JPS6265203A - Auxiliary magnetic field impressing device - Google Patents

Abstract

PURPOSE:To increase the convergence of magnetic flux upon a photomagnetic recording medium by arranging the upper sides of side yokes at both sides which constitute an auxiliary magnetic field impressing device closely to a folded main yoke when information is recorded on the magnetic recording medium by using a light beam and the auxiliary magnetic field impressing device which is linked to the beam. CONSTITUTION:The auxiliary magnetic field impressing device 1 is arranged on the outer peripheral reverse surface of a photomagnetic disk 8 to record or erase information on the disk in cooperation with the light beam. The device 1 consists of the main yoke 2 wound with a coil 5 and side yokes 3 between which the main yoke 2 is sandwiched and the bottom surfaces are integrated by a yoke plate 6, but the upper ends of the side yokes 3 and 4 are bent at right angles to make the end parts closer to the main yoke 2. Further, the end surfaces of the main yoke 2 which are positioned at the outer peripheral side and inside of the disk 8 as to the surfaces of the yoke 2 which face the disk 8 are slanted downward to increase the distance from the disk 8. Consequently, the degree of the convergence of magnetic flux upon the disk 8 is increased.

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 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 the magnetization is digitally modulated by an information signal. The perpendicularly magnetized film is irradiated with a Rade beam to raise the temperature of the perpendicularly magnetized film 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 information recorded on a magneto-optical disk, a perpendicularly magnetized film is irradiated with a reading laser beam, and the magnetic Kerr effect is used to change the direction of the polarization plane of the reflected beam due to the difference in the magnetization direction of the perpendicularly magnetized film. is being read. When erasing a recorded pit, a laser beam is irradiated onto the recorded pit portion while tracking the recorded pit row, and a direct current bias magnetic field with a magnetization direction opposite to that of the recorded 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: a method using a permanent magnet and a method using an electromagnet. However, the method using a permanent magnet requires a mechanism to reverse the magnetization, and the disadvantage is that it takes time to reverse the magnetization. Therefore, electromagnets are often 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 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 generally has a wire diameter of φO.
A copper wire of about 13 to 0.6 mm 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, the yoke plate 26, and the 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, in the configuration described above, the magnetic lines of force coming out of the main yoke 22 pass through the air and enter the side yokes 23, 24, so only a small amount of the magnetic flux generated by the auxiliary magnetic field application device is concentrated on the pit to be recorded, and is not necessary. In order to obtain a strong magnetic field, it was often necessary to wind several hundred turns of coils with a large current flowing through them.

In addition, a large and expensive power supply is required to flow a large current, and the temperature rise cannot be ignored.

Furthermore, when increasing the number of turns, the size of the auxiliary magnetic field application device is unavoidable, and there are disadvantages such as increasing the coil acmeance depending on the number of turns, and lengthening the time required to switch from recording to erasing or vice versa. there were.

[Means for solving problems]

SUMMARY OF THE INVENTION An object of the present invention is to provide an auxiliary magnetic field applying device that eliminates the drawbacks of the conventional example described above and concentrates the magnetic flux generated by passing a current through a coil at a beam irradiation position. The above purpose is to have a main yoke, a coil wound around the main yoke, two side yokes provided on both sides of the main yoke, and a yoke plate that connects the main yoke and the two side yokes. This is achieved by an auxiliary magnetic field applying device characterized in that a portion of the side yoke close to the magneto-optical recording medium is extended in the direction 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 trapping magnetic field application @1 consists of a main yoke 2, side yokes 3 and 4 arranged on both sides of the main yoke 2, a main coke 2, a side yoke 3,
It consists of a yoke plate 6 connecting one end of the main yoke 4 and a coil 5 wound around the main yoke 2. The auxiliary magnetic field applying device 1 is arranged on the opposite side of the objective lens 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, and yoke plates are all made of magnetic material, and the coil 5 is similar to the coil 25 of the previous example. The main yoke 2 has a T-shape so that the coil 5 can be easily wound. The side yoke 3.4 has an L-shape in which the magneto-optical medium side portion extends toward the main yoke side.

FIG. 2 shows a cross-sectional view of the auxiliary magnetic field applying device of the present invention. In the figure, the shaded area shows a cross section of the magneto-optical disk 8. Figure 3 is a graph showing the relationship between δ in Figure 2, that is, the distance between the main yoke 2 and side yokes 3 and 4, and the magnetic flux density B at the spot position on the magneto-optical medium, where the horizontal axis is the distance. , the vertical axis is the magnetic flux density B.

In FIG. 3, when δ is close to 0, the magnetic flux emitted from the main yoke 2 hardly reaches the magneto-optical medium and enters the side yokes 3 and 4, so that B becomes small.

In addition, when δ=L, that is, in the case of the conventional example, the distance between the main yoke 2 and the side yokes 3 and 4 is too large, and the magnetic flux is not concentrated and B decreases.

Therefore, it can be seen that the highest magnetic flux density can be obtained if the value of δ is set in the shaded area shown in FIG. As shown in Fig. 2, the value of δ in this shaded area varies depending on the distance d between the main yoke 2 and the magneto-optical medium surface, but within the practical range, the magnetic flux density on the magneto-optical medium is around δ = d. It has been experimentally found that the maximum By setting the distance δ between the main yoke 2 and the side yoke 3°4 equal to the distance between the main yoke 2 and the magneto-optical medium surface by #1 point, the magnetic flux can be concentrated most efficiently on the magneto-optical medium surface. can.

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 auxiliary magnetic field applying device depends on the shape of the recording medium used and the light)I
The size and configuration of the main yoke are determined by the method of accessing the recording medium, and the shape of the main yoke varies depending on the device.

This is because the strength and spread 9 of the magnetic field required on the recording medium differ slightly depending on the device. However, it is clear that the structure of the present invention can be applied to such various auxiliary magnetic field applying devices.

〔Effect of the invention〕

As explained in detail above, according to the present invention, the magnetic flux can be more concentrated simply by changing the shape of the side yoke without changing the number of turns of the coil, the current value, etc., and the auxiliary magnetic field is applied with high efficiency. equipment can be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing an auxiliary magnetic field applying device of the present invention, and FIG. 2 is a schematic sectional view. FIG. 3 is a diagram showing the relationship between the distance between the main yoke and the side yokes and the magnetic flux density on the recording medium. FIG. 4 is a schematic perspective view showing a conventional auxiliary magnetic field applying device. I: Auxiliary magnetic field application device, 2: Main yoke, 3, 4: Side yoke, 5: Coil, 6: Yoke plate. Agent Patent Attorney Minoru Yamashita Children 2 Figure 3 Shaku

Claims (2)

[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, a main yoke, a coil wound around the main yoke, It has two side yokes provided on both sides of a main yoke and a yoke plate that connects the main yoke and the two side yokes, and a portion of the side yoke close to the magneto-optical recording medium extends in the direction of the main yoke. An auxiliary magnetic field applying device characterized by: (2) Applying an auxiliary magnetic field according to claim 1, characterized in that the closest distance δ between the main yoke and the side yokes is approximately equal to the distance d from the main yoke to the magneto-optical recording medium. Device.