JPH05290416A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To enable the sure execution of overwriting without increasing the influence on an intermediate layer by external magnetic fields at the time of recording even if the film thickness of the intermediate layer is increased and the magnetic field for initialization is decreased in an overwriting system by a change in light intensity using multilayered films. CONSTITUTION:This recording medium has the magnetic films constituted of three layers; a recording layer 1, the intermediate layer 2 and an auxiliary layer 3 from the incident direction of a laser beam. All of the recording layer 1, the intermediate layer 2 and the auxiliary layer 3 consist of amorphous alloy films of rare earth metals and transition metals. The recording layer 1 and the intermediate layer 2 as well as the intermediate layer 2 and the auxiliary layer 3 are respectively exchange bonded. At least the recording layer 1 and the auxiliary layer 3 are perpendicularly magnetized films. Further, the recording layer 1, the intermediate layer 2 and the auxiliary layer 3 satisfy the following conditions: Tcomp2 Tc1, Ku2<Ku1, Ku2<Ku3, Hc3<Hc1 at room temp., where Ku1, Ku2, Ku3 are respectively the perpendicular magnetic anisotropy constants of the recording layer, the intermediate layer and the auxiliary layer 3; Tc1 is the Curie temp. of the recording layer; Tcomp2 is the compensation temp. of the intermediate layer; Hc1, Hc3 are the coercive forces of the recording layer and the auxiliary layer.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, magneto-optical recording has been actively developed because it has a larger capacity than conventional magnetic recording and can rewrite information, and some have already been commercially available. .. However, many of the magneto-optical recording devices currently on the market require a step of erasing the original information in advance and then writing new information when rewriting the information, so the erasing operation is time-consuming and time-consuming. It's a loss. Various magneto-optical recording methods that allow overwriting have been proposed, but there are many problems.

The following are known conventional magneto-optical recording methods. General optical modulation method (for example, Journal of Applied Magnetics Vol.8, No.
5 (1984) etc.). Magnetic field modulation method using a fixed magnet (Materials MAG-86-95 (1986) etc. of the Institute of Electrical Engineers of Japan, Magnetics Research Group). Magnetic field modulation method by flying head (Materials MAG-87-178 (1987) of the Institute of Electrical Engineers of Japan Magnetic Research Group, JP-A-63-204532)
JP-A-63-217548, etc.). Overwrite method using a magnetic head with a resonant circuit and a pulsed laser (IEEE Trans.Magn.24, P.666 (1
988), JP-A-63-37842). Overwrite method by changing the light intensity using a two-layer film (H. Iida et. Al .: JJ of Appl. Phys., Vol.28 (19
89), P367, Y. Mutoh et. Al .: Proceedings of the 14th Japan Society for Applied Magnetics (1990) 376). This is an overwrite method that uses a two-layer film to change the light intensity, and overwrites by changing the temperature distribution in the film thickness direction, eliminating the need for a magnetic field initialization process (T. Fukami et. al.:JJ of Appl. Phys., Vol.
28 (1989), P.371-374).

[0004]

Among the above-mentioned conventional magneto-optical recording methods, the optical modulation method generally has a drawback that an erasing operation is required because overwriting cannot be performed and rewriting takes a long time. Therefore, it is impossible to use the hard disk as a substitute.

Further, in the magnetic field modulation method using a fixed magnet, the magnet needs to have a certain size, resulting in a large power consumption. Further, it is very difficult to increase the speed, and it seems that digital recording of about 1 MHz is the limit.

Further, in the magnetic field modulation method using the floating magnetic head, the magnetic head is brought into contact with the medium almost, and the merit of non-contact of the optical disk is lost. Moreover, it is necessary to use a single plate, and there are problems in terms of storage capacity, substrate warpage, and protection of the magnetic film.

The method using the magnetic head having the resonance circuit and the pulsed laser has the same problem as the above method, although it is better than the above method.

Further, in the overwrite method using the change in light intensity using the two-layer film, a large initializing magnetic field is required, and there is a problem that the magnet for that is considerably large and the apparatus is large. In order to solve this problem, an attempt has been made to lower the interfacial domain wall energy and lower the initializing magnetic field by sandwiching an intermediate layer made of an in-plane magnetized film such as FeCo between the two layers and increasing the film thickness. However, since the saturation magnetization of the intermediate layer is large, there is a problem in that the intermediate layer is affected by an external magnetic field during recording and reliability of overwriting is lowered.

The present invention has been made in view of the above-mentioned circumstances of the prior art. Even when the initializing magnetic field is reduced by increasing the thickness of the intermediate layer in the above method, the intermediate layer due to the external magnetic field during recording is used. SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical recording medium that can surely perform overwriting without increasing the influence on the recording medium.

[0010]

[Means for Solving the Problems]
Therefore, according to the present invention, the number of laser beams should be less than the incident direction of laser light.
Is composed of three layers, a recording layer, an intermediate layer and an auxiliary layer.
It has a film, and the recording layer, intermediate layer and auxiliary layer are all rare earth
A metal-transition metal amorphous alloy film, and a recording layer
The intermediate layer, the intermediate layer and the auxiliary layer are exchange-coupled,
At least the recording layer and the auxiliary layer are perpendicular magnetic films, and
The recording layer, intermediate layer and auxiliary layer meet the following conditions.
A magneto-optical recording medium is provided. Tcomp₂≒ Tc₁ Ku₂<Ku₁ Ku₂<Ku₃  Hc at room temperature₃<Hc₁ (However, Ku₁, Ku₂, Ku₃Are the recording layer, intermediate layer and
And auxiliary magnetic layer perpendicular magnetic anisotropy constant, Tc₁Is the recording layer curly
-Temperature, Tcomp₂Is the compensation temperature of the intermediate layer, Hc₁, Hc₃Is
(Coercive force of recording layer and auxiliary layer)

FIG. 1 is a sectional view schematically showing an example of the layer structure of a magnetic layer of a magneto-optical recording medium according to the present invention.
It has a three-layer structure in which the intermediate layer 2 and the auxiliary layer 3 are laminated, and the recording / reproducing laser beam is incident from the recording layer 1 side. The recording layer 1 stores a signal given by changing the laser power at at least a binary level without being erased by the initializing magnetic field. Auxiliary layer 3
Is to transfer a signal given by changing the laser power at least at a binary level to the recording layer 1 through the intermediate layer 2 and then the magnetic moment is aligned in one direction by the initialization magnetic field and the next overwrite is performed. Prepare for The intermediate layer 2 lowers the domain wall energy and reduces the initializing magnetic field. Of these layers, at least the recording layer 1 and the auxiliary layer 3 are perpendicular magnetization films, and the recording layer 1 and the intermediate layer 2, and the intermediate layer 2 and the auxiliary layer 3 are exchange-coupled, respectively. The recording layer 1, the intermediate layer 2 and the auxiliary layer 3 are all made of a rare earth metal-transition metal amorphous alloy film, and particularly preferable as the recording layer 1 and the auxiliary layer 3 are TbDyFeCo and TbG.
Examples thereof include dFeCo. The intermediate layer 2 does not necessarily have to be a perpendicularly magnetized film, but rare earth metals such as Gd, N
A combination of d, Dy, etc. and Fe, Co, etc. as a transition metal, such as GdCo, GdFe, etc. is preferably used. The recording layer 1, the intermediate layer 2 and the auxiliary layer 3 must satisfy the following conditions. In the following, Ku is the perpendicular magnetic anisotropy constant, Tc is the Curie temperature, Ms is the saturation magnetization, Hc is the coercive force, and the subscript 1 is the recording layer, 2 is the intermediate layer, and 3 is the auxiliary layer. _{(a) Tcomp 2 ≒ Tc 1} (b) Ku 2 <Ku 1 (c) Ku 2 <Ku 3 (d) Hc 3 at room temperature <Hc ₁ Tcomp ₂ is substantially Tc ₁ and equal, the temperature Tc ₁ If Ms ₂ does not exceed 200 (emu / cc), then Tc ₁
It doesn't matter if there is a difference. If Ms ₂ is 200 (emu / cc) or more near Tc ₁ , the magnetization of the intermediate layer 2 is affected by the external magnetic field, which hinders signal transfer from the auxiliary layer 3 to the recording layer 1. If Ku ₂ is Ku ₁ or more, the interface domain wall may move to the recording layer 1, which causes instability in signal storage. When Ku ₂ is Ku ₃ or more, the interfacial domain wall is the auxiliary layer 3
May result in instability in the next signal recording. If Hc ₃ is higher than Hc ₁ at room temperature, the initialization magnetic field Hi (Hc ₃ <Hi <Hc ₁ ) cannot be set. Figure 2
An example of the magnetic temperature characteristics of the recording layer 1, the intermediate layer 2 and the auxiliary layer 3 is shown in FIG. The thickness of the recording layer 1 and the auxiliary layer 3 was 30 n.
It is preferable that m-500 nm and the thickness of the intermediate layer 2 are 100 nm or less.

The above-mentioned magnetic film is provided on the substrate, and the substrate material is preferably glass, glass having guide tracks formed of an ultraviolet curable resin, polycarbonate, polymethylmethacrylate, epoxy resin or the like.

Although the most basic medium structure has been shown above, a protective layer, a reflective layer, a guide track layer, a dielectric layer, a fourth magnetic layer and the like may be provided if necessary. Also, two media may be stuck together to form a double-sided recording type medium.

Next, a magneto-optical recording method using the magneto-optical recording medium having the above structure will be described. In this method, the initial magnetic field Hi (Hc ₃ <Hi <Hc ₁ , the intermediate layer 2 is inserted in the magneto-optical recording medium in advance to lower the interfacial domain wall energy, and the initializing magnetic field can be reduced to about 1 (kOe).)
Is applied to align the magnetization direction of the auxiliary layer 3. During recording, an external magnetic field Hb is applied in the direction opposite to Hi. Then, as shown in FIG. 3, the recording laser power is changed at a minimum binary level in accordance with the recording signal. When changing at two levels, the temperature of the recording layer 1 is set to the temperature Tl near the Curie temperature Tc ₁ (≈Tcomp ₂ ) as the value of the low level Pl.
As a value of the high level Ph, the temperature of the auxiliary layer 3 is substantially the Curie temperature Tc ₃ or higher, and the temperature of the intermediate layer 2 is a temperature T that is substantially the Curie temperature Tc ₂ or higher.
Use a value that raises the temperature to h. Since the temperature of the recording layer 1 is in the vicinity of the Curie temperature Tc ₁ of the laser irradiation of the low level Pl, the magnetic moment of the recording layer 1 is the external magnetic field H.
It is cooled in the same direction as b. At high level Ph laser irradiation, the temperature of the entire magnetic layer becomes Tc ₃ or higher and Tc ₂ or higher, the magnetic moment of the auxiliary layer 3 is directed in the same direction as the external magnetic field Hb, and the transition metal of the transition layer of the recording layer 1 is cooled in the cooling process. The sublattice magnetic moment is also aligned with it. At that time, since Tc ₃ ≈Tcomp _2, it is not necessary to be influenced by the magnetization of the intermediate layer 2.

[0015]

EXAMPLES Examples of the present invention will be described below. (Example) As shown in FIG. 4, a protective layer 5 was formed on a glass substrate 4.
As the SiN film, the recording layer 1 as a TbDyFeCo film (transition metal rich, film thickness 80 nm), and the intermediate layer 2 as G
dFeCo film (thickness 30 nm), TbF as auxiliary layer 3
A magneto-optical recording medium was produced in which an eCo film (rare earth metal rich, film thickness 200 nm) and a SiN film as a protective layer 6 were sequentially stacked. The magnetic temperature characteristic of this recording medium is shown in FIG. As can be seen from FIG. 5, Tcomp ₂ = Tc ₁ , Hc ₃ at room temperature
<Hc ₁ . Further, Ku ₂ <Ku ₁ and Ku ₂ <Ku ₃ .

When writing and erasing experiments were conducted on this recording medium, overwriting could be reliably performed under the following conditions. Initializing magnetic field Hi: 1 kOe External magnetic field Hb: 200 Oe High laser power: 9 mW Low laser power: 4 mW

(Comparative Example) The structure is the same as that shown in FIG. 4, but the magneto-optical recording medium has the magnetic temperature characteristics of the magnetic layers (recording layer, intermediate layer and auxiliary layer) as shown in FIG. Was produced. As can be seen from FIG. 6, Tcomp ₂ <Tc ₁ and Hc ₃ <Hc ₁ at room temperature. Also, Ku ₂ <Ku ₁ , Ku ₂ <K
u ₃ . When writing and erasing experiments were performed on this recording medium, reliable overwrite could not be performed.

[0018]

According to the present invention, since the magneto-optical recording medium is constructed as described above, the following effects can be obtained. (1) High-speed recording is possible without changing the magnetic field. (2) Non-contact and highly reliable. (3) At room temperature, the coercive force of the auxiliary layer is smaller than that of the recording layer, and the size of the initializing magnetic field can be reduced by reducing the interfacial domain wall energy by the action of the intermediate layer. Is advantageous to. (4) By setting the compensation temperature of the intermediate layer near the Curie temperature of the recording layer and making the saturation magnetization of the intermediate layer small, the influence of the external magnetic field on the intermediate layer during recording can be avoided and overwrite can be ensured. You will be able to do it. (5) Overwrite method for exchange-coupling multilayer film that does not require initialization (JJ of Appl. Phys., Vol.28 (1989) p.371)
, The external magnetic field during recording is very large, so FeC
Although a medium having an intermediate layer with a large saturation magnetization such as o could not be used, the recording medium of the present invention can be applied to this system and exhibits an excellent effect.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a magnetic film of a magneto-optical recording medium according to the present invention.

FIG. 2 is a diagram showing an example of magnetic temperature characteristics of the recording medium.

FIG. 3 is a diagram showing an example of laser irradiation conditions.

FIG. 4 is a cross-sectional view showing the layer structure of the recording medium of the example.

FIG. 5 is a diagram showing a magnetic temperature characteristic of a recording medium of an example.

FIG. 6 is a diagram showing a magnetic temperature characteristic of a recording medium of a comparative example.

[Explanation of symbols]

 1 recording layer 2 intermediate layer 3 auxiliary layer 4 glass substrate 5 and 6 protective layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motoharu Tanaka 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (1)

[Claims] 1. A magnetic film comprising at least three layers of a recording layer, an intermediate layer and an auxiliary layer in the direction of incidence of laser light, wherein each of the recording layer, the intermediate layer and the auxiliary layer is a rare earth metal-transition metal non-metal. It is composed of a crystalline alloy film, and the recording layer and the intermediate layer and the intermediate layer and the auxiliary layer are exchange-coupled with each other. At least the recording layer and the auxiliary layer are perpendicular magnetization films, and the recording layer, the intermediate layer, and the auxiliary layer. Satisfying the following conditions, a magneto-optical recording medium. Tcomp ₂ ≈Tc ₁ Ku ₂ <Ku ₁ Ku ₂ <Ku _{3 At} room temperature, Hc ₃ <Hc ₁ (where Ku ₁ , Ku ₂ and Ku ₃ are the perpendicular magnetic anisotropy constants of the recording layer, the intermediate layer and the auxiliary layer, respectively). , Tc ₁ is the Curie temperature of the recording layer, Tcomp ₂ is the compensation temperature of the intermediate layer, and Hc ₁ and Hc ₃ are the coercive forces of the recording layer and the auxiliary layer).