Stock material or miscellaneous articles – All metal or with adjacent metals – Having magnetic properties – or preformed fiber orientation...
Patent
1995-01-13
1997-12-30
Resan, Stevan A.
Stock material or miscellaneous articles
All metal or with adjacent metals
Having magnetic properties, or preformed fiber orientation...
428635, 428668, 428670, 428694TM, 428694MM, 428694EC, 428900, 428928, 369 13, G11B 566
Patent
active
057028303
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION
The present application was filed as PCT International application Ser. No. PCT/GB93/01575, international filing date Jul. 26, 1993.
FIELD OF THE INVENTION
This invention relates to a platinum/cobalt materials system for use in magneto-optical recording, and especially to a system, comprising a plurality of platinum/cobalt multilayers, which is suitable for use in direct overwrite operations with laser power modulation.
BACKGROUND OF THE INVENTION
Magneto-optical (MO) materials comprising multilayer films of platinum and cobalt have not yet reached the stage of commercial production, mostly because until recently it had seemed to be impossible to achieve the necessary characteristics in a Pt/Co multilayer. It has long been appreciated, however, that a successful Pt/Co MO material would offer a range of advantages over the dominant commercial material, amorphous rare earth transition metal (RE-TM) alloy films. European patent application, publication number 0 549 246 A2, describes a Pt/Co multilayer film materials system having necessary requirements of a MO-recording material, including sufficient room temperature coercivity, H.sub.c, perpendicular magnetic anisotropy, a square polar Kerr hysteresis loop, and a sufficient polar Kerr rotation. Once commercialised, such a Pt/Co system could become the dominant commercial product in this field. However, as aforementioned, it was thought that the necessary properties could not be achieved in a Pt/Co system, and work has continued towards improving RE-TM films.
Particularly interesting is the work which has been done towards the development of "direct overwrite" (DOW) RE-TM systems. Conventionally, when new data is written to MO films, previously-written data is completely erased prior to writing of the new data. This two-step process is time-consuming and of course a one-step process wherein no separate erasure of previously-written information is necessary would be extremely advantageous. No such product has yet been made commercially available.
One type of laser-power modulated direct overwrite RE-TM film which has been investigated typically contains at least two magneto-optic layers with separately-controlled magnetic properties; one layer, hereinafter referred to as the "memory layer", having a relatively high room temperature coercivity and a relatively low Curie temperature is used to store the written data, and the other, hereinafter referred to as the "reference layer", having a relatively low room temperature coercivity and a relatively high Curie temperature. Lin (J. Appl. Phys. 67 (9), 1 May 1990) discusses the requirements of such a bilayer. The scheme he discusses requires two permanent magnetic fields; one (H.sub.b) is used together with laser beam heating for writing domains, and the other (H.sub.ini) is used to reset the reference layer to the erased state (in which the magnetisation is in the reverse direction to the "written" state) at ambient temperature without disturbing domain walls in the memory layer. At room temperature, H.sub.c (memory layer) >H.sub.ini >H.sub.c (reference layer); H.sub.b <H.sub.ini ; H.sub.c (reference layer) >H.sub.b >H.sub.c (memory layer). Direct overwrite is accomplished by modulating the writing laser beam at high power (P.sub.H) and low power (P.sub.L) levels according to the data stream. The MO material is exposed in rotation to H.sub.ini and H.sub.b at P.sub.H or P.sub.L. At P.sub.H, wherein both layers are heated to a temperature above T.sub.c of the reference layer, H.sub.b causes domain patterns to be created in the reference layer. Subsequently, these domain patterns are copied (at what is known as "the copying temperature") to the memory layer through exchange coupling upon cooling. Exposure to H.sub.ini at ambient temperature then causes the domains in the reference layer to be erased such that the written domains are confined only to the memory layer while the reference layer is again ready for new domains to be written. At P.sub.L, wherein
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Journal of Applied Physics, vol. 67, No. 9, 1 May 1990 pp. 4409-4414, C. J. Lin `Critical assessment of the physics underlying direct overwrite in magneto-optic recording`.
Tsutsumi et al, "Direct overwrite in magneto-optic recording", Journal of Magnetism and Magnetic Materials, 118 Jan. (1993), Elsevier Science Publishers B.V., pp.231-247.
Lin, "Critical assessment of the physics underlying direct overwrite in magneto-optic recording (invited)", Journal of Applied Physics, 67 (9), 1 May 1990, American Institute of Physics, pp. 4409-4414.
Kobayashi et al, "Magnetization Process of Exchange-Coupled Ferrimagnetic Double-Layered Films", Japanese Journal of Applied Physics, vol. 20, No. 11, Nov., 1981, pp. 2089-2095.
Miller Joseph
Pearson Derek P. A.
Pitcher Philip G.
Johnson Matthey Public Limited Company
Resan Stevan A.
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