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

Patent metadata

Field	Value
Publication number	US-2020303104-A1
Application number	US-202016895648-A
Country	US
Kind code	A1
Filing date	Jun 8, 2020
Priority date	Dec 12, 2014
Publication date	Sep 24, 2020
Grant date	—

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

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,
a 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,
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 satisfy 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 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 covers an entire surface of the core portion.

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

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 satisfies a second relation 0.4 nm≤δ 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 as 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 including 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 a 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, 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 satisfy 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.

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 covers an entire surface of the core portion.

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

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 satisfies a second relation 0.4 nm≤δ 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 as that satisfies a relation 10 emu/g≤σs≤100 emu/g.

Assignees

• Sony Corp

Inventors

• Terakawa Masaru
• Yamaga Minoru

Classifications

• B22F1/054

  Nanosized particles · CPC title

• B22F1/18

  Non-metallic particles coated with metal · CPC title

• B22F1/142

  Thermal or thermo-mechanical treatment · 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