JPS61187101A - Magnetic field impressing device - Google Patents

Abstract

PURPOSE:To switch a large magnetic field at a high speed by providing a permanent magnet and a core part made of a high magnetic permeability magnetic material which has at least one part opposite to the magnetic pole of said magnet and a coiled part. CONSTITUTION:The titled device is constituted of the plate-like permanent magnet 22 and the core part 23 made of the L-type high magnetic permeability magnetic material composed of the part opposite to one magnetic pole of the magnet 22 and the coil 24, which is connected to a current source 24. When a current flowing to the coil 24 does not flow, the core part 23 forms a magnetic path leading the flux generated from one magnetic pole of the magnet 22 to other magnetic pole as shown in figure (a), whereby a magnetic field will not be impressed downward the core part 23. On the other hand, when the current I flows in the coil 24, only the flux component caused by the current I leaks outside from the magnetic pole of the magnet 22, and a bias magnetic field is impressed in the vertical direction downward the core part 23. Accordingly, when a recording medium 1 is disposed downward the core part 23, the impression of the magnetic field to the medium 1 in the vertical direction can be controlled by a coil current.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic field application device capable of switching a large magnetic field at high speed.

(Prior art and its problems) For example, in conventional magneto-optical recording, when erasing recorded information, an external magnetic field is applied with the opposite polarity to that during recording, and a laser beam is used to record with the same intensity as during recording. The magnetization state of the recording medium returns to the initial state before recording by applying an external magnetic field that uniformly irradiates the medium, which performs so-called batch erasing.

Here, known external magnetic field applying means include, for example, a method using an air-core coil and a method using an electromagnet.

Alternatively, there is a method using a permanent magnet〇However,
This is because an applied magnetic field of several hundred oersted or more is usually required during recording and erasing.

When using an air-core coil, the coil becomes larger.

Along with this, the magnetic field switching speed becomes slower.

There is a drawback that the required applied magnetic field cannot be obtained unless the distance between the recording medium and the coil is made sufficiently close.

In addition, when using an electromagnet, the magnetic field applying means is large and the magnetic field switching speed is slow. Furthermore, when using a permanent magnet, the magnetic field is switched using a mechanical drive means, so a complicated mechanism is required. is necessary, and in this case too, the magnetic field switching speed will be slow.

As mentioned above, since the magnetic field switching speed is slow with any conventional external magnetic field application means, the above-mentioned batch erasing method is used for erasing, and for recording, the laser power is set at high speed while a constant magnetic field is applied. In other words, with conventional devices, it was impossible to provide so-called override performance in which new information is overwritten at high speed on already recorded information.In addition, there are various methods other than magneto-optical recording. In this field, there is a need for a device that can switch large magnetic fields at high speed.

(Object of the Invention) The object of the present invention is to eliminate such conventional drawbacks! 1. It is an object of the present invention to provide a novel means for applying an external magnetic field that is capable of high-speed switching of a large magnetic field.

(Structure of the Invention) The magnetic field application device of the present invention includes a permanent magnet and a core portion made of a high magnetic permeability magnetic material having a portion facing at least one magnetic pole of the permanent magnet and a portion provided with a winding. (Detailed explanation of the configuration) Next, the configuration of the present invention will be explained in detail using one drawing.0 Figure 1 shows an example of the configuration of the magnetic field applying means according to the present invention. The figure shows a core part 23 made of a high permeability magnetic material made of L plastic, which is made up of a plate-shaped permanent magnet 22, a part facing one magnetic pole of the permanent magnet, and a part having a winding 24. Consists of. And winding @24 is connected to the current source and 1 winding @24
As shown in Figure 2 (aL tb), depending on the presence or absence of current to
That is, when no current flows through the first winding M24, the core section 23 creates a magnetic path that efficiently guides the magnetic flux generated from one magnetic pole of the permanent magnet 22 to the other magnetic pole, as shown in FIG. Because of this, almost no magnetic field is applied below the core. On the other hand, as shown in Fig. 2(b), a current I is applied to the winding @24.
If it flows, by the electrician.

Since the magnetic flux generated in the core portion 23 leaks to the outside from the magnetic poles of the permanent magnet 22, a bias magnetic field is applied in the vertical direction below the core.

Figure 2 (C) shows the current I flowing through the winding and the bias magnetic field H.
The zero bias magnetic field H8, which shows the relationship with II, increases as the current I increases, and as the magnetization in the core portion 23 approaches saturation, the bias magnetic field H3 also tends to be saturated, and the current When the value is 8 or more, a large bias magnetic field equivalent to that of a conventional permanent magnet bias can be obtained. For example, when this magnetic field applying means 1- is applied to a magneto-optical recording device, the recording medium 1 is disposed below the core portion 23 as shown in FIG. 2 (aHb). The vertical magnetic field application to is controlled by the single winding current.

Here, a permanent magnet is several millimeters thick.

A samarium cobalt magnet, alnico magnet, or ferrite magnet with a width and length of several millimeters to several tens of millimeters is used, and the core portion 23 is made of NiFe with a thickness of several millimeters and a magnetic path length and width of several millimeters to several tens of millimeters. An alloy or a soft ferrite such as NiZn ferrite or MnZn 7 The appropriate current value is several tens to hundreds of milliamperes. With the magnetic field applying means configured in this way, it is easy to reduce the winding noise inductance L to 1 μH or less, so it is on the order of several hundred oersteds. High-speed switching to the Kurashiki magnetic field can be easily achieved at a position several millimeters away from the end face of the core.

FIGS. 3 to 7 are diagrams showing other configuration examples of the external magnetic field applying means.

In FIG. 3, the core portion 27 is characterized in that the width of the portion where the winding 28 is applied is smaller than the portion facing the magnetic pole of the permanent magnet 22.

In FIG. 4, the thickness of the portion of the core portion 29 where one winding 30 is applied is smaller than that of the portion facing the magnetic pole of the permanent magnet 22.

In FIG. 5, the core portion 31 is characterized in that both the width and thickness of the portion where the winding @32 is applied are smaller than the portion facing the magnetic pole of the permanent magnet 22.

In each of these configuration examples, the cross-sectional area of the core of the winding portion is made smaller than that of the first configuration example shown in FIG. 3, so that the magnetization of the winding portion is saturated at a lower current value. This facilitates high-speed switching of the applied magnetic field.

In FIG. 6, the core part 37 is formed into a U-shaped metal. Therefore, the magnetic flux generated from the magnetic pole of the permanent magnet 22 can be guided to the other magnetic pole more efficiently than in the first configuration example. The core part 40 is provided with a hole 42 of the same size as the inner diameter of the ax when the power is not applied to the axe 36, and the hole is aligned with the inner diameter t-S. When applied to magneto-optical recording, the hole 42 can be used as a path for the light beam, so it is suitable when the external magnetic field applying means is placed on the same side of the recording medium as the original head. An adhesive or the like may be formed between the magnetic pole and the high magnetic permeability magnetic material, and a certain distance may exist between the magnetic pole and the high magnetic permeability magnetic material. It is desirable that the current source 20 has the same shape as the magnetic pole end face or a larger shape, but it may be smaller than the shape of the magnetic pole end face as long as it does not affect recording or erasing. A magnet having a current control function may be used, or a current control means may be provided separately.Furthermore, the high magnetic permeability magnetic material may be formed at a position facing both magnetic poles of the permanent magnet.

(Example) Using the magneto-optical recording/reproducing/erasing device shown in FIG. 8, information was recorded, reproduced, and erased on a magneto-optical disk. As the external magnetic field applying means, the one shown in FIG.
mm alnico magnet is used, and the core part is Mn
Zn ferrite with a thickness of 2 mr at the part facing the magnetic pole.
r) One winding part was molded into a flit of 35 mm with a thickness of 1 m and a height of 10 mm.

The zero winding, which is made by bonding these two together with an adhesive, is made by winding 50 turns of a wire with a wire diameter of 100 μm. In FIG. 8, such external magnetic field applying means 4 and 5 are arranged on both sides of the recording medium so that the magnetic poles N of the permanent magnets face each other. The angle indicated by the blade S is preferably 45° or more.0 Therefore, while the coil 4 is energized, a downward bias magnetic field is applied to the recording medium, and while the coil 5 is energized, an upward magnetic field is applied.◎Here, 20 is It is a current source. The magneto-optical recording head 3 is the same as the conventional one, and has the following configuration.

6 is a linearly polarized laser light source, for example, a semiconductor laser is used. 7, 8.9 are beam splitters 0 Laser beam focusing lens 10 is actuator I
It is supported by IK. The focus error and tracking error signals are received by a focus error detection light receiving element 12 and a tracking error detection light receiving element 1, respectively.
3 and input to the servo control circuits 14 and 15, and fed back to the actuator 11 as a servo signal. After passing through the polarizing filter 16, the reproduced signal is detected by the reproduced signal detection light receiving element 17, and is amplified by the reproduced signal amplification circuit 18. As the polarizing filter 16, for example, a Gram-Thompson prism is used. As the reproduction signal detection light receiving element 17, for example, a PIN photodiode or an aberration photodiode is used.
A laser light source modulation circuit is used to modulate the laser light source 6 using a diode, and the power of the laser light is modulated during recording, erasing, and reproduction.

As a magneto-optical disk, a disk was used in which a tl TbFe film having a thickness of 800× was formed on a 120 mmφ plastic substrate by sputtering. The board has a width of 0.8 fim, a pitch of 2.5 #m, and a depth of 70 m.
A so-called pre-group substrate in which 6X grooves were formed was used.

FIGS. 9(a) to (d) show recording operation mode diagrams.

External magnetic field application means 4 and 5 are applied while irradiating a laser beam of a certain intensity that can raise the recording medium to a Chieri temperature or higher.
windings IA and 1. respectively. An external magnetic field corresponding to the recording pattern is applied by alternating the modulation current of ◎ First, while irradiating the disk surface with a constant intensity laser beam of 4 mW at a linear velocity of 9 (n/sec), a modulated current of %200 mA at IMHz is applied to the winding of the external magnetic field applying means. As a result, good recording was achieved. When a new recording magnetic field of t-0, 5 MHz was applied to this recording track under the same conditions, recording corresponding to this recording magnetic field was completed. No residue was seen.

Needless to say, it can also be used as a magnetic field applying means in conventional systems.

(Effects of the Invention) As described above, according to the present invention, it is possible to provide an external magnetic field application device capable of high-speed switching of a large magnetic field. As an application of this, for example, the 1-optical magneto-optical recording/reproducing/erasing method can achieve override performance that allows direct desired recording without the need for conventional batch erasing.

[Brief explanation of drawings]

FIGS. 1, 3 to 7 are diagrams showing configuration examples of the present invention, FIGS. Figure 9(a)
~(dl is an operation mode diagram of an embodiment of the present invention. In the figure, 1... magneto-optical disk, 2... magnetic thin film, 3... magneto-optical recording head, 4, 5, 26° 33
．． 34, 35, 38... External magnetic field applying means, 6...
Laser light source, 7, 8.9... Beam splitter. 10... Laser beam focusing lens, 11... Actiniator, 12.13... Light receiving element for error detection,
14.15... Servo control circuit, 16... Polarizing filter, 17... Light receiving element for detecting reproduced signal %18...
Amplification circuit, 19... Laser light source modulation circuit, 2o...
PA ε flow source, 21... Recording medium running direction, 22.39.
・Permanent magnet, 2B, 27, 29, 31, 37, 40・
...core made of high-speed magnetic material, 24.28, 30°32...winding, 42...hole. ￥1 Figure 2 Figure 2 (C) Ls I Taisho Otsu Figure 7 n Figure 0 Figure 9 Words Chestnut Lo Edge Ahi 4 Defect 1

Claims (1)

[Claims] 1. A magnetic field applying device comprising a permanent magnet and a core portion made of a high magnetic permeability magnetic material and having a portion facing at least one magnetic pole of the permanent magnet and a portion provided with a winding.