JP2573281B2 - Magneto-optical disk playback method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for reproducing information recorded on a magneto-optical disk.

(Prior Art) A magneto-optical disk has an easy axis of magnetization in a direction perpendicular to a film surface, for example, a rare earth-transition metal amorphous alloy (RE).
-TM) A recording medium in which a magneto-optical recording layer represented by a film is formed on a substrate. Recording on the magneto-optical disk is performed by irradiating the recording layer with a laser beam and, if necessary, further applying a magnetic field from the outside to invert the magnetization direction reversibly. Reproduction is performed using the polar Kerr effect according to the direction of magnetization of the recording layer.

Such a magneto-optical disk is manufactured by forming a recording layer on a substrate by sputtering or vapor deposition. Since the recording layer immediately after film formation is in a demagnetized state macroscopically, it is necessary to perform magnetization prior to use as a disk and make the direction of magnetization uniform over the entire track or over the entire disk. The recording / erasing operation selectively reverses or eliminates the magnetic domain of the recording layer in which the magnetization direction is made uniform in this manner. The Kerr effect is determined by the presence or absence of the recording magnetic domain in which the magnetization reversal occurs. The reproduction operation is used for detection.

The reproduction signal intensity is the laser power P of the reproduction laser beam.
And the product of the car rotation angle θk. Therefore, the reproduction signal
In order to increase the C / N (carrier-to-noise ratio), it is desirable to increase the laser power P. However, if it is too high, the temperature of the recording layer increases and the Kerr rotation angle θk decreases. P that gives the maximum of the θk product
Has been preferred.

However, since the leakage magnetic field Hl of the recording layer itself is always applied to the recording magnetic domain, the laser power P of the reproducing laser beam is increased, and the coercive force Hc of the recording layer of the reproducing laser beam irradiation unit is increased. Is smaller than the leakage magnetic field Hl, the recording or erasing operation is performed as if the reproducing operation is performed, and the magnetic domain of the recording is deformed (however, when the applied magnetic field Hex at the time of reproducing is 0). . The minimum laser power Pc that causes such deformation of the recording magnetic domain (the maximum laser power that does not deform the recording magnetic domain) Pc is
As long as it is sufficiently higher than P that gives the maximum of the xθk product, there is substantially no problem. However, the RE-TM film or the like often used as a recording layer of a magneto-optical disk often does not satisfy the condition that Pc is sufficiently larger than P that gives a maximum of the product of P × θk. Setting the maximum of the product of P × θk is not preferable because there is a risk of causing deformation of the recording magnetic domain.

(Problems to be Solved by the Invention) As described above, in the reproducing operation of the magneto-optical disk, depending on the reproducing conditions, deformation of the recording magnetic domain such as re-magnetization reversal due to irradiation of the reproducing laser beam occurs, and recorded information is damaged. Although there is a possibility, conventionally, no particular consideration has been given to such danger.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of reproducing a magneto-optical disk capable of increasing the C / N of a reproduction signal without impairing recorded information.

[Constitution of the Invention] (Means for Solving the Problems) The present invention reduces the leakage magnetic field of the recording layer of a magneto-optical disk when the information recorded on the magneto-optical disk is reproduced.
In the range, 0.5Hl ≦ Hex ≦ 1.5Hl, and data indicating the applied magnetic field Hex in the direction opposite to the direction of Hl as the optimal application time, and the reproduction was performed by selecting the applied magnetic field Hex in the above range. When the maximum laser power that does not impair the information recorded on the magneto-optical disk is Pc, data indicating P as the optimum laser power in the range of 0.6Pc ≦ P ≦ Pc is a specific area on the magneto-optical disk. In which the applied magnetic field and the laser power of the reproducing laser beam are set based on these data.

(Function) According to the present invention, the applied magnetic field required for reproduction and the laser power of the reproduction laser beam are automatically set to optimal values, and the information recorded by deforming the recording magnetic domain by the irradiation of the reproduction laser beam is obtained. There is no loss.

Further, in the reproducing method according to the present invention, the applied magnetic field Hex is set in the range of 0.5Hl ≦ Hex ≦ 1.5Hl after the direction of the applied magnetic field Hex is set to be opposite to the leakage magnetic field Hl. Effective magnetic field Heff (Hl and Hex
) Is suppressed to a small value, so that the critical coercive force Hc (≦ Heff) when the recording magnetic domain is deformed becomes small. Corresponding to the decrease in the critical coercive force Hc, the deformation critical laser power Pc (maximum laser power that does not impair recorded information) Pc of the recording magnetic domain increases, and as a result, the C / N
Is improved. The range of 0.5Hl ≦ Hex ≦ 1.5Hl was found by confirming the effect of improving the C / N of the reproduced signal for various recording layers.

Further, by setting the reproducing laser power P to be equal to or less than the deformation critical laser power Pc of the recording magnetic domain, deformation of the recording magnetic domain is reliably prevented even under the condition of Hex ≒ H1, and by setting P to 0.6Pc or more, Hex ≒ The C / N of the reproduced signal is larger than in the case of not Hl.

(Example) Hereinafter, an example of the present invention is described with reference to drawings.

FIG. 1 shows an outline of a magneto-optical disk according to one embodiment of the present invention. A magneto-optical recording medium layer 2 is formed on a substrate 1. The magneto-optical recording medium layer 2 has at least a recording layer made of, for example, an RE-TM film. This magneto-optical recording medium layer 2
Is the lead-in area 3 and the other part is the user data area 4. Here, in the lead-in area 3, in addition to various control data normally required at the time of recording / reproducing of the magneto-optical disk, data of the optimal applied magnetic field and data of the optimal laser power at the time of reproducing based on the present invention are recorded in advance. .

An example of a method for manufacturing the magneto-optical disk shown in FIG. 1 will be described. First, a 130 mmφ, 1.2 mmt resin substrate provided with a tracking groove in advance as a substrate 1 is prepared, and a SiN film / 250 mm thick Tb25Co75 recording layer / SiN film / TiN film is formed thereon by sputtering.
After a four-layer film is formed as the magneto-optical recording medium layer 2, it is magnetized and the direction of magnetization of the recording layer is changed from the substrate 1 surface to the film surface (upward in FIG. 1) over the entire surface of the disk. Aligned.

Next, the disk was rotated at 120 rpm, and a recording test was performed in the user data area 4 (radius 5 cm). Recording conditions were such that a pulse having a repetition frequency of 1 MHz and a duty of 50% was used as a recording laser beam, and an auxiliary applied magnetic field of 400 Oe was applied from the substrate 1 toward the film surface (upward in FIG. 1). The reason why the direction of magnetization is the same as the direction of the auxiliary applied magnetic field during recording is that the recording layer is a Tb-rich ferrimagnetic film in this embodiment.

The recording laser beam is 5.5mW which is the optimum laser power.
After forming a recording magnetic domain (recording bit) row by setting to, a reproduction test was performed. The parameter is the applied magnetic field Hex during playback.
And the laser power of the reproducing laser beam (hereinafter referred to as reproducing laser power) P. FIG. 2 and FIG. 3 show the results of the regeneration test.

FIG. 2 shows the C / N of the reproduction signal with respect to the reproduction laser power P.
And the change in the noise level, the two applied magnetic fields Hex = 0, Hex
= + 200 Oe (the upward direction is defined as the + direction in FIG. 1). As is clear from the figure, the noise level (however, the return light noise due to the increase in the reproduction laser power P is shown after subtraction) is a certain reproduction laser power P (= Pc: deformation critical laser power of the recording magnetic domain). , But rises when P exceeds Pc. Also,
It can be seen that C / N increases substantially in proportion to P up to Pc, that is, increases by a rate of 6 dB when P is doubled, but decreases when Pc or more. Pc also depends on Hex, Hex =
0m is about 2mW, whereas Hex = + 200 Oe is 3.5mW
W and big. Further, the maximum value of C / N is 52 dB at Hex = 0, whereas it is 57 dB at Hex = + 200 Oe.

Here, the Kerr rotation angle θk of the TbCo film serving as the recording layer hardly decreases due to an increase in the film temperature (that is, an increase in the reproducing laser power P). Accordingly, in FIG. 2, the decrease in C / N in the region where the reproducing laser power P exceeds Pc is not caused by the carrier level exceeding the maximum of P × θk, but by a change in the recording magnetic domain, and as a result, the noise level is reduced. Can be determined to have increased. In fact, the reproduction laser power P
Observation of the recording magnetic domain of the track reproduced at a value exceeding Pc confirmed that at Hex = 0, the edge of the recording magnetic domain fluctuated, and the length of the magnetic domain was shortened. On the other hand, when the reproducing laser power P was equal to or less than Pc, the recording magnetic domain had a length corresponding to the recording pulse width, and the edge was circular.

As described above, when Hex = 0, the influence on the recording magnetic domain depending on the reproduction laser power P appears or does not appear. When Hex = 0, the leakage magnetic field Hl of the recording layer decreases the recording magnetic domain in the region where the reproduction laser power P is large. By acting in the erasing direction, local remagnetization reversal of the recording magnetic domain occurs in the region of P> Pc where the coercive force Hc of the recording layer is smaller than the leakage magnetic field Hl, and the remagnetization reversal is microscopic. This is considered to be due to uneven generation. On the other hand, the applied magnetic field is Hex = + 200
It is considered that in the Oe region, Hex completely cancels out the leakage magnetic field Hl, so that the coercive force Hc causing re-magnetization reversal decreases, and as a result, the deformation critical laser power Pc of the recording magnetic domain increases.

FIG. 3 shows the deformation critical laser power Pc of the recording magnetic domain obtained by changing the applied magnetic field Hex of the same disk at various values. Hex ≒ + 200 Oe shows the maximum Pc, and the leakage magnetic field of the recording layer. It can be seen that Hl has the opposite direction and the same size as Hex, that is, Hl ≒ −200 Oe.

As described with reference to FIGS. 2 and 3, if the applied magnetic field Hex and the reproducing laser power P at the time of reproducing are made appropriate,
The reproducing laser power P can be increased without accompanying the deformation of the recording magnetic domain, and the C / N can be increased. Therefore, the user data area 4 in which the recording test was performed as described above
After erasing all the information in the data, data indicating the optimum reproduction condition of the magneto-optical disk, that is, data indicating information of Hex: +100 Oe to +300 Oe, P: 2 mW to 3.5 mW, is recorded in the lead-in area 3. If these data are read from the lead-in area 3 during reproduction and the applied magnetic field Hex and the reproduction laser power P are automatically set, the C / N of the reproduction signal can be maximized without losing the recorded information. Can be higher.

In the above embodiment, a magneto-optical disk using a TbCo film having a relatively large leakage magnetic field Hl as the recording layer has been described. However, no matter what material the recording layer is, H1 cannot be 0. The present invention is effective. For example, the compensation composition
The TbCo film is an example of a recording layer in which the leakage magnetic field Hl is minimized. However, since Hl of about several tens Oe is applied, reproduction is performed based on the present invention by setting the applied magnetic field Hex to Hex ≒ Hl (however, in the opposite direction). This is effective in increasing the reproduction laser power P to increase the C / N of the reproduction signal.

In the present invention, the applied magnetic field Hex at the time of reproduction is particularly preferably Hex ≒ Hl (about 0.9Hl to 1.1Hl) as described above.
bCo, TbFe, GdTbCo, TbFeCo, GdTbFe etc.
x is in the range of 0.5Hl ≦ Hex ≦ 1.5Hl, and its direction is Hl
In the opposite direction, it was confirmed that the effect of improving the C / N of the reproduced signal was remarkable.

On the other hand, the reproduction laser power P is preferably in the range of 0.6 Pc to Pc. The basis for this is that if P exceeds Pc, the probability of deforming the recording magnetic domain is significantly increased even under the condition of Hex ≒ Hl, and if the P is less than 0.6Pc, the reproduced signal is higher than when Hex ≒ Hl is not used. This is because the C / N improvement effect cannot be expected so much.

Practically, it is desirable to select Hex and P within the above-described range in consideration of a reproduction margin and the like.

[Effects of the Invention] In the present invention, data of the optimum applied magnetic field during reproduction and the optimum laser power of the reproduction laser beam are recorded in a specific area on the disk, so that large reproduction can be performed without losing the recorded information. The optimum applied magnetic field and the optimum laser power for obtaining C / N can be automatically set at the time of reproduction.

Further, the reproducing method of the present invention, when reproducing information recorded on such a magneto-optical disk, in the range of 0.5Hl ≦ Hex ≦ 1.5Hl with the leakage magnetic field of the recording layer as Hl, and the direction of Hl Data indicating the applied magnetic field Hex in the opposite direction as the optimum applied magnetic field, and the maximum laser power (deformation of the recording magnetic domain) which does not impair the information recorded on the magneto-optical disk when reproducing by selecting the applied magnetic field Hex within the above range. Critical laser power) as Pc, and read data from a specific area on the magneto-optical disk, which indicates P in the range of 0.6Pc ≦ P ≦ Pc as an optimum laser power, and apply an applied magnetic field and a reproducing laser beam based on these data. By setting the laser power of the recording domain to an optimum value, the critical deformation coercive force Hc of the recording magnetic domain can be reduced, so that the critical deformation laser power Pc of the recording magnetic domain can be increased, and the C of the reproduction signal can be increased. / N improves more effectively.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a magneto-optical disk according to an embodiment of the present invention, and FIG. 2 is a view for explaining a reproducing method based on the embodiment of the present invention. FIG. 3 is a diagram showing changes in N and noise level using an applied magnetic field as a parameter, and FIG. 3 is a diagram showing a relationship between the applied magnetic field and the deformation critical laser power of the recording magnetic domain. 1 ... substrate, 2 ... magneto-optical recording medium layer, 3 ... lead-in area, 4 ... user data area.

Claims (1)

(57) [Claims] When the leakage magnetic field of a recording layer in a magneto-optical disk is Hl, an applied magnetic field Hex in a range of 0.5Hl ≦ Hex ≦ 1.5Hl and opposite to the direction of Hl is designated as an optimum applied magnetic field. When the maximum laser power which does not impair the information recorded on the magneto-optical disk when the data and the applied magnetic field Hex are selected in the above range and the reproduction is performed is Pc, 0.6Pc ≦ Pc
Data indicating P as the optimum laser power in the range of ≤Pc is recorded in a specific area on the magneto-optical disk, and applied when reproducing the information recorded on the magneto-optical disk based on these data. A method for reproducing a magneto-optical disk, comprising setting a magnetic field and a laser power of a reproducing laser beam.