JPS6187245A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a photomagnetic recording medium which has a high S/N ratio and permits high-density recording and high-speed recording by forming said medium so as to have a photomagnetic recording layer consisting of an alloy added with specific elements and a low coercive force material layer consisting of a specific alloy and dominantly amorphous alloy and forming a non-magnetic layer having a specific thickness or below between these layers. CONSTITUTION:The photomagnetic recording medium has the photomagnetic recording layer consisting of the alloy composed of elements of at least >=1 kinds of Ce, Pr and Nd as well as Fe and impurities or said alloy added further with elements of >=1 kinds among Ti, Zr, Ta, Hf, Nb, W, Y, Mo, or the alloy added further with >=1 kinds among Cr, Co, Cu, Ni and Mn and the low coercive force material layer of which the coercive force is <=1/5 the coercive force of the photomagnetic recording layer and <=100 oersted and which consists of the alloy composed of elements of >=1 kinds among Si, B and P as well as Fe and impurities or the alloy added further with >=1 kinds among Co, Ni, Cr, Mo and W to said alloy and the dominantly amorphous. The non-magnetic layer having <=100 nonometer thickness is formed between the magnetic recording layer and the low coercive force material layer.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a magnetic recording medium that has an axis of easy magnetization in a direction perpendicular to the film surface and can be read using magneto-optic effects such as the magnetic Kerr effect. It is.

[Prior art]

Research on magneto-optical memory is said to have its beginnings in 1957, when recording was performed on a MnB1 thin film using a hot pen, and the written magnetic domain was observed using the magneto-optic effect. Spurred by the subsequent development of lasers, MnB
Although intensive research has been carried out mainly on 1-based materials, practical application has not been achieved because laser light sources and the technology for using them are still immature.

However, in the 1970s, advances in optical information processing related technology and research into new magnetic thin film materials such as amorphous rare earth transition metal alloy thin films progressed (Patent Application Publication 1982-
57607), (l17e.

Alloy thin films such as Tb1Fe, D7Fe, and GdCo have been developed. These materials generally have the following characteristics.

Magneto-optical recording media for compensation point recording such as GdFe and Ga0o have a larger Kerr rotation angle than magneto-optical recording media for single-point Curie recording, and have excellent optical reproduction characteristics, but have a small coercive force (several hundred oersteds) of 1μ. It is not possible to stably obtain small bits with a diameter of about 100 ml.・TbFe, DylFe
Curie magneto-optical recording media for single point recording, contrary to the above, have a large coercive force (several kilo Oersteds) and can stably obtain minute bits with a diameter of about 1μ, but their Kerr rotation angle is small and their optical reproduction characteristics are poor. It had drawbacks such as not being very good. Also, Tb, G(1, Dy, Ho
, etc.

Heavy rare earths are expensive and unsuitable for practical use.

In order to compensate for the drawbacks of these binary alloy thin films, three methods have been attempted in the past.

(1) Make ternary or quaternary ◇For example, binary GdF
GdTbIr takes advantage of the strengths of e and TbFe and compensates for their weaknesses.
Method 0 of diversification such as e ternary alloy or GdTblFe0o quaternary alloy (Japanese Patent Application Laid-open No. 126907/1983
JP-A-57-94948) (2) A method of improving the properties of a binary alloy thin film by improving the manufacturing method or by using a new manufacturing method. (Japan Society of Applied Magnetics 27th Research Meeting Material 2.7-5) (3) Method of forming a multilayer structure. A dielectric layer is layered on the recording medium to increase the Kerr effect due to multiple reflections.

In addition, the recording layer and the reproducing layer are separated, and a reflective layer is provided on the back side of the recording medium using materials suitable for each.
This method uses not only the light reflected from the surface but also the light that has passed through the medium. (Unexamined Japanese Patent Publication No. 58-20
044 y) In addition, heavy rare earth-transition metals are used for magneto-optical recording, and permalloy, Fe, Co is used instead of the reflective film.
, using Ni (Japanese Unexamined Patent Publication No. 58-222455)
), but since the bits only exist stably and permalloy, Fe, Oo, and Ml are polycrystalline, they cause noise and do not cause S/H deterioration. Although the Kerr rotation angle increases, the reflectance decreases, and even if the rotation angle improves somewhat, the Curie temperature increases, making laser writing difficult.There are advantages and disadvantages, and no fundamental improvement has been achieved. Ta.

〔the purpose〕

The present invention has the disadvantage of having a small Kerr rotation angle of 1 μm.
We have fundamentally improved the drawbacks such as not being able to obtain stable bits,
High S/IN by improving contradictory characteristics.

The purpose of the present invention is to provide a magneto-optical recording medium with high density, high stability, and high speed read/write capabilities.

〔overview〕

The present invention provides a magneto-optical recording medium in which recording and reproduction is performed by irradiating light onto a magneto-optical recording layer in which the direction of magnetization is perpendicular to the film surface and has a binary value of either upward or downward. ), praseodymium (Pr), neodymium (
An alloy consisting of at least one element among ma), iron (Pr), and an impurity, or an alloy further comprising titanium (Pr) and an impurity.
'ri)s Zirconium (Zr), Tantalum (Ta),
hafnium (ar), niobium (nb), tungsten (
W), yttrium (Y), and molybdenum (Mo), or the alloy further contains chromium (Or), cobalt (Co), and copper (C).
u) a magneto-optical recording layer made of an alloy to which at least one element selected from the group consisting of nickel (al) and manganese (Mn) is added; Silicon (Sl), boron (
B), an alloy consisting of at least one element among phosphorus (P), iron (Fe'), and impurities, or the alloy is roughly coated with cobalt (CO), nickel (Ni)? Chromium (Or), molybdenum (M), tungsten (W)
), and a low coercive force material layer made of a predominantly amorphous alloy, and a layer having a thickness of 100 mm between the magnetic recording layer and the low coercive force material layer. It is characterized by forming a non-magnetic material layer of nanometer size or less.

〔Example〕

Hereinafter, the present invention will be explained in detail using figures.

The basic structure of the present invention is shown in FIG. 1 (α) and FIG. 1 (6).

11 is a substrate, 1248 recording layer, 13 is a low coercive force material layer.
14 is a nonmagnetic layer.

゛ In this case, the substrate is a transparent substrate such as glass or plastic, and the optical head for reading and writing faces the substrate side.
Although I wrote about the case of reading and writing through the substrate, this is not essential, and it is possible to form a low coercive force material layer, a magneto-optical recording layer, a low coercive force material layer, a nonmagnetic layer, and a magneto-optical recording layer on the substrate. There is no problem even if the optical head is arranged facing the magneto-optical recording medium side with respect to the substrate for reading and writing. Further, the present invention is not limited to the above-mentioned structure, and it is possible to provide a protective film, an antireflection film, a multiple interference enhancement film, a transparent conductive film, etc.

Example t (1) The substrate 23 is made of a medium having the structure shown in FIG. 2 (α).
Using well-cleaned glass, amorphous NcLFeTi with a thickness of 500A was deposited on a glass substrate using a sputtering method.
A perpendicular magnetization film 22 was formed, and a Fe5iB amorphous film 21 was formed thereon at 1000× using a sputtering method. The coercive force of the Fe5iE amorphous film is about 7 oersted, and the sample ratio is 1. Also, for comparison, the above Fe
A instead of 5iB amorphous film! 1ooo by sputtering method
The sample ratio of the X-formed sample is 2.

(2) In the medium having the structure shown in FIG. 2(b), as in Example 1, 23 is a glass substrate, 22 is an NdFeTi film,
21 is an lFe5iB film, and 24 is a dielectric layer made of Sin.

It is formed at 800X. This is because Si0. By forming a film, the Kerr rotation angle is enhanced. This is set as sample ratio 3.

Also, for comparison, instead of the above 1FesiE amorphous film,
2 was formed by sputtering at 1000X, and the sample ratio was set to 4.

(3) In the medium having the structure shown in FIG. 2(c), 26 is a glass substrate, 22 is an NdFeTi film,
21 is a Fe5iB film, 24 is a 5102 film. ◎25 is a 5102 film, which is formed between the Nd1FeTi film and the Fe5iB film and has a thickness of 100X. This is set as a sample ratio of 5, and for comparison, a sample ratio of 6 is set in which the FeSi, B film is replaced with an A2 film.

(4) In the medium having the structure shown in FIG. 2(d), reference numeral 26 is a PMMA substrate in which guide grooves having a depth of 700× and an interval of 16 μm are provided. Also, as in Example 1, 22 is N
dFeTi film, 21 is a Fe5iB film. This is set as a sample ratio of 7. For comparison, a sample NQ8 was prepared in which an AA film was formed instead of the lPe5iB amorphous film.

(5) The substrate 2 is a medium having the structure shown in FIG. 2 (6).
The same PMMA as in Example 4 was used as sample pigeon 6, and 5i02/NdFeTi/Fe5iB was used as in sample pigeon 6 of Example 2.
The sample ratio is 9 for the structure, and the sample ratio is 9 for comparison. The sample ratio is 10 for eSiB as AI1.

(6) The substrate 2 is a medium having the structure shown in FIG. 2 (1).
The same PMMA as in Example 4 was used as 6, and the same S i O2/N dF e T i / as in sample ratio 5 of Example 2 was used.
Sample FkL11 has a S i Ot /XFe5iB structure, and lFe5iB with a sample ratio of 11 is used for comparison.
Af! , the sample ratio is 12.

(7) In a medium having the structure shown in FIG. 2 (α), Fe5iB with a sample ratio of 1 in Example 1 is replaced with lFe0oSiB, and the sample ratio is 13. this? The coercive force of eOoSiB is approximately 5
It is Ersted.

(8) In a medium having the structure shown in FIG. 2 (α), lFe5iB of sample Nn1 of Example 1]! The sample ratio of teNiP is 14. This FeN1P coercive force is approximately 6 Oersteds.

(9) Using a medium with the structure shown in FIG.
ooX is sample Nn15, and for comparison, sample Nn15 with lFe5iB as A2 is sample 16.
The amorphous NdFeTi of Example 1 is 0elPeO with a thickness of 500X in a medium having the structure shown in Figure 2 (α).
Sample No. 17 is taken as oZr, and sample No. 18 is taken as sample No. 18 for comparison, where Fe5iB of sample No. 17 is taken as A2. Sample 19 was obtained by replacing the NdFeTi of sample 1 in Example 1 with N4PrIFeMo, and for comparison, the Fe of sample 19 was
Sample 20 is 5iB as A2. 0α21 A medium having the structure shown in FIG. 2 (,z), NdlFeTi of sample Nn1 of Example 1 is
Sample No. 21 is taken as sample No. 21, and for comparison, sample No. 22 is taken as Fe5iB of sample No. 21 at A°C.

0th Floor In the medium having the structure shown in FIG. 2(g), the sample 25 is the NdFeTi of the sample 9 of Example 5 with Tb'Fθ, and the Fe5iB of the sample 23 is AX for comparison.
The Kerr effect was measured for the above 23 types of samples. The Kerr effect was measured by applying a magnetic field of 10 kiloersted to the sample to bring it into a remanent magnetized state and using a He--Ne gas laser (wavelength: 632.8 nanometers). The measurement results are shown in Table 1.0(1)
In Samples 1 to 12 of (6), in which amorphous Fe5iB is used in all structures, the Kerr rotation angle is approximately twice as large as that in A2. Also (7).

In sample 13 and sample 14 of (8), lFe5iB
Even when using Fe-based amorphous thin films other than Sample 2
There was also an increase of about twice as compared to A2.
0eFeooZr, NdPr? eMo, N(L ae
The Kerr rotation angle also increased in the case of NbOr.

a3 is T, which has been conventionally used as a magneto-optical recording medium.
b? The Kerr rotation angle was measured using e as the recording layer, and even in this case it increased by about 15 times.

Note that magneto-optical recording media to which Or, Ni, Cu, and Mn are added have the same effect as the addition of CO in sample 21, have excellent weather resistance, and have an axis of easy magnetization perpendicular to the film surface. there were. Further, here, as a specific example of the y e /1% amory 7 ass low resistance material layer, 7e includes Si, B,
An example was given in which at least one type of P was added and CO and N1 were added to further improve the weather resistance, but Or, M
o and W had exactly the same effect.

Example 2 The relationship between the coercive force of the low coercive force material layer and the Kerr rotation angle was investigated. The results are shown in Figure 3. In FIG. 6, the horizontal axis is the coercive force, and the vertical axis is the Kerr rotation angle. All samples used are shown in Figure 2 (α)
It has the structure ~α is glass/Nd1FeTi/
Fe5iBN b is glass/NdFeTi/Fe0oS
iBSO is glass/TbFe/Fe5iB. α,
In all three types b and c, the Kerr rotation angle increases as the coercive force of the low coercive force layer becomes smaller. However, the coercive force is about 10
When it reaches about 0 Aersted, Af! It is equivalent to that provided with a reflective layer (d, g, in the figure). Furthermore, when the coercive force becomes larger, the Kerr rotation angle becomes smaller than that of A2. This is because the reflectance of the Fe-based alloy is smaller than that of A2.
l l lExample 6゜Using an optical head capable of magneto-optical recording and reproduction, Fig. 4 (α)
The frequency characteristics were investigated using the media structure shown in the figure. A semiconductor laser with a laser wavelength of 780 nrn was used.

The disk rotation speed was fixed at 1800 rpm and the radius was 5 cm, and the writing frequency was varied. Reading and writing were performed from the substrate side.@The substrate was polycarbonate 41 with groups, and a thin film was formed as shown in Table 2, creating a three-layer structure.〇The first layer was AλN42 with 80 OA, and the second layer was magneto-optical. The recording layer 43 has 100 OA, and the third layer is an A1 reflective film as a conventional example or an amorphous Fe-based low coercive force film 44 according to the present invention.
Here, the film was set to lFe5iB and the film thickness was set to 500A.

The forming means was Do magnetron sputtering. O vs. writing frequency for each magneto-optical recording medium
/Nratio is shown in FIG. 4(b). Compared to the conventional case where non-magnetic A2 is used as a radiation film, the C/N ratio is increased by providing the amorphous Fe-based low coercive force film according to the present invention. Furthermore, in the magneto-optical recording medium containing at least one of Ce, Pr, and Nd in Fe according to the present invention, the effect is even greater, and the writing frequency characteristics are dramatically improved. (expressed in atomic %) Example 4 A medium having the structure shown in Figure 2 (1) was prepared, and recording was performed using the thickness of the nonmagnetic intermediate layer between the magneto-optical recording layer and the low coercive force material layer as a parameter. I investigated the 0/N ratio when changing the power.

The medium is a layer of low coercive force material 21 in Figure 2 (1).
1000 iB, NdX as 22' magneto-optical recording layer
FeTi 1000X, 510 as 24 multi-reflection layers
2 was formed at 90OA, and S10 was formed as a nonmagnetic intermediate layer of 25.
．． I created one that changed from 100X to 1000 Father. FIG. 5 shows the C/N ratio versus writing laser power for each thickness of the nonmagnetic intermediate layer. 510
As the thickness of 2 increases, the C/N ratio becomes saturated at low laser power. In other words, writing sensitivity is improved. However, when the thickness of 5102 is increased to 2000, the laser power at which the C/N ratio is saturated is low, but the saturation value of the C/N ratio is also low. For this reason, it is desirable that the thickness of the nonmagnetic intermediate layer be equal to or less than that of the magneto-optical recording layer.

In Fig. 5, α is the thickness of the nonmagnetic layer of 100X, b is 2OOX, c is 5OOX, d is 11000, and As is 20X.
It is 00X.

〔effect〕

As shown in the above embodiments, the magneto-optical recording medium having the structure according to the present invention has a Kerr rotation angle approximately doubled and a C
/N ratio also improved.

Furthermore, since the recording magnetic domain is stable, there is little deterioration in the C/N ratio even at high recording densities, making it a medium more suitable for high-density recording.

In addition, conventional TbFe, G(100, TbA eoo
.

Compared to media containing heavy rare earths such as TbGdFe, Nd and P
Material costs are lower for those containing light rare earths such as r and Oe.
The magneto-optical recording medium according to the present invention is characterized in that the effect is greater for media containing light rare earth elements.

Since the recording layer is amorphous, it is very easy to grow an IPe-based amorphous on the recording layer, or conversely, to grow an amorphous magneto-optical recording layer on an Fe-based amorphous. It is.

In addition, writing sensitivity can be improved by providing a non-magnetic intermediate layer between the magneto-optical recording layer and the low coercive force material layer.Furthermore, if the magneto-optical recording layer allows some light to pass through, the low coercive force material layer can be used. It is also possible to enhance the Kerr rotation angle between the layer and the magneto-optical recording layer.Although the SiO□ film has been cited as an example of the intermediate layer according to the present invention, the effect of the intermediate layer according to the present invention is Not limited to. As the non-magnetic intermediate layer of the present invention, a thin film of oxide such as tantalum pentoxide, vanadium oxide, alumina, 810, etc. may be used.Furthermore, a thin film of nitride such as aluminum nitride, silicon nitride, boron nitride, etc. may have the same effect. . Furthermore, the effect of the present invention was great because the intermediate layer formed not only from an inorganic material but also from a polymeric resin by a dry method or the like has a lower thermal conductivity than an inorganic material.

[Brief explanation of the drawing]

FIGS. 1(α) and 1(6) are diagrams showing the basic layer structure of the magneto-optical recording medium according to the present invention. (α) In (b), 11...substrate 12...magneto-optical recording layer 13...low coercive force layer, or 12...low coercive force layer 13...magneto-optical recording layer, or (b) In 14... middle class. FIGS. 2(α) and 2(1) are diagrams showing the structure of a specific embodiment of the magneto-optical recording medium according to the present invention. In each figure, 21...Low coercive force layer 22...Magneto-optical recording layer 23...Substrate 24...Transparent dielectric layer 25...Intermediate layer 26...Substrate with guide grooves. FIG. 6 is a diagram showing the effect of the magneto-optical recording medium according to the present invention. a "' Kerr rotation angle with respect to the coercive force of Fe5iB in a medium with a structure of glass substrate/NdlFeTi/Fe5iB. b... Kerr rotation angle with respect to coercive force of Fe5iBP in a medium with a structure of glass substrate/NdFeTi/Fe5iBP. Indicates the rotation angle. C... Indicates the Kerr rotation angle with respect to the coercive force of Fe5iB in a medium with the structure of glass substrate/TbFe/lFe5iB. Kerr rotation angle of the medium having O 1e... Kerr rotation angle of the medium having the structure of glass substrate/TbFe/Aλ. FIG. 4 is a diagram showing the recording and reproducing frequency characteristics of the magneto-optical recording medium according to the present invention. (a) shows the structure of the medium used in the experiment, 41...Substrate 42...Anm (transparent dielectric layer) 43...Magneto-optical recording layer 44...Low coercive force material layer or Aλ (6) shows the ON ratio with respect to the writing frequency, and 1α to 5α and 1b to 5b in the figure are the sample numbers shown in Table 2. Figure 5 shows the magneto-optical recording layer and low coercive force. The CZN ratio to the writing laser power is calculated using the thickness of the nonmagnetic intermediate layer between the material layers as a parameter.

Claims (1)

[Claims] In a magneto-optical recording medium in which recording and reproduction are performed by irradiating light onto a magneto-optical recording layer in which the direction of magnetization is perpendicular to the film surface and has a binary value of upward or downward, the magneto-optical recording medium is made of cerium (C).
e), an alloy consisting of at least one element selected from praseodymium (Pr), neodymium (Nd), iron (Fe), and impurities, or an alloy containing titanium (Ti).
), zirconium (Zr), tantalum (Ta), hafnium (Hf), niobium (Nb), tungsten (W),
An alloy to which at least one element selected from yttrium (Y) and molybdenum (Mo) is added, or the alloy further contains chromium (Cr), cobalt (Co), copper (Cu),
A magneto-optical recording layer made of an alloy to which at least one element selected from nickel (Ni) and manganese (Mn) is added; An alloy consisting of at least one element among boron (B) and phosphorus (P), iron (Fe), and impurities, or the alloy further contains cobalt (Co), nickel (Ni), chromium (Cr), and molybdenum (Mo). ), and a low coercive force material layer made of an alloy to which at least one type of tungsten (W) is added and which is predominantly amorphous, the magneto-optical recording layer and the low coercive force material layer A magneto-optical recording medium characterized in that a non-magnetic layer with a thickness of 100 nanometers or less is formed between the layers.