Tdk Corporation

Fumihiko Hirata

Hitoshi Taguchi

Teruo Mori

Taku Takeishi

Yoshihiko Minachi

Kiyoyuki Masuzawa

Kazumasa Iida

Mitsuaki Sasaki

The magnetic powder and the sintered magnet of the invention contains a primary phase of a hexagonal ferrite containing A, Co or R wherein A represents Sr, Ba or Ca, and R represents at least one element which may be rare earth elements including Y, and Bi, and have at least two different Curie temperatures. wherein the two different Curie temperatures are present within a range of from 400 to 480&deg; C., and an absolute value of a difference therebetween is 5&deg; C. or more. As both the saturation magnetization and the magnetic anisotropy of the M type ferrite therein are increased, the magnetic powder and the wintered magnet have a high residual magnetic flux density and a high coercive force, which conventional M type ferrite magnets could not have, while having excellent temperature characteristics of coercive force.

Magnet powder, sintered magnet, process for producing them, bonded magnet, motor and magnetic recording medium

ferrite magnet raw material particles and a non-aqueous solvent is compacted wet in a magnetic field, while said non-aqueous solvent is removed therefrom, to obtain a compact, and the compact is sintered to obtain an anisotropic ferrite magnet. In this case, a surface active agent is allowed to exist in the slurry during the wet compaction. Alternatively, in addition to or in place of this, the raw material particles are pulverized to apply strains thereto, thereby reducing the iHc values to preferably 3.5 kOe or less. This makes some considerable improvement in the degree of orientation of the compact, thus achieving much more improved magnet properties.

Process for the production of anisotropic ferrite magnets and

The magnetic powder and the sintered magnet of the invention contains a primary phase of a hexagonal ferrite containing A, Co or R wherein A represents Sr, Ba or Ca, and R represents at least one element which may be rare earth elements including Y, and Bi, and have at least two different Curie temperatures, wherein the two different Curie temperatures are present within a range of from 400 to 480.degree. C., and an absolute value of a difference therebetween is 5.degree. C. or more. As both the saturation magnetization and the magnetic anisotropy of the M type ferrite therein are increased, the magnetic powder and the wintered magnet have a high residual magnetic flux density and a high coercive force, which conventional M type ferrite magnets could not have, while having excellent temperature characteristics of coercive force.

Magnet powder, sintered magnet, process for producing them, bonded

A slurry containing ferrite magnet raw material particles and a non-aqueous solvent is compacted wet in a magnetic field, while said non-aqueous solvent is removed therefrom, to obtain a compact, and the compact is sintered to obtain an anisotropic ferrite magnet. In this case, a surface active agent is allowed to exist in the slurry during the wet compaction. Alternatively, in addition to or in place of this, the raw material particles are pulverized to apply strains thereto, thereby reducing the iHc values to preferably 3.5 kOe or less. This makes some considerable improvement in the degree of orientation of the compact, thus achieving much more improved magnet properties.

Hexagonal system ferrite particles and their production process

An anisotropic hexagonal barium ferrite sintered magnet is prepared by molding a powder barium ferrite raw material in a magnetic field into a compact and sintering the compact; or by molding a powder barium ferrite raw material in a magnetic field into a compact, disintegrating the compact into particles, compacting the particles in a magnetic field into a second compact, and sintering the second compact. In either case, the raw material contains calcined hexagonal barium ferrite, a silicon component, and a barium component. The resulting anisotropic hexagonal barium ferrite sintered magnet has improved sintered density and coercivity while the method minimizes deformation during sintering which is otherwise caused by the difference between the shrinkage factors in axis c and a directions, and simplifies or omits post-treatment like polishing.

Preparation of anisotropic hexagonal barium ferrite sintered magnet

Process for the production of anisotropic ferrite magnets

In a method for preparing a magnet by pulverizing a calcined powder of hexagonal barium ferrite, compacting the thus pulverized ferrite magnet source particles in a magnetic field, and sintering the compact, a structure comprising barium ferrite as a primary phase and containing strontium and silicon as grain boundary components is obtained when a silicon component such as SiO.sub.2 and a strontium component such as SrCO.sub.3 are contained in the compact. This results in a hexagonal barium ferrite sintered magnet which has minimal anisotropy of shrinkage factor and minimal deformation during sintering, requires only simple or no post-polishing, and has improved sintered density and coercivity.

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Chiba, Japan

Fumihiko Hirata