# US 5,707,727 A · Magneto-optical recording medium > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,707,727 A - Document ID: US5707727A - Status: Granted - Kind: A - Application number: 08/395,165 - Filed: 1995-02-27 - Granted: 1998-01-13 - Earliest claimed: 1991-04-17 - Assignees: Sharp Kabushiki Kaisha - Inventors: Akira Takahashi; Yoshiteru Murakami; Junsaku Nakajima; Kenji Ohta; Junichiro Nakayama; Hiroyuki Katayama; Michinobu Mieda - Web page: https://patentgrep.com/patent/US5707727A ## CPC - G11B 11/10593: {for improving read-out properties, e.g. polarisation of light} - G11B 11/10506: {by modulating only the light beam of the transducer} - G11B 11/10515: {Reproducing (compensating pit shift G11B11/1053)} - G11B 11/10517: {Overwriting or erasing (G11B11/10526 takes precedence)} - G11B 11/10586: {characterised by the selection of the material} - Y10S 428/90: Magnetic feature - Y10T 428/26: Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension - 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) - Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract A magneto-optical recording medium has a recording layer whereon information is magneto-optically recorded. A readout layer is provided on the recording layer. The readout layer has a compensating temperature that is located between room temperature and the Curie temperature. In the readout layer, upon an application of a light beam, the in-plane magnetization occurs at room temperature and a transition from the in-plane magnetization to vertical magnetization occurs as the temperature of the irradiated area of the readout layer rises above a predetermined temperature. By employing this magneto-optical recording medium, with an application of a light beam that is intensity modulated into two levels, only a spot having a temperature not less than a predetermined temperature is involved in the reproduction; therefore, a recorded bit with a size smaller than the diameter of the light beam can be reproduced, thereby greatly increasing the recording density. Further, the level of the reproduced signals is increased, and crosstalk from the adjoining tracks is reduced; thus, information recording and overwriting can be conducted more easily. ## Claims ### Claim 1 A magneto-optical recording medium comprising: a recording layer wherein information is magneto-optically recorded; and a readout layer, consisting essentially of an alloy of a rare-earth metal and a transition metal, having a compensation temperature higher than room temperature, wherein in-plane magnetization inherently occurs throughout said layer at room temperature, and upon irradiation of a local area of said readout layer by application of a laser light beam having a non-uniform intensity distribution, a transition from the in-plane magnetization to vertical magnetization occurs in a portion of the local area as the temperature of the portion of the local area of the readout layer rises above a predetermined temperature, the portion being smaller than a diameter of the irradiating light beam, and wherein areas of said readout layer, other than said portion, maintain said in-plane magnetization. ### Claim 2 (depends on 1) The magneto-optical recording medium as set forth in claim 1, wherein the readout layer is constituted of a thin film of rare-earth-transition-metal alloy, a content of the rare-earth metal being greater in comparison with a compensating composition at room temperature whereat magnetic moments of the rare-earth metal and the transition-metal balance each other, the readout layer exhibiting in-plane magnetization at room temperature without showing vertical magnetization and, as temperature rises, the magnetic moment of the transition metal .becoming relatively greater until it balances the magnetic moment of the rare-earth metal, thereby providing vertical magnetization as a whole. ### Claim 3 (depends on 2) The magneto-optical recording medium as set forth in claim 2, wherein the transition from the in-plane magnetization to the vertical magnetization occurs substantially at 100.degree. C. ### Claim 4 (depends on 2) The magneto-optical recording medium as set forth in claim 2, wherein the transition from the in-plane magnetization to the vertical magnetization occurs substantially at 70.degree. C. ### Claim 5 (depends on 1) The magneto-optical recording medium as set forth in claim 1, wherein the readout layer is constituted of Gd.sub.0.28 (Fe.sub.0.8 Co.sub.0.2).sub.0.72 whose Curie temperature positions between 300.degree. C. and 400.degree. C. ### Claim 6 (depends on 5) The magneto-optical recording medium as set forth in claim 5, wherein the recording layer is constituted of Dy.sub.0.23 (Fe.sub.0.82 Co.sub.0.18).sub.0.77 whose Curie temperature positions between 150.degree. C. and 250.degree. C. ### Claim 7 (depends on 6) The magneto-optical recording medium as set forth in claim 6, wherein the readout layer has a thickness of 50 nm while the recording layer has a thickness of 20 nm. ### Claim 8 (depends on 1) The magneto-optical recording medium as set forth in claim 1, wherein the readout layer is a thin film of a rare-earth-transition-metal alloy whose magnetization directions substantially lie in-plane at room temperature. ### Claim 9 (depends on 8) The magneto-optical recording medium as set forth in claim 8, wherein the readout layer is constituted of Dy.sub.0.3 (Fe.sub.0.7 Co.sub.0.3).sub.0.7. ### Claim 10 (depends on 1) The magneto-optical recording medium as set forth in claim 1, further comprising a reflective film for enhancing the magneto-optical effect. ### Claim 11 (depends on 10) The magneto-optical recording medium as set forth in claim 10, wherein the readout layer is constituted of a thin film of rare-earth-transition-metal alloy, a content of the rare-earth metal being greater in comparison with a compensating composition at room temperature whereat magnetic moments of the rare-earth metal and the transition-metal balance each other, the readout layer exhibiting in-plane magnetization at room temperature without showing vertical magnetization and, as temperature rises, the magnetic moment of the transition metal becoming relatively greater until it balances the magnetic moment of the rare-earth metal, thereby providing vertical magnetization as a whole. ### Claim 12 (depends on 11) The magneto-optical recording medium as set forth in claim 11, wherein the transition from the in-plane magnetization to the vertical magnetization occurs at substantially at 70.degree. C. ### Claim 13 (depends on 10) The magneto-optical recording medium as set forth in claim 10, wherein the readout layer is constituted of Gd.sub.0.28 (Fe.sub.0.8 Co.sub.0.2).sub.0.72 whose Curie temperature positions between 300.degree. C. and 400.degree. C. ### Claim 14 (depends on 10) The magneto-optical recording medium as set forth in claim 10, wherein the recording layer is constituted of Dy.sub.0.23 (Fe.sub.0.82 Co.sub.0.18).sub.0.77 whose Curie temperature positions between 150.degree. C. and 250.degree. C. ### Claim 15 (depends on 14) The magneto-optical recording medium as set forth in claim 14, wherein the readout layer and the recording layer are respectively 15 nm thick. ### Claim 16 (depends on 10) The magneto-optical recording medium as set forth in claim 10, wherein the readout layer is a thin film of a rare-earth-transition-metal alloy whose magnetization directions substantially lie in-plane at room temperature. ### Claim 17 (depends on 10) The magneto-optical recording medium as set forth in claim 10, wherein the readout layer is constituted of Dy.sub.0.3 (Fe.sub.0.7 Co.sub.0.3).sub.0.7. ### Claim 18 (depends on 1) The magneto-optical recording medium as set forth in claim 1, wherein the readout layer is constituted of Gd.sub.0.25 Co.sub.0.75. ### Claim 19 (depends on 10) The magneto-optical recording medium as set forth in claim 10, wherein the readout layer is constituted of Gd.sub.0.25 Co.sub.0.75. ### Claim 20 (depends on 1) The magneto-optical recording medium as set forth in claim 1, wherein the readout layer is made of Gd.sub.x (Fe.sub.y Co.sub.1-y).sub.1-x, where a composition rate x is set to be within 0.20<x<0.35. ### Claim 21 (depends on 1) The magneto-optical recording medium as set forth in claim 1, wherein the compensating temperature of the readout layer is not lower than the Curie temperature of the recording layer. ### Claim 22 (depends on 1) The magneto-optical recording medium as set forth in claim 1, further comprising a cooling member provided on the recording layer. ### Claim 23 (depends on 21) The magneto-optical recording medium as set forth in claim 21, further comprising a cooling member provided on the recording layer. ### Claim 24 (depends on 21) The magneto-optical recording medium as set forth in claim 21, further comprising a reflective member provided on the recording layer. ### Claim 25 (depends on 1) The magneto-optical recording medium as set forth in claim 1, wherein the compensation temperature is between room temperature and the Curie temperature. ### Claim 26 (depends on 1) The magneto-optical recording medium as set forth in claim 1, wherein the light beam, applied to said read-out layer, has a diameter of not smaller than the smallest bit recorded on the recording layer. ### Claim 27 (depends on 1) The magneto-optical recording medium as set forth in claim 1, wherein the magnetization direction of recording layer is copied to the irradiated local area of the readout layer. ### Claim 28 A magneto-optical recording medium comprising: a transparent substrate; a first transparent dielectric member, between 10 nm and 80 nm thick, made of one of the group of AlN, SiN and AlSiN, which is formed on the transparent substrate; a readout layer, 50 nm thick, made of Gd.sub.0.28 (Fe.sub.0.8 Co.sub.0.2).sub.0.72 or Gd.sub.0.25 Co.sub.0.75, which is formed on the first transparent dielectric member; a recording layer, 20 nm thick, made of Dy.sub.0.23 (Fe.sub.0.82 Co.sub.0.18).sub.0.77, which is formed on the readout layer; and a second transparent dielectric member, 50 nm thick, made of a nitride, which is provided on the recording layer so as to protect the recording layer. ### Claim 29 A magneto-optical recording medium comprising: a transparent substrate; a first transparent dielectric member, 80 nm thick, made of one of the group of AlN, SiN and AlSiN, which is formed on the transparent substrate; a readout layer, 15 nm thick, made of one of the group of Gd.sub.0.28 (Fe.sub.0.8 Co.sub.0.2).sub.0.72, Gd.sub.0.25 Co.sub.0.75 and Dy.sub.0.3 (Fe.sub.0.7 Co.sub.0.3).sub.0.7, which is formed on the first transparent dielectric member; a recording layer, 15 nm thick, made of Dy.sub.0.23 (Fe.sub.0.82 Co.sub.0.18).sub.0.77, which is formed on the readout layer; a second transparent dielectric member, 30 nm thick, made of a nitride, which is provided on the recording layer so as to protect the recording layer; and a reflective film, 50 nm thick, provided on the second transparent dielectric member so as to enhance the magneto-optical effect. ### Claim 30 A magneto-optical recording medium comprising: a recording layer wherein information is magneto-optically recorded; and a readout layer, consisting essentially of an alloy of a rare-earth metal and a transition metal, wherein in-plane magnetization inherently occurs throughout said layer at room temperature and upon irradiation of a local area of said readout layer by application of a laser light beam, a transition from the in-plane magnetization to vertical magnetization occurs, as the temperature of the irradiated area of the readout layer rises above a predetermined temperature. ### Claim 31 (depends on 30) The magneto-optical recording medium as set forth in claim 30, wherein the laser light beam, applied to said read-out layer, has a diameter of greater than the smallest bit recorded on the recording layer. ### Claim 32 (depends on 30) The magneto-optical recording medium as set forth in claim 30, wherein the magnetization direction of said recording layer is copied to the irradiated local area of the readout layer. ### Claim 33 A recording method, for recording on a magneto-optical recording medium, while applying a recording magnetic field, the magneto-optical recording medium including a recording layer, whereon information is magneto-optically recorded, and a readout layer, consisting essentially of an alloy of a rare-earth metal and a transition metal, having a compensation temperature higher than room temperature, wherein in-plane magnetization inherently occurs throughout said layer at room temperature and wherein, upon irradiation of a local area of said readout layer by application of a laser light beam having a non-uniform intensity distribution, a transition from the in-plane magnetization to vertical magnetization occurs in a portion of the local area as the temperature of the portion of the local area of the readout layer rises above a predetermined temperature, the portion being smaller than a diameter of the irradiating light beam, and wherein areas of said readout layer, other than said portion, maintain said in-plane magnetization, the recording method comprising the steps of: applying, to the local area of the readout layer, a first light beam so that a temperature increases up to a point in the vicinity of the Curie temperature in the portion of the local area, at which temperature the coercive force of the portion is greater than that of the recording layer; and applying, to the local area, a second light beam so that the temperature of the portion of the local area of the readout layer is raised to a point within a range of not less than the temperature at which a transition from the in-plane magnetization to the vertical magnetization occurs in the portion of the local area. ### Claim 34 (depends on 33) The recording method as set forth in claim 33, wherein the first light beam has a first-pulse section and a second-pulse section, and in projecting the first light beam onto the magneto-optical recording medium, the second-pulse section has a light intensity not more than that of the first-pulse section, and is applied to said medium after a predetermined time has elapsed since the application of the first-pulse section. ### Claim 35 (depends on 33) The recording method as set forth in claim 33, wherein the first light beam has a first-pulse section and a second-pulse section, and in projecting the first light beam onto the magneto-optical recording medium, the second-pulse section has a light intensity not more than that of the first-pulse section, and is successively applied to said medium after the application of the first-pulse section. ### Claim 36 A method of reproducing data from a magneto-optical recording element having a substrate, a recording layer formed on the substrate, and a readout layer formed on the recording layer of an alloy of a rare-earth metal and a transition metal so composed that, at room temperature, said alloy exhibits inherent in-plane magnetization, comprising the steps of applying, to a local area of said readout layer, a circular laser light beam having a first diameter, thereby temporarily raising temperature of a spot, having a second diameter smaller than said first diameter, above a temperature at which a magnetic moment of said transition metal balances a magnetic moment of said rare-earth metal and causes said in-plane magnetization to disappear within said spot, permitting magnetization of a portion of said recording layer, directly adjacent to said readout layer spot, to be copied by exchange coupling force onto said spot, and detecting a direction of magnetization of said spot which has resulted from said copying. ### Claim 37 (depends on 36) The method of claim 36, wherein said applying step comprises applying a laser light beam of a duration and intensity sufficient to raise the temperature of the spot to approximately 70 degrees C. ### Claim 38 (depends on 36) The method of claim 36, wherein said detecting step comprises detecting polarization of light reflected from said spot and deducing magnetization direction from said polarization. ### Claim 39 (depends on 36) The method of claim 36, wherein said applying step comprises applying a laser light beam having a Gaussian intensity distribution. ### Claim 40 (depends on 33) The magneto-optical recording method as set forth in claim 33, wherein, in the step of applying of the second light beam, the range is neither less than the temperature at which a transition from the in-plane magnetization to the vertical magnetization occurs, nor more than the compensation temperature of the readout layer, and wherein the compensation temperature of the readout layer is between room temperature and the Curie temperature. ### Claim 41 A magneto-optical recording medium comprising: a recording layer wherein information is magneto-optically recorded, said recording layer being made of a vertical magnetization film; and a readout layer, consisting essentially of an alloy of a rare-earth metal and a transition metal, having a compensation temperature higher than room temperature, wherein in-plane magnetization inherently occurs throughout said layer at room temperature, and upon heating of a local area of said readout layer, by means which heat a first portion of said area more than a second portion, a transition from the in-plane magnetization to vertical magnetization occurs in said first portion of the local area as the temperature of the first portion of the local area of the readout layer rises above a predetermined temperature, the area of said first portion being smaller than the aggregate area of said first and second portions, and wherein areas of said readout layer, other than said first portion, maintain said in-plane magnetization. ### Claim 42 A magneto-optical recording medium comprising: a recording layer wherein information is magneto-optically recorded; and a readout layer, consisting essentially of an alloy of a rare-earth metal and a transition metal, having a compensation temperature higher than room temperature, wherein in-plane magnetization inherently occurs throughout said layer at room temperature, and upon irradiation of a local area of said readout layer by application of a laser light beam, a transition from the in-plane magnetization to vertical magnetization occurs in a portion of the local area as the temperature of the portion of the local area of the readout layer rises above a predetermined temperature, the portion being smaller than a diameter of the irradiating laser light beam, and wherein areas of said readout layer, other than said portion, maintain said in-plane magnetization, said readout layer being so arranged on said recording layer that the laser light beam is incident on said readout layer. ### Claim 43 A recording method for recording on a magneto-optical recording medium while applying a recording magnetic field, the magneto-optical recording medium including a recording layer, whereon information is magneto-optically recorded, and a readout layer having a compensation temperature higher than room temperature, wherein in-plane magnetization inherently occurs at room temperature and wherein, upon heating of a local area, a transition from the in-plane magnetization to vertical magnetization occurs as the temperature of the heated local area of the readout layer rises above a predetermined temperature, the recording method comprising the steps of: heating said local area of the magneto-optical recording medium, so that a temperature thereof rises up to a point in the vicinity of the Curie temperature of the readout layer, at which temperature the coercive force of the readout layer is greater than that of the recording layer; and further heating said local area of said recording medium, so that the temperature of the readout layer is raised to a point within a range of not less than the temperature at which a transition from the in-plane magnetization to the vertical magnetization occurs. ### Claim 44 A magneto-optical recording medium comprising: a recording layer wherein information is magneto-optically recorded; and a readout layer, consisting essentially of an alloy of a rare-earth metal and a transition metal, having a compensation temperature higher than room temperature, wherein in-plane magnetization inherently occurs throughout said layer at room temperature, and upon irradiation of a local area of said readout layer by application of a laser light beam, said medium being movable relative to said laser light beam, a transition from the in-plane magnetization to vertical magnetization occurs in a portion of the local area subjected to a sufficiently long duration of beam application as the temperature of that portion of the local area of the readout layer rises above a predetermined transition temperature, a remaining portion of the local area being subjected to an insufficiently long duration of beam application and thus staying below said predetermined transition temperature, and wherein areas of said readout layer, other than said transitioning portion, maintain said in-plane magnetization.