Insulating magnectic metal particles and method for manufacturing insulating magnetic material

• US 20080029300A1
• Filed: 07/23/2007
• Published: 02/07/2008
• Est. Priority Date: 08/07/2006
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Suenaga, Seiichi, Suetsuna, Tomohiro, Harada, Kouichi, Yonetsu, Maki
• Granted Patent: US 7,740,939 B2
• Time in Patent Office: Days
• US Class Current: 174/391
• CPC Class Codes: B22F 1/054 Nanosized particles
• CPC Class Codes: B22F 1/16 Metallic particles coated with a non-metal coated with lubricating or binding agents or with organic material B22F1/10
• CPC Class Codes: B22F 2998/00 Supplementary information concerning processes or compositions relating to powder metallurgy
• CPC Class Codes: C22C 2202/02 Magnetic
• CPC Class Codes: H01F 1/24 the particles being insulated
• CPC Class Codes: H01F 41/0246 Manufacturing of magnetic circuits by moulding or by pressing powder magnetic cores made by moulding or by pressing powder H01F27/255; soft magnetic particles H01F1/20, H01F1/36
• CPC Class Codes: Y10T 428/12181 Composite powder [e.g., coated, etc.]
• CPC Class Codes: Y10T 428/2991 Coated

Abstract

An insulating magnetic metal particle includes a magnetic metal particle containing at least one metal selected from the group consisting of Co, Fe, and Ni and having a diameter of 5 to 500 nm, a first inorganic insulating layer made of an oxide that covers the surface of the magnetic metal particle, and a second inorganic insulating layer made of an oxide that produces a eutectic crystal by reacting together with the first inorganic insulating layer at the time of heating them, the second inorganic insulating layer being coated on the first inorganic insulating layer. A thickness ratio of the second inorganic insulating layer with respect to the first inorganic insulating layer is set so that the first inorganic insulating layer remains on the surface of the magnetic metal particle after producing the eutectic crystal.

Claims

1. An insulating magnetic metal particle, comprising:

a magnetic metal particle containing at least one metal selected from the group consisting of Co, Fe, and Ni and having a diameter of 5 to 500 nm;

a first inorganic insulating layer made of an oxide that covers the surface of the magnetic metal particle; and

a second inorganic insulating layer made of an oxide that produces a eutectic crystal by reacting together with the first inorganic insulating layer at the time of heating them, the second inorganic insulating layer being coated on the first inorganic insulating layer,

wherein a thickness ratio of the second inorganic insulating layer with respect to the first inorganic insulating layer is set so that the first inorganic insulating layer remains on the surface of the magnetic metal particle after producing the eutectic crystal.

2. The insulating magnetic metal particle according to claim 1, wherein the magnetic metal particle has a diameter of 10 to 100 nm.

3. The insulating magnetic metal particle according to claim 1, wherein the magnetic metal particle has a diameter of 10 to 50 nm.

4. The insulating magnetic metal particle according to claim 1, wherein each of the first and second inorganic insulating layers has a resistivity of 1×

10² Ω

·

cm or more at room temperature.

5. The insulating magnetic metal particle according to claim 1, wherein the first inorganic insulating layer is made of an oxide containing at least one selected from the group consisting of CeO₂, CoO, Cr₂O₃, MgO, Al₂O₃, SnO₂, NiO₂, GaO, GeO₂, Li₂O, Y₂O₃, HfO₂, La₂O₃, ZnO, ZrO₂, WO₃, TiO₂, Sc₂O₃, BaO, Eu₂O₃, SiO₂, Cs₂O, MoO₃, Nb₂O₅, TeO₂, Bi₂O₃, copper oxides, and iron oxides, and

the second inorganic insulating layer is made of an oxide different from that of the first inorganic insulating layer and containing at least one selected from the group consisting of B₂O₃, Bi₂O₃, PbO, V₂O₅, TeO₂, Na₂O, K₂O, and MoO₃.

6. The insulating magnetic metal particle according to claim 1, wherein the first inorganic insulating layer is made of an oxide (A) while the second inorganic insulating layer is made of an oxide (B) in which a combination (B-A) of them is any one selected from B₂O₃—

Al₂O₃, B₂O₃—

GeO₂, B₂O₃—

SiO₂, B₂O₃—

WO₃, B₂O₃—

Cr₂O₃, B₂O₃—

MoO₃, B₂O₃—

Nb₂O₅, B₂O₃—

Li₂O₃, B₂O₃—

BaO, B₂O₃—

ZnO, B₂O₃—

La₂O₃, B₂O₃—

CoO, B₂O₃—

Cs₂O, B₂O₃—

K₂O, K₂O—

GeO₂, K₂O—

SiO₂, K₂O—

WO₃, K₂O—

MoO₃, K₂O—

Nb₂O₅, Na₂O—

GeO₂, Na₂O—

SiO₂, Na₂O—

WO₃, Na₂O—

MoO, Na₂O—

Nb₂O₅, MoO₃—

Cs₂O, MoO₃—

Li₂O, MoO₃—

WO₃, Cs₂O—

SiO₂, and Cs₂O—

Nb₂O₅.

7. The insulating magnetic metal particle according to claim 6, wherein the combination B-A is B₂O₃—

SiO₂, and a ratio t2/t1 of an average thickness t2 of the second inorganic insulating layer with respect to an average thickness t1 of the first inorganic insulating layer is 1.2 or less.

8. A method for manufacturing an insulating magnetic material, comprising:

forming a first inorganic insulating layer made of an oxide on the surface of a magnetic metal particle containing at least one metal selected from the group consisting of Co, Fe, and Ni and having a diameter of 5 to 500 nm;

forming a second inorganic insulating layer made of an oxide that produces a eutectic crystal by reacting together with the first inorganic insulating layer at the time of heating them on the first inorganic insulating layer thereby to produce an insulating magnetic metal particle, wherein a thickness ratio of the first and second inorganic insulating layers is set so that the first inorganic insulating layer remains on the surface of the magnetic metal particle after producing the eutectic crystal;

molding the insulating magnetic metal particles to form a molded body; and

heating the molded body to produce the eutectic crystal by reacting between the first and second insulating layers, while the first inorganic insulating layer remains on the surface of the magnetic metal particle.

9. The method according to claim 8, wherein the magnetic metal particle has a diameter of 10 to 100 nm.

10. The method according to claim 8, wherein the magnetic metal particle has a diameter of 10 to 50 nm.

11. The method according to claim 8, wherein each of the first and second inorganic insulating layers has a resistivity of 1×

10² Ω

·

cm or more at room temperature.

12. The method according to claim 8, wherein the first inorganic insulating layer is made of an oxide containing at least one member selected from the group consisting of CeO₂, CoO, Cr₂O₃, MgO, Al₂O₃, SnO₂, NiO₂, GaO, GeO₂, Li₂O, Y₂O₃, HfO₂, La₂O₃, ZnO, ZrO₂, WO₃, TiO₂, Sc₂O₃, BaO, Eu₂O₃, SiO₂, Cs₂O, MoO₃, Nb₂O₅, TeO₂, Bi₂O₃, copper oxides, and iron oxides, and

the second inorganic insulating layer is made of an oxide different from that of the first inorganic insulating layer and containing at least one member selected from the group consisting of B₂O₃, Bi₂O₃, PbO, V₂O₅, TeO₂, Na₂O, K₂O, and MoO₃.

13. The method according to claim 8, wherein the first inorganic insulating layer is made of an oxide (A) while the second inorganic insulating layer is prepared from an oxide (B) in which a combination (B-A) of them is any one selected from B₂O₃—

Al₂O₃, B₂O₃—

GeO₂, B₂O₃—

SiO₂, B₂O₃—

WO₃, B₂O₃—

Cr₂O₃, B₂O₃—

MoO₃, B₂O₃—

Nb₂O₅, B₂O₃—

Li₂O₃, B₂O₃—

BaO, B₂O₃—

ZnO, B₂O₃—

La₂O₃, B₂O₃—

CoO, B₂O₃—

Cs₂O, B₂O₃—

K₂O, K₂O—

GeO₂, K₂O—

SiO₂, K₂O—

WO₃, K₂O—

MoO₃, K₂O—

Nb₂O₅, Na₂O—

GeO₂, Na₂O—

SiO₂, Na₂O—

WO₃, Na₂O—

MoO, Na₂O—

Nb₂O₅, MoO₃—

Cs₂O, MoO₃—

Li₂O, MoO₃—

WO₃, Cs₂O—

SiO₂, and Cs₂O—

Nb₂O₅.

14. The method according to claim 8, wherein the first inorganic insulating layer has an average thickness of 1 to 10 nm, while the second inorganic insulating layer has an average thickness of 1 to 5 nm.

15. The method according to claim 8, wherein a ratio t2/t1 of an average thickness t1 of the first inorganic insulating layer and an average thickness t2 of the second inorganic insulating layer is 0.1 to 2.

16. The method according to claim 13, wherein the combination B-A is B₂O₃—

SiO₂, and a ratio t2/t1 of a thickness t2 of the second inorganic insulating layer with respect to a thickness t1 of the first inorganic insulating layer is 1.2 or less.

17. The method according to claim 14, wherein an average thickness of the remaining first inorganic insulating layer is 1 to 5 nm.

18. The method according to claim 8, wherein the magnetic metal particles covered with the remaining first inorganic insulating layer are dispersed into an insulating matrix made of the eutectic crystals at intervals of 0 to 10 nm.

19. The method according to claim 8, wherein a compound containing at least one element selected from Fe, Co, and Ni is added in case of forming the insulating magnetic particles.