JPH09204699A - Multilayer magnetooptic recording medium capable of multilevel recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a step for recording an intermediate level state conventionally required in field modulation recording system or magnetic transfer system in order to initially bring about a magnetization state of an intermediate level recording layer, i.e., a third magnetization layer, having recording density smaller than the diameter of light spot. SOLUTION: A multilayer magnetooptic recording medium 18 comprises first to third magnetic layers 11, 12, 13 having perpendicular magnetic anisotropy laminated on a substrate 10. Adjacent layers are mutually exchange coupled wherein the intermediate level recording layer, i.e., the third magnetization layer 13, employs a material having such composition as (a) the Curie points Tc1, Tc2 and Tc3 of respective magnetic layers satisfy the following relations Tc1<Tc2, Tc3<Tc2, and (b) the ratio of remanent magnetization and saturation magnetization, i.e., the squareness ratio θ, satisfies a relation 0<θ<1 and a plurality of domains are present within the diameter of spot light employed for recording/reproduction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layered magneto-optical recording medium capable of multilevel recording of three or more levels. More specifically, the present invention relates to a multi-layered magneto-optical recording medium in which the median value recording layer exhibits magnetic characteristics such that the squareness ratio θ is 0 <θ <1.

[0002]

2. Description of the Related Art FIG. 7 shows, for example, JP-A-6-22343.
FIG. 3 is a cross-sectional explanatory view showing a configuration of a conventional multi-layered magneto-optical recording medium capable of multi-valued recording shown in Japanese Patent Publication No. In the figure, reference numeral 20 is a substrate, and 21 to 24 are first magnetic layers (memory layers) 21, second magnetic layers (recording layers) 22, and third magnetic layers formed on the substrates and having perpendicular magnetic anisotropy. Layer (switch layer) 23 and fourth magnetic layer (intermediate value recording layer) 24
These layers are bonded to the adjacent layers by the exchange force, and the substrate 20 and the magnetic layers 21 to 24 constitute the conventional multilayer magneto-optical recording medium 27. Here, the exchange forces act so that the sublattice magnetizations of the adjacent magnetic layers are parallel to each other. A magnetic field modulation head 26 generates an external magnetic field. Each magnetic layer 21
The relationship between the Curie temperatures of ~ 24 is that when the respective Curie temperatures are expressed as Tc1, Tc2, Tc3, and Tc4,
It is expressed by the following equation.

Tc4>Tc2>Tc1> Tc3 Formula (1) Next, the recording operation of the conventional magneto-optical recording medium configured as described above will be described. FIG. 8 is an explanatory view schematically showing the operation of the above-mentioned conventional multilayered magneto-optical recording medium for each temperature range. Since the substrate 20 is not directly related to the above operation, the substrate 20 is omitted in FIG. After such a conventional magneto-optical recording medium is formed into a film, first, in the conventional multi-layered magneto-optical recording medium 27, a magnetic field modulation recording method or It is recorded in the magnetization state of the fourth magnetic layer 24 by a magnetic transfer method to form an intermediate value recording layer. In FIG. 8, the white arrow indicates the transition metal sublattice magnetic moment, the shaded portion indicates the magnetization (intermediate value recording) state with a recording density smaller than the light spot diameter, and the white portion rises above the Curie temperature to lose ferromagnetism. , And the horizontal stripe arrow indicates the external magnetic field. In FIG. 8, the first magnetic layer 2 is shown with the intermediate value recording layer formed (illustrated as z).
The first, second magnetic layer 22 and the third magnetic layer 23 are shown as shaded portions, and the fourth magnetic layer 24 is shown as an upward white dot portion, a shaded portion and a downward shaded portion.

Since the rare earth-transition metal alloy film used as the magneto-optical recording material used in such a magneto-optical recording medium is a ferrimagnetic material, the magnetic moment of the rare earth metal and the magnetic moment of the transition metal are opposite to each other. They are in a parallel state, and the apparent magnetization is observed as the difference between their magnetic moments. The magnetic moment of the rare earth metal is the rare earth sublattice magnetic moment.

In FIG. 8, when each magnetic layer is heated to near the Curie temperature Tc1 of the first magnetic layer 21 by irradiation with laser light having a light intensity PL (shown as PL), the second magnetic layer in an intermediate value recording state. The sublattice magnetization state of 22 is transferred to the first magnetic layer 21, and the first magnetic layer 21 enters the intermediate value recording state. Here, the vicinity of Tc1 means that the exchange force received by the first magnetic layer is higher than Tc1 and not higher than the magnetization reversal temperature of the second magnetic layer (lower than Tc2 and higher than Tc1). Temperature above the coercive force of the layer (T
temperature lower than c1). In the following description, the expression TcX neighborhood is described with the same meaning.
At this time, the third magnetic layer 23 and the fourth magnetic layer 24 do not particularly contribute to the operation, and even if the magnetization of the third magnetic layer 23 disappears (b-2), the fourth magnetic layer 24 and It is magnetized so as to return to the original state by the exchange force, and the intermediate value recording state "0", that is, the low power process (b-2 and b-
3) is performed.

Further, in FIG. 8, by irradiating a laser beam having a light intensity PH (shown as PH ⁺ or PH ⁻ including the direction of the external magnetic field), each magnetic layer is moved to near the Curie temperature Tc2 of the second magnetic layer 22 (Tc4 The temperature lower than Tc2 and higher than Tc2 to a temperature at which the exchange force received by the second magnetic layer is equal to or higher than the coercive force of the second magnetic layer), the first magnetic layer 21 and the third magnetic layer 23. Magnetization disappears, but the fourth
The magnetization direction of the magnetic layer 24 does not change. The sub-lattice magnetization of the second magnetic layer 22 does not receive the exchange force from the first magnetic layer 21 and the third magnetic layer 23, and when the external recording magnetic field is upward (shown as PH ⁺ ), the magnetic field is increased. The direction is upward (a-1). Next, when each magnetic layer is cooled to a temperature lower than the Curie temperature Tc1 of the first magnetic layer 21, the sub-lattice magnetization of the second magnetic layer 22 is transferred to the first magnetic layer 21, and the first magnetic layer 21 is transferred. The sublattice magnetization of 21 is upward (a-2). Further, when the temperature of each magnetic layer is lowered to a temperature lower than the Curie temperature Tc3 of the third magnetic layer 23, the third magnetic layer 23 and the fourth magnetic layer 24 are in the intermediate value recording state. When the temperature further lowers, the second magnetic layer 22 is aligned with the fourth magnetic layer 24 through the third magnetic layer 23 to be in the intermediate value recording state (a-3), and the upward magnetization state is "+1".
The high power processes (a-1, a-2 and a-3) are performed. Similarly, when the external recording magnetic field is downward (shown as PH ⁻ ) when the laser beam having the light intensity PH is irradiated, the high power process (c-1, c-2) of the downward magnetization state “−1” is performed.
And c-3) are performed. As described above, the state “−1”, the state “0”, and the state “+” are obtained by modulating the direction of the external recording magnetic field and the recording laser intensity into at least two values.
It becomes possible to record three values of "1".

[0007]

In the conventional multi-level recordable multi-layered magneto-optical recording medium, the magnetization state of the fourth magnetic layer, which is the intermediate value recording layer, is first set to a portion smaller than the size of the light spot diameter. In order to obtain a recording density that magnetizes only, recording is performed by a magnetic field modulation recording method or a magnetic transfer method. According to the magnetic field modulation recording method, it is not possible to increase the modulation speed of the external recording magnetic field for recording at a recording density that magnetizes only a portion smaller than the size of the optical spot diameter. In addition, it takes a long time to form the intermediate value recording state, so that there is a problem that productivity is low.

In the magnetic field modulation recording method or the magnetic transfer method, it is assumed that the temperature is higher than the Curie temperature of the fourth magnetic layer, which is the intermediate value recording layer, which is estimated to be 300 ° C. or higher. It may damage the magnetic film. That is, polycarbonate, which is a commonly used substrate material, is deformed or deteriorated at about 150 ° C., while the magnetic film is deteriorated in magnetic property when kept at a high temperature of 300 ° C. or higher for a long time.

According to the present invention, the productivity of the conventional multi-level recordable multi-layered magneto-optical recording medium as described above, especially the risk of damage to the substrate and the magnetic film due to temperature rise in forming the intermediate value recording layer. It was made for the purpose of solving the problem that, by selecting the material and the magnetic characteristics used for the intermediate value recording layer, the intermediate value recording forming step itself becomes unnecessary,
An object of the present invention is to obtain a multi-layered magneto-optical recording medium capable of multi-valued recording with excellent productivity.

[0010]

According to the present invention, the ratio between the residual magnetization and the saturation magnetization is a squareness ratio θ (hereinafter simply referred to as a squareness ratio θ).
When the squareness ratio θ is room temperature, a magnetic material having a magnetic characteristic of 0 <θ <1 and a size of a light spot used for recording / reproducing having a composition including a plurality of magnetic domains are intermediate. By using it for the value recording layer, the light intensity at the time of recording is modulated and the intermediate value recording state is transferred as it is, and the magnetization states “+1” and “−1” determined by the direction of the external recording magnetic field. The three values are recorded. The squareness ratio θ is the saturation magnetization, which is the magnitude of magnetization when the magnetic layer is uniformly magnetized by a sufficient external magnetic field (in the absence of domain walls), and the magnitude of magnetization when the external magnetic field is zero. And the residual magnetization (equation 2). The method of observing the squareness ratio will be described later.

Squareness ratio θ = remanent magnetization / saturation magnetization (2) In the multilayer magneto-optical recording medium of the present invention, three layers from a first magnetic layer having perpendicular magnetic anisotropy to a third magnetic layer are laminated on a substrate. And (a) the Curie temperature of the first magnetic layer is Tc1 and the Curie temperature of the second magnetic layer is Tc.
When the Curie temperatures of the second and third magnetic layers are expressed as Tc3, the Curie temperatures Tc1, Tc2, and Tc3 have a relationship of Tc1 <Tc2 and Tc3 <Tc2, and (b) the squareness ratio θ of the third magnetic layer is room temperature. At
It is characterized in that it exhibits magnetic characteristics such that 0 <θ <1, and the size of the light spot diameter used for recording / reproduction is a size including a plurality of magnetic domains.

In the multilayer magneto-optical recording medium of the present invention, it is preferable that the third magnetic layer is made of a rare earth-transition metal alloy.

Further, it is preferable that the rare earth metal of the rare earth-transition metal alloy is Tb, the transition metal is one of Fe and FeCo, and the magnetic characteristics are 0 <θ <1.

In the multilayer magneto-optical recording medium of the present invention, it is preferable that the Curie temperature Tc3 of the third magnetic layer is 200 ° C. or lower.

The recording method of the present invention uses the multilayer magneto-optical recording medium of the present invention. (C) When the recording laser beam is irradiated with a low power, the multi-domain magnetization state of the third magnetic layer is irrespective of the direction of the external magnetic field. The multi-domain intermediate value recording state is achieved by transferring to the first magnetic layer, and (d) high power irradiation causes the first and second magnetic layers to be recorded.
And a multi-layered magneto-optical recording method that enables at least ternary recording by setting each of the third magnetic layers into a magnetized state determined by the direction of the external magnetic field.

In the multilayer magneto-optical recording medium of the present invention, four layers of the first, second, third and fourth magnetic layers having perpendicular magnetic anisotropy are laminated on the substrate, and the layers are adjacent to each other. Is a multilayer magneto-optical recording medium exchange-coupled to each other, wherein (e) the coercive force of the first magnetic layer is larger than the exchange-coupling force received from the second magnetic layer, and (f) the first magnetic layer. The Curie temperature is Tc1, and the Curie temperature of the second magnetic layer is Tc.
When the Curie temperature of the second and third magnetic layers is represented by Tc3, the Curie temperatures Tc1, Tc2 and Tc3 have a relationship of Tc1 <Tc2 and Tc3 <Tc2, and (g) the second magnetic layer and the third magnetic layer. The sublattice magnetization directions of the magnetic layer and the fourth magnetic layer are aligned, and (h) the squareness ratio θ of the fourth magnetic layer is 0 <θ at room temperature.
The magnetic characteristic is <1 and the size of the light spot diameter used for recording and reproduction is a size including a plurality of magnetic domains.

In the multilayer magneto-optical recording medium of the present invention, it is preferable that the Curie temperature Tc4 of the fourth magnetic layer is higher than the Curie temperature Tc2 of the second magnetic layer.

In the multilayer magneto-optical recording medium of the present invention, it is preferable that the fourth magnetic layer has a magnetic characteristic of 0 <θ <1 and is made of CoCr.

In the multilayer magneto-optical recording medium of the present invention, it is preferable that the fourth magnetic layer has a magnetic characteristic of 0 <θ <1 and is made of either TbCo or TbFeCo.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, the squareness ratio θ exhibits magnetic characteristics such that 0 <θ <1 at room temperature, and the size of the light spot diameter used for recording / reproducing is a size including a plurality of magnetic domains. By using a material having the following composition for the intermediate value recording layer, the light intensity at the time of recording is modulated and the intermediate value recording state is directly transferred to "0" and the magnetization state "+1" determined by the direction of the external recording magnetic field. And -1 are recorded. The squareness ratio θ is determined by the ratio between the saturation magnetization and the remanent magnetization as described above, but the value of the saturation Kerr rotation angle is used as the saturation magnetization by the measurement of the Kerr hysteresis loop as shown in FIG. Is the external magnetic field =
Using the value of the Kerr rotation angle at 0, the squareness ratio θ can be obtained by the above equation (1). Alternatively, it can be obtained by measuring a magnetic hysteresis loop using a vibrating sample magnetometer (VSM).

The recording mechanism of the multi-layered magneto-optical recording medium including the intermediate value recording layer according to the present invention is as described below. That is, when the recording laser intensity PH is applied, the recording state "-" is changed depending on the direction of the external recording magnetic field.
When "1" or "+1" is recorded and the recording laser intensity PL of which the recording laser intensity is lower than PH is irradiated, the magnetization state is determined by the intermediate value recording layer regardless of the direction of the external recording magnetic field magnetic field. The intermediate value recording state “0” is recorded by transferring the magnetization state of the magnetic layer to the first magnetic layer.
In this way, by modulating the direction of the external recording magnetic field and the recording laser intensity to at least two values or more, three-value recording of “upward”, “downward”, and “intermediate value (multi-domain)” states on the first magnetic layer. do.

An intermediate layer can be provided between the above-mentioned magnetic layers. Further, in both the first and second aspects, a reproduction layer can be provided to increase the reproduction signal.

The multi-layer recordable magneto-optical recording medium according to the present invention will be described in more detail below with reference to the accompanying drawings. However, the present invention is not limited to the following examples.

[Embodiment 1] FIG. 1 is a sectional view showing the structure of a multi-layered magneto-optical recording medium capable of multilevel recording according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 10 is a substrate, and 11, 12 and 13 are respectively a first magnetic layer, a second magnetic layer and a third magnetic layer having perpendicular magnetic anisotropy formed on this substrate. Are coupled to layers adjacent to each other by exchange force, and these substrate 10 and magnetic layer 1 are
The multilayer magneto-optical recording medium 18 of the present invention is composed of 1, 12 and 13. An external magnetic field generator 17 generates an external magnetic field.

The recording operation of the magneto-optical recording medium of the present invention configured as described above will be described below. FIG. 2 is an explanatory view schematically showing the recording mechanism of the present invention. Since the substrate 10 is not directly related to the recording operation, the substrate 10 is omitted in FIG. In FIG. 2, the white arrow indicates the transition metal sublattice magnetic moment, the shaded area indicates the magnetization (intermediate value recording) state with a recording density smaller than the light spot diameter, and the white area increases the temperature above the Curie temperature and the ferromagnetism is lost. The state
The horizontal stripe arrows indicate the external magnetic field. FIG.
In the state where the intermediate value recording layer is formed (shown as z), the first magnetic layer 11 and the second magnetic layer 12
Shows a shaded portion, and the third magnetic layer has an upward arrow, a shaded portion, and a downward shaded portion.

In FIG. 2, when each magnetic layer is heated to near the Curie temperature Tc1 of the first magnetic layer 11 by irradiation with laser light having a light intensity PL (shown as PL), the second magnetic layer in the intermediate value recording state. The sublattice magnetization state of No. 12 is transferred to the first magnetic layer 11, and the first magnetic layer 11 enters the intermediate value recording state (b-2). At this time, the third magnetic layer 13 does not particularly contribute to the operation, and the intermediate value recording state is "0", that is, the low power process (b-2 and b-).
3) is performed.

In FIG. 2, each magnetic layer is heated to near the Curie temperature Tc2 of the second magnetic layer 12 by irradiation with laser light having a light intensity PH (shown as PH ⁺ or PH ⁻ including the direction of the external magnetic field). Then, the magnetizations of the first magnetic layer 11 and the third magnetic layer 13 disappear, and the first magnetic layer 11
And the exchange force from the third magnetic layer 13 is not received. Also,
At this time, the direction of the sub-lattice magnetization of the second magnetic layer 12 is upward (a-1) which is the magnetic field direction when the external recording magnetic field is upward (shown as PH ⁺ ). Next, when each magnetic layer is cooled to a temperature lower than the Curie temperature Tc1 of the first magnetic layer 11, the state of the sub-lattice magnetization of the second magnetic layer 12 is transferred to the first magnetic layer 11, and the first magnetic layer The direction of the sublattice magnetization of 11 is upward (a-2). Further, when the temperature of each magnetic layer is lowered to a temperature lower than the Curie temperature Tc3 of the third magnetic layer 13, the third magnetic layer 13 has a magnetic characteristic that the squareness ratio θ is smaller than 1. It means that it is energetically unstable, and stabilizes in a state in which a domain wall is formed and multi-domains are formed (multi-domain state). At this time, the size of the light spot diameter of the laser light irradiation is a size including a plurality of magnetic domains. The multi-domain state of the third magnetic layer 13 is transferred to the second magnetic layer 12,
The magnetic layer 12 is in a multi-domain state. At this time, since the coercive force of the first magnetic layer 11 is larger than the exchange coupling force that the first magnetic layer 11 receives from the second magnetic layer 12, the magnetization state of the first magnetic layer 11 does not change (a-3). . In this way, the high power process (a) of the upward magnetization state “+1” is applied to the first magnetic layer 11.
-1, a-2 and a-3) are performed. Light intensity as well
If the external recording magnetic field at the time the laser beam irradiation of PH is downward ^- downward magnetization state "-1" in the high power process is (c-1, c-2 and c-3) is performed (PH shown as). As described above, by modulating the direction of the external recording magnetic field and the recording laser intensity into at least two values, three-value recording of the state "-1", the state "0" and the state "+1" becomes possible.

FIG. 3 is an explanatory view schematically showing the recording / reproducing method of multi-valued (three-valued) information according to the first embodiment.
(A), 3 (b), 3 (c) and 3 (d) are shown in FIG.
Magnetization sections on the recording track of (a) and FIGS.
The values of the reproduction signal, the value of the recording power, and the value of the external recording magnetic field shown in (c) and 3 (d) are shown so as to correspond to each other. In FIG. 3A, 31 is a recording track,
Reference numeral 32 denotes a light spot, which indicates that the area is irradiated with the light spot, whereby FIG. 3A shows the magnetization state on the recording track 31. FIG.
In (b), the reproduction signal has, for example, an S-state magnetization (white).
"-1" in case of, "+" in case of N state (black)
1 ”, it becomes“ 0 ”in the state of plural magnetic domains (recording of intermediate value). In the recording method, in order to perform the recording shown in FIG. 3A, the laser light intensity at the time of recording is set to "PH (PH ⁺ or P when the magnetization state is" S "or" N ".
H ⁻ ) ”, the external magnetic field at this time is“ −Hb ”or“ + Hb ”, and the laser light intensity is“ PL ”at the time of recording the intermediate value (FIGS. 3C and 3D). The external magnetic field at the time of recording the intermediate value may be either “+ Hb” or “−Hb”.

[0029]

[Table 1]

The composition, film thickness and Curie temperature of each magnetic layer of the multi-layered magneto-optical recording medium according to the present invention capable of recording multi-valued information are 1
An example is shown in Table 1. In Table 1, the numerical values in the composition formula represent the composition ratio of elements and the like. For example, Tb ₂₄ (Fe ₉₅ Co ₅ ) ₇₆ of the first magnetic layer has Tb of ₂₄ atom% and F
e ₉₅ Co ₅ is 76 atom%, and Fe ₉₅ Co ₅ is Fe.
Is 95 atom% and Co is 5 atom%. The relationship between the Curie temperatures of the magnetic layers according to this embodiment is Tc1 <
Tc2 and Tc3 <Tc2, and the third magnetic layer has a rare earth-transition metal alloy Tb having a magnetic property of 0 <θ <1.
₁₂ (Fe ₉₃ Co ₇ ) ₈₈ was used. Since the rare earth-transition metal alloy Tb ₁₂ (Fe ₉₃ Co ₇ ) ₈₈ has a large magnetic anisotropy at room temperature, a fine magnetic domain state can be obtained and the exchange force from the second magnetic layer can be obtained. Does not cause magnetization reversal. The Curie temperature Tc3 of the third magnetic layer is 20.
The temperature was set to 0 ° C. or lower so as not to affect the magnetization reversal of the second magnetic layer by the external magnetic field in the high power process. This multilayered magneto-optical recording medium was formed on a glass substrate having a groove by a sputtering method. In addition to these multilayer magnetic films, a silicon nitride film was formed between the substrate and the first magnetic layer and on the third magnetic layer. Although the glass substrate with the groove is used as the substrate in the first embodiment, a resin substrate such as polycarbonate may be used.

FIG. 4 is a graph showing the Kerr hysteresis loop of the multilayer magneto-optical recording medium of the present invention measured from the side of the third magnetic layer at room temperature after film formation. While the squareness ratio of the magnetic film normally used for the magneto-optical recording medium was "1", the squareness ratio θ of the third magnetic layer of Example 1 was "0.1" from FIG. Squareness ratio of hysteresis loop θ <
A value of 1 indicates that the multi-domain state is stable under no magnetic field.

In the conventional example, since a magnetic film having a squareness ratio of θ = 1 is used for the fourth magnetic layer in the multi-domain state, it is necessary to form an intermediate value recording state by a magnetic field modulation recording method or a magnetic transfer method after film formation. Although a step was required, an intermediate value recording state forming step is performed by using a material having magnetic characteristics such that the squareness ratio θ is 0 <θ <1 as in the first embodiment of the present invention. Could be eliminated.

[Embodiment 2] In this embodiment, an example in which an intermediate layer is provided between magnetic layers will be described. FIG. 5 shows a second embodiment of the present invention.
FIG. 3 is an explanatory sectional view showing the structure of the multi-layered magneto-optical recording medium capable of multi-valued recording. In FIG. 5, 10 is a substrate, 11 and 1
Reference numerals 2 and 13 respectively denote a first magnetic layer, a second magnetic layer, and a third magnetic layer having perpendicular magnetic anisotropy formed on this substrate, and these layers are coupled to adjacent layers by exchange force. 15 is an intermediate layer and 16 is a reproducing layer. Table 2 shows an example of the composition, film thickness and Curie temperature of each magnetic layer and the intermediate layer of the multilayer magneto-optical recording medium according to this example. The relationship between the Curie temperatures of the magnetic layers and the materials used for the magnetic layers are the same as in the first embodiment. Here, a reproducing layer 16 exchange-coupled with the first magnetic layer 11 and having perpendicular magnetic anisotropy is provided between the first magnetic layer and the substrate 10 in order to increase a reproduced signal. An intermediate layer 15 is provided between the first magnetic layer 11 and the second magnetic layer 12 to control the exchange coupling force between these magnetic layers. Here, by using a magnetic layer having a small perpendicular magnetic anisotropy or an in-plane magnetic anisotropy as the intermediate layer 15, the interface domain wall energy between the first magnetic layer 11 and the second magnetic layer 12 is reduced. You can Thus, the first magnetic layer 11 and the second magnetic layer 12 are formed by the intermediate layer 15.
The exchange coupling force between can be controlled. Recording layer and intermediate layer
This is added to improve the reproduction characteristics and performance such as stability, and basically the basic characteristics of the present invention can be obtained by the first, second and third magnetic layers. The recording operation mechanism of this embodiment is similar to that of the first embodiment. In addition to this, there is a case where a good thermal conductor layer is added to the third magnetic layer directly or through an insulator or the like. In such a case, aluminum or the like is formed as a good thermal conductor by the sputtering method in the same manner as in the case of each of the other magnetic layers when the recording film is formed.
As a result of the fact that the temperature distribution of the recording film due to the irradiation of the recording laser beam can be controlled by adding the thermal conductive layer, (1) the effect of expanding the margins of the recording laser intensity PH and PL, (2) the four-layer structure medium It is possible to obtain the effect of suppressing the temperature rise up to the Curie temperature Tc4 or higher of the fourth magnetic layer or the magnetization reversal temperature.

[0034]

[Table 2]

[Embodiment 3] FIG. 6 is a sectional view showing the structure of a multi-layered magneto-optical recording medium capable of multilevel recording according to Embodiment 3 of the present invention. In FIG. 6, 10 is a substrate, and 1
Reference numerals 1, 12, 13 and 14 denote a first magnetic layer, a second magnetic layer, a third magnetic layer and a fourth magnetic layer having perpendicular magnetic anisotropy formed on this substrate, respectively, and these layers are mutually The first magnetic layer is coupled to an adjacent layer by exchange force, and the coercive force of the first magnetic layer is made larger than the exchange coupling force received from the second magnetic layer, so that the substrate 10 and the magnetic layers 11, 12, 13 and 14 are connected. , And an intermediate layer and a reproducing layer which will be described later constitute the multilayer magneto-optical recording medium 18 of the present invention. Also, the second, third and fourth
The sub-lattice magnetization directions of the three magnetic layers are aligned. Further, the relationship of Curie temperature of each magnetic layer is Tc1 <Tc
2 and Tc3 <Tc2. In the recording medium 18, a reproducing layer 16 exchange-coupled with the first magnetic layer 11 and having perpendicular magnetic anisotropy is provided between the substrate 10 and the first magnetic layer 11 to increase a reproduced signal, and An intermediate layer 15 is provided between the first magnetic layer 11 and the second magnetic layer 12 to control the exchange coupling force between these magnetic layers. An external magnetic field generator 17 generates an external magnetic field.

[0036]

[Table 3]

The recording operation of the magneto-optical recording medium of the present invention configured as described above will be described with reference to FIG. FIG.
FIG. 4 is an explanatory view schematically showing the above-mentioned conventional multilayered magneto-optical recording medium for each temperature range.
The recording operation of the magneto-optical recording medium of this embodiment will be described with reference to the recording operation of the magnetic layer. In addition, the four magnetic layers 11, 12, 13, 14 of the first to the fourth according to the present embodiment.
Since the structural arrangement is the same as that of the conventional multi-layered magneto-optical recording medium, the magnetic layer 1 of this embodiment will be described with the same FIG. 8 for convenience.
1, 12, 13, and 14 in FIG.
3 and 24 will be described. Since the reproducing layer and the intermediate layer according to this embodiment are not related to the recording operation itself, their description will be omitted. In FIG. 8, the white arrow indicates the transition metal sublattice magnetic moment, the shaded portion indicates the magnetization (intermediate value recording) state with a recording density smaller than the light spot diameter, and the white portion rises above the Curie temperature to lose ferromagnetism. , And the horizontal stripe arrow indicates the external magnetic field.
In FIG. 8, when the temperature of each magnetic layer is raised to near the Curie temperature Tc1 of the first magnetic layer 21 by irradiation with a laser beam having a light intensity PL (illustrated as PL), the sub magnetic field of the second magnetic layer 22 in the intermediate value recording state is increased. The state of lattice magnetization is transferred to the first magnetic layer 21, and the first magnetic layer 21 becomes the intermediate value recording state (b-2). At this time, the third magnetic layer 23 and the fourth magnetic layer 24
Does not particularly contribute to the operation, and even if the magnetization of the third magnetic layer 23 disappears (b-2), it is magnetized so as to return to the original state by the exchange force with the fourth magnetic layer 24, The intermediate value recording state "0", that is, the low power process is performed. Further, in FIG. 8, when the temperature of each magnetic layer is raised to near the Curie temperature of the second magnetic layer 22 by irradiation with laser light having a light intensity PH (shown as PH ⁺ or PH ⁻ including the direction of the external magnetic field), The magnetizations of the first magnetic layer 21 and the third magnetic layer 23 do not receive exchange forces from other magnetic layers due to disappearance, and the direction of sublattice magnetization of the second magnetic layer 22 is when the direction of the external recording magnetic field is upward. (Illustrated as PH ⁺ )
The magnetic field direction is upward (a-1). Next, the Curie temperature Tc1 of the first magnetic layer 21 is set to each magnetic layer.
When the temperature is lowered to a lower temperature, the sub-lattice magnetization of the second magnetic layer 22 is transferred to the first magnetic layer 21 and the first magnetic layer 2
The sub-lattice magnetization of 1 is upward (a-2). Furthermore the third
When the temperature is lowered to below the Curie temperature Tc3 of the magnetic layer 23 and the magnetization occurs, the third magnetic layer 23 is magnetized by the fourth magnetic layer 24 due to the exchange force, that is, the multi-domain state in the intermediate value recording state. Then, the second magnetic layer 22 also enters the intermediate value recording state by the exchange force from the third magnetic layer 23. At this time, since the coercive force of the first magnetic layer 21 is larger than the exchange coupling force that the first magnetic layer 21 receives from the second magnetic layer 22, the magnetization state of the first magnetic layer 21 does not change. Thus, the high power process (a-1, a-2 and a-3) is performed. Similarly, when the external recording magnetic field is downward (shown as PH ⁻ ) when the laser beam with the light intensity PH is irradiated, the high power process (c-1, c-2) of the downward magnetization state “−1” is performed.
And c-3) are performed. As described above, by modulating the direction of the external recording magnetic field and the recording laser intensity into at least two values, three-value recording of the state "-1", the state "0" and the state "+1" becomes possible.

The composition, film thickness and Curie temperature of each magnetic layer of the multi-layered magneto-optical recording medium according to the present invention capable of recording multi-valued information are 1
An example is shown in Table 3. The fourth magnetic layer according to this embodiment includes
Cr ₁₅ Co ₈₅ having a magnetic property of 0 <θ <1 was used. Since Cr ₁₅ Co ₈₅ has a large perpendicular magnetic anisotropy from room temperature to the recording operation temperature, it is possible to obtain a fine magnetic domain state and the fourth magnetic layer using Cr ₁₅ Co ₈₅ has T
Since c4> Tc2, the magnetization reversal due to the exchange force from the second magnetic layer does not occur. This multi-layered magneto-optical recording medium was formed by sputtering on a glass substrate with grooves. In addition to these multilayer magnetic films, a silicon nitride film was formed between the substrate and the reproducing layer and on the fourth magnetic layer. Example 3
Although the glass substrate with the groove is used as the substrate, a resin substrate such as polycarbonate may be used. The reproducing layer and the intermediate layer are added to improve recording / reproducing characteristics and performance such as stability, and basically, the present invention includes the first, second, third and fourth magnetic layers. The basic characteristics of can be obtained.

The Kerr hysteresis loop measured from the fourth magnetic layer side at room temperature after the formation of the four magnetic layers, the reproducing layer and the intermediate layer was the same as that shown in FIG. Normally, the squareness ratio of the magnetic film used for the magneto-optical recording medium was "1", while from Fig. 4, the squareness ratio θ of the fourth magnetic layer of Example 1 was "0.1". The fact that the squareness ratio θ of the hysteresis loop is θ <1 indicates that the multi-domain state is stable in the absence of a magnetic field.

In the conventional example, since a magnetic film having a squareness ratio θ = 1 is used for the fourth magnetic layer, a step for forming an intermediate value recording state by magnetic field modulation recording or magnetic transfer is required after the film formation. However, by using a material having magnetic characteristics such that the squareness ratio θ is 0 <θ <1 as in the third embodiment of the present invention, the intermediate value recording state forming step can be omitted. It was

[Embodiment 4] In this embodiment, an example in which a material different from that of Embodiment 3 is used for the fourth magnetic layer and an intermediate layer 15 is provided between the magnetic layers as in Embodiment 3 will be described. The structure of the multi-layered magneto-optical recording medium capable of multi-valued recording according to the present embodiment is the same as that of the third embodiment, and will be described below with reference to FIG.

Table 4 shows an example of the composition, film thickness and Curie temperature of each magnetic layer and the intermediate layer of the multilayered magneto-optical recording medium according to this example.

[0043]

[Table 4]

Tb ₁₂ Co ₈₈ shown in Table 4 having a magnetic characteristic of 0 <θ <1 was used for the fourth magnetic layer according to this example. Although not shown in the table, TbFeC was formed in the fourth magnetic layer.
It is also possible to use o and it has the same effect. TbCo and TbFeCo whose magnetic properties are 0 <θ <1
Has a large magnetic anisotropy from room temperature to the recording operating temperature, it is possible to obtain a fine magnetic domain state, and the fourth magnetic layer using any of these has a second magnetic layer.
The magnetization reversal due to the exchange force from the magnetic layer does not occur. Here, a reproducing layer 16 exchange-coupled with the first magnetic layer 11 and having perpendicular magnetic anisotropy is provided to increase a reproduced signal. In addition, the first magnetic layer 11 and the second magnetic layer 12
In between, an intermediate layer 15 is provided to control the exchange coupling force between these magnetic layers. The reproducing layer and the intermediate layer are added for improving performance such as recording / reproducing characteristics and stability. Basically, the four magnetic layers of the first magnetic layer to the fourth magnetic layer form the basic characteristics of the present invention. available. The recording operation mechanism of this embodiment is similar to that of the third embodiment. In addition to this, there is a case where a good thermal conductor layer is added to the fourth magnetic layer directly or through an insulator. The structure and operation in this case are the same as those in the second embodiment.

The most practically preferred embodiment of the present invention will be described.

First, a multi-layered magneto-optical recording medium consisting of four layers of magnetic films, first to fourth, was formed on a grooved substrate by a sputtering method. In addition to these four layers of magnetic film, a silicon nitride film was formed between the substrate and the reproducing layer and on the fourth magnetic layer to a film thickness of 700Å and 1000Å, respectively. Table 4 shows the composition, film thickness and Curie temperature of each magnetic layer. T having a large perpendicular magnetic anisotropy in the fourth magnetic layer
By using a composition of magnetic characteristics with a squareness ratio of about 0.1 in the bCo film, the fourth magnetic layer is always multi-domain with a domain size of 1000 Å or less, linear velocity LV = 9 m / sec, frequency f = 1 MHz, recording magnetic field. Ternary recording was obtained by binary modulation of (± 250 Oe) and recording laser intensity (PH / PL = 10 mW / 4 mW). Due to these effects, the multi-layered magneto-optical recording medium of the present invention capable of multi-valued recording eliminates the step of forming the intermediate value recording state, which has been conventionally required, and improves the productivity.

[0047]

EFFECTS OF THE INVENTION The median value recording layer exhibits a magnetic characteristic that the squareness ratio θ is 0 <θ <1 at room temperature, and the size of the light spot diameter used for recording / reproducing is a size including a plurality of magnetic domain states. By using a material having the following composition, the light intensity at the time of recording is modulated and the intermediate value recording state is directly transferred to "0", and the magnetization states "+1" and "-1" determined by the direction of the external recording magnetic field. Is recorded.

In the multilayer magneto-optical recording medium of the present invention, three layers, that is, a first magnetic layer to a third magnetic layer having perpendicular magnetic anisotropy are laminated on a substrate, and adjacent layers are exchange-coupled with each other. (A) the Curie temperature of the first magnetic layer is Tc1, the Curie temperature of the second magnetic layer is Tc2, and the Curie temperature of the third magnetic layer is Tc.
When expressed as 3, the Curie temperatures Tc1, Tc2 and T
The relationship of c3 is Tc1 <Tc2 and Tc3 <Tc2, and (b) the squareness ratio θ of the third magnetic layer is at room temperature,
Since the magnetic property of 0 <θ <1 is exhibited and the size of the light spot diameter used for recording / reproducing is a size including a plurality of magnetic domains, the step of forming the intermediate value recording state which is conventionally required is unnecessary. Has the effect of

Further, since the third magnetic layer is made of a rare earth-transition metal alloy and has a large perpendicular magnetic anisotropy at room temperature, it becomes a fine magnetic domain state and the exchange force from the second magnetic layer. This has the effect that the magnetization reversal due to the magnetic field does not occur.

Further, the rare earth-transition metal alloy is composed of Tb as a rare earth metal and one of Fe and FeCo as a transition metal, and has a magnetic characteristic of 0 <θ <1, so that a large perpendicular magnetic anisotropy is obtained at room temperature. Because it has
The magnetic domain is in a fine magnetic domain state, and the magnetization reversal due to the exchange force from the second magnetic layer does not occur.

The Curie temperature Tc3 of the third magnetic layer
Is 200 ° C. or less, the Curie temperature is exceeded in the high power process, and there is an effect that it does not affect the magnetization reversal of the second magnetic layer due to the external magnetic field.

The recording method of the present invention uses the multi-layered magneto-optical recording medium of the present invention, and (c) multi-domain magnetization state of the third magnetic layer under low power irradiation of the recording laser light regardless of the direction of the external magnetic field. Is transferred to the first magnetic layer to be in a multi-domain intermediate value recording state, and (d) in high power irradiation, each of the first to third magnetic layers is in a magnetization state determined by the direction of the external magnetic field. There is an effect that three-value recording of the magnetization states “+1” and “−1” and the intermediate value recording state “0” can be performed by the light intensity modulation and the direction of the external recording magnetic field.

In the multilayer magneto-optical recording medium of the present invention, four layers from a first magnetic layer having a perpendicular magnetic anisotropy to a fourth magnetic layer are laminated on a substrate, and adjacent layers are exchange-coupled with each other. (E) the coercive force of the first magnetic layer is larger than the exchange coupling force received from the second magnetic layer, and (f) the Curie temperature of the first magnetic layer is T.
c1, the Curie temperature of the second magnetic layer is Tc2, and the third
When the Curie temperature of the magnetic layer is represented by Tc3, the Curie temperatures Tc1, Tc2 and Tc3 have a relationship of Tc1 <Tc2 and Tc3 <Tc2, and (g) the second magnetic layer, the third magnetic layer and the third magnetic layer. The sublattice magnetization directions of the four magnetic layers are aligned, and (h) the squareness ratio of the fourth magnetic layer is 0 <θ <at room temperature.
The magnetic property of 1 is obtained, and the size of the light spot diameter used for recording / reproducing includes a plurality of magnetic domains, so that there is an effect that the step of forming the intermediate value recording state, which is conventionally required, is unnecessary. .

The Curie temperature Tc4 of the fourth magnetic layer
Is higher than the Curie temperature Tc2 of the second magnetic layer, there is an effect that the magnetization reversal due to the exchange force from the second magnetic layer does not occur.

The magnetic characteristic of the fourth magnetic layer is 0 <
When θ <1, since it is made of CoCr and has a large perpendicular magnetic anisotropy from room temperature to the recording operation temperature, it is in a fine magnetic domain state, and there is an effect that magnetization reversal due to exchange force from the third magnetic layer does not occur. .

The magnetic characteristic of the fourth magnetic layer is 0 <
When θ <1, since it consists of either TbCo or TbFeCo and has a large perpendicular magnetic anisotropy from room temperature to the recording operating temperature, it becomes a fine magnetic domain state, and the magnetization reversal due to the exchange force from the third magnetic layer is caused. The effect that it does not occur is produced.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing a configuration of a multi-layered magneto-optical recording medium capable of multilevel recording according to Example 1 of the present invention.

FIG. 2 is an explanatory diagram illustrating a recording mechanism according to the first embodiment.

FIG. 3 is an explanatory diagram for explaining a method of recording / reproducing multi-valued (three-valued) information according to the first embodiment.

FIG. 4 is a graph showing a Kerr hysteresis loop obtained by measuring the magnetic characteristics of the multilayered magneto-optical recording medium of the present invention.

FIG. 5 is a cross-sectional explanatory view showing a configuration of a multi-layered magneto-optical recording medium capable of multilevel recording according to Example 2 of the present invention.

FIG. 6 is a cross-sectional explanatory view showing the structure of a multi-layered magneto-optical recording medium capable of multilevel recording according to Example 3 of the present invention.

FIG. 7 is an explanatory sectional view showing the structure of a conventional multi-layered magneto-optical recording medium capable of multilevel recording.

FIG. 8 is an explanatory diagram for explaining a recording mechanism of a conventional example.

[Explanation of symbols]

10 substrate, 11 first magnetic layer, 12 second magnetic layer, 1
3 3rd magnetic layer, 14 4th magnetic layer, 15 intermediate layer, 1
6 reproducing layer, 17 external magnetic field generator, 18 multilayered magneto-optical recording medium of the present invention, 20 substrate, 21 first magnetic layer, 22 second magnetic layer, 23 third magnetic layer, 24 fourth magnetic layer, 26 magnetic field Modulation head, 27 conventional multilayered magneto-optical recording medium, 31 recording tracks, 32 light spots.

Claims (9)

[Claims] 1. A first having perpendicular magnetic anisotropy on a substrate,
A multilayer magneto-optical recording medium in which three layers of a second magnetic layer and a third magnetic layer are laminated, and adjacent layers are exchange-coupled to each other, and (a) the Curie temperature of the first magnetic layer is Tc.
1. When the Curie temperature of the second magnetic layer is Tc2 and the Curie temperature of the third magnetic layer is Tc3, the Curie temperatures Tc1, Tc2 and Tc3 are Tc1 <Tc2 and Tc3 <Tc2, and (b) When the ratio of the residual magnetization to the saturation magnetization is represented by a squareness ratio θ, the squareness ratio of the third magnetic layer is
A multi-layered magneto-optical recording medium exhibiting a magnetic characteristic of 0 <θ <1 and having a size of a light spot diameter used for recording / reproducing that includes a plurality of magnetic domains. 2. The multilayer magneto-optical recording medium according to claim 1, wherein the third magnetic layer is made of a rare earth-transition metal alloy. 3. The multilayer magneto-optical recording according to claim 2, wherein the rare earth-transition metal alloy comprises Tb as a rare earth metal and one of Fe and FeCo as a transition metal, and has magnetic characteristics of 0 <θ <1. Medium. 4. The multilayer magneto-optical recording medium according to claim 1, wherein the Curie temperature Tc3 of the third magnetic layer is 200 ° C. or lower. 5. The multilayered magneto-optical recording medium according to claim 1, 2, 3 or 4, wherein (c) the recording laser beam is irradiated with a low power, the multi-layered multi-layered magnetic layer is formed regardless of the direction of the external magnetic field. The magnetic domain magnetized state is transferred to the first magnetic layer to form a multi-domain intermediate value recording state, and in (d) high power irradiation, each of the first, second and third magnetic layers is determined by the direction of the external magnetic field. A multilayer magneto-optical recording method capable of recording at least ternary value by being in a magnetized state. 6. A first having perpendicular magnetic anisotropy on a substrate,
A multilayer magneto-optical recording medium in which four layers of a second magnetic layer, a third magnetic layer and a fourth magnetic layer are laminated, and adjacent layers are exchange-coupled to each other, and (e) a coercive force of the first magnetic layer. Is larger than the exchange coupling force received from the second magnetic layer, (f)
When the Curie temperature of the first magnetic layer is Tc1, the Curie temperature of the second magnetic layer is Tc2, and the Curie temperature of the third magnetic layer is Tc3, the relationship between Curie temperatures Tc1, Tc2, and Tc3 is Tc1 <Tc2, and Tc3 <Tc2, (g) the sublattice magnetization directions of the second magnetic layer, the third magnetic layer, and the fourth magnetic layer are aligned, and (h) the ratio between the residual magnetization and the saturation magnetization is square. When expressed as a ratio θ, the squareness ratio of the fourth magnetic layer is 0 <θ <1 at room temperature.
A multi-layered magneto-optical recording medium having the following magnetic characteristics, wherein the size of the light spot diameter used for recording / reproducing is a size including a plurality of magnetic domains. 7. The multilayer magneto-optical recording medium according to claim 6, wherein the Curie temperature Tc4 of the fourth magnetic layer is higher than the Curie temperature Tc2 of the second magnetic layer. 8. The magnetic characteristic of the fourth magnetic layer is 0 <θ.
The multilayer magneto-optical recording medium according to claim 7, wherein <1 and CoCr is used. 9. The magnetic characteristic of the fourth magnetic layer is 0 <θ.
8. The multilayer magneto-optical recording medium according to claim 7, wherein <1 and it is made of one of TbCo and TbFeCo.