JPH0319155A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To adequately diminish the exchange bond strength between two magnetic layers by constituting a recording film of a specific 1st magnetic layer which has perpendicular magnetic anisotropy and a specific 2nd magnetic layer which has the perpendicular magnetic anisotropy and is formed on the magnetic layer. CONSTITUTION:This recording medium is constituted by laminating a substrate 5, a spacer layer 4, the 1st magnetic layer (recording and reproducing layer) 3 consisting of a Dy-Fe-Co alloy, the 2nd magnetic layer (auxiliary recording layer) 2 consisting of a Gd-Dy-Fe-Co alloy, and a protective layer 1 in this order. The boundary magnetic wall energy density is decreased and the saturation magnetization is increased in order to diminish the exchange bond strength when the film thicknesses are made constant. Two-layered films 3, 2 combined with the perpendicularly magnetized films formed by adding Dy and Gd to FeCo are, therefore, used. The two-layered films 3, 2 having the adequately small exchange bond strength are formed in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an overwritable magneto-optical recording medium.

(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. This method uses, as a recording medium, a multilayer magneto-optical recording medium in which the first layer with perpendicular anisotropy serves as a recording/reproduction layer, and the second layer with perpendicular anisotropy serves as a recording auxiliary layer. , b. Moving the recording medium; C. Applying an initial auxiliary magnetic field to align either the upward or downward direction of the magnetization of the recording auxiliary layer before recording; d. , irradiating the recording medium with a laser beam; e. modulating the intensity of the laser beam into a pulse according to the binarized information to be recorded; f. recording on the portion of the recording medium irradiated with the laser beam; applying a magnetic field, g. forming either a bit with upward magnetization or a bit with downward magnetization when the intensity of the pulsed laser beam is at a high level, and when the intensity of the beam is at a low level; This is an overwritable recording method, which is characterized by forming the other bit when
.

In this method, the conditions required for the recording medium are that the coercive force of the recording/reproducing layer (first layer) is Hcl, the recording auxiliary layer (second layer) is
layer) is Hcz, the temperature at which the recording/reproducing layer is magnetically coupled to the recording auxiliary layer is Ts1, the temperature at which the magnetization of the recording auxiliary layer is reversed by the recording magnetic field Hb is T82, the room temperature is TR, and the low level laser beam Tt is the temperature when irradiated with a high-level laser beam, To is the temperature when the high-level laser beam is irradiated, Tel is the cue temperature of the recording/reproducing layer, TC2 is the cue temperature of the recording auxiliary layer, and is the recording temperature that the recording/reproducing layer receives. The magnetic field is HDl, the coupling magnetic field received by the recording auxiliary layer is HD2, and the initial auxiliary magnetic field is H.
ini. When closed, formula (1) is satisfied, and formulas (2) to (5) are satisfied at room temperature.

TR<TSI=Tct=TL<TS2=TC2=T
M (1) HCI > HC2 + lHD1 King HD2
1 (2) MCI>HDI
(3) HC2 > HD2
(4) Hc2+Hn2
<lHini. l<Hct+Hm (5)
Here, the saturation magnetization of the recording/reproducing layer is MSI, the saturation magnetization of the recording auxiliary layer is MS2, the film thickness of the recording/reproducing layer is hx, the film thickness of the recording auxiliary layer is h2, and the interfacial domain wall energy per unit area is Ow. If, Hnx=aw/(2Msth), H
D2 = ow/(2Ms2h2).

In addition, in the above formula, the upper row is A (a
ntiparallel) type of media,
The lower row shows the case of P (parallel) type media.

In other words, in the case of a P-type medium, for example, just before recording, only the magnetization of the recording auxiliary layer is uniformly aligned, and when irradiated with a low-level laser beam, the magnetization of the recording/reproducing layer is adjusted to match the magnetization of the recording auxiliary layer. Recording was performed by magnetizing both the recording auxiliary layer and the reproducing layer in the opposite direction to the direction of magnetization of the previous auxiliary layer when irradiated with a high-level laser beam.

(Problems to be Solved by the Invention) In the above-mentioned overwriting method, M. The H-Lube must have a two-stage reversal magnetic field as shown in Figure 2 at ambient temperature. For example, in a 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 the same direction, the condition for the reversal magnetic field to be in two stages is Hcl-ow/2Mst.
h1>HC2+aw/2Ms2h2. However, if the exchange coupling force between the two layers is too strong, σ in the above equation becomes too large, so the M-H loop becomes
This results in a loop with only one level of reversal magnetic field as shown in the figure. Conventionally, T was used as a multilayer magneto-optical recording medium.
A two-layer film combining b-Fe and Tb-Fe-Co was used, but in this two-layer film, the exchange coupling force between the two layers was too strong, so the M-H loop of the two-step reversal magnetic field was used. It was difficult to create a magneto-optical recording medium with this.

An object of the present invention is to provide a magneto-optical recording medium in which the exchange coupling force between two magnetic layers constituting a magneto-optical recording film has an appropriate value.

(Means for solving the problem) Amorphous Dy-F having perpendicular magnetic anisotropy in the recording film
A first magnetic layer made of an e-Co alloy, and an amorphous Gd-
2 consisting of a second magnetic layer made of Dy-Fe-Co alloy
By using a layer film.

(Function) When the interfacial domain wall energy density is ow, the saturation magnetization is Ms, and the film thickness is t, the exchange coupling force is given by the value ow/2Mst. Therefore, when the film thickness is kept constant, in order to reduce the exchange coupling force, it is necessary to reduce ow and increase Ms.

On the other hand, the relational expression ow = (AKu)'' is known (Y. Mimura et al., J. Appl. Ph.
ys. Vol. 49, p. 1208, 1978). Here, A is an exchange stiffness constant and Ku is a uniaxial anisotropy constant. Therefore, in order to reduce σW, A or Ku may be reduced.

Therefore, by using a two-layer film that combines a perpendicularly magnetized film in which Dy is added to reduce A and Gd is added to reduce Ku to FeCo, a two-layer film with an appropriately small OW is created. I can do it.

Note that the first magnetic layer is a recording/reproducing layer and must not be reversed by the initial auxiliary magnetic field, so it needs to have a large coercive force at ambient temperature. Therefore, an amorphous Dy-Fe-Co film having relatively hard magnetic properties is used. On the other hand, since the second magnetic layer is a recording auxiliary layer and needs to be able to be initialized by a preceding auxiliary magnetic field, it must have a small coercive force at ambient temperature. Therefore, an amorphous Gd-Dy-Fe-Co film, which is a relatively soft film, is used. Furthermore, since the first layer must have a lower temperature at which it cools than the second layer, the temperature at which it cools is adjusted by adjusting the amount of Co.

(Example) FIG. 1 shows a schematic diagram of a magneto-optical recording dual-layer film medium representing an example of the present invention. The medium is the substrate 5 base layer 4 Dy-Fe-
A first magnetic layer (recording/reproduction layer) made of a Co alloy, a second magnetic layer (recording auxiliary layer) made of a Dy-Fe-Co alloy, a second magnetic layer (recording auxiliary layer) 1 made of a Dy-Fe-Co alloy, and a protective layer 1 are laminated in this order. Here, as the substrate 5, a substrate made of polycarbonate resin, epoxy resin, glass, or a substrate in which groups are formed on glass with ultraviolet curing resin or the like is used. As the spacer layer 4 and the protective layer 1, silicon nitride, silicon oxide, tantalum oxide, aluminum nitride, aluminum oxide, etc. can be used.

In addition, a first magnetic layer 3 made of a Dy-Fe-Co alloy and a second magnetic layer 2 made of a Gd-Dy-Fe-Co alloy.
It is also possible to add small amounts of Ti, Mo, etc.

A magneto-optical recording medium having the film structure and properties as a single layer shown below was formed by continuous sputtering using an RF magnetron spa-soter device.

Membrane structure polycarbonate substrate/silicon nitride (800 people)/Dy-
Fe--Co alloy/Gd--Dy--Fe--Co alloy 1 Silicon nitride (800A) Example 1 A two-layer medium was prepared whose various properties in a single layer are shown in the following table.

As a result, a Kerr loop with a two-stage reversal magnetic field as shown in FIG. 2 was obtained. In this case, the reversal magnetic fields of the Dy-Fe-Co alloy layer and the Gd-Dy-Fe-Co alloy layer were 7.2 KOe and 2.6 KOe, respectively.

Also, the interfacial domain wall energy density σ1 is 1.3erg/c
m2, and the exchange coupling force aw/2Mst was 6000e.

Next, magneto-optical recording and reproduction were performed using the above medium under the following recording and reproduction conditions. The recording and reproducing conditions are shown below.

Linear velocity: 11.3 m/s Laser power at high level: 10 mW (on disk) Laser power at low level: 7 mW (on disk) Laser power during playback: 1 mW (on disk) First, the beam is modulated at IMHz. The medium was irradiated while When the reproduced signal from the laser irradiation section was analyzed with a spectrum analyzer, a signal with a C/N ratio of 55 dB was detected at the IMHz position, confirming that bits were recorded.

Next, add a frequency of 5M to the already recorded area of the medium.
The Hz signal was recorded as new information. When this information was similarly analyzed, new information was reproduced with a C/N ratio of 50 dB. The error rate was 1o-5 to 1o-6. At this time, the IMHz signal (previous information) did not appear at all.

As a result, it was found that overwriting is possible.

Note that under these conditions, the temperature of the medium is 250°C during high-level laser irradiation and 170°C during low-level laser irradiation.
reach °C.

Example 2 A two-layer medium was prepared whose properties in a single layer are shown in the following table.

As a result, a Kerr loop with a two-stage reversal magnetic field as shown in FIG. 2 was obtained. In this case, the reversal magnetic fields of the Dy-Fe-Co alloy layer and the Gd-Dy-Fe-Co alloy layer were 9.5 KOe and 2.2 KOe, respectively.

Also, the interfacial domain wall energy density σ. is 1.3erg/c
m, and the exchange coupling force ow/2Mst was 7000e.

Next, magneto-optical recording and reproduction were performed using the above medium under the following recording and reproduction conditions. The recording and reproducing conditions are shown below.

Linear velocity: 11.3 m/s Laser power at high level: 9 mW (on disk) Laser power at low level: 7 mW (on disk) Laser power during playback: 1 mW (on disk) First, the beam is
The medium was irradiated while modulating at MHz. When the reproduced signal from the laser irradiation section was analyzed with a spectrum analyzer, a signal with a C/N ratio of 56 dB was detected at the IMHz position, confirming that bits were being recorded.

Next, add a frequency of 3H to the already recorded area of the medium.
The z signal was recorded as new information. When this information was similarly analyzed, new information was reproduced with a C/N ratio of 52 dB. The error rate was 10-5 to 10-6. At this time, the IMHz signal (previous information) did not appear at all.

As a result, it was found that overwriting is possible.

Note that under these conditions, the temperature of the medium is 230°C during high-level laser irradiation, and 170°C during low-level laser irradiation.
reach °C.

(Effects of the Invention) As shown in the Examples section, according to the present invention, the exchange coupling force between the magnetic layers can be appropriately reduced, and a magneto-optical recording medium with a two-step reversal magnetic field can be obtained. can. As a result, overwriting becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing an example of the magneto-optical recording medium of the present invention,
Figure 2 shows the overwrite 2 obtained by applying the present invention.
A conceptual diagram showing an M-H loop of a layered film medium. FIG. 3 is a conceptual diagram showing an M-H loop of a conventional two-layered film medium.

Claims (1)

[Claims] In a magneto-optical recording medium, the recording film includes a first magnetic layer made of an amorphous Dy-Fe-Co alloy having perpendicular magnetic anisotropy, and a first magnetic layer having perpendicular magnetic anisotropy formed on the magnetic layer. A magneto-optical recording medium comprising a second magnetic layer made of an amorphous Gd-Dy-Fe-Co alloy.