JPS63200343A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To permit easy overwriting by a method for modulating an external magnetic field by forming a 1st rare earth-transition metal alloy film which has a Curie point TC1 and in which the auxiliary lattice magnetization of the rare earth is dominant right below TC1 and the same kind of the alloy film having the Curie point TC2 higher than TC1 directly adjacently to each other in such a manner that the films make exchange coupling with each other. CONSTITUTION:This magneto-optic disk 17 is constituted of the laminate of a transparent substrate 13, an interference film 14, a perpendicular magnetized film 10, and a protective film 15. The film 10 in this constitution is constituted of a thin amorphous TbFeCoCr film and is formed of a 1st magnetic film 11 having different compsn. ratios of Tb to FeCoCr and a 2nd magnetic film 12 sandwiching the same by a two-dimensional magnetron sputtering method using a Tb target and FeCoCr alloy target. The Curie point TC2 of the magnetic film 12 is made higher than the Curie point TC1 of the magnetic film 11 at this time. The magnetic film 12 is functioned as a magnetically thin single-layer film by the difference in the Curie point at the time of projecting laser light to the medium. The external magnetic field necessary at the time of recording and erasing is thereby lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording medium, particularly a magneto-optical recording medium having a rare earth-transition metal alloy film.

[Summary of the invention]

The present invention provides a magneto-optical recording medium having a rare earth-transition metal alloy film, in which first and second rare earth metals having different Curie points TC1 and TC2 (TCI<TIJ) and having different compositions are used. A perpendicularly magnetized film is formed by having a transition metal alloy film and arranging the second rare earth-transition metal alloy film directly adjacent to the first rare earth-transition metal alloy film to be exchange-coupled. Construct a magneto-optical recording medium that enables recording and erasing under an external magnetic field.

[Conventional technology]

A rare earth-transition metal alloy film (perpendicular magnetization film) constituting a conventional magneto-optical recording medium is usually composed of a magnetic layer having a single composition.

FIG. 13 shows a cross-sectional structure of the main part of a conventional magneto-optical recording medium, such as a magneto-optical disk.
A pair of transparent substrates (1) each having grooves for detecting the recording track position formed on one surface are prepared, and a perpendicular magnetization l made of an amorphous rare earth-transition metal alloy is provided on the surface where these grooves are formed. @ (21 is deposited and these perpendicular magnetization films (2
) is on the inside and both substrates (1) are bonded using an adhesive (3).

(4) is an interference film deposited between each perpendicular magnetization film (2) and the substrate (1), and (5) is a protective film deposited on the surface of the perpendicular magnetization film (2).

The saturation magnetization Ms (hereinafter referred to as magnetization MS) of this perpendicular magnetization film (2) is, as schematically shown in FIG. is given by

When recording on this perpendicularly magnetized film (2), for example by Curie point recording, as shown in FIG. One perpendicular magnetization II! is to be recorded through the condenser lens system (8). (On the substrate 21, the perpendicularly magnetized film (2) is irradiated from the back side on the 11 side in a focused manner to heat the temperature here to the Curie point, and the direction of magnetization is reversed by an external magnetic field to record. .

In a magneto-optical disk having a single layer film made of such an amorphous rare earth-transition metal alloy, the
An external magnetic field of about 3000e is required.

If this external magnetic field can be reduced, it becomes possible to easily miniaturize the magnet and perform overwriting (rewriting previously written information with new information by overwriting) using an external magnetic field modulation method.

[Problem that the invention seeks to solve]

By the way, in order to obtain a magnetized film in which the required external magnetic field during recording and erasing is low, (i) the required external magnetic field Hw during recording and the required external magnetic field Hg during erasing become Hw = -Hg. (ii) to reduce IH SoI and 1Hil.

However, in the conventional perpendicular magnetization film mentioned above, IHυ
A magnet that provides lHg1 is used, and its direction is switched between recording and erasing. In addition, when overriding by external magnetic field modulation method, HW
--If it is possible to set the H section, the direct current component of the current flowing through the magnet coil can be reduced to zero or the alternating current component can be reduced, contributing to miniaturization of the coil drive power source and prevention of heat generation in the coil. However, conventionally lHwl<lHg1 is due to 'r<'rc(TC
This is caused by stray magnetic fields from the region of

Figure 15 shows a state in which the perpendicularly magnetized film (2) is irradiated with a laser beam (7) to heat a portion a to the Curie point. However, a stray magnetic field Hs is given here by the magnetized MO around it. Therefore, when recording or erasing is performed by applying an external magnetic field to this portion a, this floating magnetic field H3F has an effect. That is, since the external magnetic field Hν during recording is in the same direction as the floating magnetic field H3F, and the external magnetic field HE during erasing is in the opposite direction to the floating magnetic field Hsr, the external magnetic field Hε (〉Hw) is larger during erasing than during recording. It becomes necessary.

When using a single-layer perpendicularly magnetized film, in order to reduce this stray magnetic field, the temperature near the laser irradiation position (TI <
TC), the magnetization is zero, that is, TL=TCOMP (T
CO)4P: magnetic compensation temperature), but it is not easy to explode such a perpendicularly magnetized film, and T
The magnetization near C also decreases, and the energy (Zeeman energy) that causes the magnetization to move in the direction of the external magnetic field decreases.

Next, the following method can be considered to reduce l11w1 and lHg1 - If a magnetized film heated above the Curie temperature is cooled and reaches the Curie temperature again and magnetization occurs, what kind of magnetic domain structure (in rotational magnetization It is determined by the magnetostatic energy Ed due to the Zeeman energy 22% demagnetizing field and the domain wall energy Eψ. Among these, Zeeman energy Ez and magnetostatic energy Ed, which are energies related to magnetization, are considered. Zeeman energy Ez is energy that causes magnetization to move in the direction of an external magnetic field (if a floating magnetic field is present, this magnetic field is added), and from this point of view, it is advantageous to have a larger magnetization. However, as the magnetization increases, the magnetostatic energy Ed due to the demagnetizing field increases, resulting in a multi-domain state (thermally demagnetized state). By the way, the Zeeman energy Ez and the magnetostatic energy Ed due to the demagnetizing field are both functions of the film thickness, and the thinner the film is, the more stable the single domain state is than the multidomain state even against large magnetization. Therefore, a thin film is effective for a film that does not have a multi-domain state and has large magnetization.

However, in the case of a single N film, a thin magnetization l1l (<200 people) with large magnetization just below 'rc (temperature lower than TC)
It is difficult to make such a material in terms of reliability (surface oxidation, corrosion, etc.).

In view of the above-mentioned points, the present invention provides a magneto-optical recording medium that can record and erase information using an external magnetic field.

[Means for solving problems]

The present invention provides a first rare earth-transition metal alloy film (1
1) and has a Curie point TC2 higher than Tax and TC1
Directly below the second rare earth-transition metal alloy film (12) in which transition metal sublattice magnetization is dominant, the second rare earth-transition gold alloy film (hereinafter referred to as the second magnetic film) (12) is independent. A perpendicularly magnetized film (10) is arranged directly adjacent to and exchange-coupled with a first rare earth-transition metal alloy film (hereinafter referred to as the first magnetic film) (11).

For example, when the perpendicular magnetization film (10) has a so-called multilayer structure in which the distribution of the Curie point TC and magnetization M in the film thickness direction is changed in a square wave manner as shown in FIG.
Alternatively, as shown in FIGS. 5 to 7, which will be described later, it is possible to have a film structure in which the Curie point TC and the distribution of magnetization M9 in the film thickness direction are continuously changed. In order to achieve this, a case will be explained taking as an example a case where the first and second magnetic films (11) and (12) shown in FIG. 1 are laminated alternately to form a 57if film structure.

The first magnetic film (11) and the second magnetic film (12) are T
Rare earth metals such as b, Gd, Dy, Ho..., and F
It is composed of one or more amorphous alloys with transition metals such as e*Co+Nt... (a small amount of other elements may be added). In this case, the first magnetic film (11)
For the second magnetic film (12), by making the amount of rare earth metals larger than the compensation composition and making the amount of transition metals more than the same compensation composition for the second magnetic film (12), arrows MRE and M are shown in FIG.
As shown by TM, in the first magnetic film (11), the rare earth metal sublattice magnetization MR acts dominantly to generate the magnetization M1 shown in FIG. 1, and in the second magnetic film (12), is such that transition metal sublattice magnetization M TM acts dominantly to produce magnetization M2 in the opposite direction (magnetization M1.M2 is T
(represents the magnetization direction at a temperature just below TC1, which is lower than CI). At this time, regarding the magnetization distribution shown in FIG. 1, the magnetization of each magnetic film (11) and (12) is made as small as possible as a whole (total), that is, they cancel each other out. However, regarding the sublattice magnetization, As shown in Figure 2, each magnetic field 19! Regarding (11) and (12), it is necessary that the same sublattice magnetization M and MTM are arranged in parallel so that they are aligned, and such a structure is roughly equivalent to each magnetic film (11) and (12). This can be achieved when the effective magnetic field due to exchange coupling between each magnetic film (11) and (f2) is larger than the coercive force of ).

In Figure 1, in the perpendicularly magnetized film (lO), the first layer, the third layer
The layer and the 5th N are the first magnetic film (11
), and the second and fourth layers are composed of a second magnetic film (12) having a Curie point TC2 higher than TCI. When such a perpendicularly magnetized film (10) is formed on a transparent substrate (13) and a laser beam (7) is focused and irradiated onto this perpendicularly magnetized IFJ (10), the temperature and magnetization at each position are shown in Fig. 3. As shown in the direction, when the temperature T is below TC1, the magnetization Ml of each adjacent layer.

The direction of M2 is reversed, and the stray magnetic field generated from this region is small or almost zero. The required external magnetic field HW + HE during striking recording and erasing is ■(C-HE).In addition, in the region 7'>TCt, the second and fourth layers are magnetically thin single-layer films. Therefore, if the film material and composition are determined so that the magnetization becomes large in this temperature range, the magnetization will be easily suppressed even by a weak external magnetic field Hex (i.e. Hw or HE) as shown in Figure 4A. Direction during cooling in the direction of the external magnetic field (.

From this state, it is cooled down, and as shown in Fig. 4B (TCI<T<
When T = T CL after cooling to TC2), the magnetization directions of the first, third and fifth layers are the second layer or the 41'! as shown in FIG. 4C. It is determined by the exchange bonding force with. This allows recording and erasing with a weak external magnetic field.

The Curie temperature of the magnetized film used in the present invention is 80°C to 2
A range of 50° C. is preferred and is recorded by Curie point recording. The Curie point and magnetization are controlled by the film material and composition.

As perpendicular magnetization 11 (10), first and second magnetism 15
1(11) and (12) are arranged alternately to form a multi-1'if film structure, it is possible to form a multilayer film of two or more layers, preferably three or more layers.

In addition, the perpendicularly magnetized film (10) may include a multilayer film structure in which the Curie point and magnetization distribution in the film thickness direction changes in a square wave manner (see, for example, Fig. 1), as well as, for example, Figs. 5A, B, Figure 6A, B or Figure 7A.

It is also possible to configure the Curie point and magnetization to change continuously in the film thickness direction, as shown by B.

Note that the temperature directly below the Curie point TC1 (the lowest Curie point in the film thickness direction) is the temperature at which the direction of magnetization is determined during the cooling process from the Curie point TC1.
1 to about TCt-70°C (preferably TCL 10
℃ to 30℃) refers to low temperatures, and the above-mentioned perpendicular magnetization III! The total magnetization in (10) represents the average value of magnetization in the film thickness direction, and therefore, the total magnetization is controlled by the magnitude, direction, and film thickness of each layer's magnetization.

If the perpendicular magnetization film (10) has a multilayer film structure in which the Curie point changes in a square wave manner in the film thickness direction, the Curie point T is high.
The second magnetic film (12) of C2 can have a film thickness of 300 Å or less, preferably 100 Å or less, and a rare earth-transition metal alloy film containing a large amount of transition metal, which has large magnetization near the Curie point, is effective. be.

In addition, in the case of a multilayer film structure, the first and second magnetic films (11
) and (12), the relationship between the magnetizations M1 and M2 allows Mz>Mx when viewed at the temperature directly below the TCL.

[Effect]

As described above, in the present invention, the first rare earth-transition metal alloy film (11) has a Curie point TCI and has a dominant rare earth sublattice magnetization immediately below TCI, and the first rare earth-transition metal alloy film (11) has a Curie point TC2 higher than TC1 and has a dominant rare earth sublattice magnetization immediately below TC1. A second rare earth-transition metal alloy It! with dominant transition metal sublattice magnetization. fl (12) are arranged directly adjacent to each other so as to be exchange-coupled with each other, thereby making it possible to reduce the stray magnetic field to zero or extremely small, and to make the second rare earth element - Since the transition metal alloy film (12) becomes a magnetically thin single Iil film, the required external magnetic field during recording and erasing can be reduced.

〔Example〕

The magneto-optical disk (17) and (
18) was prepared and the dependence of its recording characteristics on external magnetic field was evaluated. Each magneto-optical disk (17) and (1st) has a transparent substrate (13), an interference film (14) and a perpendicular magnetization film (10).
and a protective film (15).

The magneto-optical disk (17) in FIG. 8 has a perpendicular magnetization film (10
) is composed of an amorphous Tb Fe Co Cr thin film, and T
Tb was deposited by a binary DC magnetron sputtering method using a b target and a Fe Co Cr alloy target.
The first magnetic film (11
) and the second magnetic film (12) to form a 3N structure.

The magneto-optical disk (18) in FIG. 9 has a perpendicular magnetization film (10
) is composed of an amorphous Tb Fe Co Cr thin film as shown in FIG. It was made to have a structure.

The first magnetic film (11) is a so-called Tb-rich film from room temperature to the Curie temperature, and the Curie temperature is 130
The coercive force at room temperature and temperature is 2K Oe.

The second magnetic film (12) is a so-called iron-rich film from room temperature to the Curie temperature, and the Curie temperature is 160°C,
The coercive force at room temperature is 2K Oe. First magnetic film (1
The ratio of the magnetization of 1) and the magnetization of the second magnetic film (12) is 100.
℃, so in order to make the total magnetization around this temperature zero, the total film thickness of the first magnetic film (11) was set to 600, and the second magnetic film ( 12), the total film thickness was 200 people. In addition, a second magnetic I! with a high Curie temperature! 1 (12), each film thickness was 100 people.

For such magneto-optical disks (17) and (18) in FIGS. 8 and 9, a carrier wave frequency of 2.7 MHz and a linear velocity of 3
．． The dependence of the recording characteristics on the external magnetic field under the condition of 8 va/sec was evaluated. In addition, these magneto-optical disks (17) (
18) and a conventional magneto-optical disk, we used TbFe, which has a magnetic compensation temperature between room temperature and the Curie temperature, which has a relatively small stray magnetic field during recording as a magnetic single layer film.
We also evaluated a magneto-optical disk made of a CoCr single N film (thickness: 800 mm). Figure 10 shows the evaluation results for the magneto-optical disk (17) in Figure 8, Figure 11 shows the evaluation results for the magneto-optical disk (18) in Figure 9, and Figure 12 shows the evaluation results for the conventional magneto-optical disk. shows. As is clear from FIGS. 10 and 11, in the case of a magneto-optical disk in which the perpendicularly magnetized film has a multilayer structure (the present invention), a complete recording and erasing state can be achieved with an external magnetic field of approximately ±1000 e. On the other hand, as shown in FIG. 12, in the case of a conventional magneto-optical disk with a single magnetic layer, recording is performed with an external magnetic field of +1000e, and the data is erased with an external magnetic field of 3000e. Therefore, by forming the perpendicularly magnetized film into the multilayer structure of the present invention, the external magnetic field required for recording and erasing can be reduced to about half compared to the conventional one.

In addition, in the case of a magnetic disk made of an iron-rich film (200 layers) and a Tb-rich layer of 1111J (600 layers), which have almost the same Curie temperature, the recording characteristics are better than that of a conventional magneto-optical disk with a magnetic fR layer film. was inferior, and erasing could not be performed unless approximately -50,000 voltage was applied.

〔Effect of the invention〕

According to the magneto-optical recording medium according to the present invention, the generation of stray magnetic fields is eliminated, and the magnetically thin single Nl! If, the required external magnetic field during recording and erasing can be reduced. Therefore, overriding using the external magnetic field modulation method can be easily performed.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the spontaneous magnetization of the perpendicularly magnetized film of the magneto-optical recording medium according to the present invention, and FIG. 2 is a diagram schematically showing the arrangement of sublattice magnetization that forms the magnetization state of FIG. 1. , FIG. 3 and FIG. 4 A to C are diagrams for explaining the operation of the perpendicular magnetization film,
Figures 5 to 7 are Curie temperature and magnetization distribution diagrams in the film thickness direction showing other examples of perpendicularly magnetized films of the present invention, respectively, and Figures 8 and 9 are diagrams used to evaluate the recording characteristics of the present invention. Examples of magneto-optical disks, FIG. 10 is a diagram of the evaluation results of the magneto-optical disk of FIG. 8, FIG. 11 is a diagram of the evaluation results of the magneto-optical disk of FIG. 9, and FIG. 12 is a diagram of the conventional magneto-optical disk. FIG. 13 is a cross-sectional structural diagram of a conventional magneto-optical recording medium, FIG. 14 is an explanatory diagram of its magnetization state, and FIG. 15 is an explanatory diagram of the generation of a stray magnetic field. (10) is a perpendicular magnetization film, (11) is a first magnetic layer, (1
2) is the second magnetic layer.

Claims (1)

[Claims] a first rare earth-transition metal alloy film having a Curie point T_C_1 and having a dominant rare earth sublattice magnetization immediately below the T_C_1;
Curie point T_C higher than the above Curie point T_C_1
_2 and a second rare earth-transition metal alloy film in which the transition metal sublattice magnetization is dominant directly under the T_C_1, and the second rare earth-transition metal alloy film is solely connected to the first rare earth-transition metal alloy film. A magneto-optical recording medium characterized in that it is arranged directly adjacent to a metal alloy film so as to be exchange-coupled.