JPH06309711A - Magneto-optical recording medium and its production - Google Patents

Abstract

PURPOSE:To produce a magneto-optical recording medium capable of performing satisfactory recording with a small magnetic field in magnetic field modulated recording and hardly undergoing a change in the sensitivity to a magnetic field with the lapse of time. CONSTITUTION:A recording layer 13 and a recording assisting layer 14 are laminated. The Curie temp. Tc2 of the recording assisting layer 14 is higher than the Curie temp. Tc1 of the recording layer 13. The thickness of the recording assisting layer 14 is <=70Angstrom and that of the recording layer 13 is >=80Angstrom . When the recording assisting layer 14 is formed, the optimum pressure of sputtering gas is determined. After film formation, heat treatment is carried out or the recording layer 13 is flattened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium using light and a method for manufacturing the same. In particular, it relates to a magneto-optical recording medium using a magnetic field modulation method as a recording method.

[0002]

2. Description of the Related Art Recording methods for a magneto-optical recording medium are roughly classified into an optical modulation method and a magnetic field modulation method. The magnetic field modulation method is, as shown in JP-A-51-107121 and JP-B-60-48806,
This is a recording method in which the light intensity for heating is kept constant and the magnetic field is modulated based on the data. The magnetic field modulation method is easy to overwrite, and is suitable for recording the mark length, so that the density can be easily increased. However, the magnetic field modulation method requires a magnetic head, and in order to switch the magnetic field at high speed, it is necessary to reduce the head inductance and switch a large current. Further, in order to bring the magnetic head close to the recording layer of the recording medium as much as possible and to maximize the magnetic field acting on the recording layer, a floating magnetic head is used as described in JP-A-63-217548. Things are practically advantageous.

In any case, however, it is desirable that the magneto-optical recording medium for the magnetic field modulation method can record in a low magnetic field so that the magnetic field acting on the recording layer can be as small as possible.
Therefore, as described in Japanese Patent Laid-Open No. 1-116944, the fourth method such as Nd
By adding an element to improve the characteristics in a low magnetic field,
As described in JP-A No. 62-128040, magnetic layers having different compositions are exchange-coupled to reduce a stray magnetic field to improve response to an external magnetic field, or disclosed in JP-A-61-71437. As can be seen, a device such as stacking a perpendicular magnetic film and an in-plane magnetic film to efficiently collect a magnetic flux in the perpendicular magnetic film to reduce the modulation magnetic field has been made. Alternatively, as shown in Japanese Patent Laid-Open No. 4-281239, a method aiming at improvement of magnetic field sensitivity by stacking TbFeCo and GdFeCo having perpendicular magnetization anisotropy smaller than TbFeCo or DyFeCo to limit the stability of minute magnetic domains. was there. Although the mechanism is unknown, the magnetic field can be increased by increasing the oxygen content in the transition metal-rare earth metal amorphous alloy or by holding the amorphous alloy film in an atmosphere containing oxygen after the film formation. A method for improving sensitivity is disclosed in
156754 and JP-A-3-276440.

[0004]

However, in practice, it is difficult for these conventional techniques to reduce the modulation magnetic field to ± 100 Oe or less, and the addition of the fourth element or the lamination with the in-plane magnetized film is required. Alternatively, the oxidation of the magnetic film may deteriorate the reproduction signal characteristics. It has been difficult to always manufacture a magneto-optical recording medium having a high magnetic field sensitivity by a method such as a method of oxidizing a magnetic film because the recording characteristics are likely to change.

Therefore, an object of the present invention is to provide a magneto-optical recording medium for magnetic field modulation capable of sufficient recording with a smaller modulation magnetic field than the conventional one, and further to provide a manufacturing method for stably manufacturing the same. is there. Another object of the present invention is to provide a magneto-optical recording medium or a manufacturing method in which the magnetic field sensitivity characteristics are less likely to change with time.

[0006]

The magneto-optical recording medium of the present invention has a recording auxiliary layer laminated in contact with the recording layer in the magneto-optical recording medium having a recording layer having a Curie temperature of Tc1.
The Curie temperature Tc2 of the recording auxiliary layer is higher than Tc1, the film thickness of the recording auxiliary layer is 70 Å or less, and the film thickness of the recording layer is 80 Å or more. Further, in the method of manufacturing the magneto-optical recording medium, when forming the recording auxiliary layer by the sputtering method, the sputtering gas pressure is controlled.
The feature is that it is performed at 10 mTorr or less. Also, after forming the recording layer and recording auxiliary layer by the sputtering method,
The heat treatment is performed at the above temperature. Alternatively, when the recording layer and the recording auxiliary layer are formed in this order, the recording auxiliary layer is formed after the surface of the recording layer is flattened.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows a sectional structure of a magneto-optical recording medium capable of recording by magnetic field modulation according to the present invention.
On the surface of the transparent substrate 11, a first dielectric layer 12, a recording layer 13, a recording auxiliary layer 14, a second dielectric layer 15 and a reflective layer 16 are sequentially laminated. Here, if one example of the material of each layer is shown, a transparent substrate
11 is a polycarbonate (PC) substrate, the first dielectric layer 1
2. The second dielectric layer 15 is an AlSiN layer and the recording layer 13 is NdDyTb
FeCo layer, recording auxiliary layer 14 is DyFeCo layer, reflective layer
15 is an AlTi layer. Many other variations of materials other than this are also known. For example, recording layer 13, recording auxiliary layer
For 14, TbFeCo, DyFeCo, GdFeCo, GdTbFeCo, Gd
DyFeCo, TbDyFeCo, GdDyTbFeCo, NdTbFeCo, PrTbFeCo,
Various rare earth-transition metal amorphous alloys such as NdDyFeCo and PrDyFeCo are known. It is practically important to add elements such as Cr, Ti, Al and Pt to these compositions for the purpose of improving corrosion resistance. In order to make the Curie temperature higher than that of the recording layer 13, the recording auxiliary layer 14 increases the content of transition metal in the rare earth-transition metal alloy, particularly the content of Co, or increases the content of Gd as a rare earth metal. It is preferable to reduce the content of Nd, Pr. It is easy to increase the Curie temperature of the recording auxiliary layer 14 with respect to the recording layer 13 by adjusting the composition as described above.

Here, the recording layer 13 is Nd5.4at% Dy15.7a.
A rare earth-transition metal alloy having a composition of t% Tb5.1at% Fe58.5at% Co15.3at% was used. A thin film was formed by magnetron DC sputtering using a cast alloy target under an argon gas pressure of 1.8 mTorr and a power of 300 W. The Curie temperature is 180 ° C. The recording layer 13 alone exhibits magnetic properties of transition metal sublattice dominant at room temperature, as is clear from its composition. Further, as the recording auxiliary layer 14, Dy29.8at%
A rare earth-transition metal alloy having a composition of Fe35.0at% Co35.2at% was used. Argon gas pressure 0.4 mTorr by magnetron DC sputtering using cast alloy target.
A thin film was formed under the condition of power 100W. Curie temperature is 280
℃. The recording auxiliary layer, by itself, shows the magnetic characteristics of the rare earth metal sublattice dominant at room temperature, as is clear from its composition.

In order to manufacture the magneto-optical recording medium having the structure shown in FIG. 1, the first dielectric layer 12, the recording layer 13, the recording auxiliary layer 14, the second dielectric layer 15 and the reflective layer 16 are formed on the transparent substrate 11. Are sequentially stacked. At this time, the material of the first dielectric layer 12 is, for example, AlSiN, and the conditions of the sputtering method are, for example, sputter gas of Ar 60% + N 2 40%, pressure of 1.7 mTorr, and input power of RF2500W. An AlSi alloy target is used as the target. In this embodiment, the first dielectric layer 12 was not flattened. That is, after forming the first dielectric layer 12, the recording layer 13 was formed without performing any treatment. Originally, the magneto-optical recording medium in which the first dielectric layer 12 is not flattened has poor magnetic field sensitivity as previously filed by the present inventor. Signal components (carrier level) although noise is small in a low magnetic field of about ± 50 Oersted
Was very small and it was difficult to obtain a practical CN ratio.
The inventors of the present invention have confirmed that this is due to the generation of minute magnetic domains in the recording magnetic domains and the reduction of the net signal component by observing the magnetic domains with a polarization microscope.

Under the above conditions, the film thicknesses of the first dielectric layer 12, the recording layer 13, the second dielectric layer 15 and the reflective layer 16 are 75 respectively.
As 0 Å, 200 Å, 200 Å, 600 Å, a comparative example in which the recording auxiliary layer 14 is not formed, the sensitivity of the recording auxiliary layer 14 to the modulating magnetic field of the magneto-optical recording medium of the present invention formed with a thickness of 25 Å and 35 Å is investigated. It was Note that the film thickness of the recording auxiliary layer 14 is not an actually measured value, but is determined by measuring the formation speed of the recording auxiliary layer 14 in advance and calculating the sputtering time required for each film thickness. . Recording was performed at a linear velocity of 1.4 m / s, a recording frequency of 720 kHz and a recording power of 6.0 mW, while changing the magnitude of the modulating magnetic field. The relationship between the magnitude of the modulating magnetic field and the CN ratio is shown in FIG. 2 (A), and the relationship with the carrier level is shown in FIG. 2 (B). In the comparative example in which the recording auxiliary layer 14 was not formed, a CN magnetic field of about 200 Oersted was required for saturation, and a sufficient CN ratio was not obtained at 100 Oersted or less. This depends mainly on the change of the carrier level, and a large magnetic field is required for the carrier level to saturate. On the other hand, in the sample in which the recording auxiliary layer 14 is formed in a thickness of 25 liters after the recording layer 13 is formed, the CN ratio is saturated at about 50 Oersted. As can be seen by comparing with the carrier level data in FIG. 2B, the fact that the recording auxiliary layer 14 is formed allows the carrier level to be saturated even with a small modulation magnetic field, which contributes to the high magnetic field sensitivity. There is. Further, if the recording auxiliary layer 14 is formed thick, the sensitivity of the CN ratio to the modulating magnetic field deteriorates. The carrier level is saturated with a magnetic field smaller than that of the example of 25 Å, but the CN ratio deteriorates with respect to 25 Å due to an increase in noise level in this region.

Further, the film thicknesses of the first dielectric layer 12, the recording layer 13, the second dielectric layer 15 and the reflective layer 16 are 750Å, 200Å,
Set the film thickness of the recording auxiliary layer 14 from 0Å to 80Å as 200Å and 600Å
The sensitivity to the modulating magnetic field of the magneto-optical recording medium of the present invention, which was manufactured by changing to 5Å in increments of 5, was examined. Note that the film thickness of the recording auxiliary layer 14 is not an actually measured value, but is determined by measuring the formation speed of the recording auxiliary layer 14 in advance and calculating the sputtering time required for each film thickness. . Recorded linear velocity 1.4m / s, recording frequency 720kHz, recording power 6.0m
W, modulation field ± 50 Oersted. Recording auxiliary layer 1
The relationship between the film thickness of 4 and the CN ratio is shown in FIG. 3 (A), and the relationship with the carrier level is shown in FIG. 3 (B). Extremely thin recording auxiliary layer of 5Å 1
It can be seen that the effect appears only by forming 4.
The CN ratio when recording with a modulating magnetic field of ± 50 Oersted strongly depends on the thickness of the recording auxiliary layer 14. The effect is recognized from 5Å to 70Å, especially in the vicinity of 20Å to 35Å.
The CN ratio was obtained. Both the carrier level and the noise level of the CN ratio change with the film thickness. The noise level gradually decreased from 5Å to 30Å, then 35
Å It has turned to a sharp rise. On the other hand, the carrier level increases rapidly from 5Å to 25Å with increasing film thickness. At 25Å and above, the carrier level saturates. Especially, the reasonably large CN ratio was obtained in the vicinity of 20Å to 35Å because the noise level was sufficiently low and the carrier level was saturated.

The reason why the magnetic field sensitivity is remarkably improved by forming the recording auxiliary layer 14 with a certain extremely thin thickness is considered to be as follows.

As shown in FIG. 4, when a beam spot 41 formed by converging a laser beam is irradiated onto the magneto-optical recording medium, the beam spot 41 is locally heated. As a result, there are three regions that can be roughly classified. Area 4 where it is heated above the Curie temperature
2. Region 43 (hereinafter referred to as the magnetic domain formation zone) where a change occurs with respect to the modulating magnetic field above the temperature at which the domain wall is fixed below the Curie temperature.
(Referred to as 43), there are three regions (a region outside the magnetic domain forming band 43 in FIG. 4) that does not change even when a modulation magnetic field is applied at a temperature below the temperature at which the domain wall is fixed. The width of the magnetic domain forming zone 43 is estimated to be about 1 μm, and the temperature difference is estimated to be about 10 ° C to 15 ° C.
In thermomagnetic recording, the magnetic domain is recorded by the interaction between the magnetic film in the magnetic domain formation zone 43 and the applied magnetic field. In a magneto-optical recording medium using a rare earth metal-transition metal amorphous alloy film as a recording film, a high CN ratio was obtained and a practical composition was TbFeCo or Dy.
Based on FeCo, Curie temperature is 150 ℃ to 220 ℃
The composition is close to the compensation composition at room temperature. In the composition of this region, at the temperature corresponding to the magnetic domain formation zone 43, especially just below the Curie temperature, the squareness deteriorates and a Kerr hysteresis loop with a large magnetic field at which the Kerr rotation angle is saturated is obtained, as shown in FIG. When magnetic domain observation is performed at a temperature corresponding to the Kerr hysteresis loop as shown in FIG. 5, a maize magnetic domain having a very fine magnetic domain width is observed under an applied magnetic field of zero. Even if a magnetic field as small as 30 oersted is applied,
The maize domain does not disappear and is not magnetized in one direction. When magnetic field modulation recording is performed using a magneto-optical recording medium having a rare earth metal-transition metal amorphous alloy film having such a composition as a recording film, as shown in the comparative example of FIG. In that case, the carrier level is insufficient and sufficient C / N cannot be obtained. When the recorded magnetic domains are observed, very fine and irregular magnetic domains (hereinafter referred to as microdomains) are recognized in the recorded magnetic domains. Since this micro domain is finer than the resolution of the magneto-optical head used for reproduction, it is reproduced as if the contrast of the recording magnetic domain is lowered rather than worsening the noise level, resulting in a reproduction signal with an insufficient carrier level. Is obtained. The phenomenon that such a micro domain occurs in the recording magnetic domain is because the maize magnetic domain is likely to occur at the temperature just below the Curie temperature described above. The recording process will be described below with reference to FIG.

(1) Fine maize magnetic domains are generated in the high temperature portion 43a of the magnetic domain formation zone (that is, immediately below the Curie temperature).

(2) In the low temperature portion 43b of the magnetic domain formation zone, since the magnetization, the perpendicular anisotropy energy and the exchange stiffness constant are larger than those in the high temperature portion, the magnetostatic energy between the applied magnetic field and the spontaneous magnetization, or the domain wall. Energy is also large. Therefore, the maze magnetic domain approaches a single magnetic domain magnetized in the direction of the applied magnetic field. However, in order to make the maize magnetic domain once generated into a single magnetic domain, it is necessary to move the magnetic domain wall, but since the frictional force that prevents the movement of the magnetic domain wall is large in the low temperature part, a large magnetic field is required to make it into a single magnetic domain. I need.

(3) When the temperature falls and goes out of the magnetic domain forming zone 43, the frictional force increases, the movement of the domain wall stops, and the magnetic domain does not change. When the modulating magnetic field is small, the magnetic domain is fixed without being completely extinguished, so that the magnetic domain is frozen as a micro domain in the recording magnetic domain.

As described above, the microdomain and the generation of the maize magnetic domain are closely related. On the other hand, by selecting the composition of the rare earth metal-transition metal amorphous alloy film, a fine maize magnetic domain does not occur at the temperature of the magnetic domain formation zone, or even if a maize magnetic domain occurs, its magnetic domain width is set to the size of the recording domain. It is possible to make it larger than that. It is known that the domain width of the maize domain is proportional to the 1/2 power of the domain wall energy σ _W and inversely proportional to the spontaneous magnetization Ms. That is, it is possible to increase the magnetic domain width of the maize magnetic domain by selecting a composition having a large domain wall energy σ _{W and a} small spontaneous magnetization Ms at the temperature corresponding to the magnetic domain formation zone 43. Since the compensation temperature at which the magnitude of magnetization becomes zero in the composition exhibiting the magnetic characteristics in which the rare earth metal sublattice is dominant at room temperature is equal to or higher than room temperature, the magnitude of magnetization in the magnetic domain forming zone 43 can be reduced. Further, a composition based on GdFeCo can also increase the magnetic domain width of the maize magnetic domain. The perpendicular anisotropy energy Ku of the GdFeCo system is TbFeCo
It is said that the composition is smaller than that of the DyFeCo system. The domain wall energy σ _W is proportional to the 1/2 power of the perpendicular anisotropy energy Ku, so in the GdFeCo system, the domain wall energy σ _W should be rather small and the width of the maize domain should be small, but actually the maize domain was observed. On the contrary, the result shows that the width of the maize magnetic domain is increased. This is the vertical anisotropy energy
This is probably because the fluctuation of Ku is small. TbFeCo system, DyFe
The Co system is a composition with a large coercive force, but it is explained that its origin is due to microscopic fluctuations in the magnitude and angle of the perpendicular anisotropy energy Ku, which impedes the movement of the domain wall. . Since the domain wall is stably fixed near the minimum point of the magnitude of the perpendicular anisotropy energy Ku, the net domain wall energy is the average estimated from the magnitude of the average perpendicular anisotropy energy Ku. The value is much smaller than the domain wall energy. On the other hand, the GdFeCo system has a small coercive force, which means that the microscopic fluctuation of the perpendicular anisotropy energy Ku is small. At this time, the net domain wall energy is the average perpendicular anisotropy energy Ku.
A value close to the average domain wall energy estimated from the magnitude of should be obtained. In other words, GdFeCo system is TbFeCo
Although the average domain wall energy is smaller than that of the system and the DyFeCo system, the net domain wall energy is increased, and as a result, the width of the maize domain is considered to be larger because it is the net domain wall energy.

Now, if a magneto-optical recording medium is manufactured using a composition in which the width of the maize magnetic domain is large at a temperature corresponding to such a magnetic domain formation zone, it is difficult to form microdomains, and therefore the magnetic field sensitivity is high. The medium should be realized. When recording is actually performed on such a medium by the magnetic field modulation method, a practical CN ratio cannot be obtained even when a large magnetic field is applied, in addition to a high medium having a high magnetic field sensitivity. For example, DyF used for the recording auxiliary layer 14 in Example 1
Even if eCo was recorded under the optimum condition for a 200 Å single-layer film, only C / N of about 46 dB was obtained. It can be seen that the composition used for the recording layer 13 in Example 1 is not practical as compared with 53 dB being obtained. At room temperature, GdFeCo with a coercive force close to that of the compensating composition of 15 kOersted or higher has a high noise level of only 28 dB even when recorded under the optimum conditions.
Only C / N is obtained. The cause becomes clear when the recorded recording domain is observed with a polarization microscope. Figure
Figure 6 shows a schematic diagram of the observation results. FIG. 6 (a) shows a shape called a Yaba shape in a recording magnetic domain of a medium that can obtain a high CN ratio, which faithfully reflects the temperature distribution when heated by a recording beam. The rear end portion 61 of the arrow-shaped magnetic domain is sharply recorded. On the other hand, FIG. 6 (b) is a recording magnetic domain of a medium having a large maize magnetic domain width at the temperature corresponding to the magnetic domain forming zone 43. Micro domains are not recognized in the recording magnetic domain, but the shape of the magnetic domain is irregular. It is fluctuating. In particular, the rear end portion 61 of the arrow-shaped magnetic domain
Is transformed into a rounded shape. If the formation of the recording magnetic domain exactly follows the temperature distribution, it should be an arrow blade type magnetic domain, but the rear end portion 61 of the arrow blade type magnetic domain has an unstable shape in terms of domain wall energy. A round ellipse is more stable. That is, if the domain wall energy is large and the domain wall is easily moved, a force that reduces the domain wall energy of the recording domain and minimizes the energy acts on the domain wall to change the shape of the domain. Then, it becomes difficult to record the arrow-shaped magnetic domain according to the temperature distribution, and the noise is increased as a result of recording the magnetic domain as shown in FIG. 6 (b) in which the arrow-shaped magnetic domain is deformed non-uniformly. It will be.

The magneto-optical recording medium of the present invention is intended to obtain an unprecedented excellent magnetic field sensitivity by laminating magnetic films which cannot obtain sufficient characteristics by these two types of magnetic field modulation. is there. A magnetic domain forming zone is formed on the recording layer 13.
The composition that produces fine maize magnetic domains at a temperature corresponding to 43
The Curie temperature of the recording auxiliary layer 14 is higher than that of the recording layer 13,
A composition in which the magnetic domain width of the maize magnetic domain is larger is laminated. Moreover, the recording auxiliary layer 14 should be formed to a very thin thickness of 70 angstroms or less. The mechanism by which the magnetic field sensitivity is improved by such a configuration will be described with reference to FIG.

(1) In the high temperature portion 43a of the magnetic domain formation zone (that is, near the Curie temperature of the recording layer 13), the spontaneous magnetization of the recording layer 13 is very small, so that the recording auxiliary layer 14 having a high Curie temperature affects the magnetic domain formation. Is. Since the characteristic of the recording auxiliary layer 14 that the maize magnetic domain has a large magnetic domain width is dominant, the generation of a fine maize magnetic domain can be suppressed even with a small applied magnetic field.
That is, it is possible to form a single domain structure in which the directions of magnetization are aligned in one direction even under a small applied magnetic field.

(2) When the temperature drops to the low temperature portion 43b of the magnetic domain formation zone, the spontaneous magnetization of the recording layer 13 is restored. Since the thickness of the recording layer 13 is about 10 times that of the recording auxiliary layer 14, when the spontaneous magnetization of the recording layer 13 is restored, the influence of the recording layer 13 on the magnetic domain formation increases. In other words, the characteristics in which the maize magnetic domain is likely to occur but the frictional force that prevents the movement of the domain wall is large become dominant. If this temperature is maintained for a long time, a maize magnetic domain will be generated, but during the actual recording process, that is, in the case of rapid cooling, the maize magnetic domain is suppressed by the high temperature portion 43a of the magnetic domain formation zone, and the inside of the recording magnetic domain is isolated. Since it is a magnetic domain, no maize magnetic domain is generated in the low temperature portion 43b of the magnetic domain formation zone. Rather, the frictional force that hinders the movement of the domain wall retains the single domain structure obtained in the high temperature portion 43a of the domain forming zone, and fixes the arrow-shaped magnetic domain according to the temperature distribution. As a result, the rear end portion 61 of the arrow-shaped magnetic domain is also sharply recorded.

As described above, in the magnetic domain forming zone 43, the recording auxiliary layer 14 is dominant in the high temperature portion which is the initial stage of magnetic domain formation, and the recording layer 13 is dominant in the low temperature portion which determines the shape of the recording magnetic domain. It is considered that the suppression of magnetic domains and the sharp and stable recording of the arrow-shaped magnetic domains were compatible with each other.
The effect of making the magnetic layer into two layers is exactly 2 by each layer.
It is connected to the realization of one recording phase in the magnetic domain formation zone 43. On the side where the film thickness of the recording auxiliary layer 14 is thinner than the optimum film thickness, the temperature region where the recording layer 13 is dominant in the magnetic domain formation zone 43 is wide, and on the side where the film thickness of the recording auxiliary layer 14 is thicker than the optimum film thickness, the magnetic domain is formed. In the formation zone 43, the temperature region where the recording auxiliary layer 14 is dominant becomes wider. For example, if the recording auxiliary layer 14 is too thick, the recording auxiliary layer 14 becomes dominant in most of the region in the magnetic domain formation zone 43, and as a result, the characteristics of the recording auxiliary layer 14 have an excessive influence on recording and the magnetic domain shape is It can be explained that the noise level rises as a result of the unevenness as shown in FIG. 6 (B). Magnetic domain formation zone 43
Is a narrow range of 10 ℃ to 15 ℃ in the temperature range.
The magnetic field sensitivity is improved under the condition that the area where the recording auxiliary layer 14 is dominant and the area where the recording layer 13 is dominant are mixed in this narrow area. Therefore, a phenomenon occurs in which the magnetic field sensitivity changes very sensitively to the film thickness of the recording auxiliary layer 14.

Even in the conventional magneto-optical recording medium, there have been attempts to improve magnetic field sensitivity by laminating magnetic films having different properties. For example, in Japanese Unexamined Patent Publication No. 62-128040, an applied magnetic field effectively acts by stacking a composition of a transition metal sublattice dominant and a composition of keeping a rare earth metal sublattice dominant up to the Curie temperature to reduce the magnitude of the stray magnetic field. Such a configuration is disclosed. In this example, the directions of the stray magnetic fields of the respective magnetic films are opposite to each other so that they cancel each other out. Therefore, it is necessary that each magnetic film has a sufficient thickness. As in the configuration of the present invention, for example, when the film thickness ratios are 10: 1, it is largely deviated from the purpose of canceling the stray magnetic field. However, since the magneto-optical recording medium of the present invention does not require a composition having characteristics of a rare earth metal sublattice predominant near the Curie temperature, it has a completely different structure from the multilayer magnetic film structure disclosed in JP-A-62-128040. It is a medium. Further, Japanese Patent Laid-Open No. 4-281239 discloses a structure in which GdFeCo and TbFeCo are laminated. Among them, GdFe
When the Curie temperature of the Co layer is set higher than that of the TbFeCo layer, the GdFeCo
The combinations of the thicknesses of the layers, TbFeCo layer, of 60 Å and 190 Å, 100 Å and 150 Å, and 150 Å and 100 Å are shown in the examples. It is described here that the second combination exhibits the most excellent properties. Thus, the GdFeCo layer is thicker than the recording auxiliary layer 14 of the present invention because the recording mechanism is essentially different from that of the two-layer structure of the present invention. The conventional structure in which two layers with different Curie temperatures are stacked is recorded through the "process in which the layer with the higher Curie temperature is recorded first" and then the "process in which the recording magnetic domain is transferred to the layer with the lower Curie temperature". The method can be classified into a method (hereinafter, referred to as a transfer method). However, this transfer method has not been essentially successful in improving the magnetic field sensitivity. In other words, the shape of the recording domain and the state of the microdomains are determined in the process of recording the layer with the higher Curie temperature first, and after that, this is simply transferred to the layer with the lower Curie temperature, so that the layer with the higher Curie temperature is This is because the magnetic field sensitivity of the transfer type two-layer structure is determined by the magnetic field sensitivity of the constituent magnetic film.
Therefore, in the transfer type two-layer structure, the two-layer structure may provide characteristics superior to the magnetic field sensitivity of the magnetic film single layer constituting the layer having a low Curie temperature, but the high Curie temperature. It is not possible to obtain characteristics superior to the magnetic field sensitivity of the magnetic film single layer constituting the layer. On the other hand, in the magneto-optical recording medium of the present invention, the two-layer structure of the ultra-thin film can improve the magnetic field sensitivity as compared with the structure in which each layer is formed alone. This is started by making the layer having the higher Curie temperature an ultrathin film of 70 Å or less, and the recording layer 13 and the region where the recording auxiliary layer 14 is dominant in the magnetic domain formation zone 43 as described above. The mixture with the dominant region occurred and the magnetic field sensitivity was improved. The reason why the layer having the higher Curie temperature, that is, the recording auxiliary layer 14 must be 70 Å or less is that when the recording auxiliary layer 14 having a Curie temperature of more than 70 Å is formed, recording is performed by the transfer method described above. The recording auxiliary layer 14 exceeding 70 Å has spontaneous magnetization independently even at a temperature exceeding the Curie temperature of the recording layer 13, and further has a large coercive force and perpendicular anisotropy energy.
The formation of the recording magnetic domain progresses due to the above characteristics. On the other hand, in the recording auxiliary layer 14 of 70 Å or less, at a temperature exceeding the Curie temperature of the recording layer 13, the spontaneous magnetization, the coercive force, and the perpendicular anisotropy energy rapidly decrease with the temperature increase.
This is because in an extremely thin magnetic thin film of 70 Å or less, the magnitude of spontaneous magnetization decreases and the Curie temperature lowers compared to the bulk. At a temperature lower than the Curie temperature of the recording layer 13, the recording auxiliary layer 14 can keep spontaneous magnetization like a sufficiently thick thin film by exchange coupling with the recording layer 13,
At a temperature equal to or higher than the Curie temperature of the recording layer 13, the recording layer 13 is merely a paramagnetic metal that has lost its spontaneous magnetization.
As a result, the characteristics of the ultra-thin magnetic film appear strongly, and as a result, spontaneous magnetization, coercive force, and perpendicular anisotropy energy are rapidly reduced. Therefore, the transfer type recording process does not occur. Thus, the recording auxiliary layer 14 being an extremely thin film is an essential requirement for the two-layer structure of the present invention.

(Embodiment 2) Here, an embodiment in which the thickness of the recording layer 13 is changed will be described. As shown in FIG. 1, a first dielectric layer 12, a recording layer 13, and a recording auxiliary layer 1 are formed on a transparent substrate 11.
4. A magneto-optical recording medium in which the second dielectric layer 15 and the reflective layer 16 were laminated was produced. Nd5at% Dy16at% Tb5at% as recording layer 13
A rare earth-transition metal amorphous alloy having a composition of Fe59at% Co15at% was used. Argon gas pressure 1.2 mTorr by magnetron DC sputtering using a cast alloy target.
To form a thin film. The Curie temperature is 180 ° C. Recording layer 1
As shown by its composition, 3 alone shows the magnetic properties of the transition metal sublattice dominant at room temperature. Further, as the recording auxiliary layer 14, a rare earth-transition metal alloy having a composition of Dy30at% Fe35at% Co35at% was used. Thin films were formed by magnetron DC sputtering using a cast alloy target at an argon gas pressure of 0.4 mTorr. Curie temperature is 280 ℃
Is. The recording auxiliary layer, by itself, shows the magnetic characteristics of the rare earth metal sublattice dominant at room temperature, as is clear from its composition. The compensation temperature is 130 ° C, and at higher temperatures, the transition-metal sublattice-dominant magnetic property is exhibited. The first dielectric layer 12 and the second dielectric layer 15 were made of Si ₃ N ₄ to have film thicknesses of 750Å and 200Å, respectively. The reflection layer 16 was made of AlTi alloy with a film thickness of 600 Å. A polycarbonate substrate was used as the transparent substrate 11.

The thickness of the recording layer 13 was set to 120Å, 200Å, 320Å. Further, the recording auxiliary layer is formed by the thickness of each recording layer 13.
The sensitivity of the magneto-optical recording medium of the present invention produced by changing the film thickness of 14 from 0Å to 80Å in 5Å increments was examined. Note that the film thickness of the recording auxiliary layer 14 is not an actually measured value, but is determined by measuring the formation speed of the recording auxiliary layer 14 in advance and calculating the sputtering time required for each film thickness. . Recorded linear velocity 1.4m / s, recording frequency 720kH
z, recording power 6.0 mW, modulation magnetic field ± 50 Oersted. FIG. 7 shows the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio. It can be seen that even if the film thickness of the recording layer 13 changes to 120Å, 200Å, 320Å, a particularly high CN ratio is obtained when the film thickness of the recording auxiliary layer 14 is 20Å to 30Å. Recording layer in this range
The film thickness of 13 is the most practical film thickness for the structure having the reflective layer 16 as shown in FIG. Recording layer in this range
It can be seen that even if the film thickness of 13 changes, the film thickness required for the recording auxiliary layer 14 does not change significantly. Furthermore, the recording layer 13 is set to 40
In an experiment in which the recording auxiliary layer 14 has a film thickness of 70 Å or less, a sufficient effect was obtained, and a film thickness of 50 Å or less obtained a more desirable effect in an experiment in which the film thickness of the recording auxiliary layer 14 was changed from 0 Å to 2000 Å. As described above, in the two-layer structure of the present invention, the magnetic field sensitivity can be improved by forming the recording auxiliary layer having a thickness of 70 Å or less without being significantly affected by the film thickness of the recording layer 13. However, when the thickness of the recording layer 13 is less than 80 Å, a tendency of magnetic field sensitivity is recognized, but even with the optimum thickness of the recording auxiliary layer 14, a practically sufficient CN ratio cannot be obtained.
Therefore, the film thickness of the recording layer 13 of the magneto-optical recording medium of the present invention is
80Å or more is desirable.

(Example 3) In Examples 1 and 2, the recording auxiliary layer 14 was used.
DyFeCo was used as the recording auxiliary layer 14 in this example.
The case of using FeCo and TbFeCo will be described.

As shown in FIG. 1, on a transparent substrate 11, a first dielectric layer 12, a recording layer 13, a recording auxiliary layer 14, a second dielectric layer 15,
A magneto-optical recording medium having the reflective layer 16 laminated was produced. As the recording layer 13, a rare earth-transition metal amorphous alloy having a composition of Nd6at% Dy15at% Tb6at% Fe56at% Co17at% was used. Thin films were formed by magnetron DC sputtering with a cast alloy target at an argon gas pressure of 1.9 mTorr. The Curie temperature is 180 ° C. The recording layer 13 alone exhibits magnetic properties of transition metal sublattice dominant at room temperature, as is clear from its composition. Further, as the recording auxiliary layer 14, Gd25at
A rare earth-transition metal alloy having a composition of% Fe70at% Co5at% was used. Magnetron DC with cast alloy target
A thin film was formed by sputtering at an argon gas pressure of 1.2 mTorr. The Curie temperature is 230 ° C. Recording auxiliary layer 14
Shows magnetic properties near the compensation composition at room temperature. Figure 8 shows the Kerr hysteresis loop near the Curie temperature of this GdFeCo single layer. It can be seen that the magnetic film has a small coercive force but maintains the squareness ratio at 1 just below the Curie temperature. As another example, a rare earth-transition metal alloy having a composition of Tb30at% Fe32at% Co38at% was used for the recording auxiliary layer 14. Thin films were formed by magnetron DC sputtering with a cast alloy target at an argon gas pressure of 1.2 mTorr. Curie temperature is 300 ℃
Above that, it is about 360 ℃. The recording auxiliary layer, by itself, shows the magnetic characteristics of the rare earth metal sublattice dominant at room temperature, as is clear from its composition. The compensation temperature is 150 ° C, and at higher temperatures, the transition metal sublattice-dominant magnetic property is exhibited. First
Si ₃ N ₄ is used for the dielectric layer 12 and the second dielectric layer 15, respectively.
It was prepared with a film thickness of 750Å and 200Å. The reflection layer 16 was made of AlTi alloy with a film thickness of 600 Å. A polycarbonate substrate was used as the transparent substrate 11.

The film thickness of the recording auxiliary layer 14 is changed from 0Å to 50Å 10
The sensitivity to the modulating magnetic field of the magneto-optical recording medium of the present invention manufactured by changing it in Å steps was examined. Note that the film thickness of the recording auxiliary layer 14 is not an actually measured value, but is determined by measuring the formation speed of the recording auxiliary layer 14 in advance and calculating the sputtering time required for each film thickness. . Record speed
Recording was performed at 1.4 m / s, recording frequency of 720 kHz, recording power of 6.0 mW, and modulation magnetic field of ± 50 Oersted. The film thickness of the recording auxiliary layer 14 and
Figure 9 shows the relationship with the CN ratio. GdFe with Curie temperature of 230 ℃
When Co was used for the recording auxiliary layer 14, the film thickness was 40Å, and when TbFeCo having a Curie temperature of about 360 ° C was used for the recording auxiliary layer 14, the film thickness was 20Å, and the magnetic field sensitivity was improved. As with DyFeCo, it can be seen that even with these compositions, there is a film thickness that improves magnetic field sensitivity in a very thin region. But GdFeCo,
In TbFeCo, the CN ratio drops sharply when the optimum film thickness is exceeded. When GdFeCo is used as the recording auxiliary layer 14, the noise level becomes extremely large, which is the main reason for the decrease in the CN ratio, and the carrier level has not changed. On the other hand, when TbFeCo is used as the recording auxiliary layer 14, the carrier level also drops significantly. The Curie temperature of TbFeCo used here is 360.
Since the temperature is as high as about 0 ° C., the optimum recording power increases as the recording auxiliary layer 14 becomes thicker. Since the experiment was performed with the recording power fixed at 6 mW, the fact that the difference from the optimum recording power became large affects the results in Fig. 9. On the other hand, the decrease in the CN ratio when GdFeCo of 50 Å is used for the recording auxiliary layer 14 is characterized by high noise regardless of the recording power. When observing the recording magnetic domain in the double-layered structure of this GdFeCo with a thickness of 50 Å, no microdomains are found in the recording magnetic domain, but the shape of the magnetic domain is to be seen as an irregular shape that is greatly deviated from the ideal arrow shape. I was able to. As described above, when GdFeCo is used as the recording auxiliary layer 14, a significant noise increase occurs when the optimum film thickness is exceeded.
It is more desirable to use a composition containing Co or TbFeCo as the main component for the recording auxiliary layer 14.

Example 4 Next, a method of manufacturing the magneto-optical recording medium described in Examples 1, 2 and 3 will be described. In this embodiment, the influence of the sputtering gas pressure when forming the recording auxiliary layer 14 will be described.

As the sputtering gas, Ar gas which is an inert gas is generally used. The sputtered particles that have jumped out of the target collide with the sputter gas and are scattered by the time they reach the substrate. The higher the sputtering gas pressure, the shorter the mean free path of sputtered particles and the more the number of collisions. Therefore, the pressure of the sputtering gas is one of the important factors that influence the distribution of the incident angle of the sputtered particles on the substrate and the energy distribution of the sputtered particles. For example, when the ratio of the incidence angle of sputtered particles on the substrate is obliquely more than vertical, the self-projection effect becomes remarkable, and a thin film having a columnar structure is completed. Even in the step of forming the recording auxiliary layer 14, the magnetic field sensitivity characteristics may change significantly by changing the pressure of the sputtering gas.

As shown in FIG. 1, on a transparent substrate 11, a first dielectric layer 12, a recording layer 13, a recording auxiliary layer 14, a second dielectric layer 15,
A magneto-optical recording medium having the reflective layer 16 laminated was produced. As the recording layer 13, a rare earth-transition metal amorphous alloy having a composition of Nd5at% Dy16at% Tb5at% Fe59at% Co15at% was used. Thin films were formed by magnetron DC sputtering with a cast alloy target at an argon gas pressure of 1.2 mTorr. The Curie temperature is 180 ° C. The recording layer 13 alone exhibits magnetic properties of transition metal sublattice dominant at room temperature, as is clear from its composition. Further, as the recording auxiliary layer 14, DyFeCo showing a magnetic characteristic of a rare earth metal sublattice dominant at room temperature was used. Thin films were formed by magnetron DC sputtering using a cast alloy target having a composition of Dy36at% Fe34at% Co30at%. At that time, the argon gas pressure was 0.42 mTor
r, 1.5mTorr, 3.5mTorr, 5.5mTorr, 7.5mTorr, 9.5mTor
A sample having a different r was prepared. Argon gas pressure was measured by BA type ionization vacuum gauge.
May cause a measurement error of 20%. The composition changes slightly depending on the argon gas pressure, but the Curie temperature is 25
0 to 280 ° C. The first dielectric layer 12 and the second dielectric layer 15 were made of Si ₃ N ₄ to have film thicknesses of 750Å and 200Å, respectively. The reflection layer 16 was made of AlTi alloy with a film thickness of 600 Å. A polycarbonate substrate was used as the transparent substrate 11.

The recording auxiliary layer 14 has a film thickness of 5Å from 0Å to 70Å
The sensitivity to the modulating magnetic field of the magneto-optical recording medium of the present invention, which was produced by changing it in steps or in steps of 10Å, was examined. Note that the film thickness of the recording auxiliary layer 14 is not an actually measured value, but is determined by measuring the formation speed of the recording auxiliary layer 14 in advance and calculating the sputtering time required for each film thickness. . Recording was performed at a linear velocity of 1.4 m / s, a recording frequency of 720 kHz, a recording power of 6.0 mW, and a modulating magnetic field of ± 50 Oersted. FIG. 10 shows the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio. 0.42mT
When the recording auxiliary layer 14 is formed with an argon gas pressure of orr and 1.5 mTorr, a high CN ratio is obtained when the recording auxiliary layer 14 has a thickness of 10Å to 70Å. Even if the recording auxiliary layer 14 is formed with an argon gas pressure of 3.5 mTorr to 9.5 mTorr, some CN
Although an improvement in the ratio is recognized, the improvement rate of the CN ratio becomes smaller as the argon gas pressure becomes higher. Moreover, when a similar magneto-optical recording medium was prepared with an argon gas pressure exceeding 10 mTorr and the improvement of the magnetic field sensitivity was examined, the improvement of the CN ratio was 1 dB or less, and no remarkable effect was observed.

As described above, it is desirable that the pressure of the sputter gas in the step of forming the recording auxiliary layer 14 is 10 mTorr or less. Moreover, it is more preferable to perform the operation at 3.5 mTorr or less. A more desirable sputtering gas pressure is 1.5 mTorr or less. The lower the sputtering gas pressure when forming the recording auxiliary layer 14 is, the better the magnetic field sensitivity characteristic obtained with the optimum film thickness is. However, the range of film thickness at which excellent characteristics are obtained is narrowed.

(Embodiment 6) In this embodiment, a manufacturing method in which a heat treatment is performed after forming the recording layer 13 and the recording auxiliary layer 14 will be described.

When manufacturing a magneto-optical recording medium having an ultrathin film two-layer structure of the present invention, it is important that no change with time occurs after manufacturing. However, when a rare earth-transition metal amorphous alloy is used for the recording layer 13 and the recording auxiliary layer 14, a change in magnetic characteristics due to structural relaxation is an unavoidable problem. Structural relaxation refers to a phenomenon in which a slight change in atomic position in short-range order occurs in an amorphous metal even at a temperature as low as room temperature. FIG. 11 schematically shows the activation energy spectrum of the structural change of the amorphous metal, and the spectrum 111 immediately after the production has a wide energy distribution. Therefore, the structure changes even with the thermal energy corresponding to a low temperature of about 100 ° C from room temperature. However, once activated, the frequency of structural relaxation corresponding to the energy gradually decreases, and finally the activation energy spectrum changes to 112 and the low energy region becomes an empty state 113. As a result, the structural relaxation does not proceed any more at room temperature to a low temperature of about 100 ° C.

Description will be given of what kind of change in magnetic characteristics occurs when structural relaxation occurs in the rare earth-transition metal amorphous alloy. Macroscopically, the coercive force decreases and the perpendicular anisotropy constant decreases. It is because the short-range order of atoms determines these properties. In addition, in connection with the decrease in coercive force, as described above, it is considered that the net domain wall energy increases and the width of the maize magnetic domain widens. As a result, the generation tendency of microdomains in the recording layer 13 when recording by magnetic field modulation changes, and it becomes difficult to generate extremely minute magnetic domains that affect the carrier level. From the functional side of the recording auxiliary layer 14, it can be said that the effect of suppressing the generation of microdomains and improving the carrier level is further enhanced.

The magneto-optical recording medium of the present invention manufactured by the same composition, constitution and manufacturing method as the magneto-optical recording medium manufactured in Example 1 was heat-treated in air. 10 heat treatment conditions
It was carried out at 0 ° C. for 1 hour and 2 hours. FIG. 12 shows the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio when recording was performed at a linear velocity of 1.4 m / s, a recording frequency of 720 kHz, a recording power of 6.0 mW, and a modulation magnetic field of ± 50 Oersted. The optimum thickness range of the recording auxiliary layer 14 before the heat treatment was 20Å to 30Å, but it changed from 10 to 20Å after the heat treatment at 100 ° C. At the film thickness of 5Å to 15Å where the effect of the recording auxiliary layer 14 was insufficient before the heat treatment, a remarkable improvement in magnetic field sensitivity was obtained. However, even if the heat treatment time was increased from 1 hour to 2 hours, there was almost no difference due to time. It can be seen that such a heat treatment at a relatively low temperature causes an important change in the two-layer structure of the magneto-optical recording medium of the present invention and the ultrathin film. As can be seen from the result of the conventional magneto-optical recording medium in which the recording auxiliary layer 14 is not formed in FIG. 12 (that is, the film thickness of the recording auxiliary layer 14 is 0Å), the magnetic field sensitivity characteristics change significantly even if heat treatment is performed. It is not allowed.

The magneto-optical recording medium of the present invention heat-treated under the above conditions and the magneto-optical recording medium of the present invention not heat-treated at 85 ° C. and 95% relative humidity for 100 hours, 200 hours, 500. The acceleration test was performed for 1,000 hours. In the magneto-optical recording medium without heat treatment, the magnetic field sensitivity characteristics changed in 100 hours. This change was exactly the same as when the heat treatment was performed at 100 ° C. In other words, the optimum film thickness of the recording auxiliary layer 14 before the accelerated test was 20Å to 30Å, but it changed from 10 to 20Å after 100 hours of the accelerated test.
Furthermore, a significant improvement in magnetic field sensitivity was obtained at a film thickness of 5Å to 15Å where the effect of the recording auxiliary layer 14 was insufficient before the acceleration test. However, the accelerated test time was increased to 200 hours, 5
No significant change was observed from the magnetic field sensitivity characteristics of 100 hours even if it was lengthened to 00 hours and 1000 hours. On the other hand, in the magneto-optical recording medium of the present invention which was heat-treated, no change in the magnetic field sensitivity characteristics was observed even after the acceleration test. Comparing the acceleration test results of Examples in which the heat treatment time was changed to 1 hour and 2 hours, almost no difference was observed. As described above, by performing the heat treatment, it is possible to suppress the change over time of the magnetic field sensitivity characteristics. In other words, the recording auxiliary layer 14 that provides the best magnetic field sensitivity characteristics without heat treatment.
When the thickness of the magnetic recording medium is Dmax, a magneto-optical recording medium having excellent magnetic field sensitivity characteristics and having no change over time in the magnetic field sensitivity characteristics is formed by performing heat treatment after forming the recording auxiliary layer 14 with a film thickness less than Dmax. It is possible to manufacture. By changing the manufacturing conditions and the composition of the recording layer 13 and the recording auxiliary layer 14,
Dmax varies from 0Å to 70Å. In the case of performing heat treatment, it was possible to obtain excellent magnetic field sensitivity characteristics by forming the recording auxiliary layer 14 with a film thickness of ⅛ to ⅔ of Dmax.

Regarding the heat treatment temperature, an effect was recognized from about 50 ° C., but at 50 ° C., a long treatment time was required, or the heat treatment was insufficient and changed with time.
The higher the temperature, the shorter the processing time. For example, a processing temperature of 80 ° C required a processing time of 50 hours,
At 100 ° C, 40 minutes was enough. In terms of manufacturing, it is desirable that the heat treatment be as short as possible, so it is desirable to perform the heat treatment at the highest temperature possible. However, when polycarbonate was used for the transparent substrate 11 of the magneto-optical recording medium, the polycarbonate began to soften above 120 ° C., so 120 ° C. was the upper limit of the treatment temperature. At this time, 120
A sufficient effect was obtained with a treatment time of 5 minutes or less at ℃.

As described above, the temporal change of the magnetic field sensitivity can be suppressed by heat-treating the magneto-optical recording medium of the present invention at a relatively low temperature, because the structural relaxation of the amorphous metal caused by the temporal change can be suppressed in advance. This is because it was caused by heat treatment. That is, as described above, since the activation energy spectrum 111 of the structural change of the amorphous metal has a wide energy distribution, the structure changes even with a sufficiently low thermal energy and the low energy of the activation energy spectrum 113 after the heat treatment. The area becomes empty 113. As a result, structural relaxation at room temperature to a low temperature of about 100 ° C. does not proceed any more, and thus the change with time is suppressed.

(Embodiment 7) As the activation energy spectrum 111 of the structural change of the amorphous metal shown in FIG. 11 does not have a low energy portion, the change with time can be suppressed. The activation energy spectrum 111 changes depending on the manufacturing conditions and composition. In this embodiment, as one of the manufacturing conditions, a manufacturing method for flattening the surface of the first dielectric 12 and the surface of the recording layer 13 will be described. The first dielectric layer 12 formed prior to the recording layer 13 is made of Si. It is common to use a composition based on ₃ N ₄ , AlN or AlSiN. It is known that when a dielectric layer of this composition is formed to a thickness of several hundred Å by a sputtering method, a few tens of microscopic irregularities are formed on the surface. When the rare earth-transition metal amorphous alloy is formed on the dielectric having the fine irregularities, the magnetic properties are affected by the fine irregularities. A relatively large coercive force can be obtained by forming a rare earth-transition metal amorphous alloy on a dielectric having irregularities of several tens of liters. Further, when the dielectric having minute irregularities is dry-etched by plasma of an inert gas, the height of the irregularities is reduced, that is, flattened.
When the rare earth-transition metal amorphous alloy is formed on the thus flattened dielectric, the coercive force is reduced as compared with the case where the flattened dielectric is not formed. The present inventors have found that the change with flattening of the dielectric surface not only lowers the coercive force but also widens the width of the maize magnetic domain generated near the Curie temperature. Therefore, it also affects the magnetic field sensitivity characteristics of the magneto-optical recording medium thus manufactured.

As shown in FIG. 1, on a transparent substrate 11, a first dielectric layer 12, a recording layer 13, a recording auxiliary layer 14, a second dielectric layer 15,
A magneto-optical recording medium having the reflective layer 16 laminated was produced. As the recording layer 13, a rare earth-transition metal amorphous alloy having a composition of Nd5at% Dy16at% Tb5at% Fe59at% Co15at% was used. Thin films were formed by magnetron DC sputtering with a cast alloy target at an argon gas pressure of 1.2 mTorr. The Curie temperature is 180 ° C. The recording layer 13 alone exhibits magnetic properties of transition metal sublattice dominant at room temperature, as is clear from its composition. Further, as the recording auxiliary layer 14, Dy30t%
A rare earth-transition metal alloy having a composition of Fe35at% Co35at% was used. Magnetron DC with cast alloy target
A thin film was formed by sputtering under the conditions of an argon gas pressure of 0.4 mTorr and a power of 100 W. The Curie temperature is 280 ° C. The recording auxiliary layer, by itself, shows the magnetic characteristics of the rare earth metal sublattice dominant at room temperature, as is clear from its composition. As the material of the first dielectric layer 12 at this time, for example,
With AlSiN, the conditions for the sputtering method are, for example, sputter gas Ar 60% + N ₂ 40%, pressure 1.7 mTorr, and input power.
RF2500W. An AlSi alloy target is used as the target. In order to flatten the fine irregularities on the surface, as described above, the method of re-sputtering the surface of the first dielectric 12 using the dry etching method using RF plasma was used. The conditions of RF plasma etching at this time are, for example, an etching gas of Ar, a pressure of 1.8 mTorr,
The input power is RF50W. After the first dielectric layer 12 was formed on the transparent substrate 11 by 770Å, RF plasma etching was performed for 20 minutes for flattening. After that, the recording layer 13 is set to 200 Å,
Recording auxiliary layer 14, second dielectric layer 15 is 200Å, reflective layer 16 is 600
Å Stacked. The recording auxiliary layer 14 was formed from 0 to 50 Å with a thickness of 5 Å. And linear velocity 1.4m / s, recording frequency 720k
FIG. 13 shows the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio when recording was performed at Hz, recording power of 6.0 mW, and modulation magnetic field of ± 50 Oersted.
Shown in. The figure also shows the results of the magnetic field sensitivity characteristics of the magneto-optical recording medium in which RF plasma etching was not carried out after the first dielectric layer was formed with 750 Å. As a result of flattening the base by RF plasma etching, it can be seen that the same effect can be obtained with the recording auxiliary layer 14 which is thinner than that without flattening. That is, in the magneto-optical recording medium without flattening, a remarkably large CN ratio was obtained in the vicinity of the recording auxiliary layer 14 thickness of 20 Å to 30 Å, whereas in the magneto-optical recording medium with flattening. A particularly large CN ratio was obtained near 15Å to 25Å.

The magneto-optical recording medium thus manufactured was subjected to an acceleration test for 100 hours, 200 hours, 500 hours and 1000 hours in an environment of a temperature of 85 ° C. and a relative humidity of 95%. First
In the magneto-optical recording medium in which the dielectric layer 12 is not flattened, the optimum film thickness range of the recording auxiliary layer 14 before the acceleration test is 20Å
From 30 Å to 10 to 20 after 100 hours of accelerated testing
In particular, the magnetic field sensitivity was remarkably improved in the film thickness of 5 Å to 15 Å where the effect of the recording auxiliary layer 14 was insufficient before the acceleration test. On the other hand, in the flattened magneto-optical recording medium, the optimum film thickness of the recording auxiliary layer 14 before the acceleration test was 15Å to 25Å.
It changed only from 0 to 20Å, but stayed. In addition, the results after 200 hours were almost the same as the results after 100 hours regardless of the presence or absence of flattening. In this way, when the flattening is performed, by making the recording auxiliary layer 14 have a thickness of 15Å to 20Å, it is possible to reduce the change over time in the magnetic field sensitivity characteristics.

Next, a manufacturing method for forming the recording auxiliary layer 14 after forming the recording layer 13 and then flattening the surface thereof will be described. When the recording layer 13 is formed without flattening the fine irregularities on the surface of the dielectric, the recording layer formed is
Fine irregularities also occur on the surface of 13. If the recording auxiliary layer 14 is formed after the unevenness on the recording layer 13 is flattened, the magnetic characteristics of only the recording auxiliary layer 14 can be changed.

After the first dielectric layer 12 is formed on the transparent substrate 11 by 750 Å, the recording layer 13 is 210
Å formed. Then, the surface of the recording layer 13 was subjected to RF plasma etching treatment. The conditions of the RF plasma etching at this time are, for example, an etching gas of Ar, a pressure of 1.8 mTorr, and an input power of RF50W. The RF plasma etching processing time is 5 minutes. Then, the recording auxiliary layer 14 was formed at intervals of 0Å to 70Å and 5Å. Furthermore, the second
The dielectric layer 15 was formed in 200Å and the reflective layer 16 was formed in 600Å. The linear velocity of the magneto-optical recording medium thus manufactured was 1.4 m /
s, recording frequency 720kHz, recording power 6.0mW, modulation magnetic field ± 50
The film thickness and CN of the recording auxiliary layer 14 when recorded by Oersted
The relationship with the ratio is shown in FIG. The figure also shows the magnetic field sensitivity characteristics after the same magneto-optical recording medium was subjected to an acceleration test for 200 hours at a temperature of 85 ° C and a relative humidity of 95%. The optimum thickness of the recording auxiliary layer 14 is 15 Å to 40 Å and does not change before and after the acceleration test. It can be seen that when the recording auxiliary layer 14 is formed after the surface of the recording layer 13 is flattened in this manner, the magnetic field sensitivity characteristics hardly change before and after the acceleration test.

(Embodiment 8) In the above embodiments, the structure in which the recording auxiliary layer 14 is formed after the recording layer 13 shown in FIG. 1 is formed (hereinafter referred to as a post-attached structure) has been described. In this embodiment, a magneto-optical recording medium having a configuration in which the recording layer 13 and the recording auxiliary layer 14 are changed as shown in FIG. 15 will be described. FIG. 15A shows the recording auxiliary layer 14 and the recording layer 13
FIG. 15B shows a magneto-optical recording medium (hereinafter referred to as a pre-attached structure) formed by sandwiching the recording auxiliary layer 14 in the recording layer 13. FIG. 15C shows a magneto-optical recording medium in which the recording auxiliary layer 14 is formed on both sides of the recording layer 13 (hereinafter, referred to as a double-sided structure). In this embodiment, the first dielectric layer 12,
Although the reflective structure having the second dielectric layer 15 and the reflective layer 16 is used, the gist of the present invention is not limited to this structure.

Here, the recording layer 13 is Nd5at% Dy16at% T
A rare earth-transition metal alloy having a composition of b5at% Fe59at% Co15at% was used. Argon gas pressure 1.8mTor by magnetron DC sputtering using cast alloy target
A thin film was formed under the conditions of r and power of 300W. Curie temperature is 1
80 ° C. The recording layer 13 alone exhibits magnetic properties of transition metal sublattice dominant at room temperature, as is clear from its composition. Further, as the recording auxiliary layer 14, Dy30t% Fe35at% Co35a
A rare earth-transition metal alloy having a composition of t% was used. A thin film was formed by magnetron DC sputtering using a cast alloy target under an argon gas pressure of 0.4 mTorr and a power of 100 W. The Curie temperature is 280 ° C. The recording auxiliary layer, by itself, shows the magnetic characteristics of the rare earth metal sublattice dominant at room temperature, as is clear from its composition.

In order to manufacture the magneto-optical recording medium having the structure shown in FIG. 15, the first dielectric layer 12 is first formed on the transparent substrate 11. The material of the first dielectric layer 12 at this time is, for example, AlSiN.
The conditions for the sputtering method are, for example, sputter gas Ar 60% + N2 40%, pressure 1.7 mTorr, and input power RF2500.
W. An AlSi alloy target is used as the target. In this example, the planarization treatment of the first dielectric layer 12 was not performed. In this embodiment, the thickness of the first dielectric layer 12 is 750Å. Then, a magnetic layer is formed. In the case of the pre-attached structure, the recording layer 15 is formed after the recording auxiliary layer 14 is formed. In this example, the film thickness of the recording layer 13 was set to 200Å, and the film thickness of the recording auxiliary layer 14 was changed from 0Å to 80Å.
In the case of the intermediate structure, after forming the first half 13a of the recording layer,
The recording auxiliary layer 14 was formed, and then the second half 13b of the recording layer was formed. In this embodiment, the thickness of the first half 13a of the recording layer and the thickness of the second half 13b of the recording layer are both 100 Å, and the total thickness of the recording layer 13 is 200 Å. Further, the film thickness of the recording auxiliary layer 14 was changed from 0Å to 100Å.
In the double-sided structure, after forming the front half portion 14a of the recording auxiliary layer,
The recording layer 13 was formed, and the second half 14b of the recording auxiliary layer was further formed. In this embodiment, the film thickness of the first half 14a of the recording auxiliary layer is 15Å, the film thickness of the recording layer 13 is 200Å, and the film thickness of the second half 14b of the recording auxiliary layer is changed from 0Å to 65Å. In addition,
The film thickness of the recording auxiliary layer 14 is not a measured value, but is determined by measuring the formation speed of the recording auxiliary layer 14 in advance and calculating the sputtering time required for each film thickness. After forming the magnetic layer as described above, the second dielectric layer 1
5, the reflective layer 16 was formed. In this embodiment, the second dielectric layer 1
AlSiN was formed as 200Å as 5 and AlTi as 600Å was formed as the reflective layer 16.

The magnetic field sensitivity characteristics of the magneto-optical recording medium thus manufactured were examined. Linear velocity 1.4m / s, recording frequency 720kHz,
FIG. 16 shows the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio when recording was performed with a recording power of 6.0 mW and a modulation magnetic field of ± 50 Oersted. The figure also shows the results for the magneto-optical recording medium having the retrofit structure shown in FIG. The data of the double-sided structure is plotted with the film thickness of the latter half portion 14b of the recording auxiliary layer as the horizontal axis. As can be seen from this result, the magnetic field sensitivity characteristic is improved in any structure in which the recording layer 13 and the recording auxiliary layer 14 are stacked in different orders. However, the dependency of the magnetic field sensitivity characteristic on the recording auxiliary layer thickness is different in each structure. Comparing the post-attachment structure and the pre-attachment structure shows a similar tendency. In both cases, the recording auxiliary layer 14 has a film thickness of 15Å
It exhibits excellent magnetic field sensitivity characteristics at 45Å. From 20Å
It shows a particularly excellent characteristic at 35Å. In addition, the change in the CN ratio with respect to the film thickness is more gradual in the middle-attached structure than in the post-attached structure. The thickness of the recording auxiliary layer 14 is 15 in the intermediate structure.
It exhibits excellent magnetic field sensitivity characteristics in a wide range from Å to 80Å. In addition, it exhibits particularly excellent characteristics in the range of 30Å to 70Å. In this embodiment, the best characteristics are exhibited when the film thickness of the recording auxiliary layer 14 is 50Å. Compared with the post-attached structure and the pre-attached structure, the slope of the rise in the carrier level is gentle, so the optimum film thickness is about
The value of the CN ratio obtained at that time is a little small. In other words, the middle-attached structure is inferior to the post-attached structure and the pre-attached structure in obtaining the most excellent magnetic field sensitivity characteristic, but since the film thickness range in which the excellent magnetic field sensitivity characteristic is obtained is wide, the manufacturing margin is wide. Further, the double-attached structure shows a tendency similar to the post-attached structure or the pre-attached structure. However, in this embodiment, since the film thickness of the first half portion 14a of the recording auxiliary layer is fixed to 15Å, in FIG. 16, for example, the film thickness on the horizontal axis is 10Å.
At that time, the recording auxiliary layer 14 as a whole has a film thickness of 25 Å.
However, at that thickness, it shows only characteristics that are not so different from the case where the latter half portion 14b of the recording auxiliary layer is not formed. Rather, excellent magnetic field sensitivity characteristics are obtained when the film thickness of the second half 14b of the recording auxiliary layer is in the range of 20Å to 45Å, and the first half 14a of the recording auxiliary layer is
If the film thickness of 15 Å is added, excellent properties will be exhibited from 35 Å to 60 Å. The film thickness of the second half 14b of the recording auxiliary layer is 20Å to 4
The excellent magnetic field sensitivity characteristic in the range of 5Å almost coincides with the range of the film thickness showing excellent characteristics in the post-installed structure and the pre-mounted structure. It is shown that, in the combination of the compositions of the recording layer 13 and the recording auxiliary layer 14 used in this example, it is important to form the recording auxiliary layer 14 alone within this range of film thickness.

What is characteristic of the magneto-optical recording medium of the present invention is that
That is, the recording auxiliary layer 14 is formed with an extremely thin film thickness of 70 Å or less. However, in order to fabricate a continuous film in which the planes are continuously connected with such an extremely thin film thickness, a single crystal substrate or a limited combination of elements is used to form a thin film in an ideally controlled environment. Needs to be done. However, in the manufacture of the magneto-optical recording medium like the present invention, it is not possible to form a thin film under such limited conditions. As described above, the surface of the dielectric layer formed prior to the magnetic layer has undulations of tens of undulations. Even if the recording auxiliary layer 14 is formed on such a surface with an extremely thin film thickness of 70 Å or less, it is unlikely that a continuous film can be produced. Rather, it is considered that island-shaped structures are formed on the unevenness as shown in FIG. Island 17 of each recording auxiliary layer
1 is structurally separated from each other. However, magnetically, the islands 171 of the recording auxiliary layer are exchange-coupled with each other by interchanging the exchange coupling with the recording layer 13 formed in contact therewith. In other words, magnetically, it can be said that the virtual continuous film 172 of the recording auxiliary layer is formed. The magnetic field sensitivity characteristics at the time of recording are determined by the characteristics of the virtual continuous film 172 of the recording auxiliary layer, and the "composition" of the virtual continuous film 172 of the recording auxiliary layer that affects the characteristics is the recording layer 13 The composition will be between the composition of (1) and the composition of the recording auxiliary layer 14.
Which composition in the meantime depends on the film thickness of the recording auxiliary layer 14, the manufacturing conditions, and the arrangement with the recording layer 13. For example, since the recording layer 13 is in contact with the upper and lower sides of the island 171 of the recording auxiliary layer in the intermediate mounting structure, the virtual continuous film 17 of the recording auxiliary layer is compared to the post-installed structure or the pre-attached structure in which only one side is in contact.
The “composition” of 2 means a composition closer to the recording layer 13.
Therefore, the characteristic of the virtual continuous film 172 of the recording auxiliary layer is that the Curie temperature is lower than that in the case of the pre-attached structure or the post-attached structure, and the effect of suppressing the maize magnetic domain is also reduced, resulting in a gradual increase in the carrier level. It is thought that it became. That is, it is possible to produce a magneto-optical recording medium in which the carrier level changes remarkably even in the intermediate structure by forming the recording auxiliary layer 14 with a composition in which the ratio of the heavy rare earth metal and Co is increased. In addition, a phenomenon in which the film thickness range of the second half portion 14b of the recording auxiliary layer exhibiting excellent magnetic field sensitivity characteristics in the double-attached structure is substantially the same as the film thickness range exhibiting excellent characteristics in the post-attached structure or pre-attached structure It is natural from the viewpoint of the “composition” of the virtual continuous film 172 of the auxiliary layer.

Next, an acceleration test of a magneto-optical recording medium having a structure in which the laminated structure of the recording layer 13 and the recording auxiliary layer 14 was changed was conducted to examine the change with time of the magnetic field sensitivity characteristics. The conditions for the accelerated test are a temperature of 85 ° C, a relative humidity of 95%, a test time of 100 hours, and a 200
Time, 500 hours and 1000 hours. As a result, it was found that the prefabricated structure has a very small change over time in the magnetic field sensitivity characteristics. In addition, the structure of the in-mold structure has a very small change over time in the magnetic field sensitivity characteristics. These structures are superior to retrofit structures in this respect.

[0053]

The magneto-optical recording medium of the present invention has a recording auxiliary layer laminated in contact with the recording layer in a magneto-optical recording medium having a recording layer having a Curie temperature of Tc1, and the Curie temperature Tc2 of the recording auxiliary layer is Tc1. At a higher temperature than the recording auxiliary layer thickness
The thickness of the recording layer is 70 angstroms or less, and the film thickness of the recording layer is 80 angstroms or more.The manufacturing method of the magneto-optical recording medium is that the sputtering gas pressure is 10 mTorr or less when the recording auxiliary layer is formed by the sputtering method. The recording layer and the recording auxiliary layer are formed by a sputtering method, and then heat treatment is performed at a temperature of 50 ° C. or higher, or the recording layer and the recording auxiliary layer are formed in this order. At this time, since the recording auxiliary layer is formed after the surface of the recording layer is flattened, the magnetic field sensitivity is remarkably improved and recording can be performed with a weak magnetic field. Therefore, the magnetic head can be downsized, the power consumption of the magnetic head can be remarkably reduced, and the drive circuit of the magnetic head can be inexpensive. Further, it is possible to provide a magneto-optical recording medium capable of stable recording even if the distance between the magnetic head and the magneto-optical recording medium changes. Further, it is possible to provide a magneto-optical recording medium whose magnetic field sensitivity characteristics are less likely to change with time.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a magneto-optical recording medium of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the modulation magnetic field, the CN ratio, and the carrier level in the example of the magneto-optical recording medium of the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the film thickness of the recording auxiliary layer 14, the CN ratio, and the carrier level in the embodiment of the magneto-optical recording medium of the present invention.

FIG. 4 is an explanatory diagram showing a state in which a beam spot is irradiated on the magneto-optical recording medium.

FIG. 5 is a temperature characteristic diagram of a Kerr hysteresis curve of a magnetic film used for the recording layer 14 of the present invention.

FIG. 6 is a schematic view showing the shape of a arrow-shaped magnetic domain.

FIG. 7 is a characteristic diagram showing the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio in the example of the magneto-optical recording medium of the present invention.

FIG. 8 is a temperature characteristic diagram of a Kerr hysteresis curve of the magnetic film used for the recording auxiliary layer 14 of the present invention.

FIG. 9 is a characteristic diagram showing the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio in the example of the magneto-optical recording medium of the present invention.

FIG. 10 is a characteristic diagram showing the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio of the example manufactured by the method for manufacturing a magneto-optical recording medium of the present invention.

FIG. 11 is a schematic diagram showing an activation energy spectrum for structural relaxation of an amorphous metal.

FIG. 12 is a characteristic diagram showing the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio of the example manufactured by the method for manufacturing a magneto-optical recording medium of the present invention.

FIG. 13 is a characteristic diagram showing the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio of the example manufactured by the method for manufacturing a magneto-optical recording medium of the present invention.

FIG. 14 is a characteristic diagram showing the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio of the example manufactured by the method for manufacturing a magneto-optical recording medium of the present invention.

FIG. 15 is a sectional view of an example of the magneto-optical recording medium of the present invention.

FIG. 16 is a characteristic diagram showing the relationship between the film thickness of the recording auxiliary layer 14 and the CN ratio in the example of the magneto-optical recording medium of the present invention.

FIG. 17 is a schematic diagram showing a state in which an extremely thin recording auxiliary layer 14 is laminated on the recording layer 13.

[Explanation of symbols]

 11 transparent substrate 12 first dielectric layer 13 recording layer 13a first half of recording layer 13b second half of recording layer 14 recording auxiliary layer 14a first half of recording auxiliary layer 14b second half of recording auxiliary layer 15 second dielectric layer 16 reflection Layer 41 Beam spot 42 Area heated above Curie temperature 43 Domain formation zone 43a High temperature zone of domain formation zone 43b Low temperature zone of domain formation zone 61 Rear edge of arrow-shaped magnetic domain 111 Activation energy spectrum immediately after production 112 Activation energy spectrum after heat treatment 113 Empty state 171 Island of recording auxiliary layer 172 Virtual continuous film of recording auxiliary layer

Claims (10)

[Claims] 1. In a magneto-optical recording medium having a recording layer having a Curie temperature of Tc1, a recording auxiliary layer is laminated in contact with the recording layer, and the Curie temperature Tc2 of the recording auxiliary layer is Tc1.
A magneto-optical recording medium having a film thickness of the recording auxiliary layer of 70 Å or less and a film thickness of the recording layer of 80 Å or more at a temperature higher than c1. 2. The method of manufacturing a magneto-optical recording medium according to claim 1, wherein the sputtering gas pressure when forming the recording auxiliary layer on the substrate by a sputtering method is 10 mTorr or less. Medium manufacturing method. 3. The method for manufacturing a magneto-optical recording medium according to claim 1, wherein after the recording layer and the recording auxiliary layer are formed on a substrate by a sputtering method, heat treatment is performed at a temperature of 50 ° C. or higher. A method for manufacturing a magneto-optical recording medium characterized by the above. 4. The method for manufacturing a magneto-optical recording medium according to claim 3, wherein the heat treatment is performed at a temperature lower than a temperature at which the substrate is deformed or deteriorated. 5. The method for manufacturing a magneto-optical recording medium according to claim 1, wherein the step of forming the recording layer by a sputtering method, the step of flattening the surface of the formed recording layer, and the step of flattening the surface A method of manufacturing a magneto-optical recording medium, comprising the step of forming the recording auxiliary layer on the recording layer by a sputtering method. 6. The magneto-optical recording medium according to claim 5, wherein the step of flattening the surface of the recording layer is performed by dry etching using plasma of an inert gas. 7. The magneto-optical recording medium according to claim 1, wherein the recording layer is laminated on the substrate side, and the recording auxiliary layer is laminated on the side far from the substrate. 8. The magneto-optical recording medium according to claim 1, wherein the recording auxiliary layer is laminated on the substrate side, and the recording layer is laminated on the side far from the substrate. 9. The magneto-optical recording medium according to claim 1, wherein the recording layer, the recording auxiliary layer, and the recording layer are stacked in this order from the substrate side. 10. The magneto-optical recording medium according to claim 1, wherein the recording auxiliary layer, the recording layer, and the recording auxiliary layer are laminated in this order from the substrate side.