JPH03205633A - Magneto-optical recorder - Google Patents

Abstract

PURPOSE:To obtain the high reliable magneto-optical recorder by controlling a AC voltage to be given to an exciting coil in relation to an output signal of a synchronous detection circuit. CONSTITUTION:A detected signal of reflected light in projected light to a magneto-optical recording medium 5 is synchronously detected in relation to the AC voltage V2 of the exciting coil 4 for generating a magnetic field to be given to the magneto-optical recording medium 5, and the AC voltage V2 of the exciting coil 4 is controlled in relation to this synchronously detected signal. By this method, the magnetic field intensity given to the magneto-optical recording medium 5 at the time of recording information is controlled to be always its proper magnetic intensity, and a regenerative signal level at the time of reproducing recorded information is stabilized, and then the accuracy of reproducing the information is promoted and hence the reliability is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magneto-optical recording device, and more specifically, it is capable of imparting a magnetic field strength to a magneto-optical recording medium in accordance with the magnetic field sensitivity of the magneto-optical recording medium. This paper proposes a magneto-optical recording device.

[Conventional technology]

A conventional magneto-optical recording device records information by projecting a light beam onto a magneto-optical recording medium loaded therein and applying a magnetic field generated at a constant intensity to the projection position.

On the other hand, a magneto-optical recording medium has a characteristic that the strength of a magnetic field applied thereto and a reproduction signal for reproducing recorded information are related as shown in FIG. In FIG. 4, the horizontal axis represents the magnetic field strength applied to the magneto-optical recording medium, and the vertical axis represents the amplitude of the reproduced signal.As is clear from FIG. 4, the appropriate magnetic field strength H.
When the magnetic field strength H0 is given, the maximum amplitude of the reproduced signal is obtained, and as the magnetic field strength deviates from the appropriate magnetic field strength H0, the amplitude of the reproduced signal gradually decreases.

[Problem to be solved by the invention]

By the way, the magnetic field sensitivity of a magneto-optical recording medium is uneven and not constant. Therefore, even if a magnetic field of constant strength is applied to the magneto-optical recording medium, the amplitude of the reproduced signal will differ due to the difference in magnetic field sensitivity. This poses a problem in that recorded information cannot be reproduced with high precision and a highly reliable magneto-optical recording device cannot be provided.

In view of such problems, the present invention utilizes the relationship between the magnetic field intensity applied to the magneto-optical recording medium and the amplitude of the reproduction signal of recorded information to control the magnetic field intensity applied to the magneto-optical recording medium. An object of the present invention is to provide a highly reliable magneto-optical recording device that stabilizes the amplitude of a reproduced signal.

[Means to solve the problem]

The magneto-optical recording device according to the present invention performs synchronous detection of a signal detected by the reflected light of the light projected onto the magneto-optical recording medium in relation to an alternating current voltage of an excitation coil that generates a magnetic field applied to the magneto-optical recording medium. The system is designed to control the AC voltage of the excitation coil in relation to the synchronously detected signal.

[Effect]

A photodetector detects the reflected light from the magneto-optical recording medium.

The excitation coil applies a magnetic field to the magneto-optical recording medium. The detection signal of the reflected light is synchronously detected in relation to the AC voltage of the excitation coil. The AC voltage of the excitation coil is controlled in relation to the synchronously detected signal.

Therefore, the intensity of the magnetic field applied to the magneto-optical recording medium changes, and the amplitude of the reproduced signal remains constant.

〔Example〕

The present invention will be described in detail below with reference to drawings showing embodiments thereof.

FIG. 1 is a structural diagram of main parts of a magneto-optical recording device according to the present invention. The output of the oscillator 1 that oscillates the AC voltage vI is input to one input terminal of the multiplier 15 and the first summing amplifier 2. The oscillation frequency of the oscillator 1 is lower than the frequency of the recording signal and higher than the frequency of the magnetic field sensitivity unevenness of the magneto-optical recording medium.
For example, the range is selected from 500H2 to 500KH2. The output voltage v2 of the summing amplifier 2 is applied to an excitation coil 4 having a required number of turns, which is located on the magnetic axis of the permanent magnet 3 and disposed on the magneto-optical recording medium 5 side. Thereby, the magnetic field generated by the permanent magnet 3 and the magnetic field generated by the excitation coil 4 are added together and applied to the magneto-optical recording medium 5. Further, the magnetic pole of the permanent magnet 3 is arranged to face one side of the magneto-optical recording medium 5. On the other side of the magneto-optical recording medium 5, a condenser lens 6 and a mirror 7 are arranged at positions corresponding to the permanent magnets 4. The emitted light from the laser diode 8 passes through a lens 9 and a beam splitter 10, is reflected by the mirror 7, passes through a condenser lens 6, and is projected onto the magneto-optical recording medium 5.

Further, the laser diode 8 is driven by the output of a laser diode drive circuit 11 to which the recording signal S+1 is input manually. The reflected light from the magneto-optical recording medium 5 enters the photodetector 12 via the condenser lens 6, mirror 7 and beam splitter 10. The output of the photodetector 12 is input to a photoelectric conversion amplifier 13, and its output voltage (3) is input to a detection circuit 14. The output voltage v4 of the detection circuit 14 is input to the multiplier I5,
The output voltage is input to one input terminal of a second summing amplifier 17 via a low-pass filter 16. The other input terminal of this addition amplifier 17 is connected to the reference voltage ■ of the reference power supply 18 .

is given, and the bias voltage V3, which is the output voltage of the summing amplifier 17, is inputted to the other input terminal of the summing amplifier 2. The detection circuit 14, multiplier 15, and low-pass filter 16 constitute a synchronous detection circuit.

FIG. 2 is an explanatory diagram showing the relationship between the AC voltage waveform of the oscillator 2 applied to the excitation coil 4 and the waveform of the reproduced signal based on the characteristics of the reproduced signal amplitude with respect to the magnetic field strength shown in FIG. 4. It is. As is clear from this figure, permanent magnet 3
At a magnetic field strength H0 where the magnetic field strength generated by the excitation coil 4 is appropriate, the waveform of the reproduced signal becomes wI0 with respect to the AC voltage waveform w1 applied to the excitation coil 4, which is twice the frequency with a smaller amplitude. You can get it. In addition, the magnetic field strength H+ (Hz
), for an AC voltage waveform Wz (VI'+) that has the same phase as the AC voltage waveform W applied to the excitation coil 4, the waveform of the reproduced signal is Wto (Wz.), and the AC voltage waveform W z ( A reproduced signal waveform having a slightly larger amplitude in the same phase (opposite phase) as W x ) is obtained. From these reproduced signal waveforms, it can be determined whether the magnetic field strength applied to the magneto-optical recording medium 5 is appropriate.

Next, the operation of the magneto-optical recording device configured in this manner will be explained with reference to FIG. 3, which shows the waveforms of the signals at each part. When the oscillator 1 is operated, the alternating current voltage V, which is the oscillation output of the oscillator 1, becomes a sine wave as shown in FIG. 3(A). This alternating current voltage V, is applied to the summing amplifier 2, which receives the output voltage VF of the low-pass filter 16 and the reference voltage (2) of the reference power supply 18. Given the bias voltage v which is the output voltage of addition amp 17 which is the sum of , the output voltage of addition amp 2 becomes
is as shown in FIG. 3(B). That is, the alternating current voltage vl, which is the oscillation output, changes based on the bias voltage vI.

Then, the output voltage 2 of the summing amplifier 2 is applied to the excitation coil 4, which generates a magnetic field in relation to the output voltage v2, and applies a bias magnetic field to the magnetic field of the permanent magnet 3.

By the way, when the magnetic field strength generated by the permanent magnet 3 and the excitation coil 4 is set to H, for example, a magnetic field strength greater than the appropriate magnetic field strength H0 shown in FIG. When recording , the photodetector 12 receives the reflected light from the magneto-optical recording medium 5, and the output voltage . It is obtained as an amplitude modulated wave by . Note that the waveform shown inside the envelope represents the recording signal S1. and the output voltage v
3 (D
), as shown by the solid line in Figure 3 (A), the AC voltage ■
, which is obtained with the opposite phase to the waveform of . That is, as explained in FIG. 2, a magnetic field strength H+ greater than the appropriate magnetic field strength H0 is detected. This output voltage ■4 and the output voltage v1 which is the oscillation output of the oscillator 2 are multiplied by the multiplier 15, and when the multiplied output voltage of the multiplier 15 is passed through the low-pass filter 16, the output voltage ■2 of the low-pass filter 16 is Figure 3 (
The voltage becomes negative as shown by the solid line in E). This output voltage V,
is input to the summing amplifier 17, and the bias voltage V output from the compensating amplifier 17 decreases. As a result, the output voltage vz of the summing amplifier 2 decreases, and the intensity of the bias magnetic field generated by the excitation coil 4 decreases. In other words, the strength of the magnetic field applied to the magneto-optical recording medium 5 is reduced.

Further, when the strength of the magnetic field applied to the magneto-optical recording medium 5 is small, the operation is similar to that described above, and the output voltage V4 of the detection circuit l4 becomes as shown by the broken line in FIG. 3(D), and the low-pass filter 16 The output voltage VF becomes a positive voltage as shown by the broken line in Figure 3(E). Then, the bias voltage increases and the intensity of the bias magnetic field generated by the excitation coil 4 increases.

Furthermore, when the magnetic field strength applied to the magneto-optical recording medium 5 is appropriate, the output voltage v4 of the detection circuit 14 is as shown in FIG. 3(D).
As shown by the dashed line, the amplitude becomes twice the frequency with a smaller amplitude. Then, the output voltage VF of the low-pass filter 16 becomes zero.

In this way, the reflected light from the magneto-optical recording medium 5 is received,
The bias generated by the excitation coil 4 by the feedback loop that synchronously detects the signal obtained by photoelectric conversion using the AC voltage output from the oscillator 1 to obtain the output voltage and supplies the related voltage to the excitation coil 4. Always keep the magnetic field at an appropriate magnetic field strength H. will be controlled. Thereby, a magnetic field corresponding to the magnetic field sensitivity is applied to the magneto-optical recording medium 5, and information based on the recording signal S1 is recorded.

As a result, the level of the signal for reproducing the recorded information is constant, and the accuracy of reproducing the recorded information can be improved.

In this embodiment, a bias magnetic field is applied to the magnetic field of the permanent magnet 3, but the reference voltage (2) of the reference power supply 18 is applied. By increasing the value, the strength of the magnetic field generated by the excitation coil 4 can be increased, and in this case, a magnetic field of the required strength can be applied to the magneto-optical recording medium 5 using only the excitation coil 4.

Moreover, when the permanent magnet 3 and the excitation coil 4 are used together, the excitation power of the excitation coil 4 becomes small, and of course it is possible to achieve miniaturization and reduction of power consumption.

The magneto-optical recording medium on which information is recorded in this example has characteristics in which the magnetic field intensity applied to it and the reproduction signal that reproduces the recorded information are related as shown in FIG. This is particularly effective when information is recorded on the magneto-optical recording medium described in the earlier application (Patent Application No. 119244 of Heikai 1) shown in FIG.

FIG. 5 is an enlarged sectional view of the magneto-optical recording medium. Fifth
In the figure, 19 is a magneto-optical recording medium, and 20 is a substrate made of glass or plastic.

A first magnetic layer 21 is laminated on the substrate 20 and has perpendicular magnetic anisotropy.

22 is a second magnetic layer laminated on the first magnetic layer 21;
It has perpendicular magnetic anisotropy and is coupled to the first magnetic layer 21 by exchange force, so that the magnetization is maintained in a fixed direction without reversing the magnetization during recording and reproduction.

Reference numeral 23 indicates a region of the information recorded in the first magnetic layer 21, in which the magnetization direction of the first magnetic layer 21 is upward, in this case as "l" of the binary data.

The first magnetic layer 21 and the second magnetic layer 22 have T C I <
T C Z (however, Tc+, T"cz are the Curie temperatures of the first magnetic layer 21 and the second magnetic layer, respectively) and room temperature H
c+>Hw++Hb , Hcz>Hwt+Hb (H
c+ and Hcz are the coercive forces of the first magnetic layer 21 and the second magnetic layer near room temperature, respectively, HWI+ }Iwz are the exchange coupling forces of the first magnetic layer 21 and the second magnetic layer near room temperature, respectively, and H is not shown. The external magnetic field generated by the magnetic field generator is formed by, for example, a rare earth metal-transition metal alloy composition.

In other words, the magneto-optical recording medium of the prior application has at least a first magnetic layer that has perpendicular magnetic anisotropy and whose magnetization direction is reversible, and a second magnetic layer that has perpendicular magnetic anisotropy and whose magnetization direction cannot be reversed. It is a magneto-optical recording medium that is laminated with a magnetic field, and there is no need to reverse the direction of the external magnetic field when recording information, so information can be recorded using a permanent magnet in the external magnetic field.

In addition, a separate patent application No. 15491 has already been filed.
It is also effective when recording information on the magneto-optical recording medium described in the specification of No. 8.

FIG. 6 is an enlarged sectional view of a magneto-optical recording medium having four magnetic layers described in the specification of Patent Application No. 154918 of 1999.

This magneto-optical recording medium 19 has a dielectric layer 40A on a substrate 20 made of glass, for example, and a recording layer 40B, a recording auxiliary layer 40C, and a control layer 4 on the dielectric layer 40A.
0D, initialization layer 40E, and protective layer 40F are laminated in that order. Note that the recording layer 40B (first layer) and the initialization layer 40E (fourth layer) are the first magnetic layer 21 and the magneto-optical recording medium 19 having the first magnetic layer 21 and the second magnetic layer 22 described above. It has the same function as the second magnetic layer 22.

Then, each layer is formed by sputtering or the like, for example, as shown in Table 1.
It is made of materials and thicknesses shown in the table below.

Table 1 These magnetic layers have the following characteristics.

Adjacent magnetic layers are coupled by exchange forces. Recording layer (first
Layer) 40B records and retains information. Recording auxiliary layer (second layer) 40C, control layer (third layer) 40D and initialization layer (
The fourth layer>40E is an additional layer that has the function of retaining information and enables optical modulation direct overwrite. does not reverse the current, but acts against the bias magnetic field. The control layer 400 functions to block the exchange force from the initialization layer 40E in a high temperature range.

Here, Tel is the Curie temperature of the i-th layer (where i = 1 to 4), HCI is the magnetic field width (corresponding to coercive force) half of the reversal magnetic field of the i-th layer, and HwI is the magnetic field width from the adjacent magnetic layer. The exchange force that the i-th layer receives (the transition width of the loop in the i-th layer, the second
The third layer is defined for magnetization reversal as shown in FIG.

FIG. 7 shows a conceptual diagram of sublattice magnetization. Here the i-th
For example, if the layer is the third layer, the upper and lower layers, that is, the second,
The magnetization directions of the fourth layer and the third layer are shown in FIG.
) or (b). Further, as shown in FIG. 7(a), when the direction of magnetization of the i-1th layer and the direction of magnetization of the i+1th layer are in directions that are separated from each other, the direction of magnetization of the i-th layer is The state is such that it faces toward the 1st layer or the i+1th layer. On the other hand, as shown in FIG. 7(b), when the direction of magnetization of the i-1th layer and the direction of magnetization of the i+1th layer approach each other, the direction of magnetization of the i-th layer is Or it will be in a state of facing towards the i-1th layer.

Defined in this way, the magnetization property is Tca>(TCOIIP4)>TC! ＞TC
I>(Tcopg)>Tct>Room temperature
...(1) Recording layer 40B
: H@+ < Hc+ :~Room temperature...(2)H
wI>Hc+'~TCI...(3)
Recording auxiliary layer 40C: Hwz> Hcz: ~TC
3...(4) Hwt< Hcz: ~Tc+
-(5) Control layer 400: Hl. l*＞H
C3:~T. 3.(6) Initialization layer 408:
H. ．． la < Hca: ~ within operating temperature range...
・(7) (However, Tcompz. Tcomp= is the compensation temperature of the second and fourth layers), and in equation (2), the magnetization of the recording layer 40B is not reversed at room temperature due to the magnetization reversal of the recording auxiliary layer 40C,
(4L Equations (6) and (7) indicate that the magnetization directions of the recording auxiliary layer 40C, control layer 40B, and initialization layer 40H are aligned downward at room temperature after recording.

Also in such a magneto-optical recording medium, when recording information, there is no need to reverse the direction of the external magnetic field, and information can be recorded using a permanent magnet in the external magnetic field.

However, this magneto-optical recording medium has a narrow range of magnetic field strength for recording information. Therefore, the magneto-optical recording device of the present invention, which can control the magnetic field produced by the excitation coil to control the strength of the total magnetic field produced by the permanent magnet and the excitation coil, is ideal for recording information on such a magneto-optical recording medium.

Further, although this embodiment has been described with respect to a magneto-optical recording device which is a recording-only device, similar effects can be obtained even if the present invention is applied to a magneto-optical recording and reproducing device which is a dual-purpose device for recording and reproducing.

〔Effect of the invention〕

As described in detail above, according to the present invention, the magnetic field strength applied to the magneto-optical recording medium during information recording is controlled and can always be maintained at an appropriate magnetic field strength. Thereby, it is possible to stabilize the level of the reproduced signal when reproducing recorded information, improve the accuracy of information reproduction, and provide an excellent effect of providing a highly reliable magneto-optical recording device.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of main parts of a magneto-optical recording device according to the present invention,
Figure 2 is an explanatory diagram showing the relationship between the AC voltage waveform of the oscillator and its reproduced output waveform, Figure 3 is a waveform diagram of various signals, and Figure 4 is the magnetic field strength applied to the magneto-optical recording medium and the reproduced signal amplitude. Figure 5 is an enlarged cross-sectional view of a magneto-optical recording medium, Figure 6 is an enlarged cross-sectional view of a magneto-optical recording medium with four magnetic layers, and Figure 7 is a conceptual diagram of sublattice magnetization. It is. 1... Oscillator 2... Adding amplifier 3... Permanent magnet 4... Excitation coil 5... Magneto-optical recording medium 8.
...Laser diode 10...Beam splitter
12... Photodetector 13... Photoelectric converter 21...
・First magnetic layer 22... Second m-layer 40B... Recording layer 40C... Recording auxiliary layer 400... Control layer 4
0E...Initialization layer In the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] (1) An excitation coil that generates a magnetic field applied to a magneto-optical recording medium, an oscillator that applies an alternating current voltage to the excitation coil, a photodetector that detects reflected light from the magneto-optical recording medium, and a photodetector that detects reflected light from the magneto-optical recording medium. and a synchronous detection circuit that synchronously detects an output signal in relation to the AC voltage of the oscillator, and is configured to control the AC voltage applied to the excitation coil in relation to the output signal of the synchronous detection circuit. Features of magneto-optical recording device.