JPH11283290A - Information signal reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately reproduce an information signal by cyclically displacing a boundary position between the movable and immovable areas of a magnetic wall back and forth in a scanning direction so as to temporally separate the first and second movements of the magnetic wall, and thereby selectively extracting a signal change corresponding to the first movement of the magnetic wall or a signal change corresponding to the second movement. SOLUTION: A signal track 21 is provided with a means for forming a movable area of a magnetic wall so as to move the same, a means for detecting the movement of the magnetic wall, and a means for reproducing an information signal based on the detected movement of the magnetic wall. The magnetic wall moving means cyclically displaces a boundary position between the movable and immovable areas of the magnetic wall back and forth in a scanning direction while scanning the signal track 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an information signal reproducing apparatus for reproducing an information signal recorded on a recording medium, and more particularly to an information signal reproducing apparatus for reproducing an information signal by a domain wall displacement reproducing method.

[0002]

2. Description of the Related Art Conventionally, various methods for reproducing recorded information on a recording medium are known. In particular, the applicant of the present application has previously proposed a domain wall motion reproducing method in Japanese Patent Application Laid-Open No. 6-290496. The domain wall motion reproduction method uses a magneto-optical recording medium in which an information signal is formed by domain walls on a signal track, moves the domain wall at high speed by applying a driving force to the domain wall, and detects the movement by detecting the movement. A signal is reproduced, and an information signal recorded at a very high recording density can be reproduced. Hereinafter, the principle of reproduction by the domain wall displacement reproduction method will be described.

FIGS. 9A and 9B are partially enlarged views showing the configuration of a magneto-optical recording medium 30, in which FIG. 9A is a side sectional view and FIG. In FIG. 9, first, the magneto-optical recording medium 3
0 is a substrate 31 made of a transparent material such as polycarbonate,
And a band-like signal track 32 formed on the substrate 31. The signal track 32 has a configuration in which three layers made of a magnetic material, that is, a domain wall displacement layer 33, a switching layer 34, and a magnetic recording layer 35 are stacked. The domain wall displacement layer 33 is a perpendicular magnetization film having a smaller domain wall coercive force and a larger domain wall mobility than the magnetic recording layer 35, and the switching layer 34 is a film of a magnetic material having a lower Curie temperature than the domain wall displacement layer 33 and the magnetic recording layer 35. The recording layer 35 is a perpendicular magnetization film. The signal track 32 and regions on both sides thereof are not magnetically coupled at least in the domain wall motion layer 33.

[0004] In the signal track 32, a row of magnetized regions having an upward or downward magnetization is formed as shown by an up and down arrow in the figure, and information is provided at a boundary between the magnetized region and the preceding and succeeding magnetized regions. Domain walls Q1, Q2, ... which are signal marks
., Q9 are formed in a line. These domain walls are exchange-coupled between the domain wall displacement layer 33, the switching layer 34, and the magnetic recording layer 35.

Next, a method of reproducing an information signal from the magneto-optical recording medium 30 by a magneto-optical reproducing device will be described. Usually, a magneto-optical reproducing device has an optical head,
The optical head scans the signal track 32 while the light beam for reproduction converges and irradiates the signal track 32 of the magneto-optical recording medium. FIG. 10 is a diagram for explaining the principle of signal reproduction.
FIG. 2A is an enlarged cross-sectional view of a portion of the magneto-optical recording medium 30 irradiated with a reproducing light beam, and FIG. The reproduction light beam is applied to the substrate 31 of the magneto-optical recording medium 30.
Is transmitted to the signal track 32 so as to converge on a minute light spot 36. The light spot 36 of the reproducing light beam scans the signal track 32 in the direction of arrow A.

When the reproducing light beam is irradiated as described above,
The signal track 32 is heated, and a temperature distribution having a peak at a position Xp slightly behind the center of the light spot 36 is formed. Here, reference numeral 37 denotes an isotherm indicating a region where the temperature reaches Ts which is a temperature near the Curie temperature of the switching layer 34. As described later, in the domain wall displacement layer 33 of the signal track 32, a region where the temperature is equal to or higher than Ts, that is,
The domain wall can move in a region surrounded by the isotherm 37, and cannot move in other regions. Further, Xf and Xr in the drawing are a first boundary position and a second boundary position of a region where the domain wall is movable and a region where the domain wall is not movable in the domain wall displacement layer 33 of the signal track 32.

The temperature at a certain point on the signal track 32 rises above the temperature Ts at the first boundary position Xf in the process of passing through the irradiation area of the light spot 36, and after reaching a peak at the position Xp. The temperature starts to fall, and falls again below the temperature Ts at the second boundary position Xr. At a position distant from the light spot 36 of the reproducing light beam, the temperature of the signal track 32 is sufficiently low. At this position, the domain wall displacement layer 33, the switching layer 34, and the magnetic recording layer 35 are exchange-coupled to each other. The domain wall formed on the recording layer 35 is also transferred to the switching layer 34 and the domain wall moving layer 33. Further, since the temperature distribution around the periphery is substantially uniform, no driving force for moving the domain wall transferred to the domain wall moving layer 33 acts, and thus the domain wall is fixed.

However, the portion of the switching layer 34 between the first boundary position Xf and the second boundary position Xr has a temperature T.
Since the magnetization has been lost higher than s, the domain wall displacement layer 3
3, the switching layer 34 and the magnetic recording layer 35 are not exchange-coupled to each other, and the domain wall displacement layer 33 is
The domain wall is movable in the domain wall motion layer 33 because it is not magnetically coupled to the two regions on both sides. Moreover, the domain wall reaching the first boundary position Xf (Q in FIG. 10)
5) receives the driving force due to the temperature gradient. For this reason, the domain wall is in the first domain wall moving layer 33 as shown by the arrow Bf.
Starts moving from the boundary position Xf at a high speed to a position Xp where the temperature is high and the domain wall energy is low. As the domain wall moves, a magnetized region Rfex having a magnetization in one direction (upward in the illustrated example) is formed while extending. Here, the movement of the domain wall starting from the first boundary position Xf is referred to as a first movement here. The magnetic recording layer 35
Is made of a material having a small domain wall mobility, the domain wall does not move in the magnetic recording layer 35.

Thus, the domain walls Q1, Q2,..., Q9
Causes a first movement each time the first boundary position Xf is reached, and a magnetization region Rfex having an upward and downward magnetization is alternately formed each time. The polarization plane of the reflected light of the reproducing light beam from the magnetization region Rfex rotates according to the direction of magnetization of the magnetization region Rfex due to the magneto-optical effect (Kerr effect). Such rotation of the polarization plane is detected by an optical head, and the detection signal includes a change in a signal corresponding to the movement of the domain wall. Therefore, if the domain wall is formed at a position corresponding to the information signal, the signal is obtained. The information signal can be reproduced from the timing of the change.

[0010]

As described above, the information signal is reproduced by detecting the first movement of the domain wall that has reached the first boundary position Xf. on the other hand,
Since magnetization is generated again in the switching layer 34 at the second boundary position Xr, the domain wall displacement layer 33, the switching layer 34, and the magnetic recording layer 35 are exchange-coupled to each other.
The domain wall (Q1 in FIG. 10) in the magnetic recording layer 35 that has reached the second boundary position Xr is transferred to the domain wall moving layer 33 via the switching layer. Further, when the magnetized region is transferred to the domain wall motion layer 33 after the domain wall,
A new domain wall (Q1 ′ in FIG. 10) is formed on the domain wall displacement layer 33 so as to face the transferred domain wall (Q1).
The domain wall receives a driving force due to a temperature gradient, and the second boundary position Xr in the domain wall displacement layer 33 as indicated by an arrow Br.
, Starts moving at a high speed toward a position Xp where the temperature is high and the domain wall energy is low.

Along with the movement of the domain wall, a magnetized region Rrex having magnetization in one direction (upward in the illustrated example) is formed while extending. Such a second boundary position Xr
Here, the movement of the domain wall starting from is referred to as a second movement (the actually moved domain wall is a newly formed domain wall Q1 ', which is referred to as "the domain wall Q1 moves" for convenience). As described above, the domain wall causes not only the first movement at the first boundary position Xf but also the second movement at the second boundary position Xr, and the detection signal of the optical head indicates the second movement of such a domain wall. The change in the signal corresponding to the second movement at the boundary position is mixed.

Here, when the temperature peak position Xp in the signal track 32 is close to the center of the light spot 36 of the reproducing light beam, the change of the signal corresponding to the second movement at the second boundary position Xr of the domain wall. Is the first boundary position Xf
Has a magnitude that cannot be ignored compared to the change in the signal corresponding to the first movement at In such a case, the first domain wall
It is difficult to distinguish and separate a signal change corresponding to the first movement at the boundary position Xf from a signal change corresponding to the second movement at the second boundary position Xr. Could not play.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide an information signal reproducing apparatus capable of temporally separating the first and second movements of the domain wall and accurately reproducing information. Aim.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an information signal reproducing apparatus for reproducing an information signal recorded on a signal track of an information recording medium by a domain wall. A means for moving the domain wall by forming a magnetic field, a means for detecting the movement of the domain wall, and a means for reproducing an information signal based on the detected movement of the domain wall. This is achieved by an information signal reproducing device, wherein a boundary position between a region where the domain wall is movable and a region where the domain wall is not movable is periodically shifted back and forth while scanning.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of an information signal reproducing device according to the present invention. In FIG. 1, the magneto-optical recording medium 1 has a disk shape, and has three magnetic layers 21 laminated on a transparent substrate 20. The magneto-optical recording medium 1 is rotated by driving a spindle motor 2. On the lower surface of the recording medium 1, an optical head 3 that converges and irradiates a reproducing light beam through a substrate 20 on a signal track of the recording medium 1 is arranged. The optical head 3 includes a laser light source 11, an optical sensor 12, an optical system (not shown) such as an objective lens, and an actuator (not shown) for driving the objective lens in a focus direction and a tracking direction. Although not shown in FIG. 1, the actuator in the optical head 3 is controlled to displace the objective lens in the focusing direction and the tracking direction so that the light beam from the optical head 3 is positioned on the signal track of the recording medium 1. A servo control circuit for performing focus control and tracking control so as to converge accurately and scan so as to follow a signal track is provided.

The output of the optical sensor 12 is connected to an amplifier circuit 5, and the output of the amplifier circuit 5 is connected to a first information signal reproducing circuit 6, a second information signal reproducing circuit 7, and a clock signal generating circuit 8. I have. The first information signal reproducing circuit 6 generates a first information signal including only a change in a signal corresponding to the first movement of the domain wall, as will be described later in detail. The second information signal generating circuit 7 generates a first information signal of the domain wall. A circuit for generating a second information signal including only a signal change corresponding to the second movement, that is, a clock signal generating circuit 8 is a circuit for detecting a clock signal recorded on the recording medium 1.

The output of the clock signal generation circuit 8 is supplied to a first gate signal generation circuit 9, a second gate signal generation circuit 10,
And the laser drive circuit 4. The first gate signal generation circuit 9 generates a gate signal indicating a period in which information of the first information signal reproduction circuit 6 is detected based on the clock signal, and the second gate signal generation circuit 10 similarly generates a clock signal. This is a circuit that generates a gate signal indicating a period for detecting information of the second information signal reproducing circuit 7 based on the signal.
Further, the laser drive circuit 4 supplies a drive current that increases and decreases at a constant cycle in synchronization with the generated clock signal.
Circuit.

FIG. 2 is a partially enlarged view showing the configuration of the magneto-optical recording medium 1. (A) is a side sectional view, and (b) is a view as seen from a lower surface direction. In FIG. 2, the magneto-optical recording medium 1 includes a substrate 20 made of a transparent material such as polycarbonate, and a band-like signal track 21 formed on the substrate 20. The signal track 21 has three layers made of a magnetic material,
That is, the configuration is such that the domain wall displacement layer 22, the switching layer 23, and the magnetic recording layer 24 are stacked. The domain wall displacement layer 22 is a perpendicular magnetization film having a smaller domain wall coercive force and a larger domain wall mobility than the magnetic recording layer 24, and the switching layer 23 is a domain wall displacement layer 2
2 and a magnetic material film having a lower Curie temperature than the magnetic recording layer 24, and the magnetic recording layer 24 is a perpendicular magnetization film. The signal track 21 and the regions on both sides thereof are not magnetically coupled at least in the domain wall motion layer 22.

In the signal track 21, a row of magnetized regions having an upward or downward magnetization is formed as shown by the up and down arrows in the figure, and at the boundary between the magnetized region and the front and rear magnetized regions, Domain walls Q1, Q2, which are information signal marks
., Q9 are formed in a line. Each of these domain walls is
Domain wall displacement layer 22, switching layer 23, magnetic recording layer 24
Exchange-coupled between In FIG. 2, the information signal is a digital signal composed of “0” and “1”, and an NRZI (Non Return to Zeus) that forms a domain wall corresponding to “1”.
ro Inverted) An information signal is recorded by a recording method. At this time, the formation interval of each domain wall is kLm
(Where k is an integer of 1 or more and Lm is a constant).

FIG. 3 shows a signal track 2 of the magneto-optical recording medium 1.
1 is a diagram showing a configuration of FIG. An information signal recording area 25 in which a domain wall as an information signal mark is formed in the signal track 21.
In addition, a clock signal recording area 26 for recording a clock signal mark for obtaining a clock signal necessary for reproducing the information signal by using a magnetic wall, a pit, or the like is provided. The information signal recording area 25 and the clock signal recording area 26 are provided alternately at a constant cycle. Each clock signal recording area 26
Have about 2 to 10 domain walls, which are clock signal marks. In the example of FIG. 3, four clock signal marks, ie, domain walls Qc1, Qc2, Qc3, and Qc4 are formed at equal intervals Lm. Here, the domain walls Qc1, Qc2,
It is desirable that Qc3 and Qc4 be formed sufficiently apart from the domain wall serving as the information signal mark (at least not less than the length of a region where the domain wall can be moved in a signal track described later).

Next, the information signal reproducing operation of the present embodiment will be described. When reproducing an information signal, first, the magneto-optical recording medium 1 is rotationally driven by the spindle motor 2,
Thus, the optical head 3 scans the magneto-optical recording medium 1 at the speed Vs. Next, a current is supplied from the laser drive circuit 4 to the laser light source 11 of the optical head 3 to turn on the laser light source 11. The reproduction light beam emitted from the laser light source 11 is focused on a minute light spot through an optical system such as an objective lens.
The signal track 21 is transmitted through the substrate 20 and irradiated. At this time, in the servo control circuit, focusing control and tracking control are performed so that the reproducing light beam accurately converges on the rotating signal track 21 of the magneto-optical recording medium 1 and performs tracking scanning.

The reflected light of the reproducing light beam from the recording medium 1 is detected as an electric signal by the optical sensor 12, and the detected signal is amplified by the amplifier circuit 5. The clock signal generation circuit 8 detects a clock signal mark formed on the magneto-optical recording medium 1 from the output signal of the amplification circuit 5 and generates a clock signal of a constant frequency based on the detected signal. To send to. The period (the basic period of the information signal) T of the clock signal generated here is Lm / Vs
Is assumed to be equal to When the clock signal mark is formed by the domain wall, it can be detected by the domain wall movement reproduction method as described above.

In this case, a small number (for example, about 2 to 10) of domain walls serving as clock signal marks are formed at short intervals, for example, at equal intervals Lm, and the domain walls serving as information signal marks are sufficiently formed (at least signal tracks described later). In this case, the first and second movements of the domain wall, which is a clock signal mark, are temporally separated from each other, so that the information signal can be separated from the information signal. The movement of the domain wall as a mark can be temporally separated. Therefore, the movement of the domain wall, which is the clock signal mark, can be detected without necessarily displacing the boundary position between the region where the domain wall can be moved and the region where the domain wall cannot be moved as described later.

Next, the laser drive circuit 4 supplies the laser light source 22 with a drive current that increases and decreases at a constant cycle Th in synchronization with the clock signal input from the clock signal generation circuit 8. Here, as an example, the period Th is assumed to be equal to the period T (= Lm / Vs) of the clock signal. Thereby, the irradiation intensity of the reproducing light beam repeatedly increases and decreases in the cycle Th. The irradiation intensity of the reproducing light beam is half a cycle Th /
2 and decrease during the remaining half cycle Th / 2.

FIGS. 4 and 5 show the state of the irradiated area of the reproduction light beam on the signal track 21 when reproducing the information signal recorded on the magneto-optical recording medium 1 of FIG. FIG.
(A) to (c) and FIGS. 5 (a) and (b) show the states of the signal tracks 21 at times t1 to t5 for each half cycle Th / 2 of the change in the irradiation intensity of the reproduction light beam. . FIG. 6 is a graph showing the time change of the position of each domain wall in FIGS. 4 and 5 during the time points t1 to t5. FIG.
The horizontal axis indicates the position of each domain wall at the irradiation position of the reproducing light beam in FIGS. 4 and 5, and the vertical axis indicates time. T1 in FIGS. 4 and 5
To t5 respectively correspond to t1 to t5 in FIG. 4 (a), (c) and FIG. 5 (b) show time points t1 and t, respectively.
FIGS. 4B and 5A show the state where the irradiation intensity of the reproducing light beam is minimum at times t3 and t5, respectively.
2 and t4, a state in which the irradiation intensity of the reproducing light beam is maximized.

First, in the drawing, reference numeral 27 denotes a light spot of a reproducing light beam. The speed V of the signal track 21 is changed in the direction indicated by the arrow A (leftward in the drawing) as the magneto-optical recording medium 1 rotates.
Scan with s. However, FIGS. 4A to 4C and FIG. 5A
6 (b) and FIG. 6 show that the horizontal position of the light spot 27 of the reproduction light beam is fixed and the signal track 21 moves relatively to the light spot 27. 4, 5, and 6, the domain walls Q 1, Q 2,..., Q 9 formed on the signal track 21 have a direction opposite to the scanning direction of the reproducing light beam indicated by the arrow A with the passage of time. (To the right in the drawing).

When the reproducing light beam is irradiated in this manner, the signal track 21 is heated, and a temperature distribution having a peak at a position Xp located behind the center of the light spot 27 is formed. Here, reference numeral 28 denotes an isotherm indicating a region where the temperature reaches Ts which is a temperature near the Curie temperature of the switching layer 23, and a region where the temperature is equal to or higher than Ts in the domain wall displacement layer 22 of the signal track 21 as described later. The domain wall is movable in a region surrounded by the isotherm 28,
In other regions, the domain wall cannot be moved.
In the drawing, Xf and Xr are the first boundary position and the second boundary position of the domain where the domain wall is movable and the domain where the domain wall is not movable in the domain wall motion layer 22 of the signal track 21.

Here, the isothermal line 28 repeats the expansion during Th / 2 and the reduction during Th / 2 as the irradiation intensity of the reproducing light beam increases or decreases.
The region in which the domain wall is movable above s is also enlarged and reduced accordingly. In addition, the first boundary position Xf
4 (a) to 4 (c) and FIG.
As shown in FIGS. 6A and 6B and FIG. 6, the light beam is displaced back and forth with respect to the scanning direction of the reproducing light beam. However, the directions of displacement of the first boundary position Xf and the second boundary position Xr are opposite to each other. Here, the amplitudes of the periodic displacements of the first boundary position Xf and the second boundary position Xr are both Lm / 2.
It is assumed that the change in the irradiation intensity of the reproducing light beam is adjusted so that

Next, when an information signal is reproduced by the domain wall displacement reproducing method, the temperature of a certain point on the signal track 21 is changed in the process of passing through the irradiation area of the light spot 27 as the magneto-optical recording medium 1 rotates. Temperature Ts at first boundary position Xf
After reaching the peak at the position Xp, it starts to fall, and again at the second boundary position Xr, the temperature T
s. At a position distant from the light spot 27 of the reproducing light beam, the temperature of the signal track 21 is sufficiently low. At this position, the domain wall displacement layer 22, the switching layer 23, and the magnetic recording layer 24 are exchange-coupled to each other. The domain wall formed in the recording layer 24 includes the switching layer 23,
It is also transferred to the domain wall motion layer 22. Further, since the temperature distribution around the periphery is almost uniform, no driving force for moving the domain wall transferred to the domain wall moving layer 22 acts, and the domain wall is fixed.

However, the portion of the switching layer 23 between the first boundary position Xf and the second boundary position Xr has a temperature T.
Since the magnetization has been lost higher than s, the domain wall displacement layer 2
2. Since the switching layer 23 and the magnetic recording layer 24 are not exchange-coupled to each other, and the domain wall motion layer 22 is not magnetically coupled to the regions on both sides of the signal track 21, the domain wall moves in the domain wall motion layer 22. It is possible. And the first
The domain wall that has reached the first boundary position Xf receives a driving force due to the temperature gradient, and as a result, the domain wall that has reached the first boundary position Xf has a higher domain wall energy than the first boundary position Xf in the domain wall moving layer 22. Starts moving at a high speed toward the position Xp having a lower value. This is the first movement of the domain wall,
Along with this, a magnetized region Rfex having a unidirectional magnetization is formed while extending. Since the magnetic recording layer 24 is made of a material having a low domain wall mobility, the magnetic recording layer 2
In No. 4, the domain wall does not move.

On the other hand, since magnetization is generated again in the switching layer 23 at the second boundary position Xr, the domain wall motion layer 2
2. The switching layer 23 and the magnetic recording layer 24 are exchange-coupled to each other. As a result, the domain wall in the magnetic recording layer 24 reaching the second boundary position Xr is transferred to the domain wall moving layer 22 via the switching layer 23. Further, when the magnetization region following the domain wall is transferred to the domain wall motion layer 22, a new domain wall is formed in the domain wall motion layer 22 so as to face the transferred domain wall. The newly generated domain wall receives the driving force due to the temperature gradient, and the second boundary position X
It starts moving at a high speed from r to a position Xp where the temperature is high and the domain wall energy is low. This is the second movement of the domain wall, and accompanying this, the magnetization region Rre having one-way magnetization.
x is formed while elongating.

Here, what actually moves is not the first transferred domain wall itself but the newly formed domain wall, but this is simplified and described as "the domain wall causes the second movement". Since the magnetic recording layer 24 is made of a material having a small domain wall mobility, the domain wall does not move in the magnetic recording layer 24. 4 and 5, the domain walls of the magnetic recording layer 24 that do not move at positions overlapping the magnetization regions Rfex and Rrex formed by extending the domain wall motion layer 22 as a result of domain wall motion are indicated by dotted lines.

Thus, the domain walls Q1, Q2,..., Q9
Generates a first movement each time the first boundary position Xf is reached, and an elongated magnetized region Rfex having an upward and downward magnetization is formed alternately each time. Each time the second boundary position Xr is reached, a second movement is generated, and each time the second boundary position Xr is reached, the elongated magnetized region R having the upward and downward magnetization is generated.
rex is formed alternately. These magnetized regions Rfex and Rre
The polarization plane of the reflected light of the reproducing light beam from x rotates according to the direction of magnetization of the magnetized region due to the magneto-optical effect (Kerr effect).

The rotation of the polarization plane is converted into a change in light intensity by the optical system of the optical head 3 shown in FIG.
To detect and output as an electric signal. The detection signal includes a signal change corresponding to the first movement of the domain wall and a signal change corresponding to the second movement. However, in the present embodiment, the first boundary position Xf and the second boundary position Xr
Is displaced back and forth with respect to the scanning direction of the reproducing light beam, thereby temporally separating the first movement and the second movement of the domain wall. Hereinafter, the reason will be described with reference to FIGS.
It will be described in detail based on.

First, at the time point t1, the irradiation intensity of the reproducing light beam is minimum. At this time, as shown in FIG. 4A and FIG. The second boundary position Xr is located at the leftmost position (in the direction opposite to the scanning direction), and the second boundary position Xr is located at the leftmost position (in the scanning direction of the reproduction light beam). Further, between the first boundary position Xf and the second boundary position Xr of the domain wall displacement layer 22, as a result of the movement of the domain wall immediately before the illustrated state, the elongated magnetized regions Rfex and Rrex having downward magnetization (Since the magnetization directions of the magnetized regions Rfex and Rrex are the same, they are integrated and no domain wall is formed between the magnetized regions Rfex and Rrex).

Next, from time t1, the irradiation intensity of the reproducing light beam starts to increase, and at the same time, the isothermal line 28 of the temperature Ts starts to expand. Accordingly, the first boundary position Xf moves to the left (in the scanning direction of the reproducing light beam), and the second boundary position Xr moves to the left.
Is displaced rightward (the direction opposite to the scanning direction of the reproducing light beam). The irradiation intensity of the reproducing light beam becomes maximum at the time point t2 when the time of Th / 2 has elapsed from the time point t1.
At this time, as shown in FIG. 4B and FIG. 6, the first boundary position Xf reaches the leftmost position, and the second boundary position Xr reaches the rightmost position.

Here, during the period from the time point t1 to the time point t2, the first boundary position Xf includes the domain walls Q1, Q2,.
9, the domain wall Q5, which comes closest to the first position, reaches the first boundary position Xf, and at the same time, as shown by a rightward arrow in FIG. A first movement occurs towards position Xp.
With the movement of the domain wall, a magnetized region Rfex having an upward magnetization is extended and formed in the domain wall displacement layer 22 as shown in FIG. Also, Th from time t1 to time t2
Since the amount of displacement of the second boundary position Xr to the right during L / 2 (= T / 2) is Lm / 2, the average speed of the second boundary position Xr is Lm / T, which is Lm / T. , Equal to the scanning speed Vs of the reproducing light beam, and the direction of the displacement is opposite. Accordingly, during this time, no domain wall reaches the second boundary position Xr, and no second movement occurs.

Next, from time t2, the irradiation intensity of the reproducing light beam starts to decrease, and at the same time, the isothermal line 28 of the temperature Ts starts to decrease. Accordingly, the first boundary position Xf is displaced rightward (the direction opposite to the scanning direction of the reproduction light beam), and the second boundary position Xr is displaced leftward (the scanning direction of the reproduction light beam). At the time point t3 when the time of Th / 2 has elapsed from the time point t2, the irradiation intensity of the reproducing light beam becomes minimum.
At this time, as shown in FIG. 4C and FIG. 6, the first boundary position Xf reaches the position closest to the right, and the second boundary position Xr reaches the position closest to the left. Here, during the period from time t2 to time t3, the second boundary position Xr is the domain wall Q1, Q2.
2,..., Q9 are displaced in the opposite direction (left direction), and at the same time the magnetic domain wall Q1 approaching closest reaches the second boundary position Xr, and at the same time, the magnetic domain wall moves as shown by the leftward arrow in FIG. A second movement occurs in layer 22 towards temperature peak position Xp.

With the movement of the domain wall, a magnetized region Rrex having an upward magnetization is extended and formed in the domain wall displacement layer 22 as shown in FIG. Since the magnetization direction of the magnetized region Rrex is the same as that of the previously formed magnetized region Rfex, the two are integrated and the moved domain wall disappears. Further, since the amount of displacement of the first boundary position Xf in the rightward direction between Th / 2 (= T / 2) from time t2 to time t3 is Lm / 2, the average of the first boundary position Xf is averaged. The speed is Lm / T, which is equal to the scanning speed Vs of the reproducing light beam,
The direction of displacement is opposite. Accordingly, during this time, none of the domain walls reaches the first boundary position Xf, and the first movement does not occur.

Next, at time t3, the irradiation intensity of the reproducing light beam starts to increase, and at the same time, the isothermal line 28 of the temperature Ts starts to expand. Accordingly, the first boundary position Xf moves to the left (in the scanning direction of the reproducing light beam), and the second boundary position Xr moves to the left.
Is displaced rightward (the direction opposite to the scanning direction of the reproducing light beam). The irradiation intensity of the reproducing light beam becomes maximum at the time point t4 when the time of Th / 2 has elapsed from the time point t3.
At this time, as shown in FIGS. 5A and 6, the first boundary position Xf reaches the leftmost position, and the second boundary position Xr reaches the rightmost position. Here, during the period from time t3 to time t4, the first boundary position Xf is the domain wall Q1, Q2.
2,..., Q9 are displaced in the opposite direction (left direction), and soon the domain wall Q6, which comes closest, reaches the second boundary position Xf, and at the same time, the domain wall moves as shown by the rightward arrow in FIG. A first movement takes place in the layer 22 towards the temperature peak position Xp.

As shown in FIG. 5A, a magnetization region Rfex having a downward magnetization is formed in the domain wall displacement layer 22 along with the movement of the domain wall. In addition, since the amount of displacement of the second boundary position Xr in the rightward direction between Th / 2 (= T / 2) from time t3 to time t4 is Lm / 2, the average of the second boundary position Xr is calculated. The speed is Lm / T, which is equal to the scanning speed Vs of the reproducing light beam, and the direction of displacement is opposite. Accordingly, during this time, no domain wall reaches the second boundary position Xr, and no second movement occurs.

Next, at time t4, the irradiation intensity of the reproducing light beam starts to decrease, and at the same time, the isothermal line 28 of the temperature Ts starts to decrease. Accordingly, the first boundary position Xf is displaced rightward (the direction opposite to the scanning direction of the reproduction light beam), and the second boundary position Xr is displaced leftward (the scanning direction of the reproduction light beam). At the time point t5 when the time of Th / 2 has elapsed from the time point t4, the irradiation intensity of the reproducing light beam becomes minimum.
At this time, as shown in FIGS. 5B and 6, the first boundary position Xf reaches the position closest to the right, and the second boundary position Xr reaches the position closest to the left.

Here, during the period from time t4 to time t5, the second boundary position Xr is the domain wall Q1, Q2,.
9 is displaced in the opposite direction (left direction), but during this time there is no domain wall reaching the second boundary position Xr, and the second movement does not occur. In addition, Th / 2 (= from time t4 to time t5)
T / 2), the amount of displacement of the first boundary position Xf in the right direction is Lm / 2, so that the average velocity of the first boundary position Xf is Lm / T, which is the reproducing light beam. Scanning speed V
s and the direction of displacement is opposite. Accordingly, during this time, none of the domain walls reaches the first boundary position Xf, and the first movement does not occur.

As described above, during the period in which the first boundary position Xf is displaced in the direction opposite to the scanning direction of the reproducing light beam, the average speed is used as the scanning speed V of the reproducing light beam.
s, the domain wall does not reach the first boundary position Xf during this period, so that the first movement of the domain wall does not occur, and the first boundary position Xf is used for reproduction. The first movement of the domain wall can occur only during the period of displacement in the scanning direction of the light beam. Similarly, during a period in which the second boundary position Xr is displaced in the direction opposite to the scanning direction of the reproducing light beam, the average speed is made substantially equal to the scanning speed Vs of the reproducing light beam, so that this period is reduced. Since none of the domain walls reaches the second boundary position Xr, the second movement of the domain wall does not occur, and during the period when the second boundary position Xr is displaced in the scanning direction of the reproducing light beam. Only the movement of the second domain wall can occur.

During the period in which the irradiation intensity of the reproducing light beam increases, the first boundary position Xf is displaced in the scanning direction of the reproducing light beam, and the second boundary position Xr is shifted in the scanning direction of the reproducing light beam. Since the displacement is performed in a direction opposite to the direction, the first movement of the domain wall can occur during this period, but the second movement does not occur. Conversely, during the period in which the irradiation intensity of the reproducing light beam decreases, the first boundary position Xf is displaced in the direction opposite to the scanning direction of the reproducing light beam, and the second boundary position Xf is displaced.
Since r is displaced in the scanning direction of the reproducing light beam, the first movement of the domain wall does not occur during this period, but the second movement can occur. Therefore, the first movement and the second movement of the domain wall can be temporally separated.

By the above operation, the optical sensor 12 of FIG. 1 outputs a detection signal including a change in a signal corresponding to the first and second movements of the domain wall separated in time.
Hereinafter, the operation of reproducing the information signal from the detection signal will be described. FIG. 7 shows signal waveforms at various points between time points t1 and t5 in FIGS. T1 to t5 in FIG.
6 to t1 to t5 in FIG. First, the detection signal of the optical sensor 12 is amplified by the amplification circuit 5 and then sent to the first information signal reproduction circuit 6, the second information signal reproduction circuit 7, and the clock signal generation circuit 8. The clock signal generation circuit 8 detects a change in the signal corresponding to the clock signal mark from the input signal, and based on the detected change,
A clock signal having a constant frequency T (= Lm / Vs) as shown in FIG. This clock signal is supplied to the laser drive circuit 4 as described above,
Supplies the laser light source 11 with a drive current that increases and decreases at a constant cycle Th in synchronization with a clock signal. Here, as an example, the period Th is assumed to be equal to the period T of the clock signal. Thus, the irradiation intensity of the reproducing light beam repeatedly increases and decreases at a cycle Th as shown in FIG. 7B. The irradiation intensity of the reproducing light beam increases during the half cycle Th / 2, decreases during the remaining half cycle Th / 2, and has a minimum value P1 at times t1, t3, and t5, and a maximum value at times t2, t4. It becomes P2. As a result, as described with reference to FIGS. 4 and 5, the state of the signal track 21 at the irradiation position of the reproduction light beam changes, and the detection signal as shown in FIG.
2 is output.

Here, the polarity of the signal shown in FIG.
And-correspond to the magnetization in the upward direction and the magnetization in the downward direction of the magnetization region formed in the domain wall displacement layer 22 at the light spot irradiation position, respectively. That is, the change of the signal in the + direction indicated by Sf5 between the time points t1 and t2 in the signal waveform causes the first movement of the domain wall Q5 to change the signal in the + direction indicated by Sr1 between the time points t2 and t3. The change corresponds to the second movement of the domain wall Q1, and the change of the signal in one direction indicated by Sf6 between the time points t3 and t4 corresponds to the first movement of the domain wall Q6. Thus, the detection signal of the optical sensor 12 includes
Both a signal change corresponding to the first movement of the domain wall and a signal change corresponding to the second movement are included. However, as described above, the first movement and the second movement of the domain wall are temporally separated, and the first movement can occur only during a period in which the irradiation intensity of the reproducing light beam increases, Can occur only during the period when the irradiation intensity of the reproducing light beam decreases.

On the other hand, the clock signal generated by the clock signal generation circuit 8 is supplied to the first gate signal generation circuit 9 and the second gate signal generation circuit 9.
Is also supplied to the gate signal generation circuit 10. The first gate signal generation circuit 8 uses the clock signal as shown in FIG.
As shown in (c), a first gate signal is generated which has a high level during a period in which the irradiation intensity of the reproduction light beam increases and a low level during a period in which the irradiation intensity of the reproduction light beam decreases. To the first information signal reproducing circuit 6.
Further, the second gate signal generation circuit 10 sets the low level during the period in which the irradiation intensity of the reproduction light beam increases as shown in FIG. A second gate signal which is at a high level during a period in which is decreased is sent to the second information signal reproducing circuit 7.

The first information signal reproducing circuit 6 detects a change in the signal included in the detection signal input from the amplifier circuit 5 only during the period when the input first gate signal is at the high level, and FIG. A first information signal including only a signal change corresponding to the first movement of the domain wall as shown in f) is generated and output from the output terminal T1. Further, the second information signal reproducing circuit 7 detects a change in a signal included in the detection signal input from the amplifier circuit 5 only during a period when the input second gate signal is at a high level. ), A second information signal including only a signal change corresponding to the second movement of the domain wall is generated and output from the output terminal T2.

As a result, the output terminal T1 outputs the signal shown in FIG.
, Sf, the signal changes Sf1, Sf2,..., Sf corresponding to the first movement of the domain walls Q1, Q2,.
9 is output from the output terminal T2 as shown in FIG.
As shown in (b), signal changes Sr1, Sr2,... Corresponding to the second movement of the domain walls Q1, Q2,.
And a second information signal including Sr9 is output. Here, as shown in FIG. 8, the second information signal obtained by detecting the second movement of the domain wall is delayed by a certain time from the first information signal obtained by detecting the first movement of the domain wall. However, since the contents are the same, it is not necessary to obtain information signals from both the first movement and the second movement of the domain wall, respectively, and at least the information signals of the first movement and the second movement of the domain wall are required. An information signal may be obtained from one side. When information signals are obtained from both the first movement and the second movement of the domain wall, for example, when a detection error occurs in one of the information signals, the information signal is replaced with the other information signal. Reliability can also be improved.

In the above embodiment, the interval between the domain walls formed on the signal track 21 of the magneto-optical recording medium 1 is KL.
m (where k is an integer equal to or greater than 1 and Lm is a constant), and when the scanning speed of the signal track 21 of the reproducing light beam is Vs,
Period Th of periodic increase / decrease of irradiation intensity of reproduction light beam
Is equal to the cycle T (= Lm / Vs) of the clock signal. However, if the increase / decrease of the irradiation intensity of the reproducing light beam is performed in synchronization with the clock signal, the cycle Th is not limited to this, and mT ( However, m is an integer of 1 or more), or T /
n (where n is an integer of 1 or more) may be used.

Further, in order to temporally separate the first movement and the second movement of the domain wall, the first boundary position Xf is displaced in the direction opposite to the scanning direction of the reproducing light beam during the period. The average speed is made substantially coincident with the scanning speed Vs of the reproducing light beam, and the average speed is changed during the period in which the second boundary position Xr is displaced in the direction opposite to the scanning direction of the reproducing light beam. Need to be substantially equal to the scanning speed Vs. Therefore, if the period Th for increasing / decreasing the irradiation intensity of the reproduction light beam is different from the above example, the scanning direction of the reproduction light beam at the first boundary position Xf and the second boundary position Xr is opposite to the scanning direction. The amplitude of the displacement between the first boundary position Xf and the second boundary position Xr must also be appropriately set in accordance with the cycle Th so that the average speed during the period of the displacement becomes Vs. The amplitude of the displacement between the first boundary position Xf and the second boundary position Xr can be arbitrarily set by adjusting the minimum value P1 and the maximum value P2 of the irradiation intensity of the reproduction light beam.

Further, at the start of the movement of the domain wall, there may be a case where the jitter occurs due to the noise of the reproducing light beam or the partial unevenness of the thermal properties of the signal track.
However, the first boundary position Xf or the second boundary position Xr
If the domain wall starts the first movement or the second movement on average at a time near the middle of the displacement period in one direction, even if there is some fluctuation at the time of the movement start, The first or second movement of the domain wall can be reliably detected. Therefore, the domain wall is closer to the middle point between the rightmost displacement point and the leftmost displacement point than the rightmost displacement point or the leftmost displacement point of the first boundary position Xf or the second boundary potential Xr. It is desirable to have a first movement and a second movement when reached. For this purpose, the distance between at least the first boundary position Xf and the second boundary position Xr when they are closest to each other may be set to approximately iLm (where i is an integer of 1 or more).

Considering such circumstances, as an example, Lm
0.15 μm, Vs 3 m / s, Th equal to T and 5
Assuming that the amplitude of the displacement between the first boundary position Xf and the second boundary position Xr is 0.075 μm, the first boundary position Xf and the second boundary position Xr are in the scanning direction of the reproducing light beam. The average speed during the period of Th / 2 displacing in the opposite direction can be equal to Vs. At this time, in order to set the distance between the first boundary position Xf and the second boundary position Xr when they are closest to each other to be 1.2 μm (8 Lm), for example, the minimum irradiation intensity of the reproducing light beam is required. Value P1
May be set to 1.4 mW, and the maximum value P2 may be set to 1.6 mW.

The region where the domain wall in the signal track 21 is movable is formed by irradiating the reproducing light beam to partially raise the temperature of the signal track 21 and forming another region different from the reproducing light beam. The signal track 21 may be formed by partially raising the temperature of the signal track 21 by irradiation of a heating light beam or other heating means. In addition to detecting the movement of the domain wall from the reflected light of the reproducing light beam from the magnetized region formed by extension, the magnetic flux generated by the magnetized region formed by extension is generated by a coil or a magnetoresistive element. It may be detected by a magnetic head provided.

[0056]

As described above, according to the present invention, the boundary position between the movable region of the domain wall and the non-movable region is periodically displaced back and forth in the scanning direction.
Since the first movement and the second movement of the domain wall can be temporally separated, a signal change corresponding to the first movement of the domain wall and a signal change corresponding to the second movement can be selectively extracted. The information signal can be accurately reproduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an information signal reproducing device according to the present invention.

FIG. 2 is a diagram showing a configuration of a magneto-optical recording medium used in the embodiment of FIG.

FIG. 3 is a diagram showing a configuration of a signal track of the magneto-optical recording medium of FIG.

FIG. 4 is a diagram for explaining an operation of reproducing an information signal according to the embodiment of FIG. 1;

FIG. 5 is a diagram for explaining an information signal reproducing operation of the embodiment of FIG. 1;

FIG. 6 is a diagram showing the relationship between the position of each domain wall and the time at the irradiation position of the reproducing light beam in FIGS. 4 and 5;

FIG. 7 is a diagram showing signal waveforms of respective units in the embodiment of FIG.

FIG. 8 is a diagram showing a waveform of a reproduced information signal of the embodiment of FIG. 1;

FIG. 9 is a diagram showing a configuration of a magneto-optical recording medium used in a domain wall displacement reproducing method.

FIG. 10 is a diagram for explaining the principle of signal detection by the domain wall motion reproduction method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 magneto-optical recording medium 2 spindle motor 3 optical head 4 laser drive circuit 5 amplifier circuit 6 first information signal reproduction circuit 7 second information signal reproduction circuit 8 clock signal generation circuit 8 first gate signal generation circuit 10 second Gate signal generation circuit 11 laser light source 12 optical sensor 20 substrate 21 signal track 22 domain wall moving layer 23 switching layer 24 magnetic recording layer 25 information signal recording area 26 clock signal recording area 27 light spot 28 isotherm

Claims (10)

[Claims] 1. An information signal reproducing apparatus for reproducing an information signal recorded on a signal track of an information recording medium by a domain wall, means for forming a region on the signal track where the domain wall can move, and moving the domain wall. A means for detecting the movement of the domain wall, and means for reproducing an information signal based on the detected movement of the domain wall, wherein the domain wall moving means,
An information signal reproducing apparatus, wherein a boundary position between a region where the domain wall is movable and a region where the domain wall is not movable is periodically displaced back and forth in the scanning direction while scanning the signal track. 2. The apparatus according to claim 1, wherein the scanning speed of the domain wall moving unit is substantially the same as an average speed during a period in which the boundary position is displaced in a direction opposite to a scanning direction of the domain wall moving unit. The information signal reproducing device according to the above. 3. The information signal reproducing apparatus according to claim 1, wherein the domain wall moving unit moves the domain wall in synchronization with a periodic displacement of the boundary position. 4. The information signal reproducing apparatus according to claim 1, wherein the domain wall moving unit moves the domain wall during a period in which the boundary position is displaced in a scanning direction. 5. The information signal reproducing apparatus according to claim 1, wherein the domain wall moving unit does not move the domain wall during a period in which the boundary position is displaced in a direction opposite to a scanning direction. 6. The information signal reproducing apparatus according to claim 1, wherein the domain wall moving unit periodically displaces the boundary position in synchronization with the information signal. 7. The domain wall moving means, when a basic cycle of the information signal is T, a cycle Th of displacement of the boundary position.
2. The information signal reproducing apparatus according to claim 1, wherein m is an integer of 1 or more, or T / n (n is an integer of 1 or more). 8. The domain wall moving means forms a first boundary position and a second boundary position between a region where the domain wall is movable and a region where the domain wall is not movable, and wherein the first and second boundaries are formed. 2. The information signal reproducing apparatus according to claim 1, wherein the position is periodically shifted back and forth with respect to the scanning direction. 9. The domain wall moving unit, while the first boundary position is displaced in the scanning direction of the domain wall moving unit, displacing the second boundary position in a direction opposite to the scanning direction, Moving the domain wall at the first boundary position;
9. The information signal reproducing apparatus according to claim 8, wherein the domain wall is not moved at the second boundary position. 10. The domain wall moving means includes a light beam irradiating means for irradiating the signal track with a light beam, and the boundary position is periodically displaced by changing the irradiation intensity of the light beam. The information signal reproducing device according to claim 1, wherein