JPH04184734A - Magnetic-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain excellent writing characteristics and reading characteristics and, further, improve the stability of information holding and reproduce durability by a method wherein (n) layers (wherein (n) denotes an even number not smaller than 3) of magnetic layers composed of magnetic thin films are laminated on a substrate with mutual exchange couplings and the respective magnetic layers satisfy specific conditions. CONSTITUTION:If the Curie point of an (i)th magnetic layer (wherein (i) denotes a natural number not larger than (n)) is denoted by Tc1 and it is defined that Tcn+1 = ambient temperature, for any natural number (m) which is not larger than (n-1)/2, the vertical magnetic anisotropy (Ku) and the saturated magnetization (Ms) of a (2m+1)th magnetic layer at a room temperature are 7X10<5> erg/cm<3> or larger and 300 emu/cm<3> or smaller respectively and Tc2m+1>=Tc1>=Tc2m and Tc2m>=Tc2(m+1). The magnetization of the (2m+1)th magnetic layer is so oriented as to provide the stable state of a coupling state produced by an exchange interaction with a (2m-1)th magnetic layer when the temperature of a (2m)th magnetic layer drops to its Curie point Tc2m or lower. With this constitution, excellent writing characteristics and reading characteristics and, further, excellent reproduce durability can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used in magneto-optical memories, magnetic recording, display elements, etc., and can read out records using magneto-optical effects such as the magnetic Kerr effect or the Faraday effect. It relates to magneto-optical recording media.

[Prior Art] In magneto-optical recording, a bias magnetic field is applied to the magnetic layer region of a magneto-optical recording medium while a laser beam or the like is irradiated onto the surface of the magnetic layer, so that the irradiated area is near the Curie point of the magnetic layer. Alternatively, information may be written (recorded) by heating to near the compensation point and orienting the magnetization of this portion in the opposite direction to that of other portions. On the other hand, in order to read and reproduce written information, the surface of the magnetic layer is irradiated with a linearly polarized laser beam that is lower in output than during recording, and a rotating analyzer is used that uses the magneto-optical effect of the polarization plane of the reflected light. This is done by optical detection via

A magneto-optical recording medium used for such magneto-optical recording is desired to have good writing efficiency, to stably store written information, and to have good read characteristics. However, it is extremely difficult to meet all of these requirements with a single material. For example, in the case of Curie point writing, it is necessary to lower the Curie temperature in order to increase the writing efficiency, but on the other hand, a drop in the Curie temperature lowers the magneto-optic effect, leading to deterioration of read characteristics. In addition, in the case of compensation point writing, since a material whose coercive force rapidly decreases near the compensation point is used, it is possible to write to materials with a high Curie temperature with relatively low power, but the storage stability of the written information may be affected. There is a problem with the magnetic domain shape.

For this reason, magneto-optical recording media using composite films with separate functions have been proposed. In other words, a magnetic layer with a large magneto-optical effect and good read characteristics and a magnetic layer with a relatively low Curie temperature, large perpendicular magnetic anisotropy, and good write characteristics are magnetically coupled and laminated to improve the write characteristics. Information written in a layer with good read characteristics is transferred by magnetic coupling force to a layer with good read characteristics, and this transferred information is read out. In particular, a composite membrane bonded by exchange bonding force is advantageous in terms of information transferability and preservation of transferred information.
2 and JP-A-63-302448, etc., Gd-Fe/Tb-Fe exchange-coupled bilayer films and Tb-F
Magneto-optical recording media using eCo/Tb-FeGo exchange-coupled double-layer films have been disclosed.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional magneto-optical recording medium using a composite film, the magnetic layer, which has a large magneto-optic effect and good read characteristics, cannot stably hold the magnetic domains generated by writing in a single layer. It is composed of materials and compositions that cannot be used. That is, this magnetic layer can form and maintain a magnetic domain well only by being exchange-coupled with a magnetic layer having excellent writing characteristics. Therefore, as a reaction to this, the magnetic domains formed in the magnetic layer with excellent write characteristics are forced to collapse due to exchange coupling with the unstable magnetic layer (magnetic layer with excellent read characteristics). The effect of is at work. However, there is a second problem in that the storage stability of information in a magneto-optical recording medium using a conventional composite film is disadvantageous compared to a case where a readout layer is not laminated. In particular, it was inferior in durability upon repeated reproduction, that is, reproduction durability.

In addition, in order to obtain sufficient improvement in readout characteristics, it is necessary to make the readout layer thicker to some extent, but increasing the thickness of this layer may result in the inability to form good magnetic domains or the preservation of magnetic domains. There was a problem that stability deteriorated.

In order to avoid these problems, it is considered that the characteristics of the readout layer should be made so that the formed magnetic domain can be stably maintained even when the layer exists alone. To this end, this layer must be made of a material and composition that has a large perpendicular magnetic anisotropy and a relatively small saturation magnetization.

However, in this case, it is extremely difficult to realize the process of transferring information written in the writing layer to the reading layer, and in particular, it is difficult to make the reading layer thick enough for reproduction. The problem is that it is impossible.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a magneto-optical recording medium that has excellent writing and reading characteristics, and has improved information storage stability, particularly reproduction durability.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the magneto-optical recording medium of the present invention has a functionally separated exchange-coupled composite film in which the characteristics of the magnetic layer for reading are changed by the characteristics of the magnetic layer. In order to ensure that the information from the write magnetic layer is transferred to this magnetic layer reliably, the magnetic layer has a property that allows the formed magnetic domain to be stably maintained even when it exists alone. The layer structure is designed so that the thickness of the magnetic layer can be made thick enough to improve the readout characteristics.

That is, in the magneto-optical recording medium of the present invention, n magnetic layers made of magnetic thin films, from the first magnetic layer to the n-th magnetic layer (n is an odd number of 3 or more), are sequentially laminated on a substrate. In the magneto-optical recording medium, each of the magnetic layers is exchange-coupled with each other at room temperature, the Curie temperature of the i-th magnetic layer (where i is a natural number equal to or less than n) is defined as Tc, and TCn+r is defined as the ambient temperature, For all natural numbers m less than or equal to (n-1)/2, the following four conditions are met: (a) The perpendicular magnetic anisotropy constant (Ku) of the (2m+1)th magnetic layer at room temperature is 7 X 10 'erg/ cm
' or more, and the saturation magnetization (Ms) at room temperature is 3
00 emu/cm' or less, (b) TCim++≧Tc+ ≧Tc2m,
(C) TC2 amount≧Tct l+a◆1) and (cl
) Cooling after heating a portion of the magneto-optical recording medium to a temperature close to the Curie temperature Tc of the first magnetic layer and transitioning the magnetization orientation state of the portion of the first magnetic layer to a state different from that before heating. In the process, when the temperature of the (2m) magnetic layer falls below the Curie temperature T c 2m of the (2m) magnetic layer, the (2m) magnetic layer and the (2m+1)
The magnetization of the magnetic layer is oriented so that the bonding state due to exchange interaction with the (2m-1)th magnetic layer is stable, and the magnetization of the (2m-1)th magnetic layer is oriented to the (2m-1)th magnetic layer. ) The magnetic layer maintains the orientation state immediately before the temperature of the magnetic layer falls below the Curie temperature TCn of the (2m)th magnetic layer.

It is preferable that each magnetic layer is made of a rare earth-iron group amorphous alloy, and under the condition (a) above, the (2mth
+1) Perpendicular magnetic anisotropy constant (K
u) is I x 10 'erg/cm'' or more, and the saturation magnetization (Ms) at room temperature is 200 emu/c
It is preferable that it be less than or equal to m'.

[Function] The function of the magneto-optical recording medium of the present invention having a composite film structure in which n magnetic layers (n is an odd number of 3 or more) consisting of magnetic thin films are laminated on a substrate while being exchange-coupled with each other is as follows. It is as expected. In addition, in the following explanation, m is (n-1)/2
Represents all the following natural numbers. In other words, the (2m)th magnetic layer means the even-numbered magnetic layer counting from the first magnetic layer, and the (2m+1)th magnetic layer means the odd-numbered magnetic layer from the third magnetic layer onwards. means the magnetic layer of Further, Tc+ is the Curie temperature of the i-th magnetic layer.

In the magneto-optical recording medium of the present invention, the first magnetic layer corresponds to the magnetic layer for writing, and the (2m+1)th magnetic layer corresponds to the magnetic layer for reading. 2nd (2nd
m) The magnetic layer is a zero-order magnetic layer for breaking the magnetic coupling between each layer. Next, we will explain the process by which magnetic domains are formed in a magneto-optical recording medium made of such a composite film.

After erasing, the surface of the magnetic layer is irradiated with laser light while applying a bias magnetic field for recording, and the irradiated portion is heated to around the Curie temperature Tc+ of the first magnetic layer. In the cooling process from this temperature after laser irradiation, first,
A magnetic domain with reversed magnetization orientation is formed in the first magnetic layer. At this time, since the temperature of the second magnetic layer is higher than the Curie temperature, the magnetic coupling between the first magnetic layer and the third magnetic layer is severed.

Further, the (2m+1)th magnetic layer has a Curie temperature of Tc+
Since it is made of a material with a perpendicular magnetic anisotropy higher than 100% and a large perpendicular magnetic anisotropy, normally magnetization reversal does not occur at temperatures around this temperature and the magnetization orientation in the erased state is maintained. (However, depending on the material, magnetization reversal may occur. Also, due to the temperature gradient within the laser irradiation area, a minute magnetic domain may be formed in the center of the area. In either case, the following explanation will be provided. ) Now, when the medium temperature drops below the Curie temperature of the second magnetic layer, the first
Exchange interaction begins to act between the magnetic layer and the second magnetic layer, and between the second magnetic layer and the third magnetic layer, and each layer is magnetically coupled. Since the temperature of the fourth magnetic layer is higher than its Curie temperature, the magnetic coupling between the third magnetic layer and the fifth magnetic layer is severed. Here, since the spin orientations of the first and third magnetic layers are reversed, a spin transition region is formed between these two layers, and energy due to exchange interaction is accumulated here. . As the temperature drops further, this energy increases, causing the magnetization of one layer to reverse and aligning the spin directions of both layers. At this time, the film thickness and physical properties of each magnetic layer are controlled so that the energy required to reverse the magnetization of the third magnetic layer is smaller than the energy required to reverse the magnetization of the first magnetic layer at this temperature. When the third magnetic layer is left in place, the magnetization of the third magnetic layer is preferentially reversed and aligned with the spin direction of the first magnetic layer. (Design guidelines for film thickness and physical property values for realizing this process will be explained in more detail in Examples.) In this way, the magnetic domains of the first magnetic layer are transferred to the third magnetic layer.

When the medium temperature falls below the Curie temperature of the fourth magnetic layer, the fifth magnetic layer is magnetically coupled through this layer, and the magnetic domains of the layers below the third magnetic layer are transferred to the fifth magnetic layer. In this way, the magnetic domains are transferred one after another, and finally, when the medium temperature becomes equal to or lower than the Curie temperature Tcn-+ of the (n-1)th magnetic layer, the magnetic domains are transferred to the n-th magnetic layer. The formation of magnetic domains in this composite film is completed.

Reading recorded information from the magneto-optical recording medium on which information has been recorded as described above is performed by irradiating the n-th magnetic layer side with a linearly polarized, low-power laser beam. Since the incident laser beam is reflected by the high Curie temperature magnetic layer of the - group, that is, the (2m+1)th magnetic layer, a high magneto-optic effect is obtained. In addition, these magnetic layers have a high Curie temperature, large perpendicular magnetic anisotropy, and relatively low saturation magnetization, so they are resistant to temperature increases in the medium caused by incident laser and the application of external magnetic fields. Recorded information can be stably held.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing the structure of a magneto-optical recording medium according to an embodiment of the present invention. This magneto-optical recording medium has a structure in which an undercoat layer 2, a magnetic composite film 3, and a protective layer 4 are sequentially laminated on a transparent substrate 1 made of glass or plastic. The undercoat layer 2 is for making light incident on the magnetic composite film 3 well by optical interference effect and for preventing corrosion of the magnetic composite film 3, and is made of, for example, 5isNn, AIN, 5in2. S
It consists of galvanic materials such as in, ZnS, and MgF*.

The magnetic composite film 3 consists of n layers (where n is 3) consisting of a magnetic thin film.
The above (odd number) magnetic layers are laminated so as to have an exchange effect with each other, and in order from the underlayer 2 side, the n-th magnetic layer, the (n-1)-th magnetic layer, etc. They are stacked one on top of the other, and the topmost layer, that is, the side opposite to the undercoat layer 2, is the first magnetic layer. The Curie temperature of the i-th magnetic layer (where i is a natural number equal to or less than n) is expressed as Tc+, and Tc11.
When I = ambient temperature, for all natural numbers m less than or equal to (n-1)/2, the following four conditions (a) Perpendicular magnetic anisotropy (Ku ) is 7 x 10 * erg/cm' or more, and the saturation magnetization (Ms) at room temperature is 300
emu/cm' or less, (b) Tc2m+l≧Tc+ ≧Tch, and (c
)Tc==≧Tca (, ell, (CI) A part of this magneto-optical recording medium is set to the Curie temperature T of the first magnetic layer.
In the cooling process after heating to the vicinity of c+ and transitioning the magnetization orientation state of the heated portion of the first magnetic layer to a state different from that before heating, the temperature of the (2m) magnetic layer becomes equal to or lower than its Curie temperature Tczm. , the magnetization of the (2m)-th and (2m+1)-th magnetic layers is oriented so that the bonding state due to exchange interaction with the (2m-1)-th magnetic layer is stable. , the magnetization of the (2m-1)th magnetic layer is
The temperature of the (2m)th magnetic layer is its Curie temperature Tczwa
All the conditions of maintaining the orientation immediately before descending below are satisfied.

Of the above four conditions, the transition of the orientation state of magnetization of the first magnetic layer under condition (d) may be caused by applying an external bias magnetic field or by a magnetic field generated by the magneto-optical recording medium itself. In any case, it is sufficient that a magnetic field is effectively applied to the portion of the first magnetic layer to be heated to change its orientation state.

The protective layer 4 covers the magnetic composite film 3 to prevent corrosion of the magnetic composite film 3, and is made of a dielectric material such as 5iaN<. The undercoat N2, magnetic composite film 3, and protective layer 4 are as follows:
For example, it is deposited on the substrate 1 by continuous sputtering using a magnetron sputtering device or by a continuous vapor deposition method. In particular, when forming the magnetic composite film 3, each magnetic layer is formed successively without breaking the vacuum, so that each magnetic layer is well exchange-coupled with each other.

In the magneto-optical recording medium, each magnetic layer may be made of various magnetic materials, such as Pr.
, Nd, Sm, Gd, Tb, Dy, Ho, etc., one or more rare earth metal elements such as 10
~40 at%, and 90 to 60 at% of one or more iron group elements such as Fe, Co, and Ni
It is composed of a rare earth-iron group amorphous alloy containing a certain degree.

In addition, in order to improve corrosion resistance, etc., Cr, Mn,
Small amounts of elements such as Cu, Ti, AI, Si, Pt, and In may be added, however, the (2m+1)th
Regarding the magnetic layer, in order to satisfy the above-mentioned condition regarding perpendicular magnetic anisotropy (condition (a)), T is used as a rare earth element.
It is preferable to use non-S state elements such as b and Dy.

In rare earth-iron group amorphous alloys, the rare earth element is Gd
In the case of heavy rare earth elements such as , Tb, Dy, and Ho, the magnetic moment of the rare earth element and the magnetic moment of the iron group element are coupled antiparallel to each other, exhibiting so-called ferrimagnetism. In this case, the net magnetization is appears as a difference in the respective sublattice magnetizations, so by adjusting the composition ratio of both, the saturation magnetization can be freely controlled.

Furthermore, when the rare earth element is a light rare earth element such as Pr, Nd, or Sm, the magnetic moment of the rare earth element and the magnetic moment of the iron group element are coupled in parallel to each other, exhibiting so-called ferromagnetism. Although it is difficult to control the saturation magnetization, it can be adjusted to some extent by adding heavy rare earth elements.

The Curie temperature can also be controlled by the composition ratio of rare earth elements and iron group elements, but in order to control it independently of saturation magnetization, it is necessary to control the Curie temperature by adding Fe as the main component to the iron group elements and some Co. More preferably, a method can be used in which the amount of substitution is controlled using a substituted substance. That is, by substituting 1 atomic % of Fe with CO, it is expected that the Curie temperature will increase by about 5° C., so using this relationship, the amount of Co added is adjusted to obtain the desired Curie temperature. Furthermore, by adding a small amount of non-magnetic elements such as Cr and Ti, it is also possible to lower the Curie temperature. Alternatively, the Curie temperature can be controlled by using two or more types of rare earth elements and adjusting their composition ratio. These methods allow the Curie temperature to be controlled freely, so the conditions regarding the Curie temperature (condition (b),
(c) ) is easy to realize. However, considering the operating environment temperature and recording sensitivity, the Curie temperature of the first magnetic layer is in the range of about 120 to 200°C, the Curie temperature of the (2m) magnetic layer is in the range of about 70 to 200°C, and the Curie temperature of the (2m+
1) The Curie temperature of the magnetic layer is suitably about 180° C. or higher.

The temperature dependence of various physical properties of magnetic materials has a complex mechanism and is quite difficult to control. Therefore, in carrying out the present invention, the condition (condition (d)) that defines the transition process of the magnetization orientation state due to temperature change of the magneto-optical recording medium is set to "
We will conduct experiments using "film thickness" as the main parameter and determine the film thickness to satisfy the conditions.However,
From the point of view of recording sensitivity, the total thickness of the magnetic layer is 25 mm.
It is desirable that the number of participants be about 0.00 or less. In addition, 100 to 500 people were assigned to the first magnetic layer, 5 to 100 people were assigned to the (2m)th magnetic layer, and 10 to 500 people were assigned to the (2m+1)th magnetic layer.
A suitable thickness is about 0.00 mm, and the total thickness of the (2m+1)th magnetic layer is preferably about 200 mm or more.

Here, in order to provide rough design guidelines for the film thickness and various physical property values of each magnetic layer in order to satisfy condition (d), a simplified theory for a typical case will be presented.

In general, the energy involved in the magnetization state of a magnetic thin film includes Zeeman energy, interfacial domain wall energy, Bloch domain wall energy, demagnetizing field energy, etc., and the state energy chi of one magnetization state is determined by the sum of these energies.

When focusing on a single-layer magnetic thin film with uniform physical properties, the state energy EA in a certain magnetization state A of this layer is higher than the state energy Es in another magnetization state B of the same layer, and the difference is the coercive force of this layer. When the energy becomes larger than that, a state transition from state A to state B occurs.

Now, suppose that a magneto-optical recording medium having an exchange-coupled magnetic multilayer structure is in an initial state in which all the spin orientations of the magnetic layers are aligned. If a part of the medium is heated and the magnetic state of the first magnetic layer in this part is changed to a state different from the initial state, then during the cooling process, the third magnetic layer maintains its initial state. , there must be a misaligned region of spin orientation somewhere between the first, second, and third magnetic layers.

In the following explanation, the saturation magnetization of the i-th magnetic layer at temperature t is assumed to be MSI(t), the coercive force is Hc+m, and the film thickness is . The interfacial domain wall energy density is σW (1, Jl (t), Ht is the magnitude of the external magnetic field, and the angle between the direction of magnetization of the i-th magnetic layer and the direction of the external magnetic field HE at temperature t is Let be θ(1).

Now, let us consider a case where the thickness of the (2m)th magnetic layer is relatively thin and the Zeeman energy and coercive force energy of this layer can be ignored. When the second magnetic layer is below its Curie temperature Tcz and exchange interaction begins to act between spins, the spin mismatch region between each layer has a relatively small exchange interaction because it is close to its Curie temperature. It is formed intensively within the second magnetic layer. And here the interfacial domain wall energy σ
W(1,3) is stored. Considering the case where the fourth magnetic layer becomes lower than its Curie temperature T C4 in this state, it is also necessary to consider the spin matching with the fifth magnetic layer, but the fifth magnetic layer also has to be at this point. If the initial state is maintained, no mismatch will occur and no energy will be accumulated. Therefore, the third
The state energy EA of the magnetic layer is E a”-MSs (t)・h3・1E-cos θ,
(t) 1σW(1,3+ (t), the first term corresponds to Zeeman energy.Bloch domain wall energy, demagnetizing field energy, etc. are considered to have relatively little influence on the magnetization state, so they are not considered here. ignore.

If each layer is a perpendicularly magnetized film, and assuming that the magnetization of the third magnetic layer is reversed by 180 degrees at this temperature, the spin directions of the first and third magnetic layers will be aligned, and the domain wall at this interface will disappear. . Conversely, a spin mismatch region is generated in the fourth magnetic layer between the third magnetic layer and the fifth magnetic layer, and the interfacial domain wall energy OW[3,s+ is stored there. (However, when the fourth magnetic layer has a Curie temperature of TC4 or higher, σW is,
81 = 0. ) in this virtual state B
The state energy El of the magnetic layer is Ee;-Mss(t)・hs-)1x・cos(θ, (
t)+180 @)+σwas, sr (t). Therefore, E A−E B =1−2・Mss (t)・hs
・Hc-cosθs (t) + awn, *)(
t) -a W (3,y)(t) > 2・Mss (t) ・hs・Hcs (t)
When (1) is established, the third magnetic layer actually undergoes a state transition. Here, the right side is the coercive force energy of the third magnetic layer.

In addition, as a condition for the magnetization of the first magnetic layer not to be reversed before equation (1) holds true, that is, at a temperature higher than the highest temperature t111 at which equation (1) holds true, -2・Ms+ (t) ・hl ・Ht-cosθ1(
t) + a w r+, sr (t) < 2・Ms
+ (t) ・b+ ・)Ic+ (t) (2) must always hold true.

Hereinafter, the conditions for the state transition of the magnetization of the (2m+1)th magnetic layer when the (2m)th magnetic layer becomes lower than its respective Curie temperature Tc are determined using the same concept. This can be summarized as follows.

■In the temperature range below Tcm, 2・Mszwa+ I(to) '11zm++ H(
HC211*I (to)+Ht-cosθx−-+
(to))kuσw, 1. -113. . u(to)−σ
Temperature t that satisfies wT2sii1.2m+31 (jo)
0 must exist.

■At least the highest temperature t among the temperatures t, □
In the temperature range of 8 or more and Tcxm or less, Σm"2-M5+ (t) ・h+'(Hat (t)
+HE-cos θ+(1))〉0w(2m-1,2
m+Il m always holds true.

The above is just a rough guideline. in fact,
The Zeeman energy and coercive force energy of the (2m)th magnetic layer also affect the magnetization process to some extent, and the Bloch domain wall energy cannot be completely ignored.

It is possible to confirm whether condition (d) actually holds or not, as shown in Example 1 below, so we conducted repeated trials based on the above design guidelines, and determined the film thickness and Curie temperature of each layer. Condition (d) can be realized by adjusting.

Next, examples of the present invention will be described in more detail while contrasting with comparative examples.

Example 1 As shown in FIG. 2, the magnetic layer 2 has seven magnetic composite layers 13.
Magneto-optical recording media consisting of Nos. 1 to 27 were produced. This magneto-optical recording medium has a substrate 11 made of polycarbonate, and
Undercoat layer 12 made of SiN, magnetic composite film 13, SiN
A protective layer 14 consisting of the following is sequentially laminated. The magnetic composite film 13 includes a seventh magnetic layer 27 . Sixth magnetic layer 26. ... are sequentially laminated, and the first magnetic layer 21 is on the protective layer 14 side.

The method for manufacturing this magneto-optical recording medium will be described in detail below.

8 diameter diameter pre-formed track grooves and format signals in a sputtering equipment with 4-way target source.
A 6 mm disc-shaped polycarbonate substrate 11 was set and rotated so that the distance between it and the target was 20 cm.

In an argon atmosphere with a pressure of 0.15 Pa, first,
Sputtering was carried out using a target of 5jsN4, and a SiN underlayer 12 with a thickness of 600 nm was deposited on the substrate 11 at a deposition rate of about 40 nm/min.

Next, simultaneous sputtering was performed using three targets of Tb, Fe, and Co at a deposition rate of 50 people/min.
FeCo sublattice magnetization dominant Tbo, z+(
Fe0. A seventh magnetic layer 27 of tocOo, so) o, 7@ was formed. The composition of Tb-Fe-Co was controlled by adjusting the power applied to each target of Tb, Fe, and Co.

The magnetic properties of this layer as a single layer film at room temperature include a coercive force of 15 kOe, a saturation magnetization of 100 emu/cm', and a perpendicular magnetic anisotropy constant of 2. OX 10'erg/cm3
Met. Further, the Curie temperature was 270°C.

Subsequently, using three targets of Tb, Fe, and Co, and changing the power applied to each target, the film formation rate was 20 people/min, the film thickness was 10 people, the coercive force was 19 kOe at room temperature, and the saturation magnetization was 50 emu/min. cm' Tb sublattice magnetization dominant Tbo, a, (Feo, eacOo,
04) O,? 4 of the sixth magnetic layer 26 was formed. Curie temperature was 140°C.

Subsequently, the power applied to each target was changed again, and the film formation rate was 50 g/min, and the FeCo sublattice magnetization was dominant Tbo, gos (Feo, tocOo) with a film thickness of 140 g/min.
, so) o, Will's fifth magnetic layer 25 was formed. The magnetic properties of this layer as a single layer film are as follows: coercive force: 12.5 kOe, saturation magnetization: 120 emu/c at room temperature
m3. Perpendicular magnetic anisotropy constant2. OX 10 'erg/
cm'. Further, the Curie temperature was 270°C.

Next, the power applied to each target was changed again, and the film was deposited at a deposition rate of 20 min/min, a film thickness of 10 min, a coercive force of 19 kOe at room temperature, and a Tb sublattice magnetization dominant Tbo, t4(Fen) with a saturation magnetization of 50 emu/cm'. , *4Coo,
as) A fourth magnetic layer 24 of 0.74 was formed. Curie temperature was 150°C.

Subsequently, the power applied to each target was changed again, and at a film formation rate of 50 g/min, FeCo sublattice magnetization dominant Tbo, go (Feo, tocOo,
so). ,. A third magnetic layer 23 was formed. The magnetic properties of this layer as a single layer film are as follows: at room temperature, the coercive force is 10
．． 7kOe.

The saturation magnetization was 140 emu/cm', the perpendicular magnetic anisotropy constant was 2, and OX 10'erg/cm'. Further, the Curie temperature was 270°C.

Furthermore, the power applied to each target was changed again, and a T film was obtained at a deposition rate of 20 min/min, a film thickness of 10 min, a coercive force of 20 kOe at room temperature, and a saturation magnetization of 50 emu/cm'.
b sublattice magnetization dominant Tbo, 211 (Feo, 11
A second magnetic layer 22 of 2CO(1, oa) o, ta was formed. Curie temperature was 160°C.

Finally, the film thickness was 350 at a deposition rate of 50 people/min.

Coercive force 12 kOe, saturation magnetization 100 emu at room temperature
/cm” FeCo sublattice magnetization dominant Tbo, zl(F
eo, eocOo, to) 0. t.

A first magnetic layer 21 was formed. Curie thermometer 170
It was ℃.

As a result, an exchange-coupled magnetic seven-layer film satisfying each of the conditions (a) to (d) above was formed. The interfacial domain wall energy density between each magnetic layer is approximately 6 er (at room temperature).
g/cm". Here, the total thickness of the magnetic layers 21 to 27 is 800, and the total thickness of the third magnetic layer 23, fifth magnetic layer 25, and seventh magnetic layer 27 is 420 people.The characteristics of each magnetic layer are shown in Table 1.In addition, the temperature dependence of the coercive force and saturation magnetization of each magnetic layer as a single layer is shown in Table 3.
It is shown in the figure. In addition, in Table 1, “+” in the column of saturation magnetization
"-" indicates the sublattice magnetization dominance of the rare earth element, and "-" indicates the dominance of the iron group element sublattice magnetization.

On top of this, a protective layer 14 of SiN with a thickness of 600 layers was provided using a 5lsN4 target at a deposition rate of about 40 layers/min.

After that, this substrate 11 is taken out from the sputtering device, and an ultraviolet curable resin is spin-coded on the film surface side and then cured to form a protective coating layer (not shown) with a thickness of about 8 μm.
A single-plate magneto-optical disk was fabricated.

Next, one wavelength of laser light is 820 nm, NA = 0.
This magneto-optical disk was mounted on a magneto-optical disk drive having 52 optical heads, rotated at a rotational speed of 3600 rpm, and measurements were performed by irradiating a laser beam at a radius of 24 mm from the center of the magneto-optical disk.

First, when the medium temperature is 30° C., a bias magnetic field of 3000e is applied and recording is performed while laser light is intermittent at a frequency of 5.8 MHz and a duty ratio of 33%.
Perform playback using 5mW laser power to improve C/N of playback.
(carrier/noise) was calculated. At this time, when the recording power was changed, the reproduction C/N was saturated at a recording power of about 6.0 mW, and at this time the C/N value was 51 dB.
Met.

Next, with a magnetic field of 6000e applied in the erasing direction,
One recorded track was repeatedly reproduced 1×10 5 times. The deterioration of the reproduced signal after repeated reproduction can be determined by setting the reproduction power during this repeated reproduction to various values, performing reproduction with a reproduction nozzle of 1.5 mW after the repeated reproduction, and checking the C/N of the reproduced signal. I looked into it. As a result, it was found that if the reproduction power is up to 3.5 mW, the reproduction signal does not deteriorate even if reproduction is repeated.

Next, the conditions for the process of transition of the magnetization orientation state with a change in medium temperature, which is a feature of the present invention, are set in this magneto-optical recording medium.
That is, it was investigated whether the above-mentioned condition (d) was satisfied.

A test sample was prepared in the same manner as the magneto-optical disk described above, except that a glass substrate was used instead of the polycarbonate substrate. This sample and the above-mentioned magneto-optical disk have completely identical magnetic characteristics i'i.

In FIG. 4, a bias magnetization HE of 3000 e is applied in the positive direction at room temperature to a sample that has been previously magnetized in the negative direction [magnetization orientation state (a)].

With the bias magnetic field still applied, it is heated to 170° C. or higher [magnetization orientation state (b)], and then cooled [magnetization orientation state (c) to (e): 1. This diagram schematically shows the change in the magnetization orientation state during the heating and cooling process such that the magnetization orientation state (f) returns to room temperature [magnetization orientation state (f)]. The magnetization orientation state is expressed by the direction of saturation magnetization (the blank arrow in the figure) and the direction of the magnetic moment of the iron group element (the black arrow in the figure).

In the figure, a magnetic layer without an arrow indicates that the magnetic layer has a temperature equal to or higher than its Curie temperature. The magnetization orientation state (a) and the magnetization orientation state (f) are magnetization orientation states at room temperature that respectively correspond to binary recording.

Next, an experiment conducted to confirm the transition of the magnetization orientation state will be explained.

First, this sample was mounted on a vibrating sample magnetometer (VSM) so that a magnetic field was applied in the direction perpendicular to the film surface, and a bias magnetic field HE of about 20 kOe was applied in the negative direction to adhere each layer in one direction. After magnetizing, reversely turn 30 in the positive direction.
The voltage was applied up to 00e. A magnetization curve showing this magnetization process is shown in FIG. 5('a). The black dots in the figure correspond to the final state of this process, that is, the magnetization orientation state (a) (FIG. 4).

Next, from the magnetized state (a), the temperature of the sample was heated to 170° C. or higher while applying the bias magnetic field HE. Next, the change in magnetization of the sample when the temperature is lowered while the bias magnetic field HE is applied is shown in the sixth graph.
As shown in the figure. It can be seen that magnetization reversal occurs at temperatures where magnetization changes rapidly. Therefore, from the heated state of 170°C or higher, the magnetization was cooled to each temperature before and after the magnetization reversal (165°C, 155°C, 145°C, and 135°C), and the magnetization curves at that time were measured. The results are shown in FIGS. 5(b) to (e).

FIG. 5(b) is a magnetization curve at 165°C. At this temperature, the second. 4th. Since the sixth magnetic layers 22, 24 and 26 each have a temperature higher than the Curie temperature, the first. Third. Fifth. The seventh magnetic layers 21, 23, 25, 27 do not interact, and the independent magnetization curves of each layer overlap to form a four-stage loop.

As shown in Figure 3, since the coercive force and saturation magnetization of each layer as a single layer film at this temperature are known,
It is possible to determine which magnetic layer's magnetization reversal corresponds to each stage of the stage loop. In this case, the first row starts from the lower row on the right side of the loop. Third. Fifth. 7th
It can be seen that the magnetic layers 21.23° correspond to 25 and 27.

In the figure, the black dot indicates the starting point of the loop.
The magnitude of magnetization corresponds to the magnetization orientation state of each layer when the temperature drops from the above temperature to this temperature. In Figure 6, the minor loop including the broken line is the magnetization curve of the first magnetic layer alone. be. Based on these loops and the position of the starting point of the loop within them, the magnetization orientation state of each layer when the temperature drops to this temperature is the magnetization orientation state (b) (Figure 5)
It can be determined that it was. Comparing the magnetization orientation state (b) and the magnetization orientation state (a), it can be seen that the magnetization of the first magnetic layer is reversed.

FIG. 5(c) is a magnetization curve at 155°C. At this temperature, the temperature of the second magnetic layer 22 is below the Curie temperature. Second. The third magnetic layers 21, 22, 23 are supposed to undergo a magnetization process that causes mutual interaction. The upper two stages on the right side of the loop are 5th. Seventh magnetic layer 25.2
7 corresponds to magnetization reversal independently. Therefore, the minor loop including the broken line part is the first. Second.
It can be seen that the magnetization curve is obtained by simultaneous magnetization reversal of the third magnetic layers 21, 22, and 23 due to exchange coupling. Then, the position of the starting point of the loop indicated by the black dot in the figure and the first point at this temperature. Second. Third magnetic layer 21.2
Considering the magnitude of magnetization in 2.23, the magnetization orientation state of each layer when the temperature dropped from 170"0 or higher to this temperature was the magnetization orientation state (c) shown in Figure 5. In other words, the magnetization of the third magnetic layer 23 is reversed, and the magnetization of the second and third magnetic layers 22 and 23 is in a stable state of coupling with the first magnetic layer 21 by exchange interaction. The magnetization of the first magnetic layer 21 is 165
The orientation state confirmed at ℃ is maintained.

Similarly, the magnetization orientation state (d) in FIG. 5 was obtained from the magnetization curves shown in FIGS. 5(d) and (e) at 145° C. and 135° C., respectively.

(8) can be confirmed.

As described above, the structure of the magneto-optical recording medium according to Example 1 is as follows.
It was confirmed that the condition for the process of transition of the magnetization orientation state due to a change in medium temperature, which is a feature of the present invention, that is, the condition (d) was realized.

In addition, in the configuration of the magnetic layer described above, each layer (2m)
The magnetic layer, i.e. the second. 4th. Sixth magnetic layer 22, 24.2
Since the compensation temperature of No. 6 is between room temperature and each Curie temperature, as shown in FIG. 2m) The compensation temperature of the magnetic layers is passed, and the polarity of the magnetization of these layers is reversed without any state transition, resulting in the magnetization orientation state (f).

Comparative Example 1 After forming a SiN underlayer on a substrate in the same manner as in Example 1, simultaneous sputtering was performed using three targets of Gd, Fe, and Co, and the film formation rate was 50 people/min.
Then, FeCo sublattice magnetization dominant Gdo with a film thickness of 400 people,
** (Feo, 'FOCoo, so) o,
A magnetic layer for reading ta was formed. The magnetic properties of this layer as a single layer film are as follows: at room temperature, the coercive force is 0.5 k
Oe, saturation magnetization 50 emu/2 m', perpendicular magnetic anisotropy constant 4. OX 1×10 5 erg/2 m”, and the Curie temperature was 300° C. or higher.

Subsequently, using three targets of Tb, Fe, and Co, F was deposited at a deposition rate of 50 people/min and a film thickness of 400 people.
eC.

Sublattice magnetization dominant Tbo, i+(Feo, eoCoo, +
o) A magnetic layer for writing o and to was formed. The magnetic properties of this layer as a single layer film are exactly the same as the first magnetic layer in Example 1, and the coercive force is 12 kO at room temperature.
e.

The saturation magnetization was 100 emu/cm', and the Curie temperature was 170°C.

Except for the magnetic layer, the structure and manufacturing method were exactly the same as in Example 1,
A magneto-optical disk was fabricated. The magneto-optical disk according to Comparative Example 1 was evaluated in exactly the same manner as in Example 1. As a result, the C/N was saturated at a recording power of about 6.0 mW, and the C/N value at this time was 51 dB, which was the same recording characteristic as in Example 1. However, the maximum reproducing power without causing reproduction deterioration in a magnetic field was 2.1 mW, which was lower than in Example 1.

Comparative Example 2 After forming a SiN underlayer on a substrate in the same manner as in Example 1, simultaneous sputtering was performed using three targets of Tb, Fe, and Co, and the film formation rate was 50 people/min.
Then, FeCo sublattice magnetization dominant Tbo with a film thickness of 200 people,
A magnetic layer for reading ra (Feo, 70CO0,30)O,@2 was formed. The magnetic properties of this layer as a single layer film are as follows: coercive force of 2 kOe, saturation magnetization of 250 emu/cm', and perpendicular magnetic anisotropy constant of 1.5 at room temperature.
The Curie temperature was approximately 300°C.

Subsequently, using three targets of Tb, Fe, and Co, F was deposited at a deposition rate of 50 people/min and a film thickness of 600 people.
eC.

Sublattice magnetization dominant Tbo, ml (Feo, *oCO
A magnetic layer for writing (o, to') a, ts was formed. The magnetic properties of this layer as a single layer film are similar to those of the first magnetic layer in Example 1, with a coercive force of 12 kOe at room temperature.

The saturation magnetization was 100 emu/2 m', and the Curie temperature was 170°C.

Except for the magnetic layer, the structure and manufacturing method were exactly the same as in Example 1,
A magneto-optical disk was fabricated. The magneto-optical disk according to Comparative Example 2 was evaluated in exactly the same manner as in Example 1. As a result, the C/N was saturated at a recording power of about 6.0 mW, and the C/H value at this time was 49 dB. In addition, the maximum playback power that does not cause playback deterioration in a magnetic field is 2.8m.
W, which was lower than that in Example 1.

In the case of Comparative Example 2, the thickness of this layer was set to 200 because recording noise would increase if the thickness of the read magnetic layer was increased. Therefore, the C/N is slightly lower than that of Example 1 and Comparative Example 1.

Comparative Example 3 After forming a SiN underlayer on a substrate in the same manner as in Example 1, simultaneous sputtering was performed using three targets of Tb, Fe, and Co, and the film formation rate was 50 people/min.
, FeCo sublattice magnetization dominant Tbo, m with a film thickness of 800
A magnetic layer of r(Feo, eocoo, +o) o, to was formed. The magnetic properties of this layer are similar to those of the first magnetic layer as a single layer film in Example 1,
At room temperature, coercive force 12 kOe, saturation magnetization 100 e
mu/cm', and the Curie temperature was 170°C.

Except for the magnetic layer, the structure and manufacturing method were exactly the same as in Example 1,
A magneto-optical disk was fabricated.

Regarding the magneto-optical disk according to Comparative Example 3, Example 1
The same evaluation was carried out.

As a result, the C/N saturates at a recording power of approximately 6.0 mW,
The C/N value at this time was 47 dB. Further, the maximum reproducing power without causing reproduction deterioration in a magnetic field was 3.0 mW.

In the case of Comparative Example 3, since there is no magnetic layer for readout, the C/N is lower than that of Examples and other comparative examples.On the other hand, since the unstable layer of magnetic domains is not bonded, the readout durability is low. is higher than that of Comparative Example 1. However, in the medium of Example 1, which is inferior to Example 1, the magnetic domain of the readout layer is stable, and the written magnetic domain is retained in this readout layer having a high Curie temperature. This is thought to be due to the

Comparative Example 4 3rd. Fifth. The seventh magnetic layer has a perpendicular magnetic anisotropy constant of 4. The structure and manufacturing method were exactly the same as in Example 1 except that GdFeCo with OX 10'erg/cm" was used.
A magneto-optical disk was fabricated. The structure and characteristics of the magnetic layer are
In the column of saturation magnetization in Table 2, "+" indicates dominance of rare earth element sublattice magnetization, and "-" indicates dominance of iron group element sublattice magnetization.

Regarding the magneto-optical disk according to Comparative Example 4 of 2, Example 1
The same evaluation was carried out. As a result, the C/N saturates at a recording power of approximately 6.0 mW, and the C/N value at this time is 51.
It was dB. However, the maximum reproducing power without causing reproducing deterioration in a magnetic field was 1.9 mW, and the reproducing durability was inferior to that of Example 1. In this magneto-optical disk, of the four conditions mentioned above, condition (a) is not satisfied.

Example 2 A magneto-optical disk was manufactured using the same structure and manufacturing method as in Example 1, except that the structure of the magnetic layer was changed as shown in Table 3.

In each of the following examples, all characteristic values are values at room temperature for a single layer film. In addition, in each table following Table 3, in the saturation magnetization (M5) column, add "+" if rare earth element sublattice magnetization is dominant, and "-" if iron group element sublattice magnetization is dominant. This is an indication.

Regarding the magneto-optical disk according to Example 2, Example 1
The same evaluation was carried out. As a result, the C/N saturates at a recording power of approximately 5.4 mW, and the C/N value at this time is 51.
It was dB. Further, the maximum reproducing power without causing reproduction deterioration in a magnetic field was 3', ImW.

Since the Curie temperature of the first magnetic layer is lower than in Example 1, the required minimum recording power is 0.6 mW smaller, that is, the sensitivity is improved.

However, the C/N values are the same. Also, although the maximum reproducing power decreases with sensitivity, the ratio to the minimum recording power is 0.58 in Example 1 and 0.57 in Example 2, which is almost the same, which is good. It has excellent replay durability.

Example 3 A magneto-optical disk was manufactured using the same structure and manufacturing method as in Example 1, except that the structure of the magnetic layer was changed as shown in Table 4.

Regarding the magneto-optical disk according to Example 3, Example 1
The same evaluation was carried out. As a result, the C/N saturates at a recording power of approximately 6.2 mW, and the C/N value at this time is 51.
It was dB. Furthermore, the maximum reproducing power without causing reproduction deterioration in a magnetic field was 3.3 mW, and it had good reproduction durability.

Example 4 A magneto-optical disk was manufactured using the same structure and manufacturing method as in Example 1, except that the structure of the magnetic layer was changed as shown in Table 5. In the configuration of the magnetic layer of this disk, there is substantially no second magnetic layer, the Curie temperature is virtually the same as that of the first magnetic layer, and the film thickness is zero. In this way, the second Eu
The reason why the magnetic layer can be omitted is that the saturation magnetization of the third magnetic layer is relatively large and magnetization reversal occurs even at temperatures near the Curie temperature of the first magnetic layer, so the spins of the first and third magnetic layers are cooled. This is because they have been in place from the beginning of the process.

Furthermore, in the configuration of the magnetic layer of this disk, the Curie temperature of the fourth magnetic layer is equal to the Curie temperature of the sixth Mi layer, but even in such a case, laser light is not irradiated for recording. Therefore, there is a slight temperature gradient in the thickness direction of the magnetic layer, and the recording process of the present invention is possible.

In Example 4, the magneto-optical disk was evaluated in exactly the same manner as in Example I. As a result, the recording power was approximately 6.
C/N is saturated at 0 mW, and the C/N value at this time is 51 dB.
Met. Furthermore, the maximum reproducing power without causing reproduction deterioration in a magnetic field was 3.3 mW, and it had good reproduction durability.

Example 5 A magneto-optical disk was manufactured using the same structure and manufacturing method as in Example 1, except that the structure of the magnetic layer was changed as shown in Table 6. In the configuration of the magnetic layer of this disk, the (2m)th magnetic layer is a ferromagnetic in-plane magnetized film;
+1) Since the perpendicular magnetic anisotropy of the Ml layer is large, it is possible to form and preserve good magnetic domains. Furthermore, the use of light rare earth elements improved the magneto-optical effect at short wavelengths.

Example 6 A magneto-optical disk was manufactured using the same structure and manufacturing method as in Example 1, except that the structure of the magnetic layer was changed as shown in Table 7. The structure of the magnetic layer of this disk is also similar to that of Example 5, in which the (2m)th magnetic layer is an in-plane magnetized film. and,
On the fifth magnetic layer, another magnetic layer was exchange-coupled and laminated for the purpose of improving the magneto-optic effect at short wavelengths.

In this way, the scope of the present invention also includes laminating other magnetic layers before and after the magnetic composite film of the present invention, or forming one layer of the magnetic composite film of the present invention into a composite film.

By comparing Examples 1 to 6 and Comparative Examples 1 to 4 above, it was found that n layers (where n is an odd number of 3 or more) of magnetic layers were stacked so as to be mutually exchange-coupled, and further under the four conditions described above. (a
) to (d), magneto-optical recording has good reproduction characteristics, high C/N, excellent reproduction durability, and does not deteriorate in reproduction characteristics even when the reproduction power is increased. It was found that the medium was obtained.

Next, experiments conducted on still other embodiments of the present invention will be described.

In these embodiments, the thickness of the entire magnetic layer is reduced to about 300 mm, allowing a portion of the reproduction light to pass through the magnetic layer.
This is an example of reading information written using the Faraday effect in addition to the magnetic Kerr effect. In this case, the thickness of the first magnetic layer is preferably about 50 to 200 people, and the thickness of the (2m)th magnetic layer, that is, the even-numbered magnetic layers, is preferably about 5 to 50 people. In addition, the thickness of the (2m+1)th magnetic layer, that is, the odd-numbered magnetic layers excluding the first magnetic layer, is approximately 5 to 100, and the total thickness of the (2m+1)th magnetic layer is 100.
It is desirable that the amount is about the same amount as a person.

Example 7 In the same manner as in Example 1, 1100 mm thick S was deposited on the substrate.
After forming the iN undercoat layer, magnetic layers having the configurations shown in Table 8 were laminated in order from the fifth magnetic layer.

A SiN interference layer with a thickness of 500 mm was provided on top of this, and an A1 reflective layer with a thickness of 600 mm was further provided on top of this.

This substrate was taken out from the sputtering apparatus and subjected to the same steps as in Example 1 to produce a magneto-optical disk.

Regarding the magneto-optical disk according to Example 7, Example 1
The same evaluation was carried out. As a result, the C/N saturates at a recording power of approximately 5.5 mW, and the C/N value at this time is 52.
It was dB. Furthermore, the maximum reproducing power without causing reproduction deterioration in a magnetic field was 3.3 mW, and it had good reproduction durability.

Example 8 A magneto-optical disk was manufactured using the same structure and manufacturing method as in Example 7, except that the structure of the magnetic layer was changed as shown in Table 9. The configuration of the magnetic layer in this disk is an application and development of the present invention, in which the first magnetic layer is shared, and the basic magnetic layer configuration of the present invention is formed before and after the first magnetic layer. According to this configuration, since a layer with a high magneto-optic effect is also formed on the surface of the magnetic layer on the interference layer side, the reproduced signal quality is further improved.

Regarding the magneto-optical disk according to Example 8, Example 1
The same evaluation was carried out. As a result, the C/N saturates at a recording power of approximately 5.8 mW, and the C/N value at this time is 53.
It was dB. Further, the maximum reproducing power without causing reproduction deterioration in a magnetic field was 3.5 mW, and it had good reproduction durability.

Example 9 Example 7 except that the structure of the magnetic layer was changed as shown in Table 10.
A magneto-optical disk was fabricated using exactly the same configuration and manufacturing method. The configuration of the magnetic layer in this disk is an application and development of the present invention, in which the third magnetic layer is shared, and the basic magnetic layer configuration of the present invention is formed before and after the third magnetic layer.

Regarding the magneto-optical disk according to Example 9, Example 1
The same evaluation was carried out. As a result, the C/N is saturated at a recording power of approximately 5.5 mW, and the C/N value at this time is 50.
It was dB. Further, the maximum reproducing power without causing reproduction deterioration in a magnetic field was 3.1 mW, and it had good reproduction durability.

From the results of Examples 7 to 9 above, even when the thickness of the magnetic layer is reduced and reproduction is performed using the Faraday effect, the magneto-optical recording medium of the present invention has excellent reproduction characteristics. It can be seen that the quality is good and the reproduction durability is excellent.

Although the embodiments of the present invention have been described above, the magneto-optical recording medium of the present invention can be applied in various ways other than the above-mentioned embodiments. Further, the present invention is not limited to a structure in which the interface between each magnetic layer is sharp and clear, but may be a structure in which the material/composition gradually changes in the film thickness direction. moreover,
The magneto-optical recording medium of the present invention does not necessarily require an external magnetic field for recording and erasing, but can also perform recording and erasing using, for example, diamagnetic field energy or Bloch domain wall energy. The present invention encompasses all such applications insofar as they do not depart from the scope of the claims.

[Effects of the Invention] As explained above, the present invention has an n-layer (
In a magneto-optical recording medium in which magnetic layers (blue wL, where n is 3 or more) are laminated on a substrate while being exchange-coupled with each other, by clarifying the conditions that the characteristic values of each magnetic layer should satisfy, it is possible to improve the writing characteristics. Excellent, the written information is stored stably even after repeated reproduction, that is, it has excellent reproduction durability, and during reproduction, the reproduction laser beam is reflected by a group of magnetic layers with a high Curie temperature, so the C/N ratio is low. This has the effect that a magneto-optical recording medium with high reproduction characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the structure of a magneto-optical recording medium according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view showing the structure of an example of a magneto-optical recording medium of the present invention comprising seven magnetic layers. , FIG. 3 is a characteristic diagram showing temperature changes in the magnetic properties of each magnetic layer constituting the magneto-optical recording medium illustrated in FIG. 2, and FIG. 4 is a heating and cooling process of the magneto-optical recording medium illustrated in FIG. 2. Explanatory diagrams schematically showing changes in the magnetization orientation state in FIGS. 5(a) to (
e) is a characteristic diagram showing the magnetization curve measured at each temperature for the magneto-optical recording medium illustrated in FIG. FIG. 3 is a characteristic diagram showing temperature rhombicization of magnetization during the cooling process. 1.11...Substrate, 2.12...Undercoat layer, 3
．． 13... Magnetic composite film, 4.14... Protective layer, 21... First magnetic layer, 22
...Second magnetic layer, 23...Third magnetic layer, 24...
-Fourth magnetic layer, 25...Fifth magnetic layer, 26...
6th magnetic layer, 27... 7th magnetic layer. Patent applicant Representative of Canon Co., Ltd. Patent attorney Tadashi Kuwai

Claims (1)

[Claims] 1. An optical device in which n magnetic layers made of magnetic thin films, from the first magnetic layer to the n-th magnetic layer (where n is an odd number of 3 or more) are sequentially laminated on a substrate. In the magnetic recording medium, each of the magnetic layers is exchange-coupled with each other at room temperature, and when the Curie temperature of the i-th magnetic layer (where i is a natural number less than or equal to n) is defined as Tc_i and Tc_n_+_1 is defined as the ambient temperature, (n- 1) For all natural numbers m less than /2, the following four conditions: (a) The perpendicular magnetic anisotropy constant (Ku) of the (2m+1)th magnetic layer at room temperature is 7 x 10^5 erg/cm^3 or more and the saturation magnetization (Ms) at room temperature is 300
em/cm^3 or less, (b) Tc_2_m_+_1≧Tc_1≧Tc_2_m
and (c) Tc_2_m≧Tc_2_(_m_+_
1_), and (d) heating a part of the magneto-optical recording medium to around the Curie temperature Tc_1 of the first magnetic layer,
In the cooling process after transitioning the magnetization orientation state of the first magnetic layer of the portion to a state different from that before heating,
m) When the temperature of the magnetic layer falls below the Curie temperature Tc_2_m of the (2m)th magnetic layer, the magnetization of the (2m)th magnetic layer and the (2m+1)th magnetic layer becomes the (2m-1)th magnetic layer.
The magnetization of the (2m-1)th magnetic layer is such that the temperature of the (2m)th magnetic layer is such that the (2m)th magnetic layer is oriented so that the bonding state due to exchange interaction is stable with respect to the magnetic layer. 1. A magneto-optical recording medium that satisfies all of the following conditions: maintaining the orientation state just before the layer's Curie temperature Tc_2_m drops below. 2. The magneto-optical recording medium according to claim 1, wherein each magnetic layer is composed of a rare earth-iron group amorphous alloy. 3. For all natural numbers m less than or equal to (n-1)/2, the perpendicular magnetic anisotropy constant (Ku) of the (2m+1)th magnetic layer at room temperature is 1 x 10^5 erg/cm^3 or more, And the saturation magnetization (Ms) at room temperature is 200 emu/
3. The magneto-optical recording medium according to claim 1, which has a diameter of cm^3 or less.