JPH056592A - Method and device for magneto-optical recording and reproducing - Google Patents

Abstract

PURPOSE:To suppress the formation of an unwanted magnetic domain and the generation of an erasure remaining magnetic domain in the thermomagnetic recording of data to the perpendicular magnetizing film of a medium. CONSTITUTION:The medium 11 is driven to rotate by a motor 12. When the medium 11 passes through a magnetic field from a magnet 14, a recording light beam irradiates from an optical head 13, thus, the data is recorded in the perpendicular magnetizing film of the medium 11 as a bubble magnetic domain. At a position different from the position performing this recording, the medium 11 passes through a correcting magnetic field generated with the magnet 15, thus, the unwanted magnetic domain and the erasure remaining magnetic domain disappear.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention carries out thermomagnetic recording of information by causing thermal energy of convergent light such as a laser beam to act on a magnetic layer in a magnetic field, or the recorded information is subjected to a magneto-optical effect. The present invention relates to a method and an apparatus for reproducing by using (collectively referred to as "magneto-optical recording / reproducing").

[0002]

2. Description of the Related Art In recent years, as one of rewritable optical recording methods, a magneto-optical recording method using a perpendicularly magnetized film of a recording medium as a recording layer has been actively researched and has been commercialized. The information writing operation is performed by thermomagnetic recording. That is, an energy beam such as a constant or pulse-modulated laser beam is focused on the recording layer in a modulating magnetic field or a static magnetic field to heat the recording area. Due to the magnetic interaction between the heated recording layer and the external magnetic field, an inverted magnetic domain corresponding to information is formed in the recording layer and the recording operation is completed.

[0003]

However, in the recording according to the prior art, the reversed magnetic domain which should not be formed is erroneously formed due to the non-uniformity of the recording medium, the focusing error, or the like, or the recorded magnetic domain has a different shape. There is a problem that distortion occurs, which adversely affects reproduced signal quality as recording noise. Also, in the case of so-called direct overwrite that does not require an erasing operation, after initiating new recording, the inversion magnetic domain remains as unerased residue even though no trace of previously recorded information should be left. It may happen.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to form an unnecessary inversion domain or a recording domain shape which causes recording noise during thermomagnetic recording. Suppress the occurrence of distortion, or
It is an object of the present invention to provide a magneto-optical recording / reproducing method and device capable of removing such unnecessary inversion domain distortion or domain-domain distortion before magneto-optical reproduction.

[0005]

The present invention provides a method for recording data on a perpendicular magnetization film provided on a recording medium, comprising:
A recording process of forming bubble magnetic domains (plurality) for recording the data in the perpendicular magnetization film by simultaneously applying a recording light and a recording magnetic field to the recording medium, and the perpendicular magnetization after the recording process. A magneto-optical recording method comprising: a correction step of applying a correction magnetic field in a direction perpendicular to the film surface of the film.

Further, according to the present invention, in an apparatus for recording data on a perpendicularly magnetized film provided on a recording medium, a moving means for moving the recording medium and a device arranged at a predetermined position in a moving path of the recording medium, A recording unit that applies a recording light and a recording magnetic field to the recording medium to form a bubble magnetic domain for recording the data in the perpendicular magnetization film, and is arranged downstream of the recording unit along the movement path. There is provided a magneto-optical recording device comprising: a correction unit that applies a correction magnetic field to the perpendicular magnetization film in a direction perpendicular to the film surface.

Further, according to the present invention, in a method for reproducing data recorded as bubble magnetic domains in a perpendicular magnetic film provided on a recording medium, a correction magnetic field is applied to the film surface of the perpendicular magnetic film in a vertical direction. And a step of reading the data by utilizing a magneto-optical effect by simultaneously applying a reproducing light and a reproducing magnetic field to the recording medium after the correcting step. provide.

Further, according to the present invention, in an apparatus for reproducing data recorded as bubble magnetic domains in a perpendicularly magnetized film provided on a recording medium, a moving means for moving the recording medium and a moving path of the recording medium. Is arranged at a predetermined position of, and applies a reproducing light and a reproducing magnetic field to the perpendicular magnetization film,
A reproducing means for reading the data by utilizing a magneto-optical effect; and a correcting means arranged upstream of the reproducing means along the movement path for applying a correcting magnetic field to the perpendicular magnetization film in a direction perpendicular to the film surface thereof. There is provided a magneto-optical reproducing device having:

[0009]

[Function] The bubble domain theory of the perpendicular magnetization film has been studied for a long time toward the application of the magnetic bubble memory. According to the bubble magnetic domain theory, under the condition that the influence of the demagnetizing field is negligible, in the absence of an external magnetic field, the domain wall coercive force is Hc, the saturation magnetization is Ms, and the cylindrical domain wall energy density is σ _B ,
The minimum bubble magnetic domain radius R that can stably exist in the single-layered perpendicular magnetization film can be expressed as R = σ _B / 2MsHc (1). The expression (1) means that the bubble magnetic domain having a radius smaller than R is crushed by the compressive force caused by the domain wall energy and cannot exist. On the other hand, when the correction magnetic field Hs perpendicular to the film surface is applied, the minimum stable magnetic domain radius R is R = σ _B / {2Ms (Hc-Hs)} (2). Here, the sign of Hs is defined as positive in the direction opposite to the magnetization direction of the bubble magnetic domain. From this equation (2), the corrected magnetic field H
It can be seen that the minimum stable magnetic domain radius can be made larger than in the case of no magnetic field by appropriately selecting s in the range smaller than the coercive force Hc.

The same applies to a plurality of magnetic layers exchange-coupled to each other. In this case, the minimum stable domain radius can be determined by considering the interface domain wall energy density σ _w between the magnetic layers in addition to the above consideration in the case of a single layer.

Therefore, in thermomagnetic recording in which information is stored in the perpendicularly magnetized film as a bubble magnetic domain, a magnetic field Hs having an appropriate strength after recording is performed regardless of whether it is a single-layer film or an exchange-coupled multi-layer film. By applying, it becomes possible to extinguish only the reversed magnetic domains having an arbitrary size or less.

On the other hand, the distortion of the recording magnetic domain shape in thermomagnetic recording is caused by the fact that recording is performed in a thermally non-equilibrium state. In the thermal equilibrium state, the domain wall energy E _w and the energy E _H of the interaction between the magnetization and the external magnetic field are
The magnetic domains are shaped so that the total sum of the demagnetizing field energy E _M is minimized, and generally settles into a magnetic domain shape that makes the total extension of the domain wall as short as possible. Therefore, after the thermomagnetic recording is finished, by applying an appropriate magnetic field in the direction perpendicular to the film surface to give a driving force of the domain wall exceeding the domain wall coercive force Hc, a thermally non-equilibrium thermomagnetic recording process is performed. It is possible to reshape the distorted shape of the recording magnetic domain that has been produced through the above process into a magnetic domain shape with small distortion.

As described above, the concept that the imperfect recording can be corrected by applying a magnetic field having an appropriate intensity after recording is a completely new concept. Based on this novel concept, the apparatus of the present invention records information on a recording medium by a general thermo-magnetic recording method and then reproduces the information (for example, when a rotated disc-shaped recording medium is recorded). During the subsequent one rotation), a vertical magnetic field is applied to the recording medium to control the reversal magnetic domain responsible for storage at a position different from the optical head.

[0014]

The present invention will be specifically described based on the following examples.

[First Embodiment] FIG. 1 shows an embodiment of the thermomagnetic recording apparatus of the present invention. In FIG. 1, a disc-shaped magneto-optical recording medium 11 is rotated by a rotating mechanism 12 such as a motor. The medium 11 has a single-layered perpendicular magnetization film as a recording layer, and this recording layer is pre-magnetized in one direction for each track. While the medium 11 passes through the recording magnetic field generated by the electromagnet 14, the recording light focused by an optical head 13 using a semiconductor laser arranged so as to face the electromagnet 14 across the medium 11 is used as a light source. Upon irradiation, thermomagnetic recording of data is performed on the recording layer of the medium 11. The electromagnet 14 is connected to the control circuit 18 through the driver 17.
The intensity of the recording magnetic field is kept constant by being controlled by. The optical head 13 is driven by the optical head driver 19 and modulates the recording light so that its intensity becomes a high level or a low level according to the data. As a result, magnetic domains in which data is recorded (recording magnetic domains) are formed in the recording layer.

Immediately after recording the data, the medium 11 passes through a correction magnetic field generated by an electromagnet 15 arranged so as to sandwich the medium 11 at a position different from the optical head 13. The electromagnet 15 is controlled by the control circuit 20 through the driver 19 to generate a correction magnetic field of constant strength. The direction of this correction magnetic field is perpendicular to the film surface of the recording layer (disc surface of the medium 11). This direction may be the same as or opposite to the magnetization direction of the recording magnetic domain. By applying this correction magnetic field, it can be expected that the distortion of the shape of the recording magnetic domain is corrected.

When the data recorded on the medium 11 is reproduced, the medium 11 is rotated, and when passing through the reproducing magnetic field generated by the electromagnet 14, the reproducing light is emitted from the optical head 13 to utilize the magneto-optical effect. Data is read.
The reproducing magnetic field and the intensity of the reproducing light are also controlled by the control circuit 18 and the optical head driver 19, respectively.

Electromagnet 14 for generating recording and reproducing magnetic fields
May be replaced with a reversible permanent magnet.

In this apparatus, the inventors set the relative velocity between the disk surface of the medium 11 and the laser spot of the recording light at 5.6 m /
sec, recording light modulation frequency (recording frequency) 3.7 MHz,
Recording light pulse width 60 nsec, objective emission pulse intensity 6.0
Recording was performed at mW and a recording magnetic field intensity of 250 Oe, then a correction magnetic field having an intensity of 4000 Oe was applied in the same direction as the recording magnetization, and thereafter reproduction was attempted using continuous light with an objective emission laser intensity of 1.0 mW. As a result, the carrier level at the recording frequency of the power spectrum of the reproduced signal is -2.
5dBm, the noise level in the vicinity is -53.3dBm,
Good reproduction can be performed. On the other hand, for comparison,
When reproducing was attempted without applying a magnetic field after recording under the same conditions, the carrier level showed almost no difference of -2.4 dBm, but the noise level was -50.
It was confirmed that the value was 1 dBm, which was about 3 dB higher than that of the example according to the present invention. As described above, according to the present invention, it is understood that the recording noise can be reduced as compared with the prior art. Similar results were obtained when a correction magnetic field was applied in the direction opposite to the magnetization of the recording domain.

[Second Embodiment] This embodiment is described in JP-A-1-
The present invention is applied to a direct overwrite system as disclosed in Japanese Patent No. 125747, and a device having basically the same configuration as that shown in FIG. 1 is used.

In FIG. 1, the recording magnetic field generated by the electromagnet 14 is controlled to have a constant strength. On the other hand, the recording light from the optical head 13 has a pulse having a relatively long width and a low energy density (referred to as a recording pulse) and a pulse having a relatively short width and a high energy density (referred to as an erasing pulse) as shown in FIG. ), And is modulated to. The recording pulse corresponds to "1" (or "0") of digital data, and the erase pulse corresponds to "0" (or "1") of digital data. As a modulation method, for example, in synchronization with a channel clock generated from clock pits formed in advance on the recording medium 11,
By adopting the modulation method, the recording magnetic domain formed before the medium 11 is irradiated with the recording pulse and the erasing pulse at the coincident timing. A new recording magnetic domain is formed in the portion irradiated with the recording pulse, and the previous recording magnetic domain is erased in the portion irradiated with the erasing pulse, thereby realizing direct overwrite.

After the direct overwrite, the medium 11 passes through the correction magnetic field generated by the electromagnet 15. The direction of the correction magnetic field is opposite to the magnetization direction of the recording magnetic domain.

Data can be reproduced by a general method utilizing the magneto-optical effect as in the case of the first embodiment.

Electromagnet 14 for generating recording and reproducing magnetic fields
May be replaced by a fixed or reversible permanent magnet.

The effect of the correction magnetic field in this embodiment will be described in detail below.

Japanese Laid-Open Patent Publication No. 1-125747 discloses a magnetic material and an erase method such that a radius of a magnetic domain formed by irradiation of an erase pulse is smaller than a minimum stable magnetic domain radius R defined by the above-mentioned equation (1). It is disclosed that direct overwrite can be completely realized by selecting conditions such as pulse and recording magnetic field. However, in a general rare earth-transition metal alloy thin film as a recording layer, the minimum stable magnetic domain radius R is about 0.05 μm, and under a recording magnetic field of such an intensity that a sufficiently large recording magnetic domain can be formed by irradiation of a recording pulse. Then, it is virtually impossible to form such a small magnetic domain only by changing the condition of the erase pulse. Therefore, the small magnetic domains formed by the irradiation of the erasing pulse do not disappear and remain as recording noise (hereinafter referred to as unerased magnetic domains).

In this embodiment, when a correction magnetic field He in the direction opposite to the magnetization of the recording magnetic domain, that is, in the direction opposite to the residual magnetic domain, is applied to the medium having the residual magnetic domain, the minimum stable magnetic domain radius R is (2). ) Size will be determined by the formula. This (2)
According to the formula, by appropriately selecting the correction magnetic field He in a range smaller than the coercive force Hc, the minimum stable magnetic domain radius R can be made larger than in the case of no magnetic field. Therefore, if the magnetic domain diameter formed by the recording pulse is larger than the minimum stable magnetic domain radius R of the equation (2) and the magnetic domain diameter formed by the erase pulse is smaller than that, only the unerased magnetic domain is affected by the external magnetic field. Can be eliminated. In order to make the ratio of the magnetic domain radii sufficiently large, as shown in FIG. 2, the erase pulse may be a single optical pulse having a shorter pulse width and a higher energy density than the recording pulse. It is effective.

Specific values of the pulse width and the intensity of the recording pulse and the erasing pulse differ depending on the film structure and structure of the recording medium or the rotation speed of the recording medium. Further, the magnitudes of the recording magnetic field and the correction magnetic field are different depending on the case, but from a practical viewpoint, the recording magnetic field is preferably about 100 to 600 Oe and the correction magnetic field is preferably about 3000 to 6000 Oe.

In this embodiment, TbFeCo, DyFe
A recording medium having a perpendicular magnetization film such as a rare earth transition metal amorphous film such as Co or NdDyFeCo or a noble metal cobalt-based composition modulation periodic multilayer film such as Co / Pt can be used.

For the evaluation test of this example, a Si ₃ N ₄ film 22, a TbFeCo film (recording layer) 23, and a Si ₃ N ₄ film were formed as a medium 11 on a polycarbonate substrate 21 having a diameter of 90 mm as shown in FIG. 24 is a film thickness of 80 nm,
A layer having 90 nm and 80 nm sequentially laminated and then coated with a protective layer 25 made of an ultraviolet curable resin was prepared.
Using this recording medium 11 and the apparatus of FIG. 1, the number of rotations of the medium is 1800 rpm, the recording magnetic field is 200 Oe, and the correction magnetic field is 5000 Oe.
Digital recording was performed by the optical modulation method. Medium 11
The recording layer 23 is a so-called rare earth-rich film in which the sublattice magnetization of the rare earth element is dominant at room temperature and has a compensation point between the room temperature and the Curie temperature, so the recording magnetic field and the correction magnetic field are in the same direction. The recording light has an objective laser output of an erasing pulse of 14 mW, a pulse width of 20 nsec, an objective laser output of a recording pulse of 8 mW, and a pulse width of 90 ns.
Modulated to be ec.

Under the conditions described above, first, the random pattern digitally modulated to the 4/11 code is written on the recording medium, and then the random pattern of the 4/11 code is also recorded to determine the byte error rate of the reproduction signal. When measured, it was 6 × 10 ⁻⁶ . This value is on the same level as the error caused by the medium noise and the medium defect, and indicates that the direct overwrite was favorably performed. On the other hand, for comparison, recording was performed by a conventional method with a corrected magnetic field of zero, and the same evaluation test as above was performed. As a result, a byte error of about 3 × 10 ^−3, which was thought to be due to the residual magnetic domains, was observed. .

Next, using a polarization microscope, magnetic domains of the recording medium recorded by the method of the present invention and the recording medium recorded by the conventional method were observed. As a result, in the former,
Inverted magnetic domains other than the intentionally formed recording magnetic domains were not observed, whereas in the latter case, inversion magnetic domains with a diameter of about 0.2 μm, which are thought to be small erased magnetic domains, were observed in the intentionally recorded magnetic domains. Was done.

[Third Embodiment] The first or second embodiment shown in FIG.
In the apparatus of the embodiment, the electromagnet 1 which is the generation source of the correction magnetic field
5 may be replaced with a permanent magnet. FIG. 4 shows the configuration of an embodiment modified in such a manner. In the third embodiment, the permanent magnets 26 arranged so as to sandwich the medium 11 generate a correction magnetic field in the vertical direction on the board surface of the medium 11. The electromagnet 14 may be replaced with a fixed or reversible permanent magnet.

[Fourth Embodiment] FIG. 5 shows an apparatus according to a fourth embodiment. In this apparatus, recording of data on the medium 31 is performed by irradiating recording light of constant intensity in a recording magnetic field whose intensity is modulated according to the data. This is a type of direct overwrite.

The medium 31 is a disk having a single-layered perpendicular magnetization film as a recording layer. The medium 31 is rotated by the rotating mechanism 32, and while passing through the modulated recording magnetic field generated from the magnetic head 33, the recording head receives irradiation of the condensed recording light from the optical head 34, thereby recording is performed. The magnetic head 33 is controlled by the magnetic head driver 36 to change the strength and direction of the recording magnetic field in accordance with the data, whereby the recording magnetic field is modulated into a combination of a positive rectangular pulse and a negative rectangular pulse. The optical head 34 is the optical head driver 3
The intensity of the recording light is kept constant under the control of 7. In the recording layer of the medium 31, recording magnetic domains magnetized in opposite directions according to the modulated direction of the recording magnetic field are formed.

Immediately after recording, the medium 31 sequentially passes through the first and second correction magnetic fields formed by the two permanent magnets 38 and 39 arranged at positions different from the optical head. The directions of these first and second correction fields are
Are perpendicular to the wall surface of the recording layer, that is, the film surface of the recording layer, and opposite to each other. As the main effect of these correction magnetic fields, it can be expected that the previously recorded magnetic domains (erasure remaining magnetic domains) that were left unerased during direct overwrite are erased. Since the magnetization directions of the recording magnetic domains are two directions opposite to each other, the first and second correction magnetic fields in the opposite directions are adopted. However, even if only the correction magnetic field in one direction is adopted, some effect can be expected. The permanent magnets 38, 39
May be replaced by an electromagnet.

Data reproduction in this embodiment can be performed by a general method utilizing the magneto-optical effect.

An evaluation test for this implementation was conducted under the following conditions. That is, a modulated recording magnetic field of 200 Oe modulated at 2.0 MHz under the conditions that the relative speed of the disc surface of the medium 31 and the laser spot of the recording light is 5.6 m / sec, and the intensity of the objective emitted laser light of the recording light is 8.0 mW. Recording using 3.7MHz
Recording with a recording magnetic field of the same intensity modulated by was alternately performed, and reproduction was performed with reproduction light having an objective emission laser intensity of 1.0 mW. The strengths of the first and second correction magnetic fields were both 3000 Oe. This test was conducted under various temperature conditions. As a result, no inconvenience such as unerased part was observed.

On the other hand, for the purpose of comparison, a similar evaluation test was conducted with the first and second correction magnetic field strengths set to zero, and it was found that the region previously recorded at a high environmental temperature was overwritten in a relatively low temperature environment. , A noise component, which is thought to be due to the unerased portion of the side edge of the previous recording magnetic domain, was observed in the reproduced signal.

[Fifth Embodiment] This embodiment is described in JP-A-62 / 62.
The present invention is applied to an optical modulation overwrite method (a kind of direct overwrite method) using a recording medium having exchange-coupled multilayer magnetic films as disclosed in U.S. Pat. 6 shows.

In FIG. 6, a disk-shaped medium 41 having a guide groove for tracking servo is a rotating mechanism 4 such as a motor.
Rotated by 2. A permanent magnet 46 that generates a correction magnetic field, a permanent magnet 44 that generates an initialization magnetic field, and an optical head 45 driven by an optical head driver 47 are sequentially arranged along the rotation direction (arrow). A permanent magnet 45 that generates a recording / reproducing magnetic field is arranged so as to face the optical head 43 with the medium 41 interposed therebetween. As the medium 41 rotates, the medium 41 repeatedly and repeatedly passes through the correction magnetic field from the permanent magnet 46, the initialization magnetic field from the permanent magnet 44, and the recording / reproducing magnetic field from the permanent magnet 45.
The directions of the correction magnetic field, the initialization magnetic field, and the recording / reproducing magnetic field are perpendicular to the board surface of the medium 41. The correction field is in the opposite direction to the initialization field.

In the recording operation, the medium 11 is the magnet 45.
While passing through the recording / reproducing magnetic field from, the optical head 43 irradiates the recording light (laser beam) whose intensity is modulated to the low level and the high level according to the data.

In the reproducing operation, the medium 11 is the magnet 45.
While passing through the recording / reproducing magnetic field from the optical head 43, reproduction light (laser beam) of a predetermined level is emitted from the optical head 43, and data is read from the medium 41 by the optical head 43 by utilizing the magneto-optical effect.

The permanent magnets 44, 45 and 46 may be replaced by electromagnets.

The principle of direct overwrite in this embodiment will be described below.

The recording medium 41 has a first magnetic layer called a recording layer and a second layer called an auxiliary layer which are exchange-coupled to each other at room temperature.
And an exchange-coupling bilayer film including a magnetic layer of. The recording layer has a relatively large coercive force at room temperature and a low Curie point. On the other hand, the auxiliary layer has a relatively small room temperature coercive force and a high Curie point.

First, by applying an initialization magnetic field having an appropriate magnitude, only the magnetization direction of the auxiliary layer is aligned in one direction without changing the magnetization direction of the recording layer. After that, at the same time as applying a recording magnetic field of an appropriate magnitude, irradiation with a low-level laser beam that produces a relatively low medium temperature (hereinafter referred to as L recording) or a high level that produces a relatively high medium temperature. Irradiation of laser light (hereinafter referred to as H recording) is selectively performed according to the data. In L recording, the magnetization direction of the auxiliary layer does not change, and the magnetization of the recording layer is
The exchange coupling energy becomes lower than the magnetization of the auxiliary layer. In H recording, the direction of the magnetization of the auxiliary layer is reversed by the recording magnetic field, and then the magnetization of the recording layer is in a state where the exchange coupling energy becomes lower than the magnetization of the auxiliary layer.
As a result, data is recorded as the direction of magnetization of the recording layer.

By applying the initializing magnetic field again, only the magnetization of the auxiliary layer is aligned in one direction.

By the way, as a result of a deep study of this direct overwrite system, it was found that an unerased magnetic domain was generated in the L recording. In FIGS. 7A to 7C, the directions of apparent magnetization of each layer when L recording is performed are indicated by arrows. 7A to 7C, the recording layer 51 is a rare earth transition metal alloy ferrimagnetic film rich in transition metal magnetic moment at room temperature, and the auxiliary layer 52 has a compensation temperature between room temperature and Curie temperature. A case of a ferrimagnetic film of a rare earth transition metal alloy rich in a rare earth metal magnetic moment is shown.

If L recording is ideally performed, FIG.
As shown in (a), the magnetization of the recording layer 51 is oriented in the direction without the interface domain wall with respect to the auxiliary layer 52. However, in reality
As shown in FIG. 7B or FIG. 7C, the reversed magnetic domain 53 or 54 left unerased in the recording layer 51 is often observed.
The cause of the unerased magnetic domains 53 or 54 is that, due to fluctuations in the magnetic characteristics of the recording medium, delay in tracking the focus servo, or the like, a part of the recording layer is not transferred by the magnetization of the auxiliary layer, or a small magnetic domain is formed. It is considered that the non-inverted region remains in the auxiliary layer during the conversion process. In order to prevent the unerased portion, it is conceivable to increase the laser light intensity for L recording or increase the initializing magnetic field, and some improvement is recognized by these methods. However, the former has a drawback that the allowable range of the laser light intensity suitable for L recording is narrowed. Further, the latter method is not a practical method because it is difficult to generate a large initializing magnetic field due to design restrictions of the recording device.
Further, there is a demand to use a magnetic film having a high Curie temperature for the recording layer in order to improve the quality of the reproduced signal. In order to meet this requirement, there is a problem that the laser power required for L recording becomes high.

In the apparatus of this embodiment shown in FIG. 6, the medium 41 passes through the correction magnetic field generated by the magnet 46 and the initialization magnetic field generated by the magnet 44 after direct overwriting. This contributes to the erasure of unerased magnetic domains in L recording.

The principle of erase residual magnetic domain erase will be described in detail below.

As disclosed in JP-A-62-175948 and JP-A-63-153752, the magnetic characteristics of the medium at room temperature must satisfy the following expression (3).

Σ _w / 2M _s2 h ₂ <H _c2 <H _c1 (3) where σ _w is the interface domain wall energy density between the recording layer and the auxiliary layer, M _s2 is the saturation magnetization of the auxiliary layer, and h ₂ is the auxiliary layer. Film thickness of
H _c1 is the coercive force of the recording layer, and H _c2 is the coercive force of the auxiliary layer.

As described above, the unerased magnetic domain in the L recording is in the state as shown in FIG. 7B or 7C.

First, consider the case where a correction magnetic field H _s, which is in the opposite direction to the initialization magnetic field, is applied to the unerased magnetic domain 53 of the type shown in FIG. 7B, as shown in FIG. 8A. Now, let the domain wall energy density of the cylindrical domain wall in the recording layer 51 be σ _B ,
The saturation magnetization of the recording layer 51 is M _s1 , the film thickness of the recording layer 51 is h ₁ , and the radius of the unerased magnetic domain 53 is R. When the modified magnetic field strength H _s satisfies 0 <H _s <H _c2 + σ _w / 2M _s2 h ₂ (4), it is possible to use a simple bubble magnetic domain theory regarding the cylindrical magnetic domain, which is assumed to be a perfect circle, by ignoring the demagnetizing field term. From the consideration, when the radius R of the unerased magnetic domain 53 satisfies R <σ _B h ₁ / {− σ _w + 2M _s1 h ₁ (H _c1 −H _s )} (5), the unerased magnetic domain 53 disappears, Figure 8
It can be seen that the state shifts to the correct state as shown in (b). When the corrected magnetic field strength Hs satisfies 0 <H _c2 + σ _w / 2M _s2 h ₂ <H _s <H _c1 + σ _w / 2M _s1 h ₁ (6), the radius R of the unerased magnetic domain is R <σ _B When h ₁ / {σ _w + 2M _s1 h ₁ (H _c1 −H _s )} (7) is satisfied, the auxiliary layer 52 is uniformly magnetized as shown in FIG.
It can be seen that the state of magnetization shown in FIG. 8D is obtained through the state of (c). After that, the initialization magnetic field H _Ini is applied to shift to the correct state of FIG.

On the other hand, in the case of the unerased magnetic domain 54 of the type shown in FIG. 7C, when the correction magnetic field strength H _s satisfies the expression (4), the unerased magnetic domain 5 immediately after the correction magnetic field is passed.
4 does not disappear, but when the initialization magnetic field is passed, the auxiliary layer 52
Are uniformly magnetized and the state shown in FIG.
By applying a second correction magnetic field with the further rotation of 1,
Following the same process as the case described above, the unerased magnetic domain 54 remains.
Disappears according to equation (5). In addition, when the corrected magnetic field strength H _s satisfies the expression (6), the previously-considered FIG.
Following the same process as the type of (b), the unerased magnetic domain 5
4 disappears according to equation (7).

The states immediately after and immediately before passing through the correction magnetic field and the initialization magnetic field of the reversal magnetic domain (recording magnetic domain) formed by H recording are the unerased magnetic domains in FIGS. 7B and 7C, respectively. And have a similar shape except that the magnetic domain diameter is larger. Therefore, this recording magnetic domain also behaves in accordance with the above-mentioned magnetic domain theory. Therefore, when the recording magnetic domain diameter is large and the expressions (5) and (7) are not satisfied, the recording magnetic domain does not disappear. Therefore, according to the equations (5) and (7), an appropriate magnitude of the correction magnetic field strength H _s is selected such that the erased magnetic domains having a relatively small diameter disappear and the recording magnetic domains having a relatively large diameter do not disappear. It is essential.

By the way, the disappearance of the unerased magnetic domain due to the correction magnetic field can be realized both when the correction magnetic field strength H _s is in the range of the expression (4) and when it is in the range of the expression (6). However, as can be seen from the equations (5) and (7), the magnetic extinction of the unerased portion can be realized with a much smaller correction magnetic field when the equation (4) is satisfied. Therefore, practically, it is preferable to satisfy the expression (4).

Now, an important point in the light modulation overwrite method using this exchange coupling multilayer film is that the auxiliary layer must be uniformly magnetized before the irradiation of the recording light. That is, it is necessary to apply the initializing magnetic field before the next recording operation. Therefore, in order to make the disappearance of the unerased magnetic domains by the application of the correction magnetic field satisfying the above-mentioned expression (4) compatible with the direct overwrite, after the irradiation of the recording light, immediately before the next recording or reproduction is performed,
It is necessary to sequentially apply the correction magnetic field and the initialization magnetic field to the medium.

FIG. 9 shows a minor loop of the magnetization curve of the auxiliary layer. As described above, when two magnitudes H ₁ and H ₂ of the reversal magnetic fields of different auxiliary layers are defined as shown in FIG.
After irradiating the medium with the recording light, a correction magnetic field H _{s in} the range of 0 <H _s <H _{1 in} the opposite direction to the initializing magnetic field and an initializing magnetic field larger than H ₁ are sequentially applied to erase the medium. It is possible to realize a good direct overwrite in which the remaining magnetic domains are suppressed. The lower limit of the corrected magnetic field strength H _s for obtaining a practical effect varies depending on the recording medium used, but is generally about 500 to 1000 Oe.

The principle of erasure residual magnetic domain described above is as follows.
An exchange coupling membrane of a different type from that used for the explanation,
The same can be applied to a recording medium provided with an intermediate layer effective for suppressing the domain wall energy between the two layers.

According to this principle, in the embodiment shown in FIG. 6, at least one rotation is performed after the recording light is irradiated, and in some cases, two rotations are performed.
All operations required for recording are completed during rotation.

For the evaluation test on this example,
As shown in FIG. 10, a protective layer 6 having a thickness of 80 nm is formed on the resin substrate 61.
A recording medium was prepared in which a recording layer 63 having a thickness of 2,50 nm, an auxiliary layer 64 having a thickness of 100 nm, and a protective layer 65 having a thickness of 80 nm were sequentially laminated. Here, in the recording layer 63, NdDyTbFeCo in which the sublattice magnetization of the transition metal is dominant (TM rich) at room temperature is used.
For the auxiliary layer 64, DyFeCo having a dominant rare earth metal sublattice magnetization (RE rich) was used, and for the protective layer 65, AlSiN was used. Two types of media (medium A and medium B) having such a structure and different magnetic characteristics were prepared. Apparent coercive force H _m , H of the recording layer 63 and the auxiliary layer 64 of each medium sample
_r is shown in Table 1. Here, the apparent coercive force means the recording layer 6
As a result of exchange-coupling between 3 and the auxiliary layer 64, the amount after shifting from the coercive force in the single-layer film. However, for the auxiliary layer 64, the one of the reversal magnetic field of the minor loop of the magnetization curve, which has the larger absolute value (that is, H ₁ in FIG. 9), is indicated.

[0065] As described above, these media have a composition in which the recording layer 63 is TM-rich and the auxiliary layer 64 is RE-rich.

In this case, the initialization magnetic field is applied in the same direction as the recording magnetic field, and the correction magnetic field is applied in the opposite direction to the recording magnetic field.

Laser power allowable range in L recording,
That is, the power margin was evaluated by recording the 7 MHz signal in advance and then overwriting the 2 MHz signal, and measuring the intensity of the 7 MHz signal that had disappeared with a spectrum analyzer. The relative movement speed of the recording medium to the laser spot during recording / reproduction is 15 m.
/ Sec, the laser wavelength was 780 nm, and the H recording laser power was 15 mW.

FIGS. 11A and 11B are plots of the unerased signal strength levels after overwriting of the medium A and the medium B, respectively, with respect to the laser power of L recording. Here, the initializing magnetic field was 4.0 kOe, and the correction magnetic field was two levels of 2.0 kOe and 4.0 kOe. For comparison, the case of the conventional method in which the correction magnetic field is not applied is also shown. It can be seen from FIGS. 11A and 11B that the power margin of L recording is expanded by applying a correction magnetic field of appropriate strength. In particular, regarding both the media A and B, when the correction magnetic field strength is 2.0 kOe, the minimum allowable laser power is reduced by about 1.5 mW, which is clear to be effective in expanding the power margin of L recording. is there.

Next, the correction magnetic field is changed from 0.0 Oe to 7.0 kOe.
12A and 12B show the changes in P _L , which is the minimum value of the laser power allowable in the L recording when changing every 0.5 kOe. Here, the initializing magnetic field is 4.0 kOe. FIG. 12 (a),
As is clear from (b) and Table 1, the correction magnetic field is 0.0 Oe.
From increasing to the apparent coercive force (H _r ) of the auxiliary layer,
P _L continues to decrease, and when the correction magnetic field exceeds H _r , P _L again returns to a discontinuous state near the value when the correction magnetic field is zero, and gradually decreases from there. Therefore, it is understood that the correction magnetic field greatly contributes to the reduction of P _L , that is, the expansion of the power margin of L recording, especially in the region of H _r or less.

In this example, it is further clarified that the Kerr rotation angle of the medium can be increased by raising the Curie temperature of the recording layer without deteriorating the power margin of L recording and the L recording sensitivity. The test was conducted. Regarding the recording medium, in FIG. 10, as the recording layer 63, NdDyTbFeCo having a thickness of 50 nm is used.
DyFeCo having a thickness of 100 nm was used as the auxiliary layer 64, and AlSiN having a thickness of 80 nm was used as the protective layers 62 and 65.
Two types of media (medium C and medium D) having the above-described structure and different magnetic characteristics were prepared. In both media, the recording layer 63 is TM-rich and the auxiliary layer 64 is RE-rich. The composition of the auxiliary layer 64 was the same for both media C and D. Curie temperature T _c of the recording layer 63 of these media,
And the apparent coercive force H _{m of} the recording layer 63 and the auxiliary layer 64,
_Hr is shown in Table 2.

[0071] In both of these media, the recording layer is TM rich and the auxiliary layer is R
Since it has an E-rich composition, the initialization magnetic field is applied in the same direction as the recording magnetic field, and the correction magnetic field is applied in the opposite direction to the recording magnetic field. The relative movement speed of the medium surface during recording / reproduction is 1
7m / sec and 2MHz on the pre-recorded 7MHz signal
The signal of was overwritten. H recording laser power is 1
It was fixed at 5 mW and the initializing magnetic field was 4.0 kOe. The correction magnetic field strength is 2.0 kOe, and the correction magnetic field is 0.0 kOe for comparison.
We also examined the case of e.

Table 3 shows L obtained from the above-mentioned test.
The minimum laser power P _L allowed for recording and the carrier-to-noise ratio (C / N ratio) of the overwritten signal are shown.

Table 3 Medium C Medium D Corrected magnetic field P _L C / N ratio P _L C / N ratio 0.0kOe 4.8mW 53dB 5.3mW 55dB 2.0kOe 4.3mW 53dB 4.7mW 55dB From Table 3 The medium D having a higher Curie temperature of the recording layer is C
It can be seen that the / N ratio is high. On the other hand, it can be seen that the medium D having a higher Curie temperature of the recording layer also has a higher P _L. However, even with the medium D having a high Curie temperature, when the correction magnetic field is introduced, P _L can be lowered to a level corresponding to the case where the medium C is recorded without the correction magnetic field. this is,
This means that the sensitivity of the L recording to the laser power is increased. That is, by using the correction magnetic field, the Kerr rotation angle can be increased and the C / N ratio of the medium can be increased by increasing the Curie temperature of the recording layer without deteriorating the power margin and recording sensitivity in L recording. It proved possible.

Furthermore, the magnetic layers 63 to 64 shown in FIG. 10 are TbFeCo, TbFeCoCr, and DyTbF, respectively.
eCo, NdDyFeCo, SmDyFeCo, PrD
The same tendency as that described above was obtained for the medium composed of yFeCo and other components.

[Sixth Embodiment] FIG. 13 shows a sixth embodiment which is a modification of the fifth embodiment shown in FIG. In this embodiment, a second correction magnetic field generating permanent magnet 48, a first correction magnetic field generating permanent magnet 46, and an initialization magnetic field generating permanent magnet 44 are sequentially arranged along the rotation direction of the medium 41. ing. The permanent magnets 48, 46, 44 may be replaced with electromagnets. The second correction field and the initialization field are in the same direction, whereas the first correction field is in the opposite direction. As the medium 41 rotates, the medium 41 repeatedly and repeatedly passes the second correction magnetic field from the magnet 48, the first correction magnetic field from the magnet 46, the initialization magnetic field from the magnet 44, and the recording / reproducing magnetic field from the magnet 45.

The recording / reproducing operation is the same as in the fifth embodiment.

In this embodiment, since a magnetic field in the opposite direction to the first correction magnetic field is applied immediately before and after the application of the first correction magnetic field, recording is required during one rotation after irradiation with the recording light. All operations are completed.

For the evaluation test of this embodiment, a 50 nm thick NdDyTbFeC film was used as the recording layer 63 in FIG.
o, 100 nm thick DyFeCo as the auxiliary layer 64,
80 nm thick AlSiN as the protective layers 62 and 65
By using two types of media (medium E,
F) was prepared. Recording layer 63 and auxiliary layer 6 of these media
Table 4 shows the apparent coercive forces H _m and H _r of No. 4.

[0079] In both media, the recording layer 63 is TM rich and the auxiliary layer 64 is
Is RE rich. Therefore, the second correction magnetic field and the initialization magnetic field are applied in the same direction as the recording / reproducing magnetic field, and the first correction magnetic field is applied in the opposite direction to the recording / reproducing magnetic field.

FIGS. 14 (a) and 14 (b) show the signals of 7 MHz prerecorded for the media E and F respectively at a medium linear velocity of 17 m / sec during recording / reproduction, a laser wavelength of 780 nm, and a laser power of 15 mW for H recording. 2 is a plot of the unerased signal strength level when a 2 MHz signal is overwritten with respect to the laser power of L recording. Here, the second correction magnetic field and the initializing magnetic field were both 4.0 kOe, and the first correction magnetic field was 2.0 kOe. For comparison, a conventional method in which a correction magnetic field is not applied is also shown. FIG. 14 (a),
According to (b), it is understood that the minimum value P _L of the laser power allowed in the L recording can be reduced by 1.5 mW or more by applying the correction magnetic field having an appropriate magnitude.

By the way, in this evaluation test, one track jump is performed immediately after the recording operation is completed, and during the transition from the recording operation to the reproducing operation, the second correction magnetic field, the first correction magnetic field, and the initialization magnetic field are sequentially only once. Playback was performed after application to the recording area. Therefore, it can be expected that one rotation after recording erases not only the unerased magnetic domains 53 of the type shown in FIG. 7B but also the unerased magnetic domains 54 of the type shown in FIG. 7C. For comparison, the medium E is used to detect the unerased residual signal both in the absence of the second correction magnetic field (corresponding to the fifth embodiment) and in the absence of the second and first field correction magnetic fields (corresponding to the conventional method). The L recording laser power dependence was measured. The result is shown in FIG. In FIG. 15, graph (a) shows the case without the second correction magnetic field, graph (b) shows the case without both the second and first correction magnetic fields, and graph (c) shows the case with both the second and first correction magnetic fields. The result is shown. According to this, the minimum value of the allowable L recording power of the graph (a) is lower than that of the graph (b),
It can be seen that the power margin of L recording is wider. When comparing the graphs (a) and (c), it can be seen that there is no difference in the minimum value of the allowable L recording power, but there is a difference of about 5 dB in the signal level of the unerased portion. That is, in this embodiment, the unerased magnetic domain 54 of the type shown in FIG. 7 (c), which cannot be erased in one rotation in the fifth embodiment, is improved in one rotation by further introducing the second correction magnetic field. It is thought to have been erased.

Further, the magnetic layers 63 to 64 shown in FIG. 10 are TbFeCo, TbFeCoCr, and DyTbF, respectively.
eCo, NdDyFeCo, SmDyFeCo, PrD
The same tendency as that described above was obtained for the medium composed of yFeCo and other components.

Each of the above embodiments is an apparatus capable of re-recording and reproducing operations. However, it goes without saying that any of these embodiments can be used as a recording-only machine or a reproduction-only machine. A common feature of these embodiments is that the correction magnetic field is applied to the medium after the recording operation, before the reproducing operation, or at a time between the recording operation and the reproducing operation.

In the above, some embodiments of the present invention have been described. These examples do not limit the scope of the present invention thereto alone, and various other modifications and changes can be made without departing from the gist of the present invention.

[0085]

According to the present invention, since the correction magnetic field is applied to the medium after recording the data or before reproducing the recorded data, the effect of the correction magnetic field causes distortion of the shape of the unerased magnetic domain or the recording magnetic domain. Such recording noise can be removed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of first and second embodiments of a recording / reproducing apparatus of the present invention.

FIG. 2 is a diagram showing a waveform of modulated intensity of recording light in the second embodiment.

FIG. 3 is a cross-sectional view showing the structure of a medium used in the evaluation test of Example 2.

FIG. 4 is a block diagram showing the configuration of a third embodiment that is a modification of the first or second embodiment.

FIG. 5 is a perspective view showing the configuration of a fourth embodiment of the present invention.

FIG. 6 is a perspective view showing the configuration of a fifth embodiment of the present invention.

FIG. 7 is a schematic diagram showing a process in which an unerased magnetic domain is generated in the fifth embodiment.

FIG. 8 is a schematic diagram showing a process in which an unerased magnetic domain is erased in the fifth embodiment.

FIG. 9 is a diagram showing a minor loop of a magnetization curve of an auxiliary layer of a medium used in a fifth example.

FIG. 10 is a cross-sectional view showing the structure of a medium used for evaluation and examination of Example 5.

FIG. 11 is a diagram showing the evaluation test results of the fifth embodiment.

FIG. 12 is a diagram showing the evaluation test results of the fifth embodiment.

FIG. 13 is a perspective view showing the configuration of a sixth embodiment that is a modification of the fifth embodiment.

FIG. 14 is a diagram showing the evaluation test results of the sixth embodiment.

FIG. 15 is a diagram showing the evaluation test results of the sixth embodiment.

[Explanation of symbols]

11, 31, 41 recording medium 13, 34, 43 Optical head 14 Recording / reproducing magnetic field generating electromagnet 33 Magnetic head for generating recording / reproducing magnetic field 45 Permanent magnet for recording / reproducing magnetic field 15 Electromagnet for generating modified magnetic field 26,46 Permanent magnet for generating modified magnetic field 44 Permanent magnet for initializing magnetic field 48 Second Permanent Magnet for Generating Modified Magnetic Field

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Ito             Seiko, 3-3-3 Yamato, Suwa City, Nagano Prefecture             -In Epson Corporation (72) Inventor, Kazuya Ishida             Seiko, 3-3-3 Yamato, Suwa City, Nagano Prefecture             -In Epson Corporation (72) Inventor Houji Akira             Seiko, 3-3-3 Yamato, Suwa City, Nagano Prefecture             -In Epson Corporation

Claims (4)

[Claims] 1. A method of recording data on a perpendicular magnetization film provided on a recording medium, wherein recording data and data are recorded in the perpendicular magnetization film by simultaneously applying a recording light and a recording magnetic field to the recording medium. 2. A magneto-optical recording method comprising: a recording step of forming a bubble magnetic domain, and a correction step of applying a correction magnetic field in a direction perpendicular to the film surface of the perpendicular magnetization film after the recording step. 2. An apparatus for recording data on a perpendicularly magnetized film provided on a recording medium, wherein a moving means for moving the recording medium and a recording medium arranged on a predetermined position in a moving path of the recording medium. Applying recording light and recording magnetic field,
A recording unit that forms a bubble magnetic domain for recording the data in the perpendicular magnetization film, and a recording unit that is arranged downstream of the recording unit along the movement path and that is perpendicular to the film surface of the perpendicular magnetization film. A magneto-optical recording apparatus comprising: a correction unit that applies a magnetic field. 3. A method of reproducing data recorded as bubble magnetic domains in a perpendicular magnetization film provided on a recording medium, wherein a correction process of applying a correction magnetic field in a vertical direction to a film surface of the perpendicular magnetization film, After the correction step, a step of reading the data by utilizing a magneto-optical effect by simultaneously applying a reproducing light and a reproducing magnetic field to the recording medium, the magneto-optical reproducing method. 4. An apparatus for reproducing data recorded as bubble magnetic domains in a perpendicularly magnetized film provided on a recording medium, a moving means for moving the recording medium, and a predetermined position on a moving path of the recording medium. A reproducing means arranged to apply a reproducing light and a reproducing magnetic field to the perpendicular magnetization film to read the data by utilizing a magneto-optical effect; and a reproducing means arranged along the moving path, upstream of the reproducing means. A magneto-optical reproducing device comprising: a correction means for applying a correction magnetic field in a direction perpendicular to the film surface of the perpendicular magnetization film.