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

Patent metadata

Field	Value
Publication number	US-11355270-B2
Application number	US-202016895648-A
Country	US
Kind code	B2
Filing date	Jun 8, 2020
Priority date	Dec 12, 2014
Publication date	Jun 7, 2022
Grant date	Jun 7, 2022

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 magnetic recording medium, comprising:
a nonmagnetic support; and
a magnetic layer including a magnetic powder, wherein
the magnetic powder includes a plurality of core-shell particles,
each core-shell particle of the plurality of core-shell particles includes:
a core portion comprising a hard magnetic material; and
a shell portion comprising a soft magnetic layer and an oxide film, wherein
the oxide film has an average thickness Γ barrier and the soft magnetic layer has an average thickness Γ soft ,
the oxide film and the soft magnetic layer satisfy relations 0.4 nm≤Γ barrier ≤11 nm and 0.1 Γ soft /Γ barrier ≤10, and
Γ soft /Γ barrier is a ratio of the average thickness Γ soft of the soft magnetic layer to the average thickness Γ barrier of the oxide film.

2. The magnetic recording medium according to claim 1 , wherein the hard magnetic material comprises an ε-Fe 2 O 3 crystal.

3. The magnetic recording medium according to claim 2 , wherein the ε-Fe 2 O 3 crystal includes a crystal derived from ε-Fe 2 O 3 by partial substitution of Fe sites with a metal element M.

4. The magnetic recording medium according to claim 3 , wherein the metal element M includes at least one of Al, Ga, or In.

5. The magnetic recording medium according to claim 3 , wherein a molar ratio of M to Fe in the ε-Fe 2 O 3 crystal satisfies M:Fe=x:(2−x), 0≤x<1.

6. The magnetic recording medium according to claim 1 , wherein the hard magnetic material comprises a Co-containing spinel ferrimagnetic material.

7. The magnetic recording medium according to claim 1 , wherein the shell portion of each core shell particle of the plurality of core shell particles covers an entire surface of a respective core portion of each core shell particle of the plurality of core shell particles.

8. The magnetic recording medium according to claim 2 , wherein the soft magnetic layer includes an α-Fe-based soft magnetic material.

9. The magnetic recording medium according to claim 6 , wherein the soft magnetic layer includes an Fe-based soft magnetic material.

10. The magnetic recording medium according to claim 1 , wherein
the magnetic powder has an average particle size R core/shell that satisfies a first relation 4.9 nm≤R core/shell ≤15 nm, and
the shell portion of each core-shell particle of the plurality of core-shell particles satisfies a second relation 0.4 nm≤Γ soft ≤11 nm.

11. The magnetic recording medium according to claim 1 , wherein
the magnetic powder has a percentage ratio D of D half to D ave ,
D is one of less than or equal to 40%,
D= ( D half /D ave )×100,

D ave is an average particle size of the magnetic powder, and
D half is a half width of a particle size distribution of the magnetic powder.

12. The magnetic recording medium according to claim 1 , wherein the magnetic powder has a coercivity Hc that satisfies a relation 2,000 Oe≤Hc≤6,000 Oe.

13. The magnetic recording medium according to claim 1 , wherein the magnetic powder has a saturation magnetization that satisfies a relation 10 emu/g≤σs≤100 emu/g.

14. The magnetic recording medium according to claim 1 , wherein the nonmagnetic support includes polyesters.

15. The magnetic recording medium according to claim 1 , further comprising a nonmagnetic layer that includes each of a nonmagnetic powder and a binder.

16. The magnetic recording medium according to claim 1 , further comprising a back coat layer.

17. A magnetic powder, comprising:
a plurality of core-shell particles, wherein each core-shell particle of the plurality of core-shell particles includes:
a core portion comprising a hard magnetic material; and
a shell portion comprising a soft magnetic layer and an oxide film, wherein
the oxide film has an average thickness Γ barrier and the soft magnetic layer has an average thickness Γ soft ,
the oxide film and the soft magnetic layer satisfy relations 0.4 nm≤Γ barrier ≤11 nm and 0.1≤Γ soft /Γ barrier ≤10, and
Γ soft /Γ barrier is a ratio of the average thickness Γ soft of the soft magnetic layer to the average thickness Γ barrier of the oxide film.

18. The magnetic powder according to claim 17 , wherein the hard magnetic material comprises an ε-Fe 2 O 3 crystal.

19. The magnetic powder according to claim 18 , wherein the ε-Fe 2 O 3 crystal includes a crystal derived from ε-Fe 2 O 3 by partial substitution of Fe sites with a metal element M.

20. The magnetic powder according to claim 19 , wherein the metal element M includes at least one of Al, Ga, or In.

21. The magnetic powder according to claim 19 , wherein a molar ratio of M to Fe in the ε-Fe 2 O 3 crystal satisfies M:Fe=x:(2−x), 0≤x<1.

22. The magnetic powder according to claim 17 , wherein the hard magnetic material comprises a Co-containing spinel ferrimagnetic material.

23. The magnetic powder according to claim 17 , wherein the shell portion of each respective core shall particle of the plurality of core shell particles covers an entire surface of a respective core portion of each core shell particle of the plurality of core shell particles.

24. The magnetic powder according to claim 18 , wherein the soft magnetic layer includes an α-Fe-based soft magnetic material.

25. The magnetic powder according to claim 22 , wherein the soft magnetic layer includes an Fe-based soft magnetic material.

26. The magnetic powder according to claim 17 , wherein
the magnetic powder has an average particle size R core/shell that satisfies a first relation 4.9 nm≤R core/shell ≤15 nm, and
the shell portion of each core-shell particle of the plurality of core-shell particles satisfies a second relation 0.4 nm≤Γ soft ≤11 nm.

27. The magnetic powder according to claim 17 , wherein
the magnetic powder has a percentage ratio D of D half to D ave ,
D is one of less than or equal to 40%,
D =( D half /D ave )×100,

D ave is an average particle size of the magnetic powder, and
D half is a half width of a particle size distribution of the magnetic powder.

28. The magnetic powder according to claim 17 , wherein the magnetic powder has a coercivity Hc that satisfies a relation 2,000 Oe≤Hc≤6,000 Oe.

29. The magnetic powder according to claim 17 , wherein the magnetic powder has a saturation magnetization that satisfies a relation 10 emu/g≤σs≤100 emu/g.

Assignees

• Sony Corp

Inventors

• Terakawa Masaru
• Yamaga Minoru

Classifications

• B22F1/18

  Non-metallic particles coated with metal · CPC title

• B22F1/054

  Nanosized particles · CPC title

• B22F1/142

  Thermal or thermo-mechanical treatment · CPC title

• B22F9/22 Primary

  using gaseous reductors · CPC title

• G11B5/712

  characterised by the surface treatment or coating of magnetic particles · CPC title