CA1298704C - Magnetooptical recording medium - Google Patents
Magnetooptical recording mediumInfo
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- CA1298704C CA1298704C CA000569719A CA569719A CA1298704C CA 1298704 C CA1298704 C CA 1298704C CA 000569719 A CA000569719 A CA 000569719A CA 569719 A CA569719 A CA 569719A CA 1298704 C CA1298704 C CA 1298704C
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- magnetooptical recording
- atom
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- recording film
- magnetooptical
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Abstract
ABSTRACT OF THE DISCLOSURE
Disclosed is a magnetooptical recording medium which includes a substrate and magnetooptical recording film comprising, (i) Pt and/or Pd, (ii) rare earth element (RE), and (iii) Fe and/or Co, wherein Pt and/or Pd is present in an amount of more than 10 atom% but not more than 30 atom%, Fe and/or Co is present in an amount of at least 40 atom% but not more than 70 atom%, and a Co/(Fe + Co) ratio [atomic ratio] is 0-0.3. The magnetooptical recording medium of the present invention is excellent in resistance to oxidation and is capable of being used over a long period of time and, moreover, it is large in C/N ratio and low in noise level, and excellent in bias magnetic field dependability.
Disclosed is a magnetooptical recording medium which includes a substrate and magnetooptical recording film comprising, (i) Pt and/or Pd, (ii) rare earth element (RE), and (iii) Fe and/or Co, wherein Pt and/or Pd is present in an amount of more than 10 atom% but not more than 30 atom%, Fe and/or Co is present in an amount of at least 40 atom% but not more than 70 atom%, and a Co/(Fe + Co) ratio [atomic ratio] is 0-0.3. The magnetooptical recording medium of the present invention is excellent in resistance to oxidation and is capable of being used over a long period of time and, moreover, it is large in C/N ratio and low in noise level, and excellent in bias magnetic field dependability.
Description
12987~4 FIELD OF THE INVENTION
This invention relates to magnetooptical recording medium having excellent resistance to oxidation and excellent magnetooptical recording characteristics and more partlcularly to magnetooptical recording films in the magnetooptical recording medium having an easy axis of magnetization perpendicular to the film as well as excellent resistance to oxidation and excellent magnetooptical recording characteristics.
BACKGROUND OF THE INVENTION
It is known that magnetooptical recording films comprising transition metals such as iron, cobalt, etc. and rare earth elements such as terbium (Tb), gadolinium (Gd), etc., have and easy axis of magnetization perpendicular to the film and are capable of forming a small inverse magnetic domain with magnetization antiparallel to the magnetization of the film. By corresponding the existence or nonexistence of this inverse magnetic domain to "1" or "0", it becomes possible to record a digital slgnal on such magnetooptical recording films as mentioned above.
As magnetooptical recording films composed of such .~
12987~
transition metals and rare earth elements as mentioned above, there are disclosed those of Tb-Fe system containing 15-30 atom% of Tb, for example, in Japanese Patent Publication No. 20691/1982. There are also used magnetooptical recording films of Tb-Co system to which a third component metal ha~ been added. Furthermore, magnetooptical recording films of Tb-Fe system, Tb-Fe-Co system and the like are known as well.
Though these magnetooptical recording films have excellent recording reproducing characteristics, they still involved such a serious problem from a practical standpoint that they are subject to oxidation in the course of ordinary use thereof and their characteristics come to change with the lapse of time.
The mechanism of oxidation deterioration of magnetooptical recording films containing such transition metals and rare earth elements as mentioned above is discussed, for example, in Journal of Applied Magnetism Society of Japan, Vol.9, No.2, pp.93-96, and this paper reports that this mechanism of oxidative deterioration may be claqsified into three types as mentioned below.
a) Hole corrosion By hole corrosion is meant the occurrence of pinholes in the magnetooptical recording film. This corrosion proceeds mainly under the circumstances of high 12,~1 37Q~
humidity, and it markedly proceeds, for example, in the recording films of such system as Tb-Fe, Tb-Co or the like.
b) Surface oxidation Surface oxide layers are formed on magnetooptical recording films, whereby Kerr-rotation angle~ k of the films changes with time and eventually comes to decrease.
c) Selective oxidation of rare earth element Rare earth elements present in magnetooptical recording films are selectively oxidized, thereby coercive force Hc of the films comes to largely change with time.
Various attempts have heretofore been made to inhibit such oxidative deterioration of magnetooptical recording films as mentioned above. For instance, there is propo~ed a procedure in which a magnetooptical recording film is designed to have a three-layer structure wherein the film is sandwitched between anti-oxidizing protective layers such as those of Si3N4, SiO, SiO2, AlN, etc. The anti-oxidizing protective layers as proposed above, however, involved such problems that they are relatively expensive and, at the same time, they require much time and labor to be formed on magnetooptical recording films, and that a sufficient inhibition of oxidative deterioration of the recording films is not always expected even when such anti-oxidizing protective ïZ91!3';~ 4 layers are formed on said recording films.
Furthermore, various attempts are being made to improve resistance to oxidation of magnetooptical recording films by incorporating a third component metal into the recording films.
For instance, Journal of Applied Magnetism Society of Japan cited above discloses an attempt to improve resistance to oxidation of magnetooptical recording films of Tb-Fe or Tb-Co system by incorporation into the films of such third component metal as Co, Ni, Pt, Al, Cr, Ti and Pd in an amount of up to 3.5 atom%. In connection with the attempt, the said Journal reports that the incorporation of small amounts of Co, Ni and Pt into Tb-Fe or Tb-Co ls effective in inhibiting the surface oxidation and hole corrosion of the resulting magnetooptical recording film but has no effect on inhibition of the selective oxidation of Tb contained as a rare earth element in this magnetooptical recording film. This disclo~ure means that when small amounts of Co, Ni and Pt are added to Tb-Fe or Tb-Co, Tb present in the resulting magnetooptical recording film is selectively oxidized, and coercive force Hc of the film largely changes. Thus, even when small amounts up to 3.5 atom% of Co, Ni and Pt are added to Tb-Fe or Tb-Co, no sufficient improvement in resistance to oxidation of the resulting magnetooptical ~Z~t~704 recording film i5 made.
With the view of improving resistance to oxidation of magnetooptical recording films, a teaching on the magnetooptical recording films which are obtained by adding Pt, Al, Cr and Ti in an amount up to 10 atom~ to Tb-Fe or Tb-Fe-Co is disclosed in page 209 of the Proceedings of The Nineth Conference of Applied Magnetism Society of Japan (November 1985). Even when Pt, Al, Cr and Ti in an amount up to 10 atom% are added to Tb-Fe or Tb-Fe-Co, however, inhibition of selective oxidation of Tb present in the resulting magnetooptical recording films is not sufficient, though the surface oxidation and hole corrosion can be inhibited to a fairly effective extent.
Thus, there was still left such a problem that coercive force Hc of the resultant magnetooptical recording films will largely change with time, and eventually the coercive force Hc will largely decreases.
Japanese Patent L-0-P Publn. No. 255546/1986 di~close~ magnetooptical recording films which have been improved in resistance to oxidation by adding such noble metal elements as Pt, Au, Ag, Ru, Rh, Pd, Os and Ir within such range that ~err-rotation angle necessary for regeneration is to magnetooptical recording films comprising rare earth elements and transition metals, obtained.
12~8 7(:~4 Furthermore, Japanese Patent L-O-P Publn. No.
7806/1983 discloses magnetooptical recording films comprising polycrystalline thin films having the composition of PtCo in which Pt is contained in an amount of 10-30 atom%.
However, the above-mentioned polycrystalline thin films having this composition of PtCo involved such problems that said polycrystalline thin films as formed require heat treatment such as annealing because that are polycrystalline, that particle-particle boundaries among the crystals sometimes appear as noise signals, and that these polycrystalline thin films are high in Curie point.
In the manner as described above, magnetooptical recording films comprising Tb-Fe or Tb-Co and further incorporated with such third metal components as Co, Ni, Pt, Al, Cr, Ti and Pd have heretofore been known.
However, these known magnetooptical recording films involve at least one of such problems that they are not suf f icient in resistance to oxidation, small in C/N ratio and high in noise level, and that no high C/N ratio can be obtained unless a large bias magnetic f ield is applied (i.e. they are poor in bias magnetic f ield dependability).
With the purpose of providing magnetooptical recording films which are excellent in resistance to oxidation, usable over a long period of time, high in C/N
lZ91~37~4 ratio and low in noise level and, moreover, excellent in such bias magnetic field dependability that a sufficiently high C/N ratio is obtained even in a small bias field, the present inventors prosecuted extensive researches and eventually have accomplished the present invention on the basis of their finding that magnetooptical recording films which contain specific amounts of Pt and/or Pd, specific amounts of Fe and/or Co and also rare earth elements such as Tb will exhibit excellent magnetooptical recording characteristics.
DISCLOSURE OF THE INVENTION
The magnetooptical recording film of the magnetooptical recording medium of the present invention contains:
(i) Pt and/or Pd, (ii) rare earth element (RE), and (iii) Fe and/or Co, the Pt and/or Pd being present in an amount of more than 10 atom% but not more than 30 atom%, the Fe and/or Co being present in an amount of at least 40 atom% but not more than 70 atom%, and having a Co/(Fe + Co) ratio [atomic ratio]
of 0-0.3. The magnetic recording medium, which may be in a disc form, includes a substrate on which the magnetooptical recording film is formed.
The magnetooptical recording medium is excellent in resistance to oxidation, usable over a long period of time, large in C/N ratio and low in noise level and, moreover, excellent in bias magnetic field lZ9~371;?~
dependability.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph showing the relationship between the content (atom%) of Pt and/or Pd in a magnetooptical recording film and resistance to oxidation (~C/N ratio).
Fig. 2 is a graph showing the relationship between bias magnetic field (Oe) and C/N ratio of a magnetooptical recording film. Fig. 3 is a graph showing the relationship between the content (atom%) of Pt and/or Pd and mlnimum bias magnetic field (Hsat. (Oe) ) in a mage~ntooptical recording film. Fig. 4 is a graph showing the relationship between the CO/(Fe + Co) ràtio tatomic ratio~ and noise level (dBm) in a magnetooptical recording film containing Pt. Fig. 5 is a graph showing the relationship between the Co/(Fe + Co) ratio ~atomic ratio]
and noise level (dBm) in a magnetooptical recording film containing Pd. Fig. 6 is a graph showing the relationship between the Co/(Fe + Co) ratio [atomic ratio] and erasion deterioration (~C/N ratio (dB) ) in a magnetooptical recording film.
All of the magnetooptical discs in Figs. 1-6 is a single layer of 1000 A.
BEST MODE OF P~ACTICING THE INVENTION
129~3'7C~4 g The magnetooptical recording films of the present invention are illustrated below in detail.
The present magnetooptical recording films contain as essential components the following components (i) Pt and/or Pd, (ii) a rare earth element, and (iii) Fe and/or Co.
Furthermore, it is preferable that the present magnetooptical recording films are amorphous when measured by the wide-angle X-ray diffraction method.
(i) Pt and/or Pd The present magnetooptical recording films contain Pt or Pd, or both, and the amount of Pt and/or Pd contained in the magnetooptical recording films is more than 10 atom% but not more than 30 atom%, preferably more than 10 atom% but less than 20 atom%, and more preferably at least 11 atom% but not more than 19 atom%.
The presence in the magnetooptical recording film of Pt and/or Pd in an amount exceeding 10 atom% brings about such advantages that resistance to oxidation of said recording film becomes excellent, no hole corrosion occurs and C/N ratio becomes low in the recording film.
Fig. 1 shows the relationship between the content of Pt and/or Pd in the magnetooptical recording film and C/N ratio when said recording film is retained for 1000 lZ9~3704 hours under the circumstances of 85% RH and 80 C.
It is thus understood from Fig. 1 that when the amount in the magnetooptical recording film of Pt and~or Pd exceeds 10 atom%, resistance of said recording film improves, no hole corrosion occurs even after a long-term use and also C/N ratio will not deteriorate.
For instance, the magnetooptical recording film of the present invention having the composition represented 13 28 50Cog or Pd12Tb28Fe53Co~ will not change in C/N ratio at all even when it is retained under the circumstance of 85% RH and 80C. In contrast thereto, a magnetooptical recording film having the composition represented by Tb25Fe68Co7 but containing no Pt or Pd will greatly decrease in C/N ratio when it is retained for 1000 hours under the circumstances of 85% RH and 80C.
By incorporation into a magnetooptical recording film of Pt and/or Pd in an amount within the range as specified above, a sufficiently high C/N ratio can be obtained even by a small bias magnetic field when an information is recorded on the magnetooptical recording film or when the information recorded is read out therefrom. If a sufficiently high C/N ratio is obtained by a small bias magnetic field, a magnet for producing a bias magnetic field can be made small in size and, moreover, heat generation from the magnet can be inhibited 1298~04 and hence simplification of a driving devlce for an optical disc bearing the magnetooptical recording film thereon is made possible. Moreover, because a sufficiently large C/N ratio is obtained by a small bias magnetic field, it becomes easy to design a magnet for magnetic field modulation recording capable of overwrite.
Fig. 2 shows the relationship between bias magnetic field and C/N ratio (dB) of the present magnetooptical recording film having the composition represented by Ptl3Tb28Fe50Cog and of a magnetooptical recording film having the composition represented by b25 68 7-It is understood from Fig. 2 that in theconventionally known magnetooptical recording film represented by Tb25Fe68Cog, the C/N ratio is not saturated unless a bias magnetic field of more than 250 Oe is applied, whereas in the present magnetooptical recording film represented by Ptl3Tb28Fe50Cog, recording can be pçrformed even by a small bias magnetic field and the C/N
ratio is saturated at a level of 120 Oe or more. In the following examples and comparative examples, a Hsat value of the minimum bia~ magnetic field of each magnetooptical recording film is shown in Table 1, at which the C/N ratio is saturated. The smaller is this Hsat value, it follows that the C/N ratio is saturated by a small bias magnetic :lZ98704 field.
Fig. 3 shows the relationship between the content of Pt and/or Pd and the minimum bias magnetic field (Hsat, (Oe) ) of a magnetooptical recording film of PtTbFeCo system and of a magnetooptical recording film of PdTbFeCo system.
It is understood from Fig. 3 that the minimum bias magnetic field, Hsat, becomes sufficiently small when the content of Pt and/or Pd exceeds 10 atom%.
(ii) Rare earth element (RE) In the present magnetooptical recording films, rare earth element (RE) is contained, and usable as the rare earth element is Nd, Sm, Pr, Ce, Eu, Gd, Tb, Dy or Ho.
Of the rare earth elements illustrated above, preferably usable are Nd, Pr, Gd, Tb and Dy, and particularly preferred is Tb. The rare earth elements may be used in combination of two or more, and in this case the combination preferably contains at least 50 atom% of Tb.
From the standpolnt of obtaining an optical magneti~m having an easy axis of magnetization perpendicular to the film, it is preferable that this rare earth element present in a magnetooptical recording film in such an amount as 0.25 < x ~ 0.45, preferably ~zg8704 0.3 < x < 0.4, wherein x represents RE/(RE + Fe + Co) [atomic ratio].
(iii) Fe and/or Co In the present magnetooptical recording films, Fe or Co or both are contained, and Fe and/or Co is r_-.
pre~e~Ably.present in the magnetooptical recording film in an amount of at least 40 atom% but not more than 70 atom%, preferably at least 40 atom% but less than 60 atom%, and more preferably at least 40 atom% but not more than 59 atom%.
Further, Fe and/or Co present in the magnetooptical recording film is proforably in such an amount that Co/(Fe + Co) ratio [atomic ratio~ is from 0 to 0.3, preferably from 0 to 0.2, and more preferably from 0.01 to 0.2.
When the amount of Fe and/or Co is in the range of at least 40 atom% but not more than 70 atom%, there is such an advantage that a magnetooptical recording film which is excellent in resistance to oxidation and has an easy axis of magnetization perpendicular to the film is obtained.
In this connection, when Co is incorporated into a magnetooptical recording film, there are observed such phenomena as (a) Curie point of the magnetooptical recording film increases and (b) Kerr-rotation angle ~ k) lZ987(;~4 becomes large. As the result, recording sensitivity of a magnetooptical recording film can be ad~usted by the amount of Co to be incorporated and, moreover, a carrier level of reproducing signal increases by incorporating Co. According to the study conducted by the present inventors, however, it has been found that when Co is incorporated excessively into a magnetooptical recording film, a noise level of reproducing signal rises and the C/N ratio decreases. Accordingly, in the present magnetooptical recording film, Co/(Fe + Co) ratio [atomic ratio] is from O to 0.3, preferably from O to 0.2, and more preferably from 0.01 to 0.2.
Fig. 4 shows the relationship between Co/(Co ~ Fe) ratio ~atomic ratio] and noise level (dBm) in a magnetooptical recording film of PtTbFeCo system, and Fig.
5 show~ the relationship between Co/(Co + Fe) ratio [atomic ratio~ and noise level (dBm) in a magnetooptical recording film of PdTbFeCo system.
Concretely, in the present magnetooptical recording film (Co/(Fe + Co) ratio ~atomic ratio]: 0.15) having the composition represented by Pt13Tb28Fe50Cog, the noise level is -56 dBm, whereas in a magnetooptical recording film (Co/(Fe + Co) ratio [atomic ratio]: 0.39) having the composition represented by Pt13Tb28Fe36Co23, the noise level is as large as -50 dBm. Furthermore, in ~zg8704 the present magnetooptical recording film (Co/(Fe + Co) ratio [atomic ratio]: 0.12) having the composition represented by Pdl4Tb2~Fe52Co~, the noise level is -56 dBm, whereas in a magnetooptical recording film (Co/(Fe Co) ratio [atomic ratio]: 0.31) having the composition y dl4Tb27Fe41Col8, the noise level is as large as -51 dBm.
Furthermore, when the Co/(Fe + Co) ratio [atomic ratio] exceeds 0.3, erasion deterioration is observed in the resulting magnetooptical recording film. That is, the Co/(Fe + Co) ratio [atomic ratio] in a magnetooptical recording film which is larger than 0.3 or more strictly in excess of 0.2 is not preferable since the maynetooptical recording film sometimes subject to change of property when an energy with which said recording film is irradiated is made large in order to erase the information once recorded in the magnetooptical recording film.
Fig. 6 shows the relationship between Co/(Fe + Co) ratio [atomic ratio] and erasion deterioration (~C/N ratio (dB) ) in a magnetooptical recording film.
In the concrete, no change in film property occurs at all even when the present magnetooptical recording film having the composition of Ptl3Tb28Fe50Cog (Co/(Fe + Co) ratio [atomic ratio] : 0.155) is irradiated with an ~29B'7~4 increased energy at the time of erasing the information once recorded in the recording film, and even a new information having the same value, as a value of C/N
ratio, as that prior to erasion can also be recorded on the erased recording film. In contrast thereto, in a magnetooptical recording film having the composition of 13 28 40 19 or Pt13Tb28Fe36Co23 and containing Co in an amount of more than 0.3 in terms of Co/(Fe + Co) ratio [atomic ratio], change in film property occurs and magnetooptical characterisitcs decrease, and the C/N ratio of a newly recorded information will also becomes smaller than that of the information recorded prior to erasion when the information once recorded is erased with an energy larger than necessary.
Furthermore, no change in film property will occur even when recording and erasing the information are performed repeatedly. For instance, no decrease ln C/N
ratio is observed even when the recording and erasing operations are performed 100,000 times in the present magnetooptical recording film having the composition of Ptl3Tb28Fesoco9 In the present invention, it is also possible to improve Curie temperature, compensation temperature, coercive force Hc or Kerr-rotation angle 9k, or cheapen the cost of production by incorporating various elements :12:~8'~
into the magnetooptical recording films. These elements for the purpose intended may be used, for example, in the proportion of less than 10 atom% based on the total number of elements constituting the recording film.
Examples of useful elements for this purpose other than those constituents of the magnetooptical recording film include such elements as mentioned below.
(I) 3d transition elements other than Fe and Co Concretely, such transition elements include Sc, Ti, V, Cr, Mn, Ni, Cu and Zn.
Of these elements exemplified above, preferably used are Ti, Ni, Cu and Zn.
(II) 4d transition elements other than Pd Concretely, such transition elements include Y, Zr, Nb, Mo, Tc, Ru, Rh, Ag and Cd.
Of these transition elements exemplified above, preerably used are Zr and Nb.
(III) 5d transition elements other than Pt Concretely, such transition elements include Hf, Ta, W, Re, Os, Ir, Au and Hg.
Of these transition elements, preferably used is Ta (IV) Group III B elements Concretely, B, Al, Ga, In, and Tl are used.
Of these elements, preferably used are B, Al and t, lZ987C~4 Ga.
(V) Group IV B elements Concretely, C, Si, Ge, Sn and Pb are used.
Of these elements, preferably used are Si, Ge, Sn and Pb.
(VI) Group V B elements Concretely, N, P, As, Sb and Bi are used.
Of these elements, preferably used is Sb.
(VII) Group VI B elements Concretely, S, Se, Te and Po are used.
Of these elements, preferably used is Te.
The composition of the recording film is determined by ICP emission spectroscopic analysis.
A process for preparing the magnetooptical recording films of the present invention is illustrated hereinafter.
The present magnetooptical recording films may be prepared by depositing a magnetooptical recording film having the predetermined composition on a substrate, wherein the substrate i5 maintained at about room temperature, and a composite target with chips of elements constituting the present magnetooptical recording film in the predetermined proportions thereon or an alloy target having the predetermined composition is deposited by the sputtering method or electron beam evaporation method on C
lZ987~14 _ 19 _ said substrate (this substrate may be fixed, or may rotates on its axis or may rotates on its axis while revolving).
The present magnetooptical recording films as illustrated above may be formed at room temperature, and the films as formed are not always in need of such heat treatment as annealing or the like that is usually required for allowing the films to have a magnetic easy axis perpendicular to the film.
If necessary, in this connection, an amorphous alloy thin film can also be formed on a substrate while heating the substrate to 50-600C, or while cooling the substrate to -50C.
At the time of sputtering, moreover, biasing a substrate i5 also possible so that the substrate comes to have a negative potential. By doing so, ions of an inert gas such as argon accelerated in the electric field will hit not only target substances but also a magnetooptical recording film being formed and consequently a magnetooptical recording film having excellent characteristics is sometimes obtained.
The alloy targets which are used for the preparation of the magnetooptical recording films of the present invention contain (i) Pt and/or Pd, (ii) a rare earth element, and (iii) Fe and/or Co, said Pt and/or Pd lZ987~4 being present in an amount of more than 5 atom% but not more than 40 atom~, and sald Fe and/or Co being present in an amount of at least 30 atom% but not more than 80 atom%, and have a Co/(Fe + Co) ratio [atomic ratio] of from O to 0.4.
Such alloy targets as illustrated above may be prepared by either the melting method or the sintering method by the use of the metals mentioned above.
The melting method is a process in which the metals are melted with a low-frequency melting furnace and then casted into targets, and the targets of better quality may be obtained when impurities such as oxygen and the like are removed from the molten metal by using a calcia crucible.
On one hand, the sintering method is a process of sintering metallic powder, in which the sintering of powder of each component metal, or powder of alloy of component metals, or of mixtures of powder of alloy of several kinds of metals and metals is effected to give desired alloy targets.
Such alloy targets as used in the present invention, in comparison with TbFeCo alloy targets, are excellent in resistance to oxidation and, moreover, excellent in toughnesc so that after casting and processing, the resulting alloy targets are prevented from lZ987~
their cracking. Accordingly, the alloy targets used in the present invention are not always in need of pre-sputtering that is required for the conventionally used TbFeCo alloy targets.
In the targets of the present invention, moreover, permeability of target becomes small so that the targets can be increased in thickness in comparison with the conventional TbFeCo alloy targets and utility efficiency of the present targets can also be enhanced.
In general, the composition of alloy target deviates from that of a film obtained from said alloy target to a maximum extent of 10 atom% according to the sputtering conditions employed. On that account, the composition of the alloy target is decided according to the composition of the film and to the sputtering conditions to be employed.
Since the magnetooptical recording films of the present invention have a magnetic easy axis perpendicular to the film, they are utilizable in such various fields as films, magnetic recording materials such as vertical magnetic recording magnetic bubble memories or magnetooptical recording films, and photomodulaters that utilize magnetooptical effects.
The present magnetooptical recording films having the compostion mentioned above have a magnetic easy axis perpendicular to the film and exhibit Kerr hysterisis loop ~z9~
of a favorable square-shaped form.
In the present specification, by "exhibition of Kerr hysterisis loop of a favorable square-shaped form" is 2/~kl ratio of the Kerr-rotation a saturation magnetization (~kl) in the maximum external magnetic field to the Kerr-rotation angle at a remanent magnetization (~k2) in the external magnetic field of zero is at least than 0.8.
In the present invention, a thickness of magnetooptical recording film is desirably 20 A - 5~ m, preferably 50-5000 A, and more preferably 100-3000 A or thereabout.
The case where the present magnetooptical recording films have been utilized as recording films of magnetooptlcal discs in illustrated hereinafter.
r~ The pre~ent magnetooptical recording films ~-film ~ith a magnetization with easy axis perpendicular to the film and, at the same time, in most of them, Kerr hysterisis loop has a square-shaped form, ~ k under the circum~tances where no external magnetic field exist~ is practically the same as~ k at a saturation magnetization in the maximum external magnetic field, and also coercive force Hc is large, and hence they are suitable as magnetooptical recording films. Furthermore, that ~k is favorable means that ~f is also favorable, and accordingly lZ98~
the present magnetooptical recording films are utilizable in both of Kerr effect utilization system and Faraday effect utilization system.
Furthermore, since the present magnetooptical recording films are excellent in resistance to oxidation, they are not always in need of use of such protective film for prevention of oxidation as used in the conventional magnetooptical recording films comprising heavy rare earth elements and 3d transition metal alloys such as Tb-Fe, Tb-Fe-Co, etc. .
Moreover, it is not always necessary to use anti-oxidizing material~ in a substrate adjacent to the recording film or other functional films (e.g. enhancing film and reflective film), or adhesive layers for lamination purposes.
Further, even when enhancing film and/or reflection film is formed on the present magnetooptical recording films, the film can be formed by the wet film forming method such as the spin or spray coating procesq that could not be employed in the conventional magnetooptical recording films, in addition to the dry film forming method quch as vacuum evaporation or sputtering.
Accordingly, the structure of magnetooptical discs bearing the present magnetooptical recording films as 129871~9L
recording films thereon may include such structures as mentioned below.
(i) Substrate/recording film, (ii) Substrate/enhancing film/recording film, (iii) Substrate/recording film/reflection film, (iv) Substrate/enhancing film/recording film/
reflection film, and (v) Substrate/enhancing film/recording film/
enhancing film/reflection film.
The magnetooptical discs having such structures illustrated above may also have on the outermost layer of the recording film side a protective film or protective lable for imparting scratch resistance or resistance to oxidation to said outermost layer.
The enhancing films may be of organic or inorganic materials so long as they have a refractive index larger than that of a substrate.
As the substrate, there may be used inorganic materials such as glass, aluminum, etc. and organic materials such a~ polymethyl methacrylate, polycarbonate, polymer alloy of polycarbonate and polystyrene, amorphous polyolefins as di~closed in U.S. Patent 4,614,7~8, poly-4-methyl-1-pentene, epoxy resin, polyether sulfone, polysulfone, polyether imide, etc.
The reflective films may be of any materials so 12987~!4 long as they have a reflection index of at least 50%.
Further, the structure of the magnetooptical discs is not limited only to the structures ~ v) mentioned above, and the discs may be provided with a subbing layer, anti-oxidizing film or highly permeable soft magnetic film, if necessary, and the discs may be used either singly or in the form of a laminated disc obtained by bonding two discs each other.
It is also possible to prepare a magnetooptical recording film by providing two layers of magnetooptical recording films on a substrate. In that case, the magnetooptical recording film having this structure is preferably such that when coercive force and Curie temperature of a first magnetooptical recording-film are taken as Hc1 and Tc1, respectively, and when coercive force and Curie temperature of a second magnetooptical recording film are taken as Hc2 and Tc2, respectively, the relationship of Hc1 > Hc2 and that of Tc1 < Tc2 are established and that an outer layer (a layer on the side opposite to a substrate, i.e., the second magnetooptical recording film) comprises such magnetooptical recording film as specified in the present invention.
~,t The magnetooptical recording film having such 2-A' o~ ~r~ g r~ layer structure may be sub~ect to o~or~irite.~ The recording process wherein such two-layer magnetooptical e~,,~/r/ ~
recording film is subjected to ovor~ritc is illustrated below.
A magnetooptical recording apparatus has a magnetic field (Ha) generating an upward magnetic field (or a downward magnetic field) for writing, right below a head through which a laser light is irradiated and in front of said magnetic field, i.e. an upright side, a magnetic field (Hb) generating a downward magnetic field (or an upward magnetic field) having the relationship of Hc1 > Hb > Hc2.
The magnetooptical recording film first passes through above Hb, whereby magnetization direction of the second magnetooptical recording film is arranged downwardly (or upwardly). In that case, the magnetization direction of the first magnetooptical recording film does not change from the relationship of Hc1 > Hb.
Subsequently, the magnetooptical recording film, when it passes through above Ha, is irradiated with a laser light modulated either to a high level or low level in correspondence to an information signal. The high level laser light heats the magnetooptical recording film to a level higher than the Curie temperature Tc2 of the ~econd magnetooptical recording film, and hence both the magnetization directions of the first and second magnetooptical recording films are arranged by the weak 129~37~
magnetic field Ha to the magnetization direction of the weak magentic field, that is, upwardly (or downwardly).
On one hand, the low level laser light heats the magnetooptical recording film only to a temperature higher than Curie temperature Tc1 of the first magnetooptical recording film and less than Tc2, and hence only the first magnetooptical recording film is magnetized by Ha, and the magnetization direction of the second magnetooptical recording film remains downwardly (or upwardly).
Therefore, the magnetization direction of the first magnetooptical recording film, after passing through Ha and in the course of back to room temperature, reverse to the magnetization direction of the second magnetooptical recording film and turns downward (or upward).
Accordingly, the magnetooptical recording film can be sub~ected to overwrite by modulating an energy level of laser light for writing.
Apart from the above-mentioned, in the case of a magnetooptical recording film having a two-layer structure wherein coercive force of a first magnetooptical layer (an inner layer) is smaller than that of a second magnetooptical recording film (an outer layer) and at least the outer layer (a layer on the side opposite to a substrate) comprises a magnetooptical recording film as defined in the present invention, the magnetooptical ~Z9~7~
recording film so designed is found high in C/N ratio and excellent in long-term reliability. That is, a recording sensitivity depends on Curie point of the outer layer, the information recorded in the outer layer i5 transferred to the inner layer having a small coercive force and a large Kerr-rotation angle, and when the recorded information is read out, a high C/N ratio is obtained. In that case, to obtain a high C/N ratio, it is desirable that Kerr-rotation angle of the inner layer is at least 0.25 deg, preferably at least 0.3 deg, coercive force of the inner layer is not greater than 3 KOe, preferably not greater than 2 KOe, and coercive force of the outer layer i9 at least 3 KOe, preferably at least 4 KOe, and Curie point of the outer layer is 100-300C.
In the magnetooptical recording film as mentioned above, recording sensitivity depends on Curie point of the second magnetooptical recording film, and because of a small coercive force, the information recorded in the second magnetooptical recording film is transferred to the first magnetooptical recording layer having a large Kerr-rotation angle, and a C/N ratio is obtained on reading-out of the transferred information.
The present invention is illustrated below with reference to examples, but it should be construed that the invention in no way limited to those examples.
lZ9l37~4 - 28a - 72932-6 In the following examples, the composition of the magnetooptical recording film is shown in atomic %. For instance, Pt12Tb30Fe49Cog of Example 1 means 12 atom.% of Pt, 30 atom.% of Tb, 49 atom.% of Fe and 9 atom.% of Co.
1~9~3704 Examples 1-25 and Comparative Examples 1-19 Using a composite target with chips of Pt and/or Pd and a rare earth element arranged in a predetermined proportion on Fe or Fe-Co target as a target, there was deposited on a glass substrate at 20-50C by DC magnetron sputtering a magnetooptical recording film having the composition as denoted in Table 1. The condition under which the film was formed included Ar pressure of 5 m Torr., Ar flow rate of 3 sccm, ultimate degree of vacuum of not more than 5 x 10 6 Torr, and a film thickness of the alloy thin film of loO0 A.
As a result of determination by the wide angle X-ray diffraction method, the magnetooptical films obtained were all amorphous. The composition of the recording films obtained was determined by ICP emission ~pectroscopic analysis.
The Kerr-rotation angle was measured by the inclination incidence method ( ~ = 780 nm) at a remanent magnetization in the external magnetic field of zero from the side of the glass substrate. A concrete method of measurement and apparatus therefor to be employed in the inclination incidence method are described in "Measuring Techniques of Magnetic Materials", compiled by Kazuo Yamakawa (published by Torikepps K.K. on December 15, 1985), pp.261-263.
987~
Table 1 shows x value, Fe + Co amount (atomic %), Co/(Fe + Co) ratio [atomic ratio], Kerr-rotation angle (9k) and coercive force ~Hc) of the magnetooptical recording films ohtained.
Furthermore, on a substrate comprising an amorphous ethylene-tetracyclododecene copolymer was deposited a magnetooptical recording film having a predetermined composition by DC magnetic sputtering method to prepare a magnetooptical disc bearing a single layer of 1000 A.
The magnetooptical disc obtained had a diameter of 130 mm, and using this magnetooptical disc, recording and reproducing were carried out with a driving apparatus .r~ (Nakamichi OMS-1000) under the conditions of recording frequency number 1 MHZ (Duty ratio 50%), linear speed of 11.1 m/s, bias magnetic field o f 200 Oe at the time o f writing, and readout laser power of 1.0 mW.
Table 1 also shows a carrier to noise ratio (C/N
ratio) and noise level when the recording was carried out with a recording power (optimum recording power), of which a level of second harmonic frequency as measured by spectrum analyzer became minimum.
Then, the information recorded was erased with a power larger by 3.0 mW than this optimum recording power, and a new information was recorded on the erased recording A~ r~ade~ fk 12987~4 film. This operation was repeated 10 times, and thereafter the difference between C/N ratio before and after erasion was measured and represented asa C/N ratio.
As regards bias magnetic field dependability, the bias magnetic field dependability (H sat) was obtained by a change in C/N ratio when the bias magnetic field under the above-mentioned conditions was changed upto 50-500 Oe.
Further, with the purpose of long-term reliability, the disc obtained was subjected to life test, wherein the disc was allowed to stand in an oven under the circumstances of high temperature and humidity of 80C and 85% ~H, and after the lapse of 1000 hours, C/N ratio was measured to obtain the results as shown in Table 1.
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12987~4 Example 26 On an amorphous polyolefin substrate were deposited a film comprising Pt13Tb28Fe55Co4 as a fir9t magnetooptical recording film and a film comprising Pt13Tb30Fe48Cog as a second magnetooptical recording film so that the second magnetooptical recording film became an outer layer. In this case, the magnetooptical recording film thus prepared had such relation that coercive force of the first magnetooptical recording film is larger than that of the second magnetooptical recording film, and Curie temperature of the first magnetooptical film is lower than that of the second magnetooptical recording film.
Then, using a disc drive having an upward magnetic field (0.2 KOe) for writing and a downward magnetic field (5 KOe) provided ad~acent to an upright side of said upward magnetic field larger than coercive force of the second magnetooptical recording film and smaller than coercive force of the first magnetooptical recording film, the abovementioned magnetooptical disc was sub~ected to overlight under the conditions of linear speed of 11 m/s, low laser power of 4 mW, and high level laser power of 6 mW by single beam modulation, whereupon the overwrite was possible.
Furthermore, this magnetooptical recording disc lZ98'7(;~L
was subjected to life test, wherein the disc was allowed to stand under the circumstances of 80C and 85% RH for 1000 hours, whereupon no change in recording characteristics was observed.
Example 2~
In the same procedure as described in Example 25, a film comprising Pt5Tb20Fe60Col5 was deposited to a film thickness of 300 A as a first magnetooptical recording film and a film comprising Ptl3Tb28Fe51Co8 p to a film thickness of 800 A as a second magnetooptical recording film (an outer layer).
This first magnetooptical recording film thus deposited had ~k of 0.40, Hc of 1.2 KOe, and Tc of 270C.
The second magnetooptical recording film thus deposited had ~k of 0.24, Hc of 8.3 KOe, and Tc of 170C.
The magnetooptical recording film thus prepared had a C/N ratio of 55 dB.
The magnetooptical disc bearing the above magnetooptical recording film thereon was subjected to life test, wherein the disc was allowed to stand under the circumstances of 80C and 85% RH for 1000 hours, whereupon no change in recording characteristics was observed.
This invention relates to magnetooptical recording medium having excellent resistance to oxidation and excellent magnetooptical recording characteristics and more partlcularly to magnetooptical recording films in the magnetooptical recording medium having an easy axis of magnetization perpendicular to the film as well as excellent resistance to oxidation and excellent magnetooptical recording characteristics.
BACKGROUND OF THE INVENTION
It is known that magnetooptical recording films comprising transition metals such as iron, cobalt, etc. and rare earth elements such as terbium (Tb), gadolinium (Gd), etc., have and easy axis of magnetization perpendicular to the film and are capable of forming a small inverse magnetic domain with magnetization antiparallel to the magnetization of the film. By corresponding the existence or nonexistence of this inverse magnetic domain to "1" or "0", it becomes possible to record a digital slgnal on such magnetooptical recording films as mentioned above.
As magnetooptical recording films composed of such .~
12987~
transition metals and rare earth elements as mentioned above, there are disclosed those of Tb-Fe system containing 15-30 atom% of Tb, for example, in Japanese Patent Publication No. 20691/1982. There are also used magnetooptical recording films of Tb-Co system to which a third component metal ha~ been added. Furthermore, magnetooptical recording films of Tb-Fe system, Tb-Fe-Co system and the like are known as well.
Though these magnetooptical recording films have excellent recording reproducing characteristics, they still involved such a serious problem from a practical standpoint that they are subject to oxidation in the course of ordinary use thereof and their characteristics come to change with the lapse of time.
The mechanism of oxidation deterioration of magnetooptical recording films containing such transition metals and rare earth elements as mentioned above is discussed, for example, in Journal of Applied Magnetism Society of Japan, Vol.9, No.2, pp.93-96, and this paper reports that this mechanism of oxidative deterioration may be claqsified into three types as mentioned below.
a) Hole corrosion By hole corrosion is meant the occurrence of pinholes in the magnetooptical recording film. This corrosion proceeds mainly under the circumstances of high 12,~1 37Q~
humidity, and it markedly proceeds, for example, in the recording films of such system as Tb-Fe, Tb-Co or the like.
b) Surface oxidation Surface oxide layers are formed on magnetooptical recording films, whereby Kerr-rotation angle~ k of the films changes with time and eventually comes to decrease.
c) Selective oxidation of rare earth element Rare earth elements present in magnetooptical recording films are selectively oxidized, thereby coercive force Hc of the films comes to largely change with time.
Various attempts have heretofore been made to inhibit such oxidative deterioration of magnetooptical recording films as mentioned above. For instance, there is propo~ed a procedure in which a magnetooptical recording film is designed to have a three-layer structure wherein the film is sandwitched between anti-oxidizing protective layers such as those of Si3N4, SiO, SiO2, AlN, etc. The anti-oxidizing protective layers as proposed above, however, involved such problems that they are relatively expensive and, at the same time, they require much time and labor to be formed on magnetooptical recording films, and that a sufficient inhibition of oxidative deterioration of the recording films is not always expected even when such anti-oxidizing protective ïZ91!3';~ 4 layers are formed on said recording films.
Furthermore, various attempts are being made to improve resistance to oxidation of magnetooptical recording films by incorporating a third component metal into the recording films.
For instance, Journal of Applied Magnetism Society of Japan cited above discloses an attempt to improve resistance to oxidation of magnetooptical recording films of Tb-Fe or Tb-Co system by incorporation into the films of such third component metal as Co, Ni, Pt, Al, Cr, Ti and Pd in an amount of up to 3.5 atom%. In connection with the attempt, the said Journal reports that the incorporation of small amounts of Co, Ni and Pt into Tb-Fe or Tb-Co ls effective in inhibiting the surface oxidation and hole corrosion of the resulting magnetooptical recording film but has no effect on inhibition of the selective oxidation of Tb contained as a rare earth element in this magnetooptical recording film. This disclo~ure means that when small amounts of Co, Ni and Pt are added to Tb-Fe or Tb-Co, Tb present in the resulting magnetooptical recording film is selectively oxidized, and coercive force Hc of the film largely changes. Thus, even when small amounts up to 3.5 atom% of Co, Ni and Pt are added to Tb-Fe or Tb-Co, no sufficient improvement in resistance to oxidation of the resulting magnetooptical ~Z~t~704 recording film i5 made.
With the view of improving resistance to oxidation of magnetooptical recording films, a teaching on the magnetooptical recording films which are obtained by adding Pt, Al, Cr and Ti in an amount up to 10 atom~ to Tb-Fe or Tb-Fe-Co is disclosed in page 209 of the Proceedings of The Nineth Conference of Applied Magnetism Society of Japan (November 1985). Even when Pt, Al, Cr and Ti in an amount up to 10 atom% are added to Tb-Fe or Tb-Fe-Co, however, inhibition of selective oxidation of Tb present in the resulting magnetooptical recording films is not sufficient, though the surface oxidation and hole corrosion can be inhibited to a fairly effective extent.
Thus, there was still left such a problem that coercive force Hc of the resultant magnetooptical recording films will largely change with time, and eventually the coercive force Hc will largely decreases.
Japanese Patent L-0-P Publn. No. 255546/1986 di~close~ magnetooptical recording films which have been improved in resistance to oxidation by adding such noble metal elements as Pt, Au, Ag, Ru, Rh, Pd, Os and Ir within such range that ~err-rotation angle necessary for regeneration is to magnetooptical recording films comprising rare earth elements and transition metals, obtained.
12~8 7(:~4 Furthermore, Japanese Patent L-O-P Publn. No.
7806/1983 discloses magnetooptical recording films comprising polycrystalline thin films having the composition of PtCo in which Pt is contained in an amount of 10-30 atom%.
However, the above-mentioned polycrystalline thin films having this composition of PtCo involved such problems that said polycrystalline thin films as formed require heat treatment such as annealing because that are polycrystalline, that particle-particle boundaries among the crystals sometimes appear as noise signals, and that these polycrystalline thin films are high in Curie point.
In the manner as described above, magnetooptical recording films comprising Tb-Fe or Tb-Co and further incorporated with such third metal components as Co, Ni, Pt, Al, Cr, Ti and Pd have heretofore been known.
However, these known magnetooptical recording films involve at least one of such problems that they are not suf f icient in resistance to oxidation, small in C/N ratio and high in noise level, and that no high C/N ratio can be obtained unless a large bias magnetic f ield is applied (i.e. they are poor in bias magnetic f ield dependability).
With the purpose of providing magnetooptical recording films which are excellent in resistance to oxidation, usable over a long period of time, high in C/N
lZ91~37~4 ratio and low in noise level and, moreover, excellent in such bias magnetic field dependability that a sufficiently high C/N ratio is obtained even in a small bias field, the present inventors prosecuted extensive researches and eventually have accomplished the present invention on the basis of their finding that magnetooptical recording films which contain specific amounts of Pt and/or Pd, specific amounts of Fe and/or Co and also rare earth elements such as Tb will exhibit excellent magnetooptical recording characteristics.
DISCLOSURE OF THE INVENTION
The magnetooptical recording film of the magnetooptical recording medium of the present invention contains:
(i) Pt and/or Pd, (ii) rare earth element (RE), and (iii) Fe and/or Co, the Pt and/or Pd being present in an amount of more than 10 atom% but not more than 30 atom%, the Fe and/or Co being present in an amount of at least 40 atom% but not more than 70 atom%, and having a Co/(Fe + Co) ratio [atomic ratio]
of 0-0.3. The magnetic recording medium, which may be in a disc form, includes a substrate on which the magnetooptical recording film is formed.
The magnetooptical recording medium is excellent in resistance to oxidation, usable over a long period of time, large in C/N ratio and low in noise level and, moreover, excellent in bias magnetic field lZ9~371;?~
dependability.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph showing the relationship between the content (atom%) of Pt and/or Pd in a magnetooptical recording film and resistance to oxidation (~C/N ratio).
Fig. 2 is a graph showing the relationship between bias magnetic field (Oe) and C/N ratio of a magnetooptical recording film. Fig. 3 is a graph showing the relationship between the content (atom%) of Pt and/or Pd and mlnimum bias magnetic field (Hsat. (Oe) ) in a mage~ntooptical recording film. Fig. 4 is a graph showing the relationship between the CO/(Fe + Co) ràtio tatomic ratio~ and noise level (dBm) in a magnetooptical recording film containing Pt. Fig. 5 is a graph showing the relationship between the Co/(Fe + Co) ratio ~atomic ratio]
and noise level (dBm) in a magnetooptical recording film containing Pd. Fig. 6 is a graph showing the relationship between the Co/(Fe + Co) ratio [atomic ratio] and erasion deterioration (~C/N ratio (dB) ) in a magnetooptical recording film.
All of the magnetooptical discs in Figs. 1-6 is a single layer of 1000 A.
BEST MODE OF P~ACTICING THE INVENTION
129~3'7C~4 g The magnetooptical recording films of the present invention are illustrated below in detail.
The present magnetooptical recording films contain as essential components the following components (i) Pt and/or Pd, (ii) a rare earth element, and (iii) Fe and/or Co.
Furthermore, it is preferable that the present magnetooptical recording films are amorphous when measured by the wide-angle X-ray diffraction method.
(i) Pt and/or Pd The present magnetooptical recording films contain Pt or Pd, or both, and the amount of Pt and/or Pd contained in the magnetooptical recording films is more than 10 atom% but not more than 30 atom%, preferably more than 10 atom% but less than 20 atom%, and more preferably at least 11 atom% but not more than 19 atom%.
The presence in the magnetooptical recording film of Pt and/or Pd in an amount exceeding 10 atom% brings about such advantages that resistance to oxidation of said recording film becomes excellent, no hole corrosion occurs and C/N ratio becomes low in the recording film.
Fig. 1 shows the relationship between the content of Pt and/or Pd in the magnetooptical recording film and C/N ratio when said recording film is retained for 1000 lZ9~3704 hours under the circumstances of 85% RH and 80 C.
It is thus understood from Fig. 1 that when the amount in the magnetooptical recording film of Pt and~or Pd exceeds 10 atom%, resistance of said recording film improves, no hole corrosion occurs even after a long-term use and also C/N ratio will not deteriorate.
For instance, the magnetooptical recording film of the present invention having the composition represented 13 28 50Cog or Pd12Tb28Fe53Co~ will not change in C/N ratio at all even when it is retained under the circumstance of 85% RH and 80C. In contrast thereto, a magnetooptical recording film having the composition represented by Tb25Fe68Co7 but containing no Pt or Pd will greatly decrease in C/N ratio when it is retained for 1000 hours under the circumstances of 85% RH and 80C.
By incorporation into a magnetooptical recording film of Pt and/or Pd in an amount within the range as specified above, a sufficiently high C/N ratio can be obtained even by a small bias magnetic field when an information is recorded on the magnetooptical recording film or when the information recorded is read out therefrom. If a sufficiently high C/N ratio is obtained by a small bias magnetic field, a magnet for producing a bias magnetic field can be made small in size and, moreover, heat generation from the magnet can be inhibited 1298~04 and hence simplification of a driving devlce for an optical disc bearing the magnetooptical recording film thereon is made possible. Moreover, because a sufficiently large C/N ratio is obtained by a small bias magnetic field, it becomes easy to design a magnet for magnetic field modulation recording capable of overwrite.
Fig. 2 shows the relationship between bias magnetic field and C/N ratio (dB) of the present magnetooptical recording film having the composition represented by Ptl3Tb28Fe50Cog and of a magnetooptical recording film having the composition represented by b25 68 7-It is understood from Fig. 2 that in theconventionally known magnetooptical recording film represented by Tb25Fe68Cog, the C/N ratio is not saturated unless a bias magnetic field of more than 250 Oe is applied, whereas in the present magnetooptical recording film represented by Ptl3Tb28Fe50Cog, recording can be pçrformed even by a small bias magnetic field and the C/N
ratio is saturated at a level of 120 Oe or more. In the following examples and comparative examples, a Hsat value of the minimum bia~ magnetic field of each magnetooptical recording film is shown in Table 1, at which the C/N ratio is saturated. The smaller is this Hsat value, it follows that the C/N ratio is saturated by a small bias magnetic :lZ98704 field.
Fig. 3 shows the relationship between the content of Pt and/or Pd and the minimum bias magnetic field (Hsat, (Oe) ) of a magnetooptical recording film of PtTbFeCo system and of a magnetooptical recording film of PdTbFeCo system.
It is understood from Fig. 3 that the minimum bias magnetic field, Hsat, becomes sufficiently small when the content of Pt and/or Pd exceeds 10 atom%.
(ii) Rare earth element (RE) In the present magnetooptical recording films, rare earth element (RE) is contained, and usable as the rare earth element is Nd, Sm, Pr, Ce, Eu, Gd, Tb, Dy or Ho.
Of the rare earth elements illustrated above, preferably usable are Nd, Pr, Gd, Tb and Dy, and particularly preferred is Tb. The rare earth elements may be used in combination of two or more, and in this case the combination preferably contains at least 50 atom% of Tb.
From the standpolnt of obtaining an optical magneti~m having an easy axis of magnetization perpendicular to the film, it is preferable that this rare earth element present in a magnetooptical recording film in such an amount as 0.25 < x ~ 0.45, preferably ~zg8704 0.3 < x < 0.4, wherein x represents RE/(RE + Fe + Co) [atomic ratio].
(iii) Fe and/or Co In the present magnetooptical recording films, Fe or Co or both are contained, and Fe and/or Co is r_-.
pre~e~Ably.present in the magnetooptical recording film in an amount of at least 40 atom% but not more than 70 atom%, preferably at least 40 atom% but less than 60 atom%, and more preferably at least 40 atom% but not more than 59 atom%.
Further, Fe and/or Co present in the magnetooptical recording film is proforably in such an amount that Co/(Fe + Co) ratio [atomic ratio~ is from 0 to 0.3, preferably from 0 to 0.2, and more preferably from 0.01 to 0.2.
When the amount of Fe and/or Co is in the range of at least 40 atom% but not more than 70 atom%, there is such an advantage that a magnetooptical recording film which is excellent in resistance to oxidation and has an easy axis of magnetization perpendicular to the film is obtained.
In this connection, when Co is incorporated into a magnetooptical recording film, there are observed such phenomena as (a) Curie point of the magnetooptical recording film increases and (b) Kerr-rotation angle ~ k) lZ987(;~4 becomes large. As the result, recording sensitivity of a magnetooptical recording film can be ad~usted by the amount of Co to be incorporated and, moreover, a carrier level of reproducing signal increases by incorporating Co. According to the study conducted by the present inventors, however, it has been found that when Co is incorporated excessively into a magnetooptical recording film, a noise level of reproducing signal rises and the C/N ratio decreases. Accordingly, in the present magnetooptical recording film, Co/(Fe + Co) ratio [atomic ratio] is from O to 0.3, preferably from O to 0.2, and more preferably from 0.01 to 0.2.
Fig. 4 shows the relationship between Co/(Co ~ Fe) ratio ~atomic ratio] and noise level (dBm) in a magnetooptical recording film of PtTbFeCo system, and Fig.
5 show~ the relationship between Co/(Co + Fe) ratio [atomic ratio~ and noise level (dBm) in a magnetooptical recording film of PdTbFeCo system.
Concretely, in the present magnetooptical recording film (Co/(Fe + Co) ratio ~atomic ratio]: 0.15) having the composition represented by Pt13Tb28Fe50Cog, the noise level is -56 dBm, whereas in a magnetooptical recording film (Co/(Fe + Co) ratio [atomic ratio]: 0.39) having the composition represented by Pt13Tb28Fe36Co23, the noise level is as large as -50 dBm. Furthermore, in ~zg8704 the present magnetooptical recording film (Co/(Fe + Co) ratio [atomic ratio]: 0.12) having the composition represented by Pdl4Tb2~Fe52Co~, the noise level is -56 dBm, whereas in a magnetooptical recording film (Co/(Fe Co) ratio [atomic ratio]: 0.31) having the composition y dl4Tb27Fe41Col8, the noise level is as large as -51 dBm.
Furthermore, when the Co/(Fe + Co) ratio [atomic ratio] exceeds 0.3, erasion deterioration is observed in the resulting magnetooptical recording film. That is, the Co/(Fe + Co) ratio [atomic ratio] in a magnetooptical recording film which is larger than 0.3 or more strictly in excess of 0.2 is not preferable since the maynetooptical recording film sometimes subject to change of property when an energy with which said recording film is irradiated is made large in order to erase the information once recorded in the magnetooptical recording film.
Fig. 6 shows the relationship between Co/(Fe + Co) ratio [atomic ratio] and erasion deterioration (~C/N ratio (dB) ) in a magnetooptical recording film.
In the concrete, no change in film property occurs at all even when the present magnetooptical recording film having the composition of Ptl3Tb28Fe50Cog (Co/(Fe + Co) ratio [atomic ratio] : 0.155) is irradiated with an ~29B'7~4 increased energy at the time of erasing the information once recorded in the recording film, and even a new information having the same value, as a value of C/N
ratio, as that prior to erasion can also be recorded on the erased recording film. In contrast thereto, in a magnetooptical recording film having the composition of 13 28 40 19 or Pt13Tb28Fe36Co23 and containing Co in an amount of more than 0.3 in terms of Co/(Fe + Co) ratio [atomic ratio], change in film property occurs and magnetooptical characterisitcs decrease, and the C/N ratio of a newly recorded information will also becomes smaller than that of the information recorded prior to erasion when the information once recorded is erased with an energy larger than necessary.
Furthermore, no change in film property will occur even when recording and erasing the information are performed repeatedly. For instance, no decrease ln C/N
ratio is observed even when the recording and erasing operations are performed 100,000 times in the present magnetooptical recording film having the composition of Ptl3Tb28Fesoco9 In the present invention, it is also possible to improve Curie temperature, compensation temperature, coercive force Hc or Kerr-rotation angle 9k, or cheapen the cost of production by incorporating various elements :12:~8'~
into the magnetooptical recording films. These elements for the purpose intended may be used, for example, in the proportion of less than 10 atom% based on the total number of elements constituting the recording film.
Examples of useful elements for this purpose other than those constituents of the magnetooptical recording film include such elements as mentioned below.
(I) 3d transition elements other than Fe and Co Concretely, such transition elements include Sc, Ti, V, Cr, Mn, Ni, Cu and Zn.
Of these elements exemplified above, preferably used are Ti, Ni, Cu and Zn.
(II) 4d transition elements other than Pd Concretely, such transition elements include Y, Zr, Nb, Mo, Tc, Ru, Rh, Ag and Cd.
Of these transition elements exemplified above, preerably used are Zr and Nb.
(III) 5d transition elements other than Pt Concretely, such transition elements include Hf, Ta, W, Re, Os, Ir, Au and Hg.
Of these transition elements, preferably used is Ta (IV) Group III B elements Concretely, B, Al, Ga, In, and Tl are used.
Of these elements, preferably used are B, Al and t, lZ987C~4 Ga.
(V) Group IV B elements Concretely, C, Si, Ge, Sn and Pb are used.
Of these elements, preferably used are Si, Ge, Sn and Pb.
(VI) Group V B elements Concretely, N, P, As, Sb and Bi are used.
Of these elements, preferably used is Sb.
(VII) Group VI B elements Concretely, S, Se, Te and Po are used.
Of these elements, preferably used is Te.
The composition of the recording film is determined by ICP emission spectroscopic analysis.
A process for preparing the magnetooptical recording films of the present invention is illustrated hereinafter.
The present magnetooptical recording films may be prepared by depositing a magnetooptical recording film having the predetermined composition on a substrate, wherein the substrate i5 maintained at about room temperature, and a composite target with chips of elements constituting the present magnetooptical recording film in the predetermined proportions thereon or an alloy target having the predetermined composition is deposited by the sputtering method or electron beam evaporation method on C
lZ987~14 _ 19 _ said substrate (this substrate may be fixed, or may rotates on its axis or may rotates on its axis while revolving).
The present magnetooptical recording films as illustrated above may be formed at room temperature, and the films as formed are not always in need of such heat treatment as annealing or the like that is usually required for allowing the films to have a magnetic easy axis perpendicular to the film.
If necessary, in this connection, an amorphous alloy thin film can also be formed on a substrate while heating the substrate to 50-600C, or while cooling the substrate to -50C.
At the time of sputtering, moreover, biasing a substrate i5 also possible so that the substrate comes to have a negative potential. By doing so, ions of an inert gas such as argon accelerated in the electric field will hit not only target substances but also a magnetooptical recording film being formed and consequently a magnetooptical recording film having excellent characteristics is sometimes obtained.
The alloy targets which are used for the preparation of the magnetooptical recording films of the present invention contain (i) Pt and/or Pd, (ii) a rare earth element, and (iii) Fe and/or Co, said Pt and/or Pd lZ987~4 being present in an amount of more than 5 atom% but not more than 40 atom~, and sald Fe and/or Co being present in an amount of at least 30 atom% but not more than 80 atom%, and have a Co/(Fe + Co) ratio [atomic ratio] of from O to 0.4.
Such alloy targets as illustrated above may be prepared by either the melting method or the sintering method by the use of the metals mentioned above.
The melting method is a process in which the metals are melted with a low-frequency melting furnace and then casted into targets, and the targets of better quality may be obtained when impurities such as oxygen and the like are removed from the molten metal by using a calcia crucible.
On one hand, the sintering method is a process of sintering metallic powder, in which the sintering of powder of each component metal, or powder of alloy of component metals, or of mixtures of powder of alloy of several kinds of metals and metals is effected to give desired alloy targets.
Such alloy targets as used in the present invention, in comparison with TbFeCo alloy targets, are excellent in resistance to oxidation and, moreover, excellent in toughnesc so that after casting and processing, the resulting alloy targets are prevented from lZ987~
their cracking. Accordingly, the alloy targets used in the present invention are not always in need of pre-sputtering that is required for the conventionally used TbFeCo alloy targets.
In the targets of the present invention, moreover, permeability of target becomes small so that the targets can be increased in thickness in comparison with the conventional TbFeCo alloy targets and utility efficiency of the present targets can also be enhanced.
In general, the composition of alloy target deviates from that of a film obtained from said alloy target to a maximum extent of 10 atom% according to the sputtering conditions employed. On that account, the composition of the alloy target is decided according to the composition of the film and to the sputtering conditions to be employed.
Since the magnetooptical recording films of the present invention have a magnetic easy axis perpendicular to the film, they are utilizable in such various fields as films, magnetic recording materials such as vertical magnetic recording magnetic bubble memories or magnetooptical recording films, and photomodulaters that utilize magnetooptical effects.
The present magnetooptical recording films having the compostion mentioned above have a magnetic easy axis perpendicular to the film and exhibit Kerr hysterisis loop ~z9~
of a favorable square-shaped form.
In the present specification, by "exhibition of Kerr hysterisis loop of a favorable square-shaped form" is 2/~kl ratio of the Kerr-rotation a saturation magnetization (~kl) in the maximum external magnetic field to the Kerr-rotation angle at a remanent magnetization (~k2) in the external magnetic field of zero is at least than 0.8.
In the present invention, a thickness of magnetooptical recording film is desirably 20 A - 5~ m, preferably 50-5000 A, and more preferably 100-3000 A or thereabout.
The case where the present magnetooptical recording films have been utilized as recording films of magnetooptlcal discs in illustrated hereinafter.
r~ The pre~ent magnetooptical recording films ~-film ~ith a magnetization with easy axis perpendicular to the film and, at the same time, in most of them, Kerr hysterisis loop has a square-shaped form, ~ k under the circum~tances where no external magnetic field exist~ is practically the same as~ k at a saturation magnetization in the maximum external magnetic field, and also coercive force Hc is large, and hence they are suitable as magnetooptical recording films. Furthermore, that ~k is favorable means that ~f is also favorable, and accordingly lZ98~
the present magnetooptical recording films are utilizable in both of Kerr effect utilization system and Faraday effect utilization system.
Furthermore, since the present magnetooptical recording films are excellent in resistance to oxidation, they are not always in need of use of such protective film for prevention of oxidation as used in the conventional magnetooptical recording films comprising heavy rare earth elements and 3d transition metal alloys such as Tb-Fe, Tb-Fe-Co, etc. .
Moreover, it is not always necessary to use anti-oxidizing material~ in a substrate adjacent to the recording film or other functional films (e.g. enhancing film and reflective film), or adhesive layers for lamination purposes.
Further, even when enhancing film and/or reflection film is formed on the present magnetooptical recording films, the film can be formed by the wet film forming method such as the spin or spray coating procesq that could not be employed in the conventional magnetooptical recording films, in addition to the dry film forming method quch as vacuum evaporation or sputtering.
Accordingly, the structure of magnetooptical discs bearing the present magnetooptical recording films as 129871~9L
recording films thereon may include such structures as mentioned below.
(i) Substrate/recording film, (ii) Substrate/enhancing film/recording film, (iii) Substrate/recording film/reflection film, (iv) Substrate/enhancing film/recording film/
reflection film, and (v) Substrate/enhancing film/recording film/
enhancing film/reflection film.
The magnetooptical discs having such structures illustrated above may also have on the outermost layer of the recording film side a protective film or protective lable for imparting scratch resistance or resistance to oxidation to said outermost layer.
The enhancing films may be of organic or inorganic materials so long as they have a refractive index larger than that of a substrate.
As the substrate, there may be used inorganic materials such as glass, aluminum, etc. and organic materials such a~ polymethyl methacrylate, polycarbonate, polymer alloy of polycarbonate and polystyrene, amorphous polyolefins as di~closed in U.S. Patent 4,614,7~8, poly-4-methyl-1-pentene, epoxy resin, polyether sulfone, polysulfone, polyether imide, etc.
The reflective films may be of any materials so 12987~!4 long as they have a reflection index of at least 50%.
Further, the structure of the magnetooptical discs is not limited only to the structures ~ v) mentioned above, and the discs may be provided with a subbing layer, anti-oxidizing film or highly permeable soft magnetic film, if necessary, and the discs may be used either singly or in the form of a laminated disc obtained by bonding two discs each other.
It is also possible to prepare a magnetooptical recording film by providing two layers of magnetooptical recording films on a substrate. In that case, the magnetooptical recording film having this structure is preferably such that when coercive force and Curie temperature of a first magnetooptical recording-film are taken as Hc1 and Tc1, respectively, and when coercive force and Curie temperature of a second magnetooptical recording film are taken as Hc2 and Tc2, respectively, the relationship of Hc1 > Hc2 and that of Tc1 < Tc2 are established and that an outer layer (a layer on the side opposite to a substrate, i.e., the second magnetooptical recording film) comprises such magnetooptical recording film as specified in the present invention.
~,t The magnetooptical recording film having such 2-A' o~ ~r~ g r~ layer structure may be sub~ect to o~or~irite.~ The recording process wherein such two-layer magnetooptical e~,,~/r/ ~
recording film is subjected to ovor~ritc is illustrated below.
A magnetooptical recording apparatus has a magnetic field (Ha) generating an upward magnetic field (or a downward magnetic field) for writing, right below a head through which a laser light is irradiated and in front of said magnetic field, i.e. an upright side, a magnetic field (Hb) generating a downward magnetic field (or an upward magnetic field) having the relationship of Hc1 > Hb > Hc2.
The magnetooptical recording film first passes through above Hb, whereby magnetization direction of the second magnetooptical recording film is arranged downwardly (or upwardly). In that case, the magnetization direction of the first magnetooptical recording film does not change from the relationship of Hc1 > Hb.
Subsequently, the magnetooptical recording film, when it passes through above Ha, is irradiated with a laser light modulated either to a high level or low level in correspondence to an information signal. The high level laser light heats the magnetooptical recording film to a level higher than the Curie temperature Tc2 of the ~econd magnetooptical recording film, and hence both the magnetization directions of the first and second magnetooptical recording films are arranged by the weak 129~37~
magnetic field Ha to the magnetization direction of the weak magentic field, that is, upwardly (or downwardly).
On one hand, the low level laser light heats the magnetooptical recording film only to a temperature higher than Curie temperature Tc1 of the first magnetooptical recording film and less than Tc2, and hence only the first magnetooptical recording film is magnetized by Ha, and the magnetization direction of the second magnetooptical recording film remains downwardly (or upwardly).
Therefore, the magnetization direction of the first magnetooptical recording film, after passing through Ha and in the course of back to room temperature, reverse to the magnetization direction of the second magnetooptical recording film and turns downward (or upward).
Accordingly, the magnetooptical recording film can be sub~ected to overwrite by modulating an energy level of laser light for writing.
Apart from the above-mentioned, in the case of a magnetooptical recording film having a two-layer structure wherein coercive force of a first magnetooptical layer (an inner layer) is smaller than that of a second magnetooptical recording film (an outer layer) and at least the outer layer (a layer on the side opposite to a substrate) comprises a magnetooptical recording film as defined in the present invention, the magnetooptical ~Z9~7~
recording film so designed is found high in C/N ratio and excellent in long-term reliability. That is, a recording sensitivity depends on Curie point of the outer layer, the information recorded in the outer layer i5 transferred to the inner layer having a small coercive force and a large Kerr-rotation angle, and when the recorded information is read out, a high C/N ratio is obtained. In that case, to obtain a high C/N ratio, it is desirable that Kerr-rotation angle of the inner layer is at least 0.25 deg, preferably at least 0.3 deg, coercive force of the inner layer is not greater than 3 KOe, preferably not greater than 2 KOe, and coercive force of the outer layer i9 at least 3 KOe, preferably at least 4 KOe, and Curie point of the outer layer is 100-300C.
In the magnetooptical recording film as mentioned above, recording sensitivity depends on Curie point of the second magnetooptical recording film, and because of a small coercive force, the information recorded in the second magnetooptical recording film is transferred to the first magnetooptical recording layer having a large Kerr-rotation angle, and a C/N ratio is obtained on reading-out of the transferred information.
The present invention is illustrated below with reference to examples, but it should be construed that the invention in no way limited to those examples.
lZ9l37~4 - 28a - 72932-6 In the following examples, the composition of the magnetooptical recording film is shown in atomic %. For instance, Pt12Tb30Fe49Cog of Example 1 means 12 atom.% of Pt, 30 atom.% of Tb, 49 atom.% of Fe and 9 atom.% of Co.
1~9~3704 Examples 1-25 and Comparative Examples 1-19 Using a composite target with chips of Pt and/or Pd and a rare earth element arranged in a predetermined proportion on Fe or Fe-Co target as a target, there was deposited on a glass substrate at 20-50C by DC magnetron sputtering a magnetooptical recording film having the composition as denoted in Table 1. The condition under which the film was formed included Ar pressure of 5 m Torr., Ar flow rate of 3 sccm, ultimate degree of vacuum of not more than 5 x 10 6 Torr, and a film thickness of the alloy thin film of loO0 A.
As a result of determination by the wide angle X-ray diffraction method, the magnetooptical films obtained were all amorphous. The composition of the recording films obtained was determined by ICP emission ~pectroscopic analysis.
The Kerr-rotation angle was measured by the inclination incidence method ( ~ = 780 nm) at a remanent magnetization in the external magnetic field of zero from the side of the glass substrate. A concrete method of measurement and apparatus therefor to be employed in the inclination incidence method are described in "Measuring Techniques of Magnetic Materials", compiled by Kazuo Yamakawa (published by Torikepps K.K. on December 15, 1985), pp.261-263.
987~
Table 1 shows x value, Fe + Co amount (atomic %), Co/(Fe + Co) ratio [atomic ratio], Kerr-rotation angle (9k) and coercive force ~Hc) of the magnetooptical recording films ohtained.
Furthermore, on a substrate comprising an amorphous ethylene-tetracyclododecene copolymer was deposited a magnetooptical recording film having a predetermined composition by DC magnetic sputtering method to prepare a magnetooptical disc bearing a single layer of 1000 A.
The magnetooptical disc obtained had a diameter of 130 mm, and using this magnetooptical disc, recording and reproducing were carried out with a driving apparatus .r~ (Nakamichi OMS-1000) under the conditions of recording frequency number 1 MHZ (Duty ratio 50%), linear speed of 11.1 m/s, bias magnetic field o f 200 Oe at the time o f writing, and readout laser power of 1.0 mW.
Table 1 also shows a carrier to noise ratio (C/N
ratio) and noise level when the recording was carried out with a recording power (optimum recording power), of which a level of second harmonic frequency as measured by spectrum analyzer became minimum.
Then, the information recorded was erased with a power larger by 3.0 mW than this optimum recording power, and a new information was recorded on the erased recording A~ r~ade~ fk 12987~4 film. This operation was repeated 10 times, and thereafter the difference between C/N ratio before and after erasion was measured and represented asa C/N ratio.
As regards bias magnetic field dependability, the bias magnetic field dependability (H sat) was obtained by a change in C/N ratio when the bias magnetic field under the above-mentioned conditions was changed upto 50-500 Oe.
Further, with the purpose of long-term reliability, the disc obtained was subjected to life test, wherein the disc was allowed to stand in an oven under the circumstances of high temperature and humidity of 80C and 85% ~H, and after the lapse of 1000 hours, C/N ratio was measured to obtain the results as shown in Table 1.
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12987~4 Example 26 On an amorphous polyolefin substrate were deposited a film comprising Pt13Tb28Fe55Co4 as a fir9t magnetooptical recording film and a film comprising Pt13Tb30Fe48Cog as a second magnetooptical recording film so that the second magnetooptical recording film became an outer layer. In this case, the magnetooptical recording film thus prepared had such relation that coercive force of the first magnetooptical recording film is larger than that of the second magnetooptical recording film, and Curie temperature of the first magnetooptical film is lower than that of the second magnetooptical recording film.
Then, using a disc drive having an upward magnetic field (0.2 KOe) for writing and a downward magnetic field (5 KOe) provided ad~acent to an upright side of said upward magnetic field larger than coercive force of the second magnetooptical recording film and smaller than coercive force of the first magnetooptical recording film, the abovementioned magnetooptical disc was sub~ected to overlight under the conditions of linear speed of 11 m/s, low laser power of 4 mW, and high level laser power of 6 mW by single beam modulation, whereupon the overwrite was possible.
Furthermore, this magnetooptical recording disc lZ98'7(;~L
was subjected to life test, wherein the disc was allowed to stand under the circumstances of 80C and 85% RH for 1000 hours, whereupon no change in recording characteristics was observed.
Example 2~
In the same procedure as described in Example 25, a film comprising Pt5Tb20Fe60Col5 was deposited to a film thickness of 300 A as a first magnetooptical recording film and a film comprising Ptl3Tb28Fe51Co8 p to a film thickness of 800 A as a second magnetooptical recording film (an outer layer).
This first magnetooptical recording film thus deposited had ~k of 0.40, Hc of 1.2 KOe, and Tc of 270C.
The second magnetooptical recording film thus deposited had ~k of 0.24, Hc of 8.3 KOe, and Tc of 170C.
The magnetooptical recording film thus prepared had a C/N ratio of 55 dB.
The magnetooptical disc bearing the above magnetooptical recording film thereon was subjected to life test, wherein the disc was allowed to stand under the circumstances of 80C and 85% RH for 1000 hours, whereupon no change in recording characteristics was observed.
Claims (29)
1. A magnetooptical recording medium comprising:
(A) a substrate, and (B) a magnetooptical recording film which comprises:
(i) more than 10 atom% but not more than 30 atom% of at least one member selected from the group consisting of Pt and Pd;
(ii) a rare earth element (RE); and (iii) at least 40 atom% but not more than 70 atom% of at least one element selected from the group consisting of Fe and Co, wherein a Co/(Fe + Co) atomic ratio is from 0 to 0.3.
(A) a substrate, and (B) a magnetooptical recording film which comprises:
(i) more than 10 atom% but not more than 30 atom% of at least one member selected from the group consisting of Pt and Pd;
(ii) a rare earth element (RE); and (iii) at least 40 atom% but not more than 70 atom% of at least one element selected from the group consisting of Fe and Co, wherein a Co/(Fe + Co) atomic ratio is from 0 to 0.3.
2. The magnetooptical recording medium as claimed in claim 1, wherein the recording film is substantially amorphous.
3. The magnetooptical recording medium as claimed in claim 1 or 2, wherein the amount of Pt or Pd or both is more than 10 atom% but less than 20 atom%.
4. The magnetooptical recording medium as claimed in claim 1 or 2, wherein the amount of Pt or Pd or both is from 11 to 1 atom%.
5. The magnetooptical recording medium as claimed in claim 1 or 2, wherein the amount of Fe or Co or both is at least 40 atom% but less than 60 atom%.
6. The magnetooptical recording medium as claimed in claim 1 or 2, wherein the Co/(Fe + Co) atomic ratio is from 0 to 0.2.
7. The magnetooptical recording medium as claimed in claim 1 or 2, wherein the Co/(Fe + Co) atomic ratio is from 0.01 to 0.2.
8. The magnetooptical recording medium as claimed in claim 1 or 2, wherein the rare earth element is Nd, Sm, Pr, Ce, Eu, Cd, Tb, Dy or Ho.
9. A magnetooptical recording medium comprising:
(A) a substrate, and (B) a magnetooptical recording film of such a two-layer structure comprising first and second magnetooptical recording films that the first magnetooptical recording film is between the substrate and the second magnetooptical recording film, wherein the relation of Hcl>Hc2 and that of Tc1<Tc2 are established when coercive force and Curie's temperature of the first magnetooptical recording film are taken as Hcl and Tcl and coercive force and Curie's temperature of the second magnetooptical recording film are taken as Hc2 and Tc2, respectively, and at least the second magnetooptical recording film contains:
(i) more than 10 atom% but not more than 30 atom% of at least one element selected from the group consisting of Pt and Pd, (ii) a rare earth element (RE), and (iii) at least 40 atom% but not more than 70 atom% of at least one element selected from the group consisting of Fe and Co, wherein a Co/(Fe + Co) atomic ratio is from 0 to 0.3.
(A) a substrate, and (B) a magnetooptical recording film of such a two-layer structure comprising first and second magnetooptical recording films that the first magnetooptical recording film is between the substrate and the second magnetooptical recording film, wherein the relation of Hcl>Hc2 and that of Tc1<Tc2 are established when coercive force and Curie's temperature of the first magnetooptical recording film are taken as Hcl and Tcl and coercive force and Curie's temperature of the second magnetooptical recording film are taken as Hc2 and Tc2, respectively, and at least the second magnetooptical recording film contains:
(i) more than 10 atom% but not more than 30 atom% of at least one element selected from the group consisting of Pt and Pd, (ii) a rare earth element (RE), and (iii) at least 40 atom% but not more than 70 atom% of at least one element selected from the group consisting of Fe and Co, wherein a Co/(Fe + Co) atomic ratio is from 0 to 0.3.
10. The magnetooptical recording medium as claimed in claim 9, wherein the second magnetooptical recording film is amorphous.
11. The magnetooptical recording medium as claimed in claim 9 or 10, wherein the second magnetooptical recording film contains more than 10 atom% but less than 20 atom% of Pt or Pd or both.
12. The magnetooptical recording medium as claimed in claim 9 or 10, wherein the second magnetooptical recording film contains 11-19 atom% of Pt or Pd or both.
13. The magnetooptical recording medium as claimed in claim 9 or 10, wherein the second magnetooptical recording film contains at least 40 atom% but less than 60 atom% of Fe or Co or both.
14. The magnetooptical recording medium as claimed in claim 9 or 10, wherein the Co/(Fe + Co) atomic ratio in the second magnetooptical recording film is from 0 to 0.2.
15. The magnetooptical recording medium as claimed in claim 9 or 10, wherein the Co/(Fe + Co) atomic ratio in the second magnetooptical recording film is from 0.01 to 0.2.
16. The magnetooptical recording medium as claimed in claim 9 or 10, wherein the rare earth element contained in the second magnetooptical recording film is Nd, Sm, Pr, Ce, Eu, Gd, Tb, Dy or Ho.
17. A magnetooptical recording medium comprising:
(A) a substrate, and (B) a magnetooptical recording film of such a two-layer structure comprising first and second magnetooptical recording films that the first magnetooptical recording film is between the substrate and the second magnetooptical recording film, wherein coercive force of the first magnetooptical recording film is smaller than that of the second magnetooptical recording film and at least the second magnetooptical recording film contains:
(i) more than 10 atom% but not more than 30 atom% of at least one element selected from the group consisting of Pt and Pd, (ii) a rare earth element (RE), and (iii) at least 40 atom% but not more than 70 atom% of at least one element selected from the group consisting of Fe and Co, wherein a Co/(Fe + Co) atomic ratio is from 0 to 0.3.
(A) a substrate, and (B) a magnetooptical recording film of such a two-layer structure comprising first and second magnetooptical recording films that the first magnetooptical recording film is between the substrate and the second magnetooptical recording film, wherein coercive force of the first magnetooptical recording film is smaller than that of the second magnetooptical recording film and at least the second magnetooptical recording film contains:
(i) more than 10 atom% but not more than 30 atom% of at least one element selected from the group consisting of Pt and Pd, (ii) a rare earth element (RE), and (iii) at least 40 atom% but not more than 70 atom% of at least one element selected from the group consisting of Fe and Co, wherein a Co/(Fe + Co) atomic ratio is from 0 to 0.3.
18. The magnetooptical recording medium as claimed in claim 17, wherein the second magnetooptical recording film is substantially amorphous.
19. The magnetooptical recording medium as claimed in claim 17 or 18, wherein the second magnetooptical recording film contains more than 10 atom% but less than 20 atom% of Pt or Pd or both.
20. The magnetooptical recording medium as claimed in claim 17 or 18, wherein the second magnetooptical recording film contains 11 to 19 atom% of Pt or Pd or both.
21. The magnetooptical recording medium as claimed in claim 17 or 18, wherein the second magnetooptical recording film contains at least 40 atom% but less than 60 atom% of Fe or Co or both.
22. The magnetooptical recording medium as claimed in claim 17 or 18, wherein the Co/(Fe + Co) atomic ratio in the second magnetooptical recording film is from 0 to 0.2.
23. The magnetooptical recording medium as claimed in claim 17 or 18, wherein the Co/(Fe + Co) atomic ratio in the second magnetooptical recording film is from 0.01 to 0.2.
24. The magnetooptical recording medium as claimed in claim 17 or 18, wherein the rare earth element contained in the second magnetooptical recording film is Nd, Sm, Pr, Ce, Eu, Gd, Tb, Dy or Ho.
42a 72932-6
42a 72932-6
25. An alloy target for forming a magnetooptical recording film of a magnetooptical recording medium on a substrate, the target containing (i) Pt and/or Pd, (ii) a rare earth element and (iii) Fe and/or Co, wherein Pt and/or Pd is present in an amount of more than 5 atom% but not more than 40 atom%, Fe and/or Co is present in an amount of at least 30 atom% but not more than 80 atom%, and a Co/(Fe + Co) ratio atomic ratio is from 0 to 0.4.
26. A magnetooptical recording disc in which information can be written and rewritten by irradiating a laser light comprising a substrate and a magnetooptical recording film made of a substantially amorphous metal alloy thin film having a thickness of 50 to 5,000 .ANG., wherein the said metal alloy thin film has a magnetic easy axis perpendicular to the film plane, exhibits Kerr histerisis loop in such a desired square-shaped form that a .theta.k2/.theta.k1 ratio of the Kerr-rotation angel at a saturation magnetization (.theta.kl) in a maximum external magnetic field to the Kerr-rotation angle at a remanent magnetization (.theta.k2) in an external magnetic field of zero is at least 0.8 and consists essentially of:
(i) at least one member selected from the group consisting of Pt and Pd in an amount of more than 10 atom.% but not more than 30 atom.%, (ii) at least one rare earth element selected from the group consisting of Nd, Sm, Pr, Ce, Eu, Gd, Tb, Dy and Ho, and (iii) Fe alone or in combination with Co, with a Co/(Fe + Co) atomic ratio of from 0 to 0.3, in an amount of at least 40 atom.% but not more than 70 atom.%.
(i) at least one member selected from the group consisting of Pt and Pd in an amount of more than 10 atom.% but not more than 30 atom.%, (ii) at least one rare earth element selected from the group consisting of Nd, Sm, Pr, Ce, Eu, Gd, Tb, Dy and Ho, and (iii) Fe alone or in combination with Co, with a Co/(Fe + Co) atomic ratio of from 0 to 0.3, in an amount of at least 40 atom.% but not more than 70 atom.%.
27. The magnetooptical recording disc as claimed in claim 26, wherein the substrate is made of amorphous ethylene-tetracyclododecene copolymer.
28. The magnetooptical recording disc as claimed in claim 26, wherein the metal alloy is composed of:
(i) Pt, (ii) Tb, and (iii) Fe and Co.
(i) Pt, (ii) Tb, and (iii) Fe and Co.
29. The magnetooptical recording disc as claimed in claim 26, 27 or 28, wherein:
the substrate has first and second magnetooptical recording films provided on opposite sides thereof;
the second film is made of the said metal alloy; and the first film has a coercive force HC1 larger than that of the second film HC2 and has a Curie temperature TC1 lower than that of the second film TC2.
the substrate has first and second magnetooptical recording films provided on opposite sides thereof;
the second film is made of the said metal alloy; and the first film has a coercive force HC1 larger than that of the second film HC2 and has a Curie temperature TC1 lower than that of the second film TC2.
Applications Claiming Priority (12)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24293587A JPS6427211A (en) | 1987-04-17 | 1987-09-28 | Amorphous alloy thin film |
| JP24293687A JPS6484457A (en) | 1987-09-28 | 1987-09-28 | Thin amorphous alloy film |
| JP62-242937 | 1987-09-28 | ||
| JP62-242933 | 1987-09-28 | ||
| JP24293787A JPS6484715A (en) | 1987-09-28 | 1987-09-28 | Amorphous alloy thin film |
| JP24293387A JPS6427209A (en) | 1987-04-17 | 1987-09-28 | Amorphous alloy thin film |
| JP24293487A JPS6427210A (en) | 1987-04-17 | 1987-09-28 | Amorphous alloy thin film |
| JP62-242934 | 1987-09-28 | ||
| JP62-242935 | 1987-09-28 | ||
| JP62-242936 | 1987-09-28 | ||
| JP29432787A JPH01136947A (en) | 1987-11-20 | 1987-11-20 | Amorphous alloy thin film |
| JP62-294327 | 1987-11-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1298704C true CA1298704C (en) | 1992-04-14 |
Family
ID=27554152
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000569719A Expired - Fee Related CA1298704C (en) | 1987-09-28 | 1988-06-17 | Magnetooptical recording medium |
Country Status (2)
| Country | Link |
|---|---|
| CN (1) | CN1032408A (en) |
| CA (1) | CA1298704C (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPWO2007046437A1 (en) | 2005-10-19 | 2009-04-23 | 財団法人理工学振興会 | Corrosion-resistant and heat-resistant alloys for molding dies and optical element molding dies |
| JP6116928B2 (en) * | 2013-02-18 | 2017-04-19 | 山陽特殊製鋼株式会社 | CoFe-based alloy and sputtering target material for soft magnetic film layer in perpendicular magnetic recording medium |
-
1988
- 1988-06-17 CA CA000569719A patent/CA1298704C/en not_active Expired - Fee Related
- 1988-06-20 CN CN 88103789 patent/CN1032408A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| CN1032408A (en) | 1989-04-12 |
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