JPS6265202A - Auxiliary magnetic field impressing device - Google Patents

Abstract

PURPOSE:To flatten magnetic flux density on a photomagnetic recording medium by making the distance between a main yoke constituting an auxiliary magnetic field impressing device and the recording medium longer at end parts than at the lengthwise center part when information on the recording medium is recorded or erased by using a light beam and the auxiliary magnetic field impressing device which is linked to it. CONSTITUTION:The auxiliary magnetic field impressing device 1 is arranged on the outer peripheral reverse surface of a disk type photomagnetic disk 8 to record or erase information on the disk 8 in cooperation with the light beam. The device 1 consists of the main yoke 2 wound with a coil 5 and side yokes 3 and 4 arranged opposite each other across the yoke and the bottom surfaces are integrated by a yoke plate 6, but the surface of the main yoke 2 which faces the photomagnetic disk 8 is not flat unlike usual and both lengthwise end parts are formed slantingly to increase the distance to the disk 8 at those positions. Consequently, magnetic flux density to the disk 8 does not become large at both ends of the main yoke 2 and is flat on the whole, thereby obtaining an optimum magnetic field.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an auxiliary magnetic field application device that applies an auxiliary magnetic field in conjunction with a light beam to record information on a magneto-optical recording medium or erase recorded information. In particular, the present invention relates to an auxiliary magnetic field applying device using an electromagnet.

[Conventional technology]

Magneto-optical disks have been extensively researched in recent years as rewritable, large-capacity optical disks. In order to record alarm information on a magneto-optical disk, a perpendicularly magnetized film is formed on the disk surface, the magnetization direction of this perpendicularly magnetized film is first aligned in one direction, and then digitally modulated by an information signal. The perpendicularly magnetized film is irradiated with the laser beam, and the temperature of the perpendicularly magnetized film is raised to one Curie point or higher. Then, the part irradiated with the Rade beam loses its magnetization direction, and when it is cooled, it is magnetized again with the direction of magnetization reversed from the surroundings by the direction of the DC bias magnetic field.

In this way, a signal pit string is generated according to the information.

In order to read more information recorded on a magneto-optical disk, a perpendicularly magnetized film is irradiated with a reading laser beam, and the magnetic Kerr effect changes the direction of the polarization plane of the reflected beam due to the difference in the magnetization direction of the perpendicularly magnetized film. It is read using. When erasing a recorded pit, a laser beam is irradiated onto the recorded pit while tracking the recorded bit string, and a direct current/bias special field with a magnetization direction opposite to that of the recorded pit is applied to change the magnetization direction of the perpendicularly magnetized film again. Arrange.

Naturally, it is necessary to switch the magnetization direction of the above-mentioned DC bias magnetic field during recording and erasing. Generally, there are two ways to generate a DC bias magnetic field: using a permanent magnet and using an electromagnet. However, the method using a permanent magnet requires a mechanism to reverse the magnetization, and it takes time to reverse the magnetization. Because of their drawbacks, electromagnets are usually used.

FIG. 4 is a perspective view of a conventional auxiliary magnetic field applying device using an electromagnet.

In the figure, the auxiliary magnetic field applying device 21 is wound around the main yoke 22, side yokes 23 and 24 arranged on both sides thereof, and a yoke plate 26 that connects the main yoke 22 and one end of the side yokes 23 and 24. It consists of a coil 25. The main yoke 22 is T-shaped to facilitate coil winding.

The auxiliary magnetic field applying device 21 is arranged so that the opposite side of the objective lens to the magneto-optical disk 28 and the longitudinal direction of the main yoke 22 coincide with the radial direction of the magneto-optical disk 28 . The main yoke 22, side yokes 23, 24, and yoke plate 26 are made of magnetic material, and the coil 25 generally has a wire diameter of φ0.
．． A copper wire of about 3 to 0.6 order is wound around 300 to 1000 turns and fixed with adhesive or the like. When a current is passed through the coil 25, a DC bias magnetic field is generated in the main yoke 22 in a direction perpendicular to the magneto-optical disk 28. Since the main yoke 22, yoke plate 26, and side yokes 23 and 24 form a magnetic circuit, the main yoke 22 and the coil 25 alone constitute an efficient auxiliary magnetic field applying device.

[Problem that the invention seeks to solve]

However, according to the configuration described above, in the magnetic flux density distribution on the magneto-optical medium in the X direction and the radial direction of the disk, the magnetic flux density is higher at both ends than at the center, as shown in FIG. Therefore, in order to apply a suitable auxiliary magnetic field, it is necessary to change the sire power by changing the drive current of the auxiliary magnetic field application device depending on the location of recording (or erasing), and a complicated control circuit must be added. It won't happen. Of course, it is also possible to use only the flat area in the center, but this has the drawback of increasing the size of the device.

[Means for solving problems]

In the present invention, in order to solve the problems of the prior art as described above, in the auxiliary magnetic field application device as described above,
The main yoke, which is the main source of magnetic field, is shaped so that the distance between the recording medium and the surface of the main yoke facing the recording medium is larger at the ends of the main yoke than at the center of the main yoke. An auxiliary magnetic field applying device is provided.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a perspective view of the auxiliary magnetic field applying device of the present invention.

The auxiliary magnetic field applying device l consists of a main yoke 2, side yokes 3 and 4 arranged on both sides of the main yoke 2, main yoke 2, and side yokes 3.
, 4, and a coil 5 wound around the main yoke 2. Auxiliary magnetic field application W11
is arranged on the opposite side of the objective lens with respect to the magneto-optical disk 8 so that the longitudinal direction of the main yoke 2 coincides with the radial direction of the magneto-optical disk 8. The main yoke 2, side yokes 3.4, yoke plates are made of magnetic material, and the coil 5
is similar to the coil 25 in the previous example. The main yoke 2 has a T-shape to make it easy to wind the coil 5, and the surface facing the magneto-optical disk 8 is not flat.
A slope is provided at both ends so that the distance from the magneto-optical disk 8 increases toward the end. Due to this inclination, the magnetic flux density B on the magneto-optical medium corresponding to the end of the main yoke 2 becomes smaller than when the main yoke 2 is flat, so the magnetic flux density distribution on the magneto-optical medium is as shown in Figure 2. As shown, the flat area increases.

In this embodiment, the characteristics of the auxiliary magnetic field applying device are corrected by approximation using a linear inclination, but of course a curved inclination may be applied.

Furthermore, although the above embodiment describes the case where a disk-shaped recording medium is used, the method of the present invention can also be used in a card-shaped magneto-optical card recording/reproducing device. In general, the size of the auxiliary magnetic field applying device depends on the shape of the recording medium used and the method of accessing the recording medium with the optical head.
The configuration is determined, and the shape of the main yoke varies depending on the device.

This is because the strength and spread of the magnetic field required on the recording medium differ slightly depending on the device. However, even in such various auxiliary magnetic field applying devices, the phenomenon in which the strength of the magnetic flux differs between the ends and the center of the main yoke as shown in FIG. 3 similarly occurs. Even in the case of general magnetic field strength correction as described above, the present invention increases or decreases the distance between the surface of the main yoke facing the recording medium and the recording medium depending on the position on the main yoke. It is clear that this problem can be solved by some method.

〔Effect of the invention〕

As explained above in detail, according to the auxiliary magnetic field applying device of the present invention, it is possible to make the magnetic flux density distribution on the magneto-optical medium almost flat, so there is no need for electrical correction, and the auxiliary magnetic field applying device It is possible to provide an auxiliary magnetic field applying device that has an effect such as being able to minimize the size of the magnetic field.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing an auxiliary magnetic field applying device of the present invention. FIGS. 2 and 4 are diagrams showing the relationship between the disk radial distance and the magnetic flux density, respectively. FIG. 3 is a schematic perspective view showing a conventional auxiliary magnetic field applying device. 1: Auxiliary magnetic field applying device, 2: Main yoke, 3, 4: Side yoke, 5: Coil.

Claims (1)

[Claims] (1) In an auxiliary magnetic field application device that applies an auxiliary magnetic field in conjunction with a light beam to record information on a magneto-optical recording medium or erase recorded information, the main yoke, which is the main source of the magnetic field, is An auxiliary magnetic field applying device characterized in that the distance between a recording medium and a surface of a main yoke facing the recording medium is larger at an end of the main yoke than at a center of the main yoke.