# US 5,702,793 A · Magneto-optical recording medium, disk and method of manufacturing the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,702,793 A - Document ID: US5702793A - Status: Granted - Kind: A - Application number: 08/201,385 - Filed: 1994-02-24 - Granted: 1997-12-30 - Earliest claimed: 1993-02-25 - Assignees: Nippon Steel Corporation - Inventors: Kenji Shimokawa; Hitoshi Dohnomae; Toshio Mukai; Kengo Shimanoe - Web page: https://patentgrep.com/patent/US5702793A ## 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 10/3209: {Exchange coupling of garnet multilayers} - Y10S 428/90: Magnetic feature - Y10T 428/265: 1 mil or less - 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 high density magneto-optical recording medium utilizing a polycrystalline garnet two-layer film. The film thickness of an under layer of the garnet polycrystal on a glass substrate is made 100 nm or less, and a crystal grain diameter of a recording layer formed thereon is made 0.1 .mu.m or less. Furthermore, the under layer is demagnetized at room temperature. With this, a bit having a regular shape can be written, thus reducing medium noise by a large margin. ## Claims ### Claim 1 A magneto-optical recording medium comprising: a substrate; a first layer of polycrystalline garnet film formed on said substrate, for serving as an under layer, said first layer having a Curie temperature lower than a predetermined temperature, said predetermined temperature being within a range from -10.degree. C. to +50.degree. C., so that said first layer has a non-magnetic characteristic at said predetermined temperature; and a second layer of polycrystalline garnet film, formed on said first layer, for recording information, said second layer having a Curie temperature higher than said predetermined temperature so that said second layer has a magnetic characteristic at said predetermined temperature. ### Claim 2 (depends on 1) A magneto-optical recording disk comprising the magneto-optical recording medium according to claim 1 as a component of said disk. ### Claim 3 (depends on 1) A magneto-optical recording medium according to claim 1, wherein: said second layer of polycrystalline garnet film has a crystal grain diameter of 0.1 .mu.m or less; and each of said first and second layers of polycrystalline garnet film is represented by a composition of Bi.sub.x R.sub.3-x M.sub.y Fe.sub.5-y O.sub.12 where R represents at least one rare earth element, M represents at least one element selected from the group consisting of aluminum, gallium and indium, 0.ltoreq.x.ltoreq.3 and 0.ltoreq.y.ltoreq.5. ### Claim 4 (depends on 1) A magneto-optical recording medium according to claim 1, wherein: said first and second layers of polycrystalline garnet film have crystal lattice constants different from each other by .+-.0.3% or more; and each of said first and second layers of polycrystalline garnet film is represented by a composition Bi.sub.x R.sub.3-x M.sub.y Fe.sub.5-y O.sub.12 where R represents at least one rare earth element, M represents at least one element selected from the group consisting of aluminum, gallium and indium, 0.ltoreq.x.ltoreq.3 and 0.ltoreq.y.ltoreq.5. ### Claim 5 (depends on 1) The magneto-optical recording medium of claim 1 wherein said predetermined temperature is within the range of +20.degree. C. to +50.degree. C. ### Claim 6 (depends on 1) The magneto-optical recording medium of claim 1 wherein said predetermined temperature is +20.degree. C. ### Claim 7 (depends on 3) The magneto-optical recording medium according to claim 3 wherein said rare earth element includes yttrium. ### Claim 8 (depends on 3) A magneto-optical recording disk, comprising the magneto-optical recording medium according to claim 3 as a component of said disk. ### Claim 9 (depends on 3) A magneto-optical recording medium according to claim 3, wherein said second layer of polycrystalline garnet film further includes Cu in an amount of 5 atomic weight percent or less based upon the total of Bi, R, M, Fe and Cu in the composition of said second layer. ### Claim 10 (depends on 4) The magneto-optical recording medium according to claim 4 wherein said rare earth element includes yttrium. ### Claim 11 (depends on 4) A magneto-optical recording disk, comprising the magneto-optical recording medium according to claim 4 as a component of said disk. ### Claim 12 (depends on 4) A magneto-optical recording medium according to claim 4, wherein said second layer of polycrystalline garnet film further includes Cu in an amount of 5 atomic weight percent or less based upon the total of Bi, R, M, Fe and Cu in the composition of said second layer. ### Claim 13 (depends on 9) A magneto-optical recording disk, comprising the magneto-optical recording medium according to claim 9 as a component of said disk. ### Claim 14 (depends on 12) A magneto-optical recording disk, comprising the magneto-optical recording medium according to claim 12 as a component of said disk. ### Claim 15 A method of manufacturing a magneto-optical recording medium, comprising the steps of: forming on a substrate a first layer of polycrystalline garnet film for serving as an under layer such that a thickness of said first layer becomes 100 nm or less; applying reverse sputtering processing to a surface of said first layer of polycrystalline garnet film; and forming on said first layer a second layer of polycrystalline garnet film for recording information such that a crystal grain diameter of said second layer becomes 0.1 .mu.m or less and crystal lattice constants of said first and second layers becomes different from each other by .+-.0.3% or more. ### Claim 16 (depends on 15) A method of manufacturing a magneto-optical recording medium according to claim 15, wherein each of said first and second layers of polycrystalline garnet film is represented by a composition Bi.sub.x R.sub.3-x M.sub.y Fe.sub.5-y O.sub.12 where R represents at least one rare earth element, M represents at least one element selected from the group consisting of aluminum, gallium and indium, 0.ltoreq.x.ltoreq.3 and 0.ltoreq.y.ltoreq.5. ### Claim 17 (depends on 15) A method of manufacturing a magneto-optical recording medium according to claim 15, wherein said second layer of polycrystalline garnet film includes Cu in an amount of 5 atomic weight percent or less based upon the total of Bi, R, M, Fe and Cu in the composition of said second layer. ### Claim 18 (depends on 16) The method of claim 16, wherein said rare earth element includes yttrium. ### Claim 19 A method of manufacturing a magneto-optical recording medium, comprising the steps of: forming on a substrate a first layer of polycrystalline garnet film for serving as an under layer such that a thickness of said first layer becomes 100 nm or less, said first layer having a Curie temperature lower than a predetermined temperature, said predetermined temperature being within a range from -10.degree. C. to +50.degree. C., so that said first layer has a non-magnetic characteristic at said predetermined temperature; applying reverse sputtering processing to a surface of said first layer of polycrystalline garnet film; and forming on said first layer a second layer of polycrystalline garnet film for recording information such that a crystal grain diameter of said second layer becomes 0.1 .mu.m or less and crystal lattice constants of said first and second layers become different from each other by .+-.0.3% or more, said second layer having a Curie temperature higher than said predetermined temperature so that said second layer has a magnetic characteristic at said predetermined temperature. ### Claim 20 (depends on 19) A method of manufacturing a magneto-optical recording medium according to claim 19, wherein each of said first and second layers of polycrystalline garnet film is represented by a composition of Bi.sub.x R.sub.3-x M.sub.y Fe.sub.5-y O.sub.12 where R represents at least one rare earth element, M represents at least one element selected from the group consisting of aluminum, gallium and indium, 0.ltoreq.x.ltoreq.3 and 0.ltoreq.y.ltoreq.5. ### Claim 21 (depends on 19) The method of claim 19 wherein said predetermined temperature is within the range from +20.degree. C. to +50.degree. C. ### Claim 22 (depends on 19) The method of claim 19 wherein said predetermined temperature is +20.degree. C. ### Claim 23 (depends on 20) The method of claim 20 wherein said rare earth element includes yttrium. ### Claim 24 (depends on 20) A method of manufacturing a magneto-optical recording medium according to claim 20, wherein said second layer of polycrystalline garnet fill further includes Cu in an amount of 5 atomic weight percent or less based upon the total of Bi, R, M, Fe and Cu in the composition of said second layer.