Hexagonal ferrite magnetic powder, method for producing the same and magnetic recording medium

• US 20070020489A1
• Filed: 06/20/2005
• Published: 01/25/2007
• Est. Priority Date: 06/21/2004
• Status: Active Grant

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Asahi Techno Glass Corp (AGC, Inc.), Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Inventors: Yamazaki, Nobuo, Suzuki, Hiroyuki, Takahashi, Masatoshi, Manabe, Akira
• Granted Patent: US 7,381,482 B2
• Time in Patent Office: Days
• US Class Current: 428/842.800
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01G 49/0018 Mixed oxides or hydroxides, C01G49/0009 takes precedence
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: C01P 2006/12 Surface area
• CPC Class Codes: C01P 2006/19 Oil-absorption capacity, e.g. DBP values
• CPC Class Codes: C01P 2006/42 Magnetic properties
• CPC Class Codes: C04B 2235/3215 Barium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3217 Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina
• CPC Class Codes: C04B 2235/3251 Niobium oxides, niobates, tantalum oxides, tantalates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3275 Cobalt oxides, cobaltates or cobaltites or oxide forming salts thereof, e.g. bismuth cobaltate, zinc cobaltite
• CPC Class Codes: C04B 2235/3284 Zinc oxides, zincates, cadmium oxides, cadmiates, mercury oxides, mercurates or oxide forming salts thereof
• CPC Class Codes: C04B 2235/3409 Boron oxide, borates, boric acids, or oxide forming salts thereof, e.g. borax
• CPC Class Codes: C04B 2235/5409 expressed by specific surface values
• CPC Class Codes: C04B 2235/5454 nanometer sized, i.e. below 100 nm
• CPC Class Codes: C04B 2235/549 the particle size being expressed by crystallite size or primary particle size
• CPC Class Codes: C04B 2235/767 Hexagonal symmetry, e.g. beta-Si3N4, beta-Sialon, alpha-SiC or hexa-ferrites
• CPC Class Codes: C04B 2235/96 Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
• CPC Class Codes: C04B 35/2633 containing barium, strontium or calcium
• CPC Class Codes: C04B 35/265 Compositions containing one or more ferrites of the group comprising manganese or zinc and one or more ferrites of the group comprising nickel, copper or cobalt
• CPC Class Codes: C04B 35/62665 Flame, plasma or melting treatment
• CPC Class Codes: C04B 35/632 : Organic additives
• CPC Class Codes: C04B 35/63456 : Polyurethanes; Polyisocyanates
• CPC Class Codes: G11B 5/70678 : Ferrites
• CPC Class Codes: G11B 5/714 : characterised by the dimension of the magnetic particles
• CPC Class Codes: H01F 1/113 : in a bonding agent
• CPC Class Codes: Y10T 428/2982 : Particulate matter [e.g., sphere, flake, etc.]

Abstract

A hexagonal ferrite magnetic powder having an average tabular diameter of from 15 to 28 nm, a coercive force (Hc) of from 2,000 to 5,000 Oe (from 160 to 400 kA/m), a switching field distribution (SFD) of from 0.3 to 0.7 and a D70/D50 of from 1.05 to 1.25. This magnetic powder can be obtained by melting and quenching starting materials to obtain an amorphous product, and thermally treating the product, which comprises increasing a temperature at a rate of 300 to 500° C./hr in a temperature range of 550 to 600° C. in the thermal treatment before the temperature reaches the thermally treating temperature.

Claims

1. A hexagonal ferrite magnetic powder having an average tabular diameter of from 15 to 28 nm, a coercive force (Hc) of from 2,000 to 5,000 Oe (from 160 to 400 kA/m), a switching field distribution (SFD) of from 0.3 to 0.7 and a D70/D50 of from 1.05 to 1.25.

2. A method for producing a hexagonal ferrite magnetic powder according to claim 1, the method comprising:

melting hexagonal ferrite-producing materials so as to form melted hexagonal ferrite-producing materials, and quenching the melted hexagonal ferrite-producing materials to obtain an amorphous product; and

subjecting the amorphous product to a thermal treatment to precipitate a hexagonal ferrite,

wherein the thermal treatment comprises a temperature-increasing process;

in the thermal treatment for the amorphous product at a final temperature of 600 to 750°

C., a temperature is raised at a rate of 300 to 500°

C./hr in a range of from 550 to 600°

C. before the temperature reaches the final temperature.

3. A magnetic recording medium comprising:

a non-magnetic support; and

a magnetic layer containing a hexagonal ferrite magnetic powder dispersed in a binder,

wherein the hexagonal ferrite magnetic powder is a hexagonal ferrite magnetic powder according to claim 1.

4. The magnetic recording medium according to claim 3, which further comprises a non-magnetic layer containing a non-magnetic powder dispersed in a binder between the non-magnetic support and the magnetic layer.