JPH09198736A - Magneto-optical recording method and magneto-optical recording device - Google Patents

Abstract

(57) Abstract: The recording mark length fluctuates and the error rate is deteriorated due to the influence of the self-leakage magnetic field generated by the magneto-optical recording medium itself. In a magneto-optical recording method of recording information by applying an external magnetic field modulated according to a recording signal while irradiating a magneto-optical recording medium 9 with a light beam of a predetermined intensity, the maximum self-recording of the recording medium 9 is performed. The recording medium 9 is selected so that the fluctuation of the predetermined recording mark length is equal to or less than the allowable value based on the relationship between the leakage magnetic field, the amplitude of the external magnetic field, the reversal time of the external magnetic field, and the clock cycle. Further, a means for adjusting at least one of the linear velocity and the amplitude of the external magnetic field is provided so that the fluctuation of the recording mark length is equal to or less than the allowable value.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a magneto-optical recording method and a magneto-optical recording apparatus for magneto-optically recording information on a magneto-optical recording medium.

[0002]

2. Description of the Related Art In recent years, as a high-density recording system capable of rewriting information, magnetic energy is written in a magnetic thin film by applying thermal energy of a semiconductor laser or the like and a magnetic field from the outside to an information recording medium to record information. In addition, a magneto-optical recording method that reads out this information by using the magneto-optical effect has attracted attention. In this magneto-optical recording method, a weak DC external magnetic field is always applied, and a laser light is turned on for recording depending on the presence or absence of a signal, and a constant intensity laser beam is always radiated to detect the presence or absence of a signal. There is a magnetic field modulation method in which the externally applied magnetic field is reversed to perform recording.

The optical modulation method has been researched early since it requires a relatively simple device configuration. However, the optical modulation method, if you do not use a special recording medium with a complicated configuration,
It is impossible to overwrite by overwriting on the already recorded part, and in order to write new information, an erasing operation to align the magnetization direction of the recording medium in a certain direction is necessary. It has the drawback of being slow. On the other hand, the magnetic field modulation method, which has a slightly complicated device configuration, can be overwritten and is capable of high-speed recording comparable to a hard disk for a computer.

Further, in a large capacity magneto-optical disk, a CAV (constant rotation speed) method is mainly used as a recording method. The CAV method is a method in which recording mark lengths are recorded differently on the inner circumference and outer circumference of the disc. However, there is a demand for further increase in capacity in the future, and there is an M-CAV (Modifeid CAV) method as a recording method for realizing this. This is a method of recording with a fixed mark length. That is, it is a system in which the recording frequency is changed on the inner and outer circumferences of the disc (the linear velocity is different) (the recording frequency is increased toward the outer circumference).

Next, as an information signal and a recording form, mark position recording in which information is provided at the center position of a recording mark on a recording medium has been put into practical use. Mark edge recording, in which information is provided at the edge of, has been studied. Since mark edge recording has information at both ends of a single mark, higher density recording can be realized than mark position recording having information at one center of the mark. A technical problem remains that high accuracy is required.

[0006]

In the magnetic field modulation method, in order to increase the recording density at high speed in the recording track direction, the external magnetic field applying means is capable of reversing the magnetic field at an extremely high speed. Possible high frequency magnets are used, but it is difficult to generate a large external magnetic field with such magnets. Therefore, in order to achieve high-speed and high-density recording by the magnetic field modulation method, a recording medium that easily causes magnetization reversal under a small external magnetic field is required.

However, when a small external magnetic field is applied to a recording medium in which magnetization reversal is likely to occur under such a small external magnetic field and magnetic field modulation recording is performed, the recording medium itself, for example, the peripheral portion of the recording portion, for example, The phenomenon that the recording mark length fluctuates under the influence of the self-leakage magnetic field generated from the adjacent recording track, guide groove, or the like. The variation of the recording mark length due to the leakage magnetic field changes the direction and size depending on the magnetization pattern in the peripheral portion of the recording portion, so that the recording mark length apparently varies randomly, thereby increasing the jitter. It will cause it to worsen. This problem has been a particularly serious problem in mark edge recording in which information is provided at the edge position of the recording mark.

Therefore, as a method of avoiding such a problem, it is conceivable to make the self-leakage magnetic field of the recording medium as small as possible. However, in this method, the composition range of the recording layer is remarkably limited, and the manufacturing margin is pressed down. It is not preferable because it not only deteriorates the non-defective rate but also increases the cost of the recording medium. In addition, even if the same recording medium is used, the variation of the recording mark length due to the leakage magnetic field varies depending on the specifications of the recording / reproducing apparatus, which may result in excess quality and waste.

In view of the above-mentioned conventional problems, the present invention suppresses the fluctuation of the recording mark length due to the self-leakage magnetic field of the recording medium,
It is an object of the present invention to provide a magneto-optical recording method and a magneto-optical recording device capable of sufficiently supporting mark edge recording.

[0010]

An object of the present invention is to record information by applying an external magnetic field modulated according to a recording signal while irradiating a magneto-optical recording medium with a light beam having a predetermined intensity. In the magnetic recording method, based on the relationship between the maximum self-leakage magnetic field of the recording medium, the amplitude of the external magnetic field, the reversal time of the external magnetic field, and the clock cycle, the fluctuation of the predetermined recording mark length is equal to or less than an allowable value. It is achieved by a magneto-optical recording method characterized in that the recording medium is selected.

Another object of the present invention is to provide a magneto-optical recording apparatus for recording information by applying an external magnetic field modulated according to a recording signal while irradiating a magneto-optical recording medium with a light beam of a predetermined intensity. , The fluctuation of the recording mark length that is predetermined based on the relationship between the maximum self-leakage magnetic field of the recording medium, the amplitude of one wave of the external magnetic field, the reversal time of the external magnetic field, and the clock cycle is less than or equal to the allowable value. Thus, the present invention is achieved by a magneto-optical recording apparatus having a unit for adjusting at least one of the linear velocity corresponding to the clock cycle and the amplitude of the external magnetic field.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the magneto-optical recording method according to the present invention will be described. FIG. 2 is a diagram schematically showing an AC magnetic field generated by the magnetic head 24 of FIG. 1, in which the vertical axis represents the magnetic field strength and the horizontal axis represents time. It should be noted that FIG. 1 is a diagram showing an embodiment of a magneto-optical recording apparatus of the present invention, as described later in detail. The magnetic field of the magnetic head 24 is modulated according to the recording signal as shown in FIG. 2 and applied to the magneto-optical recording medium 9. Here, the center of the alternating magnetic field is indicated by the one-dot chain line X, and when there is no self-leakage magnetic field from the recording medium 9,
This center X has a magnetic field strength of zero. Therefore, the intersections A, B, and C where the alternating magnetic field intersects with the alternate long and short dash line X represent the reversal positions of the magnetic field, and when recording is performed by actually applying the alternating magnetic field, these intersections correspond to the mark edges on the recording medium. To do.

Next, the self-leakage magnetic field from the recording medium 9 is set to H
Then, the external magnetic field is offset in a DC manner by the amount of the self-leakage magnetic field H, and the line showing the magnetic field strength 0 shifts as shown by the chain double-dashed line X ′. A ', B', which are the intersections of the magnetic field and the two-dot chain line X ',
Shift to C '. When the magnetic field reversal position shifts in this way, the marks corresponding to AB and BC, which are marks of essentially the same length, on the recording medium 9 become marks between A′B ′ and B′C ′. There is a difference in mark length between A'B 'and B'C'. It is considered that the fluctuation of the recording mark length due to the leakage magnetic field is mainly caused by such a cause.

Therefore, in order to reduce the fluctuation of the recording mark length due to the self-leakage magnetic field, the AC magnetic fields AA 'and B are used.
One method is to make the inclination of the inclined portion passing through B'and CC 'steep. For example, the gradient can be made steeper as the amplitude of one wave of the externally applied magnetic field is increased by _Hext (Oe). Further, the reversal time of the externally applied magnetic field is set to T _SW (n
On the contrary, as the value of (sec) is increased, the inclination becomes gentler. Furthermore, when recording marks of the same length on the recording medium 9, the frequency of the external magnetic field increases (that is, the distance between AB decreases) when the linear velocity V (m / sec) during recording increases. Since the inversion time T _SW does not change, the ratio of T _SW to the clock cycle T becomes large, and the influence of the fluctuation of the recording mark length due to the self-leakage magnetic field on the detection window width becomes large.

This means that when the M-CAV recording method as described above is adopted, the influence of the fluctuation of the recording mark length due to the self-leakage magnetic field becomes greater toward the outer periphery of the recording medium. Also, the detection window width of the playback device (that is,
The larger the clock period T), the larger the variation of the recording mark length due to the allowable leakage magnetic field. The clock cycle T (ns) is determined by the modulation system of the information recording / reproducing apparatus, the recording linear density, the rotation speed (linear velocity), and the like. Therefore, in the information recording / reproducing apparatus, the maximum value of the self-leakage magnetic field of the recording medium that causes the fluctuation of the recording mark length due to the allowable leakage magnetic field is the amplitude H _ext (Oe) of one wave of the externally applied magnetic field.
Also, it may be considered to be proportional to the clock cycle T and inversely proportional to the reversal time T _SW (nsec) of the externally applied magnetic field.

Therefore, the error rate generally required for an optical disk is about 1 × 10 ^-6 , but in order to ensure this, the detection window width (that is, clock cycle) T
It is necessary that the jitter σ (nsec) with respect to (nsec) satisfies a condition of T / 2 ≧ 4.9σ ... (1). When the fluctuation of the recording mark length due to the self-leakage magnetic field is added to this, T / 2 ≧ 4.9σ + ΔT (2) However, ΔT (ns) is a change in the recording mark length due to the leakage magnetic field. In general, the jitter σ imposed on a recording medium in mark edge recording is 7.5 clock periods.
%, The worst condition is σ = 0.075T
Using, the equation (2) becomes: T / 2 ≧ 4.9σ × 0.075T + ΔT ΔT ≦ 0.1325T (3)

On the other hand, in FIG. 2, if the self-leakage magnetic field H exists in the recording medium, the self-leakage magnetic field H is combined with the magnetic field of the magnetic head, so that the magnetic field applied to the recording medium is the self-leakage magnetic field H. The line with no magnetic field strength is also shifted from X to X '. At this time, when the time between AB when there is no self-leakage magnetic field is T _AB and the time between A′B ′ when there is a self-leakage magnetic field is T _AB ′, when a mark is recorded on the recording medium, T _AB The time for recording the mark is reduced by the time of −T _AB ′, and the length of the recording mark is shortened accordingly. This may be considered as the change ΔT of the recording mark due to the so-called self-leakage magnetic field. Therefore, ΔT
Can be represented by ΔT = T _AB −T _AB ′ (4).

Therefore, in FIG. 2, when the point on the line X corresponding to the point B'on the line X'is D, the length between D and B is ΔT.
It corresponds to / 2. Therefore, from this relationship, ΔT is expressed as follows by the self-leakage magnetic field H of the recording medium 9, the amplitude H _ext of one side of the applied magnetic field of the magnetic head 24, and the reversal time T _SW of the applied magnetic field of the magnetic head 24. That is, the relationship of H / H _ext = (ΔT / 2) / (T _SW / 2) (5) holds, and from this, ΔT becomes ΔT = T _SW × (H / H _ext ) (6). Here, when the allowable value of ΔT is set as in the equation (3), ΔT = T _SW × (H / H _ext ) ≦ 0.1325T (7) When obtained, H ≦ 0.1325 × H _ext × (T / T _SW ) ... (8) Further, considering H as the maximum value, if the maximum value H _max of the self-leakage magnetic field satisfies H _max ≦ 0.1325 × H _ext × (T / T _SW ) ... (9), It is possible to make the variation ΔT of the recording mark length due to the self-leakage magnetic field below the allowable value. Therefore, in the present embodiment, information is recorded using the recording medium having the maximum self-leakage magnetic field that satisfies the above expression (9), that is, the expression (9) is satisfied according to the conditions such as the magnetic field of the magnetic head of the apparatus. By selectively using the recording medium to
The fluctuation of the recording mark length is kept below an allowable value. However, in this case, since the error rate allowed by the device is 1 × 10 ⁻⁶ and the jitter σ is 7.5% or less of the clock period as described above, these conditions may vary depending on the device. If they are different, the condition of equation (9) may be changed accordingly.

Next, the inventors of the present application conducted the following confirmation experiment in order to confirm whether such a recording method is correct. That is, a plurality of recording media having different self-leakage magnetic fields were produced, information was recorded by changing recording conditions by using the recording media, and the fluctuation ΔT of the recording mark length was measured to confirm the relationship with the self-leakage magnetic field. Before describing the confirmation experiment, a method of measuring the maximum self-leakage magnetic field of the recording medium adopted in the experiment will be described with reference to FIG. The self-leakage magnetic field of the recording medium becomes maximum when the magnetization around the recording portion is aligned in one direction. Therefore, in the measurement, in order to maximize the self-leakage magnetic field of the recording medium, the track to be evaluated of the magneto-optical recording medium 9 and at least three tracks before and after it,
In the case of having a guide groove, the guide groove in the range is pre-magnetized in a certain direction.

Then, the magneto-optical recording medium 9 which is rotated by the drive of the spindle motor 10 is irradiated with a light beam sufficient for thermomagnetic recording from the semiconductor laser 11 and, at the same time, an AC magnetic field H _R modulated according to the recording signal. Was applied from the magnetic head 24. The strength of the modulation AC magnetic field H _R was set to be near the minimum level at which the recording layer of the magneto-optical recording medium 9 could undergo magnetization reversal. At this time, a predetermined DC magnetic field _HDC was also applied from the magnetic head 27 provided near the magnetic head 24 at the same time to offset the AC magnetic field, and recording was performed on the recording medium. Next, the signal thus recorded by receiving the offset of the DC magnetic field H _DC was reproduced by using the magneto-optical effect.

During reproduction, the semiconductor laser 11 irradiates a linearly polarized light beam whose intensity is weaker than that during recording and is not modulated, and this magnetic beam scans the magnetic signal portion recorded on the recording medium. did. During this reproduction, the magnetic heads 24 and 27 were not driven. The light beam reflected by the magneto-optical recording medium 9 is modulated in its polarization state by the magneto-optical effect according to the recorded magnetic signal. The light beam reflected by the magneto-optical recording medium 9 is separated from the incident light by the polarization beam splitter 14, and is split into two light beams having polarization directions orthogonal to each other by the polarization means 16 such as a Wollaston prism. . The modulation of the polarization state of these light beams is converted into intensity modulation by the light detecting means 16. The light beam thus converted into the intensity modulation is condensed by the sensor lens 17, received by each of the photodetectors 18a and 18b, and converted into an electric signal. Photodetectors 18a and 18b
The output signal of 1 is subtracted by the differential amplifier 19 to reproduce the recorded signal. Then, the CN (carrier noise) ratio was measured from the reproduced signal output from the differential amplifier 19.

When this series of operations is completed, the DC magnetic field H _DC by the magnetic head 27 is changed and the reproduced signal is changed to CN.
The ratio was measured. Also, while changing this DC magnetic field H _DC , C
The operation of measuring the N ratio was repeated to find the DC magnetic field H _DC that maximizes the CN ratio. Since the intensity of the modulation AC magnetic field H _R is set near the minimum limit at which the recording layer of the magneto-optical recording medium 9 can be magnetized, the modulation AC magnetic field on the offset side is affected by a slight DC magnetic field. The magnitude of the one-sided wave is insufficient with respect to the magnetic field required for reversing the magnetization of the recording medium, resulting in increased noise and a reduced CN ratio. Accordingly, a DC magnetic field H _DC the CN ratio becomes the maximum may be considered as a magnetic field to cancel the self-leakage magnetic field of the recording medium. Further, since the magneto-optical recording medium 9 is magnetized with the evaluation track and the peripheral portion thereof aligned in a predetermined direction in advance as described above, the DC magnetic field H _DC corresponds to the maximum self-leakage magnetic field H _max of the recording medium.

In measuring the self-leakage magnetic field of such a recording medium, it is necessary to sufficiently reduce the leakage magnetic field from the measuring system such as an actuator or to take measures to cancel the influence to eliminate the influence. Needless to say. In this embodiment, the leakage magnetic field from the measurement system is measured in advance, and the leakage magnetic field component from the measurement system is subtracted from the DC magnetic field H _DC for evaluation to cancel the leakage magnetic field. Further, FIG. 3 shows the relationship between the DC magnetic field and the C / N ratio when the maximum self-leakage magnetic field is measured by the above-described measuring method using the disk 1 described later as an example. As is clear from FIG. 3, the DC magnetic field that maximizes the C / N ratio is 5
It was 0 (Oe), and from this result, the maximum self-leakage magnetic field of the disk 1 was 50 (Oe). The measurement conditions were a linear velocity of 9.05 m / sec, a recording frequency of 6.2 MHz, a modulated AC magnetic field half wave 60 (Oe), and a recording power of 8.5 mW.
The reproduction power was set to 1.5 mW.

Next, the disk-shaped magneto-optical recording medium used in this embodiment will be described. The inventor of the present application produced five disks to be described below, and used them to carry out confirmation experiments for fluctuations in recording marks due to self-leakage magnetic fields. First, the disc 1 will be described. As the disk 1, on a polycarbonate substrate with a φ90 mm pregroup, SiN is used as the first inorganic dielectric layer and 1000N is used as the first inorganic dielectric layer in order to obtain the oxidation prevention and the interference effect by using the magnetron sputtering device. Metal sublattice magnetization dominant Gd (Fe93Co7) (saturation magnetization Ms =
200 emu / cc) is 100 Å, and Tb (Fe92Co8) (Curie temperature 170 ° C., saturation magnetization Ms = 200 emu / cc) having a dominant transition metal sublattice magnetization is used as the second magnetic layer.
00 Å, then SiN 300 Å as the second inorganic dielectric layer and Al film 500 Å as the reflection layer in order to increase the anti-oxidation and interference effect, successively without breaking the vacuum, and then on the film surface. As a protective coat, an ultraviolet curable resin was coated to a thickness of 10 μm to prepare.

As the disks 2 and 3, the first magnetic layer GdFeCo and the second magnetic layer TbF of the disk 1 are used.
The same configuration as the disc 1 except that the composition of eCo was changed,
Made of material. As the disk 4, a magnetron sputtering apparatus is used on a polycarbonate substrate having a pre-group of φ90 mm, and SiN of 100 is used as a first inorganic dielectric layer in order to obtain an oxidation prevention and an interference effect.
0Å, Tb (Fe with a dominant transition metal sublattice magnetization as the magnetic layer
92Co8) (Curie temperature 170 ° C, saturation magnetization Ms = 10)
0 emu / cc) to 200 Å, and then SiN is used as a second inorganic dielectric layer in order to enhance the oxidation prevention and interference effect.
00Å, an Al film was successively formed as a reflective layer for 500Å without breaking the vacuum, and then an ultraviolet curable resin was coated on the film surface as a protective coat by 10 μm.

As the disk 5, the magnetic layer T of the disk 4 is used.
Disk 4 except that the film thickness of bFeCo was changed to 300Å
It was made with the same structure and material. The compositions of the above disks 1 to 5 are summarized in Table 1. The value of the maximum self-leakage magnetic field H _max of each disk is also shown in Table 1. Of course, the maximum self-leakage magnetic field was measured by the method described above. In addition, in the saturation magnetization in Table 1, a negative sign represents a transition metal sublattice magnetization predominant, and a positive sign represents a rare earth metal sublattice magnetization predominant.

[0027]

[Table 1] Next, the measurement result of the fluctuation ΔT of the recording mark length due to the self-leakage magnetic field of the disks 1 to 5 will be described. It should be noted that the recording mark length variation ΔT due to the self-leakage magnetic field
Was measured by the following method. At the time of measuring ΔT, it is assumed that only a DC magnetic field having a magnitude that cancels the leakage magnetic field from the measurement system is applied from the magnetic head 27 of FIG. Also,
The linear velocity of the recording medium 9 is set to V (m / sec), the amplitude of one wave of a predetermined externally applied magnetic field is set to H _ext (Oe), and the recording laser power is C / max which is the maximum for each disk at each linear velocity.
The value is set to N. Reversal time T of externally applied magnetic field
_SW (nsec) is changed by replacing the magnetic head 24. The reproducing laser power is 1.0 mw, the NA of the optical head is 0.55, and the laser wavelength is 780 nm.

Further, the magnetization states of the adjacent groove and land of the disk are set to two states, that is, the erasing direction (acting in the same direction for recording) and the recording direction (acting in the opposite direction for recording).
The pulse width was changed in each state, recording was performed at the recording frequency corresponding to the longest mark length, and the second harmonic was measured. Then, the pulse width that minimizes the second harmonic in each magnetization state is obtained, and the pulse width difference that minimizes the second harmonic in each magnetization state is halved, Variation of recording mark length ΔT due to self-leakage magnetic field
(Unit: nsec) was calculated.

Next, using the above-described measuring method, the recording mark length variation ΔT was measured by changing the recording conditions on the five disks described above. First, as the first recording condition, the disc diameter is 90 mm and the disc rotation speed is 2400 rp.
m, CAV method, 2-7 (RLL) modulation method, and shortest mark length (3T) 0.78 μm (r = 24). Further, in this case, since the CAV system has different linear velocities on the inner and outer circumferences, the mark length increases in proportion to the linear velocity and the detected window width (clock cycle) T is constant. In and, the conditions are substantially the same, and representatively, the evaluation was performed only for the inner circumference condition (r = 24). Linear velocity V =
It was set to 6.03 m / sec (fixed). Also, the amplitude of one wave of the externally applied magnetic field is H _ext = 120, 180, 225 (O
Under the three conditions of e), the reversal time of the externally applied magnetic field is T _SW = 1
There are two conditions of 8 and 25 (nsec).

The factor determined by the information recording / reproducing apparatus assumed here, that is, the detection window width (clock cycle) T of the information reproducing apparatus is 43.1 nsec. The condition of the variation ΔT of the recording mark length due to the leakage magnetic field is ΔT ≦ 0.1325T = 5.7. Table 2 shows the measurement results of the recording mark length variation ΔT due to the self-leakage magnetic field under the above setting conditions.

[0031]

[Table 2] Here, as is apparent from Table 2, ΔT smaller than 5.7 (ns) which is the variation of the recording mark length satisfying the expression (3).
(Nsec) is the measurement number 1-2, 1-3, 1
-6, 2-1 to 2-6, 3-1 to 3-6, 4-1 to 4-
6, 5-1 to 5-3, 5-5, 5-6. In addition, ΔT exceeds 5.7 (nsec) in all other cases,
Equation (3) is not satisfied. Then, looking at the relationship between the maximum self-leakage magnetic field H _max under the condition that ΔT is 5.7 (nsec) or less and 0.1325 × H _ext × (T / T _SW ), ΔT is 5.7. When it is (nsec) or less, all H _max ≦ 0.1325 × H _ext × (T /
T _SW ), and it can be seen that the equation (9) described above is satisfied. Further, it can be seen that when ΔT is 5.7 (nsec) or more, all of the expressions (9) are not satisfied. Therefore, it was confirmed from the above experimental results that the variation of the recording mark length due to the self-leakage magnetic field can be suppressed within the allowable value if the equation (9) is satisfied.

Next, ΔT was similarly measured under different conditions. The condition at this time is that the disc diameter is 90 m.
m, disk rotation speed 3600 rpm, CAV method, 2-
7 (RLL) modulation method, shortest mark length (3T) 0.78
μm (r = 24). Also in this case, since the CAV method is used, the linear velocity differs between the inner and outer circumferences, but the shortest mark length increases in proportion to the linear velocity, L / V becomes constant, and the detection window width Tw also becomes constant. The inner circumference and the outer circumference have substantially the same condition, and the inner circumference condition is representative (r = 24)
Was evaluated only for. Linear velocity V = 9.05m /
It was set to sec (fixed). Further, the amplitude of one wave of the externally applied magnetic field is set to three conditions of H _ext = 120,180,225 (Oe), and the reversal time of the externally applied magnetic field is T _SW = 18,25 (n).
sec). A factor determined by the information recording / reproducing apparatus assumed here, that is, a detection window width (clock cycle) T = 28.7 (ns) of the reproducing apparatus.
ec), and the condition of the variation ΔT of the recording mark length due to the self-leakage magnetic field satisfying the equation (3) at this time is ΔT ≦ 0.1325T = 3.8. Table 3 shows the measurement results of the recording mark length variation ΔT due to the self-leakage magnetic field under the above setting conditions.

[0033]

[Table 3] In Table 3, the measurement marks 2-1 to 2-6, 3-1 to 3-3, and 3-have ΔT smaller than the variation (3.8) of the recording mark length satisfying the expression (3). 5, 3-
6, 4-1 to 4-3, 4-5, 4-6, 5-2, 5-3
It is. In all other cases, ΔT exceeds 3.8 (nsec), which means that the formula (3) is not satisfied. Also, in Table 3, when ΔT is 3.8 (nsec) or less, all of the expressions (9) are satisfied, and ΔT is 3.8.
When it is (nsec) or more, it is understood that the formula (9) is not satisfied. Therefore, from the above measurement results,
It was confirmed that if the formula (9) is satisfied, the fluctuation length of the recording mark due to the self-leakage magnetic field can be suppressed within the allowable value.

Next, similar conditions were measured under different conditions. The condition at this time is that the disc diameter is 90
mm, disk rotation speed 3600 rpm, M-CAV method, 1-7 (RLL) modulation method, shortest mark length (2T)
Was 0.75 μm. Further, in this case, since the M-CAV system is used, the shortest mark length is constant at the inner and outer circumferences.
Since the linear velocity becomes faster toward the outer circumference and the detected window width T becomes shorter toward the outer circumference, the outer circumference condition (r = 40) with the smallest margin was evaluated. Linear velocity V =
It was set to 15.1 m / sec (fixed). In addition, the amplitude of one wave of the externally applied magnetic field is H _ext = 120, 180, 225 (O
Under the three conditions of e), the reversal time of the externally applied magnetic field is T _SW = 1
Two conditions of 8 and 25 (nsec) were set. The factor determined by the information recording / reproducing apparatus assumed here, that is, the detection window width (clock cycle) T = 24.
8 (nsec), and the condition of the variation ΔT of the recording mark length due to the self-leakage magnetic field satisfying the equation (3) at this time is ΔT ≦ 0.1325T = 3.3. Table 4 shows the measurement results of the recording mark length variation ΔT due to the self-leakage magnetic field under the above setting conditions.

[0035]

[Table 4] Also in Table 4, ΔT is smaller than the variation (3.3) of the recording mark length satisfying the expression (3) that the measurement numbers 2-1 to 2-6, 3-2, 3-3, 3- 6, 4-1
˜4-3, 4-5, 4-6, 5-3. In all other cases, ΔT exceeds 3.3 (nsec), and the formula (3) is not satisfied. Also, in Table 4, ΔT is 3.3.
When it is (nsec) or less, all of the expressions (9) are satisfied, and when ΔT is 3.3 (nsec) or more,
It can be seen that the formula (9) is not satisfied. Therefore, Table 4
It was also confirmed from the measurement result of 1 that if the formula (9) is satisfied, the fluctuation of the recording mark due to the self-leakage magnetic field can be suppressed within the allowable value.

As described above, in the present embodiment, the recording that satisfies the expression (9) is based on the relationship between the maximum self-leakage magnetic field of the recording medium, the magnetic field of the magnetic head, the reversal time of the magnetic field, and the clock cycle. By recording information using the medium, the fluctuation of the recording mark length due to the self-leakage magnetic field of the recording medium can be suppressed to be equal to or less than the allowable value. Further, in the present embodiment, the recording medium can be designed according to the specifications of the device, and the value of the self-leakage magnetic field of the recording medium can be determined according to the fluctuation of the recording mark length allowed by the device. It is possible to eliminate waste such as excessive quality of the recording medium. Furthermore, it is also possible to select and use a recording medium having a self-leakage magnetic field suitable for it according to the specifications of the apparatus, and in this case also, the fluctuation of the recording mark length due to the self-leakage magnetic field of the recording medium is kept within the allowable value. Can be suppressed,
Especially, it can be suitably used for mark edge recording.

Next, an embodiment of the magneto-optical recording apparatus of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 9 is a magneto-optical recording medium for recording and reproducing information, and a magnetic recording layer having an easy axis of magnetization in the vertical direction is provided on a transparent substrate. The recording medium 9 is rotated by driving the spindle motor 10. The semiconductor laser 11 is a light source for recording and reproduction, and is driven by the laser drive circuit 23. The laser beam emitted from the semiconductor laser 11 enters the objective lens 15 via the collimator lens 13 and the polarization beam splitter 14 as described above. Then, the laser beam is focused by the objective lens 15 and irradiated on the magneto-optical recording medium 9 as a minute light spot. A focus control and a tracking servo are applied to this laser beam by a servo control circuit (not shown), and servo control is performed so that the medium surface of the rotating recording medium 9 is focused and the information track is scanned to follow. .

The magnetic head 24 generates a magnetic field modulated according to the recording signal and applies it to the recording medium 9. When recording information, a laser beam having a constant intensity is scanned on the information track of the recording medium 9, and at the same time, a modulation magnetic field is applied from the magnetic head 24. Thereby, the magnetization of the magneto-optical recording layer of the recording medium 9 is oriented upward or downward according to the recording signal, and a series of information is recorded. The light reflected from the recording medium 9 includes the objective lens 15, the polarization beam splitter 14,
The light is detected by the photodetectors 18a and 18b via the polarization means 16 such as a Wollaston prism and the sensor lens 17. The output signals of the photodetectors 18a and 18b are the differential amplifier 1
Differential detection is performed at 9, and the recording signal is reproduced. Recording medium 9
When reproducing the recorded information, the target information track is scanned with a laser beam having a reproduction power which is not enough to record, and the reproduction signal is output from the differential amplifier 19.

The magnetic head 27 is an electromagnet that applies a DC magnetic field to the recording medium 9, and is driven by an electromagnet drive circuit 28. The magnetic head 27 is used to measure the self-leakage magnetic field of the recording medium 9. Further, in the present embodiment, the output of the differential amplifier 19 is a C for measuring the CN ratio of the reproduced signal.
An N ratio measuring circuit 30 is provided. CN ratio measuring circuit 3
0 is also used for measuring the self-leakage magnetic field of the recording medium 9. When the maximum self-leakage magnetic field of the recording medium 9 is measured, the magneto-optical recording medium 9 includes the magnetic head 2 including an electromagnet as described above.
After applying a DC magnetic field from 7 to record a predetermined signal, it is reproduced and the CN ratio measuring circuit 30 measures the CN ratio of the reproduced signal. This operation is repeated while changing the DC magnetic field of the magnetic head 27, and the DC magnetic field when the CN ratio becomes maximum is determined as the maximum self-leakage magnetic field of the recording medium.

The CPU 31 is a processor circuit forming a main control unit of the magneto-optical recording apparatus of this embodiment, and controls the laser drive circuit 23, the magnetic head drive circuit 28, etc. in the apparatus to store information on the magneto-optical recording medium 9. Record or reproduce recorded information. Further, in the CPU 31, when measuring the maximum self-leakage magnetic field of the magneto-optical recording medium 9 as described above, each unit is controlled to measure the self-leakage magnetic field. That is, each measurement process of the method for measuring the maximum self-leakage magnetic field of the magneto-optical recording medium 9 as described above is not shown in advance in RO.
Programmed in M, the CPU 31 measures each maximum self-leakage magnetic field by controlling each unit according to the control program. The motor drive circuit 32 is a drive circuit for driving the spindle motor 10, and the CPU 31
The rotational speed can be changed by controlling the. In the present embodiment, as will be described later in detail, the rotation speed of the recording medium 9 is adjusted so that the fluctuation ΔT of the recording mark length falls within an allowable value based on the maximum self-leakage magnetic field of the magneto-optical recording medium 9.

Next, the specific operation of this embodiment will be described. First, when the magneto-optical recording medium 9 is set in the device, the CPU 31 controls each unit to measure the maximum self-leakage magnetic field of the recording medium 9. As described above, the measuring method is preprogrammed, and a predetermined signal is recorded while changing the DC magnetic field of the magnetic head 27 applied to the recording medium 9, and the recorded signal is reproduced each time, and the C of the reproduced signal is reproduced. / N
Measure the ratio. The C / N ratio of the reproduced signal is the C / N measuring circuit 3
It is measured at 0, and the measurement result is loaded into the CPU 31.
When the signal is recorded while changing the DC magnetic field in this manner, and the C / N ratio is measured by reproducing the recorded signal each time the signal is recorded, the C / N ratio data for the DC magnetic field as shown in FIG. 3 is obtained. To be Based on the obtained measurement data, the CPU 31 determines the DC magnetic field when the C / N ratio becomes maximum as the maximum self-leakage magnetic field of the recording medium 9.

Next, the CPU 31 uses the obtained maximum self-leakage magnetic field to calculate the minimum clock period T that satisfies the above-mentioned equation (9). This is the maximum self-leakage magnetic field H _max measured or the magnetic head 24 which is known in advance.
It can be easily obtained by back-calculating from the equation (9) using the amplitude H _ext of the one-sided wave of the applied magnetic field and the inversion time T _SW of the applied magnetic field. Then, the CPU 31 calculates the rotation speed of the magneto-optical recording medium 9 corresponding to the obtained clock cycle T. That is, according to the number of rotations of the recording medium 9, the clock cycle T
When a mark having the same length is to be recorded as the number of rotations (linear velocity) becomes faster, the time required for recording becomes shorter and the clock cycle T becomes shorter. The rotation speed is calculated from this relationship. When the rotation speed is calculated, the CPU 31 outputs a control signal to the motor drive circuit 32 to output the spindle motor 1
Control is performed so that 0 rotates at the calculated rotation speed.

When the number of rotations of the spindle motor 10 is varied, there are two configurations of rotation control, that is, a configuration that continuously varies and a configuration that varies stepwise. C
When the PU 31 is continuously variable, the motor drive circuit 32 is controlled so that the calculated rotation speed is obtained. When the PU 31 is changed stepwise, the calculated rotation speed is selected from the set rotation speeds. The fastest rotation speed that does not exceed is selected and the motor drive circuit 32 is controlled accordingly. The number of rotations of the recording medium 9 set in this way is determined, and thereafter information is recorded and reproduced at the determined number of rotations.

In the present embodiment, the maximum self-leakage magnetic field of the recording medium 9 is measured, the minimum clock cycle satisfying the equation (9) is obtained based on the measured value, and the rotation frequency of the recording medium corresponding to the clock cycle is adjusted. As a result, the influence of the self-leakage magnetic field of the recording medium on the recording mark can be eliminated,
Regardless of the magnitude of the self-leakage magnetic field, the fluctuation of the recording mark length can be suppressed to the allowable value or less. Therefore, it is possible to prevent troubles such as deterioration of the error rate due to the fluctuation of the recording mark length due to the self-leakage magnetic field, and it is suitable for use in the mark edge recording in which the fluctuation of the edge of the recording mark requires high accuracy. You can

Next, another embodiment of the magneto-optical recording apparatus of the present invention will be described. In the previous embodiment, it was explained that the maximum self-leakage magnetic field of the recording medium 9 set in the apparatus was measured, but in this embodiment, the maximum self-leakage magnetic field of the recording medium is measured and registered in advance in the control track or the like. It is a thing. In this embodiment, when the recording medium 9 is set in the device, the CPU 31 controls each unit to reproduce the maximum self-leakage magnetic field information registered in the control track. The rest is exactly the same as the previous embodiment, and the CPU 31 reproduces the maximum leakage magnetic field reproduced, the magnetic head 2 which is known in advance.
The minimum clock period T satisfying the equation (9) is calculated by using the amplitude of one wave of the applied magnetic field and the reversal time of the applied magnetic field according to 4. Then, the CPU 31 calculates the rotation speed of the spindle motor 10 corresponding to the clock cycle T, and controls the motor drive circuit 32 accordingly to set the rotation speed of the recording medium 9.

In the present embodiment, the maximum self-leakage magnetic field is registered in advance in the recording medium 9 and is read out to adjust the rotation speed of the spindle motor 10, so that the maximum of the recording medium is the same as in the previous embodiment. It is not necessary to measure the self-leakage magnetic field, and the configuration can be greatly simplified. That is, a magnetic head 27 that applies a DC magnetic field, an electromagnet drive circuit 28 that drives the magnetic head 27, and a C that measures the CN ratio of a reproduction signal.
The N-ratio measuring circuit 30 is unnecessary, the number of rotations of the recording medium can be adjusted only by a simple calculation process, and the fluctuation of the recording mark length due to the self-leakage magnetic field can be kept within the allowable value.

In the above embodiment, an example in which the rotation speed of the recording medium 9 is adjusted has been described, but other than this, for example, the magnetic field of the magnetic head 24 may be adjusted. In this case, the CPU 31 back-calculates the magnetic field of the magnetic head 24 (amplitude H _{ext of one} wave) according to the self-leakage magnetic field of the recording medium 9 from the equation (9). Next, the CPU 31 controls the magnetic head drive circuit 25 to adjust the drive current of the magnetic head 24 so as to obtain the magnetic field obtained by the calculation. Even in this case, the fluctuation of the recording mark length can be suppressed to the allowable value or less, just as in the previous embodiment. Further, in this embodiment, since the magnetic field of the magnetic head 24 can be adjusted to the necessary minimum, there is an advantage that the power consumption of the magnetic head 24 can be saved.

[0048]

As described above, according to the present invention, the maximum self-leakage magnetic field of the magneto-optical recording medium and the amplitude of the external magnetic field,
Based on the relationship between the inversion time and the clock cycle, the recording medium is selected so that the fluctuation of the recording mark length is less than the allowable value, so the fluctuation of the recording mark length due to the self-leakage magnetic field can be effectively reduced. Therefore, it is possible to prevent the trouble caused by the deterioration of the error rate during the reproduction. Further, by adjusting the linear velocity and the external magnetic field so that the fluctuation of the recording mark length becomes equal to or less than the allowable value, it is possible to prevent the deterioration of the error rate due to the self-leakage magnetic field at the same time during reproduction.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a magneto-optical recording apparatus of the present invention.

FIG. 2 is a diagram for explaining a change in recording mark length due to a self-leakage magnetic field of a magneto-optical recording medium.

FIG. 3 is a diagram showing a relationship between a DC magnetic field and a CN ratio when information is recorded by changing a DC magnetic field applied to the recording medium and a self-leakage magnetic field of the recording medium is measured from a CN ratio of a reproduction signal thereof. is there.

[Explanation of symbols]

 9 magneto-optical recording medium 10 spindle motor 11 semiconductor laser 15 objective lens 18a, 18b photodetector 19 differential amplifier 23 laser drive circuit 24 magnetic head 25 magnetic head drive circuit 27 magnetic head 28 electromagnet drive circuit 30 CN ratio measurement circuit 31 CPU 32 motor drive circuit

Claims (4)

[Claims] 1. A magneto-optical recording method for recording information by applying an external magnetic field modulated according to a recording signal while irradiating a magneto-optical recording medium with a light beam of a predetermined intensity, wherein the maximum of the recording medium is The recording medium is selected such that the fluctuation of the predetermined recording mark length is equal to or less than an allowable value based on the relationship between the self-leakage magnetic field, the amplitude of the external magnetic field, the reversal time of the external magnetic field, and the clock cycle. A magneto-optical recording method characterized by the above. 2. The magneto-optical recording method according to claim 1, wherein the maximum self-leakage magnetic field of the magneto-optical recording medium is H _max ,
The amplitude of one wave of the external magnetic field is H _ext , the reversal time of the external magnetic field is T _SW , the clock cycle is T, and a predetermined fluctuation value ΔT of the recording mark length is about ΔT with respect to the clock cycle T. H _max ≦ 0.13 when ≦ 0.13T
A magneto-optical recording method, characterized in that a recording medium satisfying × H _ext × (T / T _SW ) is selected. 3. A magneto-optical recording apparatus for recording information by applying an external magnetic field modulated according to a recording signal while irradiating a magneto-optical recording medium with a light beam having a predetermined intensity, Based on the relationship between the self-leakage magnetic field, the amplitude of one wave of the external magnetic field, the reversal time of the external magnetic field, and the clock cycle, the clock cycle is controlled so that the fluctuation of the predetermined recording mark length is equal to or less than the allowable value. And a means for adjusting at least one of the linear velocity corresponding to the above and the amplitude of the external magnetic field. 4. The magneto-optical recording apparatus according to claim 3, wherein the adjusting means has a maximum self-leakage magnetic field of the magneto-optical recording medium H _max , an amplitude of one wave of the external magnetic field H _ext , and an external magnetic field of the external magnetic field. The inversion time is T _SW , and the allowable variation value ΔT of the predetermined recording mark length is about Δ with respect to the clock cycle T.
When T ≦ 0.13T, H _max ≦ 0.13 × H _ext
In order to satisfy × (T / T _SW ), the clock cycle T
A magneto-optical recording device, wherein at least one of a linear velocity corresponding to the above and an amplitude of the external magnetic field is adjusted.