JPH07220316A - Magneto-optical recording/reproducing method - Google Patents

Abstract

PURPOSE:To compactly record and to stably store an extremely large amount of information and also to rewrite these information any number of times by initializing or erasing a tape type recording medium by the external magnetic field of a permanent magnet or an electromagnet having no contact with the recording medium. CONSTITUTION:A magneto-optical tape 1 is initialized or erased by an external magnetic field 3 which is generated in the direction orthogonal to the tape 1 by a permanent magnet (electromagnet) 2 placed at a position ahead of an optical head and having no contact with the tape 1. As the tape 1 has no revolving action unlike a magneto-optical disk, it is difficult to erase and record the information by the same optical head like a disk. Therefore, it is most rational to initialize or erase the tape 1 at a position ahead of the optical head against the tape running direction and by means of only a magnetic field. Furthermore it is desirable to impress the magnetic field to the entire width of the tape 1 for its initialization or erasion in reference to simplification of the device constitution. Then a permanent magnet is also preferable in regard of the power consumption.

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 / reproducing method, and more particularly to a magneto-optical recording / reproducing method with improved initialization or erasing of a tape-shaped recording medium.

[0002]

2. Description of the Related Art With the increase in the amount of information in recent years, there is a demand for an information recording / reproducing system capable of compactly recording an enormous amount of documents, images and sounds and stably storing it. Magneto-optical recording has a characteristic that the recording capacity per unit area, that is, the areal recording density is high because recording and reproducing are performed by using light of about 1 μm.

A conventional recording medium (magneto-optical disk) used for magneto-optical recording has an advantage that a recording signal can be randomly accessed. Further, in the conventional magneto-optical recording, since the magnetic layer is irradiated with light through a transparent substrate having a thickness of about 1.2 mm, dust and scratches on the light incident surface of the substrate are less likely to cause an error. is doing.

However, since the magneto-optical disk has a relatively thick substrate of 1.2 mm, the recording capacity per unit volume (volume recording density) is not high. Even if the substrate is thinned to increase the volume recording density, a cartridge for handling cannot be extremely thin as long as it has a disk shape, and thus a dramatic improvement in the volume recording density cannot be expected.

On the other hand, in the case of a magnetic tape, the volume recording density can be increased due to the structural characteristics that the substrate is thin and can be stacked in a cartridge. In fact, magnetic tape is applied to digital video and the like. However, since the areal recording density is not as high as that of the optical disc, the storage capacity cannot be said to be sufficiently high. Further, the magnetic tape has a smaller coercive force of the medium and a larger saturation magnetization as compared with the magneto-optical disk. Therefore, when the magnetic tape is stored in a wound state for a long time, the transfer of the recording occurs and the recording signal deteriorates. There is.

A write-once type magneto-optical tape has been put into practical use as a recording medium having both the high areal recording density of a magneto-optical disk and the high volume recording density of a magnetic tape. The write-once type magneto-optical tape has a very high recording density and excellent storage stability. However, only additional writing is possible, and it is impossible to rewrite unnecessary information. Therefore, if the information becomes useless, the recording medium itself becomes useless, and there is a problem not only in terms of cost but also in terms of waste.

[0007]

DISCLOSURE OF THE INVENTION An object of the present invention is to enable enormous information to be compactly recorded and stably stored,
It is to provide a recording / reproducing system having a characteristic that it can be rewritten any number of times. The present inventors have formed a magneto-optical recording layer used in a magneto-optical disk on a tape-shaped substrate and irradiating it with light to perform recording / reproduction system of a magneto-optical tape. The idea was that the above objective could be easily achieved if

Incidentally, there are roughly two types of recording methods for magneto-optical recording. One is an optical modulation method in which the magnetization direction of the medium is aligned in one direction in advance, and recording is performed by irradiation intensity modulation of light while applying a recording bias magnetic field in the opposite direction. The other one is a magnetic field modulation method in which recording is performed by modulating the direction of the recording magnetic field rather than the intensity of light.

In the magnetic field modulation method, since it is necessary to switch the magnetic field at high speed, it is necessary to make the magnetic head for generating the magnetic field small and bring it close to the medium. However, in the case of a magneto-optical tape, unlike the case of a magneto-optical disk, since the medium moves relatively slowly, it is necessary to move the recording head at a high speed. It is difficult to put the recording method requiring high-speed access into practical use.

Therefore, optical modulation must be considered as a recording system of the magneto-optical tape. In the case of the light modulation method, a process of aligning the magnetization of the medium in one direction before recording, that is, erasing or initializing is necessary. In a magneto-optical disk, erasing is performed by continuously irradiating light while applying a magnetic field in the direction opposite to the recording bias magnetic field.

In the case of a magneto-optical tape, erasing is possible in principle like the magneto-optical disk, but in reality, when erasing and recording immediately, it is necessary to move the tape at a high speed. Difficult to do. Therefore, in order to realize the magneto-optical tape recording / reproducing system, it is necessary to find a method for erasing the magneto-optical tape.

[0012]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied to provide an information recording / reproducing system which has a very high volume recording density and is capable of repeating recording on a medium. It has also been found that an excellent magneto-optical recording / reproducing system can be provided by erasing by a special method.

That is, the gist of the present invention is that, when information is recorded / reproduced by irradiating the magneto-optical recording layer of a running tape-shaped recording medium with light from an optical head, the direction of running of the tape-shaped recording medium is changed. The tape-shaped recording medium is initialized or erased by an external magnetic field generated by a permanent magnet or an electromagnet that is placed in front of the optical head in a non-contact state with the tape-shaped recording medium, and then the optical head is used for recording and reproduction. The present invention resides in a magneto-optical recording / reproducing method.

The present invention will be described in detail below. The tape-shaped magneto-optical recording medium (hereinafter abbreviated as magneto-optical tape) used in the present invention has at least a magneto-optical recording layer on a substrate. The thickness of the substrate cannot be extremely thin so that the medium is not stretched by the tension applied when the tape is wound, but it is 50 μm in order to increase the volume recording density.
The following is preferable, 20 μm or less is more preferable, 1 μm
The range of up to 20 μm is particularly preferred.

In the magneto-optical tape used in the present invention, since the recording layer is heated to about 200 ° C. by the recording light beam during recording, it is desirable that the substrate has a heat resistance of at least about 100 ° C. As such a substrate,
Examples thereof include polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) films.

The substrate film may be either a single layer or a multilayer, but the tensile strength F at 5% elongation in the machine direction is F.
₅ is preferably 6 kg / mm ² or more, and 8 kg / mm ²
The above is more preferable, and 10 Kg / mm ² or more is particularly preferable. When F _{5 in} the longitudinal direction of the base film is less than 6 kg / mm ² , workability in producing a magneto-optical tape and characteristics as a magneto-optical tape tend to be poor.

The thermal shrinkage in the longitudinal direction of the substrate film after treatment at 100 ° C. for 30 minutes is preferably 5% or less, more preferably 3% or less, and particularly preferably 2% or less. If the heat shrinkage in the longitudinal direction of the substrate film exceeds 5%, the heat resistance tends to be insufficient, which may adversely affect the characteristics of the magneto-optical tape.

The surface of the substrate film on which the recording layer is provided is preferably flat, and its center line average roughness (R
a) is preferably 0.005 μm or less, and 0.003 μm
m or less is more preferable, and 0.002 μm or less is particularly preferable. When the center line average roughness exceeds 0.005 μm, the characteristics as a magneto-optical tape tend to be poor.

On the other hand, the center line average roughness of the surface (rear surface) opposite to the surface on which the recording layer is provided is 0.005 to 0.3 μm.
Is preferable, 0.007 to 0.05 μm is more preferable, and 0.008 to 0.02 μm is particularly preferable. When the center line average roughness of the back surface of the substrate is less than 0.005 μm,
The slipperiness of the substrate film tends to be poor, and the workability in manufacturing the magneto-optical tape and the characteristics as the magneto-optical tape tend to be poor.

The F ₅ value is 50 mm in length and 15 mm in width in a room adjusted to a temperature of 25 ° C. and a humidity of 50% RH using a tensile tester “Intesco Model 2001” manufactured by Intesco Corporation. Sample film of 50 mm / m
It is a value when pulled at a speed of in and extended by 5%.

The value of the above-mentioned heat shrinkage ratio was measured by using a hot air circulation furnace manufactured by Tabai Seisakusho Co., Ltd.
It is a value obtained as a dimensional change in the vertical direction before and after the treatment after heat treatment for 30 minutes.

The above center line average roughness (Ra) is
Using a surface roughness measuring instrument "SF-3F" manufactured by Kosaka Laboratory, 10 cross-section curves were obtained from the surface of the sample film, and extracted portions (reference length 2.5 m
m) is the value obtained as the average value of the center line average roughness (the tip radius of the stylus is 2 μm, the load is 30 mmg,
The cutoff value was 0.08 mm).

Since the base film is produced by the stretching method, birefringence occurs. Then, when light is incident through such a base material, the quality of the magneto-optical effect deteriorates. Therefore, in the present invention, it is preferable that the irradiation of light at the time of reproduction (reading) is performed not through the substrate but by irradiation with light from the magneto-optical recording layer side.

The magneto-optical recording layer of the magneto-optical tape used in the present invention plays a role of storing a signal by thermomagnetic recording using light and reproducing the signal by a magneto-optical effect. In order to enable thermomagnetic recording, the coercive force of the magneto-optical recording layer at high temperature is required to be sufficiently smaller than the coercive force near room temperature. Further, in order to perform reproduction by the magneto-optical effect, it is required that the magneto-optical effect of the magneto-optical recording layer, specifically, the Kerr rotation angle or the Faraday rotation angle is large.

Examples of the magnetic material for the magneto-optical recording layer which satisfies the above conditions include amorphous alloys of rare earths and transition metals. The thickness of the magneto-optical recording layer is usually 5-100.
selected from the nm range. In addition to the magneto-optical recording layer, a light interference layer made of a dielectric material and a light reflection layer made of a metal may be provided on the substrate in order to enhance the magneto-optical effect. Usually, the thickness of the light interference layer is 20 to 300 nm, and the thickness of the light reflection layer is selected from the range of 10 to 100 nm. Furthermore, a protective layer may be provided to protect the thin film from the environment and mechanical shock. The protective layer is usually made of a UV curable resin or a fluorine-based resin and has a thickness of 10 μm or less,
The refractive index is 1.1 to 1.7, and the center line average roughness is 10 nm or less, preferably 5 nm or less. The coercive force of the magneto-optical recording layer is preferably in the range of 40 to 640 kA / m.

The magneto-optical tape having the above structure has
JP-A-56-84921, JP-A-3-53924,
Concavities and convexities for signals are formed according to known methods described in JP-A-5-159384 and JP-A-6-12707. . As a method to obtain such a signal,
There is a method of utilizing the phase difference of the laser beam due to the unevenness formed by the transfer of the concave-convex roll during the film formation of the base film and existing at the position corresponding to the track groove portion on the base film. Examples of the type of signal include a magnetic signal, a magneto-optical signal, an optical signal (a signal using a reflectance difference), and an electric signal. As a method for obtaining a signal using the reflectance difference, there is a method of utilizing transformation of a crystal or the like by laser beam irradiation.

The above signal on the entire surface of the magneto-optical tape is
It is used as a track signal of a laser beam, and the signals at both ends are used as an address signal or a traveling speed control signal. The traveling speed control signal is generated by, for example, fine unevenness signals provided at equal intervals in the longitudinal direction in the range of several μm to several hundreds μm on both end portions of the magneto-optical tape.

In the present invention, when recording information, erasing is necessary in advance so that the magnetization directions of the magneto-optical tape are aligned in one direction. In the case of the conventional magneto-optical disk or magneto-optical tape, this erasing is performed by both light and magnetic field, but in the present invention, it is performed only by the magnetic field. That is, the magneto-optical tape is erased by an external magnetic field generated from a permanent magnet or an electromagnet arranged in a non-contact state with the magneto-optical tape while the magneto-optical tape is running. Also,
Initialization can be performed similarly.

FIG. 1 is an illustration of an example of the initialization or erasing method according to the present invention, and FIG. 2 is an illustration of an example of a magnetic head used in the initialization or erasing method according to the present invention.
FIG. 3 is an explanatory diagram of another example of the magnetic head used in the initialization or erasing method of the present invention.

In the present invention, the initialization or erasure of the magneto-optical tape is performed by using a permanent magnet (or electromagnet) (2) arranged in a position in front of the optical head in a non-contact state with the magneto-optical tape (1). It is performed by an external magnetic field (3) generated in a direction perpendicular to the magnetic tape (1). In the non-contact state, the distance between the running magneto-optical tape (1) and the permanent magnet (or electromagnet) (2) is usually 0.01 to 20 m.
It means in the range of m.

In the case of a magneto-optical disk, since the disk rotates on a certain orbit, erasing only with the magnetic field will erase even the signal just recorded, so erasing with only the magnetic field is impossible. is there. However, in the case of a magneto-optical tape, since the tape moves linearly, even if erasing is performed only by the magnetic field at a position before the recording optical head, the recorded portion does not return to the position of the erasing head again. Absent. Conversely, in the case of a magneto-optical tape, since it does not rotate, it is difficult to perform erasing and recording with the same optical head like a magneto-optical disk.

For the above reasons, it is most rational to initialize or erase the magneto-optical tape only by the magnetic field at a position before the optical head in the tape running direction. The magnetic field required for initialization or erasing is preferably applied so as to be applied to the entire width of the magneto-optical tape from the viewpoint of simplification of the device configuration, and further preferably from the viewpoint of power consumption using a permanent magnet. The applied magnetic field is preferably selected from the range of usually 640 kA / m or less, preferably 40 to 640 kA / m in order to reduce the size of the magnet that generates the magnetic field.

The larger the maximum value (BH) _Max of the energy product, the more preferable the permanent magnet used for the initialization or erasing head is. Therefore, it is preferable that the permanent magnet is composed of RCo (R represents a rare earth element) or NdFeB. The number of permanent magnets arranged may be single or plural as long as it is in one magnetic circuit. An example of arranging a plurality of permanent magnets is a structure in which two permanent magnets are connected so as to face each other on both sides of a yoke material. However, from the viewpoint of the leakage magnetic field, a yoke-type permanent magnet in which magnetic poles are connected by a yoke material is preferable as shown in FIGS.

The initialization or erasing head shown in FIG.
Taper part (trapezoid part) (8a), (8
b) formed of two yoke materials (4a) and (4b) and a permanent magnet (2), and the yoke material is provided on the N pole side (5) and the S pole side (6) of the permanent magnet (2). (4a), (4b)
Connect the other ends of each of the taper parts (8a), (8
It has a structure in which a gap (7) is formed between the opposed tip surfaces (9a) and (9b) of (b). In the head shown in FIG. 2, the magneto-optical tape is initialized or erased by passing through the gap (7).

The initialization or erase head shown in FIG.
Two yoke members (4a) and (4b) each having a tapered portion (8c) and (8c) formed at the tip of one end, and a permanent magnet (2).
And another yoke member (4c) having a U-shaped cross section and having tapered portions (8d) and (8d) formed at the upper and lower ends thereof.
And the other ends of the yoke members (4a) and (4b) are connected to the N pole side (5) and the S pole side (6) of the permanent magnet (2) to form tapered portions (8c) and (8c). ) And taper (8
d) and (8d) are opposed to each other, and a gap (7) is formed between the tip surfaces (9c) and (9d) of each tapered portion. In the head shown in FIG. 3, the magneto-optical tape is initialized or erased by passing through the gap (7).

The magnetic properties required for the yoke material include high magnetic permeability and high saturation magnetic flux density. The value of the maximum permeability of the yoke material (mu _m), the permalloy can be obtained a value greater than or equal to 0.01H / m be used as the material. Further, an amorphous magnetic alloy containing a transition metal, which is under development as a high magnetic permeability material, can also be used. The FeCo alloy has a maximum magnetic permeability of 0.006 H / m or more and a saturation magnetic flux density of 2.4.
Since it is as high as Wb / m ² , it is suitable as a yoke material. When the thickness of the tip of the yoke material (gear-up constituting portion) is made smaller than that of the base, a stronger external magnetic field can be formed even when the magnetic flux at the tip of the yoke is saturated.

The recording bias magnetic field of the magneto-optical disk is usually applied only in the vicinity of the portion irradiated with the recording light beam. In the case of a magneto-optical tape, the optical head needs to move at a high speed and over a relatively large distance. Therefore, if a bias magnetic field is applied in the same manner as the magneto-optical disk, it is necessary to move the magnetic head at high speed, which is a problem. Therefore, in the case of the magneto-optical tape, it is preferable that the bias magnetic field is widely applied on the track on which the optical head records. The recording bias magnetic field is preferably applied by a permanent magnet from the viewpoint of simplifying the device configuration. When the leakage magnetic field and the demagnetizing field of the erasing head are not considered, the applied magnetic field is 24 kA / m or less from the viewpoint of downsizing the magnet that generates the magnetic field, because the cross-sectional area and the length of the magnet are proportional to the gap magnetic field. Is preferably 8 kA / m
The following is more preferable.

If a magneto-optical tape having a relatively large saturation magnetization near room temperature is used, the leakage magnetic field of the magneto-optical tape itself becomes large, so that recording can be performed without an externally applied magnetic field. Therefore, the method of using such a magneto-optical tape and recording only by modulating the light intensity without using an external magnetic field is particularly preferable because the configuration of the recording apparatus becomes very simple.

[0039]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 Thickness 20 μm, F ₅ value 12.5 Kg / mm ² , 100 ° C.
After heat treatment for 30 minutes, the heat shrinkage ratio in the longitudinal direction is 1.5%, the optical recording layer forming surface (front surface) Ra is 0.002 μm, and the back surface Ra 0.
Sequentially 40 nm AlT on 009 μm PET film
a alloy layer, 30 nm TbFeCo amorphous alloy layer, 70
A SiN amorphous dielectric layer having a thickness of nm was formed by a sputtering method to prepare a magneto-optical tape.

As a result of measuring the magnetization curve of the magneto-optical tape using the Kerr effect, it was found that the magnetization was completely reversed in a magnetic field of about 500 kA / m. Further, the above magneto-optical tape was attached to the magneto-optical disk substrate using an evaluation apparatus for magneto-optical disk, and the recording / reproducing characteristics were evaluated according to the following procedure.

First, before attaching the magneto-optical tape to the spindle of the evaluation apparatus, a magnetic field of 500 kA / m was applied perpendicularly to the magneto-optical tape using the magnetic head shown in FIG.
Then, it was attached to a spindle, and while rotating the magneto-optical tape at a linear velocity of 2 m / s, a signal was read by focusing with an optical head. It was found that the signal was at the erase level and was correctly initialized.

Next, recording and reproduction were performed while changing the recording magnetic field while rotating the magneto-optical tape at a linear velocity of 2 m / s. The recording conditions are a frequency of 800 kHz, a recording laser pulse width of 625 ns, a recording laser power of 2.5 mW, and a reproducing laser power of 0.6 mW or less, and the C / N when the recording magnetic field is 0 is 48.5 dB and when the recording magnetic power is 8 kA / m. C / N is 49.0 dB, C / N in the case of 16 kA / m is 49.5 dB, and C / N in the case of 24 kA / m is 49.5.
It was set to dB. As a result, all 4 required for digital recording
It exceeded 5 dB and was a good result.

Next, the magneto-optical tape after recording was removed from the spindle, and a magnetic field of 500 kA / m was applied using the magnetic head shown in FIG. 2 as in the case of initialization. Then, it was attached to the spindle again to reproduce the signal.
It was found that the signal was at the erase level equivalent to that at the time of initialization and that the erase was completed completely. From the above results, it was confirmed that the magneto-optical tape can be initialized and erased in principle only by the magnetic field without using light.

[0045]

According to the present invention described above, a recording / reproducing system for information having a high volume recording density is provided, and a document,
It is possible to compactly record and store a huge amount of information such as video, audio and numerical data. Furthermore, since unnecessary information can be erased and rewritten, there is no problem of waste. Further, the structure of the recording / reproducing apparatus becomes simple, and the apparatus cost can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an example of an initialization or erasing method according to the present invention.

FIG. 2 is an explanatory diagram of an example of a magnetic head used in the initialization or erasing method of the present invention.

FIG. 3 is an explanatory diagram of another example of a magnetic head used in the initialization or erasing method of the present invention.

[Explanation of symbols]

 1: Tape-shaped recording medium 2: Permanent magnet 5: N pole 6: S pole 7: Gap

Claims (7)

[Claims] 1. When recording and reproducing information by irradiating the magneto-optical recording layer of a running tape-shaped recording medium with light from the optical head, a position before the optical head with respect to the running direction of the tape-shaped recording medium. In addition, the tape-shaped recording medium is initialized or erased by an external magnetic field generated from a permanent magnet or an electromagnet arranged in a non-contact state with the tape-shaped recording medium, and thereafter, recording and reproduction are performed by the optical head. Magneto-optical recording / reproducing method. 2. The magneto-optical recording / reproducing method according to claim 1, wherein initialization or erasing is performed by running a tape-shaped recording medium in a non-contact state on a gap between the poles of a permanent magnet or an electromagnet. 3. The magnetic field strength for initializing or erasing is 40.
3. The magneto-optical recording / reproducing method according to claim 1, wherein the magneto-optical recording / reproducing method is about 640 kA / m. 4. A recording method using a permanent magnet for recording.
3. The magneto-optical recording / reproducing method according to any one of 3 above. 5. The externally applied magnetic field by a permanent magnet is 24 kA.
5. The magneto-optical recording / reproducing method according to claim 4, which is not more than / m. 6. The magneto-optical recording / reproducing method according to claim 1, wherein recording is performed only by modulating the light intensity without using an external magnetic field. 7. The magneto-optical recording / reproducing method according to claim 1, wherein reproduction is performed by irradiating light from the magneto-optical recording layer side.