JPS6187247A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a photomagnetic recording medium which has a high S/N ratio and permits high-density and high-speed recording by forming a photomagnetic recording layer which holds magnetization and a low coercive force material layer into laminar structure and specifying the materials for the photomagnetic recording layer and low coercive force material layer. CONSTITUTION:The photomagnetic recording layer which holds the magnetization and the low coercive force material layer of which the coercive force is <=1/5 the coercive force of the photomagnetic recording layer and is selected to <=100 oersted are made into the laminar structure. The photomagnetic recording layer consists of the alloy consisting of elements of >=1 kinds among Ce, Pr and Nd as well as Fe and impurities or said alloy contg. further elements of >=1 kinds among B, C, Si P and Al or the alloy contg. further elements of >=1 kinds among Cr, Co, Ni, Cu and Mn. The low coercive force material layer is the alloy which consists of elements of >=1 kinds among Ti, Zr, Ta, Nb, W, Hf, Y, Mo, B and Si as well as Co and impurities and is dominantly amorphous.

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 origins in 1957, when recording was performed using a hot pen on a M n B 1 thin film, and the written magnetic domain was observed using the magneto-optic effect. Stimulated by the subsequent development of lasers, M.
Although intensive research has been carried out mainly on nB1-based materials, practical use 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 notice 1983-
37607), GdIFθ.

Alloy thin films such as TbFe, DyFe, and Gd0o have been developed. These materials generally have the following characteristics.

Compensation point recording magneto-optical recording media such as Gage and Ga0o have a larger Kerr rotation angle than Keely single-point recording magneto-optical recording media and have excellent optical reproduction characteristics, but have a small coercive force (several hundred oersteds) of 1 μm. It is not possible to stably obtain small bits with the same diameter.

In addition, magneto-optical recording media for Curie single point recording such as TblFe and DyFe have a large coercive force (several kilo Oersteds) and can stably obtain microscopic hits with a diameter of about 1 μm, contrary to the above, but have a small Kerr rotation angle. It had drawbacks such as poor optical reproduction characteristics. Also Tb
, Gd, D7, Ho, etc.

Heavy rare earths are expensive and unsuitable for practical use. Three methods have been tried to compensate for these drawbacks of binary alloy thin films.

(1) To become ternary or quaternary. For example, binary GaF
GdTbIF takes advantage of the strengths of e and TbFe and compensates for their weaknesses
@ A method of diversification like ternary alloy or Gd'l'bFe(!o quaternary alloy. (JP-A-56-12690
7, 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 27
-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
0447) In addition, there is also a type that uses heavy rare earth-transition metals for magneto-optical recording and uses Permalloy/IFe@Co/N1 instead of the reflective film (Japanese Patent Application Laid-Open No. s8-222455), but the bits remain stably. There are only features, permalloy 'Fe
Since eOo・N1 is a polycrystalline film, it caused noise and led to deterioration of s/H.

However, these methods have advantages and disadvantages, such as increasing the Kerr rotation angle but decreasing the reflectance, and even if the Kerr rotation angle is slightly improved, the Curie temperature increases, making laser writing difficult. It had not reached that point.

〔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,
Improving contradictory characteristics to achieve high S/N, high density, high stability,
The purpose of the magneto-optical recording medium of the present invention is to provide a magneto-optical recording medium that can be read and written at high speed. and a low coercive force material layer, and the magneto-optical recording layer is made of an alloy consisting of at least one element among cerium, praseodymium, and neodymium, iron, and impurities, or the alloy further includes boron, carbon, silicon, and impurities. The low coercive force material layer is made of an alloy containing at least one element of phosphorus and aluminum, or further contains at least one element of chromium, cobalt, nickel, copper, and manganese, and the low coercive force material layer is made of titanium.・It is characterized by being a predominantly amorphous alloy consisting of at least one element among zirconium, tantalum, niobium, tungsten, niobium, tungsten, hafnium, yttrium, molybdenum, boron, and silicon, cobalt, and impurities. .

〔Example〕

The present invention will be described in detail below using the drawings.

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

11 is a substrate, 12 is a magneto-optical recording layer, 13 is a low coercive force material layer, and 14 is a nonmagnetic layer.

I wrote about the case where the substrate is transparent and the optical head for reading and writing faces the substrate side, and reading and writing is done through the substrate, but this is not essential. There is no problem even if a magnetic material layer, a nonmagnetic layer, and a magneto-optical recording layer are formed, and an optical head is placed facing the magneto-optical recording medium side with respect to the substrate for reading and writing. Furthermore, the present invention is not limited to the above 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) FIG. ,
3, using well-cleaned glass, amorphous NdFe with a thickness of soo'j- is deposited on the glass substrate using the sputtering method.
An E perpendicular magnetization film was formed as 22, and an 0oTi amorphous film 1oooX was formed on it as 21 using a sputtering method. The coercive force of the above 0oTi amorphous film is about 7 Oe, and it is similar to sample part 1. do. Also, for comparison, the above CoT
i Instead of an amorphous film, Af! , by sputtering method to 1'00
The 0X formed part is designated as sample part 2.

(2) With a medium having the structure shown in FIG. 2 (&), (1)
Similarly, 23 is a glass substrate, 22 is a NdFeB film, 21
is the 0oTi film and 24 is the dielectric layer, 810. It is made up of 800 pieces. Is this Nd? The Kerr rotation angle is enhanced by interposing the eB film between the glass film and the lath substrate. This is designated as sample tJQ5. Also, for comparison, the above C!
1ooo using sputtering method of A2 instead of oTi amorphous film
0 (3) A medium having the structure shown in FIG. 2 (6), (2)
Similarly, 23 is a glass substrate, 22 is a NdFeB film, 21
is a 0oTi film, and 24 is a 5102 film. 25 is Si
O.

In the film, Nd1eB film and C! o'['i The interperitoneal layer is 100X thick @This is sample part 5, and for comparison, the one in which the 0oTi film is replaced with the A2 film is sample Nn6.
shall be.

(4) In the medium having the structure shown in FIG. 2(d), reference numeral 26 is a PMMA substrate provided with guide grooves having a spacing of 16 μm and a depth of 700×. Also, as in (1), 22 is Nd
FeB film, 21 is a 0oTi film, 0 is used as the sample part 7, and for comparison, 0oTi amorphous film is replaced by A''
The sample portion 8 is formed by forming two films.

(5) The substrate 2 is a medium having the structure shown in FIG. 2 (1).
Using the same PMMA as in (4) as 6, sample part 3 in (2)
The sample part 9 has the same Sin□/Nd1FeB/CoTi structure, and for comparison, the sample part 10 has the 0oTi of the sample part 9 changed to A2.

(6) The substrate 2 is a medium having the structure shown in FIG. 2(f).
Using the same PMMA as in (4) as sample part 5 in (2) as 6.
Similar to 51o2/Naae B/S i 02
/ Oo Ti structure is designated as the sample portion 11, and for comparison, the sample portion 11 in which 0oT1 is A2 is designated as the sample portion 12.

(7) In the medium having the structure shown in FIG.
Set it to 3. The coercive force of this 0oZrNb is about 5 oersteds.

(8) Sample FkL1 is a medium having the structure shown in FIG.
Set it to 4. The coercive force of 0oTa is about 6 oersteds. is the sample part 15, and 0o of the sample part 15 is for comparison.
The sample portion 16 is made of Ti with Aλ.

αQ A medium having the structure shown in Fig. 2 (α), in which the amorphous NaFeB of (1) is made of 0elFeAλ0 with a thickness of 500X, is used as the sample part 17, and for comparison, the sample m17 is 0oT1.
Let Aλ be the sample portion 18.

αυ” A medium having the structure shown in FIG. 2 (α), in which NdFeB tr:NdPrFe of sample part 1 in (1) is used as sample part 19, and for comparison, sample 20 is made with 0oTi of sample 19 as Aλ. shall be.

(17J In a medium with the structure shown in Figure 2 (α) (1)
The sample part 21 is the NdFeB of the sample Nn1 in which NdlFe5iOo is used, and for comparison, the 0oT of the sample
The sample portion 22 is where i is A°C.

<13) With a medium having the structure shown in Figure 2 (-) (5)
Even if NdFeEiTblFθ is set as sample NQ9, it is called sample pigeon 23, and for comparison, sample Nh23 with 0oTi set as A2 is called sample positive 24.

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.

In Samples 1 to 12 of (1) to (6), the Kerr rotation angle of all structures using amorphous 0oTi is approximately twice as large as that of Aλ. Also (7) l (8
>00 other than 0oTi in sample 16 and sample 14
Even when a non-crystalline thin film was used, the temperature increased by about twice the temperature of Sample 2.

(PrFeE, Ce as the recording layer in 9th to α2
FeAj! 0, NcLPrFe, and NdFe5iOo, the Kerr rotation angle also became large.

0→ is T, which has been conventionally used as a magneto-optical recording medium.
The Kerr rotation angle was measured using bFe as the recording layer, and even in this case it increased by about t5 times.

Note that the magneto-optical recording medium contains Or, Ni, (1!u
The one to which Mn was added had the same effect as the Co addition in sample 21, had excellent weather resistance, and was a magneto-optical recording medium having an axis of easy magnetization perpendicular to the film surface.

Furthermore, as a specific example of a co-based amorphous low coercive force material layer, Ti, Zr, and Ta are added to co.

Although the present invention has been described in detail using materials to which at least one type of Nb is added, W, Hf, Y, etc. are added to Co.
, Mo, B, and Si have 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. 3, the horizontal axis is the coercive force, and the vertical axis is the Kerr rotation angle. All the samples used had the structure shown in Fig. 2 6), where α is glass/N 6 Fe
B/Oo Ti, b is glass/N4F6B10
oZrNbSc is glass/T b? e / (!
o Ti. The Kerr rotation angle increases as the coercive force of the low coercive force layer for all three types α, b, and c decreases. However, when the coercive force becomes about 100 Oersted,
It is equivalent to having a reflective layer of 82 (d, # 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 Oo alloy is smaller than that of A2.

Table 1 Example 3゜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 nm was used, the 0 disk rotation speed was fixed at 1800 rpm, and the radius was 5 cm, and 0 reading and writing was performed from the substrate side by varying the writing frequency. The substrate was made of grouped polycarbonate 41, and a thin film was formed as shown in Table 2 to form a three-layer structure. The layer is an A2 reflective film as a conventional example or an amorphous C layer according to the present invention.

The low coercive force film 44 is made of Co, oTi□ here. Toshi, 5
The film thickness of 00A was formed using the Do magnetron sputtering method. Figure 4 (6) shows the C/N with respect to the writing frequency for each magneto-optical recording medium.
It is. The c/N was increased by providing the amorphous 00-based low coercive force layer according to the present invention compared to the conventional case where non-magnetic A2 was used as a reflective film. Furthermore, in the magneto-optical recording medium according to the present invention containing at least one of Oe, Pr, and M& in Fe, the effect is even greater, and the writing frequency characteristics are dramatically improved.

Table 2 (Composition units are expressed in atomic %) [Effects] As shown in the above examples, the magneto-optical recording medium having the structure according to the present invention has a Kerr rotation angle that is almost doubled and an O
Furthermore, since the recording magnetic domain is stable, there is little deterioration in the O/N ratio even at high recording densities, making it a medium suitable for high-density recording.In addition, conventional TblFe, Gdoo, TbFe(1
! o.

Compared to media containing heavy rare earths such as TbedFe, Nd and P
Materials containing light rare earth elements such as r and Ce are cheaper in material cost, and 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 a Co-based amorphous layer on the recording layer, or conversely, to grow an amorphous magneto-optical recording layer on a Co-based amorphous layer. Moreover, since the Co-based amorphous material is very chemically stable, reliability is improved, and weather resistance is improved.

[Brief explanation of the drawing]

FIG. 1(a)s(6) is a diagram showing the basic layer structure of the magneto-optical recording medium according to the present invention. FIGS. 2(α) to (1) show the structure of a specific example of the magneto-optical recording medium according to the present invention. Figure 3 is a diagram showing the effect of the low coercive force material layer of the present invention, in which the Kerr rotation angle of the magneto-optical recording layer is plotted against the coercive force of the low coercive force material layer. b) is a diagram showing the writing frequency characteristics of the magneto-optical recording medium of the present invention. The structure of the magneto-optical recording medium is shown in FIG. 4 (α), and the effect of the present invention when the magneto-optical recording layer is variously changed. 0 which is an example showing
11...Substrate 12...Magneto-optical recording layer 16...Low coercive force material layer 14...Nonmagnetic layer 21...Low coercivity Magnetic material layer or reflective film 22...
... Magneto-optical recording layer 23 ... Substrate 24 ... Dielectric layer 25 ... Dielectric layer 26 ... Substrate 41 ...・Polycarbonate substrate 42...
・AAN layer 46...Magneto-optical recording layer 44...Low coercive force material layer or reflective film /-(/
1l-NJ-＼ Figure 1 Figure 2

Claims (1)

[Claims] In a magneto-optical recording medium in which recording and reproduction is performed by irradiating a magnetic recording layer with light whose direction of magnetization is perpendicular to the film surface and has a binary value of upward or downward, the magneto-optical recording layer retains magnetization;
The coercive force is one-fifth or less of the magneto-optical recording layer and 100
The magneto-optical recording layer is made of cerium, praseodymium,
An alloy consisting of at least one element of neodymium, iron, and impurities, or the alloy further contains boron,
The low coercive force is characterized by being made of an alloy containing at least one element among carbon, silicon, phosphorus, and aluminum, or further containing at least one element among chromium, cobalt, nickel, copper, and manganese, and the above-mentioned low coercive force. Material layers include titanium, zirconium, tantalum, niobium,
1. A magneto-optical recording medium characterized by being a predominantly amorphous alloy consisting of at least one element selected from among tungs, niobium tungsten, hafnium, yttrium, molybdenum, boron, and silicon, cobalt, and impurities.