JPH0553003B2 - - Google Patents

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. When recording information on a magneto-optical disk, a perpendicular magnetization film is formed on the disk surface, the magnetization direction of this perpendicular magnetization film is first aligned in one direction, and information is digitally recorded using an information signal. The perpendicularly magnetized film is irradiated with a modulated laser beam to raise the temperature of the perpendicularly magnetized film to the Curie point or higher. Then, the portion irradiated with the laser 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 train is generated according to the information.

In order to read information recorded on a magneto-optical disk, a perpendicularly magnetized film is irradiated with a reading laser beam, and the magnetic force effect that changes the direction of the polarization plane of the reflected beam due to the difference in the magnetization direction of the perpendicularly magnetized film is used. I am using it to read it. When erasing a recording pit, a laser beam is irradiated onto the recording pit portion while tracking on the recording pit row, and a direct current bias magnetic field in the magnetization direction opposite to the recording pit is applied to align the magnetization direction of the perpendicularly magnetized film again.

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 includes a main yoke 22, side yokes 23 disposed on both sides thereof,
24 and the main yoke 22, a yoke plate 26 that connects one end of the side yokes 23 and 24, and the main yoke 22.
It consists of a coil 25 wound around. The main yoke 22 is T-shaped to facilitate coil winding.

The auxiliary magnetic field applying device 21 is arranged on the opposite side of the objective lens to the magneto-optical disk 28 so that the longitudinal direction of the main yoke 22 coincides 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 is generally made of copper wire with a wire diameter of about 0.3 to 0.6 mm wound around 300 to 1000 turns and fixed with adhesive or the like. ing. 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, the yoke plate 26, and the side yokes 23 and 24 form a magnetic circuit, the auxiliary magnetic field applying device is more efficient than the main yoke 22 and the coil 25 alone.

[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, that is, in the radial direction of the disk, as shown in FIG. 3, the magnetic flux density is higher at both ends than at the center. Therefore, if you try to apply the optimal auxiliary magnetic field, recording (or erasing)
It is necessary to change the drive current of the auxiliary magnetic field application device or change the laser power depending on the location, and a complicated control circuit must be added. Of course, it is also possible to use only the central flat area, but this has the disadvantage that the device becomes larger.

[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 applying device as described above, the main yoke, which is the main source of the magnetic field, is connected to the recording medium and the recording medium of the main yoke. An auxiliary magnetic field applying device is provided, characterized in that the distance from the surface facing the medium is greater at the end of the main yoke than at the center of the main yoke.

〔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 1 consists of a main yoke 2, side yokes 3 and 4 arranged on both sides thereof, a yoke plate 6 that connects one end of the main yoke 2 and the side yokes 3 and 4, and a coil 5 wound around the main yoke 2. It is completed. The auxiliary magnetic field applying device 1 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 and 4, and yoke plate are also 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 a flat surface, and the distance from the magneto-optical disk 8 increases as you go to both ends. A slope is provided such that the angle increases. 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 that in the case where the main yoke 2 is flat, so the magnetic flux density distribution on the magneto-optical medium becomes second. As shown in the figure, the flat area increases.
In this embodiment, the characteristics of the auxiliary magnetic field applying device are corrected by approximation using a linear slope, but of course a curved slope 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. Generally, the size and configuration of the auxiliary magnetic field applying device are determined by the shape of the recording medium used and the method of accessing the recording medium by the optical head, 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 the drawing]

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 application device, 2...Main yoke,
3, 4...side yoke, 5...coil.

Claims (1)

[Claims] 1. A magnetic field application device that applies a magnetic field in conjunction with a light beam to record information on a magneto-optical recording medium or erase recorded information, comprising: a yoke and a coil wound around the yoke; The yoke is arranged such that its longitudinal direction is along the radial direction of the recording medium, and the distance between the recording medium and the surface of the yoke that faces the recording medium is closer to the yoke end than the yoke center. A magnetic field applying device characterized in that the part is larger than the other part.