JPH04117645A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To allow overwriting by thinly inserting an exchange bonding strength control layer between respective magnetic layers constituting magneto-optical recording films. CONSTITUTION:The 1st to 3rd magnetic layers 3 to 5 are successively formed on a substrate 1. The 2nd magnetic layer 4 is formed of a film of <=3 Q expressed by formula Q=Hk/4piMs (where Hk denotes an anisotropic magnetic field and Ms denotes satd. magnetization). Namely, the magnetic layer 4 having weak perpendicular magnetic anisotropy, when inserted between the two layers 3 and 5, acts to smoothly connect the magnetization of the 1st layer 3 and the 3rd layer 5 and, therefore, the energy by the exchange interaction between the two layers 3 and 5 is decreased and the existence of such magnetization state as to anti-parallelly magnetize the two layers 3, 5 is allowed. The stable and good overwriting is possible in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magneto-optical recording medium, and more particularly to a magneto-optical recording medium comprising a multilayer film in which the magnetic coupling force between magnetic layers is well controlled.

(Prior art) In recent years, by using an initial auxiliary magnetic field and a magnetic multilayer film,
Magneto-optical recording methods that enable overwriting of information are attracting attention. (a) As a recording medium, a multilayer magneto-optical recording medium is used, in which the first layer having perpendicular anisotropy serves as a recording/reproducing layer, and the second layer having perpendicular anisotropy serves as a recording auxiliary layer. , (b) moving the recording medium; (c) aligning only the magnetization of the recording auxiliary layer either upward or downward before recording by applying an initial auxiliary magnetic field; (d) ) irradiating the recording medium with a laser beam; (
e) modulating the intensity of the laser beam in a pulsed manner according to the binary information to be recorded; (O applying a recording magnetic field to the portion of the recording medium irradiated with the laser beam; Forming one of the bits having upward magnetization and the bit having downward magnetization when the intensity of the laser beam modulated by the laser beam is at a high level, and forming the other bit when the intensity of the laser beam is at a low level; This is an overridable recording method characterized by
(see publication).

The M-H loop of the overridable bilayer media should be as shown in FIG. 2 at ambient temperature.

For example, in an anti-parallel type two-layer medium that is energetically stable when the magnetization of the first magnetic layer and the magnetization of the second magnetic layer are in opposite directions, the conditions for obtaining the M-H loop as shown in Figure 2 are: , Hc2-σw / 2M52t2 >0Hc2; Coercive force Ms2 of the recording auxiliary layer; Saturation magnetization L2 of the recording auxiliary layer: Film thickness of the recording auxiliary layer σW: Satisfying the interfacial domain wall energy per unit area, but the If the exchange coupling force is too strong, σ7 becomes too large, so that the above equation is no longer satisfied, and the M-H loop becomes a loop as shown in FIG.

In order to obtain the M-H loop as shown in FIG. 2, it is necessary to weaken the exchange coupling force between the recording layer and the recording auxiliary layer. One way to weaken the exchange force is to add GdFeCo between the two layers.
A method of sandwiching layers is known (K, Aratanie
t, al,, 5PIE Vol, 1078. p
, 258.0ptical Data Storag
eMeeting, 1989).

(Problem to be solved by the invention) However, since the GdFeCo control layer used to adjust the exchange coupling force between the two layers is a film with large vertical anisotropy, it is not possible to sufficiently weaken the coupling force between the two layers. In some cases, it was necessary to sandwich a fairly thick control layer between the two layers in order to weaken the bonding force between the two layers. For this reason, it was not possible to stably achieve good override characteristics.

The purpose of the present invention is to provide a magneto-optical recording film in which the exchange coupling force can be adjusted to an appropriate value by sandwiching a thin exchange coupling force control layer between each magnetic layer constituting the magneto-optical recording film, and as a result, the magneto-optical recording layer can be overridden. The goal is to provide recording media.

(Means for Solving the Problems) The present invention provides a magneto-optical recording medium in which a recording film is formed on a substrate, and information is recorded, reproduced, and erased using laser light. A second and a third magnetic layer are sequentially formed, and the second magnetic layer has a Q represented by the following formula [I].
; Q=Hk/4πMs...(■) (In the formula, Hk indicates an anisotropic magnetic field and M5 indicates saturation magnetization) is a magneto-optical recording medium characterized by being formed of a film having a value of 3 or less. be.

In the present invention, as the second magnetic layer, for example, NdD
yFeCo alloy, NdTbFeCo alloy, NdGdFe
Co alloy, DyGdFeCo alloy, NdGdFe alloy,
DyGdFe alloy, NdFeCo alloy, TbFeCo alloy film, GdTbTeCo alloy film, DyFeCo alloy film,
GdDyFeCo alloy film, DyTbFeC.

Examples include alloy films.

(The reason why the M-H loop of a two-layer film becomes a loop with a one-step reversal magnetic field as shown in Figure 3 is because the magnetization of the first layer and the magnetization of the second layer are antiparallel. This is because in the magnetized states shown in Figures 4(a) and (b), such a magnetized state cannot exist because the energy due to the exchange interaction between the two layers is large.There is no perpendicular magnetic difference between these two layers. When a weakly oriented magnetic layer is sandwiched between the layers, this layer acts to smoothly connect the magnetization of the first and second layers, as shown in Figures 5(a) and (b), so there is no exchange between the two layers. The energy due to the interaction decreases, and a magnetization state in which the magnetizations of the first and second layers become antiparallel can exist, and the M-H loop forms a two-stage reversal magnetic field as shown in Figure 2. becomes a loop with .

(Example) Next, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a partial sectional view of a magneto-optical recording medium which is an embodiment of the present invention. The medium configuration is substrate 1/spacer layer 21.
First magnetic layer 3/second magnetic layer 4/third magnetic layer 51 protective layer 6.

Here, as the substrate 1, a substrate made of polycarbonate resin, epoxy resin, glass, or the like is used. The board can be with or without groups. Groups may be formed on glass using ultraviolet curing resin or the like. As the spacer layer 2 and the protective layer 6, silicon nitride, silicon oxide, tantalum oxide, aluminum nitride, aluminum oxide, etc. can be used. Further, the first magnetic layer 3 and the third magnetic layer 5 are amorphous alloy thin films made of a combination of rare earth elements and transition metals. In this case, the rare earths include, for example, Tb, Gd,
As the transition metal, one or more elements are used from among Dy, Nd, Ho, etc., and one or more elements from Fe, Co, Ni, etc. are used as the transition metal. It is also possible to add a small amount of Ti, Mo, etc.

(1) Film thickness of recording layer and auxiliary layer is 180 and 60
In the case of 0 people, polycarbonate (with group) substrate / silicon nitride (800 Å) / TbFeCo alloy (180 people) l
GdTbFeCo alloy (600) Silicon nitride (800
We created a medium with a membrane structure called ``person''. All film formation is done by RF
By continuous sputtering using a magnetron sputtering device. Tb
Table 1 shows the characteristics of the monolayer FeCo layer and GdTbFeCo layer.

The car loop of this medium was as shown in FIG. This is because the magnetic coupling force between the TbFeCo alloy layer and the GdTbFeCo alloy layer is too strong. This medium is
Override was not possible.

(1) When using NdDyFeCo for the intermediate layer Polycarbonate (with group) substrate/Silicon nitride (800 people)
/ TbFeCo alloy (180 people) / NdDyF
eCo alloy (60 people) / GdTbFeCo alloy (60 people)
A medium was created with a film configuration of 0) l silicon nitride (800). The characteristics of a single NdDyFeCo layer are shown in Table 2.

The car loop of this medium was as shown in FIG. This is because the magnetic coupling force between the TbFeCo alloy layer and the GdTbFeCo alloy layer was weakened by the NdDyFeCo intermediate layer. At this time, the TbFeCo layer and G
The switching fields of the dTbFeCo layer were 30 kOe and 0.5 kOe, respectively.

Next, for this medium, Ta.

First, the override was performed, the linear velocity was 11.3 m/s, and the recording frequency was 3.7 MHz.
, DuTy ratio 50%, initial auxiliary magnetic field 2.9 kOe, recording magnetic field 3000e, low level laser beam power 4.
0mW, high level laser beam power 13.0mW
When recorded and played back under these conditions, a C/N of 52 dB was obtained.

On top of this, the linear velocity is 11.3 m/s, and the recording frequency is 7.4 M.
Hz, DuTy ratio 50%, initial auxiliary magnetic field 2.9KOe,
Recording magnetic field 3000e-1 Low level laser beam power 4. OmW high level laser beam power 13.0
When overriding was performed under the mW condition, a reproduced signal of 46 dB was obtained. Error rate is 10-5 to 10-6
Met. At this time, the 3.7 MHz signal (previous information) did not appear at all.

(2) When using NdTbFeCo for the intermediate layer Polycarbonate (with group) substrate/Silicon nitride (800 people)
/ TbFeCo alloy (180 people) / NdTbF
eCo alloy (70 people) lGdTbFeCo alloy (600 people)
A medium was created with a film configuration of silicon nitride (800). The characteristics of a single NdTbFeCo layer are shown in Table 3.

The car loop of this medium was as shown in FIG. This is because the magnetic coupling force between the TbFeCo alloy layer and the GdTbFeCo alloy layer was weakened by the NdTbFeCo intermediate layer. At this time, the TbFeCo layer and G
The switching fields of the dTbFeCo layer were 32 kOe and 0.7 kOe, respectively.

Next, an override was performed on this medium.

First, linear velocity 11.3 m/s, recording frequency 3.7 MHz
, DuTY ratio 50%, initial auxiliary magnetic field 2.9 kOe, recording magnetic field 3000e, low level laser beam power 4.
0mW, high level laser beam power 13.0mW
When recorded and played back under these conditions, a C/N of 52 dB was obtained.

On top of this, the linear velocity is 11.3 m/s, and the recording frequency is 7.4 M.
Hz, DuTy ratio 50%, initial auxiliary magnetic field 2.9 kOe,
Recording magnetic field 3000e, low level laser beam power 4.0mW.

When overriding was performed under the condition of a high-level laser beam power of 13.0 mW, a reproduced signal of 44 dB was obtained. - The error rate was IG-4 to 1o-5.

At this time, the 3.7 MHz signal (previous information) did not appear at all.

(3) When using NdGdFeCo for the intermediate layer Polycarbonate (with group) substrate/Silicon nitride (800 people)
/ TbFeCo alloy (180 people) / NdGdFe
Media were created with a film configuration of Co alloy (50 people), lGdTbFeCo alloy (600 people)/silicon nitride (800 people). The properties of the single NdGdFeCo layer are shown in Table 4.

The car loop of this medium was as shown in FIG. This is because the magnetic coupling force between the TbFeCo alloy layer and the GdTbFeCo alloy layer was weakened by the NdGdFeCo intermediate layer. At this time, the TbFeCo layer and G
The switching field of the dTbFeCo layer was 0.5 kOe.

29kOe and Next, an override was performed on this medium.

First, linear velocity 11.3 m/s, recording frequency 3.7 MHz
, DuTy ratio 50%, initial auxiliary magnetic field 2.9 kOe, recording magnetic field 3000e, low level laser beam power 4.
0mW, high level laser beam power 13.0mW
When recorded and played back under these conditions, a C/N of 52 dB was obtained.

On top of this, the linear velocity is 11.3 m/s, and the recording frequency is 7.4 M.
Hz, DuTy ratio 50%, initial auxiliary magnetic field 2.9 kOe,
Recording magnetic field 3000e, low level laser beam power 4.0mW.

When overriding was performed under the condition of a high-level laser beam power of 13.0 mW, a reproduced signal of 47 dB was obtained. The error rate was 10-5 to 10-6. At this time, the 3.7 MHz signal (previous information) did not appear at all.

(4) When using DyGdFeCo for the intermediate layer Polycarbonate (with group) substrate l Silicon nitride (800 people)
/TbFeCo alloy (180 people)/DyGdFeCo alloy (80 people) IGdTbFeCo alloy (600 people)/Silicon nitride (800 people) A medium was created with a film configuration. D
Various properties of the single layer yGdFeCo layer are shown in Table 5.

The car loop of this medium was as shown in FIG. This is because the magnetic coupling force between the TbFeCo alloy layer and the GdTbFeCo alloy layer was weakened by the DyGdFeCo intermediate layer. At this time, the TbFeCo layer and Gd
The reversal magnetic field of the TbFeCo layer was 37 kOe, respectively.

First, linear velocity 11.3 m/s, recording frequency 3.7 MHz
, Du, Ty coverage 50%, initial auxiliary magnetic field 2.9 kOe, recording magnetic field 3000e, low level laser beam power 4
．． 0mW, high level laser beam power 13.0m
When recording and reproducing under W conditions, a C/N of 51 dB was obtained.

On top of this, the linear velocity is 11.3 m/s, and the recording frequency is 7.4 M.
Hz, DuTy ratio 50%, initial auxiliary magnetic field 2.9 kOe,
Recording magnetic field 3000e, low level laser beam power 4.0mW, high level laser beam power 13.0
When overriding was performed under mW conditions, a reproduced signal of 45 dB was obtained. Error rate is 10-5 to 10-6
Met. At this time, the 3.7 MHz signal (previous information) did not appear at all.

(5) When using NdGdFe in the intermediate layer Polycarbonate (with group) substrate / Silicon nitride (800 people) /
A medium was created with a film configuration of TbFeCo alloy (180 pieces)/NdGdFe alloy (45 pieces), GdTbFeCo alloy (600 pieces), and silicon nitride (800 pieces). N
The characteristics of the single dGdFe layer are shown in Table 6.

The car loop of this medium was as shown in FIG. This is because the magnetic coupling force between the TbFeCo alloy layer and the GdTbFeCo alloy layer was weakened by the NdGdFe intermediate layer. The TbFeCo layer and GdT at this time
The reversal field of the bFeCo layer was 30 kOe, respectively.

First, linear velocity 11.3 m/s, recording frequency 3.7 MHz
, DuTy ratio 50%, initial auxiliary magnetic field 2.9 kOe, recording magnetic field 3000e, low level laser beam power 4.
0mW, high level laser beam power 13.0mW
When recorded and played back under these conditions, a C/N of 52 dB was obtained.

On top of this, the linear velocity is 11.3 rn/s, and the recording frequency is 7.4
MHz, DuTy ratio 50%, initial auxiliary magnetic field 2.9kOe
, recording magnetic field 3000e, low level laser beam power 4.0 mW, high level laser beam power 13.
When overriding was performed under the condition of 0 mW, a reproduced signal of 46 dB was obtained. Error rate is 10-5 to 10-
It was 6. At this time, the 3.7MHz signal (previous information)
did not appear at all.

(6) When using DyGdFe in the intermediate layer Polycarbonate (with group) substrate l Silicon nitride (800 people) /
A medium was created with a film configuration of TbFeCo alloy (180 people)/DyGdFe alloy (70 people), GdTbFeCo alloy (600 people), and silicon nitride (800 people). D
The properties of the single yGdFe layer are shown in Table 7.

The car loop of this medium was as shown in FIG. This is because the magnetic coupling force between the TbFeCo alloy layer and the GdTbFeCo alloy layer was weakened by the NdGdFe intermediate layer. The TbFeCo layer and GdT at this time
The reversal field of the bFeCo layer was 27 kOe and then an override was performed for this medium.

First, linear velocity 11.3 m/s, recording frequency 3.7 MHz
, DuTy ratio 50%, initial auxiliary magnetic field 2.9 kOe, recording magnetic field 3000e, low level laser beam power 4.
0mW, high level laser beam power 13.0mW
When recorded and played back under these conditions, a C/N of 52 dB was obtained.

On top of this, the linear velocity is 11.3 m/s, and the recording frequency is 7.4 M.
Hz, DuTy ratio 50%, initial auxiliary magnetic field 2.9 kOe,
Recording magnetic field 3000e, low level laser beam power 4.0mW, high level laser beam power 13.0
When overriding was performed under mW conditions, a reproduced signal of 45 dB was obtained. The error rate was 1σ5 to 10−6. At this time, the 3.7 MHz signal (previous information) did not appear at all.

When a three-layer film was created using a magnetic film with a Q of 3 or more as an intermediate layer, the resulting disk had symptoms such as low C/N and poor frequency characteristics, and good override characteristics were not achieved. I couldn't.

(2) When the film thickness of both the recording layer and the auxiliary layer is 1000, polycarbonate (with groups) substrate/silicon nitride (8
00 people) / TbFe alloy (1000 people) / TbFeC0
A medium with a film structure of TbFeCo alloy) l silicon nitride (800 people) was fabricated. All films were formed by continuous sputtering using an RF magnetron sputtering device. TbFe layer and T
Table 1 shows various properties of the single bFeCo layer.

The Kerr loop of this medium was a loop having only one level of reversal magnetic field as shown in FIG.

This is because the magnetic coupling force between the TbFe alloy layer and the TbFeCo alloy layer is too strong.

(1) When using NdFeCo for the intermediate layer: Polycarbonate (with group) substrate Silicon nitride (800 layers) / TbFe alloy (1000 layers) / NdFeC
A medium was prepared with a film configuration of o alloy (50 people)/TbFeCo alloy (1000 people) l silicon nitride (800 people). The properties of the single NdFeCo layer are shown in Table 2.

The Kerr loop of this medium became a loop with a two-stage reversal magnetic field as shown in FIG. TbFe alloy layer and Tb
This is because the magnetic coupling force between the FeCo alloy layers was weakened by the NdFeCo intermediate layer. At this time, the reversal magnetic fields of the TbFe layer and TbFeCo layer are each 8.2 kO.
e and 4.7 kOe.

(2) When using TbFeCo for the intermediate layer: Polycarbonate (with group) substrate l Silicon nitride (800 layers) / TbFe alloy (1000 layers) / TbFeCo
A medium was prepared with a film configuration of alloy (80 people)/TbFeCo alloy (1000 people) and silicon nitride (800 people). The properties of the second TbFeCo layer as a single layer are shown in Table 3.

The Kerr loop of this medium became a loop with a two-stage reversal magnetic field as shown in FIG. TbFe alloy layer and Tb
This is because the magnetic coupling force between the FeCo alloy layers was weakened by the TbFeCo intermediate layer. The switching magnetic fields of the TbFe layer and the third TbFeCo layer at this time were 6.8 kOe and 5.5 kOe, respectively.

Table 3 (3) When GdTbFeCo is used for the intermediate layer, polycarbonate (with groups) substrate l silicon nitride (80
0 people) / TbFe alloy (1000 people) / GdTbFe
Co alloy (100 people) / TbFeCo alloy (100 people)
A medium was fabricated with a film configuration of 0) l silicon nitride (800). The characteristics of a single GdTbFeCo layer are shown in Table 4.

The Kerr loop of this medium became a loop with a two-stage reversal magnetic field as shown in FIG. TbFe alloy layer and Tb
The magnetic coupling force between the FeCo alloy layers is GdTbFeC.

This is because it was weakened by the middle class. TbF at this time
The reversal magnetic field of the e layer and the TbFeCo layer is 8.
They were 0 kOe and 4.7 kOe.

Table 4 (4) When DyFeCo is used for the intermediate layer: Polycarbonate (with groups) substrate l Silicon nitride (800 people) / TbFe alloy (1000 people) / DyFeCo alloy (
A medium was prepared with a film configuration of 120 people)/TbFeCo alloy (1000 people) and silicon nitride (800 people). Dy
The characteristics of a single FeCo layer are shown in Table 5.

The Kerr loop of this medium became a loop with a two-stage reversal magnetic field as shown in FIG. TbFe alloy layer and Tb
This is because the magnetic coupling force between the FeCo alloy layers was weakened by the DyFeCo layer. The switching magnetic fields of the TbFe layer and TbFeCo layer at this time were 7.2 kOe and 5.3 kOe, respectively.

Table 5 (5) When GdDyFeCo is used for the intermediate layer, polycarbonate (with groups) substrate l silicon nitride (80
0 people) / TbFe alloy (1000 people) / GdDyFeC
o alloy (150 people) / TbFeCo alloy (1000 people)
A medium was fabricated with a film configuration of 1 silicon nitride (800 layers). The characteristics of a single GdDyFeCo layer are shown in Table 6.

The Kerr loop of this medium became a loop with a two-stage reversal magnetic field as shown in FIG. TbFe alloy layer and Tb
The magnetic coupling force between the FeCo alloy layers is GdDyFeC.

This is because it was weakened by the layers. At this time, the reversal magnetic fields of the TbFe layer and TbFeCo layer are each 7.8 k.
Oe and 5.2 kOe.

Table 6 (6) When DyTbFeCo is used for the intermediate layer, polycarbonate (with groups) substrate l silicon nitride (80
0 people) / TbFe alloy (1000 people) / DyTbFeC
o alloy (130 people) / TbFeCo alloy (1000 people)
A medium was fabricated with a film configuration of 1 silicon nitride (800 layers). The characteristics of a single DyTbFeCo layer are shown in Table 7.

The Kerr loop of this medium became a loop with a two-stage reversal magnetic field as shown in FIG. TbFe alloy layer and Tb
The magnetic coupling force between the FeCo alloy layers is DyTbFeC.

This is because it was weakened by the layers. At this time, the switching magnetic fields of the TbFe layer and TbFeCo layer are each 7.0k.
Oe and 5.4 kOe.

Table 7 Note that when a three-layer film was fabricated using a magnetic film with Q greater than 3 as the intermediate layer, the M-H loop became a loop with only one level of reversal magnetic field as shown in Figure 3. .

(Effects of the Invention) As explained above, according to the present invention, it is possible to adjust the magnetic coupling force between magnetic layers.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of an embodiment of the present invention, FIG. 2 is a characteristic diagram showing an M-H loop in an example of the magneto-optical recording medium of the present invention, and FIG. 3 is a diagram of a conventional magneto-optical recording medium. An example of M
The characteristic diagram showing the -H loop, FIGS. 4 and 5 are explanatory diagrams for explaining the present invention in detail.

Claims (1)

[Claims] (1) In magneto-optical recording media in which a recording film is formed on a substrate and information is recorded, reproduced, and erased using laser light,
First, second, and third magnetic layers are sequentially formed on the substrate, and the second magnetic layer has Q represented by the following formula [I]; Q=H_k/4πM_S...(I) (In the formula, H_k represents an anisotropic magnetic field and M_S represents a saturation magnetization.) A magneto-optical recording medium characterized in that it is formed of a film having a value of 3 or less.