JPH04247347A - Magneto-optical recording system - Google Patents

Abstract

PURPOSE:To prevent the deterioration in reproduced signals by the imperfect remaining of magnetic domains in overwriting. CONSTITUTION:A magnetic field generating means 4 which impresses magnetic fields in the direction perpendicular to a medium is provided in the position where the medium is irradiated with a laser beam or just behind this position. The magnetic field generated by this magnetic field generating means 4 has an intensity direction in the direction perpendicular to the information recording part (information tracks) of the medium 2 and the intensity thereof is so set as to be larger in either side than at the center in the information recording part. The magnetic domains shrink to the position deviated from the center of the information recording part in the process when the magnetic domains are annihilated at the time of information erasing. The influence exerted on the reproduced signals is drastically decreased even if the imperfect erasing arises.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overwritable magneto-optical recording system.

0002

2. Description of the Related Art In recent years, magneto-optical recording media utilizing magneto-optic effects have been actively researched and developed as rewritable optical recording media, and some have even been put into practical use. This magneto-optical recording medium is capable of high-capacity, high-density recording, non-contact recording and playback,
In addition to its advantages such as ease of access, it is also rewritable, so it is expected to be used for document information files, video/still image files, computer memory, etc. In order to make a magneto-optical recording medium a recording medium with performance equal to or better than that of a magnetic disk, there are several technical issues, and one of the major ones is overwriting technology. In order to rewrite information on currently commercially available magneto-optical recording media, it is necessary to first erase the original information and then write new information, which results in a time loss. Overwriting technology solves this drawback. Overwriting techniques that have been proposed so far are broadly classified into magnetic field modulation methods and optical modulation methods (multi-beam method, two-layer film method, etc.) depending on the recording method.

The magnetic field modulation method is a method for recording by keeping the intensity of light constant and reversing the polarity of the applied magnetic field depending on the recorded information. In this method, since the magnetic field must be reversed at high speed, it is necessary to use a floating type magnetic head, making it difficult to exchange the medium.

On the other hand, in the optical modulation method, the magnitude of the applied magnetic field is kept constant and the irradiation laser beam is turned on and off according to the recorded information.
This is a method in which recording is performed by turning off or modulating the intensity. Among these methods, the multi-beam method is a pseudo-overwrite method that uses two to three laser beams and reverses the direction of the magnetic field every rotation to record/erase on a track-by-track basis, but the device configuration is complicated. It has disadvantages such as increasing the cost and increasing the cost. Further, the two-layer film method uses a two-layer film as the recording layer of a magneto-optical recording medium to achieve overwriting, and is disclosed in, for example, Japanese Patent Laid-Open No. 175948/1983. The method described in the publication uses, for example, a magneto-optical recording medium equipped with a recording layer made of TbFe and an auxiliary layer made of TbFeCo, and after initialization, an external magnetic field is applied and a laser beam of different power is applied. The aim is to achieve overwriting by irradiating the In other words, in this method, 4 KOs are made in advance before recording.
The magnetization of the auxiliary layer is aligned in one direction using an initialization magnetic field of approximately e, and a high-power laser beam is irradiated to lower the medium temperature T>
The temperature is raised to Tc2 (Tc2 is the Curie temperature of the auxiliary layer), the recording magnetic field (in the opposite direction to the initialization magnetic field) is applied to reverse the magnetization of the auxiliary layer, and when the medium is cooled, the magnetization changes. Recording is performed by transferring the medium to the recording layer, and a low-power laser beam is irradiated to lower the medium temperature to Tc1.
Erasing is performed by raising the temperature to <T<Tc2 (Tc1 is the Curie temperature of the recording layer) and transferring the magnetization direction of the auxiliary layer to the recording layer. However, although this method has the advantage of high speed, it also has the problem of high laser power during writing and the need to apply a very large magnetic field during the initialization process prior to overwriting. .

As mentioned above, several methods have been proposed as overwriting methods for magneto-optical recording.
Each of them has both advantages and disadvantages, and it is said that several breakthroughs will have to be made in order to put them into practical use.

On the other hand, an overwrite method using a demagnetizing field has been proposed similar to the above method [for example, Ha
n-Ping; Appl. Phys. Lett.
49, p.8 (1986)]. This method is a type of optical modulation method, but the recording medium used has a single layer structure.
It is attracting attention because it is more likely to be able to write with lower power than dual-layer recording media, and there is no need to prepare a magnetic field for initialization.

[0007]

[Problem to be solved by the invention] However, in such a method using a demagnetizing field, differences in the magnitude of the demagnetizing field energy, domain wall energy, and Zeeman energy at the domain wall position due to differences in laser irradiation conditions are used. Since the generation and extinction of magnetic domains are controlled, it has the disadvantage that magnetic domains, that is, signals are likely to remain unerased due to variations in magnetic film properties or laser irradiation conditions.

An object of the present invention is to provide a magneto-optical recording system that solves the problem of deterioration of reproduced signals due to unerased magnetic domains.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides magneto-optical recording in which information can be overwritten by changing the intensity of laser light irradiated onto the medium. In the magneto-optical recording method,
A magnetic field generating means for applying a magnetic field perpendicularly to the medium is provided at or immediately after the irradiation position of the laser beam, and the magnetic field generating means generates a magnetic field that has an intensity distribution in a direction perpendicular to the information recording portion of the medium and whose intensity is A magneto-optical recording method is provided which is characterized in that a magnetic field is applied such that the magnetic field is larger on either side of the information recording section than at the center thereof.

0010

[Operation] The magnetic field generated by the magnetic field generating means provided at the laser beam irradiation position or immediately after the laser beam irradiation position acts to contract the magnetic domain to a position offset from the information recording center in the process of erasing the magnetic domain during information erasing. To make the unerased portion exist at a position off from the center of information recording even when the unerased portion is generated. Therefore, deterioration of the reproduced signal due to the presence of unerased magnetic domains can be minimized.

[0011]

EXAMPLES The present invention will be explained in detail below based on examples. First, the principle of the magneto-optical recording method according to the present invention will be described. In the overwriting method using optical modulation, the basic technology is to form magnetic domains with a high-power laser beam and eliminate the magnetic domains with a low-power laser beam. For example, as shown in FIG. 4(a), the laser output is modulated into two values during information recording, and the high output level corresponds to magnetic domain formation and the low output level corresponds to magnetic domain extinction, as shown in FIG. 4(b). ) to form a magnetic domain pattern as shown in FIG. In the figure, 21 is an information recording section (information track), and 22 is a magnetic domain.

[0012] Through the above operation, new information must be written regardless of the previously written information, but in reality, due to variations in the magnetic film characteristics of the medium used or the laser irradiation conditions, a considerable amount of information (magnetic domains) The current situation is that some parts remain unerased. This situation is shown in FIG. FIG. 5(a) shows a signal pattern (laser irradiation conditions) of information (magnetic domain) written in advance, and FIG. 5(b) shows a signal pattern (laser irradiation conditions) of newly written information. In addition, (c) and (d) in Figure 5 respectively show the unerased information that occurs when new information is overwritten under the condition (b) on the information previously written under the condition (a). This is an example showing the situation of 22'. These unerased marks often appear at the center of the information recording section 21 (usually the land section in a magneto-optical disk with groups). This is mainly
This is because the irradiated laser beam has a normal intensity distribution, and the peak position thereof is controlled to be at the center of the information recording section 21.

When reproducing information, in magneto-optical recording, the medium is irradiated with laser light and the information is detected based on the intensity of the reflected light.In this case, the intensity distribution of the laser light also depends on the information. Similar to the intensity distribution during writing, the intensity distribution is controlled so that the peak position is at the center of the information recording area. Therefore, if the remaining information remains at this position, the portion of the reproduction laser beam with the highest intensity overlaps with the position of the remaining information being erased, and the reproduced signal deteriorates significantly. In order to solve this problem, it is sufficient to eliminate the unerased portion, but as mentioned above, it has been difficult to completely remove this with conventional techniques.

Therefore, in the present invention, a magnetic field generating means for applying a magnetic field perpendicularly to the medium is provided at the position where the medium is irradiated with the laser beam or immediately thereafter (downstream position in the direction of medium movement), and the magnetic field generating means If a magnetic field is applied that has an intensity distribution perpendicular to the information recording area of the medium and is greater on either side of the information recording area than at the center of the information recording area, even if residual magnetic domains are generated, the The position is shifted from the information recording section to minimize the influence on the reproduced signal. Although the maximum strength of the applied magnetic field depends on the laser irradiation conditions, medium conditions, etc., it is preferable that it not be too large.

FIG. 1 shows the basic system configuration for implementing the method of the present invention. In the figure, 1 is a collimating lens for focusing the laser beam, 2 is a magneto-optical recording medium, 3 is the focused laser beam, 4 is a magnetic field generating means provided at the laser beam irradiation position or immediately after it, A magnetic field as described above is constantly applied to the medium 2.

According to the above system configuration, the laser beam 3 focused on the medium 2 by the collimating lens 1
A part of the medium 2 is heated to perform recording and erasing, but at this time, the magnetic field generating means 4 generates a magnetic field that has an intensity distribution in a direction perpendicular to the information recording section (information track) of the medium 2, and that intensity is Since a magnetic field is applied that is larger on either side of the information recording area than at the center, the magnetic domain contracts to a position offset from the center of the information recording area in the process of disappearing during information erasing. Even if an unerased magnetic domain occurs, the unerased domain will exist at a position away from the center of information recording. Therefore, deterioration of the reproduced signal due to the presence of unerased magnetic domains can be minimized.

Next, FIG. 2 shows an example of a magnetic head used as the magnetic field generating means in the present invention. In the figure, 5 is a magnetic head, 6 is a core portion, 7 is an information recording portion of the medium, 8 is a magnetic domain, and 8' is an unerased magnetic domain. In this magnetic head 5, a core portion 6 (about 1 to 2 mm in length) is installed obliquely with respect to an information recording portion 7, and the magnetic field is directed in a direction that eliminates magnetic domains (perpendicular to the medium). applied. When the magnetic domain 8 of the information recording section 7 of the medium passes through the magnetic head 5,
First, since the upper part of the magnetic domain 8 enters the lower part of the core part 6 before the lower part, the magnetic field at this time has a gradient in the direction perpendicular to the longitudinal direction of the information recording part 7, as described above. The magnetic domains to be erased are gathered on the lower side of the information recording section 7 in the figure during the erasure process. Therefore, even if a magnetic domain remains unerased, it will be located at a location deviated from the center of the information recording section 7, such as 8'. In this example, the maximum strength of the applied magnetic field is approximately ±100 Oe.

FIG. 3 is a diagram showing another example of the magnetic head used as the magnetic field generating means in the present invention. 9 in the diagram
10 is a magnetic head, 10 is a gap, 11 is a winding, 12 is a medium, and 13 is an information recording section. This magnetic head 9 generates a magnetic field as shown by the broken line in the figure in the gap 10 adjacent to the medium 2 by applying a current to the winding 11.
The vertical component performs the action described above. In this case, since the perpendicular component of the generated magnetic field is utilized, the maximum magnetic field strength is larger than that in FIG. 2.

[0019]

[Effects of the Invention] According to the present invention, since a magnetic field generating means for generating a magnetic field having a specific intensity distribution is provided at the laser beam irradiation position or immediately after the laser beam irradiation position, the deterioration of the reproduced signal due to the unerased magnetic domain when erasing information is prevented. can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a basic system configuration for implementing the method of the present invention.

FIG. 2 is a diagram showing an example of a magnetic head used as a magnetic field generating means in the present invention.

FIG. 3 is a diagram showing another example of a magnetic head used as a magnetic field generating means in the present invention.

FIG. 4(a) is a diagram showing the laser output level used in the overwriting method, and FIG. 4(b) is a diagram showing the formed magnetic domain pattern.

[Fig. 5] (a) is a diagram showing the signal pattern of previously written information, (b) is a diagram showing the signal pattern of newly written information, and (c) and (d) are diagrams showing the signal pattern of information that has been written in advance. FIG. 3 is a diagram showing an example of a situation.

[Explanation of symbols]

Claims (1)

[Claims] [Claim 1] Information overwriting (overwriting) by changing the intensity of laser light irradiated onto the medium
In a magneto-optical recording system that performs magneto-optical recording that allows for the recording of information on a medium, a magnetic field generating means for applying a magnetic field perpendicularly to the medium is provided at the irradiation position of the laser beam or immediately after the laser beam irradiation position, and the magnetic field generating means records information on the medium. A magneto-optical recording method characterized by applying a magnetic field that has an intensity distribution in a direction perpendicular to the information recording part and whose intensity is greater on either side of the information recording part than at the center.