JPH0684213A - Magneto-optical recording medium and its production - Google Patents

Abstract

PURPOSE:To lower a magnetic field for initialization by forming a first magnetic layer and second magnetic layer which are exchange coupled to each other adjacently to each other and incorporating at least one kind of nitrogen and oxygen into one side of the first magnetic layer in contact with the second magnetic layer. CONSTITUTION:The film of a dielectric substance layer 102 is formed on a transparent substrate 101 and a nitride, such as SiN or SiAlN, is used for the layer 102. Gaseous argon and nitrogen are introduced into a film forming chamber. The film of the first magnetic layer 103 is then formed and the substrate is moved into the film forming chamber where reverse sputtering can be executed. The reverse sputtering is then executed by using the gases formed by mixing the argon and at least one kind of the nitrogen and the oxygen. The film of the second magnetic layer 104 is then formed and thereafter, the film of the dielectric substance layer 105 is formed by the method similar to the method for the layer 102. The layer 103 is a memory layer and the layer 104 is a reference layer. As a result, the oxygen and the nitrogen are incorporated into the one side of the layer 103 in contact with the layer 104 and, therefore, the multiplier of an exchange stiffness constant and perpendicular magnetic anisotropy decreases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overwritable magneto-optical recording medium and a method for manufacturing the same.

[0002]

2. Description of the Related Art One of overwritable magneto-optical recording media is a magnetic film in which a perpendicularly magnetized film forms an exchange coupling two-layer film. As an example of this magneto-optical recording medium, a first magnetic layer (memory layer), which is a magnetic film having a dominant transition metal sublattice magnetization at room temperature, is formed on the side irradiated with a laser beam, and is in contact with the memory layer. In some cases, a second magnetic layer (reference layer), which is a magnetic film having a higher Curie temperature and a lower coercive force at room temperature than that of the memory layer at room temperature, is dominant in the rare earth metal sublattice magnetization.

In this overwritable magneto-optical recording medium, information is rewritten according to the following procedure. The magneto-optical drive is usually provided with a permanent magnet so that the recording portion of the magneto-optical disk passes through a magnetic field in which the magnitude and direction of the magnetic field called the initializing magnetic field are fixed once per turn. The process in which the recording portion passes through the initialization magnetic field is called initialization, and the initialization causes the magnetization of the reference layer to face the initialization magnetic field. Immediately after the initialization, the sublattice magnetizations of the transition metals of the memory and the reference layer are opposite to each other at the location where the magnetization of the memory layer matches the direction of the initialization magnetic field. Since the magnetic film is a ferrimagnetic material, the sublattice magnetizations of rare earth metals are also opposite to each other. In this state, an interface domain wall is generated at the interface between the memory layer and the reference layer. Interface domain wall energy is stored in the region where the interface domain wall is generated. The state of this magnetization direction is maintained unchanged from the initialization to the irradiation of the laser beam. The laser beam binary-modulates the intensity of the laser beam at the time of rewriting. The high laser power is Ph and the low laser power is Pl. At this time, the laser beam is emitted in a state in which a rewriting magnetic field smaller than the magnitude of the initialization magnetic field is applied in the same direction as the initialization direction. At the time of Ph laser irradiation, the magnetic film rises to near the Curie temperature of the reference layer and can invert the reference layer. The coercive force of the reference layer gradually increases as the temperature decreases. In this temperature range, the transition metal sublattice magnetization is dominant in the reference layer. Here, the direction of the sub-lattice magnetization in the reference layer is fixed, and the rare earth metal sub-lattice magnetization becomes predominant in the reference layer when the temperature further decreases to around room temperature.
The reference layer is magnetized in the opposite direction to the rewriting magnetic field at room temperature.

At this time, the magnetization direction of the memory layer is opposite to that of the reference layer in order to prevent an increase in energy due to generation of an interface domain wall with the reference layer. Upon irradiation with Pl laser, the magnetic film rises to near the Curie temperature of the memory layer. The reference layer has a high coercive force and cannot reverse magnetization. The memory layer has a direction opposite to the magnetization direction of the reference layer so as not to generate an interface domain wall. That is, the memory layer has a direction opposite to the rewriting magnetic field. When returning to Ph laser irradiation, the memory layer is oriented in the same direction as the rewriting magnetic field. Since the magnetization direction of the memory layer is read at the time of reproduction, it means that rewriting could be performed by binary modulation of the laser. However, initialization is normally performed from rewriting to reproduction. Therefore, during initialization, the magnetization direction of the memory layer is preserved, and only the magnetization of the reference layer needs to be oriented in the direction of the initialization magnetic field. Immediately after the Ph laser irradiation, the magnetization direction of the memory layer is in the same direction as the rewriting magnetic field, that is, in the same direction as the initializing magnetic field. Only the reference layer is inverted by the initialization, and an interface domain wall is generated. This process includes the following four conditions: the memory layer is not inverted by initialization, the reference layer is inverted by initialization, the memory layer is oriented in the direction of the initialization magnetic field before initialization, That is, the reference layer is locally opposite to the initializing magnetic field direction after the Ph laser irradiation. Each condition is represented by the following formulas 1 to 4.

[0005]

[Equation 1]

[0006]

[Equation 2]

[0007]

[Equation 3]

[0008]

[Equation 4]

From Equation 1, the upper limit value of the initialization magnetic field is determined. Then, from Equation 2, the lower limit value of the initialization magnetic field is determined. Equations 3 and 4 are not directly related to the initializing magnetic field.

As a method of applying the initialization magnetic field to the disk, a method of attaching a permanent magnet or an electromagnet to the drive and a method of attaching a permanent magnet to the cartridge of the magneto-optical disk can be considered. In any case, if the initializing magnetic field is large, the means for generating the magnetic field becomes large in scale, resulting in an increase in cost. Also, with regard to permanent magnets, dust such as iron powder easily enters the drive and the cartridge. Therefore, it is desired that the initializing magnetic field is about 4 kOe at the largest, and actually smaller.

Equation 2 defines the lower limit of the initialization magnetic field. From this equation, in order to reduce the initialization magnetic field, the following 4
There are two ways. The coercive force of the reference layer is reduced. Increase the magnetization of the reference layer. Increase the thickness of the reference layer. Reduces the domain wall energy density. Since the rare earth metal sublattice magnetization is dominant at room temperature in the reference layer, the magnetization increases and the coercive force decreases by increasing the composition ratio of the rare earth metal. However, when the magnetization of the perpendicular magnetization film becomes too large, it becomes an in-plane magnetization film. Since the magnetic film becomes thicker, the reference film formation time becomes longer,
There is a drawback that it becomes difficult to raise the temperature of the magnetic film by laser beam irradiation. It is desirable that the interface domain wall energy density be low within a range where the magnetization reversal of the memory layer is favorably performed at the time of rewriting by irradiation with Pl laser. It is also understood that the interface domain wall energy density is preferably low in order to simultaneously satisfy the conditions of Formula 3 and Formula 4.

A known method for reducing the interface domain wall energy density is to form an interface domain wall energy control layer having a small perpendicular magnetic anisotropy and having a different composition from the memory layer and the reference layer between the memory layer and the reference layer. M.Kaneko et al.; Jpn.J.Appl.Phys.28, Suppl28-3, p
27 (1989). As another method, as disclosed in Japanese Patent Laid-Open No. 4-95247, a film is formed by mixing nitrogen gas or oxygen gas into a sputtering gas near the end of film formation of a memory layer and the start of film formation of a reference layer. Therefore, the interface domain wall energy control layer was provided.

[0013]

SUMMARY OF THE INVENTION In the above technology,
A method of using an interfacial domain wall energy control layer having a composition different from that of the first magnetic layer, that is, the memory layer and the second magnetic layer, that is, the reference layer, and an interfacial domain wall energy control layer by forming a film by mixing nitrogen gas or oxygen gas into the sputtering gas. In both the methods of forming a magnetic field, the coercive force of the second magnetic layer cannot be reduced, the effect of reducing the initializing magnetic field is weak, and there is a problem that the thickness of the interface domain wall energy control layer becomes large. Therefore, the present invention is intended to overcome the above-mentioned drawbacks, and an object of the present invention is to provide a magneto-optical recording medium having a means for reducing the coercive force of the second magnetic layer and reducing the thickness of the interfacial domain wall energy control layer, and its manufacture. It is in the process of providing a method.

[0014]

The magneto-optical recording medium of the present invention uses a rare earth transition metal amorphous alloy thin film having perpendicular magnetic anisotropy and has at least two magnetic layers having different coercive forces at room temperature, In a magneto-optical recording medium in which magnetic layers having different coercive forces are exchange-coupled to each other at room temperature, the first magnetic layer and the second magnetic layer which are exchange-coupled to each other are adjacent to each other, and the first magnetic layer and the second magnetic layer are in contact with each other. One of the magnetic layers contains at least one of nitrogen and oxygen. The method for producing a magneto-optical recording medium of the present invention uses a rare earth transition metal amorphous alloy thin film having perpendicular magnetic anisotropy, has at least two magnetic layers having different coercive forces at room temperature, and has a coercive force at room temperature. In a method of manufacturing a magneto-optical recording medium in which different magnetic layers are exchange-coupled to each other, the first magnetic layer and the second magnetic layer exchange-coupled to each other are formed adjacent to each other, and the first magnetic layer is formed. The second magnetic layer is formed after the film formation, and after the first magnetic layer is formed, reverse sputtering is performed with a sputtering gas in which at least one kind of argon gas, nitrogen gas and oxygen gas is mixed. Manufacturing method of magneto-optical recording medium.

[0015]

From the above, oxygen or nitrogen is contained on one side of the first magnetic layer in contact with the second magnetic layer, so that the multiplier of the exchange stiffness constant and the perpendicular magnetic anisotropy constant decreases. It is well known that the interface domain wall energy density is proportional to the square root of the multiplier of the exchange stiffness constant and the perpendicular magnetic anisotropy constant, and when the interface domain wall exists in the region containing oxygen or nitrogen, the system Since both the energy and the interface domain wall energy decrease compared to the case where they exist in other regions, the interface domain wall exists in the region containing the non-magnetic element, and the interface domain wall energy density does not contain oxygen or nitrogen. Lower than

Reverse sputtering is the opposite of normal sputtering in which sputtering gas ions strike the target.
The sputtering gas ions are intentionally collided with the sample. It is widely known that reverse sputtering reduces unevenness on the surface to be reverse sputtered and smoothes the surface. By performing reverse sputtering after forming the first magnetic layer, the surface of the first magnetic layer is smooth without unevenness, and the second magnetic layer is formed on the surface.
When the magnetic layer is formed, the magnetization reversal of the second magnetic layer becomes easy and the coercive force of the second magnetic layer decreases.

From the above, it is possible to further reduce the initialization magnetic field expressed by the equation (2).

[0018]

EXAMPLES The present invention will be described below based on examples.

(Embodiment 1) An embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, 102 dielectric layers are formed on a transparent substrate 101 made of glass or resin. After that, the first magnetic layer 103 is formed, and the first magnetic layer 10 is formed.
No. 4, at least one of nitrogen and oxygen is contained on one side in contact with the second magnetic layer to form a second magnetic layer,
The dielectric layers are laminated. Here, the magnetic layer is shown in FIG.
The number of layers is not limited to two, and two or more layers may be used. Further, one side where the magnetic layers are adjacent to each other is not necessarily the one containing the above-mentioned oxygen or nitrogen, but may be any one place containing the above-mentioned oxygen or nitrogen.

The above structure is manufactured by the following manufacturing method. As the film forming method, a sputtering method widely used as a film forming method for a magneto-optical recording medium was selected. A dielectric layer 102 is formed on a transparent substrate 101 by high frequency sputtering. SiN, Si for the dielectric layer
A nitride such as AlN is often used, and the film formation chamber has a structure in which argon and nitrogen gases can be introduced as a sputtering gas. Next, the first magnetic layer 103 is formed by DC magnetron sputtering. Immediately after forming the first magnetic layer, the film is moved to a film forming chamber where reverse sputtering can be performed, and reverse sputtering is performed using a gas in which at least one of argon, nitrogen and oxygen is mixed in the sputtering gas. Then 104
The second magnetic layer is formed by DC magnetron sputtering. After that, the dielectric layer 105 is formed in the same manner as the dielectric layer 102. Further, in an example of the overwrite by the exchange coupling two-layer film used in this embodiment, the first magnetic layer is a memory layer and the second magnetic layer is a reference layer.

With the above-mentioned structure, since one side of the first magnetic layer in contact with the second magnetic layer contains oxygen and nitrogen, the multipliers of the exchange stiffness constant and the perpendicular magnetic anisotropy decrease. The interface domain wall energy density is expressed by Equation 5.

[0022]

[Equation 5]

That is, since the energy of the entire system of the multilayer magnetic film can be reduced, the interface domain wall is present on one side of the first magnetic layer containing oxygen or nitrogen and becomes stable, and oxygen or nitrogen is stabilized. It is lower than that which does not contain.

In this example, the effects are written following these.

FIG. 2 shows an example of changes in the interface wall energy with respect to reverse sputtering conditions. The magneto-optical recording medium here can be overwritten by an exchange coupling two-layer film. Therefore, the first magnetic layer is a memory layer and has a coercive force of 10 kOe and a film thickness of 700 at room temperature.
Å The second magnetic layer is a reference layer and has a coercive force of 1.5 kOe as a single layer at room temperature and a film thickness of 600 Å. First
The second magnetic layer was formed by DC magnetron sputtering. In FIG. 2, the horizontal axis represents the reverse sputtering time, and the vertical axis represents the interface domain wall energy density. The interfacial domain wall energy was obtained based on Equation 2 by measuring a magnetization history curve using an oscillating sample magnetometer in the above exchange-coupled medium. Reverse sputtering is performed by high-frequency bias sputtering, the input power is 50 W, the reflected wave power is 12 W, and the bias voltage to the substrate is 100V. As the sputtering gas, a mixed gas of argon and nitrogen was used. 202
To 204 are argon gas partial pressures of 1.4 × 10 ^{−3, respectively.}
Table 1 shows the partial pressure of nitrogen gas, which was fixed at Torr.

[0026]

[Table 1]

Further, 201 is an argon gas partial pressure of 1.4 ×
10 ^-3 Torr, nitrogen gas partial pressure 2.5 × 10 ^-4 Torr
2 is a comparative example in which the sample was left in r for the time shown on the horizontal axis in FIG. 2, and 202 is a comparative example in which only argon was used as the sputtering gas. Further, the case where the reverse sputtering time on the horizontal axis is 0 is a comparative example in which the reference layer is formed immediately after the memory layer is formed.

In any of the examples shown in FIG. 2, the value of the interfacial domain wall energy becomes smaller as the standing time in the mixed gas of argon gas and nitrogen gas or the reverse sputtering time increases. Compared to the one left in the mixed gas of 201 with argon gas and nitrogen gas, the one in which only the argon gas is reverse-sputtered has the interface domain wall energy sharply decreased with respect to the reverse-sputtering time, but the mixed gas of the argon gas and the nitrogen gas. Then, the interfacial domain wall energy further sharply decreases. Although 204 has a higher nitrogen partial pressure than 203,
The rate of reduction of the interfacial domain wall energy with respect to the reverse sputtering time can be adjusted by the nitrogen partial pressure.

On the other hand, reverse sputtering is widely known to have a function of eliminating unevenness on the surface to be reverse sputtered and smoothing it.
Pay attention to the coercive force when a magnetic film is formed on a smooth surface. In the process of increasing the magnetic field in the direction opposite to the magnetization direction from the state where the magnetization direction of the magnetic film is initially uniform over the entire surface, nucleation of magnetic domains, which is a region where the magnetization direction is opposite to the surrounding direction, is generated. Occurrence, and then the magnetic domain expands and grows. Coercivity is affected by both domain nucleation and domain expansion.
Although the phenomenon of nucleation is complicated and unclear, the expansion and growth of the magnetic domain is affected by the unevenness of the surface on which the domain wall, which is the boundary region of the magnetic domain, is formed. Therefore, the second magnetic layer of the first magnetic layer
The effect on the coercive force of the second magnetic layer was shown by performing reverse sputtering on the interface with the magnetic layer.

FIG. 3 shows the change in coercive force with respect to the reverse sputtering time. The sample is the same as in FIG. Therefore, the sample used with the change of the interface domain wall energy of reference numeral 201 in FIG. 2 is the same as the sample used in 301, and 202 is 302, 203 is 303, and 204 is 3 respectively.
The same as 04. Further, since the sample is the same as that of Example 1, the first magnetic layer corresponds to the memory layer and the second magnetic layer corresponds to the reference layer. The coercive force of the reference layer is determined by a vibrating sample magnetometer from the magnetization history curve of the reference layer in the state where the magnetization of the memory layer with a large coercive force does not reverse for the magnetic film in which the memory layer and the reference layer are exchange-coupled. did.

30 left in a mixed gas of argon and nitrogen
In No. 1, the coercive force of the reference layer increases as the standing time increases. Reference numerals 302, 303, and 304 indicate the results of reverse sputtering. Although the effect of reducing coercive force by reverse sputtering diminishes as the nitrogen partial pressure increases, coercive force in which reverse sputtering was performed for 0 minutes was 0 minutes. Lower than From Equation 2, the reduction of the coercive force of the reference layer leads to the reduction of the initializing magnetic field, and the reverse sputtering is advantageous for the cost reduction of the magneto-optical drive.

(Embodiment 2) In the second embodiment, there are four kinds of mixed gas at the time of reverse sputtering: argon gas and nitrogen gas, argon gas and oxygen gas, argon gas and nitric oxide gas, argon gas and carbon dioxide gas. An example of measuring the interfacial domain wall energy density using the sputtering gas of No. 1 will be described. The film composition, the film thickness, the film forming procedure, and the measuring method of the interface domain wall energy density are the same as in Example 1. Argon partial pressure 1.4 × 10
^-4 Torr, nitrogen, oxygen, nitric oxide, and carbon dioxide partial pressure were set to 7.1 × 10 ^-6 Torr, and the interfacial domain wall energy density was measured while changing the reverse sputtering time.

FIG. 4 shows an example thereof, in which the vertical axis shows the interface domain wall energy density and the horizontal axis shows the reverse sputtering time.
401 is an example of a mixed gas of argon and nitrogen.
The same as 203. 402 is argon and oxygen, 40
3 is an example of argon and nitric oxide, and 404 is an example of a mixed gas of argon and carbon dioxide. From this example, it is understood that oxygen, nitric oxide, and carbon dioxide have the effect of lowering the interfacial domain wall energy as in the case of nitrogen.

(Third Embodiment) In the third embodiment, an example of measuring the interfacial domain wall energy and the coercive force of the reference layer for the following four kinds of samples will be described. As Sample 1, the partial pressure of the sputtering gas at the time of reverse sputtering was 1.4 × 10 ⁻³ Torr and the partial pressure of nitrogen gas was 7.1 × 10 ⁻⁶ , which corresponds to 203 in FIG. 2 in the reverse sputtering. The reverse sputtering time was 40 minutes at Torr. Sample 2 starts direct current magnetron sputtering with a sputtering gas at the time of film formation of the memory layer and an argon gas pressure of 1 × 10 ⁻³ Torr at the start of film formation of the memory layer, and maintains the argon gas pressure as it is. One minute before the completion of layer formation, nitrogen gas was introduced to the sputter gas in addition to the argon so far, to obtain a mixed sputter gas having an argon gas partial pressure of 1 × 10 ⁻³ Torr and a nitrogen gas partial pressure of 1 × 10 ⁻⁴ . Since the total deposition time of the memory layer is 10 minutes, the sputtering time of sputtering using only argon as the sputtering gas is 9 minutes. After that, the reference layer is 6
00Å A film was formed.

Regarding the sputtering conditions of the memory layer and the reference layer of Sample 2, the sample 1 was not subjected to reverse sputtering after the formation of the memory layer, and nitrogen gas was mixed with the sputtering gas immediately before the completion of the formation of the memory layer. It is the same as sample 1 except that it was made. In Sample 3, the sputtering gas at the start of film formation of the reference layer was argon gas partial pressure of 1 × 10 ⁻³ T
DC gas magnetron sputtering was performed for 1 minute with a mixed gas of argon gas and nitrogen gas having a partial pressure of 1 × 10 ⁻⁴ Torr.
Sputtering was performed at × 10 ⁻³ Torr for 8 minutes. The sputtering conditions of the memory layer and the reference layer of sample 3 are sample 1
On the other hand, it is the same as the sample 1 except that the reverse sputtering is not performed after the reference layer is formed and that the nitrogen gas is mixed with the sputtering gas at the start of the formation of the second magnetic film. Sample 4 is the same as Sample 1 except that reverse sputtering is not performed after the memory layer is formed.

Sample 1, the magneto-optical recording medium of the present invention, samples 2, 3, and 4 are comparative examples.

For these samples, the interface domain wall energy density and the coercive force of the reference layer were measured in the same manner as in Example 1. The results are shown in Table 2.

[0038]

[Table 2]

Although the interfacial domain wall energy densities of Sample 1, Sample 2, and Sample 3 are decreased, Sample 1 has a smaller coercive force than the comparative examples of Sample 2 to Sample 4. Therefore, the present invention is more effective in reducing the initializing magnetic field.

[0040]

As described above, according to the present invention, the effect of lowering the interfacial domain wall energy and the effect of lowering the coercive force of the second magnetic layer are combined so that the initialization magnetic field of the exchange coupling two-layer film overwrite is reduced. It is effective for reduction.

[Brief description of drawings]

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

FIG. 2 is a diagram showing the dependence of interface domain wall energy on reverse sputtering time.

FIG. 3 is a diagram showing the dependence of the coercive force of the second magnetic layer on the reverse sputtering time.

FIG. 4 is a diagram showing the dependence of interface domain wall energy on reverse sputtering time.

[Explanation of symbols]

 103 ... First magnetic layer 104 ... Second magnetic layer

Claims (5)

[Claims] 1. A rare earth transition metal amorphous alloy thin film having perpendicular magnetic anisotropy is used, and at least two magnetic layers having different coercive forces at room temperature are provided, and the magnetic layers having different coercive forces at room temperature are exchange-coupled to each other. In the magneto-optical recording medium, the first magnetic layer and the second magnetic layer exchange-coupled to each other are adjacent to each other, and at least one of nitrogen and oxygen is provided on one side of the first magnetic layer in contact with the second magnetic layer. A magneto-optical recording medium containing one kind. 2. A rare earth transition metal amorphous alloy thin film having perpendicular magnetic anisotropy is used, and at least two magnetic layers having different coercive forces at room temperature are provided, and the magnetic layers having different coercive forces at room temperature are exchange-coupled to each other. In the method of manufacturing a magneto-optical recording medium, the first magnetic layer and the second magnetic layer exchange-coupled to each other are formed adjacent to each other, and the second magnetic layer is formed after the formation of the first magnetic layer. A method for manufacturing a magneto-optical recording medium, characterized in that after the film formation and after forming the first magnetic layer, reverse sputtering is carried out with a sputtering gas in which at least one kind of argon gas, nitrogen gas and oxygen gas is mixed. 3. The method for manufacturing a magneto-optical recording medium according to claim 2, wherein the reverse sputtering is performed with a sputtering gas in which argon gas and nitric oxide gas are mixed. 4. A rare earth transition metal amorphous alloy thin film having perpendicular magnetic anisotropy is used, and at least two magnetic layers having different coercive forces at room temperature are provided, and the magnetic layers having different coercive forces at room temperature are exchange-coupled to each other. In the present magneto-optical recording medium, the first magnetic layer and the second magnetic layer exchange-coupled to each other are adjacent to each other, and carbon and oxygen are contained in one side of the first magnetic layer in contact with the second magnetic layer. A magneto-optical recording medium characterized by the above. 5. A rare earth transition metal amorphous alloy thin film having perpendicular magnetic anisotropy is used, and at least two magnetic layers having different coercive forces at room temperature are provided, and magnetic layers having different coercive forces at room temperature are exchange-coupled to each other. In the method of manufacturing a magneto-optical recording medium, the first magnetic layer and the second magnetic layer exchange-coupled to each other are formed adjacent to each other, and the second magnetic layer is formed after the formation of the first magnetic layer. A method for manufacturing a magneto-optical recording medium, characterized in that after the film formation and the film formation of the first magnetic layer, reverse sputtering is carried out with a sputtering gas in which an argon gas and a carbon dioxide gas are mixed.