JPH04167406A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To make the Kerr angle of rotation large and to ensure a good squareness ratio by a method wherein a plurality of atrificial lattice magnetic films in which Co layers and Pt layers have been formed alternately are formed via transparent dielectric layers. CONSTITUTION:A recording layer 4 which has been sandwiched between dielectric layers 2, 3 for enhancement use is formed on a transparent substrate 1; in addition, a reflecting layer 5 composed of a metal is formed. For the recording layer 4, a plurality of Co-Pt artificial lattice magnetic films 6 and transparent dielectric layers 7 are formed alternately, and its whole film is made large. The Co-Pt artificial lattice magnetic films 6 are not formed as one continuous thick film, but have a structure which has been divided into a plurality of layers between which the transparent dielectric layers 7 are laid. Thereby, while the total sum of the whole thickness of the Co-Pt artificial lattice magnetic films 6 is made large, the squareness of a magnetization curve can be kept in a good state.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magneto-optical recording medium that records and reproduces information signals by utilizing the magneto-optic effect.
This invention relates to the improvement of a magneto-optical recording medium that uses a superlattice magnetic film as a recording layer.

[Summary of the invention]

The present invention increases the Kerr rotation angle and achieves a good squareness ratio by laminating multiple layers of artificial lattice magnetic films in which Co layers and PT layers are alternately laminated via transparent dielectric layers. This is what we are trying to secure.

[Conventional technology]

Gd is used as a recording material for a magneto-optical recording medium that records and reproduces information signals using the magneto-optic effect.

A typical example is an amorphous alloy in which rare earth elements such as Tb and Dy are combined with transition metal elements such as Fe and Co.

However, the rare earth elements and Fe constituting these amorphous alloys are very easily oxidized and have the property of easily forming oxides due to oxygen, moisture, etc. penetrating through the substrate and the like. If such oxidation progresses and leads to corrosion or pitting, signal dropout will be induced, and if rare earth elements in particular undergo selective oxidation, the coercive force and residual magnetic Kerr rotation angle will decrease, resulting in poor C/N. The problem arises of deterioration.

Therefore, the application of magnetic materials containing precious metals such as Pt and Pd instead of rare earth elements to magneto-optical recording media is being considered. We have proposed a magneto-optical recording medium whose recording layer is an artificial lattice magnetic film in which layers are alternately laminated.

The aforementioned Co--Pt superlattice magnetic film is a perpendicular magnetization film that is good as a magneto-optical recording material, and by making the film thickness about 1 Co, a large Kerr rotation angle can be obtained and a moderate reflectance can be obtained. Also, with this level of film thickness, it is possible to obtain a good square car.
loops (or magnetization curves) are easily obtained.

[Invention or problem to be solved]

By the way, in order to further improve the characteristics of the magneto-optical recording medium, enhancement of the Kerr rotation angle is sometimes performed using a so-called four-layer structure or the like.

When attempting to perform such enhancement, it may be necessary to make the Co-Pt superlattice magnetic film in the multilayer structure thicker than that of the 1Co film in order to increase the Kerr rotation angle. .

However, if the thickness of the Co--Pt superlattice magnetic film is increased, the squareness of the Kerr loop will deteriorate.

The present invention was proposed in view of the above circumstances, and an object of the present invention is to provide a magneto-optical recording medium in which the square shape of the Kerr loop does not deteriorate even when the thickness of the Co--Pt superlattice magnetic film is increased. With the goal.

[Failure to solve the problem]

In order to achieve the above object, the magneto-optical recording medium of the present invention uses an artificial lattice magnetic film in which a Co layer and a Pt layer are alternately laminated as a recording layer, and a transparent dielectric layer is interposed between the artificial lattice magnetic film and a transparent dielectric layer. It is characterized by being laminated in multiple layers.

[Effect]

By creating a structure in which the Co-Pt superlattice magnetic film is divided into multiple layers with a transparent dielectric layer interposed between them, instead of forming one continuous thick film, these Co-Pt superlattice magnetic Without increasing the total thickness of the entire film, the square shape of the magnetization curve can be maintained in good condition.

〔Example〕

Embodiments to which the present invention is applied will be described in detail below with reference to the drawings.

The magneto-optical recording medium of this example has a dielectric layer for enhancement (
A recording layer (4) sandwiched between 2) and (3) is provided, and a reflective layer (5) made of metal is further laminated.

The recording layer (4) is made up of a plurality of Co--Pt superlattice magnetic films (6) and transparent dielectric layers (7) which are alternately laminated, and the total film thickness is large.

Here, the number of layers of the Co--Pt superlattice magnetic film (6) may be two or more, and may be selected depending on the desired characteristics.

The Co-Pt superlattice magnetic film (6) has a Co layer and a Pt layer.
It is a so-called artificial lattice film, in which layers are stacked on an atomic level. At this time, the interface between the Co layer and the PT layer may be ideal because it has a so-called superlattice structure in which atoms of different metals mix with each other, but even though the interface is slightly disordered, it remains constant as a whole. The composition changes with a period of . It may have a so-called composition modulation structure.

Moreover, various elements may be added to this Co--Pt superlattice magnetic film (6) for the purpose of increasing thermal stability, lowering the Curie point, etc. Additional elements include B, C, and A.
1. Si, P, T4. V, Fe.

Ni, Cu, Ga, Ge, Zr, Nb,
Mo.

Examples include In, Sn, Sb, Gd, Tb, Dy, and Ta.

In the above-mentioned Co--Pt superlattice magnetic film (6), the thickness of each Co layer constituting the superlattice is 2 to 8 layers.

The thickness of the PT layer is set in a range of 3 to 40 layers.

This is because, outside the above range, the magneto-optical properties will deteriorate, such as the magnetic Kerr rotation angle and coercive force will deteriorate. Moreover, the film thickness of each superlattice magnetic film (6) is 50~
It is set to 8Co people, preferably 50 to 4Co people. This is because if the thickness of each Co--Pt superlattice magnetic film (6) is too large, the squareness ratio will decrease.

On the other hand, the transparent dielectric layer (7) interposed between the artificial lattice magnetic films (6) is made of Co--
It plays the role of dividing the Pt superlattice magnetic film, and is usually set in the range of 10 to 1 Co, preferably 50 to 5 Co. If the thickness of the transparent dielectric layer (7) is too small, the Co--Pt artificial lattice magnetic film will not be sufficiently divided, leading to a decrease in squareness ratio, and conversely, the thickness of the transparent dielectric layer (7) will be insufficient. If the film thickness is too large, the recording layer (
4) The ratio of the superlattice magnetic film (6) in the recording medium decreases, making efficient recording and reproduction difficult.

The transparent dielectric layer (7) must be optically transparent, and if it does not transmit reproduction light, there is no point in having a multilayer structure.

Therefore, the transparent dielectric layer (7) has S]02.
5ilN4. In addition to optical thin film materials such as TlO2 and MgO,
Materials that exhibit some light absorption, such as Co-0, NiO, and Fe-0, may also be used. In addition, this transparent dielectric layer (7) is not limited to non-magnetic materials, such as cobalt ferrite, barium ferrite, yttrium,
Materials exhibiting magneto-optical effects such as iron and garnet can also be used.

Next, the present invention will be explained based on specific experimental results.

Experimental Example 1 In this experimental example, a Co-Pt superlattice magnetic film, a Co-0 transparent dielectric layer, and a Co-Pt superlattice magnetic film were sequentially deposited on a glass substrate, and their properties were investigated.

Therefore, the divided Co-Pt superlattice magnetic film is 2
It is a layer. In addition, the Co-〇 transparent dielectric layer has a wavelength of 0.8
The material has an absorption coefficient of 1X10''ao −' or less for light of μm, and is optically sufficiently transparent.

Note that in the sample prepared in this experimental example, no dielectric layer or reflective layer for rotational angle enhancement was provided.

First, a Co--Pt superlattice magnetic film having a thickness of 90 mm was formed on a glass substrate. When forming an artificial lattice magnetic film,
For Co, DC sputtering (input power 0.
40A, 3CoV), and high frequency sputtering (input power 4CoW) was used for Pi.

Next, on this Co-Pt superlattice magnetic film, C0-0
A transparent dielectric layer was formed by reactive sputtering using a Co metal target. The conditions for this reactive sputtering are as follows.

Reaction sputtering conditions Ar gas pressure -4mTorr02 partial pressure
-0,] l 4 mTorr Input power...3CoW (RF) Furthermore, the thickness of the C0-0 transparent dielectric layer formed is 220λ.

Furthermore, on this C0-0 transparent dielectric layer, re-QCo-P
A superlattice magnetic film was formed. This C.

The conditions for forming the -Pt superlattice magnetic film were the same as those for the first superlattice magnetic film, and the film thickness was also 90 mm.

Regarding the magneto-optical recording medium thus produced, the hysteresis of each Co--Pf artificial lattice magnetic film on the glass substrate side and the surface side was investigated by measuring Kerr loops from the glass substrate side and the film surface side. Each car loop has a second
They are shown in Figure (A) and Figure 2 (B), respectively.

In this sample, Co-P placed on the glass substrate side
The coercive force H, C of the t superlattice magnetic film is 230 Oersteds, and the coercive force Hc of the Co--Pt superlattice magnetic film disposed on the surface side of the Oersted film is 2450 Oersteds. Each Kerr loop includes the contribution of both Co-pt superlattice magnetic films, but since the contribution of the film closer to the observation side is the majority, the hysteresis loop of each superlattice magnetic film You can separate it and check the square shape.

When viewed from this point of view, none of the Co-pt superlattice magnetic films of this sample exhibit any deterioration in squareness.

Experimental Example 2 The sample prepared in this experiment has the same structure as the sample prepared in Experimental Example 1, but with Co-Pt on the opposite side of the glass group 1.
The coercive forces of the superlattice magnetic film and the Co--Pt superlattice magnetic film on the film surface side are aligned.

The reactive sputtering conditions for the Co-0 transparent dielectric layer were as follows, and the film thickness was 210 mm.

Reaction sputtering conditions Ar gas pressure -4mTorr02 partial pressure
-・-0,1] OmTorr input power
...a o ow (RF) The Kerr loop measured from the glass substrate side and the membrane surface side is shown in Figure 3 (
A) and FIG. 3(B) respectively.

The coercive force Hc is 250 oersted in both the Kerr loop measured from the glass substrate side and the Kerr loop measured from the film surface side. Also, all car loops have good square shapes.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
Since the recording layer is made by laminating multiple layers of artificial lattice magnetic films such as Co layers and PT layers alternately through transparent dielectric layers, the overall film thickness of the recording layer can be reduced while maintaining a good squareness ratio. For example, it is possible to increase the Kerr rotation angle by enhancement or the like.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a main part showing an example of the configuration of a magneto-optical recording medium to which the present invention is applied. Figure 2 (A) and Figure 2 (B) are characteristic diagrams showing the Kerr loop of the sample that was actually created, and Figure 2 (A) is the Kerr loop measured from the glass substrate side. (B) is the Kerr loop measured from the membrane surface side. Figure 3 (A) and Figure 3 (B) are characteristic diagrams showing the Kerr loop of other samples that were actually prepared, and Figure 3 (A) shows the Kerr loop and Kerr loop measured from the glass substrate side. Figure 3 (B)
is the Kerr loop measured from the membrane surface side. 1...Substrate 2.3...Dielectric layer 4...Recording layer 5...Reflection layer 6...Co-Pt artificial lattice magnetic film 7...Transparent dielectric layer

Claims (1)

[Claims] A magneto-optical recording medium characterized in that the recording layer is an artificial lattice magnetic film in which Co layers and Pt layers are alternately laminated, and a plurality of layers of the artificial lattice magnetic film are laminated with transparent dielectric layers interposed therebetween.