JPS6187246A - 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 and forming a non-magnetic layer 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 B, C, Si, P and Al or the alloy added further with elements of >=1 kinds among Cr, Co, Cu, Ni, and Mn to said alloy and the low coercive force material layer of which the coercive force Si <=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 with >=1 kinds among Co, Ni, Cr, Mo and W to said element and the dominantly amorphous alloy. The non-magnetic layer having <=100 namoneter 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 origins in 1957, when recording was performed using a hot pen on a MnBi thin film, and the written magnetic domain was observed using the magneto-optic effect. Spurred by subsequent developments in lasers, MnBi
Although intensive research has been carried out mainly on the material J, it has not been put to practical use 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 NPA materials represented by amorphous rare earth transition metal alloy thin films progressed (Patent Application Publication 1983).
-57607), Gd'Fe.

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 GdFe and Gd0o have larger Kerr rotation angles than Chieri 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 minute bits from deer. In addition, magneto-optical recording media for Curie single-point recording, such as TbFe and DyFe, have a large coercive force (several kilo Oersteds) and can stably obtain minute bits of about 1 μm in diameter, contrary to the above, but the Kerr rotation angle is It had drawbacks such as being small and having poor optical reproduction characteristics. Furthermore, Tb, Gd, Dy, Ha, etc. and 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) To become ternary or quaternary. For example, the binary G
GdTb takes advantage of the strengths of ate and TbFe and compensates for their weaknesses.
Fs ternary alloy or GdTb? eC.

A method of diversification like quaternary alloys. (%Kaisei 56-
126907. (2) A method of improving the properties of a binary alloy thin film by improving the manufacturing method or using a new manufacturing method. (Japan Society of Applied Magnetics, 27th
Research meeting material 27-s) (3) Method of creating a multilayer structure. A dielectric layer is layered on the recording medium to increase the Kerr effect due to multiple reflections. Furthermore, the recording layer and the reproducing layer are separated, and materials suitable for each are used. Alternatively, a reflective layer may be provided on the back side of the recording medium to reflect and utilize not only the light reflected from the surface but also the light that has passed through the medium. (Unexamined Japanese Patent Publication No. S8-200447) Also, heavy rare earth-transition metals are used for magneto-optical recording, and permalloy, Fe, etc. are used instead of reflective films.
, Co, and Ni (Japanese Patent Application Laid-Open No. s8-22245
s) is also seen, but it only has the characteristic that bits exist stably, and permalloy,? e,C! Since Ni is polycrystalline, it causes noise and leads to deterioration of S/H.

However, in these methods, although the Kerr rotation angle increases, the reflectance decreases. Furthermore, even if the Kerr rotation angle was improved to some extent, the Curie temperature would increase, making laser writing difficult, and so on, with both advantages and disadvantages, and no fundamental improvement had been achieved.

〔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 is to provide a magneto-optical recording medium that can be read and written at high speed.

[vA required]

The present invention relates to 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.

The recording medium is made of cerium (Ce) and praseodymium (Pr).
), neodymium (N(1)), an alloy consisting of at least -m or more elements, iron (Fe), and impurities, or the alloy further contains boron (B), carbon (C), silicon ("i
) * An alloy to which at least one element selected from phosphorus (P) and aluminum (Al) is added, or the alloy is further added with chromium (Cr), cobalt ('') + copper (cu), nickel (nt), manganese (Mn). ) at least -g
A magneto-optical recording layer made of an alloy to which the above elements are added, and a coercive force of silicon (sl), boron (B), and phosphorus (P) with a coercive force of one-fifth or less and one hundred oersted or less. ) and iron (Fe )
and an impurity, or the alloy further contains cobalt (C).

), nickel (NL), chromium (cr) + molybdenum (
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 magnetic recording layer and the low coercive force material layer [Example] The present invention will be described in detail below with reference to the drawings.

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

In this case, the substrate is a transparent substrate made of glass, plastic, etc., and the optical head for reading and writing faces the substrate and reads and writes through the substrate. However, this is not essential, and the substrate has a low coercive force. Material layer, magneto-optical recording J.
or a low coercivity material layer.

There is no problem even if 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 only to the above-mentioned structure, and there is no problem in providing an anti-reflection protective film 1, a multiple interference interference film, a transparent conductive film, etc.

Example 1 A well-cleaned glass substrate 23 was used as the medium having the structure shown in FIG. Then, using sputtering method, 2
As Example 1, 10001 FociB amorphous films were formed. The coercive force of the 7θSIB amorphous film is approximately 7 oersteds, and is considered as sample No. 1. For comparison, Sample No. 2 is prepared by forming 1000^ of hL by sputtering instead of the Fe5iB amorphous film.

In the medium having the structure shown in FIG. 2Cb), as in Example 1, 23 is a glass substrate, 22 is an Nd1FeB film, and 21 is ? In the eSiB film, 24 is a negative electric layer and S10. 800λ
It is formed. This is due to the S between the NaFeB film and the glass substrate.
In, the Kerr rotation angle is enhanced by forming a film. This is Sample No. 3. For comparison, a sample in which 100X of kl was formed by sputtering instead of the Fe5iB amorphous film was Sample N[L4.

In the medium having the structure shown in FIG.
The e5iB film i,24 is 5102@. 25 is 5iO
21J, formed between the NdFeB film and the Fe5iB film, and has a thickness of 10OA. This is designated as sample Nα5, and for comparison, the sample in which the Fe5iB film is replaced with hL9 is designated as sample No. 6.

A medium having the structure shown in FIG. 2(d), 26 is a PMM.
This is the A substrate, with guide grooves spaced 1.6 μm apart and 700 mm deep. Also, as in Example 1, 22 is NaF
eB1.21 is a Fe5iB film. This is sample Nα7
shall be. For comparison, a sample m8 was prepared in which an At film was formed instead of the 1Fe81B amorphous film.

In the medium having the structure shown in FIG. 2(C), the same pMMA as in Example 4 was used as the substrate 26, and the same SiO,/NcL as in Sample No. 3 of Example 2 was used. Sample No. 9 is made of eB/Fe5iByt, and lFe5 of Sample No. 9 is used for comparison.
Sample No. 10 is obtained by setting iB to hL.

The medium has the structure shown in FIG. 2(1), the same PMMA as in Example 4 is used as the substrate 26, and the same S i O! as in Sample No. 5 of Example 2. / N a F e B / S
Sample No. 11 has the /lFe5iB structure, and for comparison, Sample No. 12 has Fe5iB of Sample No. 11 as hL.

Sample No. 13 is a medium having the structure shown in FIG. 2(cL), in which l1eSiB of sample Nil i of Example 1 is replaced with Fe0oSiB. this? The coercive force of eOoSiB is approximately 5 oersteds.

In the medium having the structure shown in FIG. 2 (α), sample N of Example 1
The sample amount is 14 with ll YeslB as FeN1P.
shall be. The coercive force of this lFeN1P is about 6 Oersteds.

Amorphous Nc of Example 1 in a medium having the structure shown in FIG. 2 (α)
The sample amount is 15, and for comparison, the sample amount is 7 of 15.
Let θSiB be AL as the sample amount 16.

Amorphous Nd of Example 1 was used in the medium having the structure shown in FIG. 2 (α).
? Let eB be Ce1FeAt (!) with thickness sooλ as sample +11117, and for comparison, sample amount 17 7e
Sample NC118 is obtained by changing SiB to ht.

In the medium having the structure shown in FIG. 2 (α), sample N of Example 1
11 NdFeB to NdPr? The sample amount is 1.
9, and sample 20 is sample 19 in which YeslB is changed to At for comparison.

In the medium having the structure shown in FIG. 2 (α), sample amount 21 is a medium in which NdFeB in sample amount 1 of Example 1 is replaced with NdFe5iCo, and for comparison, sample N[ Sample N of Example 5 with the medium having the structure shown in FIG. 2 (1).
Tb of 19 NdFeB? For comparison, the amount of sample N11L25 with Yes1B set as hL is set as sample 1a24-.

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: 63 x 8 nanometers). The measurement results are shown in Table 1.

Samples 1 to 12 of (1) to (6) have all structures of amorphous J? The Kerr rotation angle of the one using eSiB is approximately twice that of At. Also (7), (a)
In sample 13 and sample 14, other than Fe5iB? e
Even when an amorphous thin film was used, the AL increased by about twice as much as that of Sample 2.

In (9)-(12), Pr'FeB as the recording layer,
0eIFeA40. NaPr'Fe, NdlFe5in
The Kerr rotation angle also became large in the case where the angle was set to o.

(13) is Tb?, which has been conventionally used as a magneto-optical recording medium. The Kerr rotation angle was measured using e as the recording layer, and even in this case it increased by about 1.5 times.

In addition, the magneto-optical recording medium contains Or, Ni, C! The one to which u and Mn were 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, here, 1! Specific examples of the e-based amorphous low coercive force material layer include heicsi, B, and 'P.
An example has been given in which at least one type of
, 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. 5, 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
), where α is glass/NdFeBFe5iB and b is glass/NdFeB/
F e Co' S i B, c is glass/Tb
F e / F e S i B. For all three types a, b, and c, the Kerr rotation angle increases as the coercive force of the low coercive force layer becomes smaller. However, when the coercive force reaches about 100 Oersted, it becomes equivalent to that provided with an At reflective layer (d and g in the figure). Furthermore, when the coercive force becomes larger, the Kerr rotation angle becomes smaller than that of AL. This is because the reflectance of the 7θ-based alloy is lower than that of AL.

Example 3 Using an optical head capable of magneto-optical recording and reproduction, the fourth prisoner (α)
The frequency characteristics were investigated using the media structure shown in the figure.

A semi-enveloped laser with a laser wavelength of 780+m was used.

Disc rotation speed is 1800 rpm *Cow diameter 5cIn
was fixed at , and the writing frequency was varied. Reading and writing were performed from the board side. The substrate was polycarbonate 41 with groups, and a thin film as shown in Table 2 was formed to have a six-layer structure. The first layer is made of AtN42 and has a resistance of 1300A, the second layer is a magneto-optical recording layer 45 that has a resistance of 100DA, and the third layer is an At reflective film as a conventional example or an amorphous IPe-based resistive magnetic film 44 according to the present invention, here 7θSiB, and a film of 500A. Made thick. The forming means was Do magnetron sputtering. Figure 4(b) shows the /N ratio with respect to the writing frequency for each magneto-optical recording medium.
It is. Compared to the conventional case where non-magnetic hL is used as a reflective film, the provision of the amorphous Fe-based resistive magnetic layer according to the present invention reduces the ratio to 0/Nrati.

rose. Furthermore, due to non-invention? Oe in e, Pr
, N(1), the effect was even greater, and the writing frequency characteristics were dramatically improved.

Example 4 A medium having the structure shown in Fig. 2 (1) was prepared, and the recording power was changed using the thickness of the nonmagnetic intermediate layer between the magneto-optical recording layer and the low coercive force material layer as a parameter. The C/N ratio was examined.

The medium is 21 low coercive force material layers in FIG. 2 (1)]Fe
5iBNi as 1oooK, 22 magneto-optical recording layers as N
d: FeB at 100 (LX, 5 as 24 multi-reflection layers)
101 was formed as 9001, and S was used as the nonmagnetic intermediate layer of 25.
10. I created one with the value changed from 100K to 1000X. The O/N ratio versus writing laser power is shown in FIG. 5 for each thickness of the nonmagnetic intermediate layer. Sin.

As the thickness increases, the C/N ratio becomes saturated at low laser power. In other words, writing sensitivity is improved. However, S10. When the thickness is increased to 2000X, the laser power at which the C/N ratio is saturated is low, but the saturation value of the 0/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 addition, in Fig. 5, α is the thickness of the nonmagnetic layer of 100×, b is 200×, (” is sooλ, d is 1000^, C is 2
It is 000A.

〔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 is also improved.

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 that is more suitable for high-density recording.

In addition, conventional TbFe, GdCo, TbFe0o, T
bGdFe% compared to the medium containing heavy rare earths, Nd, Pr
, Ce containing light rare earth elements has a lower 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 10 is amorphous, it is very easy to grow an Fe-based amorphous layer on the recording layer, or conversely, to grow an amorphous magneto-optical recording layer on the Fe-based amorphous layer. It is.

Furthermore, writing sensitivity can be improved by providing a nonmagnetic intermediate layer between the magneto-optical recording layer and the low coercive force material layer. Furthermore, if the magneto-optical recording layer transmits some light, it is also possible to enhance the Kerr rotation angle between the low coercive force material layer and the magneto-optical recording layer.

Incidentally, although the S10° film is cited as an example of the intermediate layer according to the present invention, the present invention is not limited thereto. As the non-magnetic intermediate layer of the present invention, tantalum pentoxide, vanadium oxide, alumina, 810
The effects of the present invention were exactly the same with other oxide films. Additionally, aluminum nitride.

The same was true for nitride films such as silicon nitride and boron nitride. Furthermore, the effect of the present invention was tremendous because the intermediate layer made of not only an inorganic material but also a polymer resin treated by a dry method has a low thermal conductivity.

[Brief explanation of the drawing]

FIGS. 1(α) and 1(A) 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 1- or 12...Low coercive force layer 13... . . . magneto-optical recording layer, and in (b) 14 . . . intermediate layer. FIGS. 2(α) to 2(f) are diagrams showing the structure of a specific example of a magneto-optical recording medium according to the present invention. In each figure, 21...Low coercive force layer 22...Magneto-optical recording layer 2S...Substrate 24...Transparent dielectric layer 25... . . . Intermediate Iso 26 . . . A substrate with a guide groove. FIG. 6 is a diagram showing the effect of the magneto-optical recording medium according to the present invention. a...Glass substrate/N dF e B/
Fe in the medium with the structure 111e 8 i B
The graph shows the Kerr rotation angle for a coercive force of 5iB. b,...Glass substrate/Nd? e B
/ In a medium with a structure of F e S i B?
The graph shows the Kerr rotation angle with respect to the coercive force of eSiB. C...Glass substrate/T b Fe/I
Fe5 in a medium with the structure of FeSiB
The graph shows the Kerr rotation angle with respect to the coercive force of iIl. d...Glass substrate/N dF e B/
Kerr rotation angle of a medium having the structure of A t. ε...Glass substrate/T b IF e/
Kerr rotation angle of a medium having the structure of AL. FIG. 4 is a diagram showing the recording and reproducing frequency characteristics of the magneto-optical recording medium according to this Bimei. (α) indicates the structure of the medium used in the experiment, 41...Substrate 42...AtN (transparent dielectric layer) 45...
. . . Magneto-optical recording layer 44 . . . Low coercive force material layer or kl. Cb) 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 O/N ratio for the writing laser power using the thickness of the nonmagnetic intermediate layer between the magneto-optical recording layer and the low coercive force material layer 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) and neodymium (Nd), iron (Fe), and an impurity; or an alloy further containing boron (B);
, an alloy to which at least one element among carbon (C), silicon (Si), phosphorus (P), and aluminum (Al) is added, or further chromium (Cr), cobalt (Co), and copper (Cu) to the alloy. , nickel (Ni), and manganese (Mn), and the magneto-optical recording layer has a coercive force of 1/5 or less and 100 Oe or less. An alloy consisting of at least one element selected from silicon (Si), boron (B), and phosphorus (P), iron (Fe), and impurities, or the alloy further contains cobalt (Co), nickel (Ni), and chromium ( Cr), molybdenum (Mo), and tungsten (W) are added. A magneto-optical recording medium characterized by forming a non-magnetic layer with a thickness of 100 nanometers or less between a low coercive force material layer.