow indicates the tape running direction.

A method of recording using the method shown in FIG. 1 will be explained.

First, a minute region (spot 7) on the magnetic material is heated by the laser beam 5 to raise the temperature to near the Curie temperature. When the spot passes through this minute area and its temperature drops, it is magnetized by the weak magnetic field applied from the magnetic head 4. Therefore, while applying a magnetic field change according to the recorded information from the magnetic head 4, that part is exposed to the laser beam 5.
By heating with and running tape 1,
Information is recorded on track 8.

According to this method, since the information recording density is determined by the diameter of the laser beam spot 7,
Extremely high-density recording becomes possible.

Next, a method for reading out the information magneto-optically recorded as described above will be explained.

In the case of reading as well, a method using a magnetic head is inappropriate due to the problem of the distance between the head and the magnetic material as described above.

Therefore, a reading method using the magnetic force effect is usually used.

The magnetic force effect is a phenomenon in which when linearly polarized light is applied to a magnetized magnetic material, the plane of polarization of the reflected light (or transmitted light) rotates in proportion to the strength of magnetization. An example of this method is shown in FIG.

In FIG. 2, 9 is a magnetic material, 10 is a laser light source, 11 is a polarizer, 12 is a polarization plane of incident light, and 1
3 is a polarization plane of reflected light, 14 is an analyzer, and 15 is a photodetector.

In the configuration shown in FIG. 2, the polarizer 11 sets the plane of polarization of the magnetic field of the incident light to be perpendicular to the direction of magnetization of the magnetic body 9, and the analyzer 14
If the setting is made so that a small amount of reflected light enters the photodetector 15 when the magnetic body 9 is not magnetized, the amount of light entering the photodetector 15 will depend on the rotation angle of the polarization plane 13 of the reflected light. The information recorded on the magnetic material 9 can be read out.

However, since the rotation angle of the plane of polarization due to this magnetic force effect is very small, the signal-to-noise ratio is extremely poor due to disturbances such as unevenness on the magnetic surface, scratches, and dust, making it difficult to read out high-quality data. is quite difficult.

It is advantageous for the magnetic material used in magneto-optical recording to absorb laser beams well, since it is easier to record even with weak laser beams. However, if this is to be read out by the effect of magnetic force, it is desirable to use a magnetic material with high reflectance or transmittance.

Therefore, when reading information using the magnetic force effect, a method is generally used in which recorded information is first transferred to a magnetic material with high reflectance or transmittance, and then read out.

However, the method that requires this transfer procedure is complicated and time-consuming, so it has the problem that it is difficult to read out immediately after recording.

In addition, when recording is performed at a very high density, the lines of magnetic force are closed between adjacent minute magnetized areas, and only a few lines of magnetic force come out from the magnetic material, making transfer difficult and making reading difficult. become unable. Therefore, with this method, there is a limit to increasing the recording density.

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a magneto-optical recording and reproducing apparatus which has a simple configuration and is capable of reading out information recorded magneto-optically at high density.

As mentioned above, magnetic materials have the property that their residual magnetization changes with temperature. This situation is shown in FIG.

In FIG. 3, T _a is the room temperature, T _b is the temperature after heating, T _c is the Curie temperature, M _a is the residual magnetization at room temperature T _a , and M _b is the residual magnetization at the temperature T _b after heating.

As shown in FIG. 3, residual magnetization decreases with increasing temperature. The present invention makes use of this property by irradiating the residual magnetization recorded on the magnetic material with a laser beam and heating it from, for example, T _a to T _b .
It attempts to read information by changing M _a to M _b and detecting the change with a magnetic head.

As an example of a reading device based on the above principle, the magneto-optical recording device shown in FIG. 1 can be used as is.

When what was recorded with the device shown in FIG. 1 is traced again with the same device, the recorded minute magnetized region is heated by the laser beam spot 7, and the strength of its magnetization decreases rapidly. If the change is detected by the magnetic head 4 and processed by the detection circuit, the recorded information can be read.

In this method, the reading area is determined by the size of the laser beam spot, so it is possible to read even if the gap of the magnetic head is wide. Also, the change in magnetization strength caused by heating by the laser beam is not affected by the magnetization of other parts, so the magnetic head and magnetic body do not need to be as close as when reading with the magnetic head alone. Therefore, there is an advantage that it can be used even if the magnetic material has a protective film on its surface.

In addition, in this method, the laser beam is used to heat the magnetic material both during recording and reproduction, so the magnetic material only needs to have a low reflectance.
From this point of view as well, there is an advantage that the magnetic materials used in ordinary magnetic tapes and magnetic disks can be used as they are.

In the configuration shown in Figure 1, when reproducing what was recorded magneto-optically using the same configuration, the magnetization strength of the part irradiated with the laser beam suddenly decreases, so the information in that part is read by the magnetic head. However,
Information from areas not irradiated by the laser beam also crosses the gap of the magnetic head, so it is also detected to some extent by the magnetic head. Since this information is an unnecessary component, it becomes noise and has the problem of deteriorating the S/N ratio. Regarding this noise component, especially when the recording density is high, the level detected by the magnetic head will be quite low due to the magnetic lines of force canceling each other out and the distance between the magnetic head and the magnetic material. It cannot be ignored.

FIG. 4 shows an embodiment of the present invention that improves the above problem.

Note that when reproducing data using the data shown in Fig. 4, recording is performed using the data shown in Fig. 4. The one shown in Fig. 4 has the gap direction of the magnetic head 4 rotated by 90 degrees compared to the one shown in Fig. 1, and is set parallel to the running direction (arrow) of the magnetic body 1. 8 corresponds to the same numbered part in Fig. 1, and the magnetization information I recorded on the magnetic tape 1 is recorded by the signal component S recorded by irradiating the laser beam and the part not irradiated by the laser beam. It contains a noise component N.

In the example shown in Figure 1, as shown in Figure 1B, during reading, the entire width of the magnetic head traverses the magnetized object, so the reading magnetization change is large, and therefore the noise component N is large. .

In the example shown in FIG. 4, the noise component N is It is smaller than the one in Figure 1.

That is, when reproducing magnetization information using a magnetic head having a gap length g and a head width w (g<w) as shown in FIGS. 1B and 4B, the magnetization information in the portion not hit by the laser beam is is a kind of noise component N, but in the case of Fig. 1B, the gap length is horizontal to the tape running direction, whereas in Fig. 4B, it is perpendicular to the tape running direction.
In the case of
In the case of FIG. 4B, the gap is crossed slowly over a relatively long time (w/v).

Therefore, the electromotive force V induced in the magnetic head by the noise component N is given by Faraday's law of electromagnetic induction; V=-ndφ/dt (Number of coil turns: n, magnetic flux density: B, cross-sectional area of the coil: S, magnetic flux :φ=BS), the electromotive force _V2 generated by the noise component N in FIG. 4B is proportional to the magnetic flux change dφ/dt per unit time at the end of the magnetic head 4, while Electromotive force generated by noise component N at B
V ₁ is proportional to the change in magnetic flux dφ/dt per unit time over the entire head width W of the magnetic head 4. Here, dφ/dt in FIG. 4B is much smaller than dφ/dt in FIG. 1B, and therefore V ₂ <V ₁ . Other,
The electromotive force V ₁ due to the noise component N in Figure 1B and the fourth
The electromotive force V ₂ due to the noise component N in Figure B is: V ₁ =-ndφ/d(g/v) =-n/g・dφ/d(1/v) V ₂ =-ndφ/d(w/v ) =-n/w·dφ/d(1/v) (<V ₁ ) (gap length: g, head width: w, tape running speed: v).

Therefore, from the above, the electromotive force due to the noise component is larger in Figure 1B than in Figure 4B, and the S/N, which is the ratio of the signal component S to the noise component N, is as shown in Figure 4. B is better.

Also, as is clear from the figure, as mentioned above, in Figure 4, the information that is not irradiated with the laser beam does not cross the magnetic gap, but only passes parallel to it, so it is hardly detected. What occurs is only a slight magnetic change at the introduction part to the magnetization information of the magnetic head, and the electromotive force due to the noise component N is considerably lower than that in Figure 1B.
Therefore, the S/N ratio is also good from this point of view.

The device shown in Fig. 4 uses a gap of the magnetic head to reduce the noise caused by using the magnetic head to continue the part that is not irradiated with the laser beam in order to improve the S/N ratio. The direction is parallel to the running direction of the tape.

However, even with the configuration shown in Figure 4, the portions that are not irradiated with the laser beam as described above are
When it reaches the end of the gap of the magnetic head 4, it is detected as a noise component, albeit slightly. Therefore, as shown in Figure 5, the shape of the gap in the magnetic head is narrower in the center and wider toward the ends, or the center of the gap is closer to the magnetic material and the ends are narrower. The above noise component can be reduced by moving the distance away as the distance increases.

Furthermore, the rate of change of the noise component detected when it passes through the magnetic head is slower than the rate of change of the signal component detected when it is rapidly heated by the laser spot. That is, the frequency of the noise component is considerably lower than the frequency of the signal component. Therefore, if the signal detected by the magnetic head is extracted through a high-pass or band-pass filter and the low-frequency components are removed,
Further, the S/N ratio can be improved. In particular, when the gap direction of the magnetic head is parallel to the traveling direction of the magnetic material, the difference in frequency between the noise component and the signal component becomes large, so the S/N ratio improvement effect by removing the low frequency component is remarkable.

In the reading device shown in FIGS. 1 and 2,
Although changes in magnetization strength are detected by a magnetic head, this may also be detected by a Hall element. Even in this case, if the direction of maximum sensitivity for detecting lines of magnetic force of the Hall element is set to be perpendicular to the running direction of the magnetic body, the S/N will be advantageous, corresponding to FIG.

Although the above description has been made using a magnetic tape as an example of the magnetic material, the present invention is also effective even when the magnetic tape is used as a magnetic disk or a magnetic card.

In the case of a magnetic disk, the magnetic body rotates, and the optical system and magnetic head move in the radial direction of the magnetic body to select a recording track.

In addition, in the case of a magnetic card, fix the magnetic material,
The optical system and magnetic head may be moved to trace on the magnetic card.

By the way, a magnetic material is irradiated with a laser spot and heated, but after the laser spot passes,
Needs rapid cooling. However, for example, the fourth
In the case of the configuration shown in the figure, even after the laser spot has passed, the magnetic material remains between the gaps of the magnetic head and is not in contact with the magnetic head, making it difficult for heat to escape and resulting in incomplete cooling. There is a worry.

Therefore, in order to immediately dissipate the heat of the magnetic material after the laser spot has passed, it is effective to insert a heat dissipating non-magnetic material into the gap portion of the magnetic head.

In the reading device shown in FIGS. 1 and 4,
Apply the magnetic head to the magnetic material from one side,
Although the laser beam is irradiated from the other side, depending on the thickness and structure of the magnetic material, it may be more convenient to irradiate the magnetic head and the laser beam from the same side of the magnetic material.

In such a case, as shown in Fig. 6, a reflecting mirror or prism is installed inside the magnetic head, and the laser beam is reflected there and passed through the gap of the magnetic head to irradiate the magnetic material with the laser beam. Just do it. In FIG. 6, numeral 16 is a prism for reflecting the laser beam, which also serves as the heat dissipation function described above. Furthermore, when a laser beam is irradiated through the gap of the magnetic head, since the laser beam is reflected from the inner surface of the gap, it is easy to converge the laser beam so that it does not spread beyond the gap width.

By the way, the reading method according to the present invention detects changes in residual magnetization by applying a laser beam to a magnetic material and raising its temperature during reading. When exceeds the Curie temperature,
Since the recorded information is erased, it can only be read once.

Therefore, in order to be able to read out the information many times, it is necessary to control the temperature of the magnetic material so that it does not exceed the Curie temperature due to heating during reading.

However, it is difficult to directly and immediately detect the temperature of a minute region of a magnetic material irradiated with a laser beam. Therefore, for example, there is a method of predicting the temperature rise of the magnetic material due to laser beam irradiation based on the ambient temperature, the average temperature of the magnetic material, the moving speed of the magnetic material, etc., and controlling the output of the laser light source accordingly. is valid.

Furthermore, as can be seen from the relationship between residual magnetization and temperature shown in Figure 3, the larger the difference between room temperature T _a and temperature T _b after rising, the larger the change in residual magnetization M _a −M _b . Therefore, control can also be achieved by controlling the output of the laser light source so that the above change, that is, the signal level detected by the magnetic head does not exceed a certain value.

Note that since the reading device according to the present invention is structurally the same as a device that performs magneto-optical recording, it has the great advantage that the device can be used in common for recording and reproducing.

Also, compared to the method using magnetic force-effect,
It has the advantage of being low cost because it does not require a polarizer, analyzer, or photodetector, and since it does not require transfer, it can be played back immediately after recording, and the magnetic material is the same as that normally used. It has the advantage that it can be used. The biggest advantage is that since no transfer is required, the recording density can be increased to the limit determined by the spot diameter of the laser beam.

As described above, according to the present invention, the device is simple and
It can be used for both recording and reproduction, does not require transfer, and because the magnetic field detection means is placed in a position facing the minute area that is currently being heated, reproduction can be performed immediately after recording, and the recording density can be improved. It can be expected to have excellent effects such as being able to increase the magnetic field to its limit and also allowing the use of ordinary magnetic materials.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an example of a conventional magneto-optical recording device and a line diagram explaining its operation, Fig. 2 is a diagram of the principle of readout using the conventional magnetic force effect, and Fig. 3 is a diagram showing the temperature of the magnetic material. Fig. 4 is a perspective view of a magneto-optical recording/reproducing device according to an embodiment of the present invention and a line diagram explaining its operation; Figs. 5 and 6 are diagrams showing the structure of a magnetic head used in the present invention. It is a diagram. 1...Magnetic material, 4...Magnetic field line detection means (magnetic head), 5...Laser beam, 7...Minute region,
16... Prism (non-magnetic material for heat radiation).

Claims (1)

[Scope of Claims] 1. Laser beam irradiation means for heating a minute region of a magnetic material with a laser beam, and a change in residual magnetization that occurs in this minute region, which is placed at a position facing the minute region that is currently being heated. a magnetic field line detecting means comprising a magnetic head for detecting the magnetic field line, and a moving means for moving the magnetic body relative to the laser beam irradiation means and the magnetic field line detecting means, and a gap of the magnetic head. A magneto-optical recording/reproducing apparatus characterized in that the direction of the magnetic material is set to be substantially parallel to the direction of movement of the magnetic body with respect to the magnetic head. 2. A magneto-optical recording and reproducing device according to claim 1, characterized in that the gap of the magnetic head is constructed such that the gap is narrow at the center and widens toward the ends. 3. The magneto-optical recording and reproducing device according to claim 1, characterized in that the gap of the magnetic head has a structure in which a central portion is close to the magnetic material and the gap becomes farther away from the magnetic material toward the end portions. Device. 4. The magneto-optical recording and reproducing apparatus according to claim 1, wherein the magnetic force line detection means is comprised of a Hall element. 5. The magneto-optical recording according to claim 4, characterized in that the maximum sensitivity direction of the magnetic field line detection of the Hall element is set to be approximately perpendicular to the direction of movement of the magnetic body with respect to the Hall element. playback device. 6. A magneto-optical recording and reproducing apparatus according to claim 1, characterized in that the magnetic body is composed of a tape, and the moving means is composed of the above-mentioned tape running means. 7. In claim 1, the magnetic body is composed of a disk, and the moving means includes rotating means for the disk, and tracking means for moving the laser beam irradiation means and the magnetic field line detection means in the radial direction of the disk. 1. A magneto-optical recording and reproducing device comprising: 8. Magneto-optical recording and reproducing according to claim 1, characterized in that part or all of the laser beam irradiation means, the magnetic field line detection means, and the moving means are shared with recording components. Device. 9. The magneto-optical recording and reproducing device according to claim 1, characterized in that a non-magnetic material for heat radiation is inserted into the gap of the magnetic head. 10. A magneto-optical recording and reproducing apparatus according to claim 1, characterized in that a laser beam is irradiated onto the magnetic material from inside a magnetic head through a gap. 11. The magneto-optical recording and reproducing apparatus according to claim 10, characterized in that the laser beam is converged by utilizing reflection on the inner surface of the gap of the magnetic head. 12. The magneto-optical recording and reproducing apparatus according to claim 10, characterized in that a transparent material for heat radiation or laser beam focusing is inserted into the gap of the magnetic head. 13. The magneto-optical recording and reproducing apparatus according to claim 10, characterized in that a reflecting mirror or a prism for reflecting a laser beam is provided inside the magnetic head. 14 In claim 1, so that the temperature of a minute region of the magnetic material does not exceed the Curie temperature due to heating by laser beam irradiation,
1. A magneto-optical recording/reproducing device characterized in that the output of a laser light source in a laser irradiation means is controlled. 15. A magneto-optical recording and reproducing apparatus as set forth in claim 14, characterized in that the output of the laser light source is controlled by the temperature of the magnetic material or the ambient temperature. 16. The magneto-optical recording and reproducing apparatus according to claim 14, wherein the output of the laser light source is controlled in accordance with the relative movement speed of the magnetic body with respect to the laser beam irradiation means and the magnetic field line detection means. 17. The magneto-optical recording and reproducing apparatus according to claim 14, wherein the output of the laser light source is controlled based on the detected amount of change in residual magnetization. 18. The magneto-optical recording and reproducing apparatus according to claim 1, wherein the signal detected by the magnetic line of force detection means is passed through a high-pass or band-pass filter to remove low-frequency components.