JP2751154B2 - Magneto-optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magneto-optical recording medium, and more particularly to a magneto-optical recording medium having a rare earth-transition metal alloy film. SUMMARY OF THE INVENTION The present invention relates to a magneto-optical recording medium having a rare earth-transition metal alloy film, wherein Curie points T _C1 and T
First and second having _C2 (T _C1 <T _C2 ) and different compositions
The first rare earth-transition metal alloy film is directly adjacent to the second rare earth-transition metal alloy film so that the same sublattice magnetization is aligned, and the first and second rare earth-transition metal alloy films are By forming a perpendicular magnetization film by laminating at least one layer of the rare earth-transition metal alloy film and at least three layers in total, a magneto-optical recording medium capable of recording / erasing under a weak external magnetic field is formed. . [Related Art] A rare earth-transition metal alloy film (perpendicular magnetization film) constituting a conventional magneto-optical recording medium is usually constituted by a magnetic layer having a single composition. FIG. 13 shows a cross-sectional structure of a main part of a magneto-optical recording medium having a conventional structure, for example, a magneto-optical disk.
A pair of transparent substrates (1) each having a groove for recording track position detection formed on one surface is prepared, and a perpendicular magnetic film made of an amorphous rare earth-transition metal alloy is formed on the surface on which each groove is formed. (2) is formed, and the two substrates (1) are joined by an adhesive (3) with the perpendicular magnetization film (2) inside. (4) an interference film formed between each perpendicular magnetization film (2) and the substrate (1);
(5) is a protective film deposited on the surface of the perpendicular magnetization film (2). The saturation magnetization M _S (hereinafter referred to as magnetization M _S ) of the perpendicular magnetization film (2) is, as schematically shown in FIG. 14, the sub-lattice magnetization M _RE of the rare earth metal and the sub-lattice magnetization M _TM of the transition metal. Difference ｜ M _RE −M _TM ｜
Given by In the case of recording on the perpendicular magnetization film (2), for example, Curie point recording, as shown in FIG. 13, an external magnetic field is applied to the recording portion by the magnetic field generating means (6), and in this state, the laser beam (7) Is irradiated onto one perpendicular magnetic film (2) to be recorded through the condenser lens system (8) from the back surface on the substrate (1) side so as to focus on the perpendicular magnetic film (2). The recording is performed by reversing the direction of the magnetization at the place. In such a magneto-optical disk having a single-layer film made of a crystalline rare earth-transition metal alloy, 200 to 3
An external magnetic field of about 00 0e is required. If the external magnetic field can be reduced, it is possible to easily perform downsizing of the magnet and overwriting (rewriting previously written information with new information by overwriting) by the external magnetic field modulation method. [INVENTION AND SUMMARY Problems] Incidentally, the recording and the need an external magnetic field in the erasing obtain a magnetic layer, such as lower (i) requires an external magnetic field during erase requires external magnetic field H _W at the time of recording
The H _E is made to be _{H W = -H E, (ii} ) | H W | and | H _E | reducing the is required. However, in the above-described conventional perpendicular magnetization film, generally, | H _W
| <| H _E |, and a magnet giving | H _E | is used, and its direction is switched between recording and erasing. In the overwriting by the external magnetic field modulation method, H _W = −H _E
Can reduce the DC component of the current flowing through the coil of the magnet to zero or reduce the AC component, which contributes to downsizing of the coil driving power supply and prevention of heat generation of the coil. However, conventionally, | H _W | <| H _E | is caused by a stray magnetic field from a region of T <T _C (T _C : Curie temperature) near the irradiation position at the time of laser irradiation. That is, FIG. 15 shows a state in which the perpendicular magnetization film (2) is irradiated with the laser beam (7) and the portion a is heated to the Curie point. At this time, the magnetization disappears at this portion a, for example, at the Curie point. Suruga given stray magnetic field H _SF by the magnetization M _O surrounding here. Therefore, when an external magnetic field is applied to the portion a to perform recording or erasing, the floating magnetic field _HSF has an effect. That is, since the external magnetic field H _W during recording is in the same direction as the floating magnetic field H _SF and the external magnetic field H _E during erasing is in the opposite direction to the floating magnetic field H _SF , the external magnetic field H _E during erasing is larger than that during recording. (> H _W ) is required. In the case of using a single-layer perpendicular magnetic film, the temperature near the laser irradiation position (T ₁ <
Magnetization is zero at T _C), i.e. _{T 1 = T CO MP (T} CO MP: may be the magnetic compensation temperature), it is not easy to produce such a perpendicular magnetic film, also from T _C near The magnetization also decreases, and the energy (Zeeman energy) at which the magnetization is directed in the direction of the external magnetic field decreases. Next, the following method can be considered to reduce | H _W | and | H _E |. The magnetized film heated above the Curie temperature is cooled,
When the temperature returns to the Curie temperature and magnetization is generated, what magnetic domain structure (for a film in which magnetization reversal is caused by domain wall motion instead of rotational magnetization) is determined by Zeeman energy Ez, magnetostatic energy Ed by demagnetizing field, and It is determined by the domain wall energy E _W. Among these, the Zeeman energy Ez and the magnetostatic energy, which are energies related to magnetization
Think Ed. The Zeeman energy Ez is energy at which the magnetization tends to move in the direction of an external magnetic field (if a floating magnetic field is present, the magnetic field is applied thereto). From this point, it is advantageous that the magnetization is larger. However, when the magnetization increases, the magnetostatic energy Ed due to the demagnetizing field increases, and a multi-domain state (thermal demagnetization state) occurs. By the way, Zeeman energy
Ez and the magnetostatic energy Ed due to the demagnetizing field are both functions of the film thickness h, and the thinner the film pressure h, the more stable the magnetization is in the single domain state rather than in the multi-domain state even with a large magnetization. Therefore, a multi-domain state does not occur, and a thin film having a large magnetization is effective. However, in the case of a single-layer film, it is difficult to form a thin magnetic film (<200 _° ) having a large magnetization just below T _C (temperature lower than T _C ) in terms of reliability (surface hardening, corrosion, etc.). In view of the above, the present invention provides a magneto-optical recording medium capable of recording and erasing with an external magnetic field. The present invention [Means for Solving the problems], first rare earth is dominant rare earth sublattice magnetization at a temperature lower than T _C1 has a Curie point T _C1 - transition metal alloy film (11), T _C1 A second rare earth-transition metal alloy film (12) having a higher Curie point T _C2 and having transition metal sublattice magnetization dominant at a temperature lower than T _C1 , and a first rare earth-transition metal alloy film ( (Hereinafter referred to as a first magnetic film) (11) and a second rare earth-transition metal alloy film (hereinafter referred to as a second magnetic film) (12)
Are directly adjacent to each other so that the same sublattice magnetization is aligned, and the first and second rare earth-transition metal alloy films (11) (1)
2) constitutes (10) in which at least one layer or more and three or more layers in total are laminated. If As the perpendicular magnetic film (10), a so-called multiphase film structure example a distribution in the thickness direction of the Curie point T _C and the magnetization M _S square wave manner varied as shown in FIG. 1, or it can also be the fifth FIGS to seventh Curie point as shown in FIG. T _C and the magnetization M _S film structure continuously changing the thickness direction of the distribution of which will be described later, first, an understanding of the present invention For the sake of simplicity, a case where the first and second magnetic films (11) and (12) shown in FIG. 1 are alternately stacked to form a five-layer film structure will be described. The first magnetic film (11) and the second magnetic film (12) are Tb, Gd,
One or more amorphous metals such as rare earth metals such as Dy, Ho ‥‥ (may contain some light rare earths such as Nd, Pr, Sn) and transition metals such as Fe, Co, Ni ‥‥ It is composed of an alloy (a small amount of other elements may be added). In this case, the first magnetic film (1
1) a large amount of rare earth metal than the compensation composition is about, by the large amount of transition metal than a similar compensation composition for the second magnetic layer (12), arrows M _RE and M _TM in Figure 2
In the first magnetic film (11), the rare-earth metal sublattice magnetization _MRE predominantly acts as shown by, and the magnetization M shown in FIG.
₁ generates, in the second magnetic layer (12) so as produce the magnetization M ₂ opposite act dominantly transition metal sublattice magnetization M _TM (magnetization M _1, M ₂ is T _C1 It represents the direction of magnetization at a lower temperature, ie just below T _c1 ). At this time, with respect to the magnetization distribution shown in FIG. 1, the magnetization of each of the magnetic films (11) and (12) is made as small as possible as a whole (total), that is, the magnetizations cancel each other. each magnetic film as shown in FIG. 2 (11), it is necessary to be arranged in parallel with so that the same sublattice magnetization M _RE comrades, is M _TM comrades aligned with respect to (12), such a structure, In general, this can be achieved when the effective magnetic field due to exchange coupling between the magnetic films (11) and (12) is large due to the coercive force of the magnetic films (11) and (12). In FIG. 1, in the perpendicular magnetization film (10), the first layer, the third layer
The layer and the fifth layer are composed of a first magnetic film (11) having a Curie point T _C1 , and the second and fourth layers are each composed of a Curie point T higher than T _C1.
It is composed of _C2 second magnetic film (12). When such a perpendicular magnetization film (10) is formed on a transparent substrate (13), and this perpendicular magnetization film (10) is focused and irradiated with a laser beam (7),
As shown in the drawing, the temperature and the magnetization direction at each position are shown. When the temperature T is equal to or lower than T _C1 , the magnetizations M ₁ , M
The direction of ₂ is reversed, and the stray magnetic field generated from this region is small or almost zero. That recording time required external magnetic field H _W at the time of erasing, H _E is the H _W = -H _E. Also T> T _C1
In the region (2), the second and fourth layers are magnetically thin single-layer films. Accordingly film material so that the magnetization becomes larger in this temperature range, be determined composition, easily magnetized even to Figure 4, as shown in A weak external magnetic field H _ex (i.e. H _W or H _E) is Suitable for cooling in the direction of the external magnetic field. From this state, cooling is performed, and T = T through FIG. 4B (cooling until T _C1 <T <T _C2 ).
_In the case of _C1 , as shown in FIG. 4C, the magnetization directions of the first, third and fifth layers are determined by the exchange coupling force with the second or fourth layer. This enables recording and erasing with a weak external magnetic field. The Curie temperature of the magnetic film used in the present invention is 80 ° C to 25 ° C.
A range of 0 ° C. is preferred and is recorded by Curie point recording. The Curie point and magnetization are controlled by the film material and composition. As the perpendicular magnetization film (10), the first and second magnetic films (1
1) and (12) are alternately arranged to form a multilayer film structure, preferably a multilayer film having three or more layers. As the perpendicular magnetization film (10), in addition to the multilayer film structure in which the distribution of the Curie point and the magnetization in the film thickness direction changes in a square wave (for example, see FIG. 1), for example, FIGS. Fig. 6
A, B, or as shown in FIGS. 7A, B, the Curie point and the magnetization can be continuously changed in the film thickness direction. The temperature lower than the Curie point T _C1 (the lowest Curie point in the film thickness direction) is a temperature at which the direction of magnetization is determined in the process of cooling from the Curie point T _C1 , and T _C1 to T _C1 − About 70 ° C (preferably T _C1 -10 ° C to 30
(Approx. ° C.) refers to a lower temperature. The total (total) magnetization of the perpendicular magnetization film (10) represents the average value of the magnetization in the film thickness direction. Therefore, the overall magnetization is controlled by the magnitude, direction and film thickness of each layer. You. When the perpendicular magnetization film (10) has a multilayer structure in which the Curie point changes in a square wave in the film thickness direction, a high Curie point T
The second magnetic film (12) of _C2 can have a thickness of 300 ° or less, preferably 100 ° or less, and a rare earth-transition metal alloy film having a large amount of transition metal having a large magnetization near the Curie point is effective. is there. In the case of a multilayer film structure, the first and second magnetic films (1
1) and the relationship of the magnetization M ₁ and M ₂ (12) shall be allowed to the M _2> M ₁ when viewed at a temperature just below T _C1. [Operation] A first rare earth-transition metal alloy film (11) having a Curie point TC ₁ and having a rare earth sublattice magnetization dominant at a temperature lower than Tc ₁ and Tc
Transition metal at a temperature lower than a Tc ₁ high Curie point Tc ₂ than ₁ sublattice magnetization is dominant second rare earth - transition metal alloy film (12) and to directly adjacent so that the same sublattice magnetization is aligned with Thereby, the stray magnetic field can be reduced to zero or extremely small, and the second rare earth-transition metal alloy film (12) can be magnetically thickened by the difference of the Curie points during laser light irradiation. Since it becomes a thin single layer film, recording,
The external magnetic field required for erasing can be reduced. Then, the rare earth-transition metal alloy film (11), (12)
Are laminated, that is, a multilayer film structure having a plurality of exchange coupling interfaces, whereby the stray magnetic field can be further reduced and low magnetic field recording can be performed more effectively. [Examples] Magneto-optical disks (17) and (18) shown in FIGS. 8 and 9 were produced, and the dependence of the recording characteristics on the external magnetic field was evaluated. Each of the magneto-optical disks (17) and (18) comprises a transparent substrate (13), an interference film (14), a perpendicular magnetization film (10), and a protective film (15). The magneto-optical disk (17) shown in FIG.
Is composed of an amorphous Tb Fe CoCr thin film, and a Tb target and
The first one in which the composition ratio of Tb to Fe Co Cr is different by binary DC magnetron sputtering using a Fe Co Cr alloy target
The magnetic film (11) and the second magnetic film (12) were formed to have a three-layer structure. The magneto-optical disk (18) in FIG. 9 has a perpendicular magnetization film (10).
Is composed of an amorphous TbFeCoCr thin film as in FIG. 8, and the first magnetic film (1) having a different composition ratio of Tb to FeCoCr.
It was manufactured so as to have a five-layer structure of 1) and the second magnetic film (12). The first magnetic film (11) is a so-called Tb-rich film from room temperature to the Curie temperature, and its Curie temperature is 130 ° C.
The coercive force at room temperature is 2K Oe. The second magnetic film (12) is a so-called iron-group-rich film from room temperature to the Curie temperature, and has a Curie temperature of 160 ° C. and a coercive force of 2 K Oe at room temperature. Since the ratio of the magnetization of the first magnetic film (11) to the magnetization of the second magnetic film (12) is about 3 to 1 at 100 ° C., the total magnetization around this temperature is reduced to zero. 1 magnetic film (1
The total film thickness of 1) was set to 600 mm, and the total film thickness of the second magnetic film (12) was set to 200 mm. The thickness of each of the second magnetic films (12) having a high Curie temperature was set to 100 °. A carrier frequency of 2.7 MHz and a linear velocity of 3.8 m / sec were applied to the magneto-optical disks (17) and (18) shown in FIGS.
The external magnetic field dependence of the recording characteristics under the following conditions was evaluated. In order to compare these magneto-optical disks (17) and (18) with the conventional magneto-optical disk, the magnetic compensation temperature between room temperature and the Curie temperature is relatively small as a magnetic single-layer film with a relatively small stray magnetic field during recording. Tb Fe Co Cr single-layer film with a thickness of 800
The evaluation of the magneto-optical disk of Å) was also performed. FIG.
The evaluation result of the magneto-optical disk (17) shown in FIG.
FIG. 12 shows the evaluation result of the magneto-optical disk (18) shown in the figure, and FIG. 12 shows the evaluation result of the conventional magneto-optical disk. As is clear from FIGS. 10 and 11, in the case of a magneto-optical disk having a perpendicular magnetization film having a multilayer structure (the present invention), a complete recording and erasing state is achieved with an external magnetic field of about ± 100 Oe. On the other hand, as shown in FIG. 12, in the case of a conventional magneto-optical disk having a magnetic single-layer film, recording is performed with an external magnetic field of +100 Oe and erased by an external magnetic field of -300 Oe. Therefore, when the perpendicular magnetization film has the multilayer structure of the present invention, the external magnetic field for recording and erasing can be reduced to about half as compared with the conventional case. It should be noted that a large amount of iron group film (200
In the case of a magnetic disk consisting of Å) and a large amount of Tb film (600 Å), the recording characteristics are inferior to those of a conventional magnetic single-layer magneto-optical disk, and erasing must be performed unless approximately -500 Oe is applied. Could not. [Effects of the Invention] According to the magneto-optical recording medium of the present invention, the generation of a stray magnetic field is eliminated, and a magnetically thin single-layer film is used, so that an external magnetic field required for recording and erasing can be reduced. . Therefore, overwriting by the external magnetic field modulation method can be easily performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing spontaneous magnetization of a perpendicular magnetization film of a magneto-optical recording medium according to the present invention, and FIG. 2 is a diagram of a sub-lattice magnetization forming the state of magnetization shown in FIG. FIGS. 3 and 4A to C schematically show the arrangement, and FIGS.
5 to 7 show other examples of the perpendicular magnetization film of the present invention, showing the distribution of Curie temperature and magnetization in the film thickness direction. FIGS. 8 and 9 are used for evaluating the recording characteristics of the present invention. Example of magneto-optical disk, FIG. 10 is a diagram of the evaluation result of the magneto-optical disk of FIG. 8, FIG. 11 is a diagram of the evaluation result of the magneto-optical disk of FIG. 9, and FIG. FIG. 13 is a sectional structural view of a conventional magneto-optical recording medium, and FIG.
FIG. 14 is an explanatory diagram of the magnetization state, and FIG. 15 is an explanatory diagram of the generation of a stray magnetic field. (10) is a perpendicular magnetic film, (11) is a first magnetic layer, and (12) is a second magnetic layer.

Claims (1)

(57) [Claims] First rare earth at a temperature lower than the T _C1 has a Curie point T _C1 predominant rare earth sublattice magnetization - the comprises a transition metal alloy film, a Curie point T _C2 higher than the Curie point T _C1
A second rare earth-transition metal alloy film in which transition metal sublattice magnetization is predominant at a temperature lower than T _C1 , wherein the first rare earth-transition metal alloy film is Wherein the first and second rare earth-transition metal alloy films are each laminated at least one layer in total and three or more layers in total, so that the same sublattice magnetization is aligned. recoding media.