JPH08221823A - Magneto-optical recording medium and magneto-optical recording and reproducing device using the same - Google Patents

Abstract

PURPOSE: To unidirectionally magnetize a reproducing layer by using small magnetic fields by laminating the reproducing layer having small coercive force and having perpendicular magnetic anisotropy and a recording and holding layer across a nonmagnetic layer and cutting the exchange bond. CONSTITUTION: This magneto-optical recording medium has magnetic layers having the reproducing layer 9 and recording and holding layer 10 to be magnetically coupled onto the one surface of a transparent substrate. The recording and holding layer 10 is subjected to signal recording by an ordinary method and is irradiated with a light beam 11 from the reproducing layer 9 side to heat up the reproducing layer. While the magnetic signals recorded on the recording and holding layer 10 are transferred onto the reproducing layer 9, the magnetic signals are converted to optical signals by the magnet-optical effect possessed by the reproducing layer 9. These optical signals are read. Particularly, the reproducing layer 9 shifts from intra-surface magnetization to perpendicular magnetization in regions 13 of a prescribed temp, or above and the magnetic signals of the recording and holding layer 10 are transferred. The magneto-optical effect in the temp. regions exclusive thereof is low. Then, the parts of the prescribed temp. or below do not participate in the signals and are identical to that these parts are optically masked. The effective resolution of the spot of the light beam 11 is, therefore, enhanced and the reading out of the recording signals having a high line density and track density is made possible.

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 / reproducing apparatus and a magneto-optical recording medium for reading a recording signal according to magneto-optical characteristics.

[0002]

2. Description of the Related Art In a magneto-optical recording method, a magnetic thin film is partially heated to near the Curie point by laser light irradiation, the coercive force of this part is extinguished, and the direction of a recording magnetic field applied from the outside is reversed. By doing. On the other hand, for reproduction, the basic principle is to irradiate a laser beam with a power smaller than that for recording, convert into an optical signal by the magneto-optical effect (magnetic Kerr effect or Faraday effect) of the magnetic thin film, and read. Therefore, the magneto-optical recording medium has a recording magnetic layer (for example, a rare earth-transition metal alloy amorphous thin film) having an excellent magneto-optical effect on a transparent substrate made of, for example, polycarbonate having an easy axis of magnetization in a direction perpendicular to the film surface.
It is known that a recording layer is formed by laminating a reflective layer and a dielectric layer, and a recording film is irradiated with laser light from the transparent substrate side of this medium to record and reproduce signals.

The recording density of optical memory devices including this magneto-optical disk has a limit of resolution at the time of recording / reproducing due to the limit of narrowing down the spot of a light beam. In recent years, a method has been proposed in which a magnetic layer having a certain property is added as a read-only layer to the recording magnetic layer in order to reproduce with high resolution a recording bit smaller than the spot size of the light beam.

Now, this method will be described below with reference to FIGS. 2 and 3.

A magneto-optical recording medium of the system shown in FIG. 2 (for example, Japanese Unexamined Patent Publication No. 5-12731) has a reproducing layer 9 and a recording holding layer 1 which are magnetically coupled to at least one surface of a transparent substrate.
0 is used to perform signal recording on the recording holding layer 10 by a normal method, and the reproducing layer 9 is irradiated with a light beam 11 to raise the temperature of the reproducing layer. The magnetic signal recorded in the recording holding layer 10 is reproduced in the reproducing layer 9
It is characterized in that it is converted into an optical signal by the magneto-optical effect of the reproducing layer 9 while being transferred to and read. In particular, in the reproducing layer 9 in a region 13 having a predetermined temperature or higher, the in-plane magnetization is changed to the perpendicular magnetization to easily transfer the magnetic signal of the recording holding layer 10, and in the temperature region lower than that, the magneto-optical effect is small. . Therefore, the portion below the predetermined temperature does not contribute to the signal at all, and is optically equivalent to being masked. For this reason, the resolution of the effective spot of the light beam 11 is increased, and it becomes possible to read a recording signal with high linear recording density and track density (magnetic super-resolution).

On the other hand, the magneto-optical recording medium of the system shown in FIG. 3 (for example, Japanese Patent Laid-Open No. 3-88156) transfers the magnetic signal of the recording holding layer 15 to the reproducing layer 14 in the same manner. Since the reproducing layer 14 has perpendicular magnetic anisotropy, it has a property of being uniformly magnetized by a large magnetic field.
The magnetization direction of is aligned in a predetermined direction (downward in the figure) (initialization). Next, the light beam 16 is irradiated to locally raise the temperature to transfer the magnetic signal of the recording holding layer 15. By doing so, only the information of the region 18 in which the temperature has risen is obtained at the spot central portion of the light beam 16, so that the magnetic super-resolution effect can be obtained as in the above method.

[0007]

However, in the method shown in FIG. 2, since the in-plane magnetized film is used, the shape of the magnetic domain transferred to the reproducing layer 9 is not clear, which results in a high CN ratio. It will be an obstacle to getting it. Further, since the temperature at which the in-plane magnetization shifts to the perpendicular magnetization has to be set appropriately, it is conceivable that the composition margin at the time of forming the film becomes extremely strict.

On the other hand, in the system shown in FIG. 3, the bits whose magnetization information has been transferred from the recording holding layer 15 to the reproducing layer 14 during reproduction remain even after the reproduction is completed and the temperature of that portion is lowered. Therefore, even if the position of the light beam spot moves to reproduce the next bit, the previous bit still exists in the spot, which causes a problem of noise, which improves the recording density. It will be a limitation when making it. Further, it is necessary to prepare the auxiliary magnetic field generator 19 for initializing the reproducing layer on the front side of the spot of the light beam 16.

The present invention has been proposed in view of the above-mentioned conventional circumstances, and a magnetic super-resolution reproducing system having a relatively easy composition and structure, a high resolution, and a high CN ratio as compared with the above system is provided. An object is to provide a magneto-optical recording medium to be achieved and a magneto-optical recording / reproducing apparatus using the same.

[0010]

In order to achieve the above object, the present invention uses the following means.

Regarding a magneto-optical recording medium having a magnetic multi-layered film having a reproducing layer and a recording holding layer which are at least magnetically coupled to each other on a substrate, a small coercive force and perpendicular magnetic anisotropy are obtained from room temperature to the reproducing temperature. Using the reproducing layer 3 having and the non-magnetic layer 5 was further inserted between the recording holding layer 4 and the reproducing layer 3 to break the exchange coupling between them. Here, the perpendicular magnetic anisotropy of the reproducing layer 3 is such that at room temperature (25 degrees Celsius), the residual magnetization when the magnetic field is zero after the magnetization is once saturated is 80% or more of the saturation magnetization. Is enough. Considering that the reproduction layer with such properties is a material with a large Kerr rotation angle, Gd-Fe
Amorphous thin films of Gd-Fe-Co-based, Gd-Tb-Fe-Co-based, Gd-Dy-Fe-Co-based alloys and the like are preferable.

For recording information, the magneto-optical recording medium is irradiated with a light beam 7 to raise the temperature of the spot on the recording holding layer to near the Curie temperature, and then the magnetic field generator 6 is used. The magnetization direction of the recording holding layer is changed according to the information.

Further, as shown in FIG. 4, the reproduction of information uses the above-mentioned magneto-optical recording medium and a magnetic field generator 21 capable of applying a magnetic field around the spot of the light beam.
A reproducing light beam is emitted from the optical pickup in a state where a magnetic field larger than the coercive force of the reproducing layer is magnetized in one direction in the erasing direction in advance. Even if the exchange coupling between the recording layer and the reproducing layer is broken by adding a non-magnetic layer, the direction of magnetization of the reproducing layer is recorded by the leakage magnetic field from the magnetic domain mark recorded as a magnetic signal in the recording layer. A force (magnetostatic coupling force) that tries to align the magnetization direction of the holding layer works. However, as shown in FIG. 5, when transferring a mark having a small recording magnetic domain diameter, it is necessary to form a magnetic domain wall 28 (on a shaded portion) around the transferred magnetic domain 27. The domain wall energy at this time is 2πrhσw, where r is the radius of the magnetic domain to be transferred and h is the thickness of the reproducing layer.
Here, σw is the domain wall energy per unit area and decreases as the temperature rises, and becomes zero at the Curie temperature. Therefore, as shown in FIG. 6, at a temperature away from the Curie temperature Tc of the reproducing layer, the required energy is larger than the magnetostatic coupling force, so that the transfer does not actually occur.

When the power of the light beam is raised and the temperature of the reproducing layer is locally raised, the energy of the domain wall necessary for the transfer is reduced at the portion where the temperature rises in the center of the spot, and the recording transfer temperature Tr is reduced. It becomes possible to transfer by the magnetostatic coupling force at the boundary. Therefore, with the above configuration, a magnetic recording signal smaller than the light spot can be reproduced with high resolution.

Since the magnetostatic coupling force becomes stronger as it approaches the recorded magnetic domain mark, the reproducing layer closer to the recording holding layer has better transferability. Therefore, as the non-magnetic layer inserted between the reproducing layer and the recording holding layer, and between the reproducing layer, Au, Ag, Al, Cu, etc., which can break the exchange coupling uniformly with the thinnest possible film thickness, are used. Among them, an alloy thin film having at least one kind of low surface energy metal as a matrix is suitable.

Alternatively, if it is desired to suppress reflection from a portion other than the reproducing layer due to the difference in optical constants of the non-magnetic layer and the magnetic layer cut by inserting the non-magnetic layer as much as possible, the non-magnetic layer The layer may have an optical constant close to that of the magnetic layer. As such a non-magnetic layer, the Curie temperature is a magnetic substance at room temperature or lower Dy-Cu system, Dy-Ni system,
Alternatively, a system in which Cr is mixed in the magnetic layer is suitable.

[0017]

With the above structure, the reproducing layer having a small coercive force and perpendicular magnetic anisotropy during reproduction is aligned in the erasing direction by the external magnetic field applied to the spot portion of the light beam.

When this magnetic layer is irradiated with a light beam, the temperature distribution of the irradiated portion becomes a Gaussian distribution, and the temperature rises only in the area smaller than the diameter of the light beam.

When the size of the portion reaching the predetermined temperature or higher becomes larger than the magnetic domain to be transferred in the recording holding layer due to this temperature increase, (energy of domain wall of transferred magnetic domain) <(magnetostatic coupling energy) ), The magnetic domain of the recording layer is transferred to this portion.

Then, when the light beam moves to reproduce the magnetic domain in the magnetic layer in which the following information is recorded, the temperature of the previously reproduced portion is lowered, and the transferred magnetic domain is affected by an external magnetic field applied from the outside. Erased.

As a result, only the region having a temperature equal to or higher than the predetermined temperature is involved in the reproduction, so that the mixing of the signal from the adjacent bit can be prevented, and the relatively wide composition margin and the simple structure of the device and the medium can be realized. Thus, it was possible to obtain a magneto-optical recording / reproducing apparatus and a magneto-optical recording medium which realize a magnetic super-resolution reproducing system by using magnetostatic coupling force.

[0022]

【Example】

[Embodiment 1] An embodiment of the present invention will be described below in more detail.

FIG. 1 shows a laminated structure of a recording medium according to an embodiment of the present invention. First, a 5.25-inch polycarbonate substrate 1 provided with a guide groove for tracking was filled in a high-frequency magnetron sputtering apparatus, and after evacuating to 0.1 mPa or less, a mixed gas of N2 and Ar was introduced and the gas pressure was 0.35 Pa. , Si as a target is sputtered to deposit 85 nm of Si nitride as the dielectric layer 2a. Then, using a GdFeCo alloy target, sputtering is performed at an Ar gas pressure of 0.3 Pa to deposit a 40 nm thick Gd0.29Fe0.51Co0.20 amorphous alloy thin film as the reproducing layer 3. Next, the Al alloy thin film is similarly sputtered at an Ar gas pressure of 0.3 Pa to form an exchange coupling force cutting layer 5 with a thickness of 1 nm. Next, using a TbFeCo alloy target, sputtering is performed at an Ar gas pressure of 0.3 Pa to deposit a transition metal-rich Tb0.21Fe0.60Co0.19 amorphous alloy thin film having a thickness of 40 nm as the recording holding layer 5. The exchange coupling of the three reproducing layers 3 and the recording holding layers 4 thus laminated is completely broken by the cutting layer 5. Next, after evacuation to 0.1 mPa or less again,
Introducing a mixed gas of Ar and N2 gas, at a gas pressure of 1.3 Pa, Si
Reactive sputtering is performed with the target as a target to form a protective layer 2b.
As a result, a nitride of Si was deposited to a thickness of 85 nm.

Table 1 shows the magnetic characteristics of the reproducing layer 3 and the recording holding layer 4 in the case of a single layer of 40 nm in this example. The reproducing layer 3 has a rare earth-rich composition, and the recording holding layer 4 has a transition metal-rich composition.

[0025]

[Table 1] Compensation temperature (Tcomp) Curie temperature (Tc) Reproducing layer / GdFeCo below room temperature 300 ° C Recording holding layer / TbFeCo 210 ° C 320 ° C Also, in Fig. 7, the reproducing layer at temperatures from room temperature (30 ° C) to 200 ° C A typical example of the relationship (hysteresis characteristic) between the external magnetic field Hext applied to 3 and the magnetic Kerr rotation angle θk is shown. As can be seen from this, in this temperature range, a hysteresis characteristic with a sharp rise is shown. Further, the magnetic field (coercive force) required for reversal is as small as 100 Oe, and the direction of magnetization can be easily aligned by an external magnetic field.

The reproducing characteristics of the above recording medium were examined by using the magneto-optical recording / reproducing apparatus having the structure shown in FIG. During reproduction, a magnetic field of 100 Oe was applied to the periphery of the spot in the erasing direction, and the reproduction light beam was irradiated while rotating the disc so that the linear velocity was 4 m / s.

FIG. 9 shows the dependence of the CN ratio on the reproducing light beam power when reproducing a magnetic domain having a recording mark length of 0.4 μm. When irradiated with a light beam with a power of 3.2 mW, a CN ratio of 46 dB could be obtained. On the other hand, the power is 2.7mW under the same conditions.
, The CN ratio is 20 dB, and the power is 2.7 mW to 3.2 mW.
It can be seen that during this period, the transfer of the magnetic domain of this size to the reproducing layer 3 is started.

Here, the CN ratio of 20 dB at 2.7 mW is the light returned from the light transmitted through the reproducing layer 29 as reflected in the boundary between the non-magnetic layer 31 and the recording holding layer 30 as shown in FIG. is there. This reflection is caused by the Al thin film used as the non-magnetic layer 31 and the recording holding layer 3.
It occurs because the TbFeCo amorphous alloy used as 0 has different optical constants.

Therefore, an experiment was conducted by changing the composition of the nonmagnetic layer 31 to a Dy-Ni alloy thin film while keeping the other composition and structure the same. In this case, the CN ratio below the transferable power of the reproducing layer was about 13 dB. It can be seen that the amount of light reflected and returned on the surface of the recording holding layer is greatly reduced. The configurations of the medium and the device of the present invention are not limited to the above examples. For example, (1) As the dielectric layer 2a and the protective layer 2b, for example, SiO
x, SiAlON, ZnSx, ZnOx, etc. are used.

(2) G as the reproducing layer 3 and the recording holding layer 4
Rare earth elements such as d, Tb, Nd, Dy, Pr, Sm and Fe, Co, Ni, C
An alloy with a transition metal such as r is used. In order to improve the corrosion resistance, Nb, Ti, Pt, Cr, Ta, Ni or the like may be added.

(3) As the substrate, a sample servo substrate or a land / groove substrate may be used. Also, a shape other than a disk such as a magneto-optical tape or a magneto-optical card may be used.

(4) A permanent magnet or a floating magnetic head may be used as the magnetic field generator of the magneto-optical recording / reproducing apparatus.

[0033]

As is apparent from the above description, according to the present invention, a reproducing layer having a small coercive force and a perpendicular magnetic anisotropy and a recording retaining layer are laminated with a nonmagnetic layer interposed therebetween. By breaking the exchange coupling, the reproducing layer can be magnetized in one direction using a small magnetic field, and the energy for transferring the magnetic domain to the reproducing layer exceeds the magnetostatic coupling energy up to a certain temperature. It is configured to obtain a magnetic super-resolution effect by utilizing it.

The magnetic super-resolution reproduction by this method is advantageous in obtaining a high CN ratio because a perpendicular magnetization film is used, and a wide composition margin can be taken. Also, there is no need for a strong initializing magnet like when using an exchange coupling film,
The transferred magnetic domain is also erased due to the external magnetic field as the temperature decreases, which solves the problem of high resolution.

As described above, the magneto-optical recording / reproducing apparatus and the magneto-optical recording medium according to the present invention enable high-quality magnetic super-resolution reproduction with a simple composition and structure.

Therefore, it is very useful for achieving high density recording in the magneto-optical recording medium, and its significance is great.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a recording operation on a magneto-optical recording medium of the present invention.

FIG. 2 is an explanatory diagram showing a recording operation on a conventional type magneto-optical recording medium (for example, Japanese Patent Laid-Open No. 12731/1993).

FIG. 3 is an explanatory diagram showing a recording operation on a conventional magneto-optical recording medium (for example, Japanese Patent Laid-Open No. 3-88156).

FIG. 4 is a configuration diagram showing an example of a magneto-optical recording apparatus of the present invention.

FIG. 5 is a schematic diagram of a domain wall formed in a reproducing layer when a magnetic domain is transferred from the recording holding layer to the reproducing layer.

6 is a diagram showing the temperature dependence of the energy required to make the domain wall shown in FIG. 5;

FIG. 7 is a graph (hysteresis curve) showing a relationship between an external magnetic field applied to the reproducing layer of the present invention and a magnetic Kerr rotation angle in a temperature range from room temperature to a compensation temperature or lower.

FIG. 8 is a schematic diagram showing how a light beam transmitted through a reproducing layer is reflected back on the surface of a recording holding layer in the magneto-optical recording medium of the present invention.

FIG. 9 is a diagram showing the reproduction light beam power dependency of the CN ratio in the example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transparent substrate, 2a ... Dielectric layer, 2b ... Protective layer, 3 ... Signal reproducing layer, 4 ... Recording holding layer, 5 ... Nonmagnetic layer, 6 ... Magnetic field generator, 7 ... Light beam, 8 ... Condensing lens , 9 ... Regeneration layer,
10 ... Recording holding layer, 11 ... Light beam, 12 ... Light beam intensity distribution, 13 ... Transferable region, 14 ... Reproducing layer, 15 ...
Recording holding layer, 16 ... Light beam, 17 ... Light beam intensity distribution, 18 ... Transfer area, 19 ... Auxiliary magnetic field generator and initialization magnetic field, 20 ... Magneto-optical recording / reproducing device, 21 ... Magnetic field generating device, 22 ... Optical pickup, 23 ... Spindle motor for disc rotation, 24 ... Magneto-optical recording medium, 2
5 ... Reproducing layer (a part of), 26 ... Magnetization aligned by an external magnetic field, 27 ... Transferred magnetic domain, 28 ... Domain wall (on the shaded portion), 29 ... Reproducing layer, 30 ... Recording holding layer, 31
... non-magnetic layer, 32 ... reflection from adjacent bit, 33 ... reflection from bit to be read.

Front page continuation (72) Inventor, Jiichi Miyamoto, 1-280, Higashi Koikekubo, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72) Inventor, Masahiko Hashi 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central Research Laboratory

Claims (5)

[Claims] 1. A magneto-optical recording medium having a magnetic layer on which information is magneto-optically recorded, the recording layer having the magnetic layer magnetically recording information, and a coercive force small from room temperature to high temperature. A magneto-optical recording medium comprising a magnetic signal reproducing layer having perpendicular magnetic anisotropy, wherein a non-magnetic layer is sandwiched between the recording holding layer and the signal reproducing layer and the exchange coupling between them is cut. 2. The perpendicular magnetic anisotropy of the reproducing layer is at room temperature (30 degrees Celsius).
2. The magneto-optical recording medium according to claim 1, wherein the remanent magnetization when the magnetic field is zero after the magnetization is once saturated is 80% or more of the saturation magnetization. 3. An alloy thin film containing at least one low surface energy metal of Au, Ag, Al, Cu, etc. as a matrix is used as the non-magnetic layer for breaking exchange coupling between the magnetic layers. The magneto-optical recording medium according to claim 1 or 2, wherein 4. The material having the same optical constant as that of either or both of the cut magnetic layers is used as the non-magnetic layer for breaking the exchange coupling between the magnetic layers. The magneto-optical recording medium described. 5. A magneto-optical recording / reproducing apparatus which uses the magneto-optical recording medium according to claim 1 or 2 and reproduces a signal by irradiating light from the reproducing layer side. A magneto-optical recording / reproducing apparatus, which reproduces information while applying a magnetic field larger than the magnetic force.