GB2175160A - Magneto-optical recording medium - Google Patents
Magneto-optical recording medium Download PDFInfo
- Publication number
- GB2175160A GB2175160A GB08610978A GB8610978A GB2175160A GB 2175160 A GB2175160 A GB 2175160A GB 08610978 A GB08610978 A GB 08610978A GB 8610978 A GB8610978 A GB 8610978A GB 2175160 A GB2175160 A GB 2175160A
- Authority
- GB
- United Kingdom
- Prior art keywords
- recording medium
- magneto
- optical recording
- noble metal
- magnetic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10582—Record carriers characterised by the selection of the material or by the structure or form
- G11B11/10586—Record carriers characterised by the selection of the material or by the structure or form characterised by the selection of the material
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F10/00—Thin magnetic films, e.g. of one-domain structure
- H01F10/08—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers
- H01F10/10—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition
- H01F10/12—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being metals or alloys
- H01F10/13—Amorphous metallic alloys, e.g. glassy metals
- H01F10/133—Amorphous metallic alloys, e.g. glassy metals containing rare earth metals
Abstract
A magneto-optical recording medium is disclosed which comprises an amorphous R-TM system alloy (where R is at least one rare earth element and TM at least one 3d transition metal) and has an easy axis of magnetization in a direction perpendicular of the film surface. In accordance with the present invention, at least one noble metal element is added within a range of content less than 10%, by way of example, in which a Kerr rotation angle of more than 0.15 deg, by way of example, can be obtained for reproducing information recorded in the recording medium, whereby the progress of oxidation and corrosion of the recording medium can be suppressed for a long period of time. The noble metal element is selected from a group including Pt, Au, Ag, Ru, Rh, Pd, Os and Ir of Ib and VIII families. <IMAGE>
Description
SPECIFICATION Magneto-o;pticai rscorthing rnediuyn The present invention relates to a magneto-optical recording medium for use as a magneto-optical memory or magnetic recording and displaycell, and more particularly, to a magnetic thin film recording medium which has an easy axis of magnetization in a direction perpendicularto the film surface and permits recording of information by forming an inverted magnetic domain of a circular or any other arbitrary configuration and readout of the information through utilization of a magneto-optical effect such as the magnetic Kerr effect.
With ferromagnetic thin films, each of which has an easy axis of magnetization in a direction perpendicu lartotheirfilm surface, it is possibleto produce a small inverted magnetic domain of a magnetic polarity reverse of a homogenous magnetization polarity in the film surface homogeneously magnetized to the south or north magnetic pole. By malting the presence and absence of such an inverted magnetic domain correspond to binary information "1" and "0", respectively, the ferromagneticthin films can be employed as high density magnetic recording media.Those of such ferromagnetic thin films, which have a large coercive force at room temperature and a Curie temperature relatively close to room temperature, permit recording of information by forming inverted magnetic domains at arbitrary positions by a light beam through utilization of the Curie temperature or magnetic compensation temperature; so they are generally used as beam addressablefiles.
The conventionally know ferromagnetic thin films, which have an easy axis of magnetization in the direction perpendicularto the film surface and can be used as the beam addressable files, are polycrystalline metallic thin films represented by MnBi, amorphous metallic thin films as of Gd-Co, Gd-Fe, Tb-Fe, Dy-Fe, etc., and compound single crystal thin films represented by GIG: however, they have such merits and demerits as described below.The polycrystalline metallic thin films represented by MnBi which utilize the Curie temperature for effecting a writing operation have excellent characteristic of magnetic recording media,suchthattheyhavea large coerciveforce of several kilo-oersteds at room temperature, but have defective characteristic such that they call for a large amount of energyforthe writing operation because of their high Curie temperature (Tc = 360 C in the case of
MnBi).Moreover, since polycrystalline metals are used, these thin films must be formed to have a stoichiometric composition, which introducestech- nical difficulties in theirfabrication. The amorphous metallicthin films which effect a writing operation through utilization ofthe megnetic compensation point, such as Gd-Co and Gd-Fe thin films, possess such advantages that they can be produced on a arbitrary substrate since they are amorphous, and that their magnetic compensation temperature can freely be controlled to some extent by the addition of a small amount of impurity, butthesethinfilms have such shortcoming that their coercive forces at room temperature are small (300to 500 Oe), resulting recorded information being unstable.In addition, it is also necessary, for the fabrication of thin films of such a small coercive force, to control their composition within about 1 atom%. Accordingly, the amorphous metal thin films are not easy in terms of manufacture as well.
Furthermore, the compound single crystal thin films, represented by GIG, have serious defects of very high manufacturing costs as compared with the other thin films.
In contrast thereto, amorphous alloy thin films of
TbFe, DyFe, or the like containing 15 to 35 atom% of
Tb, Dy, or lilts rare earth element, which have been proposed as new magnetic thin film recording media free from such defects as describing above, possess thefollowing advantages: (1 ) They have an easy axis of magnetization in the direction perpendicularto the film surface and have a large coercive force of several kilooersteds at room temperature, and hence permit high density recording of information and the recorded information is very stably maintained.
(2) They have a large coercive force, and hence permit a writing operation therein of a magnetic domain of desired shape.
(3) Since they have a large coercive force in a wide range of composition and exhibitexcellent characteristics as recording media in a wide range ofcomposi- tion as well, they need not be severely restricted in composition and can be fabricated with ease and with a good yield.
(4) Since the Curie temperature is as low as 1 200C in case of TbFe and 60 C in case of DyFe, the magnetic recording operation utilizing the Curie temperature can be achieved with a very small power In recent years a high-output semiconductor laser has come into use for recording on one hand. On the other hand, there has been proposed, with a view to full utilization ofthe enhanced power for recording,
GdTbFe orTbFeCo recording media in which Gd orCo is added to TbFe to raise the Curie temperature and improve the magnetic Kerr rotation angle which affects the reproducing characteristic. Viewed from recording and reproducing characteristics alone, these recording media have already attained a high abiliity sufficient for practical use.
However, the rare earth elements and iron which constitute these amorphous alloythinfilms are highly oxidizable and readily combine with oxygen in the air to form oxides. Even a partial formation of an oxide in thethinfilm will markedlyimpairthe property, which is importanttothe magneto-optical memory, such as the magnetic Kerr rotation angle, reflectivity, Curie temperature, saturated magnetization, or coercive force of the film; so the oxidation will pose a serious problem when the amorphous alloy thin film is used as a magneto-optical recording medium. In conventional art, however, any effective idea for suppress oxidation of the amorphous alloy thin film has not yet been proposed.
An object of the present invention is to solve the problem of oxidation in the conventional magnetooptical recording media, and to provide a magnetooptical recording medium whose oxidation resistance and corrosion resistance are enhanced without im
pairing its recording and reproducing characteristics, thereby providing for its improved long-term stability.
According to the present invention, a magnetooptical recording medium is proposed which comprises an amorphous R-TM system alloy (where R is at least one rare earth element and TM at least one 3d transition metal) and has an easy axis of magnetization in a direction perpendiculartothefilm surface, wherein at least one noble metal element is added within a range in which a Kerr rotation angle can be obtained for reproducing information recorded in the recording medium, wherebythe progress of oxidation and corrosion ofthe recording medium can be suppressed for a long period oftime.
Embodiments ofthe present invention will now be described below byway of example in comparison with conventional art and with reference to the accompanying drawings, in which:
Figs. 1 A and 1 B are longitudinal sectional views illustrating structures of known magneto-optical recording media:
Fig. 2 is a graph showing relations between the content of a noble metal element and the Kerr rotation angle 6k in embodiments ofthe present invention; Fig. 3 is a series of rough sketches of reference photographs showing the oxidation preventing effect ofthe noble metal elements, and
Fig. 4is a graph showing corrosion characteristics of a conventional TbFe layer and a TbFePt layer of an embodiment of the present invention, in a NaCI solution.
To make differences between the prior art andthe present invention clear, examples of prior arts will be described first.
Aconventional method employed for preventing the oxidation is to adopt a structure in which a magnetic layer 2 is formed on a substrate 1 and a dielectricthinfilm as of SiO2 is deposited as a protective film 3 on the magnetic layer, as shown in
Fig. 1A, orthe magnetic layer2 is sandwiched between protective films 3, as shown in Fig. 1 B, thereby preventing the magnetic Iayer2from direct exposure to air. It is renown thatthis method will appreciably suppress oxidation ofthefilm in a short period oftime. Since it is considered quite probable, however, that oxygen will pass through the protective film or films 3 to reach the magnetic layer 2 in the long run, it is quite doubtful if the magnetic layer 2 could be protected from oxidation in 5,10 or more years only with this method.Accordingly, it is necessary, for attaining the long-term stability of the recording medium, to enhance the oxidation resistance ofthe magnetic layer 2 itself and a solution to this problem is now strongly demanded, but the prior art does not offer any solution.
Details ofthe present invention for solving the above problem will now be described.
A feature of the present invention resides in a thin film of an amorphous alloy which has an easy axis of magnetization in a direction perpendicularto the film surface, has the Curie temperature Tc in the range of from 100 to 250 C, and has a composition expressed bythefollowing general equation: (RxTMi.x)i.yAy ........................................ (1)
(where 0.15 s x s 0.35)
In the above R is a rare earth element, TM is a 3d transition metal element, and A is a noble metal element for increasing the oxidation resistance of the recording medium. Typically, Gd,Tb, Dy, etc. can be used as the R; Fe, Co, Ni, etc. as the TM; and Pt, Au, Ag,
Ru, Pd, Os, Ir, etc. belonging to the families VIII and Ib as the A.In the composition (1 ) each ofthe R,TM and A need not always be a single element but may also be a combination oftwo or more elements. An example of the composition in which they are each a combination of two elements is {(Gd,Tb)x(Fe,Co) x}, y(Pt,Au)y.
Next, a description will be given of the values of x and yin the composition (1). In orderto provide a sufficient magnetic anisotropy so thatthethin film of the amorphous alloy ofthe composition (1) is magnetized in the direction perpendiculartothefilm surface, the thin film must be made amorphous. This requirement can be fulfilled byforming the thin film, through a sputtering or vacuum evaporation process, on a substrate held below room temperature. To ensure the magnetization of the thin film in the direction perpendicular to the film surface and to provide thethin film with a sufficient coercive force at room termperature, it is necessary to selectthevalue of the above-mentioned range.Next,thevalueof Next, the value of y will be described in connection with TbFePt, TbFeAy, and TbFeAg. When changing the rate of Pt atoms in the range of 0 to 10 atom%,the Kerr rotation angle 8k will undergo such variations as shown in Fig. 2. In the magneto-optical recording medium the Kerr rotation angle 6i is of particular importanceto its reproducing characteristic. According to recenttechniques, when taking into account its SN ratio and so on, a Kerr rotation angle 6k of about 0.15 deg. will be sufficient forthe reproducing operation.
Therefore, the noble metal contentforsatisfying such requirementthatthe Kerr rotation angle 6k be 0.15 deg. orhigheris 10% orso, as will be evidentfrom Fig. 2. In a TbFeCo or GdTbFe thin film added with Co or Gd forthe purpose of increasing the Kerr rotation angle, since the Kerr rotation angle is usually in the range of 0.2 to 0.3, the Kerr rotation angle (approximately 0.15 deg.) necessary forthe reproducing operation can be obtained even ifthe noble metal content is increased to 20%. For example, when the
Co content oftheTbGeCo film is 10%, even if Pt is added 20%,the Kerr rotation angle 6 is 0.22 deg.
Accordingly, the oxidation resistance can befurther improved by increasing the content of the noble metal element, so long as it is added within a range in which the Kerr rotation angle 6k needed forthe reproducing operation can be obtained.
Fig. 3 shows the states of oxidation of magnetic films constituted principally of TbFe and individually added with various noble metal elements. These states of oxidation are those of magneticfilms of the present invention formed on substrates and allowed to stand for 30 hours at a temperature of 45"C and at a humidity of 90%. In Fig. 3 the white areas indicate the oxidized portions ofthe magnetic films. It will be seen that an increase in the content of the noble metal
element appreciably suppresses the oxidation.
Furthermore, the present inventor's experimental
results have revealed that Pt, Au, Ag, etc. which are
noble metal elements produce the effect of suppres sing corrosion of the magneticfilm in a solution as well, Fig. 4 shows the results of measuring, in their permeability,the progress of corrosion of a conven tonal TieFe- magneticfilm#- and the TbFePt magnetic film ofthe present invention immersed in a 2N (2
Normality) NaCI solution. It will appearfrom Fig. 4 that the permeability ofthe magneticfilm with added Pt remains almost unchanged, indicating substantially complete suppression of its corrosion.
Thus deterioration ofthe magnetic film can be avoided, ensuring significant reduction of its aging.
While in Fig. 4, Pt has been exemplified as the oxidation resisting element, other noble metal elements such as Au, Ag etc. will also produce the same effects as those obtainable with Pt.
As described above, the present invention heightens, by the addition of a noble metal element, the oxidation resistance and corrosion resistance ofthe existing magneto-optical recording medium without impairing its excellent recording and reproducing characteristics, thus offering a recording medium which is stable for a long period of time.
Although the present invention has been described mainly in connection with the TbFefilm, the same results are equally obtainable with, forexample, GdTbFe, TbFeCo and like media ofthe R-TM systems.
Moreover, it will be moreeffectiveto coverthe magneticlayerwith a protective film ortosandwich it between protective films.
As described above, the magneto-optical recording medium ofthe present invention has signifcantly improved oxidation resistance as compared with the well-known TbFe, DyFe and other amorphous alloy thin films while atthe same time retaining their features such as an easy axis of magnetization in the direction perpendicularto the film surface, a large coercive force at room temperature, the Curie temper- ature closeto room temperature, and easy fabrication.
Accordingly, by using the recording medium ofthe present invention as a storage medium of a magnetooptical memory which effects a writing operation therein by means of a light beam and readout th rough utilzation ofthe magnetic Kerr effect, such as a so-called beam addressablefile memory, it is impossible to implement a memory device which is extremely high in recording density, large in SN ratio, and very stable for a long period oftime. It is a matter of course that the writing operation can be effected not only be a light beam but a Iso by any means of supply energy necessary for producing an inverted magnetic domain, such as a needle-type magnetic head, a heat pen and an electron beam.
Claims (5)
1. A magneto-optical recording medium which comprises an amorphous R-TM system alloy (where R is at least one rare earth element and TM at least one 3d transition metal) and has an easy axis of magnetization in a direction perpendiculartothefilm surface, wherein at least one noble metal element is added within a range in which a Kerr rotation angle can be obtained for reproducing information recorded in the recording medium, whereby the progress of oxidation and corrosion of the recording medium can be suppressedfora long period oftime.
2. A magneto-optical recording medium according to claiim 1, wherein said noble metal element is selectedfrom a group including Pt, Au, Ag, Ru, Rh, Pd, OsandlroflbandVlllfamilies.
3. A magneto-optical recording medium according to claim 1 or2,wherein said Kerr rotation angle is morethanavalueof0.l5deg.
4. A magneto-optical recording medium according to any preceding claim,wherein the noble metal content is less than 10%.
5. A magneto-optical recording medium substantially as herein described with reference to Figure 2 with or without reference to Figure 3 and/or 4.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9668785A JPS61255546A (en) | 1985-05-09 | 1985-05-09 | Photomagnetic recording medium |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8610978D0 GB8610978D0 (en) | 1986-06-11 |
| GB2175160A true GB2175160A (en) | 1986-11-19 |
| GB2175160B GB2175160B (en) | 1989-08-16 |
Family
ID=14171702
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08610978A Granted GB2175160A (en) | 1985-05-09 | 1986-05-06 | Magneto-optical recording medium |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS61255546A (en) |
| GB (1) | GB2175160A (en) |
| NL (1) | NL8601069A (en) |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0293797A2 (en) * | 1987-06-02 | 1988-12-07 | Hoechst Aktiengesellschaft | Magneto-optical recording disk |
| EP0310680A1 (en) * | 1987-04-17 | 1989-04-12 | Mitsui Petrochemical Industries, Ltd. | Photomagnetic recording membrane |
| EP0316615A1 (en) * | 1987-10-30 | 1989-05-24 | Hoechst Aktiengesellschaft | Amorphous magnetooptical recording material |
| GB2211861A (en) * | 1987-10-30 | 1989-07-12 | Pioneer Electronic Corp | Memory medium and method for producing said medium |
| EP0331737A1 (en) * | 1987-08-08 | 1989-09-13 | Mitsui Petrochemical Industries, Ltd. | Photomagnetic recording medium |
| EP0383216A2 (en) * | 1989-02-16 | 1990-08-22 | Hoechst Aktiengesellschaft | Magneto-optical layer and process for its manufacture |
| US5019462A (en) * | 1988-02-02 | 1991-05-28 | Basf Aktiengesellschaft | Sheet-like, multilayer magneto-optical recording material |
| US5707728A (en) * | 1991-11-14 | 1998-01-13 | Ticona Gmbh | Magneto-optical recording medium |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61265756A (en) * | 1985-05-20 | 1986-11-25 | Pioneer Electronic Corp | Photomagnetic recording medium |
| US5265073A (en) * | 1987-03-13 | 1993-11-23 | Canon Kabushiki Kaisha | Overwritable magneto-optical recording medium having two-layer magnetic films wherein one of the films contains one or more of Cu, Ag, Ti, Mn, B, Pt, Si, Ge, Cr and Al, and a method of recording on the same |
| JPH0254448A (en) * | 1988-08-18 | 1990-02-23 | Nec Corp | Magneto-optical disk medium |
| MY104246A (en) * | 1988-10-20 | 1994-02-28 | Mitsui Chemicals Inc | Magnetooptical recording media. |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61117749A (en) * | 1984-11-13 | 1986-06-05 | Seiko Instr & Electronics Ltd | Photomagnetic recording medium |
-
1985
- 1985-05-09 JP JP9668785A patent/JPS61255546A/en active Pending
-
1986
- 1986-04-25 NL NL8601069A patent/NL8601069A/en not_active Application Discontinuation
- 1986-05-06 GB GB08610978A patent/GB2175160A/en active Granted
Cited By (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0310680A4 (en) * | 1987-04-17 | 1990-10-03 | Mitsui Petrochemical Industries, Ltd. | Photomagnetic recording membrane |
| EP0310680A1 (en) * | 1987-04-17 | 1989-04-12 | Mitsui Petrochemical Industries, Ltd. | Photomagnetic recording membrane |
| EP0293797A2 (en) * | 1987-06-02 | 1988-12-07 | Hoechst Aktiengesellschaft | Magneto-optical recording disk |
| EP0293797A3 (en) * | 1987-06-02 | 1990-12-05 | Kerdix, Inc. | Magneto-optical recording disk |
| EP0331737B1 (en) * | 1987-08-08 | 1996-06-05 | Mitsui Petrochemical Industries, Ltd. | Photomagnetic recording medium |
| EP0331737A1 (en) * | 1987-08-08 | 1989-09-13 | Mitsui Petrochemical Industries, Ltd. | Photomagnetic recording medium |
| GB2211861A (en) * | 1987-10-30 | 1989-07-12 | Pioneer Electronic Corp | Memory medium and method for producing said medium |
| GB2211861B (en) * | 1987-10-30 | 1992-01-29 | Pioneer Electronic Corp | Photomagnetic memory medium having a non-columnar structure |
| US5135819A (en) * | 1987-10-30 | 1992-08-04 | Pioneer Electronic Corporation | Photomagnetic memory medium having a non-columnar structure |
| EP0316615A1 (en) * | 1987-10-30 | 1989-05-24 | Hoechst Aktiengesellschaft | Amorphous magnetooptical recording material |
| US5019462A (en) * | 1988-02-02 | 1991-05-28 | Basf Aktiengesellschaft | Sheet-like, multilayer magneto-optical recording material |
| EP0383216A2 (en) * | 1989-02-16 | 1990-08-22 | Hoechst Aktiengesellschaft | Magneto-optical layer and process for its manufacture |
| EP0383216A3 (en) * | 1989-02-16 | 1991-09-11 | Hoechst Aktiengesellschaft | Magneto-optical layer and process for its manufacture |
| US5707728A (en) * | 1991-11-14 | 1998-01-13 | Ticona Gmbh | Magneto-optical recording medium |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8610978D0 (en) | 1986-06-11 |
| NL8601069A (en) | 1986-12-01 |
| GB2175160B (en) | 1989-08-16 |
| JPS61255546A (en) | 1986-11-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19990506 |