JPH04325946A - Magneto-optical recording system - Google Patents

Abstract

PURPOSE:To suppress the increase of inverted magnetic domain width which follows the increase of an inverted magnetic domain length and to suppress crosstalk by changing laser radiating pulse width corresponding to the length of the inverted magnetic domain recorded by a magneto-optical disk having no guide groove. CONSTITUTION:In this magneto-optical recording system, laser radiating pulse power is changed corresponding to the length of the inverted magnetic domain to be recorded. When the inverted magnetic domain length is short, the effect of stored heat hardly appears and when the inverted magnetic domain length is long, reversely, the effect easily appears. Since this effect considerably appears at the magneto-optical disk having no guide groove, when the inverted magnetic domain length is long, the effect is canceled and the laser power to be put into the magneto-optical disk is increased so as to decrease a heating amount per unit length of the inverted magnetic domain length and to decrease the inverted magnetic domain width. Since the laser power of the shortest inverted magnetic domain by utilizing this fact and the laser power is decreased with the increase of the inverted magnetic domain length, the inverted magnetic domain width is controlled, and the inverted magnetic domain width can be prevented from being increased with the increase of the inverted magnetic domain length.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording system.

0002

2. Description of the Related Art Magneto-optical disks and drives thereof that perform thermomagnetic recording have already been put into practical use. When forming reversed magnetic domains during recording in a constant external magnetic field, it is common to utilize local changes in magnetic properties that occur as the temperature of the magnetic film increases due to laser irradiation. There is a Curie point record that utilizes the decrease in coercive force.

Therefore, in this method, the shape of the reversed magnetic domain is determined by the temperature distribution and coercive force distribution of the magnetic film, and therefore the shape of the reversed magnetic domain largely depends on the laser pulse shape. Generally, the laser pulse during recording is a rectangular pulse that is modulated at a sufficiently fast response speed allowed by the laser and its drive circuit, and to change the length of the reversed magnetic domain, the pulse width is changed and the amplitude of the entire pulse is changed. I'm doing it without any trouble.

0004

[Problems to be Solved by the Invention] However, with the above-mentioned prior art, a magneto-optical disk without a guide groove in a track where the reversed magnetic domain width tends to increase has the problem of deterioration of reproduced signal quality due to fluctuations in the reversed magnetic domain width. .

[0005] When performing thermomagnetic recording on a rotating magneto-optical disk substrate, the magneto-optical disk is formed with a film structure that appropriately suppresses thermal diffusion in order to raise the temperature sufficiently until magnetic domain reversal occurs. ing. Therefore, laser irradiation causes heat accumulation. Specifically, the reversed magnetic domain is shifted from the laser irradiation position to the irradiation end position, or a droplet-shaped reversed magnetic domain is formed in which the reversed magnetic domain shape becomes wider from the irradiation start position to the end position. From this, when the pulse width is lengthened without changing the amplitude of the entire pulse in order to increase the length of the reversed magnetic domain, the width of the reversed magnetic domain increases as the length of the reversed magnetic domain increases.

[0006] In the groove portion of a magneto-optical disk that has a guide groove for tracking and forms an inverted magnetic domain in a flat portion, the incident angle is small, so the amount of reflected light is large.
Since the surface of the groove part is rougher than that of the flat part, diffused reflection is more likely to occur, which may reduce the absorption efficiency of the laser power of the magneto-optical disk and prevent temperature rise. It is difficult to spread compared to those without it. Also, during playback, since the laser spot diameter is larger than the track width, changes in the Kerr rotation angle of the reversed magnetic domain in the groove part are also observed, but the amount of reflected light in the guide groove part is smaller than that in the flat part. Therefore, the Kerr rotation angle of the reversed magnetic domain in the groove part is observed to be smaller than that in the flat part.

On the other hand, in a magneto-optical disk in which tracking is performed by a method other than a guide groove and the data recording area does not have a guide groove, the width of the reversed magnetic domain tends to increase due to the above factors, and the Kerr rotation angle of the reversed magnetic domain at the track boundary during reproduction tends to increase. Easy to retrieve information. Further, when the width of the reversed magnetic domain increases to be almost equal to the track width, the reversed magnetic domain interferes with the reversed magnetic domain of the adjacent track, and the shape of the reversed magnetic domain is disturbed.

[0008] As a result, during reproduction, crosstalk that interferes with information recorded on adjacent tracks is likely to occur, resulting in deterioration of reproduced signal quality.

The present invention is intended to solve these problems, and its purpose is to provide a magneto-optical recording system in which the reversal domain width can be controlled independently of the reversal domain length in a magneto-optical disk without a guide groove. It's about doing.

0010

[Means for Solving the Problems] The above-mentioned magneto-optical recording method is realized by a magneto-optical recording method in which the irradiation pulse power is changed depending on the length of the reversed magnetic domain to be recorded.

[0011] The effect of heat accumulation mentioned above in the above problem is difficult to appear when the reversal magnetic domain length is short, and the effect of heat accumulation is more likely to occur when the reversal magnetic domain is long. If the length of the reversed magnetic domain is long, this effect is canceled out, and by reducing the laser power input to the magneto-optical disk, the amount of heating per unit length of the reversed magnetic domain length is reduced, thereby reducing the width of the reversed magnetic domain. be able to.

By utilizing this, the laser power of the shortest reversed magnetic domain is maximized, and the laser power is decreased as the length of the reversed magnetic domain increases, thereby controlling the width of the reversed magnetic domain. This can prevent the width from increasing.

FIG. 1 shows a schematic diagram of the laser power versus time of the laser beam and the shape of the inverted magnetic domains formed accordingly in the magneto-optical recording system of the present invention. FIG. 2 shows a schematic diagram of the laser power with respect to time of the recording light of the present invention and the shape of the reversed magnetic domain formed accordingly, as a solid line, and the recording power with respect to time of the conventional recording light example and the reversed magnetic domain formed accordingly. A schematic diagram of the shape is shown with a dotted line.

[0014]

【Example】

(Example 1) The shape of reversed magnetic domains was observed using a polarizing microscope. A glass flat disk was used as the substrate. Its outer diameter is 86 mm in diameter and 1.2 mm in thickness. Films were formed by sputtering, with a dielectric layer of SiN and a reflective layer of Al.
was laminated to a thickness of 60 nm and SiN was laminated to a thickness of 75 nm. After film formation was completed, a magnetic field was applied in the erase direction to align the magnetic domain directions. The conditions for forming reversed magnetic domains are a rotational speed of 2400 r. p. m. , the laser wavelength is 830 nm, the recorded position has a radius of 30 mm, the linear velocity is 7.54 m/s, and the external magnetic field is 30 m/s in the erasing direction.
It is 0Oe.

First, for comparison, recording was performed using a conventional method with constant recording power. The power and frequency of the recording pulse were 9 mW and 2 MHz, respectively, and the length of the reversed magnetic domain was controlled by changing the pulse width, and the relationship between the length of the reversed magnetic domain and the width of the reversed magnetic domain at this time is shown by line 1 in Figure 3. Next, the recording pulse according to the present invention is the same as the above conventional example except for the power. The recording power was changed according to the following equation according to the length of the reversed magnetic domain.

[0016]

[Equation 1] Pw=a×pulse width (μs)+bPw: Recording power (mW) a, b: Constant a<0, b>0
Recording was performed using the constants shown in Table 1, and the results are shown in Figure 3 together with those of the conventional method.

[0017]

[Table 1]

[0018] In the conventional method, as the length of the reversed magnetic domain increases, the width of the reversed magnetic domain continues to increase gradually even after once increasing rapidly. The result shown by line 2 also increases, although to a lesser extent. The result shown by line 3 shows that the effect of the present invention is well exhibited, and the increase in the reversed magnetic domain width is saturated and kept constant. On the other hand, in line 4, the reversal domain width increases once and then decreases. Therefore, in this example -16<
a<-2 is suitable.

(Example 2) Next, crosstalk was evaluated using a DBF substrate. The DBF board is the aforementioned track wobbling type disk, and the data area is separated by the servo area. Its diameter is 90mm and thickness 1
．． The track width is 2 mm and the track width is 1.5 μm. The conditions for film formation and recording are the same as in Example 1 except that recording is performed on all tracks.

[0020] Measurements were made on the same disk by repeating erasing, recording, and reproducing, and the 4/11 modulation code was ``0'' or ``.
5" were alternately recorded one track at a time, and then the tracks in which "0" had been written were read out with a playback power of 1 mW, and the byte error rate (B.E.R.) was examined. The recording pulse of the conventional technology is shown in Figure 3. The recording pulse of the present invention is the number 2 which showed good results in Example 1.

[0021]

[Equation 2] Pw=-10×pulse width (μs)+9.5, which is shown in FIG.

As a result, the conventional one is B. E. R=2.
3 x 10-4, and the one of the present invention is B. E. R=6.
7×10 −5 (all averages of 5 times), and an improvement in signal characteristics was observed due to a reduction in crosstalk.

[0023]

As described above, according to the magneto-optical recording method of the present invention, in a magneto-optical disk without a guide groove in which recording is performed in a constant magnetic field, the width of the reversible domain increases as the length of the reversible domain increases. It was achieved to suppress the increase and suppress the crosstalk.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of temporal changes in recording power according to the present invention and the shape of inverted magnetic domains corresponding thereto.

FIG. 2 is a diagram showing changes in the reversal domain width with respect to the reversal domain length in the embodiment of the present invention (line 2) and the conventional example (line 1) in Example 1;

FIG. 3 is a diagram showing changes in recording power over time according to the conventional method of Example 2;

FIG. 4 is a diagram showing a temporal change in recording power according to the present invention in Example 2.

Claims (1)

[Claims] 1. A magneto-optical recording method in which recording is performed in a constant magnetic field on a magneto-optical disk without a guide groove, and the laser irradiation pulse power is changed according to the length of the reversed magnetic domain to be recorded.