# US 7,611,783 B2 · Magnetic recording medium and magnetic recording device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,611,783 B2 - Document ID: US7611783B2 - Status: Granted - Kind: B2 - Application number: 11/374,424 - Filed: 2006-03-14 - Published: 2006-10-05 - Granted: 2009-11-03 - Earliest claimed: 2005-03-31 - Assignees: Fujitsu Limited - Inventors: Ryosaku Inamura; Isatake Kaitsu; Takuya Uzumaki - Web page: https://patentgrep.com/patent/US7611783B2 ## CPC - G11B 5/672: {having different compositions in a plurality of magnetic layers, e.g. layer compositions having differing elemental components or differing proportions of elements} - G11B 5/7369: {Two or more non-magnetic underlayers, e.g. seed layers or barrier layers} - G11B 5/737: {Physical structure of underlayer, e.g. texture} - G11B 5/7379: {Seed layer, e.g. at least one non-magnetic layer is specifically adapted as a seed or seeding layer} - 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) ## Abstract A magnetic recording medium includes; a base member; an underlayer formed on the base member; a main recording layer formed on the underlayer, and a writing assist layer formed on or under the main recording layer in contact with the main recording layer. The main recording layer has perpendicular magnetic anisotropy with an anisotropic magnetic field of Hk1 and an inclination of a reversal part of a magnetization curve of a1. The writing assist layer has an anisotropic magnetic field of Hk2 and an inclination of a reversal part of a magnetization curve of a2. The anisotropic magnetic fields Hk1 and Hk2 and the inclinations a1 and a2 satisfy Hk1>Hk2 and a2>a1. ## Claims ### Claim 1 A magnetic recording medium, comprising: a base member; an underlayer formed on the base member; a main recording layer formed on the underlayer, the main recording layer having perpendicular magnetic anisotropy with an anisotropic magnetic field of Hk1 and an inclination of a reversal part of a magnetization curve of a1; and a writing assist layer formed on or under the main recording layer in contact with the main recording layer, the writing assist layer having an anisotropic magnetic field of Hk2 and an inclination of a reversal part of a magnetization curve of a2, wherein the anisotropic magnetic fields Hk1 and Hk2 and the inclinations a1 and a2 satisfy Hk1>Hk2 and a2>a1. ### Claim 2 (depends on 1) The magnetic recording medium according to claim 1, wherein the main recording layer has a granular structure composed of a non-magnetic material and magnetic grains dispersed in the non-magnetic material. ### Claim 3 (depends on 1) The magnetic recording medium according to claim 1, wherein a saturated magnetization (Ms) of the writing assist layer falls within a range of equal to or grater than 350 emu/cc and equal to or less than 850 emu/cc. ### Claim 4 (depends on 2) The magnetic recording medium according to claim 2, wherein the writing assist layer and the magnetic grains are composed of an alloy containing cobalt, chromium, and platinum. ### Claim 5 (depends on 4) The magnetic recording medium according to claim 4, wherein a content of chromium in the magnetic grains is lower than that of the writing assist layer and a content of platinum is higher than that of the writing assist layer. ### Claim 6 (depends on 2) The magnetic recording medium according to claim 2, wherein the magnetic grains are composed of an alloy containing cobalt and iron. ### Claim 7 (depends on 6) The magnetic recording medium according to claim 6, wherein the magnetic grains are added with copper or silver. ### Claim 8 (depends on 2) The magnetic recording medium according to claim 2, wherein the non-magnetic material is an oxide or a nitride of one selected from the group consisting of silicon, titanium, chromium, and zirconium. ### Claim 9 (depends on 1) The magnetic recording medium according to claim 1, wherein the writing assist layer is composed of an alloy layer containing cobalt and chromium. ### Claim 10 (depends on 9) The magnetic recording medium according to claim 9, wherein the alloy layer containing cobalt and chromium is added with one selected from the group consisting of platinum, tantalum, boron, copper, and nickel. ### Claim 11 (depends on 1) The magnetic recording medium according to claim 1, wherein the underlayer is a laminate film including a backing layer having a soft magnetic layer and a non-magnetic layer formed in a uppermost layer. ### Claim 12 (depends on 11) The magnetic recording medium according to claim 11, wherein the soft magnetic layer is composed of a soft magnetic amorphous material. ### Claim 13 (depends on 12) The magnetic recording medium according to claim 12, wherein the soft magnetic amorphous material is one selected from the group consisting of a cobalt-zirconium alloy and an iron-carbon alloy. ### Claim 14 (depends on 11) The magnetic recording medium according to claim 11, wherein the main recording layer is formed on the non-magnetic layer in contact with the non-magnetic layer and has a granular structure including a non-magnetic material and magnetic grains dispersed in the non-magnetic material, and the non-magnetic layer has a same crystal structure as that of the magnetic grains. ### Claim 15 (depends on 14) The magnetic recording medium according to claim 14, wherein the crystal structure is an hcp structure. ### Claim 16 (depends on 15) The magnetic recording medium according to claim 15, wherein the underlayer includes an orientation control layer having a fcc crystal structure, and the non-magnetic layer is formed on the orientation control layer. ### Claim 17 (depends on 16) The magnetic recording medium according to claim 16, wherein the orientation control layer is composed of one selected from the group consisting of platinum, palladium, a nickel-iron alloy, a nickel-iron-silicon alloy, aluminum, copper, and indium. ### Claim 18 A magnetic recording device, comprising: a magnetic recording medium which includes: a base member; an underlayer formed on the base member; a main recording layer formed on the underlayer, the main recording layer having perpendicular magnetic anisotropy with an anisotropic magnetic field of Hk1 and an inclination of a reversal part of a magnetization curve of a1; and a writing assist layer formed on or under the main recording layer in contact with the main recording layer, the writing assist layer having an anisotropic magnetic field of Hk2 and an inclination of a reversal part of a magnetization curve of a2; and a magnetic head opposing to the magnetic recording medium, wherein the anisotropic magnetic fields Hk1 and Hk2 and the inclinations a1 and a2 satisfy Hk1>Hk2 and a2>a1. ### Claim 19 (depends on 18) The magnetic recording device according to claim 18, wherein the main recording layer has a granular structure composed of a non-magnetic material and magnetic grains dispersed in the non-magnetic material. ### Claim 20 (depends on 18) The magnetic recording medium according to claim 18, wherein the writing assist layer and the magnetic grains are composed of an alloy containing cobalt, chromium, and platinum.