# US 5,348,800 A · Composite soft magnetic material > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,348,800 A - Document ID: US5348800A - Status: Granted - Kind: A - Application number: 08/013,210 - Filed: 1993-02-01 - Granted: 1994-09-20 - Earliest claimed: 1991-08-19 - Assignees: TDK Corporation - Inventors: Hideharu Moro; Yasuharu Miyauchi - Web page: https://patentgrep.com/patent/US5348800A ## CPC - H01F 1/33: mixtures of metallic and non-metallic particles; metallic particles having oxide skin - Y10S 428/90: Magnetic feature - Y10T 428/256: Heavy metal or aluminum or compound thereof - Y10T 428/257: Iron oxide or aluminum oxide - Y10T 428/259: Silicic material - Y10T 428/265: 1 mil or less - Y10T 428/2993: Silicic or refractory material containing [e.g., tungsten oxide, glass, cement, etc.] - 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 composite soft magnetic material is produced from soft magnetic metal (e.g., Sendust) particles by coating the particles with a non-magnetic metal oxide (e.g., .alpha.-alumina) in a mechano-fusion manner, or heat treating the particles to form a diffusion layer of .alpha.-alumina thereon, coating the coated particles with a high resistance soft magnetic substance (e.g., ferrite), and sintering the double coated particles under pressure as by hot pressing or plasma activated sintering. It exhibits high saturation magnetic flux density, magnetic permeability, and electric resistivity. The non-magnetic metal oxide intervening between the soft magnetic metal and the high resistance soft magnetic substance is effective in reducing core loss. ## Claims ### Claim 1 A composite soft magnetic material comprising soft magnetic metal particles having a mean particle diameter of 5-100 .mu.m and a coercive force of up to about 0.5 Oe as measured in bulk form, a layer of high resistance soft magnetic substance having an electric resistivity of about 10.sup.2 .OMEGA.-cm or higher intervening between the particles, and a layer of non-magnetic metal oxide intervening between each soft magnetic metal particle and the high resistance soft magnetic substance layer; wherein said material has a core loss of about 350-3,000 kW/m.sup.3 at 0.1 mT, 100 kHz and about 5-100 kW/m.sup.3 at 0.1 mT, 10 kHz. ### Claim 2 (depends on 1) The composite soft magnetic material of claim 1 which is obtained by sintering under pressure said soft magnetic metal particles and said high resistance soft magnetic substance with said non-magnetic metal oxide intervening therebetween. ### Claim 3 (depends on 2) The composite soft magnetic material of claim 2 which is obtained by coating the soft magnetic metal particles with the non-magnetic metal oxide and further with the high resistance soft magnetic substance, and sintering the coated particles under pressure. ### Claim 4 (depends on 3) The composite soft magnetic material of claim 3 wherein the step of coating the particles with the high resistance soft magnetic substance is carried out by a mechano-fusion process including applying mechanical energy to the particles. ### Claim 5 (depends on 3) The composite soft magnetic material of claim 3 wherein the non-magnetic metal oxide coating is 0.02 to 1 .mu.m thick. ### Claim 6 (depends on 2) The composite soft magnetic material of claim 2 which is obtained by heat treating the soft magnetic metal particles in an oxygen atmosphere, thereby forming a diffusion layer of non-magnetic metal oxide on the particle surface, coating the particles with the high resistance soft magnetic substance, and sintering the coated particles under pressure. ### Claim 7 (depends on 6) The composite soft magnetic material of claim 6 wherein the soft magnetic metal particles contain at least one member of Al and Si. ### Claim 8 (depends on 6) The composite soft magnetic material of claim 6 wherein the non-magnetic metal oxide diffusion layer is 3 to 300 nm thick. ### Claim 9 (depends on 6) The composite soft magnetic material of claim 6 wherein the non-magnetic metal oxide is at least one oxide selected from the group consisting of Al and Si. ### Claim 10 (depends on 3, 6) The composite soft magnetic material of claim 3 or 6 wherein the high resistance soft magnetic substance coating is 0.02 to 10 .mu.m thick. ### Claim 11 (depends on 6) The composite soft magnetic material of claim 6 wherein the step of coating the particles with the high resistance soft magnetic substance is carried out by a mechano-fusion process including applying mechanical energy to the particles. ### Claim 12 (depends on 2, 3, 6) The composite soft magnetic material of claim 2, 3 or 6 wherein the sintering step is hot press sintering or plasma activated sintering. ### Claim 13 (depends on 2, 3, 6) The composite soft magnetic material of claim 2, 3 or 6 wherein the sintering under pressure is followed by heat treatment in an oxygen atmosphere. ### Claim 14 (depends on 1) The composite soft magnetic material of claim 1, wherein said high resistance soft magnetic substance has a mean particle size of about 0.01-2 .mu.m. ### Claim 15 A composite soft magnetic material comprising soft magnetic metal particles having a mean particle diameter of 5-100 .mu.m and a coercive force of up to about 0.5 Oe as measured in bulk form, a layer of high resistance soft magnetic substance having an electric resistivity of about 10.sup.2 .OMEGA.-cm or higher and a mean particle size of about 0.01-2 .mu.m, and a 0.02-1 .mu.m thick layer of non-magnetic metal oxide intervening between each soft magnetic particle and said high resistance soft magnetic substance layer; wherein said material has a core loss of about 350-3,000 kW/m.sup.3 at 0.1 mT, 100 kHz and about 5-100 kW/m.sup.3 at 0.1 mT, 10 kHz. ### Claim 16 A composite soft magnetic material comprising soft magnetic metal particles having a mean particle diameter of 5-100 .mu.m and a coercive force of up to about 0.5 Oe as measured in bulk form, a layer of high resistance soft magnetic substance having an electric resistivity of about 10.sup.2 .OMEGA.-cm or higher and a mean particle size of abut 0.01-2 .mu.m, and a 3 to 300 nm thick layer of non-magnetic metal oxide formed by diffusion intervening between each soft magnetic particles and said high resistance soft magnetic substance layer; wherein said material has a core loss of about 350-3,000 kW/m.sup.3 at 0.1 mT, 100 kHz and about 5-100 kW/m.sup.3 at 0.1 mT, 10 kHz wherein said composite material is obtained by heat treating said soft magnetic metal particles in an oxygen atmosphere, thereby forming a diffusion layer of non-magnetic metal oxide on said particle surface, coating said particles with said high resistance soft magnetic substance and sintering said coated particles under pressure.