# US 5,702,830 A · Magneto-optical recording materials system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,702,830 A - Document ID: US5702830A - Status: Granted - Kind: A - Application number: 08/367,192 - Filed: 1995-01-13 - Granted: 1997-12-30 - Earliest claimed: 1992-07-28 - Assignees: Johnson Matthey Public Limited Company - Inventors: Joseph Miller; Derek P. A. Pearson; Philip G. Pitcher - Web page: https://patentgrep.com/patent/US5702830A ## CPC - G11B 11/10582: {Record carriers characterised by the selection of the material or by the structure or form} - B82Y 25/00: Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance - G11B 11/10586: {characterised by the selection of the material} - H01F 10/325: {the spacer being noble metal} - H01F 10/3281: {only by use of asymmetry of the magnetic film pair itself, i.e. so-called pseudospin valve [PSV] structure, e.g. NiFe/Cu/Co} - G11B 11/10521: {using a single light spot} - Y10S 428/90: Magnetic feature - Y10S 428/928: Magnetic property - Y10T 428/12465: having magnetic properties, or preformed fiber orientation coordinate with shape - Y10T 428/12632: Four or more distinct components with alternate recurrence of each type component - Y10T 428/12861: Group VIII or IB metal-base component - Y10T 428/12875: Platinum group metal-base component - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) - B82Y: SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES - H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES - Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract A materials system in which exchange coupling is achievable has the potential for allowing direct overwriting of data and comprises at least two multilayer films of platinum and cobalt with independently controlled coercivity and Curie temperatures. ## Claims ### Claim 1 A magneto-optical recording medium comprising, a composite multilayer laminate system wherein multilayer films of platinum and cobalt are exchange coupled and have perpendicular magnetic anisotropy, such system having the potential to allow direct overwriting of data, said system comprising a substrate material and at least two multilayer films comprising a platinum layer and a cobalt layer, and wherein there is provided at a multilayer interface a spacer comprising one platinum layer of one or both multilayers or a separately-deposited material, one of said multilayer films having a room temperature coercivity (H.sub.c) of 2 to 15 kOe and a low Curie temperature (T.sub.c) of 100.degree. C. to 400.degree. C. and known as the memory layer and one of said multilayer films having a low room temperature coercivity of 0.5 to 10 kOe and a high Curie temperature of 175.degree. C. to 500.degree. C. and known as the reference layer, the difference in coercivity and Curie temperature between the two multilayer films being sufficient to permit a direct overwriting process. ### Claim 2 (depends on 1) A magneto-optical recording medium according to claim 1, wherein the H.sub.c (memory layer) minus H.sub.c (reference layer) is greater than, .sigma..sub.w /(2M.sub.s (memory layer) h(memory layer))+.sigma..sub.w,/(2M.sub.s (reference layer) h(reference layer)); wherein .sigma..sub.w is the exchange coupling strength, M.sub.s is the saturation magnetization and h is the multilayer thickness. ### Claim 3 (depends on 2) A magneto-optical recording medium according to claim 2, wherein H.sub.c of the memory layer is 3-10 kOe. ### Claim 4 (depends on 3) A magneto-optical recording medium according to claim 3, wherein H.sub.c of the memory layer is 3-8 kOe. ### Claim 5 (depends on 2) A magneto-optical recording medium according to claim 2, wherein H.sub.c of the reference layer is 1-6 kOe. ### Claim 6 (depends on 5) A magneto-optical recording medium according to claim 5, wherein H.sub.c of the reference layer is 1.5-4 kOe. ### Claim 7 (depends on 1) A magneto-optical recording medium according to claim 1, wherein T.sub.c of the reference layer is greater than T.sub.c of the memory layer by 75.degree. C. to 100.degree. C. ### Claim 8 (depends on 1) A magneto-optical recording medium according to claim 1, wherein T.sub.c of the reference layer is greater than T.sub.c of the memory layer by more than 100.degree. C. ### Claim 9 (depends on 1) A magneto-optical recording medium according to claim 1, wherein T.sub.c of the memory layer is 150.degree. C. to 300.degree. C. ### Claim 10 (depends on 9) A magneto-optical recording medium according to claim 9, wherein T.sub.c of the memory layer is 150.degree. C. to 200.degree. C. ### Claim 11 (depends on 1) A magneto-optical recording medium according to claim 1, wherein T.sub.c of the reference layer is 250.degree. C. to 500.degree. C. ### Claim 12 (depends on 11) A magneto-optical recording medium according to claim 11, wherein T.sub.c of the reference layer is 200.degree. C to 400.degree. C. ### Claim 13 (depends on 1) A magneto-optical recording medium according to claim 1, wherein the spacer at a multilayer interface comprises a platinum layer of one or both multilayers. ### Claim 14 (depends on 1) A magneto-optical recording medium according to claim 1, wherein the spacer at a multilayer interface comprises separately-deposited material. ### Claim 15 (depends on 14) A magneto-optical recording medium according to claim 14, wherein the separately-deposited material is of platinum or other metal or a dielectric material or a combination of materials. ### Claim 16 (depends on 15) A magneto-optical recording medium according to claim 15, wherein the separately-deposited material is of platinum. ### Claim 17 (depends on 13) A magneto-optical recording medium according to claim 13, wherein the spacer is of average thickness up to 50 .ANG.. ### Claim 18 (depends on 1) A magneto-optical recording medium according to claim 1, wherein the spacer is of average thickness of sub-monolayer thickness to 25 .ANG.. ### Claim 19 (depends on 1) A magneto-optical recording medium according to claim 1, wherein there is provided an interlayer of platinum or other metal or dielectric material or combination of material between the substrate and the adjacent platinum/cobalt multilayer film. ### Claim 20 (depends on 19) A magneto-optical recording medium according to claim 19, wherein the interlayer is of platinum. ### Claim 21 (depends on 19) A magneto-optical recording medium according to claim 19, wherein the interlayer is of average thickness up to 50 .ANG.. ### Claim 22 (depends on 21) A magneto-optical recording medium according to claim 21, wherein the interlayer is of average thickness of sub-monolayer thickness to 20 .ANG.. ### Claim 23 (depends on 1) A composite multilayer laminate system according to claim 1, wherein each cobalt layer has a thickness of 2-5 .ANG.. ### Claim 24 (depends on 1) A magneto-optical recording medium according to claim 1, wherein each platinum layer has a thickness of 3-20 .ANG.. ### Claim 25 (depends on 1) A magneto-optical recording medium according to claim 1, which comprises 2-15 periods of the platinum/cobalt multilayer films. ### Claim 26 (depends on 1) A magneto-optical recording medium according to claim 1, wherein the medium is in the form of a disc. ### Claim 27 (depends on 1) A process for making a magneto-optical recording medium according to claim 1, comprising providing a spacer of average thickness up to 50 .ANG. between two multilayers of platinum and cobalt. ### Claim 28 (depends on 27) A process according to claim 27, wherein the spacer is subject to hyperthermal processing. ### Claim 29 (depends on 14) A magneto-optical recording medium according to claim 14, wherein the spacer is of average thickness up to 50 .ANG..