Magnetic powder, method for production thereof, and magnetic recording medium

Patent metadata

Field	Value
Publication number	US-10755841-B2
Application number	US-201515531553-A
Country	US
Kind code	B2
Filing date	Nov 13, 2015
Priority date	Dec 12, 2014
Publication date	Aug 25, 2020
Grant date	Aug 25, 2020

Abstract

A method for producing a magnetic powder includes performing a reduction treatment on the surface of particles including a hard magnetic material to form core-shell particles each having a shell portion including a soft magnetic material.

First claim

The invention claimed is:

1. A method for producing a magnetic powder, the method comprising:
subjecting a plurality of hard magnetic particles to a reduction treatment to form a plurality of core-shell particles,
wherein each core-shell particle of the plurality of core-shell particles has a shell portion comprising a soft magnetic material; and

subjecting the plurality of core-shell particles to a gradual oxidation treatment after the reduction treatment, wherein
the shell portion after the gradual oxidation treatment comprises a soft magnetic layer and an oxide film,
the oxide film has an average thickness δ barrier and the soft magnetic layer has an average thickness δ soft ,
the oxide film and the soft magnetic layer satisfies relations 0.4 nm≤δ barrier ≤11 nm and 0.1≤δ soft /δ barrier ≤10, and

δ soft /δ barrier is a ratio of the average thickness δ soft of the soft magnetic layer to the average thickness δ barrier of the oxide film.

2. The method according to claim 1 , wherein
the plurality of hard magnetic particles comprises an ε-Fe 2 O 3 crystal, and
the ε-Fe 2 O 3 crystal includes a crystal derived from ε-Fe 2 O 3 by partially substituting Fe sites with a metal element M.

3. The method according to claim 2 , wherein the soft magnetic material is α-Fe.

4. The method according to claim 1 , further comprising:
forming a coating layer on the plurality of hard magnetic particles before the reduction treatment; and
removing the coating layer from the plurality of core-shell particles after the reduction treatment.

5. The method according to claim 4 , wherein the coating layer comprises silica.

6. The method according to claim 1 , wherein
the plurality of core-shell particles have an average particle size R core/shell satisfying a first relation 4.9 nm≤R core/shell ≤15 nm, and
the shell portion satisfies a second relation 0.4 nm≤δ soft ≤11 nm.

7. The method according to claim 1 , wherein
the plurality of core-shell particles have a percentage ratio D of D half to D ave of at most 40%,
D =( D half /D ave )×100,

D ave is an average particle size of the plurality of core-shell particles, and
D half is a half width of a particle size distribution of the plurality of core-shell particles.

8. The method according to claim 1 , wherein the plurality of core-shell particles has a coercivity Hc satisfying a relation 2,000 Oe≤Hc≤6,000 Oe.

9. The method according to claim 1 , wherein the plurality of core-shell particles has a saturation magnetization σs satisfying a relation 10 emu/g≤σs≤100 emu/g.

Assignees

• Sony Corp

Inventors

• Terakawa Masaru
• Yamaga Minoru

Classifications

• B22F1/142

  Thermal or thermo-mechanical treatment · CPC title

• B22F1/054

  Nanosized particles · CPC title

• B22F1/18

  Non-metallic particles coated with metal · CPC title

• B22F9/22 Primary

  using gaseous reductors · CPC title

• H01F1/147 Primary

  Alloys characterised by their composition {(treatment thereof for enhancing their electromagnetic properties C21D8/12)} · CPC title