JPH06105483B2 - Bias magnetic field applying device for magneto-optical recording - Google Patents

Description

The present invention relates to an improvement of a bias magnetic field applying device for magneto-optical recording.

[Prior Art] In recent years, the industry related to information has made remarkable progress, and the amount of information handled has also tended to increase. Therefore, an optical recording / reproducing apparatus using a light beam has been attracting attention, instead of a recording / reproducing apparatus for recording / reproducing information using a conventional magnetic head.

Among the above optical recording / reproducing systems, the erasable magneto-optical system is in the spotlight.

In this magneto-optical method, it is necessary to apply a bias magnetic field at the time of erasing and recording, and various methods can be considered as the bias magnetic field applying device. Figure 7 shows the Institute of Electronics and Communication Engineers Technical Report Vol.83, No197 (CPM83-51-62),
The bias magnetic field applying device disclosed in 1983. In the magneto-optical recording / reproducing apparatus 1 shown in FIG. 7, the magneto-optical disk 3 rotatably driven by a spindle motor (not shown) is a laser for recording / reproducing with an objective lens 5 in a magneto-optical pickup 4. The light is focused in a spot shape and is applied to the recording surface. In order to perform recording and erasing by irradiating the laser beam, a permanent magnet 6 for generating a bias magnetic field is arranged facing the surface of the disk 3 opposite to the objective lens 5, and recording is performed. And the permanent magnet 6 depending on the erase mode
The direction of the bias magnetic field applied to the disk 3 is controlled by rotating it by 180 °. FIG. 8 shows the principle of recording and erasing in magneto-optical recording. In FIG. 3A, reference numeral 7 indicates a recording film such as TbFe, and the magnetization direction of the recorded portion 7a of the recording film 7 is opposite to the magnetization direction of the unrecorded portion 7b. Unrecorded part 7b above
The magnetization direction is magnetized in the bias magnetic field 8 direction by the irradiation of the light beam 9 in the state where the bias magnetic field 8 is applied in the opposite direction to the magnetization direction. On the other hand, in order to perform erasing, as shown in FIG. 8 (b), the light beam 9 is applied in a state in which a bias magnetic field 10 opposite to the bias magnetic field 8 at the time of recording (at the time of erasing) is applied. Unrecorded part
It will be aligned with the magnetization direction of 7b. Incidentally, reference numeral 11 is
The leakage magnetic field from an unrecorded area is shown. As shown in FIG. 8, in magneto-optical recording, bias magnetization is required to magnetize the recording film 7 at the time of recording and erasing, and the magnitude thereof depends on the material of the recording film 7, but the magnetic field strength is about several hundreds α. Is required. In FIG. 7, the permanent magnet 6 is used to obtain a magnetic field having such a magnitude, and the magnet is rotated in synchronization with the recording / erasing state to obtain the required bias magnetic field.

[Problems to be Solved by the Invention] As shown in FIG. 7, in a bias magnetic field applying device using a permanent magnet 6 whose both ends are magnetized to have S poles and N poles, a magnetic field is changed by switching between recording and erasing modes. Permanent magnet 6 to reverse
Since there is a problem in that the magnetic field cannot be reversed quickly because it has to be rotated by 180 °, and it takes time enough for the optical disk 3 to make two or more rotations when moving from recording to erasing. was there.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a bias magnetic field applying device for magneto-optical recording capable of rapidly reversing the recording and erasing magnetic fields.

[Means for Solving the Problems] In this device, a permanent magnet rotatably formed on a rotating shaft is used in order to magnetize the recording layers of the magneto-optical recording medium in mutually opposite directions according to the recording or erasing mode. In the bias magnetic field applying device, the centers of the magnetic fields of the magnetic poles different from each other exist on at least one of the halves of the rotation axis in the plane including the rotation axis.

[Operation] This device reverses the bias magnetic field applied to the magneto-optical recording medium by rotating the permanent magnet having the above configuration from the center of the magnetic field of the magnetic pole to the center of the magnetic field of the other magnetic pole.

EXAMPLES The present invention will be specifically described below with reference to the drawings.

FIG. 1 shows a principle diagram of the first embodiment of the present invention, and FIG. 2 shows a magneto-optical recording / reproducing apparatus having the first embodiment. First
As shown in the figure, the bias magnetic field applying device 21 of the first embodiment
Is a magneto-optical disk 22 as a disk-shaped magneto-optical recording medium.
A permanent magnet 23 magnetized in multiple poles is arranged so as to face one surface. An objective lens 24 is provided so as to face the other surface of the magneto-optical disk 22 so that the recording film of the magneto-optical disk 22 can be irradiated with a laser beam focused in a spot shape.

The permanent magnet 23 has a cylindrical shape, and in the example shown in the figure, each of the six parts divided in the longitudinal direction of the cylindrical shape is magnetized, and each cross section S pole, N is formed into a fan shape at every 60 ° around the rotation axis. It is a multi-pole magnetized with 6 poles in which the poles are alternately formed. Therefore, by rotating the permanent magnet 23 by 60 °, the erasing bias magnetic field and the recording bias magnetic field can be switched. For example, as shown in FIG.
If the state in which the pole faces the magneto-optical disk 22 is the direction of the center of the bias magnetic field Ha in the recording mode, the bias magnetic field Ha is rotated by 60 ° in the direction of arrow A, for example.
It can be set to the center of the bias magnetic field in the erase mode in the direction opposite to the direction of the center of (in the direction of arrow A from the bias magnetic field in the erase mode.
Switching to the bias magnetic field in the recording mode. According to the bias magnetic field applying device 21 described above, switching can be performed at a speed three times that of the conventional example shown in FIG.

FIG. 2 shows an optical system of the magneto-optical recording / reproducing apparatus having the first embodiment. That is, a magneto-optical pickup 33 is provided facing one surface of the magneto-optical disk 22 fixed to the rotation shaft of the spindle motor 31. This pickup 33
Is fixed to a carriage 34, and the carriage 34 can be moved in the radial direction of the disk 22 by a voice coil motor or the like.

A laser diode (LD) 35 as a monochromatic light source is housed in the pickup 33. The light of the laser diode 35 is collimated by a collimator lens 36 into a parallel light flux, and then a cross section is circular (polarized with) by a shaping prism 37. The light beam, which has been converted into a light beam and has passed through the beam splitter 38, is focused and irradiated in a spot shape on the surface of the disk 22 through the objective lens 24. A multi-pole magnetized permanent magnet 23 according to the first embodiment is arranged so as to face the surface of the disk 22 on the opposite side to the above, and this permanent magnet 23 is connected to the rotation shaft of a motor 39 for erasing and recording. In each case, it is rotated by 60 ° so as to form a bias magnetic field in a predetermined direction. The permanent magnet 23 has an optical disk 22 whose longitudinal direction is each S pole or N pole.
Is arranged along the radial direction (of the disk 22) in which the pickup 33 is moved so as to cover the recording area.

At the time of switching between the erasing and recording modes, a mode switching signal is applied to the motor drive circuit 40, so that the permanent magnet 23 is rotationally driven by 60 ° so that the bias magnetic field can be rapidly inverted. I am doing it. The recording film in the irradiated portion is heated to at least the Curie temperature by the light beam applied to the disk 22 and is magnetized in the direction of the bias magnetic field (during the light emission in the erasing mode and the recording mode) (the magnetization during the cooling). It will be fixed in the direction). On the other hand, in the reproduction mode, the disc 22 is irradiated with a polarized wave which is formed into a light beam having a weaker intensity than in the case of recording or erasing.

Then, the light beam applied to the disk 22 is rotated by a minute angle in opposite directions due to the magnetic Kerr effect, depending on which direction the irradiated part is magnetized. The reflected wave passes through the objective lens 24, a part thereof is reflected by the beam splitter 38, and enters the half-wave plate 41. Since the amplitude plane is set by the half-wave plate 41 so as to face the intermediate direction between the S axis and the P axis of the polarization beam splitter 42, the polarization beam splitter 42 is set in accordance with the magnetization direction of the irradiated portion. It is made possible to separate the light that is transmitted and is incident on the photodiode 43a and the light that is reflected by the polarization beam splitter 42 and is incident on the other photodiode 43b. Information recorded on the magneto-optical disk 22 can be amplified by the differential output of the two photodiodes 43a and 43b.

In the reproducing mode, in any state, the permanent magnet 23 is, according to the first embodiment described above, a permanent magnet magnetized in multiple poles in the rotation direction.
Since 23 is used, it is possible to switch from the erase mode to the recording mode bias magnetic field or from the recording mode to the erase mode bias magnetic field only by rotating the permanent magnet 23 by 60 °. Further, as shown in FIG. 3, since the permanent magnet 23 has a circular cross section (each magnetic pole is a fan shape), the magnetic field is reversed as compared with the case where the cross section indicated by the dotted line is short (the rectangular case is a conventional example). In such a state, the distance between the surface of the magneto-optical disk 22 and the tip of the permanent magnet 23 can be reduced (in the case of a circle whose radius is r, the circles can be brought closer to each other, but in the case of a rectangle, the distance d must be increased. ) Since the surface of the disk 22 can be approached, stronger magnetic field strength can be obtained.

Therefore, it is possible to obtain a required bias magnetic field with a small permanent magnet 23 used.

FIG. 4 shows a second embodiment of the present invention. In the bias magnetic field applying device 51 of the second embodiment, the permanent magnet 23 magnetized with multiple poles has a gear 52 formed on the shaft when it is rotationally driven, and the gear 52 is attached to the rotary shaft of the motor 39. Gear
It meshes with 53. The both gears 52, 53 are set to an appropriate reduction ratio by increasing the number of teeth of the gear 53 on the motor side. Therefore, in this case, the rotary shaft of the motor 39 is directly connected to the permanent magnet.
The permanent magnet 23 with a smaller rotation angle than when it is connected to the shaft of
The bias magnetic field can be reversed by rotating 60 °.

FIG. 5 shows a third embodiment of the present invention.

The bias magnetic field applying device 61 of this embodiment does not have multi-pole magnetization over the entire circumference of a cylindrical permanent magnet 62, but has a part of the circumference magnetized in a fan shape to form N poles and S poles. . The permanent magnet 62 is switched by the motor 63 so that the north pole or the south pole faces the disk 22 when switching between the erasing and recording modes. For example, at the time of switching from erasing to the recording mode, a signal for rotating the motor 63 at an appropriate angle in the direction indicated by arrow B is applied to the motor 63, while at the time of switching from the recording to the erasing mode, the signal is rotated at an appropriate angle in the opposite direction. A signal for causing the motor 63 is applied to the motor 63. This third
According to the embodiment, it is possible to obtain substantially the same operation and effect as the first embodiment without magnetizing the multi-poles.

FIG. 6 shows a fourth embodiment of the present invention. The bias magnetic field applying device 71 of the fourth embodiment is formed by using a permanent magnet 72 having a fan-shaped cross section in which the S pole and the N pole are formed in a fan shape.
By thus forming the permanent magnet 72 having a pair of S pole and N pole only on a part of the entire circumference, the size and weight of the device having the same operation as that of the third embodiment can be further reduced. realizable.

It should be noted that at least two different magnetic poles (that is, in a substantially cylindrical member or a portion obtained by dividing the cylindrical member in the longitudinal direction) (that is,
Those having two or more S and N poles) belong to the present invention. Even in the case of two poles, each magnetic pole has a shape obtained by dividing a cylinder,
A strong bias magnetic field can be formed. Therefore, there is an advantage that the size can be reduced as compared with the conventional example.

[Effects of the Invention] As described above, according to the present invention, a permanent magnet rotatably formed on a rotation axis for magnetizing recording layers of a magneto-optical recording medium in opposite directions according to a recording or erasing mode. In the bias magnetic field applying device using the magnetic field applying device, a magnetic field center of a magnetic pole different from each other is present on at least one of the two sides of the rotation axis divided into two in a plane including the rotation axis. Since it is an application device, the bias magnetic field can be reversed at a rotation angle smaller than 180 °, and information can be recorded and erased quickly.

[Brief description of drawings]

1 to 3 relate to a first embodiment of the present invention.
FIG. 1 is a diagram for explaining the principle of the first embodiment, and FIG. 2 is a configuration diagram showing an optical system of a magneto-optical recording / reproducing apparatus having the first embodiment.
FIG. 3 is an explanatory view showing that a strong bias magnetic field can be formed, FIG. 4 is a perspective view showing a second embodiment of the present invention, FIG. 5 is a constitutional view showing a third embodiment of the present invention, and FIG. Is a configuration diagram showing a fourth embodiment of the present invention, FIG. 7 is a configuration diagram showing a conventional example, and FIG. 8 is an explanatory diagram showing a bias magnetic field for recording and erasing. 21 ... Bias magnetic field applying device 22 ... Magneto-optical disk, 23 ... Permanent magnet 24 ... Objective lens, 39 ... Motor 52, 53 ... Gear

Claims (1)

[Claims] 1. A bias magnetic field applying device using a permanent magnet rotatably formed on a rotation axis for magnetizing recording layers of a magneto-optical recording medium in opposite directions according to a recording or erasing mode, A bias magnetic field applying apparatus for magneto-optical recording, wherein the centers of the magnetic fields of different magnetic poles are present on at least one of the rotation axes divided into two in a plane including the axis.