JPH064918A - Magneto-optical recording medium and its production - Google Patents

Abstract

PURPOSE:To simply and easily form a nitride layer and to provide the magneto- optical recording medium having the large max. reproducing power and max. recording magnetic field by providing a recording layer and auxiliary recording layer which respectively have the Curie temps. and coercive forces of prescribed relations and nitriding the recording layer before the formation of the auxiliary recording layer. CONSTITUTION:The recording layer and auxiliary recording layer which respectively have the Curie temps. and coercive forces Tc1 and Hc1 and Tc3 and Hc2 are provided on the substrate and the Curie temps. and coercive forces are so selected as to satisfy the conditions Tc1<Tc2, Hc1>Hc2. The surface of the recording layer is easily and simply nitrided when the gas contg. the nitrogen is discharged to the recording layer before the auxiliary recording layer is formed. The magneto-optical recording medium having the large max. reproducing power and max. recording magnetic field is obtd. by this nitriding.

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 capable of optical recording and reproduction and a method for manufacturing the same.

[0002]

2. Description of the Related Art Magneto-optical recording media are being put to practical use as high density, low cost rewritable information recording media. In particular, a medium using a recording layer of an amorphous alloy of rare earth and a transition metal shows extremely excellent characteristics. The remaining major drawback of the magneto-optical recording medium is that overwrite cannot be performed. That is, since the conventional magneto-optical recording medium needs an erasing process before recording, one rotation requires two rotations to reduce the data transfer rate.

In recent years, several methods have been proposed as a method for performing this overwriting in a magneto-optical recording medium. Among them, a particularly promising method is a light modulation overwrite method using a multilayer film. This method is discussed in Proceedings of the 34th Joint Lecture on Applied Physics 28P ZL-3 (1987). It is composed of a perpendicular magnetization layer (recording auxiliary layer) having a relatively high Curie temperature and a low coercive force with respect to the recording layer. The overwrite means is initially sufficient to align the magnetization directions of the recording auxiliary layer and has a magnitude of the initializing magnetic field (Hin) that does not affect the magneto-optical recording layer.
After the application of i), a binary modulated light beam of high power (PH) and low power (PL) is applied while applying a bias magnetic field (Hb). During the PL irradiation, there is no inversion of the recording auxiliary layer, and the magneto-optical recording layer faces in a direction in which it is stabilized by exchange coupling with the recording auxiliary layer, and during the PH irradiation, the recording auxiliary layer reverses due to the bias magnetic field (Hb), Accordingly, the magneto-optical recording layer faces in the opposite direction to the case of PL, and the binary modulation allows overwriting.

In addition to such a medium having two magnetic layers, a layer which plays a role of initialization is provided next to the recording auxiliary layer,
A three-layer or four-layer structure without the initializing magnet has also been proposed.

[0005]

In any of the above-mentioned methods, it is known that the exchange coupling force between the magneto-optical recording layer and the recording auxiliary layer greatly affects the characteristics, and the control of this exchange coupling force is known. Therefore, an intermediate layer made of a material having a small perpendicular magnetic anisotropy such as Gd-Fe-Co is usually provided.

However, when such an intermediate layer is provided, there arises a problem that the device becomes complicated and the target cost increases as the number of magnetic layers increases. From the viewpoint of increasing the sensitivity as much as possible, it is desirable to omit the intermediate layer and reduce the total film thickness. For the above reasons, there has been a demand for a method of controlling exchange coupling that does not use an intermediate layer.

[0007]

Means for Solving the Problems As a result of investigations made by the present inventors to solve the above-mentioned problems, as a result of nitriding the surface of the magneto-optical recording layer under specific conditions, an appropriate exchange coupling force can be obtained. I found what I could get. The gist of the present invention resides in a magneto-optical recording layer having a Curie temperature T _C1 and a coercive force H _C1 at room temperature and a recording auxiliary layer having a Curie temperature T _C2 and a coercive force H _C2 at room temperature on a substrate. Formed in order, T _c1 ,
T _C2, H _C1, H _C2 in the _{T c1 <T C2, H C1} > overwritable magneto-optical recording medium which satisfies the H _C2, formed after the surface of the recording layer between the recording layer and the recording auxiliary layer And a method of forming a nitride layer of the magneto-optical recording medium, characterized in that a nitride layer is formed by nitriding
That is, in the method for manufacturing a magneto-optical recording medium, after the formation of the recording layer and before the formation of the recording auxiliary layer, a gas containing nitrogen is discharged to nitride the surface of the recording gas layer under the following conditions. Exist.

[0008]

[Equation 2] 0.6 <PN × t <2.0 PN: Partial pressure of nitrogen (Pa) t: Discharge time (seconds)

The present invention will be described in detail below. Examples of the substrate used in the present invention include transparent substrates such as glass and plastics such as acrylic resin and polycarbonate resin. The substrate generally has a thickness of about 1.2 mm.

In the present invention, a magneto-optical recording layer and a recording auxiliary layer are provided on the substrate. As the magneto-optical recording layer, one having a relatively low Curie temperature T _{c1 and a} large coercive force T _c1 is used. For example, Tb-Fe, Tb-Fe-Co, Dy-Fe
-Dy-Fe-Co, Tb-Dy-Fe-Co, etc. are mentioned. T _c1 is preferably 120 ° C. or higher and 200 ° C. or lower, and H _c1 is preferably 10 kOe or higher. The film thickness is preferably about 300 to 1000Å.

As the recording auxiliary layer, one having a relatively high Curie temperature T _C2 and a coercive force H _C2 smaller than H _c1 is used. For example, Tb-Fe-Co, Dy-Fe-Co, Dy
-Co, Tb-Dy-Fe-Co, Tb-Co, Gd-
Dy-Fe, Gd-Dy-Fe-Co, Gd-Tb-F
e, Gd-Tb-Fe-Co and the like. It is preferable that T _C2 is 180 ° C. or higher and 250 ° C. or lower, but naturally it needs to be higher than T _c1 . A smaller value of H _C2 is preferable to reduce the initializing magnetic field (Hini), but the recording auxiliary layer receives an effective bias magnetic field (H W) due to exchange coupling with the magneto-optical recording layer, so that the initializing magnetic field (Hini) is initialized. H _{C2 of a} certain size in order to make the existing state stable
is necessary. H _C2 is generally 1 kOe or more and 3 k
It is preferably about Oe or less. The thickness of the recording auxiliary layer is 5
It is preferably 00 Å or more and 1500 Å or less.

Overwriting is possible by the exchange coupling force between the magneto-optical recording layer and the recording auxiliary layer. If the exchange coupling force is too weak, in the low power (PL) recording, the bias magnetic field (Hb) applied in the opposite direction causes insufficient reversal of the magnetic domain of the recording layer. If the exchange coupling force is too strong, the recording domain having the domain wall becomes unstable and the strength against the reproducing power (Pr) decreases. It is considered that the maximum bias magnetic field (H _max ) that does not deteriorate the signal characteristics is usually 400 (Oe) or more. Similarly, the maximum reproducing power (P _max ) needs to be approximately 1.5 mW or more.

In order to obtain a medium having appropriate strength for both Hb and Pr, it is necessary to control the exchange coupling force to an appropriate value. We applied for the previous application (Japanese Patent Application No. 2-1
No. 78089), it was proposed that the exchange coupling force can be reduced by providing a nitrogen-containing layer between the magneto-optical recording layer and the recording auxiliary layer. In the present invention, the nitrogen-containing layer is formed by nitriding the recording layer by discharging a nitrogen-containing gas.

The nitriding amount at this time can be controlled by two factors, that is, the nitrogen partial pressure PN at the time of causing the discharge and the discharge time t. The higher the nitrogen partial pressure is, and the longer the discharge time is, the higher the nitriding amount is. The amount will increase. The amount of nitriding is approximately represented by the product of PN and t, and 0.6 <PN × t <2.0 is a preferable range. The nitrided layer preferably has a region containing nitrogen of 10 atomic% or more in the range of 20 Å or more and 10 Å or less, and the maximum nitrogen content of the region is 30 atomic% or more.

In the present invention, other layers may be formed in addition to the recording layer and the recording auxiliary layer. For example, in order to manufacture a medium that does not use an initializing magnetic field, a control layer and an initializing layer are provided after the recording auxiliary layer. As the control layer,
It is preferable that the Curie temperature is lower than that of both the magneto-optical recording layer and the recording auxiliary layer. The initialization layer is preferably one having a higher Curie temperature than either the magneto-optical recording layer or the recording auxiliary layer. As for the film thickness, the control layer is 50 to 300 Å,
An initial layer of about 100 to 500 Å is preferably used.

Since the alloy of rare earth and transition metal used in the magnetic layer is very easily oxidized, it is a preferred embodiment of the present invention to provide protective films on both sides of the magnetic layer. As the protective layer, SiN, AlN, TaO, TiO, ZnS or the like is preferably used. The thickness of the protective layer is 500 to 2000
Å is preferable. The protective layer between the substrate and the magnetic layer also serves as an interference layer that lowers the reflectance due to the interference effect.

As a method for forming each layer on the substrate, sputtering, electron beam vapor deposition, CVD method or the like is used. The use of the sputtering method is particularly preferable because a film having high anisotropy and high quality can be obtained.

[0018]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples unless it exceeds the gist. Example A 130 mmφ polycarbonate substrate having a guide groove having a flat area at the bottom of the recording area was introduced into a sputtering apparatus having two film forming chambers, and 3 × 1 was first prepared.
Exhaust to 0 ^-7 Torr or less and reactive sputtering of Si target using mixed gas of Ar and N ₂ is performed.
_An 800 Å protective layer of ₃ N ₄ was formed.

After the substrate is moved to another chamber having a vacuum degree of 2 × 10 ^-7 Torr or less, Ar gas is introduced and T
b and Fe ₉₃ Co ₇ (atomic%, the same applies below) were simultaneously sputtered to obtain Tb ₁₉ (Fe ₉₃ Co ₇ )
400 Å was formed on the magneto-optical recording layer. After that, Ar gas and N ₂ having a predetermined partial pressure were introduced, a 100 W power was applied at a high frequency of 13.56 MHz, and discharge was performed for a predetermined time. Specifically, a partial pressure of N ₂ was kept constant at 0.025 Pa and a discharge time was changed, and a method of keeping discharge time constant at 15 seconds and a partial pressure of N ₂ was changed.

After that, Dy and Fe ₆₀ Co ₄₀ targets were simultaneously sputtered to obtain Dy ₃₀ (Fe ₆₀ C
The recording auxiliary layer having a composition of o ₄₀ ) was formed at 800Å. After returning the disk to the first chamber, re-apply Si ₃ N ₄
Was formed as a protective layer to obtain a magneto-optical recording medium. FIG. 1 shows the relationship between the maximum recording magnetic field (H _max ) and the maximum reproducing power (P _max ) of the obtained magneto-optical recording medium when the discharge time was changed while keeping the nitrogen gas partial pressure constant at 0.025 Pa. FIG. 2 shows a similar relationship when the discharge time is fixed at 15 seconds and the nitrogen partial pressure is changed.

From FIG. 1 and FIG. 2, PN × t (Pa · sec)
FIG. 3 shows the relationship between H _max and P _max .
From FIG. 3, H _max is 400 (Oe) or more and P _max is 1.5.
It can be seen that the value of mW or more is from PN × t close to 0.5 to close to 2. Of the obtained discs, H _max
And P _max satisfying the above conditions can be overwritten with an initializing magnetic field of 3 kOe, and the CNR is 47.
A high value of ˜50 dB (bit length 0.78 μm) was obtained.

[0022]

The magneto-optical recording medium obtained in the present invention is excellent in both maximum reproducing power and maximum recording magnetic field due to the function of the nitride layer. Further, according to the method of the present invention, since the recording layer is nitrided to form the nitride layer, the formation of the nitride layer is easy in terms of cost and apparatus, and is very preferable in practical use.

[Brief description of drawings]

FIG. 1 is a graph _showing the relationship between discharge time and H _max and P _max.

FIG. 2 is a graph _showing the relationship between nitrogen partial pressure and H _max and P _max.

FIG. 3 is a graph _showing the relationship between PN × t and H _max and P _max.

[Explanation of symbols]

Graph of P _max Graph of H _max

Claims (2)

[Claims] 1. A magneto-optical recording layer having a Curie temperature T _c1 , a coercive force H _C1 at room temperature, and a Curie temperature T _c1 on a substrate.
_C2, the recording auxiliary layer having a coercive force H _C2 at room temperature are formed in this _{order, T c1, T C2, H} C1, H C2 is T _c1 <T _C2, H _C1
An overwritable magneto-optical recording medium satisfying> H _C2 , wherein a nitride layer is formed by forming a recording layer between a recording layer and a recording auxiliary layer and then nitriding the surface. Magneto-optical recording medium. 2. A magneto-optical recording layer having a Curie temperature T _c1 and a coercive force H _C1 at room temperature and a Curie temperature T on a substrate.
_C2, the recording auxiliary layer having a coercive force H _C2 at room temperature are formed in this _{order, T c1, T C2, H} C1, H C2 is T _c1 <T _C2, H _C1
In an overwritable magneto-optical recording medium satisfying> H _C2 , a nitrogen-containing gas is discharged after the recording layer is formed and before the recording auxiliary layer is formed, and the surface of the recording layer is nitrided under the following conditions. A method for manufacturing a magneto-optical recording medium characterized by the above. [Equation 1] 0.6 <PN × t <2.0 PN: Partial pressure of nitrogen (Pa) t: Discharge time (seconds)